HK1152034B - Method for the production of epichlorohydrin - Google Patents

Description

Process for the preparation of epichlorohydrin

Technical Field

The present invention relates to a process for preparing epichlorohydrin by reacting allyl chloride with hydrogen peroxide.

Background

Epichlorohydrin (chloromethyl oxirane) is an important chemical intermediate, which is used, for example, for the preparation of resins.

A suitable process for preparing epichlorohydrin is the reaction of allyl chloride with hydrogen peroxide in the presence of a titanium-containing zeolite catalyst (disclosed in EP-A0100119). In order to obtain a high selectivity to epichlorohydrin in such a reaction, allyl chloride must be used in stoichiometric excess with respect to hydrogen peroxide, as disclosed, for example, in WO 2004/043941. Unreacted allyl chloride can be separated off by distillation and returned to the epoxidation reaction, as disclosed, for example, in WO 02/00634 or WO 02/14298.

Technical grade allyl chloride usually contains impurities 1-chloropropane and/or 2-chloropropane. These two impurities have boiling points similar to allyl chloride:

allyl chloride: 45 deg.C

1-chloropropane: 47 deg.C

2-chloropropane: 36 deg.C

These two chloropropanes can therefore only be separated from allyl chloride by a very complicated distillation process. If technical grade allyl chloride containing the impurity chloropropane is used for the reaction of allyl chloride with hydrogen peroxide and unreacted allyl chloride is separated off by a distillation process and returned to the epoxidation reaction, this therefore leads to an enrichment of chloropropane in the process.

It is disclosed in WO 02/00634 and WO 02/14298 that impurities in the returned, unreacted olefin can be prevented from being enriched to an undesirably high concentration by withdrawing a portion of the returned olefin from the process. However, the side stream which is discharged contains a very high proportion of the olefin which is lost as a result of this discharge.

There is thus a need for a process for preparing epichlorohydrin by reacting allyl chloride containing chloropropanes, which has a high selectivity for epichlorohydrin and an improved conversion with respect to the allyl chloride used in the known process.

Description of the invention

This object is achieved by the process according to the invention in which, in a first reaction step, allyl chloride containing chloropropane is reacted with hydrogen peroxide in excess. Unreacted allyl chloride is separated off and returned to the reaction, wherein a portion of the separated allyl chloride is conducted to a second reaction step and reacted with hydrogen peroxide, wherein the amount of hydrogen peroxide in the second reaction step is selected such that the allyl chloride is largely and preferably virtually completely reacted. Chloropropane can subsequently be separated off from the reaction mixture of the second reaction step by distillation without loss of allyl chloride. Since in the process according to the invention a large part of the allyl chloride is reacted with an excess of allyl chloride, while only a small part of the allyl chloride is reacted with a small excess or deficiency of allyl chloride, the high selectivity to epichlorohydrin achieved by the excess of allyl chloride is maintained.

The present invention accordingly provides a process for preparing epichlorohydrin, in which

a) In a first reaction step, allyl chloride and hydrogen peroxide are reacted in the presence of a titanium-containing zeolite catalyst in a molar ratio of allyl chloride to hydrogen peroxide of at least 1.5: 1 and wherein the allyl chloride used contains 1-chloropropane and/or 2-chloropropane,

b) the reaction mixture formed in the first reaction step is separated in a distillation into a mixture (A) comprising unreacted allyl chloride and 1-chloropropane and/or 2-chloropropane, and a mixture (B) comprising epichlorohydrin,

c) the mixture (A) is divided into a mixture (A1) which is returned to the first reaction step and a mixture (A2),

d) reacting the mixture (A2) in a second reaction step with hydrogen peroxide in the presence of a titanium-containing zeolite catalyst in a molar ratio of allyl chloride to hydrogen peroxide in the range from 0.5: 1 to 1.25: 1,

e) the reaction mixture formed in the second reaction step is separated in a distillation into a mixture (C) comprising 1-chloropropane and/or 2-chloropropane, and a mixture (D) comprising epichlorohydrin, and

f) the mixture (C) is removed from the process.

In the process according to the invention, allyl chloride and hydrogen peroxide are reacted in the presence of a titanium-containing zeolite catalyst to form epichlorohydrin. The allyl chloride used here contains 1-chloropropane and/or 2-chloropropane. Thus, for the process according to the invention, it is possible to use allyl chloride of industrial quality comprising 1-chloropropane and/or 2-chloropropane as by-product of the industrial preparation of allyl chloride. The content of 1-chloropropane and 2-chloropropane in the allyl chloride used is preferably in the range from 0.01 to 2% by weight, particularly preferably in the range from 0.05 to 0.8% by weight.

The hydrogen peroxide can be used as an aqueous solution, which is peroxidizedThe hydrogen content is preferably in the range of 1 to 90% by weight, particularly preferably 10 to 80% by weight, and particularly 30 to 70% by weight. The hydrogen peroxide can be used in the form of a conventional commercially available stabilized solution. Also suitable are the unstabilized hydrogen peroxide prepared by the anthraquinone process, which can be used without further purification. Preference is given to using hydrogen peroxide as disclosed in WO 2004/028962, which contains less than 50ppm of alkali metals and alkaline earth metals, less than 50ppm of pK_BLess than 4.5 and at least 100ppm of anions, in each case based on the weight of hydrogen peroxide.

In another preferred embodiment, a solution of hydrogen peroxide in methanol is used, which is preferably prepared by reacting hydrogen and oxygen in methanol over a palladium catalyst. Particular preference is given to using a hydrogen peroxide solution in methanol according to claim 9 of WO 2006/108784, which comprises 2 to 15% by weight of hydrogen peroxide, 0.5 to 20% by weight of water, 60 to 95% by weight of methanol, 10^-6～10^-2mol/l bromide, and 10^-60.1mol/l dimethyl sulfate and/or monomethyl sulfate.

As titanium-containing zeolite catalysts it is possible to use all titanium-containing zeolites known from the prior art which are catalytically active for the reaction of olefins with hydrogen peroxide. Preferably, titanium silicalite (titanosilalite) having an MFI or MEL crystal structure is used as the titanium-containing zeolite catalyst. The use of the composition (TiO) is particularly preferred₂)_x(SiO₂)_1-xThe titanium silicalite of (1), wherein x is in the range of 0.001-0.05. Most preferred is titanium silicalite prepared by the process according to WO 01/64581 or the process according to WO 01/64582.

The titanium-containing zeolite catalyst may be used in the process according to the invention in the form of a suspension catalyst. In this case, the reaction is preferably carried out such that the catalyst suspended in the reaction mixture remains in the first reaction step, for example by filtration or by sedimentation, so that the reaction mixture separated off in step b) during the distillation is free of catalyst.

Preferably, however, the titanium-containing zeolite catalyst is used in the process according to the invention in the form of a fixed bed catalyst. Particularly suitable are fixed-bed catalysts in the form of extrudates (diameter 1 to 5mm) shaped by extrusion, which preferably comprise binders in an amount of 1 to 99% by weight, particularly preferably 1 to 40% by weight, based on the titanium-containing zeolite. Suitable here are all binders which react under the reaction conditions neither with the hydrogen peroxide used nor with the epichlorohydrin formed. A particularly suitable binder is silica. Particular preference is given to fixed-bed catalysts in which, for the purpose of extrusion, pyrogenic silica, colloidal silica sols or tetraalkylorthosilicate or a combination of two of these components is used as binder precursor. Also particularly preferred is a fixed bed catalyst prepared by shaping a molded body having a plateau value of the coagulation curve (Curdkurve) in the range of 20 to 90mm according to the method disclosed in WO 01/72419.

In the process according to the invention, in step a) in the first reaction step allyl chloride and hydrogen peroxide are reacted in a molar ratio of allyl chloride to hydrogen peroxide of at least 1.5: 1. Here, the molar ratio of allyl chloride to hydrogen peroxide can be up to 100: 1. Preferably, the molar ratio is in the range of 1.5: 1 to 5: 1. Particularly preferably, the molar ratio of allyl chloride to hydrogen peroxide is 2: 1 to 4: 1. At lower molar ratios, the selectivity to epichlorohydrin in the first reaction step decreases. The disadvantage of higher molar ratios is that large amounts of unreacted allyl chloride have to be separated off and recycled with corresponding energy expenditure.

In step d) of the process according to the invention, allyl chloride and hydrogen peroxide are reacted in a second reaction step in a molar ratio of allyl chloride to hydrogen peroxide in the range from 0.5: 1 to 1.25: 1. Preferably, the molar ratio of allyl chloride to hydrogen peroxide is 0.8: 1 to 1.15: 1. The use of a molar ratio in the stated range makes it possible to convert allyl chloride completely or largely in the second reaction step, so that the mixture (C) obtained in step e) and removed from the process in step f) contains only small amounts of the allyl chloride used.

The reaction of allyl chloride with hydrogen peroxide in steps a) and d) is preferably carried out in the presence of a solvent. Solvents which dissolve allyl chloride and hydrogen peroxide under the reaction conditions and react only to a small extent (or not at all) with hydrogen peroxide or epichlorohydrin are particularly suitable. Suitable solvents are, for example, alcohols such as methanol, ethanol or tert-butanol; glycols such as ethylene glycol, 1, 2-propanediol or 1, 3-propanediol; cyclic ethers such as tetrahydrofuran or dioxane, glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether or propylene glycol monomethyl ether; and ketones such as acetone or 2-butanone. Preferred solvents are aliphatic alcohols having 1 to 4 carbon atoms. Methanol is particularly preferably used as solvent. The proportion of the solvent in the reaction mixture is preferably 10 to 95% by weight, particularly preferably 30 to 80% by weight in the first reaction step, and preferably 10 to 95% by weight, particularly preferably 30 to 80% by weight in the second reaction step.

The reaction of allyl chloride with hydrogen peroxide is preferably carried out in the first reaction step at a temperature in the range from 0 to 100 ℃, particularly preferably from 30 to 65 ℃, and in the second reaction step preferably at a temperature in the range from 0 to 100 ℃, particularly preferably from 30 to 65 ℃. The pressure in these reaction steps can be freely chosen within wide limits and is preferably chosen to be so high that the boiling point of allyl chloride at the pressure used is the same as or higher than the reaction temperature used.

The reaction conditions in the first reaction step are preferably selected such that a hydrogen peroxide conversion in the range of 50 to 100%, preferably 80 to 99.8%, is achieved. In the second reaction step, the reaction conditions are preferably selected such that the components used in molar deficiency from among the components allyl chloride and hydrogen peroxide react to 70 to 100%, preferably 90 to 99%.

For the reaction of allyl chloride and hydrogen peroxide in steps a) and d), any reactor suitable for carrying out a liquid phase reaction can be used. The reaction can be carried out batchwise or continuously, with preference being given to continuous reaction.

The reactions in steps a) and d) are preferably carried out continuously in a fixed bed reactor, wherein a mixture comprising hydrogen peroxide, optionally a solvent and allyl chloride or mixture (a2) is conducted through a fixed bed of the titanium-containing zeolite catalyst. Preference is given to using externally cooled tubular reactors, in particular tube bundle reactors, as fixed-bed reactors. The fixed bed reactor can be operated in an upflow or downflow, with downflow operation being preferred in the trickle bed position.

In both step a) and step d), the reaction may be carried out in two or more reactors in series. Preferably, two reactors in series are used in step a). In both step a) and step d), two or more reactors arranged in parallel may be used, so that one reactor is in a shutdown state for the regeneration of the catalyst and the reaction can be continued in the reactors connected in parallel.

The reaction mixture formed in the first reaction step is separated in step B) of the process according to the invention into a mixture (a) comprising unreacted allyl chloride and 1-chloropropane and/or 2-chloropropane, and a mixture (B) comprising epichlorohydrin during the distillation. The distillation is preferably carried out in the form of a continuous rectification in which the reaction mixture formed in the first reaction step is conducted to a rectification column in the middle section, the mixture (A) being taken off at the top and the mixture (B) being taken off at the bottom. A rectifying column having 10 to 50 theoretical plates (Trennstufen) is preferably used. The rectification is preferably carried out at a pressure in the range from 0.2 to 3 bar at the top of the column and preferably at a reflux ratio of from 0.5 to 5.

The distillation process is preferably operated such that the mixture (a) obtained comprises more than 95% of the allyl chloride present in the introduced reaction mixture and the mixture (B) obtained comprises more than 95% of the epichlorohydrin present in the introduced reaction mixture.

In step c) of the process according to the invention, the mixture (A) is divided into a mixture (A1) which is returned to the first reaction step and a mixture (A2) which is returned to the second reaction step.

The mixture (A) is preferably divided in such a way that 50 to 98%, particularly preferably 70 to 95%, of the allyl chloride present in the mixture (A) is returned with the mixture (A1) to the first reaction step.

In a preferred embodiment, mixture (a) is separated by a distillation process such that the chloropropanes present in mixture (a) are enriched in mixture (a 2).

In step e) of the process according to the invention, the reaction mixture formed in the second reaction step is separated during distillation into a mixture (C) comprising 1-chloropropane and/or 2-chloropropane, and a mixture (D) comprising epichlorohydrin. The distillation is preferably carried out in the form of a continuous rectification in which the reaction mixture formed in the second reaction step is conducted to a rectification column in the middle section, the mixture (C) being taken off at the top and the mixture (D) being taken off at the bottom. Preferably, a rectifying column having 10 to 50 theoretical plates is used. The rectification is preferably carried out at a pressure in the range from 0.5 to 3 bar at the top of the column and preferably at a reflux ratio of from 0.5 to 5.

The distillation is preferably operated so that the mixture (C) obtained comprises more than 90% of the chloropropanes present in the introduced reaction mixture and the mixture (D) obtained comprises more than 95% of the epichlorohydrin present in the introduced reaction mixture.

In a preferred embodiment, the mixture (D) obtained in step e) of the process according to the invention is returned to the first reaction step. This embodiment is particularly advantageous if a molar excess of hydrogen peroxide is used in step D) and the mixture (D) still contains unreacted hydrogen peroxide. Due to the return to the first reaction step, this unreacted hydrogen peroxide can still be used for the epoxidation of further allyl chloride. In a particularly preferred embodiment, the first reaction step is carried out in two reactors connected in series, and the mixture (D) is returned to the second reactor.

In another embodiment, steps d) and e) of the process according to the invention are carried out simultaneously in the form of a reactive distillation. In this embodiment, the titanium-containing zeolite catalyst of the second reaction step is arranged in the reaction section of the rectification column, the mixture (a2) is introduced into the column at a position below the reaction section and the hydrogen peroxide is introduced at a position above the reaction section. The mixture (C) was taken overhead and the mixture (D) was taken bottom.

Figure 1 shows schematically a preferred embodiment of the claimed process, wherein the reactions in steps a) and d) are carried out in fixed bed reactors and the distillation processes in steps b) and e) are carried out in distillation columns. The auxiliary equipment required for carrying out the process, such as pumps, heat exchangers, evaporators and condensers, are not shown. In the process of FIG. 1, in steps a) and e), nitrogen is additionally fed as inert gas in order to prevent the formation of combustible gas mixtures. Hydrogen peroxide (1), allyl chloride (2), methanol (3) and nitrogen (4) are introduced into the first fixed bed reactor (a). The reaction mixture obtained in the first fixed-bed reactor (a) is separated in a distillation column (B) into a top product (7) comprising allyl chloride and unreacted chloropropanes (mixture a), a bottom product (5) comprising epichlorohydrin (mixture B), and an offgas stream (6). Mixture a is subsequently divided in (c) into a stream (8) (mixture a1) which is conducted back into the first fixed-bed reactor (a), and a stream (9) (mixture a2) which is conducted into the second fixed-bed reactor (d) and reacted there with further hydrogen peroxide (10). The reaction mixture obtained in the second fixed-bed reactor (D) is separated in a distillation column (e) into a top product (12) comprising chloropropanes (mixture C) and a bottom product (13) comprising epichlorohydrin (mixture D) and being returned to the first fixed-bed reactor (a). Further, nitrogen (11) was introduced into the distillation column (e).

Examples

Example 1

Effect of the molar ratio of allyl chloride to Hydrogen peroxide on reaction Selectivity

Allyl chloride was reacted with hydrogen peroxide in methanol as solvent using a titanium silicalite catalyst with MFI structure. The reaction was carried out in two tubular reactors cooled by cooling jackets in series. The catalyst is used as a fixed bed in the form of extrudates. The first reactor contained 21.5g of catalyst and the second reactor 20.7 g. Allyl chloride and a mixture of aqueous hydrogen peroxide and methanol were continuously introduced into the first reactor. The metered feed streams, the mixture composition and the molar ratio of allyl chloride to hydrogen peroxide in the starting material are given in table 1. The reactor is operated in an upflow mode of operation, the pressure in the reactor is maintained at 7-8 bar, and the first reactor is heated to 36 ℃ and the second reactor is heated to 38 ℃. In the reaction mixture obtained, the hydrogen peroxide content was determined by redox titration and the allyl chloride and epichlorohydrin contents were determined by gas chromatography. The hydrogen peroxide conversion calculated from these contents and the epichlorohydrin selectivity based on the allyl chloride reacted off are given in table 1. Table 1 shows that epichlorohydrin selectivity increases with increasing molar excess of allyl chloride.

TABLE 1

Example 2:

method according to FIG. 1

For the process of fig. 1, the reactions in the fixed-bed reactors (a) and (d) were repeated experimentally in a tubular reactor corresponding to example 1, the molar ratio of allyl chloride to hydrogen peroxide being 4.0 in reactor (a) and 1.1 in reactor (b). For this purpose, the reactor contained 42.6g of catalyst and was heated to 40 ℃. The compositions of the metered feed streams, the mixture of hydrogen peroxide, water and methanol and the molar ratio of allyl chloride to hydrogen peroxide in the starting material are given in table 2, where the values are selected as those obtained on the basis of the back-leading procedure in the process of fig. 1. The experimentally determined selectivity and the estimation of the reactivity towards 1-chloropropene relative to allyl chloride were then used to calculate the composition of the quantitative streams 1-13 for the process of FIG. 1 using the Aspentech Plus simulation program from Aspentech. The results are given in table 3.

In the process of FIG. 1, 1.12mol of allyl chloride are required for the preparation of 1mol of epichlorohydrin. In contrast, in the process according to the prior art, in which the amount of allyl chloride contained in the effluent stream 9 from the process, 1.35mol of allyl chloride are required for the preparation of 1mol of epichlorohydrin.

TABLE 2

TABLE 3

Claims (9)

1. Process for preparing epichlorohydrin in which

a) In a first reaction step, allyl chloride and hydrogen peroxide are reacted in the presence of a titanium-containing zeolite catalyst in a molar ratio of allyl chloride to hydrogen peroxide of at least 1.5: 1 and wherein the allyl chloride used contains 1-chloropropane and/or 2-chloropropane,

b) the reaction mixture formed in the first reaction step is separated in a distillation into a mixture (A) comprising unreacted allyl chloride and 1-chloropropane and/or 2-chloropropane, and a mixture (B) comprising epichlorohydrin,

c) the mixture (A) is divided into a mixture (Al) which is returned to the first reaction step and a mixture (A2),

d) reacting the mixture (A2) in a second reaction step with hydrogen peroxide in the presence of a titanium-containing zeolite catalyst in a molar ratio of allyl chloride to hydrogen peroxide in the range from 0.5: 1 to 1.25: 1,

e) the reaction mixture formed in the second reaction step is separated in a distillation into a mixture (C) comprising 1-chloropropane and/or 2-chloropropane, and a mixture (D) comprising epichlorohydrin, and

f) the mixture (C) is removed from the process.

2. The process according to claim 1, wherein the reaction of allyl chloride with hydrogen peroxide in steps a) and d) is carried out in the presence of a solvent.

3. A process according to claim 2, characterized in that the solvent is methanol.

4. A process according to claim 3, characterized in that the hydrogen peroxide is used in the form of a solution of hydrogen peroxide in methanol.

5. The process according to any of the preceding claims 1 to 4, characterized in that the molar ratio of allyl chloride to hydrogen peroxide in step a) is in the range of 1.5: 1 to 5: 1.

6. Process according to any one of the preceding claims 1 to 4, characterized in that the partitioning of the mixture (A) in step c) is carried out by a distillation process in which the chloropropanes present in the mixture (A) are enriched in the mixture (A2).

7. The process according to any of the preceding claims 1 to 4, characterized in that the mixture (D) is conducted back to the first reaction step.

8. The process according to claim 7, wherein the first reaction step is carried out in two reactors connected in series and the mixture (D) is returned to the second reactor.

9. Process according to any of the preceding claims 1 to 4, characterized in that steps d) and e) are carried out simultaneously in a reactive distillation process.