Chemical and Biomolecular Engineering - Research Publications
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ItemSynthesis of N-Acetyllactosamine and N-Acetyllactosamine-Based Bioactives(AMER CHEMICAL SOC, 2021-06-21)N-Acetyllactosamine (LacNAc) or more specifically β-d-galactopyranosyl-1,4-N-acetyl-d-glucosamine is a unique acyl-amino sugar and a key structural unit in human milk oligosaccharides, an antigen component of many glycoproteins, and an antiviral active component for the development of effective drugs against viruses. LacNAc is useful itself and as a basic building block for producing various bioactive oligosaccharides, notably because this synthesis may be used to add value to dairy lactose. Despite a significant amount of information in the literature on the benefits, structures, and types of different LacNAc-derived oligosaccharides, knowledge about their effective synthesis for large-scale production is still in its infancy. This work provides a comprehensive analysis of existing production strategies for LacNAc and important LacNAc-based structures, including sialylated LacNAc as well as poly- and oligo-LacNAc. We conclude that direct extraction from milk is too complex, while chemical synthesis is also impractical at an industrial scale. Microbial routes have application when multiple step reactions are needed, but the major route to large-scale biochemical production will likely lie with enzymatic routes, particularly those using β-galactosidases (for LacNAc synthesis), sialidases (for sialylated LacNAc synthesis), and β-N-acetylhexosaminidases (for oligo-LacNAc synthesis). Glycosyltransferases, especially for the biosynthesis of extended complex LacNAc structures, could also play a major role in the future. In these cases, immobilization of the enzyme can increase stability and reduce cost. Processing parameters, such as substrate concentration and purity, acceptor/donor ratio, water activity, and temperature, can affect product selectivity and yield. More work is needed to optimize these reaction parameters and in the development of robust, thermally stable enzymes to facilitate commercial production of these important bioactive substances.
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ItemPurification of organic acids using electrodialysis with bipolar membranes (EDBM) combined with monovalent anion selective membranes(ELSEVIER, 2021-09-27)The feasibility of using electrodialysis with bipolar membranes (EDBM), combined with monovalent selective anion exchange membranes was investigated to purify organic acids from fermentation broths or wastewater streams. A simulated beet molasses feed containing a mixture of monobasic lactic acid and polybasic citric acid was used for this purpose. The impact of the feed pH, the configuration of the membrane stack and the voltage applied on the selectivity of the process was investigated. At a pH of 9–10 and an electric field intensity of 9 V/cm, a lactic acid product with a purity of at least 97% can be obtained by using both two chamber (BP-A) and three chamber (BP-A-C) configurations with the monovalent selective membrane. When using the BP-A configuration, the hydroxide ions generated by the bipolar membrane compete with the lactate anions to move into the acid solution and so the energy efficiency is lower than with the BP-A-C configuration. To mimic a multiple pass process and increase the lactic acid concentration of the final product, experiments were performed across a range of volume ratios between the feed and acid solutions. As this ratio is varied, the purity of lactic acid produced remains higher than 95% while the energy consumption is essentially unaffected. Due to the osmotic flow of water during experiments, the highest lactic acid concentration that can be achieved is limited to 153 g/L at a volume ratio (VA: VF) of 1:10.
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ItemDirect Air Capture of CO2 by Microalgae with Buoyant Beads Encapsulating Carbonic Anhydrase(AMER CHEMICAL SOC, 2021-07-15)Microalgae cultures have promise as a CO2 sink for atmospheric carbon and as a sustainable source of food and chemical feedstocks. However, large-scale microalgae cultivation is currently limited by the need to provide carbon dioxide from point sources, as the diffusion of atmospheric CO2 is too slow. Carbonic anhydrase (CA) is an effective enzyme to facilitate the dissolution of atmospheric CO2 that could be used to enhance the photosynthetic uptake of this greenhouse gas. Here we investigate a means of retaining CA at the surface of algae ponds to facilitate direct air capture by cross-linking CA with glutaraldehyde (GA) before encapsulation into buoyant calcium alginate beads. Coomassie Blue dyeing and Wilbur-Anderson assays confirmed the successful bonding of CA to the beads. Microscopic images showed the paraffin-embedded alginate framework. The CA-GA beads retain virtually all hydrase activity throughout 10 assay cycles. Compared with a natural growth rate of 22.7 ± 0.5 mg L-1 day-1, free CA and CA-GA beads increased the productivity of Nannochloropsis salina to 37 ± 3 mg L-1 day-1 and 40 ± 1 mg L-1 day-1, respectively. The CA-GA beads further provided a stable growth enhancement for three rounds of microalgae cultivation, confirming that these buoyant beads can be readily recovered and re-used, which is promising for industrial biomass production.
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ItemThe influence of propane and n-butane on the structure and separation performance of cellulose acetate membranes(Elsevier BV, 2021-11-15)This work presents the impact of propane and n-butane on the CO2/CH4 separation performance of both cellulose diacetate (CDA) and cellulose triacetate (CTA) membranes by exposing both pristine membranes to either propane (400 kPa) or n-butane (200 kPa) at room temperature (22 ± 2 °C) for 4 weeks. The propane and n-butane sorption isotherms in both membranes were anomalous at 35 °C. X-ray diffraction (XRD) results indicated that the crystalline nature of both polymers was altered by this exposure, although dynamic scanning calorimetry (DSC) did not detect a significant change in the overall crystallinity. Positron Annihilation Lifetime Spectroscopy (PALS) revealed that the average pore size of the CTA polymer and the number of free volume elements of both membranes also increased, even though the sorption uptake was less than 2 wt%. CO2 and CH4 permeabilities at 35 °C were essentially unaffected by the propane or n-butane exposure, indicating that while the crystalline regions of the polymer were affected, plasticization of the glassy amorphous region did not occur. There was a slight decrease in CH4 permeability for the CDA membrane after n-butane exposure, consistent with a slight decline in the CH4 solubility at this feed pressure. The propane and n-butane permeabilities were 0.029 Barrer at 300 kPa and 0.019 Barrer at 125 kPa for the fresh CTA membrane, but these fell significantly after long term exposure to these gases, possibly due to penetrant clustering.
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ItemImproved carbon dioxide stripping by membrane contactors using hydrophobic electrospun poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) membranes(ELSEVIER SCIENCE SA, 2021-07-17)Electrospun poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) nanofibre membranes are developed for CO2 stripping within a membrane contactor. The porous and hydrophobic nature of the membranes is ideal for membrane CO2 stripping applications, providing fast gas transport, high CO2 recovery and mechanical strength. Three different morphologies of the PVDF-HFP membranes are assessed: nanofibre membranes (NFM), bead-on-string membranes (NFM-BS) and microparticles on nanofibre membranes (NFM-MP). We illustrate that both the bead-on-string and microparticles on nanofibre membranes are more hydrophobic compared to nanofibre constructs and a traditional asymmetric control membrane. The NFM-BS and NFM-MP membranes both exhibit significantly improved CO2 stripping flux over short times, while the NFM-BS membranes provides significantly improved stripping flux over longer times (240 h) compared to all other treatments, including conventional asymmetric phase inversion membranes. The structures may also show promise for membrane distillation applications.
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ItemImproving beta-Galactosidase-Catalyzed Transglycosylation Yields by Cross-Linked Layer-by-Layer Enzyme Immobilization(AMER CHEMICAL SOC, 2020-11-02)The biotransformation of lactose into gut-bioactive glycans catalyzed by β-galactosidase can give economic value to lactose-rich side streams generated in the food or the dairy industry. Herein, we study the immobilization of the commercially used β-galactosidase from Bacillus circulans onto silica particles using an enzyme immobilization technology involving a cross-linked layer-by-layer encapsulation method. The immobilized β-galactosidase was used for the synthesis of N-acetyllactosamine (LacNAc) as an important precursor for numerous bioactive compounds and a prebiotic in itself. Techniques including molecular analysis, enzyme activity determination, secondary structure analysis, thermodynamic characterization, and the determination of thermal and operational stability were conducted to characterize the immobilized enzyme. Changes in the activity of the enzyme after immobilization were attributed to possible changes in electrostatic, covalent, and protein-protein interactions. Immobilization significantly improved the enzymatic LacNAc yield compared to the free enzyme. In turn, this improved the economics and the sustainability of the process. The immobilized enzyme encapsulated in multilayer films was significantly more stable in the presence of divalent cations and its thermostability also substantially increased with the thermal denaturation activation energy increasing from 53 to 294 kJ mol-1. The immobilized enzyme was successfully reused in eight consecutive reaction cycles with no significant reduction in the LacNAc yield. The improved transgalactosylation yield and productivity, higher stability, and reusability obtained with this immobilization method provide new opportunities for industrial applications.
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ItemComposite Membranes with Nanofibrous Cross-Hatched Supports for Reverse Osmosis Desalination(AMER CHEMICAL SOC, 2020-10-07)A novel membrane structure composed of cross-hatched electrospun nanofibers is developed. We illustrate that this novel structure allows for much higher water permeability when used as a support for reverse osmosis thin-film composite membranes. Reinforcement and lamination of the aligned nanofibers generates mechanically robust structures that retain very high porosity and low tortuosity when applied to high pressure desalination operations. The cross-hatched nanofiber layers support the polyamide active layer firmly and reduce resistance to water flow due to the high porosity, low tortuosity, high mechanical strength, and minimal thickness of the structures. The nanofiber composite membrane gives a water flux significantly greater than when a traditional support layer is used, at 99 ± 5 m-2 h-1 with NaCl rejection of 98.7% at 15.5 bar.
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ItemTransforming salty whey into cleaning chemicals using electrodialysis with bipolar membranes(Elsevier, 2020-10-15)Large quantities of salty whey are produced during cheese manufacturing, posing an environmental problem. Here the feasibility of electrodialysis with bipolar membranes (EDBM) is evaluated for the first time as a mechanism to transform this saline effluent into sodium hydroxide and hydrochloric acid for reuse within the factory. This work also seeks to find the maximum acid and base concentration that can be achieved. For a pure sodium chloride solution, maximum acid/base concentrations of 3.6 ± 0.2 mol/L and 3.0 ± 0.3 mol/L are achieved using a stack of ten membranes including four bipolar membranes. The effects of proton leakage and water migration limit the generation of higher concentrations. The presence of calcium phosphate also has a negative effect on the EDBM performance, suggesting that pretreatment to remove this impurity is needed. In industrial practice, this pretreatment could be achieved by recycling around 9% of the base produced to precipitate these salts. The use of a partially cyclic operation allows 99% demineralization of pretreated salty whey, with high purity acid/base solutions of concentration near 3.5 mol/L. This work demonstrates EDBM as an effective process for transforming salty whey into chemicals for clean in place and ion exchange resin regeneration.
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ItemSorption and diffusion of organic acid ions in anion exchange membranes: Acetate and lactate ions as a case study(Elsevier BV, 2020-11-15)In this study, the sorption behaviour and conductivity of two anion exchange membranes (AR103 and AR204) equilibrated with sodium acetate and sodium lactate solutions are studied across a range of concentrations and pH values. The results indicate that the dissociation equilibria of the organic acids differ between the membrane phase and the external solution. There are significant concentrations of the neutral organic acid in the membranes at pH 6.5 even though the dissociation is virtually complete in the external solution. The concentration of this neutral acid increases as the pH is lowered, leading to a reduction in membrane conductivity. The diffusion coefficients of acetate and lactate ions in these membranes are determined from conductivity data. The results show that these diffusion coefficients are relatively constant but decrease slightly with an increase of external solution concentration due to osmotic deswelling. The diffusion coefficient of the acetate anion decreases as the pH falls, possibly due to dimer formation. Models extended from Manning's condensation theory have been utilized in the prediction of the co-ion concentrations within the membrane and the diffusion coefficients of the lactate and acetate anions. There is an excellent agreement between the experimental values of these parameters and the model predictions for the sodium lactate system but the model is unable to accurately fit the sodium acetate data.