Information on the production of acetic acid and acetic anhydride using the BP method

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Process for recovering acetic acid off-gases by pressure swing adsorption 1. Introduction The off-gases generated during the acetic acid production process are, due to limitations in separation and recovery technologies, currently mostly released into the atmosphere. Acetic acid exhaust gas contains a large amount of CO, with variations depending on the specific production conditions; the common composition is shown in Table 1. For an acetic acid plant with an annual production capacity of 100,000 tons, the volume of CO in the exhaust gas is approximately 1,500–2,000 Nm3/h. CO is a basic raw material for acetic acid production. The large-scale release of CO not only wastes energy and increases the production costs of acetic acid but also pollutes the environment. Acetic acid manufacturers are in urgent need of finding a simple and efficient process for recovering acetic acid exhaust gas. Table 1 Composition of acetic acid exhaust gas. Component: CO, CO2, N2, H2, CH4, CH3I, CH3OH; Content, mol%: 60–85, 6–15, 4–7, 5–15, 1–3, 0.004–0.08, 0.1–0.6. For the separation and purification of gases, there are many mature technologies widely used in industry. However, since the volume of acetic acid exhaust gas is not very large and the composition of the gas varies over a wide range, and because it contains iodomethane, which is highly corrosive, high requirements are placed on the corrosion resistance of the equipment. Due to these characteristics of acetic acid off-gas, the application of many common gas separation and purification methods is limited, and methods for recovering acetic acid off-gas have always been a subject of research. This paper compares the advantages and disadvantages of currently commonly used CO separation and purification technologies. It specifically introduces the process flow and operation status of the first industrial unit for recovering acetic acid tail gas using pressure swing adsorption. Practice has shown that pressure swing adsorption is a relatively good process for recovering acetic acid exhaust gases at present, and it is worth further promotion. 2. Common processes for the separation and purification of CO 2.1 Types of processes for the separation and purification of CO As a basic raw material gas for carbonyl synthesis, the separation and purification of CO have been a subject of research. Currently, the techniques for purifying CO that have been industrialized or are under experimental study include: organic product decomposition method, cryogenic separation method, PSA-CO method (further divided into PSA-CO single-stage and PSA-CO two-stage methods), and Cosorb method. 2.2 Organic product decomposition methods: Organic product decomposition methods such as formamide decomposition and formic acid decomposition can be used to produce high-purity CO, but these methods are costly and are suitable only for small-scale use in laboratories or for producing small amounts of high-purity CO. 2.3 Cryogenic separation method: This method utilizes the differences in boiling points of gas components to separate gas mixtures through low-temperature distillation. To prevent various impurity components from solidifying at low temperatures and blocking the pipes, cryogenic separation of CO requires a very complex pretreatment system. Moreover, since the boiling points of N2 and CO are similar, it is difficult to obtain pure CO product from feed gas containing N2. The disadvantages of the cryogenic method are complex equipment, high investment costs, and high operating expenses. 2.4 Cosorb method: This is a solution absorption separation method that was developed by the American company Tenneco in the early 1970s. It was quite popular at one time; it involves using complexes to selectively absorb CO from the solvent, and then CO is obtained as a product gas through heating for desorption. Since components such as H2O, sulfides, and ammonia in the feed gas can undergo side reactions with the complexing solvent, resulting in a decrease in or even loss of the complexing agent’s absorption capacity, this method requires very strict purification standards for the feed gas (with requirements of H2O < 1×10-6, sulfides < 1×10-6, O2 < 1×10-6). The requirements for alkynes and unsaturated hydrocarbons are also stringent, necessitating complex pre-treatment systems. Since the CO gas obtained through heating and desorption contains toluene vapor and chloride ions, an additional post-treatment step is required. This method also requires significant equipment investment, has high operating costs, and poses environmental pollution problems. 2.5 Pressure Swing Adsorption (PSA) Method: The pressure swing adsorption gas separation technology is widely used for the separation and purification of gases such as H2, N2, O2, CO2, CH4, and CO. This method utilizes the selective adsorption property of solid adsorbents for different gases under certain pressure to achieve gas separation. Pressure swing adsorption has a wide range of adaptability to feed gases; it does not require complex pretreatment systems. The entire system operates at ambient temperature, eliminating issues such as equipment corrosion and environmental pollution. The device features a simple process, a high degree of automation, and easy operation. It has low operating costs, making it a gas separation technology with very broad application prospects. There are two processes for the separation and purification of CO using pressure swing adsorption: the one-stage process utilizing copper-loaded chemical adsorbents, and the two-stage process using conventional physical adsorbents. 2.5.1 Progress and challenges in CO separation using the one-stage method. The one-stage method for purifying CO refers to a pressure swing adsorption process in which, when purifying CO, it is not necessary to remove CO2 from the feed gas first; instead, taking advantage of the property that copper-loaded adsorbents preferentially adsorb CO, CO is directly adsorbed to obtain a high-quality product. The adsorption mechanism of this method is similar to that of the Cosorb method; therefore, the advantages and disadvantages of the one-stage method are essentially the same as those of the Cosorb method. The copper-loaded adsorbent used in this process takes advantage of the complexation of Cu+ with CO to achieve the separation and purification of CO from the feedstock. Since monovalent copper ions can be easily oxidized to divalent copper ions as well as reduced to elemental copper, they are sensitive to certain components in the gas source; this is one of the main reasons why it has not yet been used on a large scale in industry. According to literature reports, Japan built an industrial-scale pilot PSA–CO unit using the shift gas as the gas source at the Kakogawa plant, with a production capacity of 150 Nm3/h. Many universities and research institutes in the country have conducted research on this law and made certain progress. To achieve industrialization, it is necessary to overcome the following challenges: 1. The system has a low tolerance for harmful impurities in the gas supply; therefore, the levels of O2 should be less than 10×10-6, H2O should be less than 10×10-6, and H2S should be less than 1×10-6. 2. Conducted at temperatures higher than the ambient temperature. At ambient temperature, the separation coefficient is low; therefore, to improve separation efficiency, the entire separation process is usually carried out at around 70°C. 3. The adsorbent has a short lifespan. Since certain harmful components such as sulfides permanently poison the chemical adsorbents, the lifespan of these adsorbents is short. To date, there are no reports of such chemical adsorbents being used in industrial installations for long-term operation. There are also no definitive data on its lifetime regarding oxygen and H2O. 4. The price of adsorbents is high. The production process of adsorbents is complex and costly; currently, such adsorbents are manufactured in small quantities for use in experimental setups or industrial test facilities. Its manufacturing process also requires an industrial scale-up step. 5. Due to the need for complex preprocessing and similar processes, the initial investment in such equipment is high. Due to the inherent properties and defects of the chemical adsorbents used in this method, there are still many technical and engineering challenges that need to be addressed in its industrialization process. 2.5.2 Development, technical features, and promotion of the two-stage method for CO separation. While researching copper-loaded adsorbents for PSA-CO separation using the one-stage method, Sichuan Tianyi Technology Co., Ltd. also carried out research on the two-stage PSA-CO purification process; it developed China’s own two-stage process for CO purification, which was put into industrial use in 1993. Compared with the one-stage process and other CO purification methods, the two-stage process for the separation and purification of CO has the following main advantages: 1. It has a wide range of suitable feed gases; the feed gases used in the industrially implemented systems include semi-water gas, water gas, copper-cleaning regenerated gas, yellow phosphorus off-gas, Texaco furnace gas, and acetic acid off-gas. Gas sources that have completed the laboratory development stage include naphtha conversion gas, blast furnace gas, converter gas, and calcium carbide off-gas. 2. It has a high tolerance to harmful impurity components. It has a high tolerance for harmful impurity components in the gas source such as H2O, H2S, and NH3 (saturated water, H2S < 300×10-6, NH3 < 1000×10-6), which allows for the elimination of complex pretreatment systems. 3. The installation is carried out at ambient temperature, with the entire separation process—including adsorption, pressure reduction, and desorption—taking place at normal temperatures. 4. The adsorbent has a long lifespan. 5. Low operating costs. It is a purely physical separation process with no consumption of auxiliary materials. 6. The CO purity of the product is high. The two-stage CO purification technology developed in the early stages had a low separation coefficient between CO and CH4 in the gas feed, and the purity of the resulting CO was affected by the CH4 content in the raw material. In 1996, the Southwest Research Institute, which is the controlling entity of Sichuan Tianyi Technology Co., Ltd., developed a specialized adsorbent with the ability to effectively remove CH4. This adsorbent enabled more efficient removal of CH4 during the first stage of CO2 removal, thereby significantly reducing the impact of the CH4 content in the feed gas on the purity of the resulting CO. This technology operates on industrial installations. Due to the above advantages of the pressure swing adsorption two-stage method, its adoption has progressed very rapidly. Table 2 lists some domestic manufacturers that use this method for CO purification. Table 2: Some of the pressure swing adsorption CO separation units already built in China
Serial Number | Product Capacity, Nm3/h | Location of Construction | Gas Source | Purpose of the Produced CO
1 | 500 | Shandong Zibo Organic Amine Factory | Semi-water gas | DMF (used in conjunction with a unit imported from the United States)
2 | 2500 | Zhejiang Jiangshan Chemical Complex | Semi-water gas | DMF (used in conjunction with a unit imported from the United States)
3 | 1500 | Shandong Feicheng Asde Chemical Company | Water gas, semi-water gas | Formic acid (used in conjunction with a unit imported from the United States)
4 | 500 | Anhui Huainan Chemical Complex | Copper-cleaning regenerated gas | DMF (used in conjunction with a unit imported from the United States)
5 | 1000 | Hebei Cangzhou Fertilizer Factory | Water gas | TDI (used in conjunction with a unit imported from the United States)
6 | 100 | Shandong Lunan Fertilizer Factory | Texaco gas | Methyl formate

3. Pressure swing adsorption process for recovering acetic acid waste gas
3.1 Process flow for recovering acetic acid waste gas
Since acetic acid waste gas contains highly corrosive iodomethane, it is necessary to remove this substance in advance in order to reduce the investment required for equipment in subsequent stages. After iodomethane is removed, the raw gas enters a pressure swing adsorption unit to have CO purified; the specific process is shown in Figure 2. The feed gas enters the pretreatment unit at a pressure of 0.6 MPa to remove harmful impurities such as iodomethane and methanol, after which it proceeds to the PSA-1 process. Weakly adsorbed components in the feed gas, such as H2, CO, and N2, flow out from the top of the adsorption tower, yielding semi-finished gas that is then sent to PSA-2 for CO purification ； Strongly adsorbed components such as CO2 and H2O are adsorbed on the adsorbent, and are desorbed from it during pressure reduction and washing processes, allowing the adsorbent to be regenerated for use in the next cycle. After the semi-finished gas enters the PSA-2 process, CO is the strongest adsorbable component in this gas and is adsorbed on the adsorbent first; the remaining components flow out from the outlet of the adsorption tower and serve as the regeneration purge gas for PSA-1. After the adsorption process is complete, a portion of the product CO is returned as a purge gas for the adsorption bed in order to increase the purity of CO in the bed. Finally, qualified CO product is obtained through reverse discharge and evacuation. Table 3: Technical specifications of CO product. Major components/%, mol; Trace impurities, /10-5: CO ≥ 98.0, S ≤ 0.2 (wt); CO2 ~ 0.1; Chlorides ≤ 0.1 (wt); N2 ~ 0.8; Toluene ≤ 0.1 (mol); H2 ~ 0.02; Hydrocarbons ≤ 100 (mol); CH4 ~ 1.1; Benzenes ≤ 0.2 (mol); Ar ~ 0.07; Nitrides ≤ 0.1 (wt); O2 ≤ 0.01; Cyanides ≤ 0.1 (wt). Products obtained through pressure swing adsorption for CO recovery have a high purity, and their properties can be adjusted flexibly according to process requirements. With the raw gas composition shown in Table 1, the purity of the CO product can reach over 98%, while the levels of the other components can meet the values indicated in Table 3. The recovery rate of CO ranges from 70% to 85%, varying depending on the raw gas composition and the requirements for the product. 3.2 Economic viability of pressure swing adsorption for the recovery of acetic acid off-gases In the process of recovering acetic acid off-gases using pressure swing adsorption, energy and cooling water are required for the compression and evacuation of raw materials and products. A certain amount of instrument air is needed to operate the programmably controlled valves. Taking an installation with a product C0 output of 1000 Nm3/h as an example, the main utility consumptions are shown in Table 4. Table 4: Energy consumption indicators for the recovery of acetic acid exhaust gas using pressure swing adsorption method. | Parameter | Consumption per unit of product | Energy consumption per unit of product/MJ |
|---|---|---|---|
| Cooling water | 0.061 m3 | 0.0397 |
| Electricity | 0.557 KW.h | 2.0061 |
| Instrument air | 0.09 Nm3/h | 0.0001 |
| Total | | 2.0459 |

As can be seen from the table, the energy consumption associated with the recovery of acetic acid exhaust gas using pressure swing adsorption is mainly due to the electricity required for compressing the raw materials and the product, as well as for operating the vacuum pumps; this accounts for 98% of the total energy consumption. Of this amount, the energy needed to increase the pressure of the product from atmospheric pressure to 3.8 MPa constitutes 60%, and this step is essential regardless of the method used. For a tail gas recovery unit for producing 1000 Nm3/h of CO, the total investment amounts to 12–18 million yuan, and the payback period for this investment (including a 1-year construction period) is 3–5 years. The production cost of product CO is approximately 0.6–0.9 yuan per Nm3, which is far lower than the cost of CO produced by ordinary manufacturers; thus, the economic benefits are quite significant. By reducing the venting of acetic acid exhaust gases, a large amount of CO is recovered, resulting in excellent environmental benefits. 4. Conclusion The recycling of acetic acid exhaust gas holds great economic value and is also necessary for environmental protection; however, due to the special properties of this exhaust gas, no suitable method has been found to date. The newly developed pressure swing adsorption process for recovering acetic acid exhaust gas in China features advantages such as low investment, simple operation, low operating and maintenance costs, and high product purity. It has achieved excellent economic and environmental benefits, making it highly suitable for adoption by acetic acid manufacturers.

The BP technology is still under patent protection, so no one is allowed to disclose it. Moreover, the CAT is also his own property; just knowing the process isn’t enough

The main production process for acetic acid is the BP Cativa process. BP is the world’s largest supplier of acetic acid, with 70% of global acetic acid production being carried out using BP’s technology. In 1996, BP introduced the patented Cativa technology. The Cativa process utilizes a new catalyst system based on iridium, along with various new additives such as rhenium, ruthenium, and osmium. The iridium catalyst system is more active than rhodium catalysts, produces fewer by-products, and can operate at low water concentrations (less than 5%). This allows for **improvements to the traditional methanol carbonylation process, resulting in cost reductions of up to 30% in production costs and a 50% reduction in expansion costs. Furthermore, as the water concentration decreases, the CO utilization efficiency improves and steam consumption is reduced. ■ Celanese AO Plus process – Celanese is also one of the world’s largest producers of acetic acid. In 1978, the Hearst-Sellars Company (now Sellars Company) put the Monsanto process acetic acid plant into operation on Lake Claire in Texas, United States. In 1980, Syngenta patented the AO Plus method (Acid Optimization Method), **improving the Monsanto process. The AO Plus process improves the stability of the rhodium catalyst by adding a high concentration of inorganic iodine, primarily lithium iodide. After the addition of lithium iodide and iodomethane, the water concentration in the reactor is reduced to 4%–5%, yet the rate of carbonylation reaction remains very high, thereby significantly reducing the separation costs associated with the process. The change in catalyst composition enabled the reactor to operate at low water concentrations (4%–5%), improving the yield of the carbonylation reaction as well as the separation and purification capabilities. The main advantages of the AO Plus process are high yields and reduced investment and utility costs. However, it is prone to corrosion in high-iodine environments, and the residual iodine content in the final product is high; the high iodine concentration in the acetic acid product can cause catalyst poisoning in downstream applications, such as in the production of vinyl acetate. To address this issue, Selenia developed the Silverguard process to remove trace amounts of iodine impurities from acetic acid; using silver metal ion exchange resins, the iodine content can be reduced to less than 2 PPb, whereas with traditional methods the iodine content is typically around 10 PPm. Seralis has also introduced polymer resins containing metal salts, which can react with halide impurities in halide-containing solutions to form precipitates. The new method is characterized by the ability to effectively remove halide impurities in one step, eliminating the need for additional distillation and recovery steps. ■ Chiyoda Acetica process: UOP and Chiyoda Corporation have also developed a methanol carbonylation process that uses a multiphase supported catalyst system and a bubble column reactor. Chiyoda Corporation developed the Acetica process in 1997, using methanol and CO as raw materials as well. By combining a multiphase rhodium (Rd) catalyst with polyvinylpyridine resin and using iodomethane as a promoter, this supported catalyst system is said to offer high production efficiency, improve the management of rhodium, and enable an acetic acid yield of over 99%. The Monsanto process is a conventional technique for producing acetic acid; it involves the synthesis of acetic acid from methanol and CO in a stirred-tank reactor at around 175°C and 2.8 MPa, with a liquid rhodium-based composite catalyst and iodine compounds dissolved in the reaction mixture. Chiyoda Corporation’s Acetica process operates under similar reaction conditions, but it is carried out in a bubble column closed-loop reactor using a suspended, solid rhodium-based composite catalyst supported on special material spheres. After the reaction, the product is flashed and dehydrated, and then purified by distillation; the methanol conversion rate exceeds 99%.

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:D Thank you all; this information is extremely useful to me. Thank you:handshake