A method for producing acetic acid using natural gas and carbon dioxide

Abstract

The application discloses a method for preparing acetic acid by using natural gas and carbon dioxide, and the method comprises the following steps: taking methyl iodide and water vapor as a catalyst, and making carbon dioxide and methane react to generate a reaction product; and separating the reaction product to obtain the product acetic acid. The method provides a high-yield acetic acid preparation method in which methane and carbon dioxide are directly reacted without additional reaction materials.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing acetic acid in the field of organic chemistry, in particular to a method for preparing acetic acid by using natural gas and carbon dioxide. BACKGROUND

[0002] Acetic acid, also known as acetic acid, is an important raw material in the food industry and chemical industry. For example, acetic acid can be used as an acidifier, flavor enhancer and spice to prepare vinegar, beverages, canned foods and other condiments, etc. Acetic acid belongs to bulk chemical products and is one of the most important organic acids, which is widely used in vinyl acetate, acetic anhydride, acetate fiber, metal acetate and acetate ester, etc. and is widely used in pesticide, medicine, dye, photography and rubber industry. With the rapid development of downstream industries such as vinyl acetate and biodegradable PBAT plastics, the use of acetic acid has also increased substantially, and has become an important part of the national economy.

[0003] The preparation method of acetic acid includes biological synthesis method and artificial synthesis method. The biological synthesis method is to prepare acetic acid by bacterial fermentation, which currently accounts for only a small part of the world's acetic acid production, while most of the acetic acid is prepared by industrial synthesis method. In the industrial synthesis method of acetic acid, there are acetaldehyde method, ethylene direct oxidation method and methanol carbonylation method, etc. At present, the most commonly used method is methanol carbonylation method to produce acetic acid. As early as 1925, the British Seranis Company developed the first pilot plant for the production of acetic acid by methyl carbonylation. In 1970, the American Monsanto Company built a device using this process, so the rhodium catalytic methyl carbonylation method gradually became the dominant method for the commercial production of acetic acid by Monsanto method. In the late 1990s, British Petroleum successfully commercialized the Cativa catalytic method, which uses ruthenium catalyst and is more environmentally friendly and efficient than the Monsanto method.

[0004] In the methanol carbonylation process, methanol is not a naturally occurring raw material and also needs to be synthesized industrially. Moreover, both methanol and carbon monoxide have relatively high toxicity, and more attention needs to be paid to cost and safety when using these two main raw materials to produce acetic acid.

[0005] Compared with methanol, methane is the simplest organic compound in structure and is the main component of natural gas, which is abundant in nature. Carbon dioxide, corresponding to carbon monoxide, is also a gas that exists in large quantities in the air, and a large amount of carbon dioxide is generated in industrial production and daily life. Its toxicity is not high, and its treatment will have better returns in terms of cost and safety. Moreover, the world is currently facing the impact of carbon dioxide on the greenhouse effect, and with the global control of carbon peak and carbon neutralization, there is an urgent need to treat excess carbon dioxide, which is also an extremely important path for waste-to-resource.

[0006] Although theoretically and objectively desired to provide an industrialized method for preparing acetic acid rapidly and simply from methane (natural gas) and carbon dioxide, in fact, there is little progress.

[0007] Although the method for preparing acetic acid from methane and carbon monoxide and / or carbon dioxide in the presence of a catalyst containing iron carbonate or nickel at 12-50 atm and 120-300°C in gas phase has been disclosed in the earliest British patent GB 226248 (publication date December 22, 1924, the content of which is incorporated herein by reference in its entirety) in 1924. But this method does not mention its raw material conversion rate, product yield, product purity and other application data, and obviously it does not reach the level of industrial application.

[0008] WO 96 / 05163 Al (publication date February 22, 1996, the content of which is incorporated herein by reference in its entirety) discloses a method for producing acetic acid, which includes the reaction of methane and carbon dioxide at a temperature of 100 to 600°C and a pressure of 0.1 to 20 MPa, using a catalyst containing one or more metals of groups VIA, VIIA and / or VIIIA. But this method also does not mention its raw material conversion rate, product yield, product purity and other application data, only mentions that the acetic acid selectivity based on the raw material methane is 70-95%, and obviously it does not reach the level of industrial application.

[0009] Chinese patent application CN 1839110 A (publication date September 27, 2006, the content of which is incorporated herein by reference in its entirety) discloses that methane and carbon dioxide are contacted in the presence of a transition metal catalyst and a reaction promoter and an acid anhydride compound and optionally an acid in an anhydrous environment to produce a product containing acetyl anhydride, which can be recovered after further contacting with water to produce acetic acid. But this method uses additional acid and acid anhydride, trifluoroacetic anhydride / trifluoroacetic acid, fuming sulfuric acid, trifluoromethanesulfonic anhydride / trifluoromethanesulfonic acid, etc., and uses a reaction promoter such as K2S2O8 and a small amount of VO(acac)2, etc., and the conversion rate based on methane is only 7-16%, and various by-products are also produced. Obviously, this method also cannot be applied in industry.

[0010] Chinese patent application CN1309114A (published on August 22, 2001, the content of which is incorporated herein by reference in its entirety) discloses a method for synthesizing acetic acid in a heterogeneous catalytic system, using CH4 and CO2 as raw materials, on a solid heterogeneous catalyst, using CH4 and CO2 or CH4 and CO2 / H2 alternating feeding to synthesize acetic acid, the reaction temperature is 100-600℃, the reaction pressure is normal pressure-20Mpa, and the yield of the final product acetic acid is 0.020-0.137g / gcat.h. However, this method needs two steps, and needs to introduce additional hydrogen for reaction, and the catalytic system is heterogeneous, which has adverse factors in catalytic efficiency and side reactions. SUMMARY

[0011] The purpose of the present application is to provide a high-yield acetic acid preparation method by directly reacting methane and carbon dioxide without additional reaction raw materials, specifically comprising the following technical solutions:

[0012] The present application provides a method for preparing acetic acid using natural gas and carbon dioxide, characterized in that: iodomethane and water vapor are used as catalysts to make carbon dioxide and methane react to generate reaction products, and acetic acid is separated from the reaction products.

[0013] Preferably, the volume ratio of methane to carbon dioxide in the present application is 0.5-2:1.

[0014] Preferably, the volume ratio of carbon dioxide to water vapor in the present application is 3-6:1.

[0015] Preferably, the pressure of the reaction in the present application is normal pressure to 20MPa.

[0016] Preferably, the temperature of the reaction in the present application is 100-600℃.

[0017] Further preferably, the catalyst iodomethane in the present application participates in catalysis in the form of a flowing liquid.

[0018] Preferably, it further comprises recycling the gas part of the reaction product in the present application to the reactor to participate in the reaction after purifying the gas part by flash washing.

[0019] Preferably, it further comprises separating the liquid part of the reaction product in the present application by rectification to obtain the product acetic acid, and recycling the remaining liquid to the reactor to participate in the reaction after removing light and heavy components.

[0020] The present application has the following advantages:

[0021] Compared with the existing process for preparing acetic acid from methane and carbon dioxide, the present application has at least the following advantages:

[0022] 1、The reaction of the present application does not need to add other high-cost raw materials such as acid, hydrogen, oxygen, etc., and the added water vapor is a low-cost clean raw material, which can further reduce production cost and improve safety.

[0023] 2、The catalyst methyl iodide used in the present application is a cocatalyst used in the existing methanol carbonylation process to produce acetic acid, but no one has applied it to the process of preparing acetic acid from methane and carbon dioxide. The present inventors' team accidentally discovered that the combination of the catalyst and water can be directly used in the process of preparing acetic acid from methane and carbon dioxide in the present application, which can save the research cost and process adjustment cost of using other catalysts.

[0024] 3、By controlling pressure and temperature, all reaction raw materials and catalysts methyl iodide and water in the present application can participate in the reaction in liquid phase, so that homogeneous catalytic reaction in liquid phase can be carried out, which has more advantages than gas phase catalytic and / or heterogeneous catalytic reaction in the prior art in terms of catalytic effect and reaction control.

[0025] 4、Because the boiling points of the reaction raw materials and catalysts methane, carbon dioxide, methyl iodide and the product acetic acid are very different, the unreacted raw gas can be easily recycled back to the reactor (for example, by flash evaporation), and the product acetic acid can be extracted in liquid form (for example, by rectification treatment).

[0026] 5、The main reaction raw materials used in the present application can be derived from natural gas and carbon dioxide generated by various industrial activities, without the need to purchase chemical raw materials. For enterprises themselves or their partners, they can use the carbon dioxide emitted by themselves, turning waste into treasure and making positive contributions to global greenhouse effect reduction.

[0027] 6、The method for preparing acetic acid in the present application can efficiently convert raw materials, with about 60-70% of the raw material being converted into acetic acid, and the yield of the product acetic acid being as high as more than 90%. These indicators are far superior to the existing technology for preparing acetic acid from methane and carbon dioxide, and have good prospects for industrial application. DETAILED DESCRIPTION

[0028] The embodiments listed in the present application are only used to better illustrate the content of the present application, and the content of the present application is not limited to the listed embodiments. Those skilled in the art can make non-essential improvements and adjustments to the following embodiments without departing from the spirit of the present application, which still belongs to the protection scope of the present application. Specifically, the protection scope of the present application is subject to the content of the claims of the present application.

[0029] The general reaction formula of the present application is: CO2+ CH4 CH3COOH

[0030] The process in which the catalyst methyl iodide and water vapor are involved can be represented as the following two-step reactions:

[0031] CO2+ H2O + CH3I CH3COOH + HI

[0032] HI + CH4 CH3I + H2O

[0033] Therefore, the present application can obtain the target product acetic acid through one-step reaction in one reactor, or can obtain the target product acetic acid through two-step reactions in two reactors in sequence.

[0034] For the raw materials of the present application, carbon dioxide can use commercially available high-purity carbon dioxide (mass ratio of 90% or more), or can be directly used in various industrial activities or treated into high-purity carbon dioxide. Similarly, methane can use commercially available high-purity methane (mass ratio of 90% or more), or can be directly used in natural gas or treated into high-purity methane. From the perspective of improving reaction quality and reducing side reactions, it is preferred to use high-purity reaction raw materials.

[0035] For the reaction condition control of the present application, the raw material usage and the reaction temperature and pressure control are the main control points. Generally, the main raw material methane and carbon dioxide can be used in a relatively equal proportion, and the volume ratio of methane to carbon dioxide is preferably 0.5-2:1, so that both of them can fully react. For the iodomethane and water vapor which play a catalytic role, they can be provided in a smaller proportion than the main raw material, and the volume ratio of carbon dioxide to water vapor is preferably 3-6:1, and the amount of iodomethane is 0.1-2%wt of the total amount of reaction raw materials, as long as the best catalytic effect can be achieved.

[0036] For the reaction temperature and pressure of the present application, it is generally necessary to carry out at high temperature and high pressure to improve the conversion rate and yield. The reaction of the present application can be carried out at a pressure higher than normal pressure, and the highest can be carried out at 40MPa, but considering the balance of conversion rate, yield and cost, etc., the use of a reaction pressure range of 2-8MPa is the best.

[0037] For the reaction temperature and pressure of the present application, it is generally necessary to carry out at high temperature and high pressure to improve the conversion rate and yield. The reaction of the present application can be carried out at a temperature higher than 100℃, and the highest can be carried out at 220℃, but considering the balance of conversion rate, yield and cost, etc., the use of a reaction temperature range of 170-210℃ is the best.

[0038] As for the separation and recovery of the product after the reaction, reference can be made to the process of preparing acetic acid by methanol carbonylation, which is a particularly mature process for preparing acetic acid in the art. For example, by virtue of the principle that the boiling points of substances are different under high and low pressures, the mixture obtained in the liquid phase under high pressure is subjected to flash evaporation under low pressure to perform gas-liquid separation, the unreacted raw gas is returned to the reactor for recycling, and the product acetic acid is separated by rectification.

[0039] Example 1

[0040] Carbon dioxide and methane in a volume ratio of 5:5 were preheated to 100°C, and then introduced into a zirconium alloy reactor loaded with methyl iodide together with water vapor (carbon dioxide to water vapor in a volume ratio of 5:1). The temperature of the reactor was controlled at 200°C, and the reaction pressure was 3 MPa, so that the synthesis reaction was carried out in the liquid phase to generate acetic acid.

[0041] After the reaction was completed, the product at the outlet of the reactor was subjected to gas-liquid separation by a flash evaporator, the separated gas part was returned to the inlet of a compressor to return to the reactor for recycling, the separated liquid part was subjected to rectification to obtain the product acetic acid, and the remaining liquid after rectification was introduced into the inlet of a high-pressure liquid pump to return to the reactor for recycling.

[0042] The conversion rate of methane and the yield of the product acetic acid after the reaction were determined by a conventional method in the art, and the results showed that the conversion rate of methane was 70% and the yield of acetic acid was 95%.

[0043] Example 2

[0044] Carbon dioxide and methane in a volume ratio of 4.5:4.5 were preheated to 100°C, and then introduced into a zirconium alloy reactor loaded with methyl iodide together with water vapor (carbon dioxide to water vapor in a volume ratio of 4.5:1). The temperature of the reactor was controlled at 195°C, and the reaction pressure was 3.2 MPa, so that the synthesis reaction was carried out in the liquid phase to generate acetic acid.

[0045] After the reaction was completed, the product at the outlet of the reactor was subjected to gas-liquid separation by a flash evaporator, the separated gas part was returned to the inlet of a compressor to return to the reactor for recycling, the separated liquid part was subjected to rectification to obtain the product acetic acid, and the remaining liquid after rectification was introduced into the inlet of a high-pressure liquid pump to return to the reactor for recycling.

[0046] The conversion rate of methane and the yield of the product acetic acid after the reaction were determined by a conventional method in the art, and the results showed that the conversion rate of methane was 68% and the yield of acetic acid was 93%.

[0047] Example 3

[0048] Carbon dioxide and methane in a volume ratio of 5:5 were preheated to 100°C and then passed into a zirconium alloy reactor loaded with methyl iodide together with water vapor (carbon dioxide to water vapor in a volume ratio of 5:1). The temperature of the reactor was controlled at 196°C and the reaction pressure was 3.5 MPa, and the synthesis reaction was carried out in liquid phase to produce acetic acid.

[0049] After the reaction was completed, the reactor outlet product was separated into gas and liquid phases in a flasher, the separated gas was returned to the compressor inlet to be recycled into the reactor, and the separated liquid was refined to obtain the product acetic acid. The remaining liquid was refined and then entered the high-pressure liquid pump inlet to be recycled into the reactor.

[0050] The conversion rate of methane and the yield of acetic acid after the reaction were determined by conventional methods in the art, and the results showed that the conversion rate of methane was 69% and the yield of acetic acid was 94%.

Claims

1. A method for producing acetic acid using natural gas and carbon dioxide, characterized by: Carbon dioxide and methane are reacted in a reactor to produce a reaction product by using methyl iodide and water vapor as catalyst, and acetic acid is separated from the reaction product; the reaction pressure is 2-8 MPa; the reaction temperature is 170-210 DEG C.

2. The method of claim 1, wherein: The volume ratio of methane to carbon dioxide is 0.5-2:

1.

3. The method according to claim 1 or 2, characterized in that: The volume ratio of carbon dioxide to water vapor is 3-6:

1.

4. The method of claim 3, wherein: The methyl iodide participates in the catalysis in the form of flowing liquid.

5. The method of claim 4, wherein: The gas part of the reaction product is also returned to the reactor to participate in the reaction.

6. The method of claim 5, wherein: The gas part is washed and purified by flash evaporation before being returned.

7. The method of any one of claims 1, 2, and 4-6, wherein: The liquid part of the reaction product is also separated to produce acetic acid, and the remaining liquid is returned to the reactor to participate in the reaction after light and heavy components are removed.

8. The method of claim 7, wherein: The product acetic acid is separated by rectification.