China's Dimethyl Carbonate Industry Enters a Sustainable Development Track  

1. Plight

In 1996, Tangshan Chaoyang Chemical General Plant successfully developed a transesterification process to produce dimethyl carbonate (DMC), helping to change China's DMC industry. In the past, China only had small-scale DMC plants that used the phosgene process and had poor product quality and serious pollution. Since then, China's capacity to make DMC has grown rapidly. By the end of 2009, China had 12 major DMC producers, with a combined capacity of 267 000 t/a.
   The quality and output of Chinese DMC product made by the transesterification process can fully satisfy the domestic market demand. China also exports a large amount. Since 2008, due to the impact of the global economic crisis, the demand for DMC has declined sharply worldwide, causing many Chinese DMC manufacturers to reduce production or shut down. Moreover, the transesterification process of DMC can produce propylene glycol as a byproduct, which has helped DMC manufacturers earn money in the past. However, due to the impacts of cheap imported propylene glycol and domestic propylene glycol made from cheap corn by biological processes, the propylene glycol prices in China's market are RMB3 000/t lower than the production cost of propylene glycol made by propylene oxide, because the demand for polyether to be used in automobile manufacture rebounded, pushing the price of propylene oxide up, and the production cost of propylene glycol increased. Currently, the low price of propylene glycol can affect the operating rate of DMC plants.

China's DMC manufacturers and their capacity in 2009                                     
Manufacturer
    Capacity (thousand t/a)
    Process
Chaoyang Chemical Group
    30
    Transesterification
Shandong Depu Chemical Industry Science and Technology Co Ltd
    10
    Transesterification
CNPC Jinxi Refinery and Chemical General Plant
    10
    Transesterification
Shandong Taifeng Mining Industry Group
    10
    Transesterification (20 under construction)
Shandong Wells Chemicals Co Ltd
    25    Transesterification
Shandong Shida Shenghua Chemical Group
    60
    Transesterification
Dongying Hi-tech Spring Chemical Industrial Co Ltd
    50
    Transesterification
Tongling Jintai Chemical Industrial Co Ltd
    40
    Transesterification
Liaohe Oilfield Dali Group Co Ltd
    16
    Transesterification
Jinxi Natural Gas Chemical Co Ltd
    10
    Transesterification (immature)
Hubei Xinghua Chemical Co Ltd
    4
    Liquid oxidative carbonylation (immature)
Heilongjiang Chemical Group Co Ltd
    12
    Liquid oxidative carbonylation (immature)
Source: CNCIC


   In 2007, China produced 120 000 tons of DMC, twice the output of 2006. In 2008, China produced about 150 000 tons and exported about 30 000 tons. China's actual consumption of DMC was about 120 000 tons in 2008. Half of it was used for the production of coatings and adhesives; next, a large amount was used to produce pesticides and medicines. In the production of coatings, DMC is mainly used to replace solvents like toluene, ethyl acetate, butyl acetate, acetone or methyl ethyl ketone. In the pharmaceutical industry, DMC can be used as a methylation agent to replace dimethyl sulfate.

2. Ways to reduce costs

DMC has no associated pollution and has excellent performance in applications, but its major consumers - coatings and paints producers - prefer cheaper solvents like ethyl acetate and benzene series, which affects the selling price of DMC. Reducing costs is necessary for DMC to beat out the cheaper competitors.

1) Effectively reduce production costs by energy-saving technical transformations

China's DMC producers consume large amounts of heat, electricity and water in the processes of product separation and purification, which accounts for about 1/4 of the total production cost of DMC. So the rational use of heat in the production process can save a large amount of energy and water consumption, and moreover, reduce pollutant emissions. This is the best way to reduce costs.

2) Diversify products to avoid vicious competition

Currently, the pharmaceutical grade propylene glycol needed by China is almost all imported, and the annual demand is about 60 000 tons. Its price is RMB4 000/t higher than industrial grade propylene glycol. Therefore, taking into account the market capacity and investment, some DMC enterprises can profit from converting equipment to produce pharmaceutical grade propylene glycol. In addition, some companies can make conversions to produce marketable products such as 99.99% DMC and 99.95% propylene carbonate.

3) Use ethylene oxide as the raw material to produce DMC and monoethylene glycol (MEG)

In the early days of using the transesterification process to produce DMC, its byproduct propylene glycol had a lower production cost than that produced by reacting propylene oxide directly with water, and had a considerable margin. With the expansion of DMC capacity, the output of propylene glycol grow rapidly, along with the competition of biological propylene glycol, and the production of DMC became unprofitable due to the drop of propylene glycol price.
   Now, new DMC plants generally use the ethylene oxide method because this process has remarkable competitive advantages. This process uses ethylene oxide as the raw material to produce both DMC and MEG. MEG has a huge market in China. This process can greatly reduce the production cost of DMC, so the price of DMC can drop substantially. This can promote the application of DMC in gasoline and diesel additives, coatings and paints.

4) Develop and improve other production processes

Further improve relatively mature DMC production processes, such as the liquid phase oxidative carbonylation of methanol, single-step alcoholysis of urea and double-step alcoholysis of urea, to reduce the production cost of DMC. In addition, strengthen the research of new DMC production processes, such as using carbon dioxide and methanol as raw materials to produce DMC and byproduct formaldehyde, and using propylene oxide, carbon dioxide and methanol to directly produce DMC and byproducts propylene glycol and methyl ether. If these new processes can be successfully developed, DMC producers will be able to obtain huge competitive advantages.

3. Prospects

Because of its low toxicity and high reactivity, DMC attracts much attention. As an environment-friendly substance, it can replace highly corrosive or toxic raw materials and intermediates, such as dimethyl sulfate and phosgene, in many carbonylation and methylation reactions. Since the 1990s, DMC is used to replace MTBE as a fuel additive to improve the fuel's octane number.
   DMC is a very useful intermediate for organic synthesis and can react with a variety of alcohols, phenols, amines and amino alcohols. It can be used to synthesize polycarbonate (PC), isocyanates, carbamates, malonic ester and other chemicals.