Hydrogen separation alcohol reforming

Carbon dioxide-methane separation Solvent vapor recovery Hydrogen and carbon dioxide recovery from steam-methane reformer off-gas Hydrogen recovery from refinery off-gas Carbon monoxide-hydrogen separation Alcohol dehydration Production of ammonia synthesis gas Normal-isoparaffin separation Ozone enrichment... 

To establish the suitability of a membrane material for hydrogen separation, it is important to consider that around 90% of the current global H2 production is obtained by gas synthesis through steam reforming of methane or other hydrocarbons and alcohols. Therefore, a suitable Hj-separation membrane should fulfil the requirements to reliably operate in a reforming reactions environment and, at the same time, to ensure high performance in terms of permeability and selectivity. 

The reforming process (as applied to a hydrocarbon or alcohol) yields a product stream that consists predominantly of hydrogen, carbon monoxide, carbon dioxide, water, unconverted feedstock, and trace by-products. This product stream mixture, called reformate, is unsuitable for direct use in low-temperature PEMFC and AFC, and some trace by-products (notably organosulfur compounds) will poison both high-temperature fuel cells and low-temperature fuel cells. A membrane for separating and purifying hydrogen from reformate must also be chemically compatible with the compounds in the reformate stream. 

Deprotection takes place by catalytic hydrogenation in the presence of palladium under a hydrogen pressure of a few atmospheres. This reforms the hydroxyl groups and toluene is easily separated. Hydrogenolysis by transfer does not require any special equipment. An alcohol solution is heated at reflux with the protected sugar in the presence of palladium over charcoal with, as hydrogen donor, cyclohexene or cyclohexadiene which aromatizes in the reaction. 

The main thermodynamic properties of the methanol and ethanol steam reforming reactions are plotted in Fig. 18.3 for comparison. Both are endothermic. However, they are spontaneous, due to large entropy changes associated with the dissociation of the alcohols. Spontaneous methanol dissociation is obtained at a lower temperature (AG < 0 at - 325 K) compared to ethanol (AG < 0 at 475 K), which requires practical dissociation temperatures of 600 K. It is therefore possible to incorporate a palladium permeation membrane into a methanol steam reformer (in such cases, both processes are operating at the same temperature) whereas for ethanol, reforming and extraction of hydrogen are usually performed in two separate... 

A concept for a methanol (or ethanol) fuel processor based upon steam reforming and membrane separation was presented by Gepert et td. [400]. As shown in Figure 5.33, the alcohol/water mixture was evaporated and converted by steam reforming in a fixed-bed catalyst, into which palladium capillary membranes were inserted. The retenate then entered the combustion zone, which was positioned concentrically around the reformer bed at the reactor wall. Air was fed into the combustion zone and residual hydrogen, carbon monoxide and unconverted methanol combusted therein. The sealing of the membranes at the reactor top was an issue solved by air-cooled elastomers. 

Note-. Light gas + LPG reformed to hydrogen and cracked to ethylene. a-Olefins separated for use in polyethylene or detergents. Alcohols and ketones extracted. 

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