Weak Base Anion Exchange Resin Research Articles

A Whole-Process Visible Strategy for the Preparation of Rhizomucor miehei Lipase with Escherichia coli Secretion Expression System and the Immobilization.

Rhizomucor miehei (RM) lipase is a regioselective lipase widely used in food, pharmaceutical and biofuel industries. However, the high cost and low purity of the commercial RM lipase limit its industrial applications. Therefore, it is necessary to develop cost-effective strategies for large-scale preparation of this lipase. The present study explored the high-level expression of RM lipase using superfolder green fluorescent protein (sfGFP)-mediated Escherichia coli secretion system. The sfGFP(-15) mutant was fused to the C-terminus of RM lipase to mediate its secretion expression. The yield of the fusion protein reached approximately 5.1g/L with high-density fermentation in 5-L fermentors. Unlike conventional secretion expression methods, only a small portion of the target protein was secreted into the cell culture while majority of the fusion protein was still remained in the cytoplasm. However, in contrast to intracellular expression, the target protein in the cytoplasm could be transported efficiently to the supernatant through a simple washing step with equal volume of phosphate saline (PBS), without causing cell disruption. Hence, the approach facilitated the downstream purification step of the recombinant RM lipase. Moreover, contamination or decline of the engineered strain and degradation or deactivation of the target enzyme can be detected efficiently because they exhibited bright green fluorescence. Next, the target protein was immobilized with anion-exchange and macropore resins. Diethylaminoethyl sepharose(DEAE), a weak-basic anion-exchange resin, exhibited the highest bind capacity but inhibited the activity of RM lipase dramatically. On the contrary, RM lipase fixed with macropore resin D101 demonstrated the highest specific activity. Although immobilization with D101 didn't improve the activity of the enzyme, the thermostability of the immobilized enzyme elevated significantly. The immobilized RM lipase retained approximately 90% of its activity after 3-h incubation at 80°C. Therefore, D101 was chosen as the supporting material of the target protein. The present study established a highly efficient strategy for large-scale preparation of RM lipase. This innovative technique not only provides high-purity RM lipase at a low cost but also has great potential as a platform for the preparation of lipases in the future.

Adsorption and Desorption Behavior and Mechanism of Ruthenium in Nitrite-Nitric Acid System.

Ruthenium is required to separate from high-level liquid waste (HLLW) because Ru is a valuable resource and is negatively influential on the vitrification process of HLLW. However, the separation of Ru is very challenging due to its complicated complexation properties. In this study, the adsorption and desorption characteristics of ruthenium on a synthesized SiPyR-N3 (weak-base anion exchange resin with pyridine functional groups) composite were investigated in nitric acid and nitrite-nitric acid systems, respectively, and the adsorption mechanism was explored. The experimental results showed that SiPyR-N3 has a significantly better adsorption effect on Ru in the nitrite-nitric acid system than in the nitric acid system, with an increase in the adsorption capacity of approximately three times. The maximum adsorption capacity of Ru is 45.6 mg/g in the nitrite-nitric acid system. The SiPyR-N3 possesses good adsorption selectivity (SFRu/other metal ions is around 100) in 0.1 M NO2--0.1 M HNO3 solution. The adsorption processes of Ru in the two different systems are fitted with the pseudo-second-order kinetic model and Langmuir model for uptake kinetics and adsorption isotherms, respectively. The results obtained from the FT-IR, XPS, and UV absorption spectrometry indicate that NO2- was involved in the adsorption process either as a complexing species with the metal ions or as free NO2- from the solution. A 0.1 M HNO3 + 1 M thiourea mixed solution shows effective desorption performance, and the desorption efficiency can reach 92% at 328 K.

Effective isolation of succinic acid from aqueous media with the use of anion exchange resins.

The primary objective of this study was to examine the isolation of succinic acid (SA) from aqueous-based solutions through the utilization of adsorption and ion exchange methods. Four kinds of anion exchange resins were employed, two of which were strong basic (Lewatit M-500 and Lewatit M-600), and the other two were weak basic (Lewatit MP-64 and Lewatit MP-62). The impacts of various variables on the efficiency of the process were examined. The aqueous pH strongly influenced the separation yield. Weak basic exchangers achieved the maximum yield at pH 2.1. However, the highest performance with Lewatit M-600 and Lewatit M-500 was obtained at pH 5 and 6, respectively. The SA separation with the tested resins reached equilibrium in about an hour. The recovery data revealed consistency with the Langmuir isotherm and pseudo-second-order kinetics. Efficiency improved with resin dosage and reduced with SA concentration. It was found that weak basic anion exchange resins were more efficient than strong basic exchangers for the recovery process. Among the resins tested, Lewatit MP-62 demonstrated the highest sorption capacity of 321 mg g-1 and 97.5% yield. The performance of the system decreased with temperature for all alternatives tested; however, its impact was not notable. The isolation process had an exergonic, exothermic, and favorable character based on the thermodynamic constants. Acid-loaded resins were successfully regenerated using trimethylamine and HCl for weak and strong anion exchange resins, respectively.

Preparation of exopolysaccharides by heat-resistant Weizmannia coagulans using anion exchange resins

Weizmannia coagulans with high temperature tolerance and stability was selected for the production of exopolysaccharides (EPS) at the fermentation temperature of 52 °C. The weak basic anion exchange resin was employed in the fermentation for the construction of buffer system to neutralize some lactic acid and form intermolecular hydrogen bonds with hydroxyl groups on capsular polysaccharides of bacteria via tertiary amine groups, resulting in the increased growth space for capsular polysaccharides. In addition, the fermentation at relatively high temperature significantly decreased the adsorption of Ca2+ derived from CaO used for pH adjustment to the resin and sustained the ion exchange capability of the resin available for the formation of intermolecular hydrogen bonds with capsular polysaccharides. The concentration of EPS obtained achieved up to 19.8 g/L, which was increased by approximately 20-fold as compared to the concentration of EPS obtained by conventional fermentation. The conversion rate of carbohydrates to EPS reached up to 35.1%. The EPS produced under the optimized fermentation condition included neutral and acidic heteropolysaccharides with a molecular mass of 3.4 × 104–1.5 × 106 Da. The concentration and molecular mass distribution of EPS exhibited good reproducibility. This study provides a novel method for the industrial production of EPS.

Removal of perfluoroalkyl acids and common drinking water contaminants by weak-base anion exchange resins: Impacts of solution pH and resin properties

The underlying chemistry of weak-base (WB) anion exchange resins (AERs) for contaminant removal from water is not well documented in the literature. To address this, batch adsorption experiments were conducted at pH 4, 7, and 10 using two representative WB-AERs (polyacrylic IRA67 and polystyrene IRA96) and two representative strong-base (SB) AERs (polyacrylic IRA458 and polystyrene A520E), of differing polymer composition, for the removal of nitrate, sulfate, 3-phenylpropionic acid (3-PPA) as surrogate for natural organic matter, and six perfluoroalkyl acids (PFAAs). Under acidic (pH 4) and neutral (pH 7) conditions, the selectivity of AERs for each contaminant was predominantly influenced by polymer composition followed by the size of the resin functional group. This result reflected the WB-AERs being fully protonated and functioning identical to SB-AERs. Isotherm model parameters revealed WB-AER had higher capacity than SB-AER with analogous polymer composition and porosity regardless of resin selectivity for each contaminant. Under basic conditions (≥ pH 10), contaminant removal by WB-AERs declined due to deprotonation of the tertiary amine functional groups. Removal of PFAAs by the more hydrophobic polystyrene WB-AER (IRA96) remained approximately constant with changing pH, which was possibly due to electrostatic interactions with remaining protonated amine functional groups on the resin.

Extractive Fermentation as A Novel Strategy for High Cell Mass Production of Hetero-Fermentative Probiotic Strain Limosilactobacillus reuteri

This study reports on a novel technique to enhance the high cell mass and viable cell counts of the heterofermentative probiotic strain, Limosilactobacillus reuteri. This is the first report on the cultivation of L. reuteri, which was incorporated with weak base anion-exchange resins to remove the accumulating lactic acid in the fermentation broth. Two anion-exchange resins—Amberlite IRA 67 and IRA 96—were found to have a high adsorption capacity with lactic acid. Batch fermentation and fed-batch cultivation were further analyzed using IRA 67 resins, as this application resulted in a higher maximum number of viable cells. The in situ application of anion-exchange resins was found to create shear stress, and thus, it does not promote growth of L. reuteri; therefore, an external and integrated resin column system was proposed. The viable cell count from batch fermentation, when incorporated with the integrated resin column, was improved by 71 times (3.89 × 1011 ± 0.07 CFU mL−1) compared with control batch fermentation (5.35 × 109 ± 0.32 CFU mL−1), without the addition of resins. The growth improvement was achieved due to the high adsorption rate of lactic acid, which was recorded by the integrated IRA 67 resin system, and coupled with the stirred tank bioreactor batch fermentation process.

High selectivity of new thiourea-modified resins for gold: Adsorption performance, mechanism, and recovery

A thiourea-modified weak base anion exchange resin, ZGA451 (thiourea@ZGA451), was prepared. Thiourea@ZGA451 exhibited excellent potential for Au(III) adsorption. The maximum adsorption capacity of Au(III) by thiourea@ZGA451 was 995.6 mg/g at 298 K. The adsorption process followed the Freundlich and pseudo-second-order models, which are monolayer and chemisorption adsorption, respectively. The adsorption mechanism of Au(III) on thiourea@ZGA451 involves electrostatic attraction, chelation, and redox. Thermodynamic experiments showed that the reaction exhibited spontaneous endothermic behavior. Thus, thiourea@ZGA451 possesses outstanding Au(III) adsorption properties.

Bio-Inspired phosphate adsorption by Copper-Decorated weak base anion exchanger

Hybrid-based phosphate adsorbents have high adsorption ability but are challenged with regeneration because of strong bonding. Inspired by phosphate-binding proteins (PBPs) which reached a trade-off between high adsorption and regeneration ability by binding phosphate species with multiple hydrogen bonds, a weak-base anion (WBA) exchange resin was decorated with Cu2+ ions to develop an alternative advanced phosphate adsorbent. Different from the role of metal species in the promoted adsorption of existing hybrid-based adsorbents, the Cu2+ ions mainly drove phosphate diffusion from the liquid to the resin and then induced the phosphate species to bond with multiple –NH2+/–NH groups. Such adsorption exhibited a high entropy (ΔS0 = 132.47 J/mol-K) and was highly exergonic (ΔG0 = -16.83 ∼ -20.14 kJ/mol). Moreover, it enhanced the phosphate selectivity because the driving force for the sorption process originated from the complexation. During the regeneration, the Cu2+-to-Cu-O- transformation could occur under weak alkaline conditions and repelled the adsorbed phosphate species to facilitate desorption. Therefore, the Cu-WBA resin not only exhibited high phosphate adsorptions (31.94 to 61.03 mg-P/g) and high competing-anion tolerance but also was successfully recovered with a diluted NaOH solution (0.05 N). Detailed adsorption behaviors under different pHs, temperatures, and interference of competing anions were examined, and the mechanisms were elucidated.

Detailed investigation of effective trace Cr(VI) removal mechanism by anion exchange resin with phenol–formaldehyde matrix

Prolonged exposure to trace Cr(VI) concentrations in potable water can cause serious health problems in living beings. A weak base anion exchange resin, Duolite A7, showed a large capacity for trace Cr(VI) removal from a background of competing anions present at much higher concentrations, while conventional ion exchangers and adsorbents become ineffective due to lack of selectivity under similar conditions. The objective of this study was to find out the mechanism behind such significant capacity shown by the resin. Fixed-bed column studies showed that the resin was fully exhausted below 4,000 bed volumes (BVs) for pH 7, whereas no breakthrough was observed for 25,000 and 131,000 BVs at pH 5 and 3, respectively. Extensive characterization studies revealed that redox reactions were also occurring inside the resin in addition to ion exchange, where Cr(VI) oxidized the amine functional groups and phenol–formaldehyde matrix while itself getting reduced to Cr(III). Cr(III) formed was either precipitated inside the resin as Cr(OH)3 or bound with the oxidation products such as carboxylic acid groups. Analysis of treated water showed that formaldehyde, a carcinogen, was formed due to oxidative attack of Cr(VI) on the resin and was released in the effluent at trace concentrations. A detailed understanding of the mechanism would motivate the development of such redox-active sorbents for selective trace Cr(VI) removal from contaminated drinking water.

Optimization of protocatechuic acid adsorption onto weak basic anion exchange resins: kinetic, mass transfer, isotherm, and thermodynamic study

Optimization of protocatechuic acid adsorption onto weak basic anion exchange resins: kinetic, mass transfer, isotherm, and thermodynamic study

Adsorption properties of macroporous exchangers functionalized with various weak-base groups for aromatic acids: Coupling DFT simulation with batch experiments

Anion exchange resin has an excellent effect on the removal of aromatic acids in wastewater, while the adsorption affinities of the resins with different functional groups are various. In this work, six macroporous weak-base anion exchange resins were synthesized, and the adsorption characteristics of the resins for three typical aromatic acids including benzenesulfonic acid (BSA), benzoic acid (BA), phenol (PH) were investigated. The results showed that the adsorption performance for BSA and BA on these resins were more sensitive to pH than that for PH. The adsorption capacities of the secondary amine resins to aromatic acid in salt-rich environment were higher than that of the tertiary amine resins. In the binary system, when the adsorption mechanisms of the two adsorbates are overlapped to some extent, the competition between them on the resins was more significant. Density functional theory (DFT) simulations confirmed that the adsorption of BSA by the resins was mainly due to electrostatic interaction, and the adsorption of PH was attributed to hydrogen bond, while BA adsorption was the synergism of these two interactions. The functional resins with high binding energies and high natural bond orbital (NBO) charge transfer had good salt resistances. Furthermore, NaCl aqueous solution was suitable for desorption of BSA on the resins, while the proper desorbent for BA and PH was ethanol. These results indicated that DFT could guide the selection of the functional groups and provided an effective method for the design of selective separation materials for aromatic acids in wastewater.

In-situ carboxylic acid separation from mixed-acid fermentation of cellulosic substrates in batch culture

Using methane-arrested mixed cultures, organic substrates can be fermented to mixed carboxylic acids (i.e., C2 to C8 volatile fatty acids) via the carboxylate platform. A commercial example, the MixAlco® process recovers the carboxylic acids and transforms them to chemicals and fuels. To reduce product inhibition, ion-exchange resin (IR) fermentors used weak-base anion-exchange resins (Amberlite IRA-67) to recover carboxylic acids from fermentation broth and thereby maintain near-neutral pH. Control fermentors used magnesium carbonate (MgCO3) to buffer to near-neutral pH. Compared to the control, the IR fermentors increased acid yields by 2.2, 1.54, and 1.55 times for α-cellulose substrate, paper substrate, and lime-pretreated corn stover, respectively. Furthermore, extraction increased yields of valuable long-chain carboxylic acids. These results suggest further improvements are possible in advanced MixAlco® process configurations, such as countercurrent continuous fermentations.

Performance characterization of nanofiltration, reverse osmosis, and ion exchange technologies for acetic acid separation

A major obstacle to widespread implementation of bio-based fuels and chemicals is the lack of efficient and cost-effective separation methods. To purify acetic acid produced by biochemical conversion of biomass via anaerobic digestion, this work employs two commonly used separation technologies: (1) ion-exchange (IX) resin and (2) pressure-driven membranes. This study tested five commercially available strong- and weak-base anion-exchange resins and five commercially available nanofiltration (NF) and reverse osmosis (RO) membranes. The pH of the feed solution significantly affected adsorption capacity. At pH 6.3, a strong-base IX resin (IRN-78) performed best (95.1% acetate removal). With strong-base IX resins, the Langmuir isotherm model fit well, whereas for weak-base IX resins, the Freundlich isotherm provided a better fit. A pseudo-second-order kinetic model fit well for both IRN-78 and IRA-67. Regarding membrane separation, RO (BW30XFR membrane) achieved the highest rejection (98.6% acetate rejection), whereas an NF membrane (NF*) achieved the best combination of permeate flux (105 L/(h·m2)) and rejection (83.1% acetate rejection). For membrane performance, the experimental data were fit using the solution diffusion model. Increased pH in the feed solution lowered permeate flux but increased acetic acid rejection. When the acetic acid concentration in the feed solution increased, both permeate flux and acetic acid rejection decreased for membrane NF*.

Purification and polymerisation of microbial d-lactic acid from DDGS hydrolysates fermentation

A multi-step process was developed for microbial d-lactic acid purification, followed by poly-d-lactic acid (PDLA) synthesis via azeotropic polycondensation process. Several anion exchange resins were screened for their binding capacity using model lactic acid solutions. Amberlite® IRA67 (weak base anion exchange resin) showed the highest lactic acid adsorption, with maximum adsorption capacity, qmax, of 136.11 mg lactic acid / g of resin, and was further selected to purify D-lactic acid from DDGS hydrolysates through a three-step process; (1) treatment with 7% w/v activated carbon, (2) acidification of fermentation broth (Amberlite® IRA120) and (3) adsorption of lactic acid by anion exchange (Amberlite® IRA67). At the end of the purification process, 80.4% (w/w) D-lactic acid was recovered with 91.8% (w/w) purity, indicating the effectiveness of the developed downstream process. Furthermore, a clear yellowish solid polymer with a molecular weight of 3010 Da was obtained, suitable for applications in biomedical and agricultural sectors.

Remediation of radioiodine using polyamine anion exchange resins

Two weak base anion exchange resins, Lewatit A365 and Purolite MTS9850, have been tested for the removal of aqueous iodide from conditions simulating nuclear waste reprocessing streams. pH variation and relevant co-contaminant addition (nitrate, molybdate and iodine) allowed for assessment of iodide extraction behaviour of each resin. Isotherm experiments were performed and maximum uptake capacities obtained exceed current industrial adsorbents, such as silver-impregnated zeolites. Maximum loading capacities, determined by Dubinin–Radushkevich isotherm, were 761±14mg g−1 for MTS9850 and 589±15mg g−1 for A365. Uptake for both resins was significantly suppressed by nitrate and molybdate ions. The presence of dissolved iodine in the raffinate however, was found to increase iodide uptake. This was explained by characterisation of the spent resin surface by infrared and Raman spectroscopy, which determined the presence of triiodide, indicating charge-transfer complex formation on the surface. Dynamic studies assessed the effect of co-contaminants on iodide uptake in a column environment. Data was fitted to three dynamic models, with the Dose-Response model providing the best description of breakthrough. In all cases iodide breakthrough was accelerated, indicating suppression of uptake, but capacity was still significant.

Novel multistage solid–liquid circulating fluidized bed: liquid phase mixing characteristics

Liquid phase axial mixing studies have been carried out in the novel solid–liquid circulating fluidized bed (SLCFB). The SLCFB primarily consists of a single multistage column (having an inner diameter of 100 mm i.d. and length of 1.40 m) which is divided into two sections wherein both the steps of utilization, namely loading (e.g., adsorption and catalytic reaction) and regeneration of solid phase, can be carried out simultaneously in continuous mode. Weak base anion exchange resin was used as the solid phase, whereas water as the fluidizing medium. The effects of physical properties of solid phase, superficial liquid velocity, and solid circulation rate on liquid phase axial dispersion coefficient were investigated. The dispersion coefficient increases monotonically with an increase in the size of solid particle, superficial liquid velocity, and solid circulation rate. The axial dispersion model (ADM) was used to model experimental residence time distribution (RTD) data. A good agreement was found between ADM predictions and the experimental measurements. A unified correlation has also been proposed to determine dispersion coefficient as a function of physical properties of solid and liquid phases, superficial liquid velocity, and solid circulation rate based on all previous and present experimental data on multistage SLCFB.

Adsorption and desorption behavior of anion-exchange resin towards SO42− in the desulphurization process using citric method

The application of weak-base anion-exchange resin for removal the SO42− from the citrate solution to guarantee its good performance for adsorption of SO2 is proposed in this work. The weak-base anion-exchange resin that has prior adsorption towards SO42− compared with citrate, allows the effective removal of such impure anion. We initially chose four kinds of resins, namely D301R, D301G, D370 and D315, to investigate their behavior upon SO42− adsorption and then determined D301R and D315 to give a comprehensive understanding towards their adsorption performance in various condition. Results indicate that D315 possessing better adsorption ability than D301R could be a potential candidate for SO42− removal from the citrate acid solution during the desulphurization process using citric method. The pretreatment of protonation for resins could effectively facilitate their adsorption behavior towards SO42− under the same pH condition. Moreover, we assume that the protonated D315 would meet the practical requirement well given its good performance.

Growth Enhancement of Probiotic Pediococcus acidilactici by Extractive Fermentation of Lactic Acid Exploiting Anion-Exchange Resin.

Fermentation employing lactic acid bacteria (LAB) often suffers end-product inhibition which reduces the cell growth rate and the production of metabolite. The utility of adsorbent resins for in situ lactic acid removal to enhance the cultivation performance of probiotic, Pediococcus acidilactici was studied. Weak base anion-exchange resin, Amberlite IRA 67 gave the highest maximum uptake capacity of lactic acid based on Langmuir adsorption isotherm (0.996 g lactic acid/g wet resin) compared to the other tested anion-exchange resins (Amberlite IRA 410, Amberlite IRA 400, Duolite A7 and Bowex MSA). The application of Amberlite IRA 67 improved the growth of P. acidilactici about 67 times compared to the control fermentation without resin addition. Nevertheless, the in situ addition of dispersed resin in the culture created shear stress by resins collision and caused direct shear force to the cells. The growth of P. acidilactici in the integrated bioreactor-internal column system containing anion-exchange resin was further improved by 1.4 times over that obtained in the bioreactor containing dispersed resin. The improvement of the P. acidilactici growth indicated that extractive fermentation using solid phase is an effective approach for reducing by-product inhibition and increasing product titer.

Preparation and characterization of heterogeneous weak base anion-exchange membranes

The preparation of new heterogeneous anion-exchange membranes containing particles of a weak basic ion-exchange resin in a polypropylene matrix is described. For comparison, a heterogeneous membrane consisting of a strong basic functional group was also prepared. The anion-exchange membranes were prepared in a laboratory discontinuous homogenizer and extruder followed by compression of extruded membranes to ensure the homogeneity of the test sample. Parameters important for a subsequent transfer of production from laboratory to an industrial scale, torque and head pressure, were observed. Electrochemical and mechanical properties of resulting membranes, in particular their ion-exchange capacity, areal and specific resistances, permselectivies, swelling in water, 1 mol dm−3 NaOH, and 1 mol dm−3 HCl solution, were determined. Weak basic ion-exchange resin Purolite A830 behaved similarly as the strong basic ion-exchange resin during processing, and the resulting membrane showed similar electrochemical and physical properties. The heterogeneous anion-exchange membranes with other weak basic anion-exchange resins showed unsuitable swelling, which was reflected in electrochemical properties of these ion-exchange membranes.

Integrated process for scalable bioproduction of glycolic acid from cell catalysis of ethylene glycol

Glycolic acid (GA) is presently booming as a versatile raw material in the fields of high-grade cosmetics, polymer degradable materials, and drug production. The biocatalysis of ethylene glycol (EG) to GA is promising, with environmentally friendly benefits, while the effective and straight bioproduction of GA qualified for polymer synthesis purity is a challenge. In this study, we combine whole cell catalysis step and acidification-purification step. A compressed oxygen supply in the sealed aerated stirred tank reaction (COS-SSTR) and a weak basic anion-exchange resins were integrated to develop an efficient process of GA bioproduction from EG. Finally, 110.5 g/L of GA was obtained at the yield of 94.4% and the volume productivity of 2.3 g/L/h in 48 h that presently is the greatest level for GA bioproduction. After 335 resins treatment of 5.0 L catalyzed broth containing 497.2 g EG, we obtained 575.4 g GA at the recovery rate of 98.9%.