How is the Prospect for PO Production?
2019-06-13    [Source:PUdaily]
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PUdaily, Shanghai--

At the end of March, a serious fire and explosion accident occurred in a chemical industrial park in Xiangshui County. The issues of safety and environmental protection faced by the chemical industry again attracted the public’s attention. The Jiangsu Provincial Government made a major decision to completely close the industrial park. Then in April, it officially released the Plan of Jiangsu Province on Rectifying Safety and Environmental Problems in Chemical Industry. Under the guidance of the three overall objectives, namely radically improving intrinsic safety, obviously optimizing regional layout and substantially reducing obsolete capacities, the government set clear standards and strict timetable, which deeply shocked the chemical industry in Jiangsu. Recently, the Office of the Provincial Leading Group for Rectifying Safety and Environmental Problems in Chemical Industry issued the Circular on Issuing Detailed Requirements for the Rectification of Safety and Environmental Problems in Chemical Industry. Detailed Requirements for the Rectification of Safety Problem in the Chemical Industry of Jiangsu Province, the appendix to the circular, sets out detailed requirements for the rectification of safety and environmental problems and requires relevant departments to strictly enforce them. Under the item of Ten Categories that Should be Closed or Eliminated in the appendix are chemical manufacturers or production facilities that produce or use chemicals with explosive properties in the chemical industry park that have been evaluated and confirmed.

When explaining the specific chemicals with explosive properties, the appendix lists 16 chemicals, including ethylene oxide, propylene oxide, epichlorohydrin, tert-butyl peroxybenzoate, etc.

The Detailed Requirements show the determination of the Jiangsu provincial government to conduct this special rectification campaign. At the same time, it also sparks widespread concern and discussion in the industry. Will a one-size-fits-all approach be adopted to shut down all the chemical manufacturers on the list? How will the upstream and downstream sectors along the value chain be impacted after the shutdown? All these problems need to be discussed and solved.

As for propylene oxide, it is well known that there are three production processes for it in China, namely chlorohydrination process, cooxidation process and direct oxidation proccess. At present, the production capacities of PO units that have been put into operation in China total 3.367 million tons/year. The capacity of PO units using chlorohydrination process amounts to 1.762 million tons/year, accounting for about 52.33% of the total capacity. The capacity of units using cooxidation process is 1.205 million tons/year, accounting for about 35.79% of the total capacity. That of units using HPPO stands at 400,000 tons/year, accounting for about 11.88% of the total capacity. Thus, it can be seen that the chlorohydrination process is still the most widely used process in China.

Different processes as a share of the total capacity

As the earliest developed process for producing propylene oxide in China, the chlorohydrination process is simple and mature, and features high propylene conversion rate, low investments and low production costs. After several times of improvement, it has become the main process for producing propylene oxide. The long-term application shows that the process also has drawbacks that cannot be ignored. Firstly, the purity of the obtained propylene oxide is low, which means rectification is needed to obtain PO with higher purity. Secondly, the process uses a large amount of chlorine, and hypochlorous acid produced during the reaction will corrode the equipment. Finally, for 1 ton of propylene oxide about 45 tons of waste water and a large amount of waste residue and waste gas will be generated, which have an adverse impact on the environment. It is for this reason that in the National Industrial Restructuring Guidance Catalogue (2019 Edition, Draft for Comments), PO facilities using chlorohydrination process are included in the restricted category.

By contrast, cooxidation process and direct oxidation proccess are more environmental-friendly. For 1 ton of propylene oxide, 1 to 2 tons of waste water will be generated when using cooxidation process;0.5 to 1 ton of alkaline waste water will be generated when using direct oxidation proccess, and no toxic and harmful gases are produced. 150k t/a (or above) facilities using direct oxidation proccess and 200k t/a (or above) units using cooxidation process are included in the encouraged category. The cooxidation process has developed rapidly in China in recent years. It can reduce the production cost to a certain extent by selling the co-products while significantly reducing waste water and waste residue. The application of direct oxidation processes in China was later than that of the other two processes. The process, which is simple, produces a single product, with no co-product. The water produced in the reaction can be recycled as process water, making the process clean and environment-friendly.

Currently, the cooxidation process and direct oxidation processes have not been widely used in China mainly for the process reasons. The cooxidation process is long, requires diverse raw materials and high purity of propylene, and produces many co-products. Direct oxidation processes uses hydrogen peroxide as the raw material, which is not easy to store and transport. It uses specific catalyst, which increases production costs. The process is not perfect due to its relatively short history of industrialization. At present, PO plants using direct oxidation processes in China are running at relatively low production load, and therefore the process needs to be further improved.

The new and proposed PO units for the next five years will adopt cooxidation process or direct oxidation processes. In the context that environmental protection is emphasized and sustainable development is advocated, the improvement and development of environmentally friendly processes will help to promote their application in China.

Environmental and safe problems are closely linked. The reform of the chemical industry is carried out in Jiangsu Province, but its impact will spread to other regions of China. It is imperative to restructure and upgrade the chemical industry. And elimination of obsolete chemical products and production processes is a long process and needs to be carried out steadily as different sectors along the value chain are closely linked. But emphasizing environmental protection and safety in production is a trend. There are a host of issues remaining to be addressed by us.

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