TWI359791B - Chlorine dioxide from a methanol-based generating - Google Patents

Description

1359791 IX. Description of the Invention: [Technical Leading Technology of the Invention] The present invention relates to an alkali metal having a very low impurity content by a reduction source ϋ low pressure 'methanol-based chlorine dioxide production method> A method of a sub-acid salt solution. [Prior Art]

Alkali metal sulphates are well known chlorine dioxide precursors. Among them, chlorine dioxide is used in a wide range of applications, mainly in water treatment, pulp bleaching and textile bleaching. The gas sulfite is typically produced by the reaction of chlorine dioxide, a reducing agent and a base. A detailed discussion of the various manufacturing methods used for the synthesis of sulphate can be found in the basic textbook entitled: "chl〇rine Di〇xide. Chemistry and Environmental Impact of Oxychlorine Compounds" » W J.

Masschelein, 1979, pp. 130-145, the disclosures of which are incorporated herein by reference.

Various modifications to the basic concept of reacting a reducing agent and a base with a dioxide gas to form a sulphuric acid salt are disclosed in several U.S. patents discussed below. U.S. Patent Nos. 2,092,944 and 2,092,945 (Vincent) disclose the production of water-soluble sulphuric acid salts by the reaction of a oxidizing gas with an alkaline solution containing sulfur or a carbonaceous reducing agent. U.S. Patent No. 2,194,194 (Cunningham) discloses the use of a metal reducing agent for the manufacture of a sulphuric acid salt. U.S. Patent No. 2,332,180 (Soule) discloses the use of hydrogen peroxide and an alkali metal acid carbonate in the synthesis of chlorite. The same reducing agent is disclosed in U.S. Patent No. 2,616,783 (Wagner), issued to U.S. Patent No. 2, 616, 783 (Wagner), U.S. Patent No. 3,101, 248 (Hirschberg et al.). A method for synthesizing a sulphite salt of a metal and a soil-measuring metal mixture as a reducing agent. U.S. Patent No. 3,450,493 (Du Bellay et al.) discloses a method of making an alkali metal chlorite using continuous monitoring of the redox potential and pH for correcting process control.

U.S. Patent No. 3,828,097 (Callerame) discloses a method for the production of a gas-energy acid, which comprises the use of a sub-salt salt in a column comprising a cation exchange resin. U.S. Patent No. 4,087,515 (Miller) discloses the use of alkali metal amalgam as a reducing agent' whereby the process is carried out under atmospheric nitrogen to prevent excessive accumulation of chlorine monoxide.

U.S. Patent No. 5,597,544 (Barber et al.) and U.S. Patent No. 5,639,559 (Mason et al.) disclose a gas phase reaction between chlorine dioxide and a reducing agent whereby chlorous acid is formed followed by a base such as hydroxide or carbonic acid. An aqueous solution of a salt or an acid carbonate reacts to form a sulfite in a high yield. One of the major drawbacks of all of the above methods is that the finished product has certain high levels of impurities, particularly carbonates and acid carbonates, according to the published literature (see, for example, Masschelein, p. 131, lines 10 and 11). A typical, commercially available sodium oxysulfite product having a weight percent of 80% typically comprises sodium carbonate in an amount of about 5% by weight. When the alkali metal sulphate is used, especially when the chlorite is converted to chlorine dioxide for water disinfection or pulp bleaching, this high level of carbonate is harmful to 93102.doc 1359791. The presence of carbonates results in the formation of fouling deposits in the equipment in which chlorine dioxide is produced, which in turn leads to higher production costs and maintenance difficulties. Although there are known methods for purifying sodium chlorite from carbonate impurities, they are very expensive, and they often cause more problems than the problem solved. For example, 'carbonate-based The method (see Masschelein, p. 138) can cause chlorite to be contaminated with highly toxic compounds, making the product unsuitable for use in water treatment applications. In the examination of metal chlorites, the problem of minimizing the amount of carbonate impurities is clarified in the U.S. Patent No. 6'251,357 (Dick et al. The contents are hereby incorporated by reference. The purpose of this patent is to produce a high-purity alkali metal chlorite by combining a chlorine oxide production system with a gas sulphate formation reactor, wherein the dioxide production system and the sulphite formation reactor are under low pressure. operating. The chlorine dioxide production system was found to be particularly effective for the above-described preferred embodiment of the invention comprising the use of hydrogen peroxide to reduce acidified gas anhydride. Unfortunately, peroxygen reduction is a relatively expensive reductant, so its use is not always economically viable. An alternative, low cost reductant gas ion is recommended in U.S. Patent 6,251,357. Unfortunately, the latter reducing agent is used. The disadvantage is the joint formation of a highly undesirable chlorine by-product which must be separated from the oxidized & chlorinated chlorine and used alone or discarded. & Still need to develop - a test that can produce a low impurity content. This method does not have the disadvantages of the U.S. Patent 6,251,357. m + 丄 , , , , , 有 有 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 用于 93 Benefit from the existence and availability of existing dioxin chlorination generators. [Inventive content] Therefore, the present invention is directed to the production of high-purity alkali metal chlorite using a single, low capital intensive method. It is preferably sodium sulfite without any purification of the finished product. The invention comprises extracting the generated generator off-gas in a commercial low-pressure, methanol-based chlorine dioxide method into a reaction solution containing a peroxidation gas and a gold hydroxide to produce a corresponding metallurgical component. The chlorate oxime hydroxide is preferably sodium hydroxide. The method includes a gas conditioning stage selected before the chemical reaction of the extracted gas 'a gas-liquid contacting unit in which a chemical reaction is performed' and a gas-liquid separation stage immediately selectable after the chlorite reactor . Accordingly, in one aspect of the invention, there is provided a method of making an alkali metal sulphate having improved purity compared to the purity expected from the composition of the tail gas of a oxidizing gas generator, including in the first reaction zone by- In the acidic water I liquid reaction medium, the acid ions are reduced by the methanol to form a dioxide gas to realize the generation of the second gas, and the aqueous solution of the gas and the alkali metal hydroxide and the hydrogen peroxide are reacted in the second reaction zone. And an aqueous alkali metal sulphate solution having improved purity is recovered from the second reaction zone. BEST MODE FOR CARRYING OUT THE INVENTION [Embodiment] In order to understand the present invention more thoroughly, a schematic diagram of a typical commercially available low-pressure, methanol-based chlorine dioxide generator is shown in FIG. The full description of Figure 1 is 93I02.d〇c 1359791 as follows. The reaction equation is based on the following experience: 3.093 NaC103 + 0.003 NaCl +2.04 H2S04 + 1.011 CH3OH <-= = = =-^· 3 ClO2+0.0465 Cl2+ 1.056 Na3H(S04)2 + 2.481 H20 + 0.216 CH3OH + 0.660 HCOOH + 0.138 C02 The typical gas product composition during continuous operation can be estimated and presented below in Table 1: Table 1: Typical generator exhaust gas composition component % volume C102 7 Cl2 0.1 H20(V) 87 ch3oh 0.5 HCOOH 1.5 C02 0.3 Air 4.0 because it is usually assumed The chlorine dioxide generator off-gas mixture reacts with hydrogen peroxide and metal hydroxide to produce an alkali metal sulphate containing various corresponding high levels of contaminants (methanol, formic acid/formate, carbon dioxide/carbonate). The formation of this methanol-based process has never been intended for use as a source of dioxide gas in the manufacture of alkali metal chlorite. According to the typical gas composition shown in Table 1, and assuming that all gases are completely absorbed/reacted with the hydrogen peroxide and alkali metal hydroxide, the resulting metal hypoxanthate product solution is expected to have the following contaminants: 93l02.doc -10- 1359791 Table 2: Contaminated material in the alkali metal chlorite compound solution Bub Na2C〇3/NaCl〇2 (mg/g) Contaminant content ~ Methanol/NaCl〇2 (mg/ g) NaC00H/NaC102 (mg/g) 53.904 ' 25.471 ^ 165.382 The metal chlorite composition containing such high levels of impurities is considered unsuitable for use in most alkali metal chlorite applications. However, it has now surprisingly been found that by producing a sulphuric acid salt according to the process of the invention and as described in detail below, the resulting product is significantly more pure than originally intended. The process of the present invention permits the use of more economical methanol as a reducing agent in the chlorine trioxide generator and in the manufacture of gold sulphate. # The dioxin gas intended for use in the sulphuric acid salt reactor can be stripped from the chlorine dioxide product solution of the chlorine dioxide generator, such as air stripping. However, in order to minimize organic carbon dioxide contamination and thus provide a lower proportion of components other than chlorine dioxide, the dioxide generator tail gas is preferably from the indirect contact cooler (ICC) outlet. And a point between the inlet of the absorption tower (S3) (see Figure 1 for extraction. Only for the purpose of extracting the gas, the point A is preferably located at the top of the tube. At this point, most of the methanol and 0K k charge has been condensed in the The water condensate produced by ice contains a tail gas stream that is as free of organic contaminants as possible. After extracting the tail gas, a gas conditioning stage can be selected: i) further reducing the organic content by cooling gas, ii) reducing the other The content of specific gas components, such as carbon dioxide, and in) wash out possible liquid entrainment in order to handle undesired conditions often observed in commercial plant operations, such as generator liquids in a very fine manner. 93102.doc -11 The hazy form of 1359791 brings out the ICC. Thus, the carcass conditioning apparatus can include a demister, a scrubber-baffle or another similar unit or a combination thereof. In the scrubber, it is preferred that the liquid is typically water. Other suitable aqueous media are metal and alkaline earth metal hydroxide solutions which have the potential to reduce carbon dioxide and gas levels.

The chemical reaction to form the alkali metal chlorite is preferably carried out under low pressure, in any gas-liquid contacting unit, such as a conventional spray tower or packed column, typically at a pressure of from about 50 to about 500 mm Hg, preferably From about 5 〇 to about 2 mm Hg. The pH of the reaction medium entering the reactor is typically maintained in the range of from about 0.8 to about 13.0, preferably from about 12 Torr to about 12.6. The excess amount of nitrogen peroxide required for stoichiometric reaction with alkali metal hydroxide, hydrogen peroxide and sulfur dioxide is usually used. The excess of hydrogen peroxide can be maintained using the potential (〇Rp) measurement. The RP value associated with pH is typically maintained at from about -30 to about -200 mV relative to Ag/AgC1, preferably from about 90 to about about Ag/AgCl.

150 mV. The reaction to form the alkali metal chlorite is usually carried out at a temperature of from about 25 to about 4 (Γ at a temperature of preferably from about 25 to about 35 ° C. The most preferred embodiment of the process involves the use of a liquid discharger so that It also provides the vacuum source required for pumping and the physical environment in which the chemical reaction takes place. The use of a vacuum source is only used to provide the minimum contact time required for a rapid chlorite formation reaction while allowing for a relatively slow carbon dioxide absorption process. Minimizes the use of liquid dischargers in terms of the cost and simplicity of selective gas-liquid contact equipment and its particularly short gas-liquid contact time results in significant improvements in effectiveness, at a cost and simplicity 93102.doc -12· 1359791 The improvement in the properties is achieved by its dual function as a vacuum source and a reactor. In order to further minimize the contact time between the reaction gas and the chlorite reactor solution, it can be after the chemical reactor A gas separation stage is introduced immediately. Any conventional gas-liquid separation apparatus can be used, and the most preferred embodiment includes a centrifugation Separator.

It is particularly advantageous for the present invention to use only a small portion of the chlorine dioxide formed in the dioxide generator in the manufacture of the chlorite, and the remaining chlorine dioxide is sent to other suitable applications, such as bleaching unit operations. Method of operation. Such an operation allows for more efficient distribution of impurities typically present in the gaseous product of the low pressure, methanol-based dioxide gas generator, with most of the impurities being sent to the bleaching unit.

Another improvement that is particularly beneficial for the general practice of the sterol-based process maximizes the indirect contact cooler injection flow rate. This practical operation allows each of the CO 2 production systems to minimize the contaminant content of the tail gas stream at the ICC exit point. In addition to the gas product distribution of the dioxin generator between the chlorite reactor and the bleaching unit, other possible steps may be included to minimize the level of contaminant in the final sulphate product solution, particularly Acid salt. The additional steps include: i) maintaining only the minimum amount of alkali required for the reaction of Cl〇2+H202+NaOH in the sulphite reactor, i〇 maintaining the highest possible C102/C02 gas supply ratio, and iii) gas The liquid contact time is minimized. 93102.doc -13· 1359791 The appropriate program control strategy and design are important for the former, a wilderness is very important for the two possibilities, and the third possibility is best for making and crying. The liquid discharge device acts as a reactor and then immediately performs gas separation in a suitable split and knife-off state. The process equipment of the invention (gas conditioning, sub-Plutite reactor, etc.) and - the presence of chlorine dioxide It is possible to optimize the Cl〇2 device operation by minimizing the following requirements: i) Stop/standby/restart when pulp bleaching is interrupted by transferring C102 to the manufacture of sulphate The order, and _ change the chemical feed rate by changing the CK produced to the sub-salt transfer section. The target purity of the metal chlorite product depends in part on the chlorine dioxide production process. The operational effectiveness of this method will affect the yield. For - kind of low gas! In the methanol-based process, the minimum carbonate content can be obtained by running the chlorite product solution under a certain excess of yin alcohol. This will result in the highest CKVc 〇 2 ratio in the gas phase. On the other hand, this situation not only leads to an increase in operating costs, but also to a high level of undesired organic components in the exhaust gas and potentially in the chlorite product. In fact, the optimum balance must be determined based on the specific requirements of the sulphate product. The purpose of the manufacture of soda ash chlorites is primarily dependent on the characteristics of the process for the production of dioxide, and therefore the low pressure process according to the invention has the greatest chance of success. In addition to varying degrees of purity, the present invention is equally applicable to atmospheric pressure dioxide forming processes, and all reducing agents and catalysts that can be used in a variety of commercially viable commercial oxidizers 93i02.d〇c • 14 - 1359791 chlorination. (even if there is) regardless of the pressure conditions. It will be appreciated that the use of sterols as a reducing agent in the process of the invention can be readily replaced, at least in part, by the replacement of other alcohols such as ethanol or isopropanol. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figure 1, there is shown a schematic representation of a typical commercially available low pressure, methanol based dioxide generator. It can be seen that the single container provided is that the Luofa crystallizer 10 is connected at its lower end to a circulation loop 12 and to a reboiler 16 where the gasate reactant is fed through the line 14. The material enters the loop 12. The downstream side of the reboiler 16 is connected to a feed line 18 to the generator 10, and methanol and sulfuric acid are fed into the generator 1 through the feed lines 22 and 22, respectively. In the spent reactor solution, a by-product sodium sulphate crystallized slurry is removed from the recycle loop 12 via line 14 and passed through a salt cake filter 26 which causes the sodium sesquisulfate crystals to be consumed from the spent reactor solution. It is separated and returned to the circulation loop by line 28.

The gaseous products of the reaction, primarily steam and dioxide, are fed via line 30 to an indirect contact cooler 32 where they are condensed, such as steam. The gaseous dioxide gas is fed to a absorption line by a line 34 to a dioxide gas absorption column 36' by applying a vacuum to the absorption column, and the dioxide gas is dissolved in the absorption column 36 by means of a line. 38 feeds in chilled water. The resulting dioxide gas solution is transferred to storage via line 4〇. In the method of the reactor 1 , sodium sulphate, methanol and sulfuric acid are reacted in an acidic aqueous solution in which the towel is stored under a low pressure to form a state of oxidizing gas and by-product crystalline sodium sesquisulfate and according to the above Ding 93102.doc -15- 1359791 material line 112. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 3, the preferred embodiment of the present invention is illustrated, wherein the representative symbols are the same as the appropriate representative symbols of Figure 2. In this particular embodiment, the chemical reactor 100 and vacuum source 104 are replaced by a vacuum vent 130. The gaseous gaseous dioxide gas adjusted in the line u is fed to the gas side of the discharger 130, and the aqueous solution of sodium hydroxide and hydrogen peroxide in the pipe 112 is fed to the liquid side of the discharger 130. The residual gas and sodium chlorite reaction product aqueous solution is passed through line 13 through the discharge to a gas separation stage 134 of cyclone type 136. The separation gas system of the cyclone gas separation is advanced by line 138 to the absorption column (33) of the dioxide gas generator (see Figure 1). The separated liquid product is passed through line 140 into a collection vessel 142 which is passed through a collector through line 116 for storage. EXAMPLE This example illustrates the manufacture of sodium sulfite having a low level of carbonate and organic components in accordance with the process of the present invention. The commercially available, low-pressure, sterol-based cl〇2 generator (R8), as shown in Figure 1, is in the vicinity of its forehead glutinous rice gluten (20 MTPD) and its typical solution composition and pressure/pulse operating range Internal operation: 75 to 8.5: ^ acidity, 18 to 22 % sodium chlorate concentration, 119 to 121 mm Hg absolute pressure and 69 to 71. Hey. The methanol consumption is 174 174 g / g (: 1 〇 2, 1 (: (: the outlet temperature is 1 〇. (:, ci 〇 2 product solution concentration intensity is 125 g / liter. After several hours of stable operation, A tail gas sample begins to be continuously withdrawn from the top outlet of an ICC outlet line (see point A in Figure 1). The gas is directed to a 15 liter ml wash bottle (pretreatment stage) followed by i 〇〇 ml of water +3 7 ml 50% 93102.doc 17· 1359791

NaOH + 17 ml of 50% H202 is filled with a chlorite reaction bottle. A small laboratory sprinkler is used to draw gas through the experimental equipment. The concentration of the NaCl 2 was allowed to increase over the length of the period from 52 to 140 minutes in the reaction flask during the three separate tests conducted. The pretreatment stages for the three separate tests included water, CaCl2 solution, and combinations thereof. The chlorite reactor solution composition was sampled at the end of each test and found to have an average composition of: 269.3 g/l^0:1〇2, 291.7 mg/L methanol, and 2.19 g/L sodium formate. And 2.12 g / liter of Na2C03. Therefore, the relevant performance parameters are:

Na2C03/NaC102 7.89 mg/g (reduced from 53.904 mg/g as shown in Table 2) Methanol/NaCl〇2 1.08 mg/g (reduced from 25.471 mg/g as shown in Table 2) NaC00H/NaC102 8·14 mg/g (from 165.382 The mg/g reduction is shown in Table 2) These data indicate an unexpected high purity in the finished product.

result. SUMMARY OF THE INVENTION In one aspect of the present invention, a metal sulphate solution having a low content of impurities, particularly carbonates and organic impurities, is produced from a oxidizing gas produced by a sterol-based process. Modifications are possible within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a dioxide gas production system for producing a dioxide gas from an aqueous solution of sodium chlorate, sulfuric acid and decyl alcohol using the R8 method; 93102.doc -18- 1359791 FIG. 2 is a generalized according to the present invention. A schematic diagram of a method for producing chlorite using a chlorine dioxide generator off-gas; and FIG. 3 is a schematic diagram of a method for producing a sulfite using a chlorine dioxide generator off-gas in accordance with a preferred embodiment of the present invention. [Main component symbol description] 10 Evaporative crystallizer 12 occurs Loop circuit 14 Line 16 Reboiler 18 Feed line 20 Line 22 Line 26 Salt cake filter 28 Line 30 Line 32 Indirect contact cooling 34 Line 36 Absorption tower 37 Line 38 Line 40 Line 100 Chemical reactor 102 Packing tower 104 Vacuum source

93102.doc -19- 1359791 106 Line 108 Gas conditioning stage 110 Line 112 Line 114 Line 116 Line 118 Line 120 Line Feed line 122 Feed line 124 Feed line 126 Cooler 130 Vacuum discharge Unit 132 Line 134 Gas Separation Stage 136 Cyclone Separator 138 Line 140 Line 142 Collection Container 93102.doc - 20

Claims (1)

1359791 Patent application No. 093113529, replacement of Chinese patent application scope (July 1st) I~~ ---___ X. Patent application scope: ΐ· species produced a composition having a composition based on the tail gas of the chlorine dioxide generator A method for improving the purity of an alkali metal chlorite, which is characterized in that chlorine dioxide is produced by using sodium carbonate and methanol in a reaction medium containing an acidic aqueous solution of sulfuric acid in a reaction medium. The reaction is carried out at the boiling temperature while simultaneously applying a low pressure of 50 to 500 m Hg to the first reaction zone to provide a gas mixture of chlorine dioxide, steam and volatile reaction by-products, in the second reaction zone, the dioxide gas and the base The metal hydroxide and the aqueous hydrogen peroxide are reacted, and wherein the low pressure in the first reaction zone is provided by a liquid discharge state, and the alkali metal hydroxide is fed to the liquid inlet simultaneously with the aqueous hydrogen peroxide solution. 5H1 chlorine oxide is fed to a gas inlet, whereby the liquid discharge unit constitutes the second reaction zone, and the alkali having improved purity is recovered from the second reaction zone A metal chlorite aqueous solution. The method of claim 1, characterized in that the gas mixture of chlorine dioxide, steam and volatile reaction by-products is cooled to condense the vapor with at least a majority of the volatile by-products to provide for the alkali metal hydroxide and The dioxide gas is reacted with an aqueous solution of hydrogen peroxide. 3. The method of claim 2, wherein the chlorine dioxide is subjected to one or more conditioning steps to: (0 further reduce organic content by cooling chlorine dioxide, (11) reduce carbon dioxide content, and/or 93102- 100Q718.doc 135979,1 (iii) Removal of any generator liquid carry-off. 4. The method of claim 1 characterized in that after the reaction in the liquid discharge, the reaction product advances from the outlet of the liquid discharger In the separator, the aqueous alkali metal chlorate solution is separated from the remaining unreacted gas. 5. The method of claim 4, characterized in that the metal oxynitride is an aqueous solution of sodium nitrite 6. The method of any of clauses 1 to 5, wherein the sterol is at least replaced by ethanol or iso-alcohol. 93102-10007l8.doc 1359791 Patent application No. 093113829 Chinese picture replacement page next July) 106 Shame step Bu Q02 bamboo shoot 102 Bamboo Shoots Silver Bricks 108 100 110 Β2 118 116 P-0 104 120. t 0L Na〇H搽韦呦 124-VH^oroit Wei崤莽1U Antelope ramie (S3) '112 —<- Nest Cl〇2皞阼踟枷 蟒 蟒 蟒 蟒 蟒 鞞踝觫 丨脔 丨脔 丨脔 per Hs 93102-fig-1000718.doc