Carbon dioxide chemical recycling

Direct Methane Conversion, Methanol Fuel Cell, and Chemical Recycling of Carbon Dioxide... 

For my part, although I may be somewhat of a visionary, I see a solution to the problem by chemical recycling of excess carbon dioxide emissions into methyl alcohol and derived hydrocarbon products. 

Besides chemical catalytic reduction of carbon dioxide with hydrogen, which is already possible in the laboratory, we are exploring a new approach to recycling carbon dioxide into methyl alcohol or related oxygenates via aqueous eleetrocatalytic reduction using what can be called a regenerative fuel cell system. The direct methanol fuel cell... 

The chemical recycling of carbon dioxide into usable fuels provides a renewable carbon base to supplement and eventually replace our diminishing natural hydrocarbon resources. Methanol (or dimethyl ether), as discussed, can be readily converted into ethylene or, by further reaction, into propylene. 

Henkel Rearrangement of Benzoic Acid and Phthalic Anhydride. Henkel technology is based on the conversion of benzenecarboxyhc acids to their potassium salts. The salts are rearranged in the presence of carbon dioxide and a catalyst such as cadmium or zinc oxide to form dipotassium terephthalate, which is converted to terephthahc acid (59—61). Henkel technology is obsolete and is no longer practiced, but it was once commercialized by Teijin Hercules Chemical Co. and Kawasaki Kasei Chemicals Ltd. Both processes foUowed a route starting with oxidation of napthalene to phthahc anhydride. In the Teijin process, the phthaHc anhydride was converted sequentially to monopotassium and then dipotassium o-phthalate by aqueous recycle of monopotassium and dipotassium terephthalate (62). The dipotassium o-phthalate was recovered and isomerized in carbon dioxide at a pressure of 1000—5000 kPa ( 10 50 atm) and at 350—450°C. The product dipotassium terephthalate was dissolved in water and recycled as noted above. Production of monopotassium o-phthalate released terephthahc acid, which was filtered, dried, and stored (63,64). 

To complete the. set of possible chemical reactions, consider the combustion of a fuel such as methane with a recirculated flue gas containing m moles of carbon dioxide, but assuming that water vapour has been removed from the recycling flue gas. If the additional air supply (n moles) is assumed to be sufficient for complete combustion, then... 

As a matter of fact, the main advantage in comparison with HPLC is the reduction of solvent consumption, which is limited to the organic modifiers, and that will be nonexistent when no modifier is used. Usually, one of the drawbacks of HPLC applied at large scale is that the product must be recovered from dilute solution and the solvent recycled in order to make the process less expensive. In that sense, SFC can be advantageous because it requires fewer manipulations of the sample after the chromatographic process. This facilitates recovery of the products after the separation. Although SFC is usually superior to HPLC with respect to enantioselectivity, efficiency and time of analysis [136], its use is limited to compounds which are soluble in nonpolar solvents (carbon dioxide, CO,). This represents a major drawback, as many of the chemical and pharmaceutical products of interest are relatively polar. 

Important processes commercially used are the Selexol, the Sulfinol, and the Rectisol processes. In these processes, no chemical reaction occurs between the acid gas and the solvent. The solvent, or absorbent, is a liquid that selectively absorbs the acid gases and leaves out the hydrocarbons. In the Selexol process for example, the solvent is dimethyl ether of polyethylene glycol. Raw natural gas passes countercurrently to the descending solvent. When the solvent becomes saturated with the acid gases, the pressure is reduced, and hydrogen sulfide and carbon dioxide are desorbed. The solvent is then recycled to the absorption tower. Figure 1-1 shows the Selexol process. ... 

Details are given of the enzymatic transformation of polycaprolactone into repolymerisable oligomers in supercritical carbon dioxide. The object was to establish a sustainable chemical recycling system for polycaprolactone. 14 refs. 

Biomass resources are a major component of strategies to mitigate global climate change. Plant growth recycles C02 from the atmosphere, and the use of biomass resources for energy and chemicals results in low net emissions of carbon dioxide. Since the emissions of NOx and SOx from biomass facilities are also typically low, it is a technology that helps to reduce acid rain. 

C 0 and H O, unavoidable by-products of alcohols synthesis. Considering chemical reactions of table H, water and carbon dioxide appear as equiva-lentby-products due to shift conversion equilibrium, equation (1). Most other low temperature alcohol synthesis catalysts have a rather high shift activity as well. CO removal fhom reacted syngas of synthesis loop, before recycling to reactor, leads to a significant decrease of water formation which, in turn, results in a lower water content in the raw alcohols, leading to simplified fhactionation-dehydration processes. 

M. M. Hal man n, Chemical Fixation of Carbon Dioxide Methods for Recycling C02 into Useful Products, CRC Press, Boca Raton, FL, 1993. 

Preparation. The current basic comml procedure, the once-through process (Fig 1), uses liq ammonia and liq carbon dioxide at 1750 to 3000psiand 160—200°. These constituents react to form amm carbonate which is decompd at about 80psi to urea and w. Several variations of the process include a partial recycle process and, the most commonly used technique, the total recycle process. Fig 2 is a diagram of the latter process as adapted for use by the Chemical... 

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