Views: 23 Author: Site Editor Publish Time: 2022-01-14 Origin: Site
Monsanto /BP process is a traditional process for the production of acetic acid, which is synthesized by methanol and carbon monoxide in a stirred tank reactor at 175℃ and 2.8MPa. Liquid rhodium complex catalyst is dissolved with iodide in the reaction solution. The reaction conditions of Chiyoda's Acetica process are similar, except that the reactor is a bubble tower loop reactor and the catalyst is a suspended rhodium complex immobilized on a polymerization ball. After the reaction, the product was purified by flash distillation, dehydration and distillation. The acetic acid yield in methanol and CO was greater than 99% and 92% respectively.
Compared with the low concentration of catalysts in the Monsanto/BP process due to its solubility limitations, the Acetica process has the advantage of increasing the concentration of catalysts, thereby reducing the size of the reactor by 30% to 50% while reducing the by-products by about 30%. Chiyoda expects the Acetica process to reduce investment and operating costs by more than 20% compared to traditional M onsanto/BP processes.
The method can be divided into indirect method and direct method. The indirect method, namely ethylene-acetaldehyde oxidation method, developed rapidly in 1960s, but with the development of Monsanto methanol carbonylation process, the proportion of ethylene-acetaldehyde method gradually decreased, because the method is inferior to methanol carbonylation process in technical and economic indicators. At present, this process is still the main acetic acid production method in China. This process uses acetaldehyde as raw material and adopts manganese acetate, cobalt acetate or copper acetate liquid phase catalyst to carry out oxidation reaction at 50 ~ 80 ℃ and 0.6 ~ 0.8 MPa. The conversion of acetaldehyde is above 90% and the selectivity of acetaldehyde is above 95%. All equipment used in the process must be made of stainless steel.
Direct gaseous catalytic oxidation of unsaturated hydrocarbons has always been considered as a feasible acetic acid production process. However, before 1997, there was only a multi-step acetic acid production process, that is, ethylene is oxidized to acetaldehyde, then acetaldehyde is oxidized to acetic acid under the action of precious metal catalyst. Showa Denko developed a one-step gas phase process (Showa Denko process) for direct oxidation of ethylene to acetic acid, which was industrialized in 1997. The one-step ethylene gas phase process is economical for acetic acid plants with small production capacities (50-100kt /a) because of its relatively low investment costs (no infrastructure required to produce carbon monoxide).
Showa Denko's one-step gas phase process is a highly selective preparation of acetic acid from a mixture of ethylene and oxygen under a supported palladium catalyst at 160 ~ 210 ℃. The main side reactions are ethylene combustion and acetaldehyde formation. Under the reported reaction conditions, the one-way selectivity of acetic acid, acetaldehyde and carbon dioxide was 85.5%, 8.9% and 5.2% respectively. The main byproduct, acetaldehyde, can be recycled to the reactor to reduce the combustion of ethylene and increase the total yield of acetic acid.
Acetic acid purification is an energy-intensive process because a large amount of water is generated during the reaction. To solve this problem, Showa Denko has developed an energy-efficient process that combines extraction and distillation to effectively separate water from acetic acid. Showa Denko says the process is environmentally friendly because it produces only a small amount of waste water.
In 1997, Showa Denki of Japan built a acetic acid plant with a production capacity of 100 kT /a in Chiba Plant by using direct method, that is, acetic acid production process without acetaldehyde. The plant uses palladium catalyst, and the reaction is carried out in a fixed-bed reactor, the reaction temperature is about 150 ~ 160 ℃, the pressure is about 0.9 MPa. The selectivity of acetic acid, acetaldehyde and CO2 was 86.4%, 8.1% and 5.1%, respectively. Compared with methanol and acetaldehyde plants of similar scale, the construction cost of direct oxidation plant is significantly lower, and the plant size can be designed according to user requirements. In addition, the process is very simple, and the wastewater discharge is significantly reduced, only one tenth of acetaldehyde oxidation.
SABIC has developed a new process for gaseous catalytic oxidation of ethane to acetic acid (SABIC process), which has attracted considerable attention throughout the petrochemical industry. A semi-industrial acetic acid production capacity of 30kt/a is now under construction.
According to SABIC's patent, ethane reacts with pure oxygen or air at 150 ~ 450 ℃ and 0.1 ~ 5.0M Pa to produce acetic acid, with CO, CO2 and ethylene as byproducts. The novel catalyst used in the SABIC process is calcined from a mixture of Mo, V, Nb and Pd oxides, which helps to reduce by-product formation while achieving high selectivity and acetic acid yield. When using ethane and oxygen as raw materials, the selectivity of acetic acid is up to 71%, and the one-way conversion of ethane and oxygen is 13.6% and 100%, respectively. When using ethane and air as raw materials, the selectivity of acetic acid is slightly lower, at 67%, but the one-way conversion of ethane is higher, at 49.6%, and the conversion of oxygen is 100%.
Due to the low production cost of ethane, the direct oxidation of ethane for acetic acid is economically competitive with the carbonylation of methanol. The technology includes catalyst production, new oxidation reactor design, integrated process and basic process design. SABIC will continue to improve the technology and is considering building a 200kt/a acetic acid production facility.
The two processes using n-butane or light oil as feedstock are basically similar. Using light oil in the range of C5 ~ C7 as raw material, using cobalt acetate, chromium acetate, vanadium acetate or manganese acetate catalyst at 170 ~ 200℃, 1.0 ~ 5.0MPa pressure, the final product is formic acid, propionic acid and acetic acid products, acetic acid: formic acid: propionic acid ratio of 1:0.25:0.10.
In addition, ethanol acetaldehyde oxidation, mainly includes ethanol oxidative dehydrogenation to acetaldehyde and acetaldehyde oxidation to acetic acid two processes. At present, this kind of production technology is still maintained in some developing countries, but due to poor technical and economic indicators, most of them are suspended or semi-suspended.