Process Intensification Of Mixing And Conversion In A Soft-Elastic Bioreactor With Reciprocating Flow

As a clean and efficient renewable energy source,biomass energy has significant energy-saving and emission-reducing effects and is expected to become an important alternative to fossil fuels in the future.In the process of biomass conversion and utilization,it usually needs to be carried out under high concentration of biomass to ensure high product concentration,reduce the cost of product separation and purification later,and improve the overall economic feasibility of the process.However,as the concentration increases,the free water content of the system decreases dramatically,leading to an increase in the mass transfer resistance between the catalyst and the substrate,which not only reduces the accessibility between the substrate and the catalyst,but also leads to a local accumulation of products and a decrease in the conversion rate.Mixing can significantly reduce the mass transfer resistance to increase the accessibility between substrate and catalyst,further reduce the amount of catalyst.At the same time,it can strengthen the mass transfer and prevent the local accumulation of products which can reduce product inhibition,and ultimately improve the yield and conversion rate of products.In this paper,based on the bionics,we designed a soft-elastic bioreactor(SER)with reciprocating flow based on the characteristics of the digestive tract of insects and herbivores that can degrade biomass efficiently in nature,to achieve efficient mixing of high-concentration substrates and improve the conversion rate.Through visual experiments,the mixing enhancement mechanism of SER was studied,and the influence of different reactor parameters and fluid properties on the mixing performance of SER was explored.On this basis,the transfer and transformation characteristics in the SER with ABTS oxidation,starch hydrolysis and lignocellulose hydrolysis were experimentally studied.The main research results are as follows:(1)With the increase of reciprocating flow frequency,hose length and maximum expansion amplitude,the mixing performance of the SER increased and tended to be stable.When the reciprocating flow frequency increased from 8 cpm to 12 cpm,the mixing time decreased by 75 %.When the maximum expansion increased from 41 mm to 46 mm,the mixing time decreased by 58 %.When the hose length increased from 2.2cm to 3 cm,the mixing time decreased by 53 %.The influence of the maximum expansion and hose length on the mixing performance of SER can be uniformly characterized by the expansion volume.In high viscosity fluid medium,the mixing performance of soft-elastic reactor is better than that of rigid reactor.(2)The experimental results of ABTS oxidation reaction showed that under the liquid phase reaction conditions,when the fluid viscosity did not change with the reaction,the higher the working fluid viscosity was,the worse the mixing performance was,and the lower the ABTS conversion ratio in the same time was.Increasing the frequency of reciprocating flow could enhance the mixing,effectively improved the ABTS conversion rate and ratio.In addition,the higher laccase concentration was,the faster ABTS conversion rate was,and the effect of fluid viscosity on ABTS conversion rate was more obvious.(3)The experimental results of starch hydrolysis showed that the viscosity of the fluid decreased with the reaction in the initial stage in liquid phase.At this time,increasing the frequency of reciprocating flow could effectively enhance the fluid mixing,thereby increasing the initial hydrolysis rate of starch.However,as the reaction proceeded,the viscosity of the fluid decreased rapidly,the mixing of the fluid and the reaction rate in the reactor increased.The effect of the initial viscosity of the fluid and the reciprocating flow frequency on the starch conversion ratio decreased significantly.In addition,compared with the SER,the increase of fluid viscosity in the reciprocating rigid reactor significantly weakened the mixing performance of the rigid reactor,and the distribution of maltose concentration in the reactor was uneven,which significantly affected the starch hydrolysis rate.(4)The lignocellulose slurry with particle size distribution of 20～200 μm,concentration of 2.5% w/v and 5% w/v could be kept in a uniform mixing state in the SER at a reciprocating frequency of 8 cpm.Under the reciprocating flow frequency of 8cpm,the sugar concentration of lignocellulose slurry in the SER increased sharply in the first 30 min and reached a stable level around 2 h.The glucose and xylose were evenly distributed in the reactor and the glucose yield reached 75% and the xylose yield reached 27%.At the reciprocating flow frequency of 8 cpm,the mixing performance of the reactor had reached the demand of lignocellulose conversion.Further improving reciprocating flow frequency increased the shear force in the fluid,which reduced the enzyme activity and the production of glucose and xylose,resulting in a slight decrease in the sugar yield of lignocellulose.