The chemical industry traditionally uses petroleum as its basic raw material, but the escalation in crude oil prices in recent years has focused attention on the possibility of using coal instead. China’s plentiful coal reserves are fueling the development.
The use of coal as a feedstock is becoming more attractive as oil prices continue to rise, especially in countries such as China, where coal is abundant.
Methanol-to-olefins (MTO) processes are of particular interest in China, which has a shortage of ethylene and propylene but a surplus of methanol, much of it made from coal in places remote from ports and hence uneconomic to export. However, an integrated coal gasification, methanol and methanol-to-olefins complex requires a high level of investment.
Chemical industry information specialists China National Chemical Information Center (CNCIC) of Beijing and Tecnon OrbiChem, based in London and Shanghai, have announced a new study of China, where three such plants have recently been built and completed and are now undergoing commercial start-up, converting coal to olefins (mainly ethylene and propylene). CNCIC and Tecnon OrbiChem say this is an opportune time to review the entire field of MTO and methanol-to-propylene initiatives in China, to judge which and how soon the new ventures will become commercial realities, and to see what impact this will have on the olefins industry in China. As the successes become evident, other countries are likely to follow China’s lead.
This will involve not only nations with large coal reserves, like Australia, Indonesia and India, but also those with abundant natural gas — perhaps even the USA, with its newly exploited shale gas. Where the gas wells are “stranded” far from population centers, large investments are needed in pipelines or in liquefaction facilities to bring the gas to where it is needed. An alternative is to convert the gas to methanol at the wellhead, transport the methanol by pipeline or ship to chemical complexes anywhere in the world, and there use it to make olefins and derivatives.
The study will draw on the Chinese experience to assess the path that could be taken by other countries rich in coal or gas, but with little in the way of petroleum resources, to expand into chemical production.
From Coal to Olefins
The first step in using coal as a chemicals feedstock is usually its conversion to synthesis gas (syngas). The syngas can then be converted into ammonia or methanol. Ammonia is used for the production of fertilizers, while methanol can be used as a feedstock for other chemicals. The advantage of having methanol as an intermediate is that it can be purified easily by distillation, removing most of the impurities derived from the coal. Methanol is then typically converted to ethylene and propylene — the new study will focus on these — but it can also be used to make acetic acid, dimethyl ether (DME) and other chemicals.
Processes to convert methanol to olefins have been developed in Europe by Lurgi and by UOP/Norsk Hydro in conjunction with Total Petrochemical. In China, methanol-to-olefins (MTO) processes have been developed by the Dalian Institute of Chemical Physics (DICP), by Tsinghua University, by Sinopec Beijing Yanshan Petrochemical, and by Sinopec Nanjing Chemical Industry.
Two of the three Chinese plants are designed to make only propylene and are known as methanol-to-propylene plants; Lurgi has registered the name MTP for this process (Fig. 1).
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