Study On Reduction Of Carbon Dioxide By Alkali Metal And Its Borohydride

At present,energy consumption and climate change have become a severe problem due to the use of fossil fuels during various industrial activities and the emission of exhaust gases.In the exhaust gas released,a large amount of carbon dioxide emission is the leading cause of global climate change,and a large amount of CO2 emissions have a significant negative impact on the global environment.By 201 6,the concentration of CO2 in the earth's atmosphere will exceed 400 ppm for the first time,far higher than the 280 ppm levels seen before the start of the industrial revolution.However,as a readily available renewable carbon resource,CO2 is non-toxic,abundant,and economical.People began to pay more attention to the recycling of CO2 resources.One widely accepted idea is that CO2 is so thermodynamically and dynamically stable that it is rarely fully utilized.However,due to the insufficient number of electrons around the carbon atom in the carbonyl group,CO2 can react with alkaline compounds or highly reductive substances.Therefore,we explored the reaction of reducing CO2 by alkali metal and alkali borohydrideFirstly,we systematically studied the thermochemical behavior of alkali metals in the atmosphere of carbon dioxide,and for the first time,studied the properties of hydromethanation of alkali carbonate and carbon(A2CO3@C(A=Li,Na,K))composites formed by the reaction of alkali metals with CO2.The experimental results show that the A2CO3@C composite can produce COx-free methane efficiently and selectively by reacting with H2 at moderate temperatures without the use of a catalyst.In these A2CO3@C composites,the lithium carbonate and carbon(Li2CO3@C)composites showed excellent methanation properties,with methanation selectivity reaching 100%.The yield and molar percentage of methane(CH4)in the gas phase products reaching 30.3%and 26.6%mol%,respectively.It is revealed that the formation of CH4 in the process of adding H2 to A2CO3@C composite is due to the synergistic effect of alkali metal carbonate and elemental carbon.This work provides an alternative to producing methane from CO2 sourcesThen,in this paper,we systematically studied the thermochemical behavior of the alkali borohydride(ABH4(A=Li,Na))in the atmosphere of carbon dioxide,and systematically studied the gas and solid phase products generated by the reaction of ABH4 and CO2 under static pressure.The experimental results show that,through the changes of reaction conditions,such as pretreatment,reaction ratio,and reaction temperature,CO2 can be converted into methane at medium heat by the vast selection and effective use of borohydride.The methanation performance of ABH4 and CO2 after ball mill pretreatment was the best after 24 hours of reaction at a ratio of 2:1 at the temperature of 350?.The yield of CH4 in the gas phase products of LiBH4 or NaBH4 with CO2 could reach 59.63%and 57.4%,respectively This study provides a method for converting CO2 resources to CH4 using ABH4Finally,in this paper,we first studied the solid-gas non-catalytic reaction between alkali borohydride and carbon dioxide under mechanical and chemical conditions.Many researchers have made great efforts to study the reaction process and mechanism of the ABH4 solution with CO2.However,at room temperature,the conversion of CO2 by using ABH4 as a reducing agent and the solid-gas non-catalytic ball-milling reaction between hydrogen donor with CO2 is rare.At ambient temperature,we used the mechanical and chemical reaction between ABH4 and CO2 to find hydrogen and trimethylborane in the gas phase products,and borates,formates and methoxides in the solid phase products.