Jingwei Zhou

Modeling of breakthrough curves of single and quaternary mixtures of ethanol, glucose, glycerol and acetic acid adsorption onto a microporous hyper-cross-linked resin

The adsorption of quaternary mixtures of ethanol/glycerol/glucose/acetic acid onto a microporous hyper-cross-linked resin HD-01 was studied in fixed beds. A mass transport model based on film solid linear driving force and the competitive Langmuir isotherm equation for the equilibrium relationship was used to develop theoretical fixed bed breakthrough curves. It was observed that the outlet concentration of glucose and glycerol exceeded the inlet concentration (c/c0>1), which is an evidence of competitive adsorption. This phenomenon can be explained by the displacement of glucose and glycerol by ethanol molecules, owing to more intensive interactions with the resin surface. The model proposed was validated using experimental data and can be capable of foresee reasonably the breakthrough curve of specific component under different operating conditions. The results show that HD-01 is a promising adsorbent for recovery of ethanol from the fermentation broth due to its large capacity, high selectivity, and rapid adsorption rate.

Acetone-butanol-ethanol competitive sorption simulation from single, binary, and ternary systems in a fixed-bed of KA-I resin.

Separation of butanol based on sorption methodology from acetone–butanol–ethanol (ABE) fermentation broth has advantages in terms of biocompatibility and stability, as well as economy, and therefore gains much attention. In this work a chromatographic column model based on the solid film linear driving force approach and the competitive Langmuir isotherm equations was used to predict the competitive sorption behaviors of ABE single, binary, and ternary mixture. It was observed that the outlet concentration of weaker retained components exceeded the inlet concentration, which is an evidence of competitive adsorption. Butanol, the strongest retained component, could replace ethanol almost completely and also most of acetone. In the end of this work, the proposed model was validated by comparison of the experimental and predicted ABE ternary breakthrough curves using the real ABE fermentation broth as a feed solution.

Efficient nanobiocatalytic systems of nuclease P1 immobilized on PEG-NH2 modified graphene oxide: effects of interface property heterogeneity.

The use of graphene oxide (GO) nanosheets for functional enzyme support has attracted intensive interest owing to their unique planar structure and intriguing physical and chemical properties. However, the detailed effects of the interface properties of GO and its functionalized derivatives on active biomolecules are not well understood. We immobilize nuclease P1, a common industrial nucleic acid production enzyme, on pristine and amino poly(ethylene glycol) (PEG-NH2) modified GO nanosheets with interface property heterogeneity using two approaches, physical adsorption and chemical crosslinking. It is demonstrated that nuclease P1 could be stable immobilized on the surface of pristine GO by physical adsorption and on the edge of modified GO nanosheets by chemical crosslinking. The resultant loading capacity of nuclease P1 on pristine GO is as high as 6.45mg/mg as a consequence of strong electrostatic and hydrophobic interactions between the enzyme and carrier. However, it is determined that the acid resistance, thermal stability, reusability and degradation efficiency of the immobilized enzyme on PEG-NH2-modified GO are obviously improved compared to those of the enzyme immobilized on pristine GO. The enhanced catalytic behavior demonstrates that GO and its derivatives have great potential in efficient biocatalytic systems.

Mathematical modeling of the competitive sorption dynamics of acetone–butanol–ethanol on KA-I resin in a fixed-bed column

The recovery and purification of biobutanol based on the adsorption method were performed in dynamic conditions. Computational and theoretical modeling is an important tool in the characterization, development, and validation of fixed-bed columns. Relevant breakthrough curves provide valuable information for designing fixed-bed adsorption processes for field applications. In the present study, a general rate model (GRM), implementing convection/diffusion approach theory and a competitive isotherm model, was used to predict the competitive sorption dynamics of acetone–butanol–ethanol (ABE) on a KA-I resin in a fixed-bed column under different operating conditions, i.e., inlet feed flow rate, initial adsorbate concentration, and bed height. The model simulation was quantified by the absolute average deviation (AAD). The calculated AAD values, ranging from 0.05 to 0.1, indicated that the GRM gives a general prediction for experimental data. The axial dispersion, external mass transfer, and pore diffusion coefficients were calculated by a series of empirical correlations. Biot number was used to identify the rate controlling step for the adsorption process of ABE on the resin. And the pore diffusion coefficient was found to be major governing factor for adsorption of ABE. The data and modeling presented are valuable for designing the continuous chromatographic separation process and simulation of ABE.

Immobilization of Clostridium acetobutylicum onto natural textiles and its fermentation properties

Immobilized fermentation has several advantages over traditional suspended fermentation, including simple and continuous operation, improved fermentation performance and reduced cost. Carrier is the most adjustable element among three elements of immobilized fermentation, including carrier, bacteria and environment. In this study, we characterized carrier roughness and surface properties of four types of natural fibres, including linen, cotton, bamboo fibre and silk, to assess their effects on cell immobilization, fermentation performance and stability. Linen with higher specific surface area and roughness could adsorb more bacteria during immobilized fermentation, thereby improving fermentation performance; thus, linen was selected as a suitable carrier and was applied for acetone–butanol–ethanol (ABE) fermentation. To further improve fermentation performance, we also found that microbes of Clostridium acetobutylicum were negatively charged surfaces during fermentation. Therefore, we then modified linen with polyetherimide (PEI) and steric acid (SA) to increase surface positive charge and improve surface property. During ABE fermentation, the adhesion between modified linen and bacteria was increased, adsorption was increased about twofold compared with that of unmodified linen, and butanol productivity was increased 8.16% and 6.80% with PEI‐ and SA‐modified linen as carriers respectively.

Extracellular polymer substances and the heterogeneity of Clostridium acetobutylicum biofilm induced tolerance to acetic acid and butanol

The mechanisms associated with how cells in biofilms exhibit enhanced tolerance to adverse environmental stress have attracted much recent attention. In this study, we investigated the tolerance mechanisms through observation of biofilm morphology combined with detection of fermentation activity, and discovered an improved way to culture biofilms for application in acetone–butanol–ethanol (ABE) fermentation. We found that a mature biofilm exhibited enhanced tolerance to acetic acid and butanol during ABE fermentation. A mature biofilm consists of a complex, heterogeneity three-dimensional structure, with a coated extracellular polymer substance (EPS). Therefore, when exposed to a harsh environment, cells in different regions of the biofilm displayed different levels of performance, resulting in cells with higher tolerance levels capable of survival, continued growth. The EPS acted as a barrier, limiting the transfer of harmful substances, and diluting their concentration in order to protect biofilm cells. During repeated-batch fermentations, the continuous fermentation formed biofilms, and the butanol concentration, productivity, and yield were 22.08%, 26.37%, and 61.08% higher, respectively, relative to suspended fermentation.

Desorption of 1-butanol from polymeric resin: experimental studies and mathematical modeling

Desorption is essential to design an integrated recovery process for 1-butanol, a potential biofuel. The modeling of desorption processes is a significant tool to optimize the separation process of 1-butanol. In this work, we systematically studied the desorption of 1-butanol from a porous polymeric resin KA-I by solvent desorption technique. The desorption equilibrium, desorption kinetics and dynamic desorption behaviors were studied experimentally and simulated theoretically. About 1.5 bed volumes of absolute ethanol could desorb 1-butanol completely with 73.6 g L−1 1-butanol in the effluent in the fixed bed system. A pore diffusion model was used to fit the desorption kinetics of 1-butanol satisfactorily. The concentration evolution of eluent and 1-butanol in the resin pore was simulated. During desorption, the concentration of 1-butanol in the resin pore increases gradually at first, and then decreases gradually due to the slower pore diffusion. Moreover, a general rate model was used to predict the dynamic desorption profiles of 1-butanol under different operating conditions successfully. Finally, repeated adsorption and desorption dynamic cycles were predicted by the general rate model quite well.