Propylene oxide production technology and market
Overview
Propylene oxide (PO) is the third largest propylene derivative besides polypropylene and acrylonitrile. It is an important basic organic chemical raw material and is widely used. Using PO as raw material to produce polyether polyols and then produce polyurethane is its largest use; secondly, it can be used to produce polyurethane elastomers and surfactants such as propylene glycol and propylene glycol ether with wide applications; it can also be used to produce oil field demulsifiers, pesticide emulsifiers and wetting agents.
Production process and progress
At present, the main production methods of PO are chlorohydrin method, ethylbenzene co-oxidation method (POSM method for co-production of styrene) method, isobutane co-oxidation method (TBA method for co-production of tert-butanol), cumene peroxide method (CHP method), direct oxidation method (including HPPO method with hydrogen peroxide as oxidant and direct oxidation of oxygen). The world's production capacity of propylene oxide using the chlorohydrin method accounts for 40% to 45% of the total capacity, and the production capacity of propylene oxide by the co-oxidation method accounts for 55% to 60% of the total capacity. Among them, the chlorohydrin method, POSM method, TBA method, CHP method, and HPPO method have been industrialized, and the direct oxidation of oxygen is still in the experimental stage.
2.1 Chlorohydrin method
The chlorohydrin method is a classic industrial production method for synthesizing PO, which mainly includes three processes: chlorohydration, saponification and distillation. The chlorohydrin method has a long history, mature process, short process, large operation elasticity, good selectivity, high efficiency, relatively safe production, low requirements for the purity of raw propylene, and low construction investment. The disadvantage is that it is highly corrosive and has a lot of sewage, which is suitable for construction in places with conditions.
2.2 Co-oxidation
Co-oxidation is the reaction of organic peroxide and propylene to generate PO, while by-producing organic alcohol. According to the different raw materials and co-products, the co-oxidation process mainly includes the POSM process of Lyondell (Arco), Shell, NKNC, the TBA process of Lyondell (Arco) and Texaco co-producing propylene oxide and tert-butanol (or MTBE), and the CHP process of Sumitomo Corporation of Japan.
The POSM process mainly uses ethylbenzene hydrogen peroxide (EBHP) to epoxide propylene to generate PO, and by-product α-phenylethanol. α-phenylethanol is dehydrated in gas or liquid phase to produce styrene, and 2.25 tons of styrene (SM) is produced per tPO.
The problem with the co-oxidation process is that the resulting co-products may interfere with the market, thus increasing the difficulty of forming a raw material balance. For example, the co-production of tert-butanol, methyl butyl ether and styrene by the isobutane method and the ethylphenyl method all pose problems for PO producers due to the unpredictable market. Therefore, it has become a development goal in this field to decouple the production of PO from these co-products. It is under this development goal that the cumene peroxide method (CHP) came into being.
Sumitomo's new process route - cumene hydrogen peroxide (CHP) oxidation method has four steps: cumene oxidation, propylene epoxidation, removal of organic acids, and by-product alcohol dehydration and hydrogenation to return cumene. Cumene is first oxidized to cumene hydrogen peroxide, which reacts with propylene to obtain propylene oxide and dimethylbenzyl alcohol (DMBA), and then DMBA is directly dehydrated and hydrogenated to produce cumene, which is recycled. Of course, there are also necessary steps such as concentration of CHP, recycling after propylene separation, and purification of propylene oxide. The preparation of CHP by the oxidation of cumene is a very famous process because it is part of the phenol-acetone process that has long been in commercial operation. Its biggest advantage is that it does not produce any by-products, improves the flexibility of propylene oxide production, and does not have to be affected by the market demand for styrene. It can be seen that the CHP method is a very similar process to the EBHP method, with many similarities. More importantly, compared with EBHP, the former has lower investment and is easier to operate. This process has been industrialized in Chiba, Japan and Saudi Arabia. Shanghai Petroleum and Chemical Research Institute CHP process PO completed the pilot test in Tianjin Petrochemical at the end of 2012, and the propylene conversion rate and PO selectivity reached more than 99%.
2.3 Direct oxidation
Direct oxidation methods mainly include HPPO method and molecular oxygen as oxidant. The former has been very active in research and development; the latter has been almost abandoned by R & D personnel due to high activation resistance, susceptibility to deep oxidation and catalyst performance limitations. In recent years, due to environmental, cost and other factors, research on molecular oxygen as catalyst has begun to be active again, but due to low PO selectivity and slow epoxidation rate, this process has not been industrialized so far.
H202 is a green chemical product. The by-product obtained by using it as an oxidizing agent is H20, which has no pollution to the environment. Therefore, the process of catalytic oxidation of propylene to generate PO with H202 has received great attention in recent years. The process is characterized by low investment cost and high product yield. Except for H20, the amount of by-product generation can be reduced to a minimum. The disadvantage is that a large amount of H202 with higher price is consumed. At present, the HPPO process is jointly developed and industrialized by Evonik Industrial Group (formerly Degussa) and Uhde Company, Dow Chemical and BASF Company. The research on HPPO method technology has also been carried out by the Institute of Chemical Physics in our country.
Jilin Shenhua Group Co., Ltd. introduced HPPO process technology from Evonik-Uhde, Germany, and built an HPPO unit with a production capacity of 300,000 t/a, which was put into trial operation in December 2013. In 2010, Changlian completed a 1000t/a pilot plant for the propylene hydrogen peroxide to propylene oxide process independently developed in cooperation with the Institute of Petrochemical Sciences and Changling Petrochemical. The catalyst has a one-way operating life of> 1400h, a hydrogen peroxide conversion rate of> 95%, and a propylene oxide selectivity of> 97%. In 2014, the development and application of a 100,000 t-class HPPO unit was completed.
2.4 Technological progress
In theory, the simplest and most reasonable way to synthesize PO is through direct epoxidation of propylene and oxygen. The cost of direct gas-phase oxidation to produce PO is only one-quarter to one-third of that of the chlorohydrin method, and there are few by-products, easy separation and no pollution. However, when molecular oxygen reacts with organic molecules, it is prone to a more thermodynamic deep oxidation process, so highly selective direct epoxidation catalysts for propylene have become the focus of research and development,
In recent years, silver-based catalysts have been used in propylene epoxidation reaction due to the similarity between the gas-phase catalytic direct oxidation process route and the silver catalyst to produce ethylene oxide, but the research results obtained so far are still limited. In addition to silver catalysts, other catalysts for propylene epoxidation using molecular oxygen as an oxygen source include gold catalysts and copper catalysts, which are all research hotspots. Using gold catalysis, the selectivity of propylene oxide can reach more than 90%, but the preparation cost is high and the deactivation is fast. Cu is also likely to be a potential propylene epoxidation catalyst, and Cu is inexpensive and abundant in sources. Using Cu instead of Au and Ag for propylene direct oxygen epoxidation reaction will greatly reduce the production cost of propylene oxide. But so far, the conversion rate of propylene and the selectivity of propylene oxide are very low. If the polymetallic catalyst can be optimized to explore the synergy between different active metals, while improving the conversion rate of propylene and the selectivity of propylene oxide, it will be a promising idea.
Market and supply and demand forecasts
In 2014, the global PO production capacity was about 10.137 million t/a. China's production capacity was 2.77 million t/a, and the output was 1.997 million t. The average operating rate of the plant was 68.03%, and the consumption was 2.353 million t. The global propylene oxide is mainly distributed in Asia 45% and Europe 38%, accounting for more than 80% of the world. The distribution of propylene oxide in Asia clearly shows that China accounts for 61%, followed by Japan 14%. With the increase in production and apparent consumption, the Chinese market will become the largest consumer market for polyurethane in the future.
According to the downstream production demand, the domestic polyether demand in 2014 accounted for about 65%, 1.123 million tons; DMC/PG demand accounted for about 10%, reaching 190,000 tons; PM/PMA demand was about 280,000 tons, accounting for 15%; flame retardants, petroleum demulsifiers and other small products were about 190,000 tons, accounting for 10%.
In 2014, the domestic propylene oxide production capacity was 2.77 million t/a, an increase of 30% over 2013, and the output was about 1.89 million t/a, an increase of 5.4% over 2013. It is expected that the domestic propylene oxide production capacity will reach 3.257 million t/a in 2015 and 4.2 million t/a in 2020.
In 2014, the global propylene oxide capacity was about 10.137 million t/a. The production capacity is mainly concentrated in Dow Chemical and Lyondell, of which Dow Chemical is the largest producer. It has built multiple sets of propylene oxide production plants in the United States, Germany, Brazil, Belgium and other places, with a total capacity of more than 2.195 million t/a, accounting for about 21.7% of the global production capacity. The second-ranked Lyondell has a capacity of 1.9 million t/a, accounting for about 18.7% of the world's production capacity. The two companies account for nearly 1/2 of the global share and control most of the world's propylene oxide market. The statistics of the world's major propylene oxide production plants and production capacity in 2014 are shown in Table 2.
At present, there are a total of 18 companies producing propylene oxide in China, and the operation is maintained at a high level throughout the year, which shows that the market demand for propylene oxide is still tight.
Summary
PO production enterprises in our country do not need to invest too much in the development of chlorohydrin. From the perspective of the localization strategy of the imported device, some development and research should be carried out on co-oxidation technology, especially POSM technology, to break the monopoly position of foreign companies. There are many large-scale phenol/acetone production plants in our country, and there is a mature technology for the oxidation of cumene to hydrogen peroxide cumene, and the hydrolysis of benzyl alcohol to cumene is relatively mature. Therefore, the CHP system of propylene oxide is very suitable for our country's national conditions. We should speed up the development of new technologies for propylene oxide, phenol and acetone with independent intellectual property rights of Sinopec.
At the same time, we should also actively grasp the favorable opportunity for the transfer of the world's bulk organic raw material industry, strive for technical and production cooperation with multinational companies such as Dow Chemical, Sumitomo, BASF, and Lyondell in areas with sufficient propylene resources and better market conditions, and use hydrogen peroxide method and other newly developed foreign environmentally friendly new processes to build large-scale PO production plants, and support the construction of polyether and other downstream devices to form upstream and downstream integrated production to meet the needs of national energy conservation and emission reduction and industrial structure optimization and adjustment, to ensure the sustainable and healthy development of the industry.
