Study On The Alkali Diffusion And Permeation Properties Of Autohydrolyzed Poplar Sapwood Chips

Autohydrolysis is a pretreatment with a promising application and is usually combined with other methods for biomass refining.The lignocellulosic materials before and after aotohydrolysis are changed,mainly in the chemical composition and physical structure.The changes in the above two aspects of the lignocellulosic feedstock will exhibit different reaction properties during the alkaline impregnation process.Permeability and alkaline diffusion mass transfer capacity are two important criteria for measuring the impregnation performance of wood chips.In this paper,the effects of autohydrolysis on the chemical composition,pore size distribution and specific surface area of sapwood chips were studied.The NaOH solution was selected as the impregnating solution,the permeability and diffusion mass transfer capacity of sapwood chips before and after autohydrolysis were explored in the process of NaOH solution impregnation.The results showed that the content of pentosan in the sapwood chips decreased with the increase of the CHF.When CHF increased from 2.78 to 73.63,the content of pentosan in the sapwood chips decreased from 21.92%to 12.18%,and the yield of sapwood chips decreased from 98.84%to 87.68%,while the lignin content reduced slightly.The change of the physical properties of the sapwood chips was caused by the change of the chemical composition.The results showed that the specific surface area and porosity of the autohydrolyzed poplar sapwood were increased,and the volume porosity was increased from 77.66%to 79.10%.The permeation and diffusion experiments were carried out on the sapwood chips by NaOH solution before and after autohydrolysis.The radial and axial permeation and diffusion characteristics of the sapwood were studied,respectively.With the increase of CHF,the permeation capacity of the radial poplar sapwood chips increased gradually with the increase of the impregnation time,indicating that the autohydrolysis pretreatment could improve the impregnation process;the effective capillary cross-sectional area(ECCSA)of sapwood chips increased gradually,indicating that the ion transport capacity of the sapwood chips was improved;the ability of the autohydrolyzed sapwood chips to exchange mass with the outside was improved obviously;In addition,the increase of radial diffusion coefficient of the sapwood chips was much higher than that of the axial diffusion coefficient,indicating that the autohydrolysis pretreatment has a greater effect on the radial diffusion of the sapwood chips.