Let’s discuss the situation and technologies related to the synthesis of acetic acid via carbonylation

The low-pressure production of acetic acid from methanol: The earliest and most mature industrial method is the Monsanto process. The method developed by the Southwest Chemical Research Institute in China is similar to it; both use rhodium catalysts, with a catalyst concentration of around 400–500 ppm. Acetic acid serves as the solvent, and auxiliary substances such as iodomethane and water are required. The partial pressure of CO during the reaction is 3 MPa. The material obtained from the reactor goes through devices such as high-pressure separators, flash tanks, low-boiling point towers, and high-boiling point towers before acetic acid is obtained. Since the system contains HI and water, and the temperature is around 180 degrees, corrosion is severe in this system; therefore, the reaction must be carried out in a zirconium reactor or a Hastelloy B reactor. Later, Ir was used as a catalyst; it is cheaper than Rh, but a larger amount of catalyst is required, with concentrations reaching 1000 ppm. Compared to the Rh-catalyzed system, the water content can be reduced, and it is reported that the optimal level is around 5%. However, since HI is still present in this system, a water content lower than 5% would cause the HI to end up in the subsequent separation processes; therefore, the water content should be above 5% ； With the addition of a catalyst, the Ir-catalyzed system can increase the efficiency of acetic acid production by about twice. To address the issues of instability and tendency to precipitate in Rh catalytic systems, a process was developed for loading Rh catalysts on polymer materials; research reports indicate that this approach can improve production efficiency. However, it has not met industrial requirements, mainly because it is difficult to handle the softening and deformation of the polymer materials (plastics) in high-temperature environments. This process remains at the pilot scale. Furthermore, there are studies on non-rare metals, such as catalysts based on Co and Ni, but none of these have been successfully put into industrial use; they remain at the experimental research stage. Moreover, the activity of such catalysts is far inferior to that of catalysts based on Rh and Ir.

　 　　　Methanol carbonylation method The methanol carbonylation method is currently the most common approach for producing acetic acid, with the Monsanto/BP and Hal-con/Eatsman processes being the more typical ones. In recent years, three new processes have emerged, namely Celanese’s “AOPlus” process, BP’s “Cativa” process, and Chiyoda’s “Acetica” process. 　　1　Celanese AOPlus process Celanese has developed its proprietary “AOPlus” process. This process significantly improves the Monsanto process. 　　　　The AOPlus process enhances the stability of the rhodium catalyst by adding high concentrations of inorganic iodides (mainly lithium iodide). Adding iodomethane together with lithium iodide can significantly reduce the water concentration in the reactor (to about 4%-5%), while maintaining a high carbonylation rate. It significantly reduced the separation costs associated with this process. 　　In the AOPlus process, this change in catalyst composition allows the reactor to operate at low water contents and high concentrations of methyl acetate, resulting in improved production capacity and purification efficiency of the reactor. By utilizing this proprietary technology, the capacity of the methanol carbonylation unit at the Celanese plant in Celar Lake, Texas, USA, has been increased to 1200 kt/a, with relatively low investment costs. 　　To overcome the problem of high residual iodide concentrations in the final product, Celanese developed the Silverguard process for removing low-concentration iodide impurities from acetic acid. Celanese has revealed that by using silver metal ion exchange resins, the iodine mass fraction can be reduced to below 2×10-9, whereas traditional methods typically result in a value of 1×10-6. Celanese Company states that by using polymer resins coordinated with metal salts, these resins react with halide impurities and precipitate out of the halide-contaminated solution. 　2 BPCativa process: In 1996, BP claimed to have developed an iridium-based improved catalyst named “Cativa,” which was installed in previous rhodium-based systems. The Cativa process uses metal iridium as the main catalyst, with some rhenium, ruthenium, and osmium added as catalyst promoters. The reaction takes place at 190°C and 2.8 MPa, resulting in high reaction rates and product selectivity. 　　An inherent property of the Cativa process is low levels of organic iodide impurities in the acetic acid produced. Acetaldehyde is the main reason for the formation of higher concentrations of iodides. Compared to the few parts per ten thousand in traditional Monsanto/BP processes, the acetaldehyde content in the Cativa process is very low, generally less than 30×10-6. 　　It is said that new devices using this catalyst can save 10%-30% in investment and operating costs compared to rhodium-based catalysts. Since this process can operate at low water contents, it enables the modification of traditional purification systems. By modifying the Monsanto process using this new catalyst system, it is possible to increase acetic acid production capacity by 35%-40% while maintaining the same catalytic activity as the Monsanto process. Currently, the Cativa process has been applied in the BP/Samsuang joint venture plant and the methanol carbonylation to acetic acid plant at Hull in the UK. 　　In 2005, the 150kt/a capacity expansion project of Yangtze River Acetate Chemical Co., Ltd. was successfully completed and put into operation. The company is a joint venture established jointly by the British company BP, Sichuan Vinylon Plant of Sinopec, and Chongqing Construction Investment Company. In 2003, the company invested 1.2 billion yuan in expanding its acetic acid production capacity, and upgraded its first-phase acetic acid facility using BP’s state-of-the-art methanol carbonylation process, the Cativa technology (which employs H catalysts). Following the successful expansion, a comprehensive production capacity of 350 kt/a of acetic acid and 80 kt/a of acetates was established. 　　3　Chiyoda Acetica Process 　Japanese company Chiyoda has developed an acetic acid production process using the methanol carbonylation method, called “Acetica”. This process uses a (rhodium-based) supported heterogeneous catalyst system and a bubble column reactor. The Acetica process was validated through pilot-scale testing in 1999, and a transfer contract for the first industrial application of a 36kt/a acetic acid plant has now been signed with Guizhou Shui Pin Organic Chemistry Group Company in China. 　　An important feature of the Acetica process is the use of an immobilized rhodium complex catalyst supported on polymeric beads. Compared with traditional homogeneous methanol carbonylation processes, the rhodium catalyst is anchored to a polyvinylpyridine resin complex, thereby preventing the loss of the expensive precious metal rhodium. This process also uses rhodium complexed with polyvinylpyridine resin as a catalyst, and methyl iodide as a co-catalyst. It is reported that this process exhibits a high yield, with an acetic acid yield of over 99% when calculated on a methanol basis, and over 92% when calculated on a CO basis. 　　The Acetica process uses a unique bubble column annular reactor, while conventional processes use stirred-tank reactors. Due to the design of the loop reactor, there is no need for high-pressure gaskets or other moving parts required by agitators. The catalyst suffers little wear, and high gas/liquid mass transfer rates can be achieved. Furthermore, the reaction heat can be recovered through the reactor heat exchanger and used as a heat source for the distillation tower. 　　The advantage of the Acetica process is that it allows for a higher catalyst concentration than traditional processes, thereby enabling the reactor size to be reduced by 30%–50%, as well as reducing by-products by about 30%. It is expected that both the investment and operating costs of this process will be reduced by more than 20% compared to traditional processes. 　　　3 Domestic Technology In order to change the unfavorable situation in which China’s acetic acid industry had long been dependent on developed countries, the Southwest Chemical Research Institute began researching and developing methanol carbonylation technology in 1972. Eventually, it completed the process design for an industrial plant with a capacity of 200 kt/year for producing acetic acid through low-pressure liquid-phase carbonylation of methanol. This technology has been transferred to Yankuang Group’s 200 kt/a acetic acid plant in Tengzhou, Shandong ； The methanol plant at the Daqing Oilfield of CNPC has also been approved to use this technology to build a 200kt/a industrial facility. The completion of these two facilities indicates that our country now possesses the technology for synthesizing acetic acid from methanol and carbon monoxide. 　　The acetic acid catalyst developed by the Beijing Research Institute of Chemical Technology in 2005 was successfully put into use in an industrial plant with a capacity of 300 kt/year owned by Yankuang Group Company in Tengzhou, Shandong; the acetic acid produced there passed all quality tests. Thus, the supply contract for 250ke catalysts, worth over 20 million yuan, signed between the hospital and the company has been **completed**. As early as 2002, the institute applied for a pilot-scale research project on acetic acid production via carbonylation by Sinopec, and developed a method for synthesizing rhodium triiodide catalysts by melting rhodium powder with sodium bisulfate to induce ionization, followed by hydrolytic conversion. In 2003, taking into account the specific conditions of catalyst use at Chuanwei Chemical Plant, experiments were conducted on methods for regenerating deactivated catalysts in industrial production facilities. This led to the development of a comprehensive system for catalyst processing and regeneration, which was then tested on an industrial scale using a production facility with a capacity of 170 kt/year. Tests have shown that both the solubility of the catalyst and the physical and chemical parameters related to impurity content, as well as various control parameters in the production facility, meet the standards of the imported catalysts used by this factory. At present, the vast majority of domestic manufacturers that produce acetic acid via the low-pressure carbonylation of methanol use this catalyst. The successful industrialization of this catalyst will undoubtedly drive the rapid development of China’s acetic acid industry.

Unfortunately, in pursuit of petty profits, the Southwest Institute sold its acetic acid technology to Celanese, and since then there has been no more domestic acetic acid technology!

Acetic acid is produced using the low-pressure carbonylation method with methanol. The acetic acid production process equipment mainly includes processes such as acetic acid synthesis, distillation, and absorption. The acetic acid production technology via carbonylation developed by the Southwest Chemical Research and Design Institute is a proprietary technology with independent intellectual property rights. The process utilizes an evaporation approach, which **allows for an increase in the acetic acid content in the crude product. This reduces the amount of mother liquor that needs to be circulated in the evaporator, thereby lowering the load on the separation unit. It also makes process control less demanding. Additionally, reactions can be carried out at low temperatures to reduce corrosion in the equipment. This technology has been transferred to two companies, Shandong Yankuang Group and the methanol plant of Daqing Oilfield, and two production units capable of producing 200,000 tons per year of acetone carbonyl acid are set to be built.

The technology of the Southwest Institute isn’t very good either; the patent-related ideas aren’t applied in actual production, and there are theoretical errors. It was right to sell it.

Indeed, it seems that the Southwest Branch is really good at doing business!