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Converting glycerol from biodiesel production into bio-gasoline
16 December 2013
A team at the University of Idaho has demonstrated that glycerol, a byproduct from biodiesel production, could be used as a substrate for producing drop-in gasoline-range biofuel. In a paper published in the ACS journal Energy & Fuels, Guanqun Luo and Armando G. McDonald describe their study of converting methanol (MTG) and a mixture of methanol and glycerol (MGTG) into gasoline-range hydrocarbons using a bench-top, fixed-bed microreactor.
The MTG- and MGTG-generated liquids showed a similar composition, mainly methylbenzenes, to regular gasoline, and composition changed as the reaction proceeded to favor heavier aromatics.
The technology of converting methanol into gasoline was discovered and commercialized more than 3 decades ago. … Currently, the increasing consumption and limited reserves of crude oil, as well as the problem of CO2 emissions mainly caused by the usage of fossil fuels, have led to a growing interest in the production of non-fossil-based energy. Methanol can be made from biomass that is abundant, renewable, and globally available, via synthesis gas (syngas), and further converted into gasoline; therefore, the MTG process is receiving renewed attention today.
Over the years, a variety of zeolites have been tested in the MTG process, including SAPO-34, HY, H-β, and ZSM-5. The lattermost catalyst, ZSM-5, is widely accepted to be the most effective and selective catalyst to produce high-quality gasoline, which is mainly attributed to its network structure. The performance of the MTG process via ZSM-5 can be influenced by several factors, such as temperature and pressure. A major problem of the MTG process is deactivation of the catalyst because of the deposition of the carbonaceous residue; thus, it is still a key area of research to improve the catalyst lifetime by optimizing the catalyst pretreatment method and/or reaction conditions.
… For the conversion of glycerol into fuels, most research focuses on the gasification of glycerol to produce syngas that can be further converted into gasoline or diesel via Fischer−Tropsch synthesis (FTS). Nevertheless, very little research into the direct conversion of glycerol to gasoline-range hydrocarbons has been reported.—Luo and McDonald
Earlier work had found that a reacting compound with an effective H/C ratio below 2—such as glycerol which has an effective H/C ratio of 0.6—rendered the excessive deactivation of zeolite catalysts in the conversion. Luo and McDonald noted that adding methanol—which has an effective H/C ratio of 2—into glycerol could increase the combined H/C of the feed and then improve the activity of the catalyst.
In addition, they added, using a mixture of methanol and glycerol as feedstock for a MTG-like process may also reduce the costs for cleaning the crude glycerol from the transesterification process, because excessive methanol is usually used to improve the production of biodiesel.
In their study using a ZSM-5 catalyst, they found that the best MTG catalytic performance was achieved at 425 °C, at which the product yield and catalyst lifetime were 11.0 wt % and 20 h, respectively. Generally, the methanol conversion rate and the total liquid and organic-phase yield rates decreased with the reaction time at each temperature. In addition to gasoline-range aromatics, some oxygenates were also detected in the extracted aqueous phase from the MGTG process.
The best MGTG catalytic performance was achieved at 500 °C with 10% glycerol in methanol, at which the product yield and catalyst lifetime were 14.9 wt % and 8 h, respectively. The higher glycerol content disfavored the production of aromatics but favored oxygenates. With an increasing reaction time at all reaction conditions, methanol and glycerol conversion rates were ≥99%.
While they demonstrated the successful conversion of glycerol to bio-gasoline, they authors observed that further work is required to increase the catalyst lifetime.
Guanqun Luo and Armando G. McDonald (2013) “Conversion of Methanol and Glycerol into Gasoline via ZSM‐5 Catalysis.” Energy & Fuels doi: 10.1021/ef401993x
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