Low-Molecular-Weight Lignin Recovery with Nanofiltration in the Kraft Pulping Process

Abstract

Kraft lignin is an underutilized resource from the pulp and paper industry with the potential of being a key raw material for renewable fuels and chemicals. The separation of high-molecular-weight lignin from black liquor by ultrafiltration has been widely investigated, while the permeate containing low-molecular-weight lignin has received little attention. Nanofiltration can concentrate the low-molecular-weight lignin. This work, therefore, evaluates nanofiltration for the separation and concentration of low-molecular-weight lignin from the ultrafiltration permeate. For this study, eight flat polymeric sheet membranes and one polymeric hollow fiber membrane, with molecular weight cut-offs ranging from 100 to 2000 Da, were tested. A parametric study was conducted at 50 °C, 2.5–35 bar, and crossflow velocity of 0.3–0.5 m/s. At a transmembrane pressure of 35 bar, the best performing membranes were NF090801, with 90% lignin retention and 37 L/m2·h, and SelRO MPF-36, with 84% lignin retention and 72 L/m2·h. The other membranes showed either very high lignin retention with a very low flux or a high flux with retention lower than 80%. Concentration studies were performed with the two selected membranes at conditions (A) 50 °C and 35 bar and (B) 70 °C and 15 bar. The NF090801 membrane had the highest flux and lignin retention during the concentration studies. Overall, it was shown that the nanofiltration process is able to produce a concentrated lignin fraction, which can be either used to produce valuable chemicals or used to make lignin oil.

A Comprehensive Review on Pulp and Paper Industries Wastewater Treatment Advances

“…The separation of high-molecular-weight lignin from black liquor has been achieved by UF, but the presence of low-molecular-weight lignin in the UF permeate has been little studied. The results of nanofiltration of a UF permeate with polymeric membranes have demonstrated that lignin can be recovered with a maximum recovery of 94% at a TMP of 35 bar . Furthermore, separate studies examined the effects of activated carbon nanoparticles (AC) and carbon nanotubes (CNTs) on polymeric membranes, and the results indicated lignin removal of 80–98% from black liquor with a 90% water recovery due to membrane modification. , Overall, NF treatment technology is not yet cost-effective for paper recycling processes, due to the energy consumption and pretreatment unit required …”

Study of CFD-DEM on the Impact of the Rolling Friction Coefficient on Deposition of Lignin Particles in a Single Ceramic Membrane Pore

“…The commonly used lignin separation methods include acid precipitation and membrane separation methods [8]. The acid precipitation method is characterized by a simple process and a low cost, but it requires a quantity of acid, which easily causes secondary pollution.…”

Monitoring Membrane Fouling Using Fluid Dynamic Gauging: Influence of Feed Characteristics and Operating Conditions

“…Their subsequent separation can be accomplished using membrane processes [2]; however, these wood constituents can potentially foul the membrane systems employed in the fractionation and concentration of the desired components. Studies on pressure-driven membrane filtration have been conducted using process waters from thermomechanical pulp mills [3][4][5], Kraft black liquor [6][7][8], and spent sulfite liquor [9][10][11]. These studies highlight the complex interactions of wood components, necessitating advanced techniques for monitoring their fouling behavior rather than relying solely on changes in permeate flux and transmembrane pressure (TMP).…”