**3. DME fuel production**

Top Key producers of Dimethyl Ether (DME) include: a) Akzo Nobel, b) Shell, c) The Chemours Company, d) China Energy, e) Mitsubishi Corporation, f) Ferrostal GmbH, g) Grillo Werke, h) Jiutai Energy Group, i) Oberon fuels and j) Zagros. In Japan several large scale DME plants have been set-up [9]. China is the bulk producer of DME from Chinese coal and production plants have also been set-up in Trinidad and Tabago, North America, Indonesia and Uzbekistan. First bio DME production plant was constructed in Sweden. Global production of DME at present is roughly 9 million tons per year [10]. Different feedstocks can be used in the production of DME. These are natural gas, coal, waste from pulp and paper mills, forest products, agricultural by-products, municipal waste and dedicated fuel crops e.g., switch grass. Methanol dehydration is the main process for production of DME currently. Synthetic gas can however be produced by gasification of coal, biomass, natural gas reforming [11].

There are three pathways to produce DME: a. Two-step process, b. One-step process, c. Liquid-one-step process called as bio reforming. Typically, DME is produced through a two-step process with syngas the feedstock (**Table 1**). Methanol is first produced from Syngas, followed by dehydration of methanol into DME (Eqs. (1)–(4)) (**Table 1**, **Figure 5**) [12].

*Replacement of Diesel Fuel by DME in Compression Ignition Engines: Case for India DOI: http://dx.doi.org/10.5772/intechopen.104969*


#### **Table 1.**

*Two-step synthesis process of DME [12].*

#### **Figure 5.**

*Two-step process for synthesis of DME [13].*


#### **Table 2.**

*Single-step synthesis of DME [12].*

**Figure 6.** *Single-step process for DME synthesis [13].*

In Japan, Korea and China single-step process is used most commonly (Eqs. (5)–(6)) (**Table 2** and **Figure 6**). In this process, the methanol formation, methanol dehydration and water-gas shift reaction are merged. Different feedstocks can be used in this process such as methane, scrubbed bio-gas, syngas, etc. In case of methane feedstock methanedry-reforming is done before the single-step process. Japan Steel Company has reached production capacity of 100 t DME/day by this process (Olah, et al. 2009). Mass balance shows that for every gm DME produced 1.43 gm of CO2 is used in the process. In overall reaction, CO2 sequestration is 0.48 gm per gram of DME.

Third process for DME production is bio-reforming (**Table 3**, Eqs. (8)–(12)). For optimized process to produce methanol Metgas is used, which is 2:1 H2:CO ratio syngas. Two processes to produce Metgas are methane-steam-reforming and methane-dry-reforming step. Next steps are methanol formation and DME synthesis by dehydration of Methanol. Water produced during the dehydration of methanol is used in the methane-steam-reforming process. CO2 consumed during per gm formation of DME is 0.48 gm. There are no emissions of CO2 during bio-reforming process, however there will be CO2 emissions regarding process's energy requirements.

Both one-step and two-step DME production process are mature technologies. There are many companies which have developed single-step process for producing DME. Notable among these are Haldor-Topsoe A/S Denmark, JFE Holdings, Japan, Korea Gas Company, S. Korea, Air Products USA, NKK Japan, Oberon Fuels USA etc. Two-step DME production process has been developed by companies like Toyo Japan, Mitsubishi Gas Company Japan, Lurgi Germany, Udhe Germany. Several companies have developed novel processes and technologies for production of DME.

World's first bio-DME demonstration plant in Sweden (started in 2010) uses black liquor (waste from paper and pulp industry) to produce high-quality syngas which is used for synthesis of DME (**Figure 7**).

#### **3.1 Production process developed by Oberon fuels**

Oberon Fuels has developed proprietary skid-mounted, small-scale production units that convert methane and carbon dioxide to DME from various feedstocks, such as biogas from dairy manure and food waste. These small-scale plants are affordable as compared to a large plant, do not require large infrastructure and permits etc. for operation. These small-scale production units can produce 10,000 gallons (37854.12 liters) of DME per day to cater to the regional fuel markets [14].

Schematic of the plant is shown in **Figure 8**, consists of SMR, make-up syngas compressors, methanol synthesis reactors, pre-cut column and DME column and DME storage tanks.


The Oberon Fuels methane-gas-to-DME process has the following three major steps:

#### **Table 3.**

*Bio-reforming process for production of DME [12].*

*Replacement of Diesel Fuel by DME in Compression Ignition Engines: Case for India DOI: http://dx.doi.org/10.5772/intechopen.104969*

**Figure 7.** *Bio-DME production plant in Sweden [13].*

**Figure 8.** *Schematic of a small size DME production plant developed by Oberon fuels [14].*


3. Simultaneous DME synthesis and separation via catalytic distillation.

First two steps are common in large scale industrial application. Catalytic synthesis of DME with purification has been investigated in detail and has been demonstrated industrially by Oberon Fuels at Brawley California. In this plant, all production, storage, piping, tanks and valves are overground. DME produced from un-scrubbed (60% methane) HSAD (High Solid Anaerobic Digestion) of food waste, yard waste, bio-waste is called as Bio-DME. Chemically Bio-DME and DME are chemically same,

Bio-DME uses biogas (typically produced from anaerobic digester), whereas DME is produced from pipeline natural gas.
