Improvement membrane filterability in nanofiltration of prehydrolysis liquor of kraft dissolving pulp by laccase treatment

Novel TiO2/GO-Al2O3 Hollow Fiber Nanofiltration Membrane for Desalination and Lignin Recovery

Due to its greater physical-chemical stability, ceramic nanofiltration (NF) membranes were used in a number of industrial applications. In this study, a novel NF membrane was prepared by co-depositing a titanium dioxide (TiO₂) and graphene oxide (GO) composite layer directly onto a porous α-Al₂O₃ hollow fiber (HF) support. An 8 µm-thick TiO₂/GO layer was deposited to the surface of α-Al2O3 HF support by vacuum deposition method to produce advanced TiO₂/GO-Al₂O₃ HF NF membrane. Scanning electron microscope (SEM) micrographs, energy dispersive spectrometer (EDS), X-ray powder diffraction (XRD), thermogravimetric analyzer (TGA), porosity, 3-point bending strength, zeta potential analysis, and hydrophilic properties by water contact angle are used for TiO₂/GO-Al₂O₃ HF NF membrane characterization. The results show that the developed membrane's MWCO ranged from 600 to 800 Da. The water flux, rejection of lignin, and sodium ions were 5.6 L/m² h·bar, ~92.1%, and ~5.5%, respectively. In a five-day NF process, the TiO₂/GO-Al₂O₃ HF NF membrane exhibits good lignin permeation stability of about 14.5 L/m² h.

High-performance nanofiltration membranes with a sandwiched layer and a surface layer for desalination and environmental pollutant removal

To overcome the permeability-selectivity limitation and improve the performance of desalination membranes, novel methods and design strategies are needed to prepare new types of thin film composite (TFC) nanofiltration (NF) membranes. In this work, a modified TFC membrane with a sandwiched layer and a surface layer was fabricated through a facile additional two-step approach. The microfiltration (MF) substrate and TFC surface were modified by a cellulose nanocrystal (CNC) sandwiched layer and a polydopamine (PDA) layer, respectively. Scanning electron microscopy (SEM) analysis indicated that the support modified by CNCs presented a more homogeneous surface than the control TFC. Cross-sectional SEM images showed that the underneath MF support, CNC interlayer, polyamide layer and PDA deposition layer were perfectly integrated. The surface charge was determined by an electrophoretic analyzer and revealed that the CNC interlayer increased the membrane electronegativity, while the PDA layer presented the opposite effect. Compared to the control TFC membrane, the solute permeability and rejection of the resultant CNC-TFC-PDA membrane were simultaneously increased, indicating a breakthrough in the trade-off limitation. The modified membranes exhibited a high removal rate for Congo red, Rose Bengal, sodium lignosulfonate and alkaline lignin, suggesting their excellent rejection performance for textile dyes and lignin derivatives. Fouling tests indicated that both the interlayer and surface layer exhibited positive effects on fouling alleviation. The effects of each functional layer were explored, and the main factors for performance improvement, including the modified hydrophilicity, surface charge, pore size and surface roughness, were discussed.

Applications of enzymatic technologies to the production of high-quality dissolving pulp: A review

Recently, the worldwide production of dissolving pulp has grown rapidly. Enzymatic technologies play an important role in producing high-quality dissolving pulp, due to their green, mild conditions, high specificity and efficiency. In this review, the relevant publications regarding enzyme applications for dissolving pulp are summarized. Cellulase and xylanase are two major enzymes used for this purpose. Cellulase can improve the quality of dissolving pulp, such as improving the reactivity/accessibility, controlling the intrinsic viscosity and adjusting the molecular weight. Xylanase is mainly used to increase the purity of the dissolving pulp and improve the pulp brightness. Furthermore, in order to increase the enzymatic treatment efficiency, the enzymatic technology can be combined with other techniques, including mechanical refining, fiber fractionations, alkali treatment and use of additives. The advantages, disadvantages and practical implications are analyzed. Also, the potential of other enzymes (such as laccase, mannanase) are discussed.