Study On Conversion Of Acetaldehyde In Supercritical Water

Hydrogen production from biomass gasification in supercritical water has been considered as one of the most promising hydrogen production technologies since its first introduction,because of its high conversion rate,low energy consumption,strong adaptability of raw materials,high hydrogen yield,no secondary pollution,etc.The research on biomass supercritical water gasification conversion process is helpful to the development of this technology.The active inorganic potassium in biomass has a significant impact on the gasification process.Therefore,studying the effects of inorganic potassium on biomass gasification conversion process is beneficial to a deeper and more comprehensive understanding of biomass supercritical water gasification conversion process.However,the biomass gasification conversion process is extremely complicated,and the typical intermediate small molecule product acetaldehyde in the biomass gasification process is taken as the research object.Studying the effects of operating conditions and inorganic potassium on the gasification of acetaldehyde supercritical water is conducive to the understanding of the influences of operating conditions and inorganic potassium on biomass gasification,and lays an experimental and theoretical basis for a comprehensive understanding of biomass gasification process in the future.The combination of experiment and theory was used to study the process of acetaldehyde conversion in supercritical water.The effects of reaction temperature,reaction pressure,material concentration,reaction time on the gasification products of acetaldehyde conversion in supercritical water were investigated by continuous supercritical water gasification equipment.The experimental results showed that the gas products mainly included H₂,CO,CO₂,CH₄,and trace amounts of C₂H₆,C₂H₄,C₃H₈ and C₃H₆.The gas products were mainly affected by temperature.The high temperature was favorable for the conversion of acetaldehyde.By combining relevant researches and experimental data,the reaction pathways of acetaldehyde conversion in supercritical water were preliminarily obtained,at high temperature,the direct decomposition reaction of acetaldehyde was dominant.Based on the transition state theory and the quantum chemical calculation software Gaussian09,the theoretical calculations of three basic reactions?carbon monoxide methanation reaction,carbon dioxide methanation reaction,direct decomposition of acetaldehyde?of acetaldehyde conversion in supercritical water were carried out.The study obtained the microscopic reaction mechanism of each basic reaction and found the rate control steps in the microscopic reaction mechanism.Under the reaction conditions of 823K and 23MPa,the reaction path?CO+3H₂?IM1?is the rate control step of the positive reaction of CO methanation reaction.The reaction pathways?IM10?CH₄+2H₂O,CO₂+4H₂?IM1 and CO₂+4H₂?IM4?are the rate control steps of the positive reaction of CO₂ methanation reaction.The reaction route?CH₃CHO?CH₄+CO?is the rate control step of the positive reaction of the direct decomposition reaction of acetaldehyde.The effects of different inorganic potassium salts and different potassium salts concentration on the gasification products of acetaldehyde conversion in supercritical water under different reaction conditions?reaction temperature,reaction pressure,material concentration,reaction time?were investigated by using a continuous supercritical water gasification equipment.The experimental results showed that the gasification rate of acetaldehyde were increased by different potassium salts.At different reaction temperatures,the potassium salts decreased the content of H₂ and increased the content of CO₂ and CH₄,K₂CO₃ and mixed potassium salts decreased the the yields of CO and increased the yields of CO₂ and CH₄,K₂SO₄ and KCl had few effects on the yield.The order of increasing the gasification rate of acetaldehyde by potassium salts at different reaction temperatures was K₂CO₃,mixed potassium salts,KCl,K₂SO₄ from large to small.At different reaction pressures,the potassium salts decreased the content of H₂ and increased the content of CO₂.K₂CO₃promoted the yields of H₂,K₂CO₃ and mixed potassium salts decreased the yields of CO and increased the yields of CO₂.The order of increasing the gasification rate of acetaldehyde by potassium salts at different reaction pressures was K₂CO₃,mixed potassium salts,K₂SO₄,KCl from large to small.The potassium salts reduced the content of H₂ and increased the content of CO₂ at different material concentrations.K₂SO₄ and KCl increased the content of CO slightly,while K₂CO₃ and mixed potassium salts significantly reduced the content of CO,the potassium salts promoted increased the yields of CO₂,K₂CO₃ increased the yields of H₂ and other potassium salts decreased the yields,the potassium salts promoted acetaldehyde conversion,the promotion of K₂CO₃ is particularly obvious.The potassium salts increased the content of CO₂ at different reaction time,and the comprehensive effects of potassium salts on the yields were:K₂CO₃>mixed potassium salts>KCl>K₂SO₄.The order of increasing the gasification rate of acetaldehyde by potassium salts at different reaction times was K₂CO₄,mixed potassium,K₂SO₄ and KCl from large to small.The empirical rate equation for the conversion of acetaldehyde in supercritical water under different potassium salts and potassium concentrations was obtained by establishing a lumped kinetic model,and the effects of potassium salts on the conversion of acetaldehyde were quantified.The calculation results showed that the potassium salts promoted the conversion of acetaldehyde.With the increasing of potassium salts concentration of K₂CO₃,K₂SO₄,KCl and mixed potassium salts,the promotion was more obvious.