What is the mainstream catalyst currently used for the carbonylation of methanol to produce acetic acid?

Currently, the main companies involved in the technology for producing acetic acid through methanol carbonylation are Celanese and BP; the most advanced facility in this area is the Yangzi Acetate project, a joint venture between Yangzi Petrochemical and BP located in the Nanjing Chemical Industrial Park. Sialanis’ Nanjing branch is practically right next door to us: lol. Their technology originated from Mendu Mountain Company, and through subsequent development, BP now has the most advanced technology available. Their production process is likely similar to that of Sialanis; the main difference lies in the catalysts used. Therefore, BP has strict measures in place to protect its technical secrets :( Sialanis and Jiangsu Supco probably use platinum and rhodium catalysts:victory:

The Southwest Institute developed its own process package. However, BP has been accusing them of infringement. Rhodium triiodide is used as a catalyst in the carbonylation process to produce acetic acid.

A new type of cationic-anionic bimetallic active species catalyst for the carbonylation synthesis of acetic acid. The cationic active species of this catalyst is a square-planar cis-dicarbonyl structure formed from aminobenzoic acid and Rh(I), containing N and O donor atoms; the anionic active species is also a complex structure consisting of aminobenzoic acid and non-rhodium metals such as ruthenium, tin, chromium, lead, and zirconium, again containing N and O donor atoms. In carbonylation reactions, such catalysts exhibit high activity in catalyzing the carbonylation of methanol to acetic acid under relatively mild conditions, along with excellent selectivity.

In my opinion, Thorp’s patent from this year represents the most advanced technology – namely, the bimetallic catalyst. As for catalysts based on positive and negative ion-type bimetallic active species, I have always doubted their feasibility. It is very likely that, due to confidentiality reasons, a large portion of the published content is false. Acetic acid production lacks mainstream catalysts, and catalysts represent a core technology; without the capability to research and improve catalysts, all acetic acid manufacturers risk being eliminated within a year. At present, the catalysts used by the major acetic acid manufacturers are hardly identical to one another, and research on them is kept under strict confidentiality; as a result, there is no such thing as a dominant catalyst.

Sop’s technology is primarily developed in collaboration with the Institute of Chemistry of the Chinese Academy of Sciences, which provides the main technical support.

Did Hualu Hengsheng also purchase this technology?

BP’s iridium catalyst is the most advanced and mature one available today, and it has been put into large-scale production; unfortunately, BP does not sell this technology. Domestic research has still not kept up. :'(

Does China have catalysts in this area?

It is said that there are now manufacturers in China who produce BP iridium catalysts as well, but due to the BP patents, no manufacturer yet dares to use this catalyst openly; the reaction rate of iridium catalysts is twice that of rhodium catalysts

3 Production processes of acetic acid and recent advances 3.1 Production processes of acetic acid 3.1.1 Oxidation of acetaldehyde The oxidation of acetaldehyde methods include the ethanol-acetaldehyde method, the acetylene-acetaldehyde method, and the ethylene-acetaldehyde method. The acetylene-acetaldehyde method has been phased out due to severe mercury pollution. The ethanol-acetaldehyde method has been phased out abroad due to its outdated production processes and high costs; there are still some production facilities in China, but they are on the verge of shutting down. The ethylene acetaldehyde method uses acetaldehyde as the raw material, and liquid-phase catalysts such as manganese acetate, cobalt acetate, or copper acetate are employed to carry out the oxidation reaction at temperatures of 50–80 °C and pressures of 0.6–0.8 MPa. The conversion rate of acetaldehyde is over 90%, while the selectivity for acetic acid is higher than 95%. All equipment in this process must be made of stainless steel. This process developed rapidly abroad in the 1960s and 1970s, but due to its consumption of valuable ethylene resources, the cost of acetic acid products was high. Since ethylene can be used to produce polyolefin products with higher added value, this process has been phased out abroad; in China, however, it remains the main production method. 3.1.2 Butane oxidation method: The butane oxidation method uses n-butane or light oil as raw materials, and catalysts such as cobalt acetate, chromium acetate, vanadium acetate, or manganese acetate are employed in an oxidation reaction carried out at temperatures of 170–200 °C and pressures of 1.0–5.0 MPa. The final products are formic acid, propionic acid, and acetic acid, with a molar ratio of acetic acid:formic acid:propionic acid of 1:0.25:0.10. This process is complex, generates many by-products, has a low yield of acetic acid, is highly corrosive, and is only suitable for areas with abundant light oil, making it unsuitable for widespread adoption. 3.1.3 BP Cative Process: Building on the technology of its traditional process, BP replaced rhodium-based catalysts with iridium-based catalysts, resulting in the BP Cative Process; this process uses various rare metals such as rhenium, ruthenium, and osmium as co-catalysts. Iridium-based catalysts exhibit significantly higher catalytic activity compared to rhodium-based catalysts. They maintain high stability at low water contents, require less energy, produce fewer by-products such as propylene, and can operate at low water levels (with a volume ratio of less than 5%). This enables the improvement of traditional methanol carbonylation processes, thereby reducing production costs and investment requirements. Furthermore, as the water concentration decreases, the utilization efficiency of CO improves, and steam consumption is reduced. The new catalyst was first successfully applied in the acetic acid plant of South Korean company Samsung. Currently, Chongqing Yangtze River Acetate Chemical Co., Ltd. is also using this process to expand its existing 150 kt/a acetic acid plant to a capacity of 350 kt/a, and the 500 kt/a acetic acid production plant in Nanjing-BP plans to adopt this process as well. 3.1.4 Searles’ AO Plus process In 1980, the American company Searles introduced the AO Plus process (Acid Optimization Method). This process alters the composition of the catalyst by adding a high concentration of inorganic iodine (mainly lithium iodide), allowing the reactor to operate at low water concentrations (4%–5% on a volume basis), thereby increasing the yield and purification efficiency of the carbonylation reaction. This process utilizes a special patented technology that enables an acetic acid yield of 99%, features a very fast reaction rate, and results in a total iodine residue in the product solution below 5×10-12. 3.1.5 Chiyoda Corporation’s Acetica process Chiyoda Corporation developed the Acetica process using the low-pressure carbonylation of methanol in 1997. This process utilizes a combination of a multiphase rhodium (Rh) catalyst and polyvinylpyridine resin, with methyl iodide serving as a catalyst. It is said that this multiphase catalyst system enables better control of rhodium usage, resulting in an acetic acid yield of over 99%. This process is carried out in a bubble column closed-loop reactor at 175 °C and 2.8 MPa, using a suspended solid rhodium-based composite catalyst supported on special material spheres. After the reaction, the product is flashed, dehydrated, and refined, with a methanol conversion rate of over 99%. 3.1.6 Methyl acetate hydrolysis method: Some methyl acetate and acetaldehyde are generated during the production of polyvinyl alcohol. Methyl acetate and water are hydrolyzed in a certain molar ratio under the catalysis of cation exchange resin to produce acetic acid and methanol; the methanol is used for the polymerization and hydrolysis of polyvinyl alcohol, while the acetic acid is sold as a by-product or returned to the vinyl acetate plant as a raw material. The production of 1 t of PVA generates approximately 1.2 t of acetic acid as a by-product. In 2003, China’s PVA production was 431.6 kt, resulting in roughly 500 kt of acetic acid as a by-product. This method contains many impurities, and the distillation process is very complex (typically requiring 10–14 distillation columns). Compared to the carbonylation method, the production cost of acetic acid is higher (lower than that of the ethanol-acetaldehyde method). 3.2 Recent Advances in Acetic Acid Production Technology 3.2.1 Selective Catalytic Oxidation of Ethane The selective catalytic oxidation process for ethane was developed by Union Carbon Corporation in the 1980s and is known as the Ethoxene process. The main feature of this process is that, in addition to acetic acid being produced, a certain proportion of ethylene is also generated. Industrialization has not yet been achieved. SABIC in Saudi Arabia has developed a phosphorus-modified molybdenum-niobium-vanadate catalyst and a new process for co-producing acetic acid and ethylene from ethane. Ethane and air (with a volume ratio of 15:85) react at 260 °C and 1.38 MPa; when the conversion rate of ethane is 53.3%, the selectivities for acetic acid and ethylene are 49.9% and 10.5%, respectively. 3.2.2 Direct oxidation of ethylene: The traditional production process for acetic acid using ethylene involves first oxidizing ethylene to acetaldehyde, and then oxidizing acetaldehyde to acetic acid. Shōwa Denki of Japan developed a process that bypasses the step of oxidizing ethylene to acetaldehyde, allowing acetic acid to be produced directly from ethylene. In 1997, an acetic acid production facility with a capacity of 100 kt/a was built at its plant in Chiba. This process uses a palladium-based catalyst and takes place in a fixed-bed reactor; the reaction temperature is around 150–160 °C, and the pressure is approximately 0.9 MPa. The one-pass conversion rate of ethylene is 7.4%, while the selectivities for acetic acid, acetaldehyde, and CO2 are 86.4%, 8.1%, and 5.1%, respectively. Compared to methanol and acetaldehyde process plants of similar scale, the construction cost of direct oxidation process plants is significantly lower, and the plant size can be designed according to the user’s requirements. Furthermore, this process is very simple, and the amount of wastewater discharged is significantly reduced, being only one-tenth that of the acetaldehyde oxidation method. 3.2.3 Selenia’s Silverguard Process: To address the issues associated with its AO process – such as equipment corrosion under high iodine levels, high iodine residues in the product, and catalyst poisoning in downstream applications – Selenia developed the Silverguard process. This process uses silver ion exchange resin as a carrier for the rhodium (Rh) catalyst, enabling the residual iodine content in the product to be reduced to 2 μg/g, whereas with traditional methods the residual iodine content in the product is typically 10 μg/g. 3.2.4 Catalysts for the carbonylation of methanol to acetic acid In the existing processes for converting methanol into acetic acid using rhodium catalysts, iodides are used as co-catalysts, which significantly improves the activity and selectivity of the rhodium catalysts ； However, due to the strong corrosivity of methyl iodide and hydrogen iodide, high requirements are placed on the material used for the reactor; expensive precious metals such as zirconium and Hastelloy must be employed, and it is difficult to separate the product from the iodides. Therefore, the research on iodine-free carbonylation catalysts and non-rhodium catalysts represents the future direction of catalyst research. In 1994, Clafat et al. first reported a study on the carbonylation of methanol using sulfided Co-Mo/C catalysts without any promoters. A Ru-Sn heteronuclear catalytic system can be used to carbonylate methanol into acetic acid in one step, in the absence of an iodine co-catalyst. Other researchers have used solid strong acids as catalysts to study the methanol carbonylation reaction in the absence of iodine catalysis ； Acetic acid was synthesized at 300 °C using HZSM5 and HM-type mordenite catalysts with high selectivity (65.4%–68.5%). Both rhodium and iridium are very expensive metals, and in homogeneous catalytic reactions, the catalysts tend to be lost, leading to increased costs ； Cobalt catalysts have high requirements for reaction conditions. While researching traditional catalysts, researchers around the world are also turning their attention to other inexpensive metal catalysts such as iron and nickel ； Research findings have shown that nickel possesses high catalytic activity; therefore, since the 1980s, research on catalytic carbonylation reactions has primarily focused on nickel catalysts. However, nickel catalysts have lower activity compared to rhodium catalysts, and there is still a long way to go before they can be used on an industrial scale. 4 Progress and Applications of Low-Pressure Carbonylation Technology for Acetic Acid Production from Methanol in China. Currently, the low-pressure method is the primary process used for acetic acid production both domestically and internationally. In recent years, China has made rapid progress in the development and adoption of low-pressure processes for acetic acid synthesis: the Southwest Research Institute of Chemical Engineering has developed a process package for the low-pressure carbonylation of methanol to produce acetic acid with a capacity of 200 kt/a ； Shanghai Wujing Chemical Co., Ltd. has achieved significant results in adapting and adopting BP’s traditional low-pressure carbonyl synthesis process ； Significant achievements have also been made in catalyst research at the Institute of Chemistry, Chinese Academy of Sciences. 4.1 Production Process: The Southwest Chemical Research Institute began researching the technology for producing acetic acid via low-pressure carbonylation of methanol in 1972. After more than 20 years of effort, it completed the technical development of a production facility with a capacity of 100 kt/a. This process utilizes two reactors in series; the second reactor in this series allows the unreacted feed materials in the first reactor to react fully, thereby improving reaction efficiency and reducing the load on the purification and exhaust gas recovery systems. Progress has been made in this technology both domestically and internationally, though with different characteristics in each case. To address the issue of catalyst precipitation, the facility took measures such as adding another converter and reducing the water content in the reaction solution, in order to improve the reaction conversion rate and the heat resistance of rhodium-based catalysts ； By using an evaporation process for the extraction of crude acetic acid, it is possible to **increase the acetic acid content in the crude acetic acid, reduce the amount of mother liquor that needs to be recycled, and lower the load on the separation unit** ； Methanol is used as an exhaust gas absorbent; compared with acetic acid absorbents, methanol offers better absorption efficiency, requires less amount of absorbent, and causes less corrosion to equipment. The former Petrochemical Industry Bureau, after having experts conduct technical evaluations, concluded that this process features high conversion and selectivity, low amounts of by-products, minimal emissions of waste materials, and product quality that meets world-class standards. This process was industrialized in January 1998 and granted a **patent in 1999. Currently, the Southwest Chemical Research Institute is working with several domestic manufacturers on scaling up the acetic acid production process. In August 2000, by completing the upgrades to Jiangsu Suopu Company’s 100 kt/a acetic acid production facility, its production capacity was increased to 130 kt/a, thereby gaining experience in expanding production scale. A plant with a capacity of 200 kt/a is under intense construction. Based on the digestion, absorption, and introduction of existing equipment, Shanghai Wujing Chemical Co., Ltd. completed the development of the process package for a 200 kt/a methanol low-pressure carbonylation acetic acid production plant. 4.2 Catalyst Technology: Shanghai Wujing Chemical Co., Ltd. has made active efforts to absorb and apply the production technology of acetic acid production plants. It has achieved significant breakthroughs not only in the development of core technologies such as core equipment manufacturing and the Process Design Packet (PDP) software, but also in obtaining the optimal ratios for catalyst preparation. In response to the problem that in systems where there is a insufficient supply of CO or an uneven distribution of it, the carbonyl rhodium precursors, which possess catalytic activity in carbonylation reactions, become unstable and are slowly oxidized by iodide ions in the reaction mixture to RhI3, thereby losing their catalytic activity, the Dalian Institute of Chemistry, Chinese Academy of Sciences, developed a new carrier based on polyvinylpyridinium iodide. Under the same conditions regarding rhodium content and reaction parameters, this new carrier increased catalytic activity by nearly 3 times. It is reported that the patented technology for early catalysts developed by this institute was transferred and applied to an acetic acid production facility in Taiwan, China, which uses BP technology. Expert evaluations have confirmed that the performance of these early catalysts is superior to that of BP’s traditional catalysts. In October 2001, the institute collaborated with Zhenjiang Sopco Group to develop a new generation of catalysts for the carbonylation synthesis of acetic acid. Compared with the previously used catalysts, the new catalysts exhibit higher activity, stability, and selectivity, which will significantly increase the reaction rate for the carbonylation synthesis of acetic acid. Research on gas-solid phase catalysts in China focuses primarily on improving the carbon carriers used in such catalysts. Studies have shown that organic carbon molecular sieves are excellent carrier materials, effective for carbonylation reactions, and represent an important area of research for the future.