Electrochemically Assisted Pyrolysis Of Biomass In Molten Carbonates

The environmental pollution and energy shortage caused by the development of industry has drawn great attentions.As the largest developing and agricultural country,China actively develops environmental protection and energy technology.China obtain remarkable biomass resources,especially straw and stover from agriculture residues each year,while its utilization rate is still rare.In recent years,great amount of straw has been abandoned,in situ burning,which,however,not only led to energy waste,but also seriously damaged the environment.Molten salt pyrolysis technology is regarded as a potential technology for the treatment of biomass because of the significant energy conversion rate of raw materials.Previous studies have shown that the main elements of biomass are carbon,hydrogen and oxygen.Compared with the high-quality fuels,the insufficient hydrogen content and excessive oxygen content of biomass resulted in high oxygen content and low quality of its pyrolysis products.Notably,the molten carbonates owned great potential on decarboxylation and demethoxylation,which can further improve its product quality.Related studied indicated that electrochemical oxidation of biomass molecules contributed to conversion of oxygen contented function group to carboxylation and carbonyl group.As a result,it is wisdom to integrate the electrochemical oxidation together with pyrolysis in molten carbonates system,aiming to improve the pyrolysis conversion rate and product quality.In this study,straw was applied as raw material to establish the coupling system of electrochemically assisted pyrolysis of biomass in molten carbonates.The theoretical feasibility of the coupling reactions was examined at first by the measurement of linear voltammetry curve.The effects of reaction parameters such as pyrolysis temperature,particle size of material,current density on the molten carbonates system were also investigated.The results showed that the pyrolysis temperature had the most obvious effect on the pyrolysis conversion rate,as the conversion rate increased rapidly with the temperature increasing beyond 550°C.With the increase of the current density,the content of combustible gas increased first and then decreased,and met its maximum value at 600 m A/cm².In addition,the particle size of 3 mm was chosen as the optimum reaction condition,as the quality of coupling products is the best.Appropriate current density and particle size are beneficial to increase residence time,strengthen the effect of coupling reaction while reduce side-reaction.In this experiment,a simple thermogravimetric analyzer has also been established for kinetic and thermodynamic analyses.The pre-exponential factors of molten carbonates pyrolysis（MCP）and electrochemically assisted molten carbonates pyrolysis（EMCP）systems were 0.22653 and 0.28369,and the activation energy of both were around 24.5 k J/mol,which indicated the addition of electrochemical reaction increased the conversion rate and reaction rate of raw materials without changing the activation energy.The model compound experiments were conducted to illustrate the mechanism of reaction pathways in EMCP system.The results confined that the pyrolysis reactions has been taken on large molecule,such as cellulose and glucose,in the first stage,and resulted in generation of intermediates.The oxygen-containing function groups on the intermediates was oxygenated to carboxyl groups rapidly,followed by the decarboxylation and CO₂ formation.Finally,hydrogen and hydrocarbon products has been generated in both gaseous and liquid products.The EMCP system demonstrated brand new pathway of oxygen atoms transformation and opened new horizon on utilization of biomass resources.