| ii Dimethyl ether (DME) can be synthesized directly from syngas, similar to the synthesis of methanol. DME is one of the three important synthetic fuels (F-T oils, methanol and DME) by the GTL (gas-to-liquid) processes. In recent years, much attention has been drawn to the dimethyl ether utilization. DME was relatively inert, non-corrosive, non-carcinognic, with high cetane number (55), and can be stored and handled like LPG. DME was extensively used in aerosol industry, and has been recognized as an alternative for diesel fuel and a potential alternative intermediate for the synthesis of chemicals.Cold plasmas, with the relatively high electron temperature (1~10eV) and the relatively low gas temperature (as low as room temperature), can lead to the direct conversions for many reactions that would be difficult thermodynamically, and has been recognized as a promising new technology. However, due to the poor understanding on plasma chemistry, the selectivity control for the objective products, esp., the liquid products, is still very difficult.In this work, we attempt to introduce DME aerosol into the plasma chemical reaction, in order to remarkably enhance the selectivity of high valuable liquid oxygenates. Via the use of dielectric barrier discharge plasma, we have achieved the highest liquid product selectivity (as high as 58%) with the plasma synthesis reported worldwide by far. For example, the plasma DME conversion in the presence of methane using dielectric barrier discharge at atmospheric pressure and 100 0C with a total flow rate of 40 SCCM and a DME/CH4 feed ratio of 1:1, the total selectivity of liquid oxygenates reaches up to 51.8%, with which the selectivity of dimethoxymethane (DMM) and dimethoxyethane (DMET) takes 6.2% and 14.0%, respectively.Compared with the plasma conversion of low alkanes and alcohols, plasma DME conversion shows different mechanism. Free radical reactions and carbon chain propagation were widely accepted as the main mechanism for conversions of low alkanes and alcohols using cold plasmas. For the non-DME conversions, the carbon chains growth up to C7+, while for the conversions with DME, the carbon chains growth terminated at C3.On the other hand, compared with plasma conversions of methanol and ethanol, the component of liquid products in the plasma DME conversion, iscompletely different. The main component of the conversions with DME is the product of free radical combination reaction, which is mostly dimethoxy- containing compound (like DMM and DMET). However, the main component of the plasma conversions of methanol and ethanol is the product of the further oxidation. For plasma methanol conversion, acids are the major products. For plasma ethanol conversion, the main products are aldehydes and ketones.We also investigated DME combustion over the V catalyst prepared via glow discharge plasma treatment followed by calcination thermally, in order to study the un-directly DME conversion using plasmas. The plasma treated catalyst shows a higher dispersion. For 5wt%V/γ-Al2O3, surface V/Al was increased by 11%. For 5wt%V/HZSM-5, the surface V/Al and V/Si were 7.88 and 2.09 times higher, respectively, compared to the ratios over the conventional catalysts. Catalysts prepared by plasma method also exhibit a better low-temperature activity. The temperature for DME complete combustion was 50 K lower, reduced from 823 K to 773 K.
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