CN1300093C - Preparation method of dialkyl carbonate and its use in the preparation of diaryl carbonate and polycarbonate - Google Patents

Abstract

Unexpected corrosion in the downstream portion of a dialkyl carbonate production plant has been found to result from alkyl chloroformate impurities, which slowly decompose to form hydrochloric acid. An improved process and plant for synthesizing dialkyl carbonate reduces corrosion by physically removing or chemically decomposing the alkyl chloroformate impurities in a corrosion-resistant upstream portion of the plant.

Description

Process for the preparation of dialkyl carbonate and its use in the preparation of diaryl carbonate and polycarbonate

Background of the invention

Polycarbonate resins are materials of practical value because of their physical and optical properties. The preparation methods of polycarbonate resin include interface method and melting method. In the interfacial method, eg, Sikdar, US Patent 4,360,659, bisphenols are reacted with phosgene in the presence of a solvent. In the melt process, eg, Fox, US Patent 3,153,008, bisphenols are reacted with diaryl carbonates. The melt method is currently preferred because it avoids the use of phosgene and solvents.

The melt process for synthesizing polycarbonates requires an industrially efficient method for preparing diaryl carbonates. Several different methods of preparing diaryl carbonates are known, such methods are exemplified by the method described in US Patent 4,182,726 to Illuminati et al. In this method, a diaryl carbonate is prepared by reacting a dialkyl carbonate with an aryl hydroxide (see Scheme I below).

US Patent 4,182,726 also shows that diaryl carbonates can be reacted with dihydricphenols to prepare polycarbonates (see Scheme II below).

A preferred method for preparing dialkyl carbonates, as shown in Scheme III below, is described, for example, in US Patent No. 5,527,943 to Rivetti et al. and US Patent Nos. 4,218,391 and 4,318,862 to Romano et al.

US Patent 5,527,943 (hereinafter referred to as the '943 patent) also describes the well-known drawback of the dialkyl carbonate process according to scheme (III), namely the formation of water as a by-product. Likewise, hydrochloric acid (HCl) can be continuously added to the reaction mixture to maintain the desired molar ratio of chloride to copper. Thus, HCl, catalyst CuCl and water are typically found in the gas stream exiting the reactor. Because hydrochloric acid and copper chloride are highly corrosive in the presence of water, it is necessary to use equipment formed of corrosion-resistant materials in the reaction unit of the chemical plant (plant) for the preparation of dialkyl carbonate by this method, such as glass-lined reaction Container (glass-lined reaction vessel). Because corrosion-resistant equipment is expensive, it is hoped that the chemical workshop will use this equipment as little as possible.

A typical plant for the preparation of dialkyl carbonate according to scheme III consists of three units: a reaction unit for conversion of the feedstock into dialkyl carbonate, a separation unit for separation of dialkyl carbonate from unreacted monomers and by-products , a purification unit for removing water and further separating dialkyl carbonate. It is known from the '943 patent that HCl is removed from the process stream immediately after the reaction unit, at which point the amount of corrosion resistant equipment required can be minimized, which precludes the use of separation and purification units in the plant The necessity of expensive corrosion-resistant materials. The '943 patent also suggests that removal of HCl and possibly the HCl and possibly Copper halide salt. The '943 patent also shows that, in order to avoid having to reheat the mixture prior to removal of HCl, the operating conditions used are preferably adjusted prior to the acid removal section so that the gaseous mixture coming out of the reactor does not condense or only condenses into A negligible degree (col.3, lines 17-30).

In view of the above, although it would be desirable to construct a plant in which hydrochloric acid and any copper halide salts are removed from the stream after the reaction unit to avoid corrosion in the separation and purification unit, similar to the technique described in the '943 patent, That is, the technique of removing HCl and copper salts from the reaction mixture by treating the vaporized feedstock in a column using a countercurrent azeotropic fluid does not prevent corrosion of downstream separation and purification units.

Therefore, there is a need for a process for preparing dialkyl carbonates that will identify and eliminate remaining sources of corrosion.

Brief description of the invention

A process for the preparation of dialkyl carbonates which alleviates the above and other deficiencies and disadvantages of the prior art comprises: reacting alkanols, oxygen, carbon monoxide and a catalyst to form dialkyl carbonates, alkyl chloroformates , hydrochloric acid, water, a mixture of carbon dioxide and carbon monoxide; the alkyl chloroformate is then removed from the mixture.

After much effort, the inventors of the present invention discovered that the synthesis of dialkyl carbonates can form alkyl chloroformate by-products which lead to intractable corrosion. For example, in the reaction of methanol, carbon monoxide, and oxygen to form dimethyl carbonate (hereinafter referred to as "DMC"), a by-product methyl chloroformate (hereinafter referred to as MCF) may be formed. Because this MCF can pass through the HCl removal column to the separation and purification unit, where it slowly reacts with methanol and/or water to form corrosive HCl, it was determined that a MCF removal step was required prior to entering the separation and purification unit.

The present invention provides

1. A method for preparing dialkyl carbonate, comprising:

reacting alkanol, oxygen, carbon monoxide and a catalyst to form a mixture comprising dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and carbon monoxide;

The alkyl chloroformate is removed from the mixture.

2. The method according to item 1, wherein said alkanol includes alkanols having 1 to 12 carbon atoms.

3. The method according to item 1, wherein said alkanols include primary alkanols having 1 to 6 carbon atoms.

4. The method according to item 1, wherein said alkanol comprises methanol.

5. The method according to item 1, wherein said alkanol, said oxygen and said carbon monoxide are in the ratio of (about 0.5 to about 0.7 alkanol): (about 0.04 to about 0.06 oxygen): (about 0.8 to about 1.2 molar ratios of carbon monoxide).

6. according to the said method of item 1, said catalyzer comprises being selected from iron, copper, nickel, cobalt, zinc, ruthenium, rhodium, palladium, silver, cadmium, rhenium, osmium, iridium, platinum, gold or mercury A metal or a combination comprising at least one of the aforementioned metals.

7. The method according to item 1, wherein said catalyst comprises copper.

8. The method according to item 1, wherein said catalyst comprises chloride ions.

9. The method according to item 1, wherein said catalyst comprises copper and chloride ions in a molar ratio of about 0.5 to about 1.5.

10. The method according to item 1, wherein said reaction is carried out in a single reactor 50.

11. The method according to item 1, wherein said reaction is carried out in a corrosion-resistant reactor 50.

12. The method according to item 1, further comprising removing carbon dioxide and carbon monoxide from said mixture.

13. The method according to item 12, wherein at least about 90% of said carbon dioxide and at least about 90% of said carbon monoxide are removed from said mixture.

14. The method according to item 12, wherein said removing carbon dioxide and carbon monoxide comprises passing said mixture through a plurality of gas-liquid separators.

15. The method according to item 14, wherein said reaction is carried out at a first pressure, said plurality of gas-liquid separators comprising a first pressure chamber having a pressure of about 10% of said first pressure. a gas-liquid separator and a second gas-liquid separator having a pressure less than about 20% of said first pressure.

16. The process according to item 1, wherein at least about 80% of said alkyl chloroformate is removed from said mixture.

17. The method according to item 1, wherein at least about 90% of said alkyl chloroformate is removed from said mixture.

18. The method according to item 1, wherein at least about 95% of said alkyl chloroformate is removed from said mixture.

19. The method according to item 1, wherein at least about 99% of said alkyl chloroformate is removed from said mixture.

20. The method according to item 1, wherein said removing alkyl chloroformate comprises removing less than about 5% of said dialkyl carbonate.

21. The method according to item 1, wherein said removing alkyl chloroformate comprises removing less than about 1% of said dialkyl carbonate.

22. The method according to item 1, wherein said removing alkyl chloroformate comprises reducing the concentration of said alkyl chloroformate to less than about 500 ppm by weight.

23. The method according to item 1, wherein said removing alkyl chloroformate comprises reducing the concentration of said alkyl chloroformate to less than about 100 ppm by weight.

24. The method according to item 1, wherein said removing alkyl chloroformate comprises reducing the concentration of said alkyl chloroformate to less than about 30 ppm by weight.

25. The method according to item 1, wherein said removal of alkyl chloroformate comprises a method selected from the group consisting of heating, increasing pressure, increasing residence time, adding polar solvent, adsorption, membrane separation, pervaporation, passing through ion exchange resin , a technique of at least one of exposure to a stoichiometric agent and exposure to a catalytic agent, and a combination comprising at least one of the foregoing techniques.

26. The method according to item 1, further comprising removing hydrochloric acid.

27. The method according to item 26, wherein said removing hydrochloric acid comprises reducing the concentration of hydrochloric acid to less than about 1×10 ^-3 mol/L.

28. The method according to item 26, further comprising vaporizing said mixture before removing said hydrochloric acid.

29. The method according to item 28, wherein said vaporizing comprises heating said mixture, reducing the pressure applied to said mixture, or both.

30. The method according to item 26, wherein said removing hydrochloric acid comprises passing said mixture through a deacidification column 160.

31. The method according to item 26, wherein said removing hydrochloric acid comprises passing said mixture through a deacidification column 160 and an ion exchange resin.

32. The method according to item 1, wherein said method is operated continuously.

33. A method of preparing dialkyl carbonate comprising:

reacting alkanol, oxygen, carbon monoxide and a catalyst to form a mixture comprising dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and carbon monoxide;

reducing the concentration of said alkyl chloroformate in said mixture to less than about 500 ppm by weight while removing less than about 10% of said dialkyl carbonate;

Hydrochloric acid was removed from the mixture.

34. A method of preparing dialkyl carbonate comprising:

reacting an alkanol, oxygen, carbon monoxide, and a catalyst to form a first mixture comprising dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide;

removing alkyl chloroformate from said first mixture to form a second mixture;

Hydrochloric acid is removed from the second mixture.

35. The method according to item 34, wherein said first mixture comprises dialkyl carbonate vapor and alkyl chloroformate vapor.

36. The method according to item 35, further comprising condensing said dialkyl carbonate vapor and said alkyl chloroformate vapor.

37. The method according to item 36, wherein said condensing said dialkyl carbonate vapor and said alkyl chloroformate vapor forms a single liquid phase.

38. The method according to item 34, wherein said removing alkyl chloroformate comprises using at least one gas-liquid separator.

39. A method of preparing dialkyl carbonate comprising:

reacting an alkanol, oxygen, carbon monoxide, and a catalyst to form a first mixture comprising dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide;

removing hydrochloric acid from said first mixture to form a second mixture;

The alkyl chloroformate is removed from the second mixture.

40. A method of preparing dimethyl carbonate, comprising:

combining methanol, oxygen, carbon monoxide, and a copper catalyst to form a first mixture comprising dimethyl carbonate vapor, methyl chloroformate vapor, hydrochloric acid, water, carbon dioxide, and carbon monoxide;

removing a portion of said carbon dioxide and a portion of said carbon monoxide from said first mixture to form a second mixture;

at least partially condensing said dialkyl carbonate vapor and said alkyl chloroformate vapor to form a third mixture;

removing at least about 90% of said methyl chloroformate and less than about 1% of said dimethyl carbonate from said third mixture to form a fourth mixture;

Hydrochloric acid is removed from the fourth mixture.

41. A method for preparing diaryl carbonate, which comprises reacting dialkyl carbonate and aryl hydroxide, wherein dialkyl carbonate is prepared according to the method described in item 1.

42. A method for preparing polycarbonate, comprising reacting a diaryl carbonate and a dihydric phenol, wherein the diaryl carbonate is prepared according to the method of item 41.

Other embodiments involving means for producing dialkyl carbonates will be described hereinafter.

Brief description of the drawings

Figure 1 is a schematic representation of a first embodiment of the device.

Figure 2 is a schematic diagram of a comparative device susceptible to corrosion.

Figure 3 is a schematic diagram of an embodiment of the device in which two holding vessels 120 are included in the fluid channel 110.

Figure 4 is a schematic diagram of an embodiment of a device including four storage containers 120 in a fluid channel 110.

FIG. 5 is a schematic diagram of an embodiment of a device in which a fluid channel 110 includes a tubular section 130 .

FIG. 6 is a schematic diagram of an embodiment of an apparatus including a bed 190 of ion exchange resin.

FIG. 7 is a schematic diagram of an embodiment of the device, in which the fluid channel 110 includes a first gas-liquid separator 90 and a second gas-liquid separator 100 .

FIG. 8 is a schematic diagram of an embodiment of the apparatus in which the fluid channel 110 precedes the first gas-liquid separator 90 .

FIG. 9 is a schematic diagram of an embodiment of an apparatus in which fluid channel 110 follows azeotropic column 180 .

Figure 10 is a scatter plot of the concentration of chlorine at the bottom of the azeotropic column 180 as a function of device type (Figures 2 and 3) and time.

FIG. 11 is a scatter plot of methyl chloroformate concentration entering and exiting fluid channel 110 as a function of time in the device corresponding to FIG. 3 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One embodiment is a method comprising: reacting an alkanol, oxygen, carbon monoxide, and a catalyst to form a mixture comprising dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide, and carbon monoxide; Alkyl chloroformate is removed. Preferably, the reaction is carried out in a corrosion-resistant reactor (50).

The alkanol used in the method is not particularly limited, suitable alkanols include primary, secondary and tertiary alcohols containing 1 to 12 carbon atoms, preferably primary alkanols containing 1 to 6 carbon atoms, very Methanol is preferred.

Oxygen may be provided in any form, preferably in gaseous form. Suitable sources of oxygen include, for example, air and oxygen-containing bodies containing at least about 95% by weight molecular oxygen, preferably at least 99% by weight molecular oxygen. Suitable oxygenates are commercially available, for example, from Air Products.

Carbon monoxide is preferably supplied as a gas containing at least 90 wt%, preferably at least 95 wt%, more preferably at least 99 wt% carbon monoxide. Suitable carbon monoxide-containing gases are commercially available, for example, from Air Products.

Suitable catalysts include those containing iron, copper, nickel, cobalt, zinc, ruthenium, rhodium, palladium, silver, cadmium, rhenium, osmium, iridium, platinum, gold, mercury, and the like and combinations comprising at least one of the foregoing metals. A preferred catalyst may include copper. A highly preferred catalyst comprises copper and chloride ions in a molar ratio of from about 0.5 to about 1.5. Within this range, the molar ratio is preferably at least about 0.8. Also within this range, the molar ratio is preferably up to about 1.2. Very preferred catalysts include cuprous chloride and cupric chloride, with cuprous chloride being more particularly preferred. During operation of the process, a suitable concentration of chloride ions can be maintained by adding hydrochloric acid (HCl).

FIG. 1 illustrates a dialkyl carbonate plant 10 comprising a reaction unit 20 , a separation unit 30 and a purification unit 40 connected. Referring to FIG. 1 , the catalytic reaction of alkanol, oxygen and carbon monoxide can be carried out in a single reactor 50 or in two or more reactors 50 . The conditions under which this step is carried out should be chosen to maximize production of dialkyl carbonate while minimizing degradation of the dialkyl carbonate. The reaction is preferably carried out in a single reactor 50 at a temperature of from about 50°C to about 250°C. Within this range, the temperature is preferably at least about 100°C. Also within this range, the temperature is preferably up to about 150°C. The pressure in reactor 50 is preferably maintained between about 15 and about 35 bargauge (barg); within this range, the pressure is preferably at least about 20 barg; also within this range, the pressure is preferably at most 28 barg. In the case of a dual reactor system, the catalyst can be recycled between tanks. While the catalyst concentration should be high enough to produce acceptable yields, the catalyst concentration should be below a concentration that does not cause the catalyst to solidify in the reactor 50 or plug the equipment. The reactants alkanol, oxygen and carbon monoxide are each preferably added in a molar ratio of (about 0.5 to about 0.7):(about 0.04 to about 0.06):(about 0.8 to about 1.2). A highly preferred alkanol:oxygen:carbon monoxide molar ratio is (about 0.6):(about 0.05):(about 1).

The amount of catalyst used relative to the reactants will depend on the type of catalyst. For example, when the catalyst includes CuCl, a highly preferred catalyst concentration is about 140 grams to 180 grams of catalyst per liter of reaction mixture. During operation, catalyst is initially charged from catalyst tank 60 . Sufficient HCl is preferably added to reactor 50 from hydrochloric acid vessel 70 to maintain a Cu:Cl molar ratio close to 1.0 during the reaction. The HCl concentration is preferably determined and controlled continuously by adding HCl. Typically, the mass ratio of HCl feed to total liquid feed is from about 6×10 ⁻⁴ to about 8×10 ⁻⁴ .

The reaction produces a mixture containing dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and carbon monoxide. The mixture also includes residual methanol and oxygen as well as by-products such as alkyl chlorides and dialkyl ethers. This mixture is typically withdrawn from reactor 50 in the form of a gas/vapor. The term "vapor" refers to gaseous organic components of a mixture, such as evaporated dialkyl carbonates, alcohols, alkyl chloroformates, etc. and to water vapor. That is, the term "steam" refers to a fluid having a boiling point of at least -50°C at one atmosphere. In contrast, "gas" refers to gaseous oxygen, carbon dioxide, carbon monoxide, and optionally nitrogen. That is, the term "gas" refers to a fluid having a boiling point of less than -50°C at one atmosphere. The vapor may be at least partially condensed in the condenser 80 and then supplied to the first gas-liquid separator 90 . The apparatus may optionally employ a single gas-liquid separator or a plurality (ie, at least 2; preferably up to about 5) of gas-liquid separators. The pressure of the first gas-liquid separator 90 is maintained within about 10%, more preferably within about 1%, of the reactor 50 pressure. The gas flowing out of the first gas-liquid separator 90 may be recycled, for example to re-use excess carbon monoxide. This mixture is sent to the second gas-liquid separator 100, which preferably has a pressure of about 20% less than the pressure of the reactor 50 (e.g., preferably less than 3 pressures, more preferably about 0.2 pressures) A separation of at least about 90%, more preferably at least 95%, by weight of the gas remaining in the mixture is preferably obtained. Separation of gases includes removal of carbon dioxide and carbon monoxide from said mixture, preferably at least 90 wt% carbon dioxide and at least 90 wt% carbon monoxide from the mixture. Removing carbon dioxide and carbon monoxide includes passing the mixture through multiple gas-liquid separators. In a highly preferred embodiment, substantially all gases are removed from the mixture. The waste gas removed from the second gas-liquid separator 100 may also be recycled. The vapors in the mixture are preferably in partially condensed form (i.e., at least about 10% condensed) before entering the first gas-liquid separator 90 and between the first gas-liquid separator 90 and the second gas-liquid separator 100 , more preferably in fully condensed form (ie, at least about 90% condensed).

In the embodiment shown in FIG. 1 , the mixture flowing out from the second gas-liquid separator 100 may be a single liquid phase. After exiting the second gas-liquid separator 100, the mixture may continue through a fluid channel 110 for removing alkyl chloroformate from the mixture. It should be understood that the terms "remove" and "removal" with reference to a particular chemical species include any chemical or physical means of reducing the concentration of that species in a mixture.

Alkyl chloroformate can be removed from the condensate by any method, some preferred methods include heating, increasing pressure, increasing residence time, adding polar solvents, adsorption, membrane separation (including gas and liquid membrane separation), pervaporating ), by at least one of ion exchange resins, exposure to stoichiometric reagents, and exposure to catalytic reagents, etc., and combinations comprising at least one of the foregoing techniques. In a preferred embodiment, the alkyl chloroformate is removed from the mixture by reaction with water (see Scheme IV) or alcohol (see Scheme V).

It is also preferable to remove the alkyl chloroformate without passing the mixture through an ion exchange resin, since such resins are expensive to install and use. It is also preferred to remove at least about 50%, preferably at least 80% by weight, more preferably at least about 90%, still more preferably at least about 95%, even more preferably at least about 99% of the alkyl chloroformate from the mixture. In one embodiment, it may also be preferred to reduce the concentration of the alkyl chloroformate in the mixture to less than about 500 ppm, more preferably less than about 100 ppm, still more preferably less than about 30 ppm. In any of these embodiments, it may also be preferred to remove less than about 10%, more preferably less than about 5%, and even more preferably less than about 1% of the dialkyl carbonate is removed. Although the process may be referred to as "removing less than about 10% of said dialkyl carbonate", it should be understood that the concentration of dialkyl carbonate need not be reduced but even increased. For example, the concentration of dialkyl carbonate can be increased if, due to other reactions, the reaction of alkyl chloroformate and methanol to form dialkyl carbonate is faster than scheme V in which dialkyl carbonate is decomposed.

Through extensive kinetic studies on the dimethyl carbonate process utilizing changes in factors including temperature, residence time, water concentration, and concentration of methanol and hydrochloric acid, the inventors of the present invention have found that the rate of decomposition of methyl chloroformate can be given by the formula (1) means

-r _MCF = (k ₁ [H ₂ O] + k ₂ [MeOH])[MCF] (1)

Where _rMCF is the molar rate of change of methyl chloroformate (MCF) per unit volume; [H ₂ O], [MeOH] and [MCF] are the instantaneous concentrations (instantaneous concentration) of water, methanol and methyl chloroformate, respectively, Units are moles per unit volume; k and _k are rate constants as a function of temperature according to equations (2) and (3 ₎ , respectively:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="k"\; filenames="C0282032200301.png,C0282032200321.png"\; state="\{\{state\}\}">k</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="k"\; filenames="C0282032200301.png,C0282032200321.png"\; state="\{\{state\}\}">k</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 6381</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 7673</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

in ${\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="C0282032200301.png,C0282032200321.png"\; state="\{\{state\}\}">k</figure-callout>}}_1^0=2.09{\&times;10}^9\mathrm{mL}/\mathrm{mol}-\min ,$ $k_2^0=4.14{\&times;10}^{10}\mathrm{mL}/\mathrm{mol}-\min ,$ T is the absolute temperature in K.

In most cases, it is valid to assume that the concentrations of water and methanol and the density of the solutions are essentially constant. Within these general kinetic constraints, different kinetic expressions can be used to represent different processes and device types. Those of ordinary skill in the art can easily derive these expressions after possessing the knowledge of the relevant chemical reactions and rate constants provided by the application, for example, in a batch process (batch process), the rate of methyl chloroformate decomposition can be expressed as a function of residence time, as shown in formula (4):

-d[MCF]/dt=(k ₁ [H ₂ O]+k ₂ [MeOH])[MCF] (4)

where t is the residence time in minutes. The residence time t can be defined as the total time that an average molecule spends in the fluid channel 110 . In a batch process, at least about 50% of the chlorine can be removed by maintaining the mixture under conditions including water concentration ([ _H2O ]), methanol concentration ([MeOH]), temperature (T) and residence time (t) Methyl formate, so according to formula (5), the value of parameter X is less than about 0.9, X=exp{-(2.09×10 ⁹ )e ^(-6381/T) [H ₂ O]+(4.14×10 ¹⁰ ) e ^(-7673/T) [MeOH]t} (5) where the concentration of water and methanol are expressed as mol/mL, the temperature is expressed as absolute temperature K, and the residence time is expressed as minutes. The value of X may preferably be less than about 0.5, more preferably less than about 0.2, still more preferably less than about 0.1, even more preferably less than about 0.05, still more preferably less than about 0.01. The water concentration may be between about 0.1 and about 50 mol/L. Within this range, the water concentration may preferably be at least about 0.5 mol/L, more preferably at least about 1 mol/L. Also within this range, the water concentration may preferably be up to about 30 mol/L, more preferably up to about 20 mol/L, still more preferably up to about 10 mol/L, even more preferably up to about 5 mol/L. The methanol concentration can be between about 1 and about 25 mol/L. Within this range, the methanol concentration may preferably be at least about 5 mol/L, more preferably at least about 10 mol/L. Also within this range, the methanol concentration may preferably be up to about 20 mol/L, more preferably up to about 18 mol/L. The residence time can be between about 0.5 and about 10 hours. Within this range, the residence time may preferably be at least about 1 hour, more preferably at least about 2 hours. Also within this range, the residence time may preferably be up to about 8 hours, more preferably up to about 6 hours. The temperature may be between about 30°C and about 130°C. Within this range, the temperature may preferably be at least about 40°C, more preferably at least about 50°C, still more preferably at least about 60°C. Also within this range, the temperature may preferably be up to about 110°C, more preferably up to about 100°C, still more preferably up to about 90°C.

In the limit of an ideal steady-state plug flow reactor and assuming a constant density of the mixture, the methyl chloroformate decomposition rate can be expressed according to formula (3), where t represents the residence time in minutes.

For ideal steady state continuous stirred tank reactor (CSTR), the concentration of methyl chloroformate is represented by formula (6):

[MCF]=[MCF] _t=0 (1/(1+kt)) (6)

Wherein [MCF] _t=0 is the initial concentration of methyl chloroformate, and unit is mol/mL; T is residence time, and unit is minute; K is represented by formula (7):

k=k ₁ [H ₂ O]+k ₂ [MeOH] (7)

wherein k ₁ , k ₂ , [H ₂ O] and [MeOH] are as defined above.

In another embodiment of the batch reactor, the method for removing alkyl chloroformate from the mixture comprises an initial concentration of methyl chloroformate ([MCF] _{t = 0} ), a water concentration of [ _H2O ], methanol concentration [MeOH], temperature (T) and residence time (t) maintain the mixture so that the value of parameter Z calculated according to equation (8) is less than about 5 x 10 ^-6 , preferably less than about 1 ×10 ^-6 , more preferably less than about 5×10 ^-7 , even preferably less than about 5×10 ^-8 ,

Z=[MCF] _t=0 exp{-(2.09×10 ⁹ )e ^(-6381/T) [H ₂ O]+(4.14×10 ¹⁰ )e ^(-7673/T) [MeOH]t} (8)

Wherein the initial concentration of methyl chloroformate, water concentration and methanol concentration are expressed as mol/mL; temperature is expressed as absolute temperature K; residence time is expressed as minutes. The temperature, residence time, methanol concentration and water concentration in this expression are as above. Although the initial concentration of methyl chloroformate will depend on reactor conditions, it is generally about 5×10 ⁻³ to about 5×10 ⁻¹ mol/L. Within this range, the initial concentration of methyl chloroformate can be at least about 1×10 ⁻² mol/L. Also within this range, the initial concentration of methyl chloroformate may be up to about 1 x 10 ^-1 mol/L.

In a preferred embodiment concerning the batch reactor, the process for removing alkyl chloroformate comprises an initial concentration of dimethyl carbonate ([DMC] _{t = 0} ), an initial concentration of water [H ₂ O] _{t = 0} , initial concentration of methanol [MeOH] _t=0 , initial concentration of hydrochloric acid ([HCl] _t=0 ), temperature (T) and residence time (t) to process the mixture, so the value of parameter X is calculated according to formula (9) at least about 0.9,

X=exp{-(2.09×10 ⁹ )e ^(-6381/T) [H ₂ O] _t=0 +(4.14×10 ¹⁰ )e ^(-7673/T) [MeOH] _t=0 t} (9)

The value of parameter Y calculated according to equation (10) is at least about 0.9,

$\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; [</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}{{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; DMC</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}{{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; DMC</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6.6</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 6636</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; HCl</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; DMC</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}{{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; DMC</span>}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Among them, the initial concentrations of dimethyl carbonate, water, methanol, and hydrochloric acid are expressed in mol/mL, the temperature is expressed in absolute temperature K, and the residence time is expressed in minutes. The Y value is preferably at least about 0.95, more preferably at least about 0.99. Suitable analytical techniques to determine the initial concentrations of water, methanol, hydrochloric acid and dimethyl carbonate in the reaction mixture are well known in the art. The term "initial concentration" refers to the concentration of the species prior to the intentional removal of the alkyl chloroformate. The initial concentration of water and methanol is the same as the above-mentioned concentration of water and methanol (under normal reaction conditions, the concentration of water and methanol is large, and in the process of removing the alkyl chloroformate, it does not change substantially). The initial concentration of dimethyl carbonate may be between about 0.5 and about 10 mol/L. Within this range, the initial dimethyl carbonate concentration may preferably be at least about 1 mol/L, more preferably at least about 2 mol/L. Also within this range, the initial concentration of dimethyl carbonate may preferably be up to about 8 mol/L, more preferably up to about 6 mol/L. The concentration of HCl in the mixture depends on the type and concentration of the catalyst used. Although the initial concentration of hydrochloric acid will depend on the type and concentration of the catalyst, it is generally between about 1×10 ⁻³ and 2×10 ⁻¹ mol/L. Within this range, the initial concentration of hydrochloric acid may preferably be at least about 5×10 ⁻³ mol/L, more preferably at least about 1×10 ⁻² mol/L. Also within this range, the initial concentration of hydrochloric acid may preferably be up to about 1×10 ⁻¹ mol/L, more preferably up to about 7×10 ⁻² mol/L.

The process can be operated, for example, in batch, semi-batch or continuous mode.

In the particular embodiment shown in Figure 1, the mixture passes through the first heat exchanger 140 to adjust the temperature of the mixture between about 30°C and about 130°C. Within this range, the temperature may preferably be at least about 40°C, more preferably at least about 50°C. Also within this range, the temperature may preferably be up to about 80°C, more preferably up to about 70°C. The term "heat exchanger" describes a well known device for heating a chemical reaction stream, typically exchanging heat between a heat source (e.g. steam) and a cold chemical reaction stream, but it should be understood that other forms of equivalent heaters are also included (for example, electric heaters). Condensate can enter fluid channel 110, which serves to increase the mixture residence time under conditions that maximize the decomposition of the alkyl chloroformate while minimizing the decomposition of the dialkyl carbonate. The condensate may preferably remain fully condensed within the fluid channel 110 . Because at least some of the alkyl chloroformate (eg, methyl chloroformate) is more stable in the gas phase than in the liquid phase under the conditions of use of the process, it is desirable to keep the condensate fully condensed.

The residence time and temperature within the fluid channel 110 are preferably sufficient to remove significant amounts of the alkyl chloroformate to prevent unacceptable downstream corrosion, but they cannot be so excessive as to unnecessarily reduce the production and yield of the desired dialkyl carbonate product . Figure 2 shows a simplified process diagram representation of the comparative process. In this process, the mixture flows directly out of the first gas-liquid separator 90 , enters the first heat exchanger 140 , and then enters the deacidification column 160 . Three specific embodiments of the fluid channel 110 are shown in FIGS. 3 , 4 and 5 . In a preferred embodiment, at least about 50% of the alkyl chloroformate is removed, more preferably at least about 80%. In a more preferred embodiment, the alkyl chloroformate concentration is reduced to less than about 500 ppm by weight, more preferably less than about 100 ppm by weight, based on the total weight of the mixture after removal of the alkyl chloroformate, and still more preferably Less than about 30 ppm by weight. Fluid channel 110 is preferably selected such that the total residence time between reactor 50 and deacidification column 160 is between about 0.5 and about 10 hours. Within this range, the residence time may preferably be at least about 1 hour, more preferably at least about 2 hours. Also within this range, the residence time may preferably be up to about 8 hours, more preferably up to about 7 hours.

In one embodiment, as shown in FIG. 3 , fluid channel 110 includes two storage containers 120 . The storage vessel 120, for example, can maintain the mixture at a temperature of about 55°C for about 2 hours. Each storage container 120 may preferably have a length-to-volume ratio (L/V) of less than 5, more preferably less than about 2. Although 2 storage containers 120 are shown in this figure, there is no particular limitation on the number of storage containers 120 in the fluid channel 110, and it may be preferred to use at least 2 storage containers 120, including 3, 4, 5, 6 or more The configuration of the storage container 120 is also preferred.

In another embodiment, as shown in FIG. 4 , the fluid channel 110 includes four storage containers 120 . The storage vessel 120, for example, can maintain the mixture at a temperature of about 70°C for about 4 hours. Each storage container 120 may preferably have a length-to-volume ratio (L/V) of less than 5, more preferably less than about 2.

In yet another embodiment, as shown in FIG. 5 , fluid channel 110 includes a portion having an L/V of at least 5, preferably at least about 10. For simplicity, this portion may be referred to as tubular portion 130 . Such a tubular portion 130 with L/V > 5 can facilitate plug flow of the mixture through the fluid channel 110, thereby efficiently utilizing the residence time to remove the alkyl chloroformate. In this embodiment, the residence time of the mixture in the one or more constricted portions having L/V > 5 preferably accounts for at least about 50% of the total residence time in the fluid channel 110, and more preferably accounts for at least about 50% of the total residence time in the fluid channel 110. At least about 80%.

Referring again to FIG. 1 , after the mixture exits the fluid channel 110 , it may optionally pass through a second heat exchanger 150 to form an at least partially vaporized mixture. The second heat exchanger 150 may have a residence time of less than 10 minutes. The vaporization step can also be accomplished without a heat exchanger by reducing the pressure applied to the condensed mixture (eg, passing the condensate through deacidification column 160 maintained at a lower pressure). The vaporized mixture can then optionally be treated to remove HCl, preferably injected into a deacidification column 160 . Deacidification column 160 may also help remove any entrained catalyst (eg, CuCl) that could otherwise cause downstream corrosion. In deacidification column 160, the vaporized condensate may preferably encounter countercurrent liquid supplied by countercurrent liquid line 170 to a high level in the column (eg, upper third). This countercurrent liquid can capture residual HCl and other reactants that can be removed from the bottom of deacidification column 160 and recycled to reactor 50 . The dialkyl carbonate mixture may be removed from the top of deacidification column 160 and optionally passed through azeotropic column 180 . As shown in FIG. 6 , an optional ion exchange resin bed 190 may also be included after deacidification column 160 or at any downstream location relative to deacidification column 160 . It is advantageous to include an optional ion exchange resin bed in purification unit 40 after water is removed from the dialkyl carbonate product stream. In a preferred embodiment, the unit does not include ion exchange resin bed 190 .

In a preferred embodiment, the method includes, based on the total components after removal of hydrochloric acid, reducing the concentration of hydrochloric acid in the mixture to less than about 1×10 ^-3 mol/L, more preferably less than about 5×10 ^-4 mol /L, even more preferably less than about 1×10 ^-4 mol/L.

In embodiments where the hydrochloric acid is removed after the alkyl chloroformate is removed from the mixture, the dialkyl carbonate and the alkyl chloroformate are in vapor form, which also includes condensing the dialkyl carbonate vapor and the alkyl chloroformate vapor , preferably forming a single liquid phase. Included in removing the alkyl chloroformate is the use of at least one gas-liquid separator. In particular, in one embodiment of the process of the invention the dialkyl carbonate is dimethyl carbonate, the alkanol is methanol and the catalyst comprises copper, wherein the process further comprises removing a portion of the carbon dioxide and a portion of the carbon monoxide from the mixture, at least in part After condensing the dimethyl carbonate vapors and methyl chloroformate vapors, at least 90% of the above methyl chloroformate and less than 1% of the above dimethyl carbonate are removed from the mixture.

In a preferred embodiment, the portion of separation unit 30 downstream of azeotropic column 180 and purification subunit 40 need not be corrosion resistant. Equipment upstream of azeotropic column 180 is preferably corrosion resistant; for example, it may be glass-lined. The term "corrosion resistant" is meant to describe a material that is capable of resisting 500 ppm HCl in a reaction mixture at a temperature of about 50 to about 135° C. without substantial corrosion for a relatively short period of time (eg, six months). Glass-lined vessels, vessels lined with precious metals such as tantalum, and specialty steels such as HASTELLOY(R) and CHROMALLOY(R) may be considered corrosion-resistant materials, but ordinary stainless steel that has not been modified to increase corrosion resistance is not. Azeotropic column 180 may be fabricated at least in part from a corrosion-resistant material. In a preferred embodiment, the bottom of the azeotropic column 180 can be fabricated from corrosion resistant steel, while the top of the column can be fabricated from common stainless steel.

In one embodiment of the apparatus, alkyl chloroformate is removed in fluid channel 110, as shown in Figures 1 and 3-6.

In another embodiment of the apparatus, as shown in Figure 7, the mixture is held in vapor-liquid separators 90 and 100 at a sufficient temperature and for a sufficient residence time to remove the alkyl chloroformate. In other words, the fluid channel 110 includes the gas-liquid separators 90 and 100 . For example, the mixture may remain in the condensed phase of the gas-liquid separator until substantially decomposed by reaction with water and methanol. In this embodiment, the first heat exchanger 140 and storage vessel 120 may be unnecessary.

In another embodiment of the apparatus, as shown in FIG. 8 , alkyl chloroformate can be removed in fluid channel 110 prior to gas-liquid separators 90 and 100 . In this embodiment, upstream of gas-liquid separators 90 and 100, one of the techniques described above for alkyl chloroformate removal may be used.

In another embodiment of the apparatus, as shown in Figure 9, hydrochloric acid can be removed from the mixture prior to removal of the alkyl chloroformate. In this embodiment, the alkyl chloroformate is removed in the gas phase rather than the liquid phase. For example, referring to FIG. 9 , fluid channel 110 follows azeotropic column 180 ; eg, fluid channel 110 may be inserted into azeotropic column vapor outlet conduit 210 . In this embodiment, the first heat exchanger 140 and the storage container 120 shown in FIG. 3 may be omitted. In this embodiment, fluid channel 110 may preferably include means suitable for removing alkyl chloroformate from the vapor phase (eg, ion exchange resins, absorption beds, vapor phase membranes, etc.) without condensation of the alkyl chloroformate.

Preferred embodiment is a kind of preparation method of dialkyl carbonate, it comprises: make alkanol, oxygen, carbon monoxide and catalyzer react to form containing dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and A mixture of carbon monoxide; the mixture is then passed through fluid channel 110 at a temperature of about 50°C to about 80°C for a residence time of about 1 to about 10 hours.

Another preferred embodiment is a device for preparing dialkyl carbonate, which comprises: reacting alkanol, oxygen, carbon monoxide and a catalyst to form a compound containing dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and carbon monoxide A facility (means) for the mixture; a facility for removing alkyl chloroformate from the mixture.

Another preferred embodiment is a device for preparing dialkyl carbonate, which comprises: reacting alkanol, oxygen, carbon monoxide and a catalyst to form a compound containing dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbon dioxide and carbon monoxide The reactor of the mixture; For removing the fluid channel 110 of alkyl chloroformate.

The dialkyl carbonates prepared according to this method are used to prepare diaryl carbonates. For example, diaryl carbonates can be prepared by reacting dialkyl carbonates with aryl hydroxides (see Scheme I above). The diaryl carbonate can be reacted sequentially with a dihydric phenol to form a polycarbonate (see Scheme II above). For example, dimethyl carbonate prepared according to this method can be reacted with phenoxide to form diphenyl carbonate, which in turn is reacted with bisphenol A to form polycarbonate.

The invention will be further illustrated below by means of non-limiting examples.

Example 1

Build a workshop as shown in Figure 2, and operate to generate dimethyl carbonate. Corrosion damage was observed in and downstream of the azeotropic column 180 . From extensive testing, it was determined that the corrosion damage was caused by methyl chloroformate passing through the acid separation column. More specifically, methyl chloroformate was found to be present in the azeotropic column 180 at a concentration of 300 ppm by weight.

Example 2-5

The decomposition kinetics of methyl chloroformate was studied under four different conditions. The procedure for determining methyl chloroformate in a sample is as follows. In Example 2, a 250 mL flask equipped with a thermometer, condenser, and sampling port was charged with 32 mL of dimethyl carbonate, 63 mL of methanol containing 10 mL of dimethyl carbonate with a 50 mg biphenyl internal standard, and 5 mL of water. (Methanol/water solution can be replaced by toluene). The resulting homogeneous solution was placed in an oil bath, and the solution temperature was kept constant at 50 °C. At the beginning of the timing, 81.7 microliters of pure methyl chloroformate were added to the solution (1000 ppm by weight). Samples were taken at different time periods and quenched by reacting methyl chloroformate in the sample with diisobutylamine to convert methyl chloroformate to N,N'-diisocarbamate Butyl methyl ester (N, N'-diisobutyl methylcarbamate). Then use standard silver nitrate solution titration to analyze the content of N, N'-diisobutyl methyl carbamate, to quantitatively draw the existing chloride ion content. The content of methyl chloroformate can then be deduced by analyzing the chloride ion content of the original sample. Since each equivalent of methyl chloroformate releases one equivalent of chloride ion after derivatization, the difference in chlorine concentration is equal to the concentration of methyl chloroformate. Alternatively, diisobutylmethyl N,N'-carbamate can be directly analyzed using gas chromatography by using an internal standard.

Table I below shows the decomposition rate constants (k) observed at 50°C under different conditions. Embodiment 2 is consistent with the above-mentioned embodiment. Example 3 has added hydrochloric acid, which is normally present in the actual reaction mixture. Embodiment 4 tests the effect of a small amount of sodium bicarbonate. In Example 5, the ratio of dimethyl carbonate and methanol was kept constant, but the content of water was increased from 5% to 10%. The test results are summarized in Table I below.

Table I DMC(wt%) MeOH(wt%) H ₂ O (wt%) temperature(℃) k(min ^-1 ) Example 2 45 50 5 50 0.043 Example 3 ^* 45 50 5 50 0.043 Example 4 ^** 45 50 5 50 0.480 Example 5 ^*** 43 47 10 50 0.055

^* Same as Example 2, except that it also contained 1000 ppm HCl, which is similar to the off-gas from reactor 50.

^** Same as Example 2, except that 1.6 equivalents of sodium bicarbonate relative to 1000 ppm MCF was added.

^*** Same as Example 2, except that the percentage of water was increased to 10%, but the ratio of DMC/MeOH remained the same, but decreased overall.

The logarithmic plot of methyl chloroformate concentration versus time was linear and fitted to a pseudo-first-order kinetic model. This behavior was observed even in the presence of hydrochloric acid, so this method can be used to determine the concentration of methyl chloroformate in a specific sample. Comparing Examples 2 and 5 shows that only minor changes in the rate coefficient k are observed when the water content of the analyzed sample is changed by a factor of two. Comparing Examples 2 and 3 unexpectedly shows that the addition of HCl does not affect the observed rate of decomposition of methyl chloroformate. Comparing Examples 2 and 4 shows that even a small amount of base increases the reaction rate more than 10-fold. In practice, however, conditions with strong bases are best avoided, as they also increase the rate of decomposition of dimethyl carbonate.

Embodiment 6, Comparative Example 1

These tests indicated that fluid passage 110 was effective in reducing the concentration of methyl chloroformate that reacted to form HCl in downstream units of the plant. Referring to FIG. 1 , process fluids were sampled at different locations in a dimethyl carbonate plant having a configuration with a first heat exchanger 140 and 2 storage vessels 120 (i.e., a configuration consistent with FIG. 3 ), yielding two kind of sample. A first sample (Comparative Example 1) was taken immediately before the first heat exchanger 140 . A second sample (Example 6) was taken after the second storage container 120 (ie, after the fluid channel 110). Take the sample to the laboratory and determine its chlorine content as a function of sampling time. The results are shown in Table II. The data of Example 6 show that the content of chloride ions is substantially constant, which indicates that there are no species that are prone to generate chlorine, such as methyl chloroformate, in the sample. In contrast, the data for Comparative Example 1 show that the chloride ion content increases over time, consistent with the presence of methyl chloroformate in the initial sample, and decomposes over time to form excess chloride ions. Thus, these data collectively show that, in the absence of fluid channel 110, substantial chloride ion formation can occur in downstream units of the plant (after deacidification column 160), leading to corrosion, but the presence of fluid channel 110 has a significant impact on the It is effective to decompose alkyl chloroformate to chloride ions before 160°C, thereby preventing downstream corrosion.

Table II time (hours) Chloride ion concentration (ppm) Example 6 Comparative example 1 0 374 189 2 408 312 4 374 339 8 372 368 10 372 357 25 381 368

Embodiment 7, comparative example 2

For Comparative Example 2, the dimethyl carbonate plant shown in schematic diagram 2 was operated according to the conditions described in Table III below. The plant is similar to the plant detailed in FIG. 1 , except that the first heat exchanger 140 and fluid channel 110 are absent. Corrosion was observed within and downstream of the azeotropic column 180 . The plant was then modified to include a first heat exchanger 140, with the addition of 2 storage vessels 120 for extended residence times (ie, the configuration of Figure 3). FIG. 10 shows residual chloride ions found in a sample taken from the bottom of azeotropic column 180 as measured over time, compared to the configurations of FIGS. 2 and 3 . Residual chloride ions were determined by titration using silver nitrate as described above. Figure 2 configuration data has an average chloride ion concentration of 671 ppm with a standard deviation of 370 ppm; however, the Figure 3 configuration data has an average chloride ion concentration of 35 ppm with a standard deviation of 25 ppm. Therefore, these data show that the chloride ion content of the Figure 3 configuration is significantly reduced compared to the Figure 2 configuration. It is anticipated that this reduction will be even greater for the configurations of Figures 4 and 6 using 4 storage vessels 120 to provide a residence time of 4 hours at 70°C. FIG. 11 shows the results of measurements of the concentration of methyl chloroformate entering and exiting fluid channel 110 of FIG. 3 . In other words, the points indicated with a "+" in FIG. 11 and labeled "MCF enters fluid channel" correspond to measurements of the mixture as it is entering the fluid channel 110; by weight, the average of these points is 930ppm (ppmw), the standard deviation is 412ppmw. The points denoted by "■" and labeled "MCF out of fluid channel" correspond to measurements of the mixture as it exited the fluid channel 110; the mean of these points is 45 ppmw with a standard deviation of 77 ppmw. These data clearly show that the device according to Figure 3 is effective in significantly reducing the concentration of methyl chloroformate in the process stream.

Table III condition Embodiment 7 (figure 2 configuration) Comparative example 2 (configuration in Figure 3) MeOH/O ₂ /CO mass ratio 0.7/0.06/1 0.7/0.06/1 Catalyst amount fixed fixed Reaction temperature (°C) 133 133 Reaction pressure (barg) twenty three twenty three Pre-residence time heater temperature (°C) 60 -- Acid column feed vaporizer temperature (°C) 90 90 Between flush tank and acid column, excluding residence time of both (hours) 2 0.03

Table IV structure Average chloride ion concentration ± standard deviation (ppm) Figure 3 (comparison) 671±370 Figure 2 (invention) 35±25

While the invention has been described in terms of preferred embodiments, it will be understood by those skilled in the art that various modifications may be made or equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation and material to the teachings of the invention without departing from its essential scope. Therefore, the invention is not intended to be limited to the particular embodiments disclosed as the best mode for carrying out the invention. However, the invention is intended to include all embodiments falling within the scope of the appended claims.

For technical and technical terms in the present invention that are not specifically defined herein, explanations can be found in Grant and Hach's Chemical Dictionary (5 ^th ed., McGraw-Hill, Inc.).

All cited patents and other references are incorporated herein by reference in their entirety.

Claims (42)

1. method for preparing dialkyl carbonate, it comprises:

Make alkanol, oxygen, carbon monoxide and catalyst reaction form the mixture that contains dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbonic acid gas and carbon monoxide;

From said mixture, remove alkyl chloroformate.

2. according to the said method of claim 1, wherein said alkanol comprises the alkanol that contains 1～12 carbon atom.

3. according to the said method of claim 1, wherein said alkanol comprises the primary alkanol that contains 1～6 carbon atom.

4. according to the said method of claim 1, wherein said alkanol comprises methyl alcohol.

5. according to the said method of claim 1, wherein said alkanol, said oxygen and said carbon monoxide are with 0.5 to 0.7 alkanol: 0.04 to 0.06 oxygen: the molar ratio reaction of 0.8 to 1.2 carbon monoxide.

6. according to the said method of claim 1, said catalyzer comprises a kind of metal in chosen from Fe, copper, nickel, cobalt, zinc, ruthenium, rhodium, palladium, silver, cadmium, rhenium, osmium, iridium, platinum, gold or the mercury or comprises the combination one of at least of above-mentioned metal.

7. according to the said method of claim 1, wherein said catalyzer comprises copper.

8. according to the said method of claim 1, wherein said catalyzer comprises chlorion.

9. according to the said method of claim 1, wherein said catalyzer comprises that mol ratio is 0.5 to 1.5 copper and chlorion.

10. according to the said method of claim 1, wherein said reaction is carried out in single reactor (50).

11. according to the said method of claim 1, wherein said reaction is carried out in corrosion resistant reactor (50).

12., also comprise and from said mixture, remove carbonic acid gas and carbon monoxide according to the said method of claim 1.

13., wherein from said mixture, remove at least 90% said carbonic acid gas and at least 90% said carbon monoxide according to the said method of claim 12.

14. according to the said method of claim 12, wherein said carbonic acid gas and the carbon monoxide removed comprises and makes said mixture by a plurality of gas-liquid separators.

15. according to the said method of claim 14, wherein said reaction is carried out under pressure, said a plurality of gas-liquid separators comprise have reactor pressure 10% within pressure first gas-liquid separator and have second gas-liquid separator less than the pressure of 20% reactor pressure.

16., wherein from said mixture, remove at least 80% said alkyl chloroformate according to the said method of claim 1.

17., wherein from said mixture, remove at least 90% said alkyl chloroformate according to the said method of claim 1.

18., wherein from said mixture, remove at least 95% said alkyl chloroformate according to the said method of claim 1.

19., wherein from said mixture, remove at least 99% said alkyl chloroformate according to the said method of claim 1.

20. according to the said method of claim 1, the wherein said alkyl chloroformate of removing comprises and removing less than 5% said dialkyl carbonate.

21. according to the said method of claim 1, the wherein said alkyl chloroformate of removing comprises and removing less than 1% said dialkyl carbonate.

22. according to the said method of claim 1, the wherein said alkyl chloroformate of removing comprises that the concentration that reduces said alkyl chloroformate is to less than 500ppm by weight.

23. according to the said method of claim 1, the wherein said alkyl chloroformate of removing comprises that the concentration that reduces said alkyl chloroformate is to less than 100ppm by weight.

24. according to the said method of claim 1, the wherein said alkyl chloroformate of removing comprises that the concentration that reduces said alkyl chloroformate is to less than 30ppm by weight.

25. according to the said method of claim 1, wherein said remove alkyl chloroformate comprise use be selected from heating, pressure boost, the increase residence time, add polar solvent, absorption, membrane sepn, pervaporation, by ion exchange resin, be exposed to stoichiometry reagent and be exposed in the catalytic reagent at least a technology and comprise combination at least a in the above-mentioned technology.

26., also comprise and remove hydrochloric acid according to the said method of claim 1.

27. according to the said method of claim 26, the wherein said hydrochloric acid of removing comprises that the reduction concentration of hydrochloric acid is extremely less than 1 * 10 ^-3Mol/L.

28. according to the said method of claim 26, also be included in and remove before the said hydrochloric acid, the said mixture of vaporizing.

29. according to the said method of claim 28, wherein said vaporization comprises the said mixture of heating, reduces to be applied to pressure or above-mentioned two operations on the said mixture.

30. according to the said method of claim 26, the wherein said hydrochloric acid of removing comprises and makes said mixture by depickling post (160).

31. according to the said method of claim 26, the wherein said hydrochloric acid of removing comprises and makes said mixture by depickling post (160) and ion exchange resin.

32. according to the said method of claim 1, wherein said method is operate continuously.

33. according to the said method of claim 22, the wherein said alkyl chloroformate of removing comprises removing and is less than 10% described dialkyl carbonate and removes hydrochloric acid from said mixture.

34., wherein after from mixture, removing alkyl chloroformate, remove hydrochloric acid according to the said method of claim 26.

35. according to the said method of claim 34, wherein dialkyl carbonate and alkyl chloroformate are vapor form.

36., also comprise said dialkyl carbonate steam of condensation and said alkyl chloroformate steam according to the said method of claim 35.

37. according to the said method of claim 36, said dialkyl carbonate steam of wherein said condensation and said alkyl chloroformate steam generate single liquid phase.

38. according to the said method of claim 34, the wherein said alkyl chloroformate of removing comprises at least one gas-liquid separator of use.

39., wherein before from mixture, removing alkyl chloroformate, remove hydrochloric acid according to the said method of claim 26.

40. method according to claim 36, wherein dialkyl carbonate is a methylcarbonate, and alkanol is a methyl alcohol, and catalyzer comprises copper,

Wherein this method further comprises

From mixture, remove a part of carbonic acid gas and a part of carbon monoxide; And

Behind the steam of the steam of the described methylcarbonate of partial condensation at least and methyl-chloroformate, from described mixture, remove at least 90% described methyl-chloroformate and be less than 1% described methylcarbonate.

41. a method for preparing diaryl carbonate comprises

(a) with alkanol, oxygen, carbon monoxide and catalyst reaction, formation comprises following mixture: dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbonic acid gas and carbon monoxide;

(b) from the described mixture that comprises dialkyl carbonate, remove alkyl chloroformate; And

(c) reaction of dialkyl carbonate that will prepare in (b) and aryl hydroxides is with the preparation diaryl carbonate.

42. a method for preparing polycarbonate comprises

(a) alkanol, oxygen, carbon monoxide and catalyst reaction are comprised following mixture with formation: dialkyl carbonate, alkyl chloroformate, hydrochloric acid, water, carbonic acid gas and carbon monoxide;

(b) from the described mixture that comprises dialkyl carbonate, remove alkyl chloroformate;

(c) reaction of dialkyl carbonate that will prepare in (b) and aryl hydroxides is with the preparation diaryl carbonate; And

(d) diaryl carbonate and the dihydric phenol with preparation in (c) reacts.

Images