What is the principle behind the low-pressure carbonylation of methanol to produce acetic acid?

You can first search for posts containing the keyword “acetic acid” on the forum. Take a look at the post compiled by user raindy regarding acetic acid: http://bbs.hcbbs.com/thread-100031-1-1.html. It seems you’re a new member and not yet familiar with the forum’s sections; posts about acetic acid are generally found in the Methanol section: http://bbs.hcbbs.com/forumdisplay.php?fid=142. Also, remember to use the “Search” function in the upper right corner. This post was last edited by NiNi on 2007-12-30 at 21:30

I want to know too, where is it? However, acetic acid technology is a matter of confidentiality and is quite sensitive.

Our factory is currently undergoing feasibility studies, and I am also gathering information on the matter

The synthesis of acetic acid via low-pressure carbonylation of methanol is achieved through a carbonylation reaction between CO and methanol at a temperature of about 185°C and a pressure of 3.0 Mpa (absolute pressure), in a mechanically stirred gas-liquid reactor. The catalytic system for the reaction consists of a rhodium-chromium complex (catalyst) and iodomethane-hydrogen iodide (accelerant).

The main advances in the industrial production of acetic acid via methanol carbonylation in recent years include: BP’s Cativa process, Celanese’s low-water-content Celanese process, the UOP/Chiyoda Acetica process developed by UOP/Chiyoda, Haldor Topsoe’s new process for producing acetic acid from syngas using methanol/dimethyl ether, and the evaporation process developed by the Southwest Chemical Research and Design Institute in China

Information is kept confidential; it’s generally not available!

At present, the key information on acetic acid is still in the hands of foreigners, while China is still in the exploratory stage

The key technology in acetic acid production lies in catalysts, and finding catalysts that are efficient, stable, and cost-effective is currently the main challenge in this field. New types of catalysts can not only increase product output and reduce costs but also improve product quality

The Cativa process uses metal iridium as the main catalyst, with some rhenium, ruthenium, and osmium added as co-catalysts. The new catalyst was prepared by a reflux reaction at 120°C of iridium carbonyl, hydriodic acid, and an aqueous acetic acid solution.

Celanese’s low-water-content process is a new technology that is highly suitable for the modification of rhodium-based catalysts.

Acetic acid production processes and technological advancements: Low-pressure carbonylation of methanol. Established acetic acid production methods include the acetylene-acetaldehyde method, the ethanol-acetaldehyde method, the ethylene-acetaldehyde method, the butane oxidation method, and the low-pressure carbonylation of methanol 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; only a small amount is still produced in China ； The ethylene acetaldehyde method is no longer used abroad due to its high product costs resulting from the need for ethylene resources, but it remains the main production method in China at present ； The butane oxidation method is only suitable for areas with abundant light oil, and is not feasible for widespread use. The method that is widely used at present is low-pressure carbonylation of methanol. Depending on the catalyst system used, various companies have developed their own unique processes for the low-pressure carbonylation of methanol: ★ BP Cative process – BP Company modified its traditional process by replacing 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 catalysts. Iridium-based catalysts exhibit significantly higher catalytic activity compared to rhodium-based ones. At low water contents, iridium-based catalysts offer high stability, lower energy consumption, and fewer by-products such as propylene. They can be used at water contents of ≤5% (by volume), which enables **improvements to the traditional methanol carbonylation process, resulting in reduced production costs and investment requirements. Furthermore, as the water content decreases, the utilization efficiency of CO improves, and steam consumption is reduced. The Cative process was first successfully applied in Samsung’s acetic acid plant in South Korea, and currently Chongqing Yangtze River Acetyl Chemical Co., Ltd. and Nanjing also plan to adopt this process. ★　Selenia AO Plus process: In 1980, the American company Selenia 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 a low water content of 4%–5%, 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 of less than 5×10-12. ★　Celanese Silverguard Process: To address the issues associated with the AO Plus process – such as equipment corrosion due to high iodine levels, high iodine residues in the product, and catalyst poisoning in downstream applications – Celanese developed the Silverguard process. This process uses silver ion exchange resin as the rhodium catalyst ； With traditional methods, the residual iodine in the product is generally 10 μg/g. ★　Chiyoda Acetica Process Chiyoda Corporation developed the Acetica process in 1997. This process utilizes a phase carrier catalyst system composed of a multiphase rhodium catalyst in combination with polyvinylpyridine resin; this catalyst system enhances the catalytic activity of rhodium, enabling the acetic acid yield to exceed 99%. Using iodomethane as a catalyst, a suspended solid rhodium-based composite catalyst (supported on special material spheres) was employed in a bubble column closed-loop reactor at 175°C and 2.8 MPa to carry out the reaction. The reaction products were subjected to flash evaporation, dehydration, and purification to yield the final product, with a methanol conversion rate of ≥99%. Technology for producing acetic acid via ethane and ethylene feedstock routes ★ Selective catalytic oxidation of ethane The selective catalytic oxidation process of 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 for a new process that uses ethane as a feedstock to produce acetic acid and ethylene simultaneously. Ethane and air (15:85) were reacted at 260°C and 1.38 MPa; when the conversion of ethane was 53.3%, the selectivities for acetic acid and ethylene were 49.9% and 10.5%, respectively. ★　Direct oxidation of ethylene: The Shōwa Denko Company of Japan developed a process for producing acetic acid through the direct oxidation of ethylene, and in 1997 a acetic acid production facility with an annual capacity of 100,000 tons was built at its plant in Chiba. This process uses a palladium-based catalyst and carries out the reaction in a fixed-bed reactor at 150–160°C and a pressure of about 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. This process is very simple, with wastewater discharge being only 1/10 of that in the ethylene acetal method.

Domestic low-pressure carbonylation process technology for methanol ★ Industrialization progress at the Southwest Research Institute Over a period of more than 20 years, the Southwest Chemical Industry Research Institute has completed the technical development of a process package for producing acetic acid via low-pressure carbonylation of methanol, with an annual production capacity of 100,000 tons. This process utilizes two reactors in series; the second reactor ensures that the unreacted feed materials in the first reactor react completely, thereby improving reaction efficiency and reducing the load on the purification and exhaust gas recovery systems. To address the issue of catalyst precipitation, the Southwest Chemical Research Institute took measures such as adding an additional converter and reducing the water content in the reaction solution, in order to improve the reaction conversion rate and the heat tolerance of rhodium-based catalysts ； By using an evaporation process in the production of crude 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 ； Compared with acetic acid as an absorbent, the methanol absorbent has better absorption efficiency, requires less amount, 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, few by-products, low emissions of waste materials, and product quality that reaches world-class standards. This process was industrialized in January 1998 and granted a **patent in 1999.

1. Patent barrier issue: At present, the biggest challenge faced by acetic acid production in China is the technical monopoly and restrictions imposed by foreign multinational companies. The several acetic acid plants currently in operation are investing heavily to deal with the patent claims raised by these foreign companies； The key is to see **whether to intervene in this matter** ； 2. Catalyst issue: Catalysts are expensive, and poor control during operation leads to high consumption. 3. Major equipment issues: At present, the materials for the main equipment are all imported. Material prices are high and delivery times are long.

Reaction Mechanism for the Carbonylation of Methanol to Acetic Acid
I. Chemical Reactions Occurring in the Reactor
1. Main Reaction: CH3OH + CO → CH3COOH
2. Side Reactions
• Conversion reactions (accounting for 1.5–2.1×10-2 of the main reaction products):
CO + H2O ↔ CO2 + H2
• Methane formation reaction (accounting for 2.1×10-3 of the main reaction products):
CH3OH + H2 → CH4 + H2O
• Acetaldehyde formation reaction:
CH3OH + H2 + CO → CH3CH2O + H2O
• Propionic acid formation reaction (accounting for 2.5×10-3 of the main reaction products):
CH3COOH + H2 → CH3CH2OH + H2O
CH3CH2OH + CO → CH3CH2COOH
3. Equilibrium Reactions
• Esterification reaction:
CH3OH + CH3COOH ↔ CH3COOCH3 + H2O 〈1〉
• Halogenation reaction:
CH3COOCH3 + HI ↔ CH3I + CH3COOH 〈2〉

II. Reaction Mechanism
1. Mechanism of the Main Reaction
The cycle of the main reaction consists of the following 7 reaction steps:
(1) Esterification reaction:
CH3OH + CH3COOH ↔ CH3COOCH3 + H2O 〈1〉
(2) Halogenation reaction:
CH3COOCH3 + HI ↔ CH3I + CH3COOH 〈2〉
(3) Carbonylation reaction:
• Oxidative addition reaction: CH3I+ → – 〈3〉
• Insertion reaction: – → –
• CO coordination reaction: – –
• Hydrolysis reaction: – + H2O → – + CH3COOH
• Elimination reaction: – → – + HI
In summary: CH3OH + CO → CH3COOH, ΔH = -2265 kJ/kg

It’s mainly a catalyst issue; the chemical reaction is theoretically possible

Thank you! I spent a long time looking for information on acetic acid, but most of it was on its ethyl ester- -