Hot-pressed polymer nanofiber supported graphene membrane for high-performance nanofiltration.

Graphene oxide (GO) sheets can be readily surface-overlaid on hot-pressed electrospun polyacrylonitrile (PAN) nanofiber membrane to form a continuous and crack-free layer; upon thermal reduction at 150 °C for 12 h, the resulting reduced GO (rGO) layer can reject ∼90% MgSO4 with high water flux (due to the size exclusion mechanism), making the prepared PAN-rGO membranes promising nanofiltration media for water purification. It is important to note that no delamination of GO/rGO sheet layers has been observed throughout this study. We highlight that a simple processing method (i.e., hot pressing) is critical for the successful preparation of 2D materials (e.g., GO/rGO) based membranes/media. It is envisioned that the reported study can benefit many groups working on various membrane applications of 2D materials; in other words, the hot-pressed electrospun nanofiber membranes could be generally utilized as an innovative type of platform to support various 2D sheets for different separation applications such as highly efficient and cost-effective removal of dissolved components (e.g., organic molecules) and even (hydrated) ions from water.

Removal and recovery of furfural, 5-hydroxymethylfurfural, and acetic acid from aqueous solutions using a soluble polyelectrolyte.

In the cellulosic ethanol process, furfural, 5-hydroxymethylfurfural (HMF), and acetic acid are formed during the high temperature acidic pretreatment step needed to convert biomass into fermentable sugars. These compounds can inhibit cellulase enzymes and fermentation organisms at relatively low concentrations (≥ 1 g/L). Effective removal of these inhibitory compounds would allow the use of more severe pretreatment conditions to improve sugar yields and lead to more efficient fermentations; if recovered and purified, they could also be sold as valuable by-products. This study investigated the separation of aldhehydes (furfural and HMF) and organic acid (acetic acid) inhibitory compounds from simple aqueous solutions by using polyethyleneimene (PEI), a soluble cationic polyelectrolyte. PEI added to simple solutions of each inhibitor at a ratio of 1 mol of functional group to 1 mol inhibitor removed up to 89.1, 58.6, and 81.5 wt% of acetic acid, HMF, and furfural, respectively. Furfural and HMF were recovered after removal by washing the polyelectrolyte/inhibitor complex with dilute sulfuric acid solution. Recoveries up to 81.0 and 97.0 wt% were achieved for furfural and HMF, respectively. The interaction between PEI and acetic acid was easily disrupted by the addition of chloride ions, sulfate ions, or hydroxide ions. The use of soluble polymers for the removal and recovery of inhibitory compounds from biomass slurries is a promising approach to enhance the efficiency and economics of an envisioned biorefinery.

Detoxification of a lignocellulosic biomass slurry by soluble polyelectrolyte adsorption for improved fermentation efficiency.

This study investigated the detoxification of a dilute acid pretreated Ponderosa pine slurry using the polyelectrolyte polyethyleneimine (PEI). The addition of polyelectrolyte to remove enzymatic and/or fermentation inhibitory compounds, that is, acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), was performed either before or after enzymatic hydrolysis to determine the optimal process sequence. Negligible acetic acid, glucose, and xylose were removed regardless of where in the process the polymer addition was made. Maximum furfural and HMF separation was achieved with the addition of PEI to a clarified pre-enzymatic hydrolysis liquor, which showed that 88.3% of furfural and 66.4% of HMF could be removed. On the other hand, only 23.1% and 13.4% of furfural and HMF, respectively, were removed from a post-enzymatic hydrolysis sample; thus, the effects of enzymes, glucose, and wood solids on inhibitor removal were also investigated. The presence of solid particles >0.2 µm and unknown soluble components <10 kDa reduced inhibitory compound removal, but the presence of elevated glucose levels and enzymes (cellulases) did not affect the separation. The fermentability of detoxified versus undetoxified hydrolysate was also investigated. An ethanol yield of 92.6% of theoretical was achieved with Saccharomyces cerevisiae fermenting the detoxified hydrolyzate, while no significant ethanol was produced in the undetoxified hydrolyzate. These results indicate that PEI may provide a practical alternative for furan removal and detoxification of lignocellolosic hydrolysates, and that application before enzymatic hydrolysis minimizes separation interferences.

Synthesis of Cellulose-graft-Polypropionic Acid Nanofiber Cation-Exchange Membrane Adsorbers for High-Efficiency Separations.

Fabrication of membrane adsorbers with elevated binding capacity and high throughput is highly desired for simplifying and improving purification efficiencies of bioproducts (biotherapeutics, vaccines, etc.) in the biotechnological and biopharmaceutical industries. Here we demonstrate the preparation of a novel class of self-supported, cellulose-graft-polypropionic acid (CL-g-PPA) cation-exchange nanofiber membrane adsorbers under mild reaction conditions for the purification of positively charged therapeutic proteins. In our fabrication method, acrylonitrile was first polymerized and surface grafted onto cellulose nanofibers using cerium ammonium nitrate as a redox initiator to form cellulose-g-polyacrylonitrile (CL-g-PAN). CL-g-PAN was then submitted to a hydrolyzation reaction to form CL-g-PPA cationic membrane adsorbers. Morphology and structural characterization illustrated the formation of CL-g-PPA membranes with uniform coating of polyacid nanolayers along the individual nanofibers without disturbing the nanofiber structure. Benefiting from these numerous cationic polyacid binding sites and inherent large surface area and open porous structure, CL-g-PPA nanofiber membrane adsorbers showed a lysozyme static adsorption capacity of 1664 mg/g of nanofibers. These membranes showed a lysozyme dynamic binding capacity of 508 mg/g of nanofibers at 10% breakthrough (equivalent to 206 g/L capacity), with a residence time of less than 6 s. Moreover, CL-g-PPA self-supported nanofibers displayed excellent structural stability and reversibility after several cycles of protein binding studies. This dynamic binding capacity of the CL-g-PPA nanofiber membranes was 3.2 times higher than that of macroporous cellulose membranes and 8.5 times higher than that of the Sartobind S commercial membrane adsorber. Considering the simple fabrication method employed, excellent protein adsorption capacity, remarkable structural stability, and reusability, CL-g-PPA nanofiber membranes provided a versatile platform for the chromatographic separations of biomolecules (e.g., proteins, nucleic acids, and viral vaccines) as well as water purification and similar ion-exchange applications.

Electrospun Regenerated Cellulose Nanofiber Membranes Surface-Grafted with Water-Insoluble Poly(HEMA) or Water-Soluble Poly(AAS) Chains via the ATRP Method for Ultrafiltration of Water.

Electrospun nanofiber membranes (ENMs) have demonstrated promising applications for water purification primarily due to high water flux and low degree of fouling. However, the equivalent/apparent pore sizes of as-electrospun ENMs are in microns/submicrons; therefore, the ENMs can only be directly utilized for microfiltration applications. To make regenerated cellulose (RC) ENMs for ultrafiltration applications, atom transfer radical polymerization (ATRP) was studied to graft polymer chains onto the surface of RC nanofibers; specifically, monomers of 2-hydroxyethyl methacrylate (HEMA) and sodium acrylate (AAS) were selected for surface-grafting water-insoluble and water-soluble polymer chains onto RC nanofibers, respectively. With prolonging of the ATRP reaction time, the resulting surface-modified RC ENMs had reduced pore sizes. The water-insoluble poly(HEMA) chains coated the surface of RC nanofibers to make the fibers thicker, thus decreasing the membrane pore size and reducing permeability. On the other hand, the water-soluble poly(AAS) chains did not coat the surface of RC nanofibers; instead, they partially filled the pores to form gel-like structures, which served to decrease the effective pore size, while still providing elevated permeability. The surface-modified RC ENMs were subsequently explored for ultrafiltration of ∼40 nm nanoparticles and ∼10 nm bovine serum albumin (BSA) molecules from water. The results indicated that the HEMA-modified RC membranes could reject/remove more than 95% of the nanoparticles while they could not reject any BSA molecules; in comparison, the AAS-modified RC membranes had complete rejection of the nanoparticles and could even reject ∼58% of the BSA molecules.

Polyacrylonitrile nanofiber membranes modified with ionically crosslinked polyelectrolyte multilayers for the separation of ionic impurities.

Nanofiltration membranes were prepared by forming multilayers of branched polyethylenimine (BPEI) and polyacrylic acid (PAA) on a polyacrylonitrile (PAN) nanofibrous mat by layer-by-layer (LbL) assembly. The degree of ionization (DI) of PAA, estimated using FTIR spectra both in the absence and presence of added salt, was shown to have a strong influence on the BPEI/PAA film growth. BPEI/PAA multilayers grew exponentially when the DI of PAA was less than 30%, or when the pH of PAA during LbL formation was less than 3.5. Subsequently, BPEI/PAA multilayers were formed on the PAN nanofiber mats by depositing the polyelectrolytes at the experimental conditions that favored maximum film growth. The separation layer formed with 15 bilayers of BPEI/PAA has a thickness of 1100 nm. PAA ionization was favored within the BPEI/PAA multilayers due to the presence of abundant amine groups in BPEI, and as a result, a strong negative charge was seen for PAN nanofibrous membranes for solution conditions above pH 4.5. Nanofiber membranes modified with 15 bilayers of BPEI/PAA multilayers at an applied pressure of 4 bar had a pure water flux of 19.7 Lm-2 h-1 and a MgSO4 rejection of 98.7%. This performance represents 1.6 times higher flux and 1.1 times higher salt rejection than the multilayers formed on a conventional asymmetric polymeric support. The higher separation and higher flux capabilities of BPEI/PAA multilayer modified PAN nanofiber membranes was due to the combined effect of high charge density and high porosity of the nanofiber membranes.

Antibody capture from corn endosperm extracts by packed bed and expanded bed adsorption.

Topical treatments of chronic infections with monoclonal antibodies will require large quantities of antibodies. Because plants have been proven capable of producing multisubunit antibodies and provide for large-scale production, they are likely hosts to enable such applications. Recovery costs must also be low because of the relatively high dosages required. Hence, we have examined the purification of a human secretory antibody from corn endosperm extracts by processing alternatives of packed bed and expanded bed adsorption (EBA). Because of the limited availability of the transgenic corn host, the system was modeled by adding the antibody to extracts of nontransgenic corn endosperm. Complete clarification of a crude extract followed by packed bed adsorption provided antibody product in 75% yield with 2.3-fold purification (with antibody accounting for 24% of total protein). The small size of the packed bed, cation-exchange resin SP-Sepharose FF and the absence of a dense core (present in EBA resins) allowed for more favorable breakthrough performance compared to EBA resins evaluated. Four adsorbents specifically designed for EBA operation, with different physical properties (size and density), chemical properties (ligand), and base matrices were tested: SP-steel core resin (UpFront Chromatography), Streamline SP and Streamline DEAE (Amersham Biosciences), and CM Hyper-Z (BioSepra/Ciphergen Biosystems). Of these, the small hyperdiffuse-style resin from BioSepra had the most favorable adsorption characteristics. However, it could not be utilized with crude feeds due to severe interactions with corn endosperm solids that led to bed collapse. UpFront SP-steel core resin, because of its relatively smaller size and hence lower internal mass transfer resistance, was superior to the Streamline resins and operated successfully with application of a crude corn extract filtered to remove all solids of >44 microm. However, the EBA performance with this adsorbent provided a yield of only 61% and purification factor of 2.1 (with antibody being 22% of total protein). Process simulation showed that capital costs were roughly equal between packed and expanded bed processes, but the EBA design required four times greater operating expenditures. The use of corn endosperm as the starting tissue proved advantageous as the amount of contaminating protein was reduced approximately 80 times compared to corn germ and approximately 600 times compared to canola. Finally, three different inlet designs (mesh, glass beads, and mechanical mixing) were evaluated on the basis of their ability to produce efficient flow distribution as measured by residence time distribution analysis. All three provided adequate distribution (axial mixing was not as limiting as mass transfer to the adsorption process), while resins with different physical properties did not influence flow distribution efficiency values (i.e., Peclet number and HETP) when operated with the same inlet design.

Comparative technoeconomic analysis of a softwood ethanol process featuring posthydrolysis sugars concentration operations and continuous fermentation with cell recycle.

Economical production of second generation ethanol from Ponderosa pine is of interest due to widespread mountain pine beetle infestation in the western United States and Canada. The conversion process is limited by low glucose and high inhibitor concentrations resulting from conventional low-solids dilute acid pretreatment and enzymatic hydrolysis. Inhibited fermentations require larger fermentors (due to reduced volumetric productivity) and low sugars lead to low ethanol titers, increasing distillation costs. In this work, multiple effect evaporation (MEE) and nanofiltration (NF) were evaluated to concentrate the hydrolysate from 30 g/l to 100, 150, or 200 g/l glucose. To ferment this high gravity, inhibitor containing stream, traditional batch fermentation was compared with continuous stirred tank fermentation (CSTF) and continuous fermentation with cell recycle (CSTF-CR). Equivalent annual operating cost (EAOC = amortized capital + yearly operating expenses) was used to compare these potential improvements for a local-scale 5 MGY ethanol production facility. Hydrolysate concentration via evaporation increased EAOC over the base process due to the capital and energy intensive nature of evaporating a very dilute sugar stream; however, concentration via NF decreased EAOC for several of the cases (by 2 to 15%). NF concentration to 100 g/l glucose with a CSTF-CR was the most economical option, reducing EAOC by $0.15 per gallon ethanol produced. Sensitivity analyses on NF options showed that EAOC improvement over the base case could still be realized for even higher solids removal requirements (up to two times higher centrifuge requirement for the best case) or decreased NF performance.

Quantifying second generation ethanol inhibition: Design of Experiments approach and kinetic model development.

While softwoods represent a potential feedstock for second generation ethanol production, compounds present in their hydrolysates can inhibit fermentation. In this study, a novel Design of Experiments (DoE) approach was used to identify significant inhibitory effects on Saccharomyces cerevisiae D5A for the purpose of guiding kinetic model development. Although acetic acid, furfural and 5-hydroxymethyl furfural (HMF) were present at potentially inhibitory levels, initial factorial experiments only identified ethanol as a significant rate inhibitor. It was hypothesized that high ethanol levels masked the effects of other inhibitors, and a subsequent factorial design without ethanol found significant effects for all other compounds. When these non-ethanol effects were accounted for in the kinetic model, R¯(2) was significantly improved over an ethanol-inhibition only model (R¯(2)=0.80 vs. 0.76). In conclusion, when ethanol masking effects are removed, DoE is a valuable tool to identify significant non-ethanol inhibitors and guide kinetic model development.

Considerations for the recovery of recombinant proteins from plants.

The past 5 years have seen the commercialization of two recombinant protein products from transgenic plants, and many recombinant therapeutic proteins produced in plants are currently undergoing development. The emergence of plants as an alternative production host has brought new challenges and opportunities to downstream processing efforts. Plant hosts contain a unique set of matrix contaminants (proteins, oils, phenolic compounds, etc.) that must be removed during purification of the target protein. Furthermore, plant solids, which require early removal after extraction, are generally in higher concentration, wider in size range, and denser than traditional bacterial and mammalian cell culture debris. At the same time, there remains the desire to incorporate highly selective and integrative separation technologies (those capable of performing multiple tasks) during the purification process from plant material. The general plant processing and purification scheme consists of isolation of the plant tissue containing the recombinant protein, fractionation of the tissue along with particle size reduction, extraction of the target protein into an aqueous medium, clarification of the crude extract, and finally purification of the product. Each of these areas will be discussed here, focusing on what has been learned and where potential concerns remain. We also present details of how the choice of plant host, along with location within the plant for targeting the recombinant protein, can play an important role in the ultimate ease of recovery and the emergence of regulations governing plant hosts. Major emphasis is placed on three crops, canola, corn, and soy, with brief discussions of tobacco and rice.

Continuous enzymatic hydrolysis of lignocellulosic biomass with simultaneous detoxification and enzyme recovery.

Recovering hydrolysis enzymes and/or alternative enzyme addition strategies are two potential mechanisms for reducing the cost during the biochemical conversion of lignocellulosic materials into renewable biofuels and biochemicals. Here, we show that enzymatic hydrolysis of acid-pretreated pine wood with continuous and/or fed-batch enzyme addition improved sugar conversion efficiencies by over sixfold. In addition, specific activity of the hydrolysis enzymes (cellulases, hemicellulases, etc.) increased as a result of continuously washing the residual solids with removal of glucose (avoiding the end product inhibition) and other enzymatic inhibitory compounds (e.g., furfural, hydroxymethyl furfural, organic acids, and phenolics). As part of the continuous hydrolysis, anion exchange resin was tested for its dual application of simultaneous enzyme recovery and removal of potential enzymatic and fermentation inhibitors. Amberlite IRA-96 showed favorable adsorption profiles of inhibitors, especially furfural, hydroxymethyl furfural, and acetic acid with low affinity toward sugars. Affinity of hydrolysis enzymes to adsorb onto the resin allowed for up to 92 % of the enzymatic activity to be recovered using a relatively low-molar NaCl wash solution. Integration of an ion exchange column with enzyme recovery into the proposed fed-batch hydrolysis process can improve the overall biorefinery efficiency and can greatly reduce the production costs of lignocellulosic biorenewable products.

Electrospun regenerated cellulose nanofibrous membranes surface-grafted with polymer chains/brushes via the atom transfer radical polymerization method for catalase immobilization.

In this study, an electrospun regenerated cellulose (RC) nanofibrous membrane with fiber diameters of ∼200-400 nm was prepared first; subsequently, 2-hydroxyethyl methacrylate (HEMA), 2-dimethylaminoethyl methacrylate (DMAEMA), and acrylic acid (AA) were selected as the monomers for surface grafting of polymer chains/brushes via the atom transfer radical polymerization (ATRP) method. Thereafter, four nanofibrous membranes (i.e., RC, RC-poly(HEMA), RC-poly(DMAEMA), and RC-poly(AA)) were explored as innovative supports for immobilization of an enzyme of bovine liver catalase (CAT). The amount/capacity, activity, stability, and reusability of immobilized catalase were evaluated, and the kinetic parameters (Vmax and Km) for immobilized and free catalase were determined. The results indicated that the respective amounts/capacities of immobilized catalase on RC-poly(HEMA) and RC-poly(DMAEMA) nanofibrous membranes reached 78 ± 3.5 and 67 ± 2.7 mg g(-1), which were considerably higher than the previously reported values. Meanwhile, compared to that of free CAT (i.e., 18 days), the half-life periods of RC-CAT, RC-poly(HEMA)-CAT, RC-poly(DMAEMA)-CAT, and RC-poly(AA)-CAT were 49, 58, 56, and 60 days, respectively, indicating that the storage stability of immobilized catalase was also significantly improved. Furthermore, the immobilized catalase exhibited substantially higher resistance to temperature variation (tested from 5 to 70 °C) and lower degree of sensitivity to pH value (tested from 4.0 and 10.0) than the free catalase. In particular, according to the kinetic parameters of Vmax and Km, the nanofibrous membranes of RC-poly(HEMA) (i.e., 5102 µmol mg(-1) min(-1) and 44.89 mM) and RC-poly(DMAEMA) (i.e., 4651 µmol mg(-1) min(-1) and 46.98 mM) had the most satisfactory biocompatibility with immobilized catalase. It was therefore concluded that the electrospun RC nanofibrous membranes surface-grafted with 3-dimensional nanolayers of polymer chains/brushes would be suitable/ideal as efficient supports for high-density and reusable enzyme immobilization.

Membrane separations for solid-liquid clarification within lignocellulosic biorefining processes.

Membrane separations can be integrated into a biorefinery to reduce water and energy consumption. Unfortunately, current membrane materials suffer from severe fouling, which limits their applicability. Here, using analytical characterizations along with fouling models, we correlate membrane properties with performance metrics to provide a framework for optimal membrane selection during solid-liquid clarification of a biomass hydrolysate. Five membranes were evaluated: polyether sulfone, mixed cellulose esters, and three surface modified membranes with weak acid, strong acid, and weak base functionalities. Lignin was the primary component responsible for flux decline, due to physical entrapment and chemical adsorption. The best membrane performance (high and sustained flux, low fouling, and high separation factor) was correlated with higher surface roughness, lower hydrophobicity, neutral or positively charged zeta potential, and a larger number of smaller surface pores. These analyses provide valuable information for designing new materials for biorefining processes to reduce fouling and increase stability.

Surface-functionalized electrospun carbon nanofiber mats as an innovative type of protein adsorption/purification medium with high capacity and high throughput.

Due to recent advances in the production of biotherapeutics, high capacity, high throughput adsorption media for efficient and economic separation of these medically important products are in great demand. One option that has been evaluated extensively is membrane/mat adsorption. While these media allow for rapid adsorption (due to the decreased internal diffusion) and high throughput processing (due to the open porous structure), they often suffer from low capacity and poor enrichment factors. Herein, we report the fabrication, characterization, and protein adsorption evaluation of an innovative type of membrane/mat adsorption media based on electrospun carbon nanofibers. By surface-functionalization of these nanofibers with a weak acid cation-exchange ligand, the capacity was doubled for binding a model protein (i.e., lysozyme) compared to commercial products; and the capacity value was over 200 mg lysozyme per gram of adsorption media. Meanwhile, the thin nanofibers (having diameters of ~300 nm) along with open pores among nanofibers in the mats (having sizes of ~10-15 µm) allowed for higher operating flow rates and lower pressure drops. Furthermore, the incorporation of higher ligand density and the addition of a non-ionic surfactant (i.e., Triton X-305) into the adsorption buffer eliminated the non-specific binding of a competing protein (bovine serum albumin). In combination, this study suggested that electrospun carbon nanofiber adsorption media would provide a promising alternative to packed resin beds for bioseparations.

Process and economic evaluation for monoclonal antibody purification using a membrane-only process.

In recent years, the market for therapeutic monoclonal antibodies (mAb) has grown exponentially, and with this there has been a desire to reduce the costs associated with production and purification of these high-value biological products. A typical mAb purification process involves three adsorption/chromatography steps [protein A, ion exchange (IEX), and hydrophobic interaction (HIC)], along with ultrafiltration, nanofiltration, and microfiltration. With the development of membrane adsorption/chromatography as a viable alternative to traditional pack bed systems, the opportunity exists to complete the entire downstream purification process using only membrane operations. In this study, the process simulation tool SuperPro Designer was used to evaluate the application of recently developed ultra-high capacity electrospun nanofibrous adsorption membranes as a replacement for conventional chromatographic media in the downstream mAb production process. The simulation showed that nanofibrous adsorption membranes in place of the three packed bed chromatography steps reduced the required volume of protein A, IEX, and HIC adsorptive medium by 25, 80, and 80%, respectively. In addition, the membrane-only process reduced the downstream processing time by 50%, decreased the number of labor hours associated with the purification steps by 40%, generated 40% less aqueous waste, and reduced the overall downstream process operating expenses per unit product by 23%. There were also significant savings in facility construction costs and the price of fixed equipment required for separations. With these savings not only is the membrane-only process economically competitive with the traditional packed bed operations, but it offers the possibility of moving toward more disposable process.

Mathematical model using non-uniform flow distribution for dynamic protein breakthrough with membrane adsorption media.

A mathematical model has been investigated to predict protein breakthrough during membrane adsorption/chromatography operations. The new model incorporates a non-uniform boundary condition at the column inlet to help describe the deviation from plug flow within real membrane adsorption devices. The model provides estimated breakthrough profiles of a binding protein while explicitly accounting for non-uniform flow at the inlet of the separation operation by modeling the flow distribution by a polynomial. We have explored experimental breakthrough curves produced using commercial membrane adsorption devices, as well as novel adsorption media of nanolayered nanofiber membranes, and compare them to model predictions. Further, the impact of using various simplifying assumptions is considered, which can have a dramatic effect on the accuracy and predictive ability of the proposed models. The new model, using only simple batch equilibrium and kinetic uptake rate data, along with membrane properties, is able to accurately predict the non-uniform and unsymmetrical shape for protein breakthrough during operation of membrane adsorption/chromatography devices.

Removal of enzymatic and fermentation inhibitory compounds from biomass slurries for enhanced biorefinery process efficiencies.

Within the biorefinery paradigm, many non-monomeric sugar compounds have been shown to be inhibitory to enzymes and microbial organisms that are used for hydrolysis and fermentation. Here, two novel separation technologies, polyelectrolyte polymer adsorption and resin-wafer electrodeionization (RW-EDI), have been evaluated to detoxify a dilute acid pretreated biomass slurry. Results showed that detoxification of a dilute acid pretreated ponderosa pine slurry by sequential polyelectrolyte and RW-EDI treatments was very promising, with significant removal of acetic acid, 5-hydroxymethyl furfural, and furfural (up to 77%, 60%, and 74% removed, respectively) along with >97% removal of sulfuric acid. Removal of these compounds increased the cellulose conversion to 94% and elevated the hydrolysis rate to 0.69 g glucose/L/h. When using Saccharomyces cerevisiae D(5)A for fermentation of detoxified slurry, the process achieved 99% of the maximum theoretical ethanol yield and an ethanol production rate nearly five-times faster than untreated slurry.

Polyelectrolyte flocculation of grain stillage for improved clarification and water recovery within bioethanol production facilities.

Polyelectrolytes were investigated for flocculation of a corn whole stillage stream to improve solid-liquid clarification operations and reduce downstream utility requirements for evaporation and drying within a bioethanol process. Despite a negative zeta potential for the stillage solids, an anionic polyelectrolyte was found to provide the best flocculation. At the optimal dosage of 1.1mg polymer/g dry suspended solids, an anionic flocculant provided a clarified stream with only 0.15% w/w suspended solids (equivalent to a total dissolved solid to total suspended solid ratio greater than 40, and a viscosity reduction of 39% compared to an unflocculated "clarified" stream). The resulting solids cake had greater than 40% w/w solids, and more than 80% water recovery was found in the clarified stream. Addition of flocculant improved filtration flux by six fold and/or would allow for up to a 4-times higher flow rate if using a decanting centrifuge for clarification of corn stillage.

Electrospun nanofiber membranes surface functionalized with 3-dimensional nanolayers as an innovative adsorption medium with ultra-high capacity and throughput.

Electrospun nanofiber membranes surface functionalized with 3D nanolayers through ATRP provide adsorption capacities over 50-times higher than current commercial membrane adsorption systems and over 12-times higher than packed bed resins; additionally, the adsorption kinetics remain 10-times faster than packed bed resins and have over 15-times higher permeance.

Recovery of proteins from corn and soybean extracts by membrane adsorption.

Efficient separation strategies for the recovery of high-value proteins (native or recombinant) from plant agriculture are an important aspect of many different processes, from biopharmaceuticals to byproduct recovery during biofuel production. Here we report the use of membrane adsorption for the recovery of proteins from soybean and corn extracts, and compare the results with packed bed adsorption. Two alternative operating modes were investigated, a flowthrough strategy and a bind and elute method. Overall, membrane adsorption provided faster throughput, and had equal or slightly higher dynamic binding capacities compared with resin beads, without compromising yield and purity of the chosen target. Soybean was found to be an ideal plant host when capturing native protein on an anion exchange medium. This provided an opportunity to capture a large percentage (>80%) of native protein as the product, and/or allowed for elevated enrichment factors (>20) during purification of a recombinant target with pI > 7.0, using a flowthrough approach. On the other hand, for corn, a single ion-exchange step was not able to capture more than 60% of the native protein. However, the bind and elute method with corn as the host for a recombinant product allowed for higher enrichment factors compared to soybean. In all cases, the concentration of a recombinant protein (as dictated by expression level) was found to play a significant role in the level of dynamic binding capacity, with higher concentration leading to elevated capacity. Likewise, a higher concentration of competing proteins was shown to decrease the overall capacity of a recombinant target.