TWI508942B - Process and reaction system for the continuous preparation of acetic acid and / or acetic anhydride - Google Patents

Description

Method and reaction system for continuously preparing acetic acid or/and acetic anhydride

This invention relates to a process for the continuous production of acetic acid, and more particularly to a process and system for the carbonylation of by-products of polyvinyl alcohol and its copolymers for the continuous production of acetic acid or/and acetic anhydride.

Polyvinyl alcohol and its copolymers are widely used, and are commonly used as adhesives, stabilizers, emulsifiers, dispersants, sensitizers, coatings, thickeners and fillers. They are important chemical raw materials.

In the manufacturing process of polyvinyl alcohol and its copolymer, a large amount of by-product stream containing methanol and methyl acetate is generated. Currently, methyl acetate is purified from a by-product stream, and water is added to be hydrolyzed to acetic acid and methanol. After separating acetic acid and methanol, respectively, it is refined into refined acetic acid and refined methanol, and used as a raw material for producing polyvinyl alcohol and its copolymer, and recycled polyvinyl alcohol and its copolymer. However, in the process of reducing methyl acetate to acetic acid and methanol, the decomposition rate is only 50%, and the steps of separation and purification are complicated and corrosive, and the operation cost of recycling by-product stream is further improved. .

Therefore, in order to reduce the operating cost of recycling the by-product stream, the currently more commonly used method is the extractive distillation method disclosed in the Taiwan Patent No. I295990, which uses an aqueous methanol solution as an extractant to extract polyethylene. A by-product stream produced in the production of an alcohol and a copolymer thereof, and methanol carbonylation of the obtained methanol and methyl acetate aqueous solution to produce acetic acid. However, the method is effective for extracting all methanol and methyl acetate, and the extractant is produced in the process of manufacturing polyvinyl alcohol and its copolymer. The by-product streams are fed separately from different locations above the extractive distillation column, but this process consumes a greater amount of energy. In addition, the methanol and methyl acetate aqueous solution obtained by the method contains one mole of water per mole of methyl acetate, which is known from the Handbook of Corrosion Data (Bruce D. Craig, 2nd edition). At higher concentrations, there is a strong corrosive effect on the equipment. Therefore, in actual production, the purity requirements for methanol and methyl acetate are quite strict. Generally, in the methylation of methyl acetate, it is desirable to reduce the moisture to less than 3.0 wt% to avoid corrosion of equipment and damage to equipment. Therefore, water in the process of methanol carbonylation will not only promote the corrosion effect but also poison the catalyst. Furthermore, if the water content of the methyl acetate stream used to prepare acetic acid or/and acetic anhydride is high, more methyl acetate will be lost during the carbonylation process, so more methyl acetate must be added in the process. Flow to increase the yield of acetic acid or / and acetic anhydride. Therefore, how to reduce the water content in methyl acetate is also a factor that must be considered in the carbonylation process.

Further, since the polyvinyl alcohol and the copolymer thereof are subjected to alcoholysis with a basic compound, particles of sodium acetate and polyvinyl alcohol and a copolymer thereof are produced in a solution of methyl acetate and methanol, and the sodium acetate and the sodium are mixed. The vinyl alcohol and its copolymer particles are introduced into the distillation column, and solids are precipitated in the distillation tray, causing blockage of the tray, thereby affecting the distillation effect.

In order to improve this problem, an extractive distillation method is disclosed in the Taiwan Patent No. I295990 of the Serrans Corporation. When the distillation is carried out in the column, acetic acid is added to the bottom of the distillation column from the bottom of the distillation column. 73% by weight (% by weight) of aqueous methanol is distilled based on the total weight of the solution of methyl ester and methanol, and sodium acetate and polyvinyl alcohol and copolymer particles thereof are dissolved by water. After that, it is discharged from the bottom of the tower.

However, when the water content in the methyl acetate stream for the production of acetic acid or/and acetic anhydride is increased, the original unit usage of the methyl acetate for acetic acid will increase rapidly; when the water content is less than 0.1 wt%, acetic acid The ratio of methyl ester usage to acetic acid is 0.0761; when the water content of methyl acetate stream is increased to 5 wt%, the ratio of methyl acetate usage to acetic acid is increased to 0.2995; if it is increased to 10 wt%, Then the ratio of the amount of methyl acetate used to the acetic acid was increased to 0.4628.

The results show that the water content of the methyl acetate stream has a considerable influence on the amount of methyl acetate used to produce acetic acid or/and acetic anhydride. Therefore, how to control the water content in the methyl acetate stream is a very important control requirement in the process.

Therefore, there is an urgent need in the art to develop a method for increasing the production efficiency of a whole production line by utilizing a low operation cost and no need for complicated processes, that is, a by-product stream produced by producing polyvinyl alcohol and its copolymer can be effectively utilized.

The main object of the present invention is to provide a method for continuously preparing acetic acid or/and acetic anhydride, which comprises mixing water with an alkalizing solution for producing polyvinyl alcohol and a copolymer thereof to form a mixed liquid; feeding the mixed liquid with relative The bottom and top distillation columns are subjected to distillation to obtain a purified methyl acetate stream; and the purified methyl acetate stream is subjected to a carbonylation reaction to obtain acetic acid or/and acetic anhydride.

The invention further provides a reaction system for continuously preparing acetic acid or/and acetic anhydride, comprising: a mixing unit having a feeding line, receiving water and producing An alkalizing solution of polyvinyl alcohol and a copolymer thereof to form a mixed liquid, and the mixed liquid is fed out from the feed line; a distillation unit is connected to the mixing unit and used to distill the mixed liquid to obtain purified a methyl acetate stream, wherein the distillation unit has an outlet line for feeding the purified methyl acetate stream; and a reaction unit is connected to the outlet line of the distillation unit, and the purified methyl acetate stream is subjected to The carbonylation reaction gives acetic acid.

The invention adds water to the alkalizing solution containing methyl acetate, methanol, sodium acetate and trace polyvinyl alcohol and a copolymer thereof produced in the process of producing polyvinyl alcohol and its copolymer, and the water is alkalized. The liquid is mixed and dissolved so that sodium acetate and a trace amount of polyvinyl alcohol and a copolymer thereof are first dissolved in water to obtain a mixed liquid having a low solid content, which is then introduced into a distillation column for distillation. Therefore, when the mixed liquid is fed to the distillation column for distillation, it is possible to prevent the sodium acetate from solidifying on the tray in the distillation column, resulting in blockage of the tray to increase the production cost.

And using the method of the present invention, the purified methyl acetate stream of the present invention can be obtained only by azeotropic distillation, and the purified methyl acetate stream is methyl acetate and methanol having a water content of less than 3.0 wt%. Azeotrope.

In the method of the present invention, the mixed dissolution mode used may be selected from a mixing unit, wherein the mixing unit includes, but is not limited to, a mixing drum or a mixer.

In the method of the present invention, the water used may be selected from general water or recovered water containing methanol and methyl acetate to achieve water saving in the process.

In the method of the present invention, the solid content contained in the alkalizing solution obtained by the process for producing polyvinyl alcohol and its copolymer comprises sodium acetate, polyvinyl alcohol and a copolymer thereof. And the alkalizing solution obtained from the polyvinyl alcohol process Dissolved and mixed with water, and the alkalized solution before being dissolved and dissolved is detected by an ultraviolet/visible spectrometer. The detection wavelength is set at 430 nm, the transmittance is 10%, and 40 wt% is added based on the weight of the alkalizing solution. The aqueous solution is mixed and dissolved to obtain a mixed solution, and the transmittance of the mixed solution is increased to 90% or more, indicating that the method used in the present invention can effectively produce solids produced in the process of polyvinyl alcohol and its copolymer. Sodium acetate and polyvinyl alcohol and a copolymer thereof are dissolved in a transparent mixed solution, and the mixed solution is fed to a distillation column for azeotropic distillation.

The invention provides a methyl acetate which is very low in water content and suitable for the process of methyl acetate carbonylation, and can reduce the use amount of the methyl acetate stream in the carbonylation process, so as to effectively utilize the production of polyvinyl alcohol and The methyl acetate by-product obtained in the process of copolymer or copolymer thereof is subjected to carbonylation of methyl acetate to produce acetic acid or/and acetic anhydride without adding additional methyl acetate to produce an extraction apparatus.

The present invention provides a manufacturing method in which the methyl acetate has a water content of less than 3.0% by weight, and can be directly used for the production of acetic acid or/and acetic anhydride.

In other words, the present invention provides a low energy loss methyl acetate stream recovery process, the method of the present invention uses water and methyl acetate flow premixed, and then separated by azeotropic distillation, due to the use of water and alkali The weight ratio of the chemical liquid is 30 to 50%, so the energy consumption is reduced during distillation, and the ratio of the amount of steam used to the amount of methyl acetate distilled is reduced by more than 30%.

It should be noted that the structures, proportions, sizes, etc. shown in the drawings of the present specification are only used in conjunction with the contents disclosed in the specification to familiarize themselves with the art. The understanding and reading of the person is not intended to limit the conditions for the implementation of the present invention, and therefore does not have technical significance, any modification of the structure, the change of the proportional relationship or the adjustment of the size, without affecting the invention. The efficacies and the achievable objectives should still fall within the scope of the technical content disclosed in the present invention. In the meantime, the terms "a", "top" and "bottom" are used in the description of the invention, and are not intended to limit the scope of the invention. Adjustments, where there is no material change, are considered to be within the scope of the invention.

In an embodiment of the method for continuously preparing acetic acid or/and acetic anhydride of the present invention, water is added to an alkalizing solution for producing polyvinyl alcohol and a copolymer thereof, and mixed and dissolved at 20 to 53 ° C for 0.1 to 0.5 hours. To obtain a mixed liquid; then fed to the distillation column at a rate of, for example, 1 ton / hr, wherein the reflux ratio is maintained at about 1.4 to 1.8, and the top and bottom temperatures of the distillation column are 52 to 54 ° C and 71 to 75, respectively. °C; methyl acetate and methanol are included in the purified methyl acetate stream obtained by distillation. In a preferred embodiment, the ratio of methyl acetate to methanol is from 75:25 to 81:19, more preferably 81: 19; and subjecting the purified methyl acetate stream to a carbonylation reaction, more specifically to a carbonylation reaction of methyl acetate and methanol.

In one embodiment, the alkalizing solution used in the method of the present invention includes, but is not limited to, polyvinyl alcohol and copolymers thereof, methyl acetate, methanol, and sodium acetate.

In a preferred embodiment, the method of the present invention further comprises filtering the mixture before distilling the mixture, and feeding the filtered mixture into the distillation column. Row distillation. The filtered mixture includes polyvinyl alcohol and its copolymer, methyl acetate, methanol, sodium acetate, and water.

In the embodiment, when the mixed liquid is fed to the distillation column by the method of the present invention, the temperature of the top of the distillation column is 49 to 59 ° C, and the reflux ratio is maintained at about 0.68. In a more preferred embodiment, the mixed liquid is fed from about two-thirds of the height of the distillation column from the bottom of the distillation column, and the temperature of the mixed liquid fed to the distillation column is preferably but not limited to 62 to 63. °C.

The water to be added in the method of the present invention is not particularly limited, and cooling water recovered from other processes or the like may be used. In a preferred embodiment, the water added in the process of the present invention is present in an amount of from 25 to 40% by weight of the mixture.

Referring to Figure 1, a flow chart of a reaction system for the continuous production of acetic acid or/and acetic anhydride of the present invention is shown.

As shown in Fig. 1, the reaction system for continuously preparing acetic acid or/and acetic anhydride of the present invention comprises: a mixing unit 1 which receives water 101 and an alkalizing solution 102 for producing polyvinyl alcohol and a copolymer thereof to form a mixed liquid. Wherein, the mixing unit 1 has a feed-out line 10 for feeding out the mixed liquid; the distillation unit 2 is connected to the feed-out line 10 of the mixing unit 1, and is used to distill the mixed liquid to obtain purified acetic acid An ester stream, wherein the distillation unit 2 has an outlet line 20 for feeding out the purified methyl acetate stream; and a reaction unit 3, which is connected to the outlet line 20 of the distillation unit 2, to purify the purified acetic acid The ester stream is subjected to a carbonylation reaction to give acetic acid.

In the present embodiment, the distillation unit 2 is a distillation column, and the feed line 10 of the mixing unit 1 is connected to one third to two thirds of the height of the distillation column from the bottom of the distillation column. Preferably connected to the distillation The bottom of the column counts from one third to one half of the height of the distillation column.

The method of the invention does not adopt the method of extractive distillation, so that no additional water or extractant is fed into the distillation tower, and there is no salt or undesired solid blocking the tray, and the obtained purified acetic acid A The water content of the ester stream is also relatively low, and the method of the invention can be directly combined with the process of polyvinyl alcohol and its copolymer, without a large operation cost, simple process, recycling of process wastewater and reduction of energy consumption, and more Effective use of by-product streams produced by the production of polyvinyl alcohol and its copolymers.

Example

The embodiments of the present invention are further described by the specific embodiments thereof, and those skilled in the art can understand the other advantages and effects of the present invention from the disclosure of the present disclosure.

Examples 1 to 3

The mixture is mixed with a stirred tank, and an alkalizing solution for producing a polyvinyl alcohol and a copolymer thereof is added, and a water amount as shown in Table 1 is added to the alkalizing solution to form a mixed liquid. The basifying solution comprises 31.62% by weight of methyl acetate, 67.42% by weight of methanol, 0.13% by weight of sodium acetate, 0.1% by weight of polyvinyl alcohol and copolymers thereof, and the balance of water. Next, the mixture was filtered through a mesh of 200 mesh to obtain a filtered mixture, and the filtered mixture was fed into a 60-bar azeotropic distillation column at a rate of 8.6 g per minute. The filtered mixture was distilled, wherein the mixture was fed to a distillation column at a position as shown in Table 1, and the filtered mixture was fed at a temperature of 63 ° C, and the top and bottom of the distillation column were The temperatures were 53 and 75 ° C, respectively.

The results showed that the distillation columns of Examples 1 to 3 contained 23.34% of methyl acetate, 42.51% of methanol, 34.15% of water, and 0.01% of solids. The purified methyl acetate stream obtained by distillation in Examples 1 to 3 was fed out at the position shown in Table 1, and the composition of the purified methyl acetate stream was listed in Table 2.

As shown in the results of Table 2, since the method of the present invention is to add water to the alkalizing solution for producing polyvinyl alcohol and its copolymer before the feeding to dissolve the sodium acetate contained in the alkalizing solution, Knowing the method, the concentration of the solid matter contained in the distillation columns of Examples 1 to 3 was extremely low only 0.01% by weight. And implement In Examples 1 to 3, the ratio of methyl acetate to methanol discharged at the top of the distillation column was very close to azeotropic ratio, so the concentration of methyl acetate obtained was higher.

In addition, the extracted methyl acetate stream obtained by the conventional extractive distillation method still contains 5.3 wt% of water, and the water content is too high for the subsequent process of preparing acetic acid and the corrosive catalyst and corrosion equipment. In view of this, the purified methyl acetate stream obtained in Examples 1 to 3 contains only less than 0.5% by weight of water and can be directly used for subsequent preparation. Therefore, the method and system for continuously preparing acetic acid of the present invention are more suitable for the subsequent process for preparing acetic acid.

1‧‧‧Mixed unit

10‧‧‧Feedback pipeline

2‧‧‧Distillation unit

20‧‧‧Export pipeline

3‧‧‧Reaction unit

101‧‧‧ water

102‧‧‧Basified liquid

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram of a reaction system of one embodiment of the continuous production of acetic acid of the present invention.

1‧‧‧Mixed unit

10‧‧‧Feedback pipeline

2‧‧‧Distillation unit

20‧‧‧Export pipeline

3‧‧‧Reaction unit

101‧‧‧ water

102‧‧‧Basified liquid

Claims (11)

A method for continuously preparing acetic acid or/and acetic anhydride, comprising: mixing water with an alkalizing solution for producing polyvinyl alcohol and a copolymer thereof to form a mixed liquid; feeding the mixed liquid to a distillation column having a bottom portion and a top portion opposite to each other Distillation is carried out to obtain a purified methyl acetate stream; and the purified methyl acetate stream is subjected to a carbonylation reaction to obtain acetic acid or/and acetic anhydride. A method for continuously producing acetic acid or/and acetic anhydride as described in claim 1, wherein the alkalizing solution comprises polyvinyl alcohol and a copolymer thereof, methyl acetate, methanol, and sodium acetate. A method for continuously preparing acetic acid or/and acetic anhydride as described in claim 1, wherein the purified methyl acetate stream comprises methyl acetate and methanol. A method of continuously producing acetic acid or/and acetic anhydride as described in claim 1, wherein the purified methyl acetate stream is fed from the top of the distillation column. A method for continuously producing acetic acid or/and acetic anhydride as described in claim 4, wherein the distillation column has a top temperature of from 49 to 59 °C. The method for continuously preparing acetic acid or/and acetic anhydride according to claim 1, wherein the mixed liquid is from one third to two thirds of the height of the distillation column from the bottom of the distillation column. Feed in. Continuous preparation of acetic acid or/and acetic acid as described in claim 6 The method of the anhydride, wherein the mixed liquid is fed in from two-thirds to one-half of the height of the distillation column from the bottom of the distillation column. A reaction system for continuously preparing acetic acid or/and acetic anhydride, comprising: a mixing unit for receiving water and producing an alkalizing solution of polyvinyl alcohol and a copolymer thereof to form a mixed liquid, wherein the mixing unit has a feed-out line, To extract the mixed liquid; the distillation unit is connected to the mixing unit, and is used to distill the mixed liquid to obtain a purified methyl acetate stream, wherein the distillation unit has an outlet line for feeding the purified acetic acid a methyl ester stream; and a reaction unit connected to the outlet line of the distillation unit, and the purified methyl acetate stream is subjected to a carbonylation reaction to obtain acetic acid and acetic anhydride. A reaction system for continuously producing acetic acid or/and acetic anhydride as described in claim 8 wherein the distillation unit is a distillation column. The reaction system for continuously preparing acetic acid or/and acetic anhydride according to claim 9, wherein the mixing unit is one third to three of the height of the distillation column from the bottom of the distillation column. Feed in two points. The reaction system for continuously preparing acetic acid or/and acetic anhydride according to claim 10, wherein the mixing unit is one third to two of the height of the distillation column from the bottom of the distillation column. Feed in one part.