CN104529763A - Process and device for synthesizing ethyl formate with reactive distillation dividing wall column - Google Patents

Abstract

The invention discloses a process method and a device for synthesizing ethyl formate by using a reactive rectification dividing wall tower. In the device of the present invention, the esterification reaction of formic acid and ethanol and the separation of products are carried out in the same tower, that is, a dividing plate is added in the middle of the vertical direction of the traditional rectification tower, and its upper end is capped and the lower end is suspended. The feeding positions are from high to low respectively formic acid, ethanol, and acidic cation exchange resin as catalyst. The left side is the reactive distillation section, and the right side can recover ethanol. High-purity ethyl formate is discharged at the top of the left column, waste liquid is discharged at the bottom of the column, and excess ethanol is discharged at the top of the right column. This device greatly accelerates the positive reaction rate of the esterification reaction, obtains high-purity products, and can separate excess ethanol at the same time. Compared with the traditional process, it saves a rectification tower and a reboiler, and greatly reduces equipment investment and energy consumption.

Description

Process and equipment for synthesizing ethyl formate in reactive distillation dividing wall column

technical field

The invention belongs to the technical field of advanced rectification in chemical engineering, and relates to a process method and a device for a reactive rectification dividing wall tower, specifically refers to performing chemical reaction and purification operations on one side of the dividing wall, and performing unreacted grouping on the other side of the tower. points of separation. The utilization of this device can complete multiple steps such as reaction, purification and recovery in one tower.

Background technique

Ethyl formate has important industrial uses and is an intermediate in organic synthesis, widely used in the pharmaceutical industry. It can also be used as a solvent for nitrocellulose, cellulose acetate, etc. In the food industry, ethyl formate can be used as an essence to blend the aromas of peaches, bananas, apples, apricots, pineapples, berries, etc., and can also be used as spices for butter, brandy, rum, whiskey, etc. Therefore, the market demand and technological innovation of ethyl formate have great room for growth. Its main production method is the esterification reaction of formic acid and ethanol under the action of a catalyst, which is a reversible reaction. Because the forward and reverse reactions are carried out simultaneously, the yield of the traditional process is not high.

The traditional production process of ethyl formate is: adding ethanol, formic acid and catalyst into the batch tank, after reacting for a certain period of time, sending the mixture material into a rectification tower for a series of separations to obtain products, and the post-treatment of the reactants also requires After neutralization and washing with water to remove sulfuric acid. The process has a series of problems such as serious equipment corrosion, many side reactions, and difficult product separation. Moreover, the reversible reaction is limited by the equilibrium constant, and the conversion rate of the reaction is not high. And in order to make one of the reactants reach a higher conversion rate, another reactant is excessively large, but the unreacted must be recycled, so a rectifying tower is needed to purify the unreacted. It can be seen that the traditional technological process is complicated and the energy consumption is huge, but the purity of the product cannot be guaranteed even so.

Patent C07C69/06 improves the production process of ethyl formate. This patent uses absolute ethanol to react with carbon monoxide to generate ethyl formate under the action of a basic catalyst. Although this method is environmentally friendly, it has low energy consumption and no discharge of waste gas or waste liquid. But the productive rate is still not high, and the yield only reaches 85%, and the unreacted substance cannot be recovered, and the impurity of the product is difficult to separate. Especially the application in the food industry requires high-purity products.

Reactive distillation can solve this problem very well. The reactive distillation synthesis process organically couples the reaction process with the rectification separation process. The products generated during the chemical reaction are gradually separated from the reaction due to their low volatility. system, thereby effectively inhibiting the reverse reaction. Therefore, reactive distillation can effectively increase the reaction rate and the conversion of reactants.

Due to the low boiling point of ethyl formate, high-purity products can be obtained at the top of the reactive distillation tower, and the unreacted ethanol is mixed with the generated water at the bottom of the tower. If the waste is directly discharged at the bottom of the tower, it will cause waste of resources. . Therefore, this patent places dividing plate in the rectifying tower, can carry out recovery and refinement of ethanol on the right side of dividing plate, completes tasks such as esterification reaction, the purification of ethyl formate, the recovery of ethanol simultaneously in one tower like this, relatively The traditional process saves a rectification tower and a reboiler. More importantly, the reactive dividing wall rectification tower can effectively avoid the back-mixing effect of intermediate components in the multi-element rectification process, and the thermodynamic efficiency of the process is high, thereby reducing equipment Investment and energy consumption, improve economic efficiency.

Contents of the invention

The purpose of the present invention is to provide a highly coupled synthesis process and device utilizing reactive distillation dividing wall towers to realize ethyl formate synthesis and product separation. The present invention organically combines the reaction process, product separation and recovery of excess reactant ethanol in one tower at the same time, and can directly obtain high-purity ethyl formate product, simplifies the conventional reactive distillation process, and greatly reduces the Energy consumption and equipment investment costs.

The device adopted in the present invention is a reactive distillation partition tower, as shown in the figure, a vertical partition is set inside a common rectification tower, the partition extends from the top of the tower to the bottom, and its upper end is capped. The raw materials formic acid and ethanol enter the left side of the next door according to a certain ratio. The device is divided into five areas: area (1) is a rectification section with 4-7 theoretical plates, area (2) is a reaction section with 20-30 theoretical plates, area (3) is a stripping section, There are 5-10 theoretical plates, area (5) is the sideline rectification section, with 25-35 theoretical plates, and area (4) is the public stripping section, with 6-10 theoretical plates. The interior of the reactive distillation column is equipped with trays or packing or a combination of trays and packing. The reaction section is equipped with a catalyst, the catalyst is an acidic cation exchange resin, two total condensers are arranged at the top of the tower, and a reboiler is arranged at the bottom of the tower. The next wall is set eccentrically or centrally, and the cross-sectional area ratio of the rectifying section (1) and the sideline rectifying section (5) is between 0.5:1 and 2:1.

The method of the present invention is as follows: reactant formic acid is added from the top of the reaction section (2), ethanol is added at the bottom of the reaction section (2), acidic cation exchange resin is added in the reaction section as a catalyst, and the ethyl formate produced by the reaction passes through the rectification section (1) After purification, a high-purity product is obtained at the top of the tower. The water and the remaining ethanol produced in the reaction section remove a small amount of ethyl formate contained therein in the stripping section (2), and water, ethanol and a small amount of formic acid are obtained at the bottom of the partition. On the one hand, the mixture is further removed through the common stripping section to obtain a water-based waste liquid at the bottom of the tower; on the other hand, the mixture is further refined through the side stripping section (5). Since ethanol and water are azeotropic, The top of the tower can only reach their azeotropic composition, and the obtained ethanol can be recycled. The operating units in the present invention are all operated under normal pressure. During the operation, the reflux ratio of the reactive distillation tower top is 2~3.5, the tower top temperature is controlled at 50~60°C, and the temperature of the reaction section (2) is 67~3.5. 77°C, the top reflux ratio of the side line rectification section (5) is 4~6, the top temperature is controlled at 75~80°C, and the tower bottom temperature is controlled at 90~95°C. The feedstocks are all saturated liquid phase feedstocks. The ethanol feedstock can be pure ethanol or crude ethanol containing a small amount of water or other impurities, wherein the mass fraction of ethanol is greater than 90%, and the molar ratio of ethanol feedstock to formic acid feedstock is controlled at 1.2:1~1.5:1.

In the present invention, the mass fraction of ethyl formate at the top of the tower can reach 99.94%, and ethanol can also be recovered. It simplifies the conventional reactive distillation process, maximizes the reaction conversion rate, and effectively reduces energy consumption and equipment investment.

Description of drawings

Figure 1: Schematic diagram of a conventional reactive distillation process for the synthesis of ethyl formate.

Figure 2: Schematic diagram of the reactive distillation dividing wall column for the synthesis of ethyl formate.

specific implementation plan

Below in conjunction with accompanying drawing, the present invention will be described in further detail:

The reactive distillation synthesis device used in the present invention is mainly composed of a reactive distillation bulkhead tower, a condenser, a reboiler and a phase separator and the like. Among them, the reactive distillation dividing wall column is divided into five areas: area (2) is the reaction section, in which the esterification reaction occurs, and there are 25 to 35 theoretical plates. Area (1) is the rectification section, the main function is to purify ethyl formate, there are 4~7 theoretical plates. Area (3) is the stripping section, which is used to remove a small amount of ethyl formate, and obtain a mixture of water, ethanol and a small amount of formic acid at the bottom of the partition, with 5 to 10 theoretical plates. Area (4) is the public stripping section, where the waste liquid is refined. Excess ethanol enters the side line rectification section as much as possible instead of being discharged with the waste liquid. There are 6 to 10 theoretical plates. Area (5) is the side line rectification section, which separates the ethanol-water system. Since ethanol and water are azeotropic, only ethanol with a mass fraction of 95% can be obtained at the top of the tower, and all operating units operate under normal pressure.

The reaction raw material formic acid is fed from the upper part of the reaction section, and the ethanol is fed from the lower part of the reaction section. The catalyst is an acidic cation exchange resin, and the feed is a saturated liquid feed. The ethanol can be pure ethanol or crude ethanol containing a small amount of water and other impurities, but the mass fraction must be greater than 90%. The ethanol feed and formic acid feed The molar ratio is between 1.2:1~1.5:1. In the reaction section (2) formic acid contacts with ethanol countercurrently, esterification reaction occurs under the action of the catalyst to generate ethyl formate and water, the temperature in the reaction area is 67~77°C, and it is removed by rectification in the rectification section (1). Among them, the formic acid is used to obtain high-purity ethyl formate, the reflux ratio at the top of the tower is 2~3.5, and the temperature at the top of the tower is controlled at 75~80°C. Below the reaction section, the reaction product water and excess ethanol and a very small amount of formic acid pass through the stripping section to remove a small amount of ethyl formate, and a mixture containing water, ethanol and a small amount of formic acid is obtained at the bottom of the tower. On the one hand, the mixture is rectified by the side rectification section (5), and unreacted ethanol is obtained at the top after the water is removed for recycling. On the other hand, a small amount of ethanol can be removed through the common stripping section (4), so that the waste liquid is mainly water. The reflux ratio at the top of the side rectification section is 4~6, the temperature at the top is controlled at 70~88°C, the temperature at the bottom of the tower is controlled at 78~80°C, and all operating units operate under normal pressure.

The invention can be illustrated by the following examples:

Example 1: The process shown in the figure. The theoretical plate number, feed flow rate and composition of each area are shown in Table 1. The reactive distillation section adopts Interlocks packing, and the other areas adopt a sieve tray structure. The equal plate height of the reaction section is 0.45m. The ratio of the cross-sectional area of the stripping section (4) to the side stream rectifying section (5) is 1.36:1, the molar ratio of ethanol feed to formic acid feed is 1.6:1, and the feed positions of formic acid and ethanol are on the left side in turn The 5th theoretical plate and the 26th theoretical plate are fed with saturated liquid. The top reflux ratio is 2.7, the side reflux ratio is 4.7, the flow rate and composition of each material are shown in Table 1, and the mass fraction of ethyl formate obtained is 99.82%. Pure ethanol can also be recovered at the end. Both the condenser and the reboiler are equivalent to a tray.

Table 1 Instance 1 Theoretical plate numbers in each area and the mass flow rate of each stream and the mass fraction of each component

Example 2: The process shown in Figure 2. The thermal state of the feed, the position of the feed, and the number of theoretical plates in each area are the same as in Example 1, except that the molar ratio of the ethanol feed to the formic acid feed is changed to 1.43:1 after the formic acid feed is increased, and the stripping section (4) and the side line rectification section (5) The cross-sectional area ratio is 1.38:1. The top reflux ratio is 2.65, and the side line reflux ratio remains unchanged. The flow rate and composition of each stream are shown in Table 2, and the mass fraction of ethyl formate obtained is 99.81%.

Table 2 Example 2 Each logistics flow and each component mass fraction

Example 3: Same as Example 1, feed composition, flow rate and thermal state are all constant, but the number of trays or packing layer height in this area is changed, and the cross-sectional area ratio of the stripping section (4) and the side line rectifying section is 1.35:1. The top reflux ratio of the reactive distillation section is 2.7, and the reflux ratio of the side stripping section is 4.7. Formic acid is fed on the 5th tray and ethanol is fed on the 25th tray. The mass fraction of the obtained ethyl formate was 99.94%.

Table 3 Example 3 Each logistics flow rate and each component mass fraction

Claims (2)

1. the synthetic process of an ethyl formate, it is characterized in that ethyl formate synthesizes and obtains separating-purifying in the tower of reactive distillation next door, reaction next door rectifying tower has five regions, the region (1) being wherein positioned at left side top is rectifying section, the region (2) be positioned at below rectifying section is conversion zone, the region (3) be positioned at below conversion zone is stripping section, right side area (5) is side line rectifying section, and the region (4) being positioned at tower bottom is public stripping section, this process is made up of following steps: in conversion zone (2), esterification is there is and generates ethyl formate in formic acid and ethanol under the katalysis of acidic cation-exchange resin, the ethyl formate generated and water generate binary azeotrope, after the refinery distillation removing water wherein and other impurity of rectifying section (1), the ethyl formate that massfraction is more than 99% is obtained at tower top, wherein a part returns tower top as backflow, reaction product water and excessive alcohol mixture are removing a small amount of ethyl formate through stripping section (3), the less waste water of amount of alcohol can be obtained at the bottom of tower, next door tower bottom, water and ethanol form binary azeotropic system, mixture is by the refinery distillation of side line rectifying section (5), after removing a small amount of water, ethanol wherein can reach azeotropic composition at side take-off, so that backflow and recycle.

2. ethyl formate processing method as claimed in claim 1 and device thereof, it is characterized in that there are 4 ~ 7 pieces of theoretical stages in reactive distillation next door tower rectifying section (1), conversion zone (2) has 20 ~ 30 pieces of theoretical stages, stripping section (3) has 5 ~ 10 pieces of theoretical stages, side line rectifying section (5) has 25 ~ 35 pieces of theoretical stages, and public stripping section (4) has 6 ~ 10 pieces of theoretical stages; Formic acid is in the charging of conversion zone top, and ethanol is at conversion zone underfeed, and catalyst loading, in conversion zone (2), adopts acidic cation-exchange resin; Formic acid, ethanol charging is saturated liquid phase feeding, and ethanol charging can be straight alcohol, also can be the coarse ethanol that ethanol massfraction is greater than 90%, and ethanol charging and formic acid raw materials components mole ratio are 1.2:1 ~ 1.5:1; The reflux ratio of left side tower top ester is 2 ~ 3.5, and side line rectifying section (5) overhead reflux ratio is 4 ~ 6; The temperature of conversion zone (2) is 67 ~ 78 DEG C, tower top temperature 50 ~ 55 DEG C, and side line rectifying section (5) head temperature is 75 ~ 80 DEG C, and bottom temperature is 90 ~ 100 DEG C; Next door is eccentric or center is arranged, and the cross-sectional area of stripping section (4) and side stripper section is than between 0.5:1 ~ 2:1.