Carbon dioxide utilization in the food industry. Synthesis of carbohydrates and their precursors via photocatalytic reduction of carbon dioxide
Abstract: Today’s society strives to eliminate the carbon dioxide (CO2) emissions, which is the main greenhouse gas emitted through anthropogenic activities and contributes to climate change. In this project utilization of CO2 emissions from waste to energy plants to carbohydrates via photocatalytic reduction with water and further carbon coupling reactions is investigated. Two routes for the synthesis of carbohydrates have been investigated. Both methods use photocatalytic reduction of carbon dioxide to methanol and then proceed via different steps to produce carbohydrates or their precursors. The first route uses aldol condensation as the main method for the formation of carbon-carbon bonds and the second route is based on the formose reaction that uses formaldehyde as a reactant. The waste incineration plant selected for this study was the one located in Kil, Sweden. This plant processes 15590 tons of waste per year and emits 16366.5 tons of carbon dioxide per year. In order to separate carbon dioxide from the flue gas stream, MEA absorption was chosen as the best option due to its high efficiency. The presented processes have negative carbon dioxide emissions due to the fact that they convert of 16.4% of the waste incineration CO2 emissions into useful products and do not generate any emissions of their own. The aldol condensation pathway exhibits an efficiency of 1.3% when considering only food industry products and 2.5% when including other products that are useful to manufacture solvents, lubricants, or pharmaceuticals. The total amount of food industry products obtained is 3.9 kg/h with the energy requirements being was 159550 kJ/kgproduct. The formose reaction route yields 15.4 kg/h of only food industry products, mainly glucose, and exhibits an efficiency of 5%. The power requirements equal to 90099 kJ/kgproduct. The formose route was found to have higher yield and efficiency, and to be more energy consuming but also more energy efficient. Economic data was difficult to find due to the fact that photocatalytic processes are not commercial yet.
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