DME (Dimethyl Ether)
As dimethyl ether (DME) does not contain sulfur or ash, it does not generate any SOx or particulate matter when combusted. It is a clean fuel of high cetane number, excellent combustion characteristics and extremely low toxicity, which is not believed to cause global warming or destroy the ozone layer.
DME may be stored and handled in a similar manner to LPG, so expectations have grown for its use as an alternative to LPG and diesel. It is also considered to be an alternative clean energy that can indirectly alleviate the constraint on resources, as it can be made from a wide range of source materials besides natural gas, including coal, heavy oil, biomasses and waste. This is possible because DME is produced from syngas in its production process.
TOYO has developed indirect DME production technologies and catalysts by adding the DME synthesis process to the methanol plant. In the indirect method, methanol and DME may be produced together and production can be adjusted to suit market demand, enabling highly flexible production strategy. Also, the DME plant, which is highly reliable and easy to operate, may become an economic reality because it is underpinned by a large-scale methanol process that has already reached technological maturity. Four DME plants under license by TOYO are already under operation in China.
TOYO received 2006 Japan petroleum institute award for technological progress as “Commercialization of Indirect Method of DME Process”
Regardless of the process route, i.e., direct or indirect, the process to produce DME from natural gas feedstock is made up of the reactions to reform raw material methane into synthesis gas mainly composed of CO+H2+CO2 using steam or oxygen as oxidant and to generate methanol from the synthesis gas as the first step and then to dehydrate it into DME. The direct route makes methanol synthesis reaction and DME synthesis reaction occur in one reactor. On the other hand, the indirect route makes these reactions in separate reactors. TOYO DME is employing the indirect route composed of synthesis gas generation technology that has high reliability based on more than 100 project experiences and its unique methanol production technology. The principle of DME production by methanol dehydration process is as follows.
(1)MeOH-1 ：CO + 2H2 = CH3OH (91 kJ/mol)
(2)MeOH-2 ：CO2 + 3H2 = CH3OH + H2O (49 kJ/mol)
(3)MeOH De-H2O：2CH3OH = CH3OCH3 + H2O (23 kJ/mol)
The process has two reaction steps. First, methanol is produced from synthesis gas by reaction (1) and (2), and then after removing by-product water, DME is produced by methanol dehydration reaction (3). All reactions (1), (2) and (3) are exothermic.
This indirect route has the advantages such as of enabling selection of the most optimum reactor type and operating conditions for each reaction steps, and becoming easy to remove reaction heat from the reactor due to less reaction heat against the direct route. The synthesis gas containing R value (H2－CO2) / (CO+CO2)= approx. 2 is ideally fed to methanol synthesis. In case of reforming natural gas with steam, CO2 is also used for the methanol synthesis.
Application of the high performance MRF-Z® reactor developed by TOYO which has the specific features of multi-stage indirect cooling and a radial flow to the methanol synthesis unit enables to construct the unit with a capacity of 6,000 ton/day in a single train for which other licensors' technologies require multiple reactors. TOYO DME is the process combines proven technologies with the simple and low cost DME synthesis applying design philosophy of methanol plant.
The process scheme of the indirect route DME synthesis developed by TOYO is as indicated below, composed of single train methanol synthesis and single train DME synthesis even in a large capacity DME plant of 3,500 tons per day.
DME process flow
TOYO received the order for the world’s first fuel-use DME production plant in 2002 from Lutianhua Group Inc., a leading fertilizer manufacturer located in Sichuan Province in China. The plant started operation in 2003, and has enjoyed smooth operation since that time. After achieving the excellent plant performance, TOYO was awarded the 2nd DME plant of 110,000 t/y from the company. Other than these two DME plants produced from natural gas, TOYO was awarded the 3rd DME plant of 210,000 t/y from Shenhua Ningxia Coal Group Co., Ltd. and the 4th DME plant of 140,000 t/y from Shanxi Lanhua Clean Energy Co., Ltd., these are produced from coal feedstock. All these four DME plants under license by TOYO have been successfully started up and under operation helping to alleviate the energy shortages in the country.