CS231789B1 - Treatment of the methyl acetate-methanol mixture - Google Patents

Abstract

The method of processing the methyl acetate-methanol mixture. The invention relates to a method of processing the methyl acetate-methanol mixture, which is produced as a by-product during the production of polyvinyl alcohol and forms a liquid waste. The invention is based on the two-stage chlorination of a mixture of methyl acetate and methanol, in the first stage it is chlorinated with hydrogen chloride gas to form methyl chloride, and in the second stage, the oxychlorination effect of hydrogen chloride and oxygen creates a mixture of higher chlorinated methane derivatives. The use of a common chlorinating agent in both stages of chlorination makes it possible to transfer excess hydrogen chloride already through the first stage of chlorination without demands for the separation of reaction products in the first stage of chlorination. Higher chlorinated derivatives of methane after condensation after the second stage. chlorination of the compartment after extraction with reaction water. The unreacted raw materials (methyl acetate and methanol) are separated from the aqueous acetic acid solution by rectification and returned to the first stage of chlorination.

Description

The invention relates to a process for the treatment of a mixture of methyl acetate-methanol.

In the hydrolysis of methanolic polyvinyl acetate solutions to polyvinyl alcohol, methyl acetate is formed as a by-product, which dilutes the flood solvent. When methanol is recovered, methyl acetate is separated therefrom in the form of its azeotrope with methanol, yielding a relatively large amount of this by-product. The application of said waste, for example as a solvent, is limited, in particular because of its health problem. Processing of methyl acetate into its flood components by direct hydrolysis results in a very low reaction rate constant and makes industrial application virtually impossible. Since its careful use in the process is excluded, with only a few exceptions, it currently constitutes direct waste that needs to be disposed of by incineration, which worsens the economy of production.

AO 190 959 proposes to utilize the reaction of methyl acetate and methanol with hydrogen chloride to form methyl chloride, which is subsequently converted into a mixture of higher chlorinated methane derivatives by chlorination with chlorine, which, when mixed with water, forms a separate layer and is withdrawn as product. The disadvantage of this process is that for the two-stage chlorination of the methyl acetate-methanol mixture, a different chlorinating agent (hydrogen chloride and chlorine) is used at each stage, allowing excess hydrogen chloride to be used in the first chlorination stage only when the reaction mixture is subjected to condensation and separation. . Thus, each reaction step would have to be followed by a separate condensation associated with the recycling of the unreacted chlorinating agent (hydrogen chloride or chlorine respectively) back to the reactor inlet. Another disadvantage of this process is, in particular, the high energy intensity of the UV-catalyzed chlorination.

These disadvantages are overcome by the two-stage process of the present invention. chlorination of the methyl acetate-methanol mixture.

In the first step, the reaction of methyl acetate with hydrogen chloride in the presence of an acidic catalyst (cation exchanger FeCl 3) was carried out at 80 - 100 ° C in the vapor phase in apparatus 2 according to the equation:

CH 3 COOCH 3 + HCl -> CH 3 COOH + CH 3 Cl

In parallel, the reaction will take place:

CH3OH + HCl → CH3Cl + H2O

The reaction mixture containing methyl chloride, acetic acid, water and the interreacted methyl acetate, methanol and hydrogen chloride is passed through the preheater 3 to the second stage of chlorination 4. At the same time, oxygen enters through the preheater 5 together with non-condensed gasml (HCl, O2) from condenser 6. 4 in the presence of a catalyst (medium chlorides + KCl on alumosilicate, pumice, and pcd.) At 350-450 ° C, the oxychlorination of methyl chloride proceeds according to the reactions:

CH 3 Cl + HCl + 0.5 O 2 -> CH 2 Cl 2 + H 2 O

CH 2 Cl 2 + HCl + 0.5 O 2 → CHCl 3 + H 2 O

CHCl 3 + HCl + 0.5 O 2 -> CCU + H 2 O

The second stage of chlorination works adiabatically because its working temperature is maintained by the released reaction heat. A different degree of reaction is achieved by changing the molar ratio of hydrogen chloride: (methyl acetate + methanol) at the inlet to the first stage of chlorination in the range of 2 to 4: 1. Oxygen or air may be used in the oxychlorination of methyl chloride in an excess of 0-10% relative to the stoichiometrically required amount.

The reaction mixture from the chlorinator 4 transfers its heat in the exchanger 5, 5, 1, and condenses in the condenser 6 where the released condensation heat evaporates the methyl acetate and methanol passing to the preheater 1. In the separator 7, the heavier chlorinated hydrocarbon phase is separated from the aqueous the non-condensed components (HCl, O2, GH2Cl2 steppe) are returned via preheater 5 to chlorinator 4. The top aqueous layer is fed as a feed to the rectification column 8, from which the aqueous acetic acid solution is withdrawn for further processing. The distillate containing unreacted methyl acetate and methanol is returned to evaporator 6.

Advantages of the proposed process include the fact that they use the same chlorinating agent in both stages, allowing some of the required hydrogen chloride for the second stage of chlorination to pass through the first stage of chlorination, thereby obtaining the necessary excess melting component to achieve higher conversion of methyl acetate and methanol. Such a procedure allows, in addition to the conventional connection of two chlorination reactors one after the other, to carry out both chlorination stages in one apparatus, for example, according to the scheme in Figure 1. When using a common chlorinating agent in both chlorination stages, one condensation of the reaction mixture chlorinating agent. Another advantage is that oxychlorination occurring adiabatically at higher temperatures (350 to 450 ° C) is not as energy intensive as UV-catalysed chlorination. Moreover, the higher temperature of the reaction products allows heat recovery in the heat exchangers, which reduces the overall energy consumption of the proposed process compared to the process according to AO 190 959. The advantage of the proposed process is that in the separator 7 reaction water is used for phase separation. water from the outside.

Example 1

200 g. h ^{-1 of a} mixture of methyl acetate (81%) - methanol enters the top of the first catalytic layer (cation exchanger FeCl 3) together with hydrogen chloride at a flow rate of 3.3 ^l min ^-1 . Molar ratio of hydrogen chloride: (methyl acetate + methanol) = 2.6: 1.

A temperature of 95 ° C was maintained in the layer. The reaction fumes are preheated by hot gases leaving the second chlorination stage and, together with preheated oxygen (0.6 l.min ^-1 ), enter the top of the second catalytic layer (medium chlorides + KCl on alumino-silicate).

398 ° C. Since the autothermal mode is difficult to maintain in a small 40 mm diameter laboratory reactor, it was necessary to avoid heat loss by external electrical heating of the jacket. The hot reaction gases condensed in the condenser after passing through the exchanger assembly. The condensate was separated into two layers in a separator. The bottom layer (357 gh ^-1 ) contained 12.7 wt. CH 2 Cl 2, 39.8% CHCl 3, and 47.5% CCl 4. The top layer was rectified in a packed column, the distillate (29.5 gh ^-1 ) containing 74.6% methyl acetate and 25.4% methanol. The boiling liquid (228.5 gh ^-1 ) represented an approximately 45% aqueous acetic acid solution. From the original amount of methyl acetate, 86.4 were converted to chlorinated methane derivatives. and methanol 80%.

Claims (1)

Example 1 200 g of h-1 mixture of methyl acetate (81%) - methanol enters the head of the first catalytic layer (cation exchanger FeCb) together with hydrogen chloride flow of 3.3 lmin -1. The molar ratio of hydrogen chloride: (methyl acetate + methanol) = 2.6: 1. The layer is maintained at 95 ° C. The reactive products are preheated with the hot gases leaving the second cooling line and, together with the pre-heated oxygen (0.6 .mu.min-1), enter the second catalytic layer on the head (medium chlorides + KCl on alumina minosilicate) The temperature is maintained at 398 DEG C. As the autothermal regime is difficult to maintain in the small 40 mm diameter labo-boron reactor, it was necessary to avoid heat losses due to the electrical heating of the shell. the condensate was condensed in the condenser, and the bottom layer (357 gh-1) contained 12.7 wt% CH 2 Cl 2, 39.8% CHCl 3 and 47.5% The top layer was subjected to packing in the packed column, with the desilate (29.5 gh-1) containing 74.6% methyl acetate and 25.4% methanol, the boiling liquid (228.5 gh-1) being about 45 ° / aqueous solution of acetic acid from the flood methyl acetate was reacted with chlorinated methane derivatives 86.4% and 80% methanol. wherein the first step is chlorination with hydrogen chloride at 80-100 ° C in the presence of a ferric chloride catalyst and the resulting intermediates are subsequently chlorinated at a second stage temperature of 350-450 ° C. With the addition of hydrochloride and oxygen in the presence of chloride, wherein a portion of the required hydrogen chloride for chlorination in the second stage is carried out via the first step whereby the necessary excess chlorinating agent and the rising reaction mixture from the second step of chlorination are formed by chlorine extraction with the reaction water. derivatives of methane from other constituents, which are rectified to an aqueous acetic acid solution and unreacted methyl acetate and methanol, which return to the first stage of the chlorination. 1 sheet of drawings · *