Polypropylene production increase technology continues to develop

With the continuous development of the polypropylene industry, the world's propylene demand has increased from 15.2 million tons 20 years ago to 51.2 million tons in 2000, with an average annual growth rate of 6.3%. It is predicted that the world propylene demand will increase further to 86 million tons by 2010, with an average annual growth rate of approximately 5.6%; the world propylene production capacity will increase from 59.3 million tons in 2000 to 62 million tons in 2001 and 6800 in 2002. 10,000 tons, 74 million tons in 2004 and 82 million tons in 2008. The average annual growth rate of the main propylene derivatives was: polypropylene 6.3%, acrylic acid 6%, acrylonitrile 4%, propylene oxide 4%, and cumene/phenol 3.8%. Among the propylene derivatives, polypropylene accounts for the largest consumption of propylene at 57%. Others are: acrylonitrile 11%, oxo alcohol 8%, propylene oxide 7%, cumene 6%, acrylic acid 5% , Isopropanol 3%, other 3%.

To further increase propylene production, production technologies will tend to diversify. On the basis of steam cracking and catalytic cracking as the main source of propylene, catalytic cracking, propane dehydrogenation, metathesis, olefin interconversion, and MTO (Methanol to Olefin) processes will be further developed. At present, 66% of the propylene in the world comes from the by-products of steam cracking to produce ethylene, 32% from the by-products of gasoline and diesel produced by refinery fluid catalytic cracking (FCC), and a small amount (about 2%) from dehydrogenation and metathesis of propane. Steam cracking technology In the process of steam cracking ethylene, the propylene yield varies depending on the feedstock and operating conditions. Generally, naphtha, gas oil and propane are used as raw materials to produce ethylene. For each ton of ethylene produced, 0.4 to 0.6 tons of propylene are by-produced. With ethane as raw material, only 1 ton of ethylene is produced as a byproduct of 0.04 to 0.06 tons of propylene.

The Japan National Materials and Chemical Research Institute and the four petrochemical companies jointly developed a naphtha cracking process that increases propylene production and reduces energy consumption, which can increase the ratio of propylene to ethylene from the traditional 0.6:1 to 0.7:1. The process uses a ruthenium catalyst with a molecular sieve as a support in a fixed bed, which allows the yield of ethylene plus propylene to reach 61%, while the conventional steam cracking is 50%. The process is performed at 650°C and 0.1M to 0.2 MPa. Due to operation at lower temperatures, energy consumption is reduced by approximately 20%.

Fluid catalytic cracking technology extended to chemical industry Typical fluid catalytic cracking (FCC) units produce only 0.03 to 0.06 tons of propylene per ton of motor gasoline produced. In recent years, FCC has developed a variety of process technologies that increase propylene production. Petrochemical Research Institute of China Petrochemical Corporation developed a deep catalytic cracking (DCC, also known as catalytic cracking) process. The DCC unit is operated at 538°C to 582°C and 10% to 30% steam conditions. The molecular sieve catalyst is used to selectively produce propylene and butene. The device is divided into two types of maximum production of propylene DCC-1 type and maximum production of isoolefins DCC-2 type, the propylene yield was 20.5% and 14.3%. Currently, 7 DCC units have been put into production in China and Thailand.

UOP uses PetroFCC's catalytic cracking design to increase the production of light olefins from a variety of feedstocks such as gas oils and vacuum residues, especially to increase propylene production. UOP designed a dual-zone configuration using two reaction zones and a common regenerator. Using this process propylene yields up to 22.8%. The selective group splitting (SCC) process developed by Lummus uses a high content of ZSM-5 zeolite catalyst to achieve propylene yields of 16% to 17%. Naphtha selective cyclic cracking technology can also increase propylene production. % to 3%. Mobil's Maxofin process combines a high ZSM-5 content additive with improved FCC technology to achieve a propylene yield of 18%. KBR's Sperflex process reaction is based in part on KBR's FCC technology, which converts light hydrocarbons (usually C4 to C8) into propylene-rich streams. Propane dehydrogenation technology 8 sets of propane dehydrogenation plants have been built around the world with a production capacity of 1.2 million tons per year. It is predicted that by 2010, 10 new installations will be built to increase propylene production by 4 million tons/year.

There are already several installations planned for construction in Malaysia, Saudi Arabia, Spain and Qatar. At present, propane dehydrogenation processes mainly include UOP's Oleflex process, Lums' Catofin process, Phillips' Star process, and Linde's PDH process. Among them, the Oleflex process and the Catofin process have been applied industrially. The Oleflex process plant consists of a reaction zone, a continuous catalyst regeneration zone, a product separation and fractionation zone. The propylene yield is about 85% and the hydrogen yield is 3.6%. The Catofin process uses a fixed bed catalytic reactor with propane conversion greater than 90%. The propane dehydrogenation unit has a relatively high investment cost and requires long-term economical supply of propane raw materials.

Metathesis reaction technology utilizes metathesis reaction technology to react ethylene with 2-butene to produce two molecules of propylene. When the metathesis reaction device is combined with the steam cracking, the ratio of propylene to ethylene can be increased to 1.0 to 1.25. Lums' Triolefins process operates in the gas phase at temperatures of 330°C to 400°C. Tungsten-based catalysts and fixed bed reactors are currently used in a single unit. In 2001, a large-scale olefin plant jointly developed by BASF-Ferner will also use this technology. The plant will produce 950,000 tons of ethylene per year and 540,000 tons of propylene per year. Part of the produced ethylene will be converted to butylene with a metathesis reaction to produce propylene, which will increase propylene production by 58% and eventually produce 860,000 tons of ethylene per year. And 860,000 tons/year of propylene.

Metathesis reaction devices increase the propylene to ethylene ratio to above 1.0. Disadvantages of metathesis reaction technology are higher investment costs (but lower than propane dehydrogenation) and are more sensitive to raw material impurities. In addition, lowering high-value ethylene to lower-value propylene produces waste.

Mutual conversion process of olefins The olefin interconversion process (MOI) developed by Meifu Co., Ltd. adopts selective secondary conversion technology, operates in a fluidized bed reactor, and the catalyst is continuously regenerated. The use of ZSM-5 catalyst enables the acid activity and shape selectivity to be very high. Good combination promotes the oligomerization, cracking and disproportionation of olefins. This process converts steam cracking C4 and pyrolysis light gasoline into propylene and ethylene, which is also a potential raw material.

Fixed Bed Catalytic Cracking Lurgi has developed a fixed-bed catalytic cracking Propylar process that converts C4 and C5 olefins into ethylene and propylene. When it is combined with naphtha steam cracking, the ratio of propylene to ethylene can be raised to 1.0. A typical reaction product contains 42% of propylene, 13% of ethylene, and 31% of butene. A pilot plant has been built. Methanol to Propylene Process UOP/Noske-Hydro's MTO Process The technology for the production of ethylene and propylene from natural gas is available. Methane is converted to synthesis gas, and the produced crude methanol is then subjected to an MTO process to produce ethylene and propylene.

Under high propylene conditions, propylene yields up to 45%, ethylene up to 34% and butenes up to 13%. The process uses a fluidized bed reactor and regenerator design. Egypt will build the first MTO industrial unit, using natural gas as raw material to produce 320,000 tons/year of polyolefin. The MTO process combines methanol with a polymer plant to form a complete natural gas-polyolefin plant production line, which will be put into production in 2003. Lurgi also developed the MTP process, which operates at slightly elevated pressures (0.13M to 0.16MPa) and low temperatures (380°C to 480°C) and has been validated in the laboratory.

There are nearly 50 propylene production enterprises in China, of which 16 are produced by steam cracking and the rest are refinery propylene producers. By 2005, if large-scale and medium-sized ethylene plants are completed, several large-scale joint venture ethylene projects will be completed and put into production. It is expected that the ethylene production capacity will reach 8.8 million tons. According to the operating rate of 90%, it can produce 7.92 million tons of ethylene. According to the production ratio of ethylene and propylene of 1:0.52, the ethylene cracker can produce 4.12 million tons of propylene per year. If the ratio of cracked propylene production to total propylene production in the country is 61%, China's propylene production in 2005 will be approximately 6.73 million tons. By 2005, the growth rate of propylene demand in China will be calculated at 10%. At that time, the demand for propylene in China will reach 9.53 million tons, and the self-sufficiency rate will be about 70%.

At present, the raw materials and processes of the propylene industry are developing in the direction of diversification and new technologies. High cracking depth and selective FCC technologies have matured and been promoted. Other technologies for the conversion of various olefins to propylene have also been developed in competition. Some have achieved practical results, and propane dehydrogenation also has potential for development. China should also expedite the development and research of other ways to increase propylene production (such as metathesis reactions, propane dehydrogenation, and methanol to propylene), and provide technical reserves to meet the growing demand for propylene.