A composite catalyst for preparing acetic acid and a method for preparing acetic acid using the same

Abstract

The present invention discloses a composite catalyst for preparing acetic acid and a method for preparing acetic acid therefrom. Using methyl iodide as the main catalyst and ruthenium, iridium or a combination thereof as the co-catalyst, carbon dioxide and methane are reacted to form a reaction product, and acetic acid as the product is separated from the reaction product. This method provides a highly efficient catalytic system for directly reacting methane and carbon dioxide and a method for preparing acetic acid therefrom.

Description

Technical Field

[0001] The present invention relates to a catalyst and a method for preparing acetic acid in the field of organic chemistry, and particularly relates to a composite catalyst for preparing acetic acid and a method for preparing acetic acid using the same. Background Art

[0002] Acetic acid, also known as ethanoic acid, is an important raw material in both the food industry and the chemical industry. For example, acetic acid can be used as an acidifying agent, flavor enhancer and fragrance to prepare vinegar, beverages, canned foods and other seasonings. 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 acetates and acetate esters, etc., and has a wide range of applications in the pesticide, medicine, dye, photography and rubber industries. With the rapid development of downstream industries such as vinyl acetate and biodegradable PBAT plastics, the consumption of acetic acid has also increased significantly, and it has become an important part of the national economy.

[0003] The preparation methods of acetic acid include biosynthesis method and artificial synthesis method. The biosynthesis method uses bacteria fermentation to prepare acetic acid, which currently accounts for only a very small part of the total acetic acid production in the world, while most acetic acid has been prepared by industrial synthesis method. In the industrial synthesis method of acetic acid, there have been processes such as acetaldehyde method, direct oxidation of ethylene method and methanol carbonylation method, etc. Currently, the most widely used method is the methanol carbonylation method to produce acetic acid. As early as 1925, the British company Celanese developed the first pilot plant for methyl carbonylation to produce acetic acid. In 1970, the American company Monsanto built a plant using this process. Therefore, the rhodium-catalyzed methyl carbonylation to produce acetic acid gradually became the dominant Monsanto process for commercial production of acetic acid, and the catalyst used therein is mainly rhodium as the main catalyst. In the late 1990s, BP successfully commercialized the Cativa catalytic process, using ruthenium as the main catalyst, which is more environmentally friendly and more efficient than the Monsanto process.

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

[0005] Relatively speaking, methane corresponding to methanol is the simplest organic compound in structure, and it is the main component naturally present in natural gas with rich reserves; carbon dioxide corresponding to carbon monoxide is also a gas that exists in large quantities in the air. At the same time, a large amount of carbon dioxide is generated in industrial production and people's daily lives, and its toxicity is not great, and its treatment will naturally have better returns in terms of cost and safety. Moreover, the world is currently facing the impact of the greenhouse effect brought by carbon dioxide. With the global control of carbon peak and carbon neutrality, it is also urgent to treat the excessive carbon dioxide generated, which is also an extremely important path considering turning waste into treasure.

[0006] Although there is a theoretical and objective need to provide an industrial method for the rapid and simple preparation of acetic acid from methane (natural gas) and carbon dioxide, the actual progress has been rather limited.

[0007] Although a method for the preparation of acetic acid by gas-phase reaction in the presence of methane and carbon monoxide and / or carbon dioxide at 12 - 50 atmospheres and 120 - 300 °C was first disclosed in British Patent GB226248 in 1924 (publication date December 22, 1924, the full content of which is incorporated herein by reference), and the catalyst used was a catalyst containing iron carbonate or nickel. However, this method did not mention any application data regarding raw material conversion rate, product yield, product purity, etc. The catalytic effect was not clear, and it did not reach the level of being industrially applicable.

[0008] WO 96 / 05163A1 (publication date February 22, 1996, the full content of which is incorporated herein by reference) discloses a method for the production of acetic acid, including 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 Group VIA, VIIA, and / or VIIIA. However, this method also did not mention any application data regarding raw material conversion rate, product yield, product purity, etc. The catalytic effect was not obvious either, and only the acetic acid selectivity based on raw material methane was mentioned as 70 - 95%. Similarly, it did not reach the level of being industrially applicable.

[0009] Chinese Patent Application CN1839110A (publication date September 27, 2006, the full content of which is incorporated herein by reference) discloses that in the presence of a transition metal catalyst, a reaction promoter, an acid anhydride compound, and optionally an acid, methane and carbon dioxide are contacted in an anhydrous environment to produce a product containing acetyl anhydride, and acetic acid can be recovered after further contact with water. However, this method requires the use of additional acids and acid anhydrides, such as trifluoroacetic anhydride / trifluoroacetic acid, fuming sulfuric acid, trifluoromethanesulfonic anhydride / trifluoromethanesulfonic acid, etc. The main catalyst is a transition metal catalyst and a reaction promoter such as K2S2O8 and a small amount of VO(acac)2, etc. The conversion rate based on methane is only 7 - 16%, and at the same time, various by-products are also generated. The catalytic effect is still not obvious. Obviously, this method also cannot be industrially promoted and applied.

[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, acetic acid is synthesized on a solid heterogeneous catalyst by alternately feeding CH4 and CO2 or CH4 and CO2 / H2. The reaction temperature is 100 - 600 °C, the reaction pressure is from atmospheric pressure to 20 Mpa, and the yield of the final product acetic acid is 0.020 - 0.137 g / gcat.h. However, this method requires two steps and needs to introduce hydrogen additionally for the reaction. It uses transition metal catalysts of Groups IB and VIII as the main catalysts, and the catalytic system is heterogeneous, and there are still adverse factors in terms of its catalytic effect and side reactions. Summary of the Invention

[0011] The object of the present invention is to provide a more efficient composite catalyst for preparing acetic acid and a method for preparing acetic acid using the same, which specifically includes the following technical solutions:

[0012] The present invention provides a composite catalyst for preparing acetic acid, using methyl iodide as the main catalyst and noble metals as the co-catalysts.

[0013] Preferably, ruthenium, iridium or a combination thereof is used as the co-catalyst.

[0014] Preferably, the main catalyst and the co-catalyst of the present invention exist in independent forms respectively.

[0015] Further preferably, the co-catalyst of the present invention is a solid catalyst formed by being dispersed in a carrier.

[0016] More preferably, the co-catalyst of the present invention is a solid catalyst formed by being dispersed in a SiO2 carrier.

[0017] The present invention also provides a method for preparing acetic acid using natural gas and carbon dioxide, which is characterized in that: using the aforementioned composite catalyst of the present invention, reacting carbon dioxide and methane to generate a reaction product, and separating acetic acid from the reaction product.

[0018] Preferably, in the preparation method of the present invention, the volume ratio of carbon dioxide to steam is 3 - 6:1, and the volume ratio of methane to carbon dioxide is 0.5 - 2:1.

[0019] Preferably, in the preparation method of the present invention, the pressure of the reaction is from atmospheric pressure to 20 MPa, and the reaction temperature is 100 - 600 °C.

[0020] Further preferably, the preparation method of the present invention further includes passing the gas part of the reaction product through flash washing and purification and then returning the gas to the reactor to participate in the reaction in a cycle.

[0021] Preferably, it further includes separating the liquid part of the reaction product of the present invention by rectification to obtain the product acetic acid, and returning the remaining liquid to the reactor to participate in the reaction cyclically after removing the light and heavy components.

[0022] The beneficial effects of the present invention are as follows:

[0023] Compared with the existing processes for preparing acetic acid from methane and carbon dioxide, the present invention has at least the following advantages:

[0024] 1. The main catalyst methyl iodide used in the present invention is a cocatalyst used in the existing methanol carbonylation process for producing acetic acid. These traditional processes usually use transition metal or noble metal catalysts as the main catalyst, and there is no composite catalyst using methyl iodide as the main catalyst and noble metal catalyst as the cocatalyst, let alone in the process for preparing acetic acid. The inventor's team unexpectedly found that using methyl iodide as the main catalyst and noble metal catalyst as the cocatalyst can be directly used in the process of the present invention for reacting methane and carbon dioxide to prepare acetic acid, which can save the research cost and process adjustment cost of using other catalysts.

[0025] 2. The reaction of the present invention does not require additional addition of other high-cost raw materials, such as acids, hydrogen, oxygen, etc. The added water vapor itself is a low-cost clean raw material, which can further reduce the production cost and improve safety.

[0026] 3. Through pressure and temperature control, all the reaction raw materials, the main catalyst methyl iodide, and water of the present invention can participate in the reaction in the liquid phase, so that the homogeneous catalytic reaction in the liquid phase can be carried out. In terms of catalytic effect and reaction control, it can have more advantages than the gas-phase catalysis and / or heterogeneous catalytic reactions used in the prior art.

[0027] 4. Since the boiling points of the reaction raw materials and catalysts methane, carbon dioxide, methyl iodide and the product acetic acid vary greatly, it is easy to return the unreacted raw material gas in the gaseous form (for example, by flash evaporation) to the reactor for recycling, while the product acetic acid is extracted in the liquid form, for example, by rectification treatment.

[0028] 5. The main reaction raw materials used in the present invention can be respectively sourced from natural gas and carbon dioxide generated by various industrial activities. Without the need to specifically purchase chemical raw materials, for an enterprise itself or its partners with these industrial activities, the carbon dioxide emitted by itself can be utilized locally, turning waste into treasure and making a positive contribution to reducing the global greenhouse effect.

[0029] 6. The method for preparing acetic acid according to the present invention can efficiently convert raw materials. About 70-80% of the raw materials can be converted based on methane, and the yield of the product acetic acid is extremely high, all reaching over 95%. These indicators are far superior to the technologies for preparing acetic acid from methane and carbon dioxide in the prior art, and have good prospects for industrial application. Detailed Embodiments

[0030] The embodiments listed in the present invention are only for better illustrating the content of the present invention, and the content of the present invention is not limited to the listed embodiments. Those of ordinary skill in the art can make non-essential improvements and adjustments to the following embodiments without departing from the spirit of the present invention, and still fall within the protection scope of the present invention. Specifically, the protection scope of the present invention shall be subject to the content of the claims of the present invention.

[0031] A noble metal catalyst is a noble metal material that can change the rate of a chemical reaction without itself participating in the final reaction product. Almost all noble metals can be used as catalysts, but the commonly used ones are platinum, palladium, rhodium, silver, ruthenium, etc. Among them, platinum and rhodium are the most widely used. Their d electron orbits are not fully filled, the surface is easy to adsorb reactants, and the strength is moderate, which is conducive to the formation of intermediate "active compounds", having high catalytic activity. At the same time, they also have comprehensive excellent properties such as high temperature resistance, oxidation resistance, and corrosion resistance, becoming the most important catalyst materials.

[0032] In the process of carbonylation for preparing acetic acid, there are many studies on using noble metal catalysts for catalysis. Rhodium, iridium, ruthenium, etc. are all the main catalysts that have been used, but methyl iodide is used as a co-catalyst. The present invention uses a noble metal catalyst as a co-catalyst to cooperate with the main catalyst methyl iodide to catalyze the reaction of the present invention. Through the comparative research of the inventor's team, iridium, ruthenium or their combination (that is, using iridium and ruthenium simultaneously) has the best co-catalytic effect, but other noble metals well-known to those skilled in the art can also play a co-catalytic role. The present invention does not limit the type and composition of the specific noble metal.

[0033] The catalyst carrier is one of the components of the supported catalyst, the skeleton of the catalyst active component, supporting the active component, dispersing the active component, and at the same time can also increase the strength of the catalyst. Most carriers are products in the catalyst industry, and the commonly used ones include alumina carriers, silica gel carriers, activated carbon carriers, and some natural products such as pumice, diatomite, etc. Through the comparative research of the inventor's team, silica-supported iridium and / or ruthenium has the best co-catalytic effect, but other catalyst carriers well-known to those skilled in the art can also play a role. The present invention does not limit the type and composition of the specific catalyst carrier.

[0034] The overall reaction formula of the preparation process of the present invention is: CO2 + CH4 CH3COOH

[0035] The process in which the main catalyst methyl iodide and water vapor participate can be represented by the following two-step reaction:

[0036] CO2 + H2O + CH3I CH3COOH + HI

[0037] HI + CH4 CH3I + H2O

[0038] Therefore, the target product acetic acid can be obtained through a one-step reaction in one reactor in the present invention, or the target product acetic acid can be obtained through two-step reactions in two reactors successively.

[0039] For the raw materials of the present invention, carbon dioxide can be commercially available high-purity carbon dioxide (more than 90% by mass ratio), or carbon dioxide recovered from various industrial activities can be directly used or used after being processed into high-purity carbon dioxide. Similarly, methane can be commercially available high-purity methane (more than 90% by mass ratio), or methane contained in natural gas can be directly used or used after being processed into high-purity methane. From the perspective of improving the reaction quality and reducing side reactions, it is preferred to use high-purity reaction raw materials.

[0040] For the control of the reaction conditions of the present invention, the raw material dosage and the control of the reaction temperature and pressure are the main control points. Generally speaking, the main raw materials methane and carbon dioxide can be used in a relatively equal proportion. The volume ratio of methane to carbon dioxide is preferably 0.5 - 2:1 so that both of them can fully react. For methyl iodide and water vapor that play a catalytic role, they can be provided in a proportion slightly less than that of the main raw materials. The volume ratio of carbon dioxide to water vapor is preferably 3 - 6:1, and the dosage of methyl iodide is 0.1 - 2%wt of the total amount of the reaction system, as long as the best catalytic effect can be achieved. For the promoter, only a very small amount needs to be used, specifically, for example, 0.1 - 1%wt of the total amount of the reaction system.

[0041] For the reaction temperature and pressure of the present invention, it usually needs to be carried out under high temperature and high pressure to improve the conversion rate and yield. The reaction of the present invention can be carried out under conditions higher than atmospheric pressure, and the highest can be carried out at 40 MPa. However, considering factors such as the comprehensive balance of the conversion rate, yield, and cost, a reaction pressure range of 2 - 8 MPa is the best.

[0042] For the reaction temperature and pressure of the present invention, it usually needs to be carried out under high temperature and high pressure to improve the conversion rate and yield. The reaction of the present invention can usually be carried out under conditions higher than 100 °C, and the highest can be carried out at 220 °C. However, considering factors such as the comprehensive balance of the conversion rate, yield, and cost, a reaction temperature range of 170 - 210 °C is the best.

[0043] Regarding the separation and recovery of the reaction products, reference can be made to the process for preparing acetic acid by methanol carbonylation for adjustment. This process is a particularly mature acetic acid preparation process in the art. For example, based on the principle of different boiling points of substances under high and low pressures, the mixture obtained from the liquid-phase reaction under high pressure is flash-vaporized under low pressure for gas-liquid separation. The unreacted raw material gas can be returned to the reactor for recycling, and the product acetic acid present in the liquid phase can be further separated by distillation.

[0044] Example 1

[0045] Carbon dioxide and methane with 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 steam (volume ratio of carbon dioxide to steam is 5:1). In the reactor, a silica support loaded with an iridium metal promoter was also immobilized. The temperature of the reactor was controlled at 200 °C and the reaction pressure was 3.5 MPa, and the synthesis reaction occurred in the liquid phase to produce acetic acid.

[0046] After the reaction was completed, the product at the reactor outlet was subjected to gas-liquid separation through a flash separator. The separated gas part was returned to the compressor inlet to return to the reactor for recycling in the reaction, and the separated liquid part was obtained as the product acetic acid through distillation. The remaining liquid after distillation entered the high-pressure liquid pump inlet to return to the reactor for recycling in the reaction.

[0047] The methane conversion rate and the acetic acid yield of the product after the reaction were measured by conventional methods in the art. The results showed that the methane conversion rate was 75% and the acetic acid yield was 97%.

[0048] Example 2

[0049] Carbon dioxide and methane with 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 steam (volume ratio of carbon dioxide to steam is 4.5:1). In the reactor, a silica support loaded with a ruthenium metal promoter was also immobilized. The temperature of the reactor was controlled at 196 °C and the reaction pressure was 3.2 MPa, and the synthesis reaction occurred in the liquid phase to produce acetic acid.

[0050] After the reaction was completed, the product at the reactor outlet was subjected to gas-liquid separation through a flash separator. The separated gas part was returned to the compressor inlet to return to the reactor for recycling in the reaction, and the separated liquid part was obtained as the product acetic acid through distillation. The remaining liquid after distillation entered the high-pressure liquid pump inlet to return to the reactor for recycling in the reaction.

[0051] The methane conversion rate and the acetic acid yield of the product after the reaction were measured by conventional methods in the art. The results showed that the methane conversion rate was 72% and the acetic acid yield was 95%.

[0052] Example 3

[0053] Preheat carbon dioxide and methane with a volume ratio of 5:5 to 100 °C, and then introduce them together with water vapor (volume ratio of carbon dioxide to water vapor is 5:1) into a zirconium alloy reactor loaded with methyl iodide. In the reactor, a silica support loaded with iridium and ruthenium metal promoters is also immobilized. Control the temperature of the reactor at 200 °C and the reaction pressure at 3.5 MPa, and the synthesis reaction occurs in a liquid phase to produce acetic acid.

[0054] After the reaction is completed, the product at the reactor outlet is subjected to gas-liquid separation through a flash separator. The separated gas part is returned to the compressor inlet to return to the reactor to participate in the reaction in a cycle, and the separated liquid part is rectified to obtain the product acetic acid. The remaining liquid after rectification enters the high-pressure liquid pump inlet to return to the reactor to participate in the reaction in a cycle.

[0055] Use conventional methods in the art to measure the methane conversion rate and the acetic acid yield after the reaction is completed. The results show that the methane conversion rate is 76% and the acetic acid yield is 98%.

Claims

1. A method for preparing acetic acid using natural gas and carbon dioxide, characterized in that: Using methyl iodide as the main catalyst and a noble metal catalyst as the co-catalyst; reacting carbon dioxide, water vapor and methane to produce a reaction product, and separating acetic acid from the reaction product.

2. The method according to claim 1, characterized in that: The noble metal catalyst is ruthenium, iridium or a combination thereof.

3. The method according to claim 2, characterized in that: The main catalyst and the co-catalyst exist in independent forms respectively.

4. The method according to claim 3, characterized in that: The co-catalyst is a solid catalyst formed by being dispersed in a carrier.

5. The method according to claim 4, characterized in that: The co-catalyst is a solid catalyst formed by being dispersed in a SiO2 carrier.

6. The method according to claim 1, wherein: The methyl iodide participates in the catalysis in the form of a flowing liquid.

7. The method according to claim 6, wherein: The volume ratio of the carbon dioxide to the water vapor is 3 - 6:

1.

8. The method according to claim 7, characterized in that: The volume ratio of the methane to the carbon dioxide is 0.5 - 2:

1.

9. The method according to claim 8, wherein: The pressure of the reaction is from atmospheric pressure to 20 MPa.

10. The method according to claim 9, characterized in that: The temperature of the reaction is 100 - 600 °C.

11. The method according to claim 10, wherein: It also includes returning the gas part of the reaction product to the reactor to participate in the reaction cyclically.

12. The method according to claim 11, characterized in that: The gas part is washed and purified by flash distillation before being returned.

13. The method according to any one of claims 1-12, characterized in that: It also includes separating the product acetic acid from the liquid part of the reaction product, and returning the remaining liquid to the reactor to participate in the reaction cyclically after removing the light and heavy components.

14. The method according to claim 13, wherein: Rectification is used to separate the product acetic acid.