Chemical and Biomolecular Engineering - Research Publications
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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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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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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.
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ItemErratum to ‘Single and binary ion sorption equilibria of monovalent and divalent ions in commercial ion exchange membranes’ [Water Research 175 (2020) 115681] (Water Research (2020) 175, (S0043135420302177), (10.1016/j.watres.2020.115681))(PERGAMON-ELSEVIER SCIENCE LTD, 2021-05-15)The authors regret that in the original version, the y-axes of Figures 5 and 8 were labelled incorrectly. The corrected figures are presented here. The authors would like to apologise for any inconvenience caused.
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ItemLactic Acid and Salt Separation Using Membrane Technology(MDPI, 2021-02-01)Acid whey is a by-product of cheese and yoghurt manufacture. The protein and lactose within acid whey can be recovered using nanofiltration and electrodialysis, but this leaves a waste stream that is a mixture of salts and lactic acid. To further add value to the acid whey treatment process, the possibility of recovering this lactic acid was investigated using either low energy reverse osmosis membranes or an electrodialysis process. Partial separation between lactic acid and potassium chloride was achieved at low applied pressures and feed pH in the reverse osmosis process, as a greater permeation of potassium chloride was observed under these conditions. Furthermore, lactic acid retention was enhanced by operating at lower temperature. Partial separation between lactic acid and potassium chloride was also achieved in the electrodialysis process. However, the observed losses in lactic acid increased with the addition of sodium chloride to the feed solution. This indicates that the separation becomes more challenging as the complexity of the feed solution increases. Neither process was able to achieve sufficient separation to avoid the use of further purification processes.
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ItemThe application of forward osmosis to dairy processing(Elsevier, 2020-09-01)This work assesses the feasibility for concentrating process streams within dairy processing facilities using commercial forward osmosis membranes; to increase their total solids concentrations before entering energy intensive unit operations including thermal evaporators and spray dryers. These streams include demineralised whey, lactose, whey protein concentrate, sweet whey and skim milk. FTSH2O cellulose acetate (CTA) and Aquaporin flat sheet membranes are used with magnesium chloride concentrations of 1.66 ± 0.12 M as the draw solution. The experimental data are fitted to conventional mathematical models for forward osmosis, further modified by considering the nonlinear relationship between osmotic pressure and solute concentration. The diffusion coefficients of magnesium chloride in 1.6 M solutions at 10 °C, 20 °C and 50 °C are obtained and reported for the first time. Minimal fouling and a significantly smaller degree of concentration polarisation was observed on the membrane surface during lactose concentration compared to the concentration of other dairy solutions, due to the absence of proteins and calcium phosphate salts. The transfer of magnesium into the concentrated products was monitored and shown to be below 100 mg per 100 g dry powder. Acid cleaning alone was not effective in recovering pure water flux, and enzyme cleaners at neutral pH were needed given the limited pH tolerance (3–8) of the CTA membranes. Total solids concentrations of the concentrated dairy streams by forward osmosis (up to 40%) exceed those which can be achieved by nanofiltration and reverse osmosis (i.e., 15–20%). This study shows that forward osmosis is an effective approach to concentrate relevant dairy streams to achieve high concentration factors (e.g. >4 for sweet whey samples) without jeopardising product quality.
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ItemPilot Study on the Removal of Lactic Acid and Minerals from Acid Whey Using Membrane Technology(American Chemical Society (ACS), 2020-02-24)Acid whey presents a major disposal issue for the dairy industry due to its high lactic acid and mineral concentrations. In this work, the feasibility of using membrane technology to treat acid whey to produce high quality whey powder was demonstrated at pilot scale. Three process combinations were tested, namely, (1) ultrafiltration and electrodialysis; (2) ultrafiltration, nanofiltration, and electrodialysis; and (3) ultrafiltration, dia-nanofiltration, and electrodialysis. All three combinations were successful in reducing the levels of lactic acid and minerals in acid whey. However, the lowest ratio between lactic acid and lactose (0.017 g lactic acid/g of lactose) was obtained with the process that utilized dia-nanofiltration. The energy required for the electrodialysis of the ultrafiltration permeate and dia-nanofiltration retentate were comparable (7.5 and 7.8 kWh/tonne of feed, respectively). However, the dia-nanofiltration retentate was at least 3.5 times more concentrated than the ultrafiltration permeate, thus reducing the annual energy consumption and capital investment of the electrodialysis unit. The product of the nanofiltration and electrodialysis process was successfully dried to produce a powder with an ash and moisture content of 4% and 2.5%, respectively.
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ItemEutectic freeze crystallization of saline dairy effluent(Elsevier, 2020-04-15)The disposal of saline effluent in the dairy industry is subject to increasingly strict regulatory requirements. In this work, eutectic freeze crystallization (EFC) was investigated as a mechanism for the simultaneous separation of salts and ice in a typical saline effluent, namely salty whey. Experiments were conducted using salty whey samples collected from a dairy processing facility. The eutectic point of the salty whey was determined using differential scanning calorimetry and was found to be lower than that of NaCl solutions (−24 °C for salty whey vs. −21 °C for aqueous NaCl solutions). Crystallization experiments were then used to construct the phase diagram of this dairy stream under equilibrium conditions. The change in cation composition in the supernatant at the eutectic temperature was measured as a function of time and showed that pure NaCl salts and ice formed within 5 min after this temperature was reached. The energy consumption of this process was estimated to be ~120 kWh/t for salty whey, which is comparable to that for conventional thermal crystallization of brine.
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ItemSingle and binary ion sorption equilibria of monovalent and divalent ions in commercial ion exchange membranes.(Elsevier, 2020-05-15)The co-ion and counter-ion sorption of monovalent (Na+, K+, Cl- and NO3-) and divalent ions (Ca2+ and SO42-) in commercial Neosepta ion exchange membranes were systemically studied in both single and binary salt systems. The new generation of Neosepta cation exchange membrane (CSE) showed a significant difference in water uptake and co-ion sorption compared to the earlier generation (CMX). Use of the Manning model confirmed that there were significant differences between these membranes, with the estimated value of the Manning parameter changing from 1.0 ± 0.1 for CMX to 2.8 ± 0.5 for CSE. There were fewer differences between the two Neosepta anion exchange membranes, AMX and ASE. In single salt solutions, potassium sorbed most strongly into the cation exchange membranes, but in binary salt mixtures, calcium dominated due to Donnan exclusion at low concentrations. While these trends were expected, the sorption behaviour in the anion exchange membranes was more complex. The water uptake of both AMX and ASE was shown to be the greatest in Na2SO4 solutions. This strong water uptake was reflected in strong sorption of sulphate ions in a single salt solution. Conversely, in a binary salt mixture with NaCl, sulphate sorption fell significantly at higher concentrations. This was possibly caused by ion pairing within the solution, as well as the strongly hydrophobic nature of styrene in the charged polymer. Water uptake was lowest in NaNO3 solutions, even though sorption of the nitrate ion was comparable to that of chloride in these single salt solutions. In the binary mixture, nitrate was absorbed more strongly than chloride. These results could be due to the low surface charge density of this ion allowing it to bond more strongly with the hydrophobic polymeric backbone at the exclusion of water and other ions.