Selective Solar Conversion of Carbon Dioxide to Dimethyl Ether (DME) Using Unique-Architectured Nanotubular Semiconductors

ABSTRACT: Carbon dioxide feed stock can be converted into fuels of solid, liquid or gas phase by chemical, electrolytic, photocatalytic and photo-electrocatalytic methods. Reduction of CO2 to fuel form of any phase requires energy. The reduction process should be energy efficient so that we do not spend more energy and emit more (indirect) CO2 in the process of converting CO2. From this point of view, conversion processes occurring at room temperature look attractive. The major objective of the proposed project is to convert CO2 to DME using sunlight in the presence of photo catalysts. The proposed research aims at developing a novel photo-catalytic system consisting of unique-architecture of self-ordered arrays of nanotubular transition metal oxide as photo active material functionalized with nanoparticles of Pd, Cu and other sp metals as catalysts for CO2 conversion. The developed systems will selectively convert CO2 to methanol by using sunlight. The proposed low-cost technology will address the objective of the U.S Air Force that intends to develop technologies for converting CO2 into a fuel that is fungible with JP-8. The photo converted methanol will be further transformed to dimethyl ether (DME) by a catalytic dehydration process at low temperatures using a novel catalyst system. BENEFIT: The targeted potential market segment is alternate fuel in the form of dimethyl ether for transport and power generation. DME can potentially replace liquefied petroleum gas (LPG) in many applications such as large scale power generation, heating of buildings, cooking, and clean combustion for automobiles. DME has a higher cetane number (55) than diesel (cetane number 42-45) which indicates that it has a shorter delay time between ignition and combustion. DME is sulfur free and the combustion products contain less amount of toxic particulate emissions such as NOx and CO. Therefore, DME can meet very stringent emission regulations and can be used as fuel in underground mines. The established market of DME is for aerosol applications which is about 150,000 metric tons per year. For propellant applications, very high purity DME is required. However, for household applications, such as cooking and heating, a reduced purity is tolerable (about 95% DME. When DME is adopted as alternate fuel, the demand will increase exponentially. In China alone the production is expected to grow to 20 millions metric ton by 2020. Conventionally DME is manufactured through direct conversion of natural gas, which is considered as the most cost effective process. DME is also produced by catalytic dehydration of methanol at 250 oC. The sources of methanol can vary from syngas derived from coal or natural gas or biomass conversion from either agriculture or paper industry waste stream or energy crops. According to a report by DME association , the production cost is affected more by the rate of production (tons per year) than by the conversion processes such as direct or indirect method. However, it is clear that if the sources of methanol and process heat are renewable, the cost can be substantially reduced by gaining carbon credit.