1. A method for adjusting the water content in an iridium catalytic system oxo-synthesis acetic acid system is characterized in that the water content in the reaction system is controlled by adjusting the composition of reaction raw materials, and the method comprises the following steps:

1) pumping raw materials of methanol and methyl acetate into a reactor, wherein the reaction temperature is 175-198 ℃, the reaction pressure is 2.0-3.5MPa, a catalyst used for the reaction is an iridium complex, and a cocatalyst used for the reaction is alkyl iodide; the feeding ratio of the methanol to the methyl acetate is 1:10-10: 1;

2) the reaction liquid flows out of the reaction kettle and enters an evaporator for flash evaporation, the mother liquid is primarily separated from the crude acetic acid, the mother liquid returns to the reaction kettle for continuous reaction, the crude acetic acid enters a cocatalyst recovery tower along with flash evaporation gas, enters a water recovery tower after light components are removed in the cocatalyst recovery tower, enters a product tower after water in the finished product acetic acid is removed in the water recovery tower, and the finished product acetic acid is extracted after the removal of impurities is finished;

3) and arranging a first water quantity detection probe on a branch pipe of the reactor connected with the circulating cooler, arranging a second water quantity detection probe on a branch pipe of the reactor connected with the flash evaporator, and taking the average value of the detection quantities of the two detection probes by using a water quantity detector to obtain the water content in the reaction liquid of 2.5-8.0%.

2. The method for adjusting the water content in an iridium catalytic system oxo acetic acid system according to claim 1, wherein the method comprises the following steps: the feeding ratio of the methanol to the methyl acetate is 2:2-3, and the water content in the reaction liquid is 4.5-5%.

Background

Acetic acid is a bulk chemical product and is one of the most important organic acids. The method is mainly used for producing vinyl acetate, acetic anhydride, acetic ester, cellulose acetate and the like. It has wide application in pesticide, medicine and dye, photographic medicine manufacture, textile printing and dyeing and rubber industry. A process for synthesizing acetic acid by methanol carbonyl; the low-pressure method is based on iridium-iodine catalyst, takes methyl iodide as a cocatalyst, has mild reaction conditions, and has extremely high selectivity and conversion rate of acetic acid by taking methanol and CO as the basis. In recent years, with the rapid expansion of the productivity of domestic methanol and downstream products thereof, the process for synthesizing acetic acid by methanol low-pressure carbonyl becomes one of the production process routes with better market prospects. In the low-pressure oxo reaction system, water is used as a solvent, and the water content in the reaction liquid is closely related to the product quality and production consumption besides the stability of the catalyst. The water must maintain a certain concentration, and the catalyst solubility is reduced due to the excessively low water concentration, so that the catalyst loss is caused; too high water concentration increases the separation energy consumption and reduces the production capacity of the device.

Disclosure of Invention

In the reaction of synthesizing acetic acid by carbonyl of an iridium catalytic system, as the reaction of producing methane and water by methanol and hydrogen is more than that of the traditional rhodium catalytic system, the water content in the reaction system can be continuously increased; the water content in the reaction system can be controlled by adjusting the composition of the reaction raw materials, and compared with the existing device for synthesizing acetic acid by methanol low-pressure carbonyl, the device has the advantages of stable composition of the reaction system and high product quality.

The technical scheme adopted by the invention is as follows: a method for adjusting the water content in an iridium catalytic system oxo-synthesis acetic acid system controls the water content in the reaction system by adjusting the composition of reaction raw materials, and comprises the following steps:

1) pumping raw materials of methanol and methyl acetate into a reactor, wherein the reaction temperature is 175-198 ℃, the reaction pressure is 2.0-3.5MPa, a catalyst used for the reaction is an iridium complex, and a cocatalyst used for the reaction is alkyl iodide; the feeding ratio of the methanol to the methyl acetate is 1:10-10: 1;

2) the reaction liquid flows out of the reaction kettle and enters an evaporator for flash evaporation, the mother liquid is primarily separated from the crude acetic acid, the mother liquid returns to the reaction kettle for continuous reaction, the crude acetic acid enters a cocatalyst recovery tower along with flash evaporation gas, enters a water recovery tower after light components are removed in the cocatalyst recovery tower, enters a product tower after water in the finished product acetic acid is removed in the water recovery tower, and the finished product acetic acid is extracted after the removal of impurities is finished;

3) and arranging a first water quantity detection probe on a branch pipe of the reactor connected with the circulating cooler, arranging a second water quantity detection probe on a branch pipe of the reactor connected with the flash evaporator, and taking the average value of the detection quantities of the two detection probes by using a water quantity detector to obtain the water content in the reaction liquid of 2.5-8.0%.

The feeding ratio of the methanol to the methyl acetate is 2:2-3, and the water content in the reaction liquid is 4.5-5%.

In the low pressure oxo acetic acid reaction system, the following reactions occur:

main reaction:

and (3) methane generation reaction:

and (3) shift reaction:

water is used as a solvent in a reaction system for synthesizing acetic acid by low-pressure carbonyl, and certain water content plays a key role in the solubility and stability of the catalyst. The water content in the reaction liquid is too high, and because the boiling point of water is lower than that of acetic acid, the amount of the acetic acid gasified in the flash evaporation process of the reaction liquid is less, so that the production capacity of a reaction system is reduced, and meanwhile, the energy consumption of a rectification separation system is increased; if the water content in the reaction solution is too low, the solubility of the catalyst in the reaction solution is affected, resulting in precipitation and loss of the catalyst.

In the traditional rhodium catalytic reaction system, the reaction for generating methane accounts for about 0.2 percent of the main reaction product, while the shift reaction generally accounts for 1.5 to 2.0 percent of the main reaction product, so the water generated by the reaction for generating methane can be consumed through the shift reaction, and meanwhile, the water content of the reaction system can be kept stable by supplementing certain water. The reaction for generating methane in the iridium catalytic reaction system accounts for about 1.5-2.5% of the main reaction product, and the shift reaction generally accounts for 0.5-0.8% of the main reaction product, so that the water generated by the reaction for generating methane is larger than the water consumed by the shift reaction, and the water content in the system can be continuously increased due to the factors such as leakage of a pump sealing liquid, leakage of a stirrer sealing liquid, leakage of cooling water of a heat exchanger and the like in the system, so that the water content in the reaction system needs to be kept stable by a certain adjusting means.

The invention is realized by the following technical scheme:

methyl acetate with a certain proportion is mixed in raw material methanol, water in a reaction system is consumed through hydrolysis reaction, the methyl acetate is hydrolyzed to generate methanol and acetic acid, the methanol generated by hydrolysis is reacted with CO to generate acetic acid, so that 2mol of acetic acid can be generated by adding 1mol of methyl acetate.

And (3) hydrolysis reaction:

the proportion of methyl acetate mixed in the raw material methanol can be adjusted according to the water content in the reaction system.

Has the advantages that: the invention relates to a method for adjusting the water content in an iridium catalytic system oxo-synthesis acetic acid system, which can control the water content in the reaction system by adjusting the composition of reaction raw materials and adding methyl acetate. Methyl acetate is hydrolyzed to generate methanol and acetic acid, the methanol generated by hydrolysis reacts with CO to generate acetic acid, and the introduction of the methyl acetate can not only consume the water in the reaction system, but also increase the yield of the acetic acid and avoid the introduction of other impurities. The iridium catalyst system has the water content of 4.5-5% as the optimal water content, and the method can control the water content to be 4.5-5% as the optimal water content, which shows that the method well controls the water content in the reaction system. Compared with the existing device for synthesizing acetic acid by methanol low-pressure carbonyl, the reaction system has stable composition, low energy consumption and high product quality.

Drawings

FIG. 1 is a flow diagram of a methanol low pressure oxo acetic acid system.

In the figure: 1. the system comprises a fluid stirring reactor, 2, a flash evaporator, 3, a circulating cooler, 4, a flash evaporator heater, 5, a cocatalyst recovery tower, 6, a water recovery tower, 7, a product tower, 8, a water quantity detector, 8a, a first water quantity detection probe, 8b, a second water quantity detection probe, 9 and a delayer.

Detailed Description

Example 1

The feeding amount of methanol is 0.5 ton/h, the feeding amount of methyl acetate is 0.5 ton/h, and CO and methanol react in a fluid stirring reactor 1 under the action of 2000ppm of iridium complex and catalyst promoter methyl iodide under the conditions of temperature 190 ℃ and pressure 3.0 MPa; a first water quantity detection probe 8a is arranged on a branch pipe connected with the circulating cooler 3, a second water quantity detection probe 8b is arranged on a branch pipe connected with the flash evaporator 2, and the water quantity detector 8 takes the average value of the detection quantity of the two detection probes to obtain that the water content in the reaction liquid is 6%.

Then the reaction liquid flows out from the fluid stirring reactor 1 and enters an evaporator for flash evaporation, the mother liquid and the crude acetic acid are primarily separated, the mother liquid returns to the reaction kettle for continuous reaction, the crude acetic acid enters a cocatalyst recovery tower 5 along with flash evaporation gas, enters a water recovery tower 6 after light components are removed in the cocatalyst recovery tower 5, enters a product tower 7 after water in the finished product acetic acid is removed in the water recovery tower 6, and the finished product acetic acid is extracted after the removal of impurities is finished; the acetic acid yield was 1.72 ton/hr.

Example 2

The feeding amount of methanol is 1.25 ton/h, the feeding amount of methyl acetate is 0.25 ton/h, and CO and methanol react in a fluid stirring reactor 1 under the action of 1800ppm of iridium complex and catalyst promoter methyl iodide under the conditions that the temperature is 195 ℃ and the pressure is 3.2 MPa; a first water quantity detection probe 8a is arranged on a branch pipe connected with the circulating cooler 3, a second water quantity detection probe 8b is arranged on a branch pipe connected with the flash evaporator 2, and the water quantity detector 8 takes the average value of the detection quantity of the two detection probes to obtain the reaction liquid with the water content of 8%.

The reaction liquid flows out from the fluid stirring reactor 1 and enters an evaporator for flash evaporation, the mother liquid and the crude acetic acid are primarily separated, the mother liquid returns to the reaction kettle for continuous reaction, the crude acetic acid enters a cocatalyst recovery tower 5 along with flash evaporation gas, enters a water recovery tower 6 after light components are removed in the cocatalyst recovery tower 5, enters a product tower 7 after water in the finished product acetic acid is removed in the water recovery tower 6, and the finished product acetic acid is extracted after the removal of impurities is finished; the yield of acetic acid was 2.68 ton/hr.

Example 3

The feeding amount of methanol is 0.5 ton/h, the feeding amount of methyl acetate is 0.75 ton/h, and CO and methanol react in a fluid stirring reactor 1 under the action of 1500ppm of iridium complex and a cocatalyst methyl iodide under the conditions of 185 ℃ of temperature and 3.0MPa of pressure; a first water quantity detection probe 8a is arranged on a branch pipe connected with the circulating cooler 3, a second water quantity detection probe 8b is arranged on a branch pipe connected with the flash evaporator 2, and the water quantity detector 8 takes the average value of the detection quantity of the two detection probes to obtain the reaction liquid with the water content of 4.5%.

The reaction liquid flows out from the fluid stirring reactor 1 and enters an evaporator for flash evaporation, the mother liquid and the crude acetic acid are primarily separated, the mother liquid returns to the reaction kettle for continuous reaction, the crude acetic acid enters a cocatalyst recovery tower 5 along with flash evaporation gas, enters a water recovery tower 6 after light components are removed in the cocatalyst recovery tower 5, enters a product tower 7 after water in the finished product acetic acid is removed in the water recovery tower 6, and the finished product acetic acid is extracted after the removal of impurities is finished; the yield of acetic acid was 2.16 ton/hr.

Comparative example

The feeding amount of the methanol is 1.25 ton/h, and the CO and the methanol react in a fluid stirring reactor 1 under the action of 2000ppm of iridium complex and a cocatalyst methyl iodide under the conditions that the temperature is 192 ℃ and the pressure is 3.0 MPa; a first water quantity detection probe 8a is arranged on a branch pipe connected with the circulating cooler 3, a second water quantity detection probe 8b is arranged on a branch pipe connected with the flash evaporator 2, and the water quantity detector 8 takes the average value of the detection quantity of the two detection probes to obtain the reaction liquid with the water content of 12 percent and the acetic acid yield of 2.17 tons/hour.