The Research Of Mass Transfer Of Liquid Membrane In Biomass Catalytic Transformation Based On Lattice Boltzmann Method

The extensive use of fossil energy,such as oil and coal,has brought serious environmental pollution.And the fossil energy is not renewable.The development and utilization of biomass resources have attracted more and more researchers.In recent years,biomass energy has gradually become an important part of China's energy.At present,biomass conversion and utilization research has made some progress,but these studies are mainly focused on the experimental aspect,theoretical research is still very lack.In the limited theoretical research literature,most of them focus on the direction of cellulose pyrolysis and cellulose hydrolysis performed enzymatically,and the numerical simulation research on the direction of cellulose catalytic hydrolysis is rarely reported.Based on this,the numerical simulation method was applied in the liquid membrane catalyzed hydrolysis of cellulose to obtain HMF,and the synergistic mechanism of mass transport and reaction in the multiphase system was studied.In this paper,the reaction of hydrolysis of cellulose to HMF catalyzed by liquid membrane was analyzed in detail.And the corresponding reaction kinetics models were established for the water-tetrahydrofuran biphase system(closed system)and gas-liquid biphase system(open system).The lattice Boltzmann method was used to simulate the reaction and mass transfer process.Lattice Boltzmann method,as a new computational fluid dynamics method,has unique advantages in complex interface and multiphase flow.However,it has not been used in cellulose multiphase hydrolysis.In order to establish lattice Boltzmann model for the reaction,two modifications are made on the pseudo-potential multiphase model and the mass transfer model.First,based on the original pseudo-potential multiphase model,the Carnahan-Starling state equation was coupled to the lattice Boltzmann equation to achieve a stable two-phase flow with a large density ratio.The second is to add an additional collision operator into the basic Boltzmann equation for mass transfer in reference to the recoloration process of the color multiphase model,which can achieve the goal of smooth transition of solute concentration at the two-phase interface.A single particle liquid membrane catalytic model was established to simulate the process of multiphase reaction and interphase mass transfer.The self-written C++program code is verified in several ways,and the feasibility of the model is proved.The single particle liquid membrane catalytic model was applied to two biphasic catalytic systems(the boundary conditions of the model were changed correspondingly according to the differences between the two systems),and a series of multiphase reactions and mass transfer processes of cellulose hydrolysis to produce HMF were simulated.The results of the simulation clearly showed the change of solute concentration and transport direction during the reaction.THE generated HMF was quickly transferred out of the reaction system,and the HMF concentration in the liquid film remained at a low value.This is the reason why the two-phase system can efficiently catalyze the hydrolysis of cellulose to produce HMF.In addition,the effects of liquid film thickness and airflow velocity on HMF yield were investigated.The simulation results were compared with the experimental results in the literature to obtain a convincing conclusion.The results showed that a smaller liquid film thickness was beneficial to improve HMF yield in the water-tetrahydrofuran biphase system,and a larger airflow velocity was beneficial to improve HMF yield in the gas-liquid biphase system.However,when airflow velocity reached a certain value,continued increase in airflow velocity was not helpful to improve HMF yield.