On the renewable fuels horizon, an alternative is now arising that may replace, in part, diesel and the LPG (liquefied petroleum gas) in gas bottles. Known among chemists as dimethyl ether or DME, this gas has been used industrially since the 1960’s as an aerosol propellant for cosmetics, medication, insecticides and paints. It is made from methanol which, in turn, comes from natural gas or mineral coal. Considered a good substitute for oil products, it pollutes less and can also be made from biomass (BioDME), especially from the agricultural waste of corn, sugarcane (bagasse and straw) and rice husks, besides paper manufacturing remnants.
To transform this biomass into DME, one must convert the vegetable waste into gas through a process called gasification, conducted in a heated reactor. The result is syngas (synthesis gas), a mixture of carbon monoxide (CO) and hydrogen and the raw material for making methanol, the intermediate step toward obtaining DME. Better known in China, where it is used both in a pure form and mixed with LPG, DME is now drawing attention in Brazil, as shown by a study conducted in Rio de Janeiro under the coordination of INT, the National Technology Institute of the Ministry of Science and Technology, and of Cenpes, the Petrobras R&D Center. The research resulted in a DME production process that eliminates the methanol stage, jumping directly from syngas to DME. To achieve this, the researchers selected and added to the process two catalysts, i.e., substances that promote the reaction. “By physically mixing these two catalysts with syngas in a reactor, we did away with the methanol stage”, says chemical engineer Lucia Gorenstin Appel, an INT researcher and the project’s coordinator. A patent for this new technological process has already been submitted to INPI, the National Institute of Industrial Property. What is still lacking is a financial assessment of BioDME production feasibility in Brazil, a study that is likely to be carried out this year by the same group of researchers.
“BioDME from agricultural waste is an alternative for Brazil, among other reasons because it generates no particles and has a zero sulfur emission rate, an environmental advantage as compared to diesel”, says chemical engineer Eduardo Falabella Souza-Aguiar, coordinator of the GTl (gas-to-liquids) group at Petrobras. Falabella, who also teaches at the School of Chemistry of the Federal University of Rio De Janeiro (UFRJ), was the person behind the notion of making DME in Brazil. He manages the area within Petrobras that develops technology to transform natural gas into diesel, for instance, a project that may come true by 2012 or 2013. “We’re currently studying how best to gasify biomass to get DME”, says Falabella.
DME has the advantage of being manufacturable from a range of raw materials and through various processes; additionally, besides releasing no sulfur oxide and soot, its emissions of carbon dioxide (CO2) and nitrogen oxides (NOx) are as much as 90 percent lower than those of diesel. These gases add significantly to major cities’ pollution and to global warming. Toxicological and environmental analyses produced by Akzo Nobel, a Dutch firm, and by DuPont, an American company, which, along with Mitsubishi from Japan are the largest manufacturers of DME for aerosols, have shown that DME does not affect the Earth’s atmosphere and can replace CFCs, which destroy the ozone layer.
Another DME advantage is that it can be made liquid. “With pressure of about six atmospheres, which is low, one can liquefy DME”, says Lucia. “This might prove to be one more option for the transportation of natural gas from distant areas such as, for instance, the Amazon region; this gas could be turned into DME and then carried by truck or by ship”. The most immediate DME use is to replace LPG. Though it has lower calorific power and yields about 18% less energy, the Chinese have had positive experiences with it. On its own, in terms of cooking, no safety problems or corrosion issues have been reported in connection with the ovens, which, however, require minor technical adaptations to run on DME. Another Chinese use of DME consists of mixing 20% of it into LPG; this dispenses with the need to modify the ovens. For DME to replace diesel, engines must also be adapted, as yet another Chinese experiment indicated. In February, 10 buses running only on DME started operating in Shanghai. They release no smoke and are part of a joint test involving other alternative fuels. Japan, Iran, Korea, Russia and Sweden have research projects on the use of DME, besides firms such as Volvo and Nissan, which have already built trucks that run on this gas.
The use of DME as a fuel started being divulged as from 1995, thanks to the SAE – Society of Automotive Engineers congress in Detroit, USA, when the earliest initiatives indicating a promising future for DME were presented. Currently, research into DME is also considering its use in gas turbines to generate electricity and as a future source of fuel cells, devices that transform hydrogen into electric power. The generation of hydrogen from DME will perhaps be conducted at low temperatures, using a technique called vapor reforming, which has several advantages over natural gas, which demands high temperature industrial processes.
Another 10 researchers, who came from IME (the Military Institute of Engineering), PUC-RJ (the Pontifical Catholic University of Rio de Janeiro), and UFRJ, besides Cenpes and INT, took part in the Brazilian study coordinated by Lucia. The research was financed by Petrobras and by the Petroleum Sector Fund, through Finep, the Studies and Projects Finance Agency, to a total of R$895 thousand. It also won the 2008 National Technology Prize granted by Abiquim, the Brazilian Chemical Industry Association. The winner in the Researcher category was Eduardo Falabella, from Petrobras.Republish