Pieter Vandezande’s research while affiliated with Flemish Institute for Technological Research and other places

Organic solvent nanofiltration (OSN) is gradually expanding from academic research to industrial implementation. The need for membranes with low and sharp molecular weight cutoffs that are able to operate under aggressive OSN conditions is increasing. However, the lack of comparable and uniform performance data frustrates the screening and membrane selection for processes. Here, a collaboration is presented between several academic and industrial partners analyzing the separation performance of 10 different membranes using three model process mixtures. Membrane materials range from classic polymeric and thin film composites (TFCs) to hybrid ceramic types. The model solutions were chosen to mimic cases relevant to today's industrial use: relatively low molar mass solutes (330–550 Da) in n‐heptane, toluene, and anisole. A variety of organic solvent nanofiltration membranes were screened and characterized for three industrial model cases. The influence of setups and membrane type on the results were statistically verified and commented.

Lignin is a renewable and abundant source for production of bio-based chemicals and is a valuable alternative to crude oil to obtain aromatic building blocks. It is built from aromatic units with strong chemical linkages, which need to be cleaved to enable the use of the aromatic compounds in industrial applications. In addition to depolymerizing lignin, efficient fractionation and conversion of the resulting complex mixtures is an essential step in the valorization of lignin derivatives for different applications. In this work, we studied the separation of a lignin oil obtained by catalytic cleavage in supercritical ethanol (scEtOH) of technical lignin produced by means of soda pulping of wheat straw. The use of six commercial polymeric nanofiltration (NF) membranes and one in-house developed Grignard-functionalized ceramic membrane was investigated for the fractionation of a mixture of lignin derivatives. Separation by molecular weight (MW) was observed with the polymeric NP030 membrane but not with the other membranes tested. The development of a protocol using this membrane in the diafiltration mode for fractionation of crude lignin oils (CLOs) is discussed.

Hydrophobic pervaporation (PV), allowing for the separation of an organic component from an aqueous stream, was investigated for in situ acetone removal from a transamination reaction. A poly(dimethylsiloxane) membrane was applied in a coupled enzymatic process at 5 L scale. Among the four components, there was no loss of donor and product amines through PV which was highly desirable. However, in addition to removal of acetone, there was also an unwanted loss of acetophenone (substrate ketone) because of PV. The coupled enzyme‐PV process resulted in 13% more product formation compared to the control process (where no PV was applied) after 9 h. Results from a qualitative simulation study (based on partial vapor pressures and a vapor–liquid equilibrium of the feed solution) indicated that PV might have an advantage over direct distillation strategy for selective removal of acetone from the reaction medium. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2731, 2019

Pectin oligosaccharides (POS) have been indicated as a new class of potentially prebiotic compounds, which can be produced from pectin-rich food byproducts. In the present study, different technological means of POS production were explored to produce tailor-made POS mixtures starting from sugar beet pulp. The overall POS production process consisted of two steps: the extraction of pectin and the hydrolysis of pectin to tailored POS by combined hydrolysis/fractionation approaches. Different extraction as well as hydrolysis and fractionation methodologies were applied. The obtained POS were characterized for their total galacturonic acid content and, at a deeper level, using a HILIC-ESI/MS methodology, for the POS structure and composition. The composition of POS fractions was studied as function of the technology used to obtain them. Finally, the potential prebiotic properties of the POS mixtures obtained were thoroughly explored by several in vitro experiments aimed at detecting lactic acid bacteria (LAB) stimulation by POS fractions. Several fractions were very efficient in stimulation, in a species-dependent way. The best fractions overall were in general those rich in arabinans having low degree of polymerization, obtained with the enzymatic extraction of the biomass and subsequent fractionation with low-medium molecular weight cut off. Quite interestingly, no POS fraction was able to stimulate pathogenic E.coli strains. The data here reported clearly indicate the possibility to obtain diverse fractions with different prebiotic properties starting from the same biomass, and outline a clear potential for POS obtained by sugar beet pulp with the appropriate technology to act as prebiotic compounds.

Apple pomace can be used as resource for the extraction of phenolic compounds with antioxidant properties. Pressing of apple in juice and pomace at lab scale in open air (aerobic) and under N2 atmosphere (anaerobic) showed a recovery of phenolic compounds of 85% in juice and pomace after anaerobic pressing, compared to 43% after aerobic pressing, indicating loss of phenolic compounds by oxidation and the advantage of anaerobic over aerobic pressing. After a membrane screening and concentration test at lab scale, the commercial nanofiltration membrane NFX was selected to concentrate phenolic compounds in an ethanol : water extract of apple pomace. At pilot scale, the concencentration of 10 selected phenolic compounds and quinic acid increased from 59.5 mg/L in the ethanol : water extract to 1256.1 mg/L in the final retentate, that is, by a factor 21.1. The volume of the crude extract was reduced by a factor of 28.5 during the filtration, indicating some loss of phenolic compounds during pilot testing due to membrane fouling or oxidation of polyphenols. The pilot concentration test using a spiral‐wound membrane module showed good flux and concentration of phenolic compounds, indicating the technical feasibility of membrane technology for efficient concentration of polyphenols in an ethanol : water extraction solvent. Unfortunately, the extraction and concentration process was not economically feasible under the assumptions made. Practical applications The valorization of food waste for the production of high‐added value products is an increasingly hot topic. Phytochemicals are present in relatively low concentration in the fruit matrix, and concentration in the extraction solvent is necessary to develop an industrially relevant process. In this study, membrane filtration was selected for concentration due to its low energy consumption and mild processing conditions compared to other technologies. Membrane screening and testing at lab and pilot scale with techno‐economic assessment can be used by food and nutraceutical industries to evaluate membrane technology for concentration of phytochemicals extracted from agroindustrial by‐products.

Valorization of biomass calls for development of new and/or optimized process technologies. Cost-effective separation processes are of utmost importance to separate biomass components on an industrial scale. Also the complexity of biomass depolymerization/hydrolysis processes increases even further the need for efficient separation processes. Within this study, the use of commercial nanofiltration membranes and in-house developed Grignard-functionalized ceramic membranes has been investigated for the fractionation of a mixture of lignin derivatives, obtained from the depolymerization of Organosolv lignin according to the derivatization followed by reductive cleavage (DFRC) approach. Gas chromatography coupled with mass spectrometry, liquid chromatography-high resolution -mass spectrometry and gel permeation chromatography have been intensively used for the characterization of the depolymerization mixture before and after membrane separation. Higher permeation fluxes are observed with the modified ceramic membranes (25-30 L/m².h) exhibiting amphiphilic surface properties. Separation of lignin derivatives by molecular weight based on size-exclusion has been observed with the polyamide Desal-5DK membrane, while a separation governed by solute-membrane interactions appears to be possible with the functionalized ceramic membranes, where retentions for individual solutes are highly dependent on the chemistry of the grafted groups. For instance, it has been observed that aromatics such as 2,6-dimethoxy-4-propenylphenol are either rejected by or preferentially transported across the membrane, depending on the chosen membrane functionalization. This offers perspectives towards the development of membrane processes for fine separation of small lignols and to enable the use of these molecules in chemical and materials applications.

Membrane assisted extraction in a contactor, which allows for the separation of the reaction components between two immiscible liquid phases, was applied for transamination. The reaction was conducted in an organic solvent which resulted in two benefits: higher solubility of the poorly water soluble substrate benzyl acetone, and the possibility of product removal in an aqueous phase. The aqueous phase was circulated across the shell of a hollow fiber membrane module and the organic phase (n-heptane) through the lumen. Approaches to extract the product amine, 1-methyl-3-phenylpropylamine proved beneficial to reduce its inhibitory effects, while providing an equilibrium shift aiding in higher product formation. After 72 h of operation in membrane contactor, 99% substrate conversion was observed.

Lignocellulosic plant biomass is a renewable and abundant source for the production of bio-based fuels, chemicals and chemical building blocks. Efficient fractionation and conversion of these feedstocks are an essential step in the valorization of the cellulose, hemicellulose and lignin fractions. The use of a new two-stage alkaline oxidation (AlkOx) process has been investigated for the pretreatment of softwood in presence of sodium carbonate. Within this study, the use of commercial polymeric and ceramic ultrafiltration membranes for the purification and concentration of lignin from the spent liquor of the AlkOx process has been evaluated enabling further valorization thereof. Higher permeation fluxes were observed, ranging from 30 to 139 L/m² h, depending on the hydrophilicity, pore size and structure/chemistry of the membrane. High lignin retentions have been obtained for all membranes. Diafiltration of the spent liquor using the ESP04 membrane enables the purification of the lignin fraction with an efficient removal of the impurities originating from both the lignocellulosic material and the pretreatment. The integration of both processes allows the co-valorization of the lignin fraction, besides the primary C5/C6 sugar fraction produced in the two-stage alkaline oxidation of softwood. Also some preliminary techno-economic calculations have been realized on the membrane separation process to asses the economic potential of this technology.