L.A.M. van der Wielen

Pervaporation of ethanol from lignocellulosic fermentation broth

Pervaporation can be applied in ethanol production from lignocellulosic biomass. Hydrophobic pervaporation, using a commercial PDMS membrane, was employed to concentrate the ethanol produced by fermentation of lignocellulosic hydrolysate. To our knowledge, this is the first report describing this. Pervaporation carried out with three different lignocellulosic fermentation broths reduced the membrane performance by 17-20% as compared to a base case containing only 3 wt.% ethanol in water. The membrane fouling caused by these fermentation broths was irreversible. Solutions containing model lignocellulosic components were tested during pervaporation at the same conditions. A total flux decrease of 12-15%, as compared to the base case, was observed for each component except for furfural. Catechol was found to be most fouling component whereas furfural permeated through the membrane and increased the total flux. The membrane selectivity increased in the presence of fermentation broth but remained unchanged for all selected components.

Liquid-liquid extraction of fermentation inhibiting compounds in lignocellulose hydrolysate.

Several compounds that are formed or released during hydrolysis of lignocellulosic biomass inhibit the fermentation of the hydrolysate. The use of a liquid extractive agent is suggested as a method for removal of these fermentation inhibitors. The method can be applied before or during the fermentation. For a series of alkanes and alcohols, partition coefficients were measured at low concentrations of the inhibiting compounds furfural, hydroxymethyl furfural, vanillin, syringaldehyde, coniferyl aldehyde, acetic acid, as well as for ethanol as the fermentation product. Carbon dioxide production was measured during fermentation in the presence of each organic solvent to indicate its biocompatibility. The feasibility of extractive fermentation of hydrolysate was investigated by ethanolic glucose fermentation in synthetic medium containing several concentrations of furfural and vanillin and in the presence of decanol, oleyl alcohol and oleic acid. Volumetric ethanol productivity with 6 g/L vanillin in the medium increased twofold with 30% volume oleyl alcohol. Decanol showed interesting extractive properties for most fermentation inhibiting compounds, but it is not suitable for in situ application due to its poor biocompatibility. Biotechnol. Bioeng. 2009;102: 1354–1360.

Simultaneous clostridial fermentation, lipase‐catalyzed esterification, and ester extraction to enrich diesel with butyl butyrate

The recovery of 1‐butanol from fermentation broth is energy‐intensive since typical concentrations in fermentation broth are below 20 g L−1. To prevent butanol inhibition and high downstream processing costs, we aimed at producing butyl esters instead of 1‐butanol. It is shown that it is possible to perform simultaneously clostridial fermentation, esterification of the formed butanol to butyl butyrate, and extraction of this ester by hexadecane. The very high partition coefficient of butyl butyrate pulls the esterification towards the product side even at fermentation pH and relatively low butanol concentrations. The hexadecane extractant is a model diesel compound and is nontoxic to the cells. If butyl butyrate enriched diesel can directly be used as car fuel, no product recovery is required. A proof‐of‐principle experiment for the one‐pot bio‐ester production from glucose led to 5 g L−1 butyl butyrate in the hexadecane phase. The principle may be extended to a wide range of esters, especially to longer chain ones. Biotechnol. Bioeng. 2013; 110: 137–142.

On the relative motion of a particle in a swarm of different particles

Abstract The classification of dissimilar particles in a liquid suspension is exploited in many industrial unit operations. To understand and predict fluidization phenomena in general and particle classification in particular, adequate expressions for each of the governing forces—gravity, buoyancy and drag forces—are required. A possible formulation of the effective driving force and friction in multicomponent mixtures is discussed in this paper. A new expression is derived, which is based on a steady-state force balance for the classifying particle. The expression requires only the usual fluidization data of a single particle species such as the terminal velocity and the Richardson and Zaki index. The new expression is compared with some existing classification models with respect to their predictive value for a wide range of classification data. The new expression proved to be accurate over the entire range of known experimental data and can be extended easily to multicomponent fluidized suspensions. We have found strong evidence that the exact formulation of the buoyancy acting on the classifying particle originates from the bulk density of the fluidized suspension, regardless of the ratio of particle sizes. To clarify the relation between the “overall” drag force and the ratio of particle sizes, the “overall” friction on the classifying particle is decomposed into a solid-liquid and a solid-solid component. The particle-particle interaction force is proportional to the product of the hold-up of the fluidized particles and the slip velocity of dense and fluidized particles. In agreement with other authors, we found an increased friction with a decreasing ratio of classifying and fluidized particles. The particle-particle interaction coefficient was correlated with a modified Stokes-Einstein equation.

Diffusivities of organic electrolytes in water

Abstract The diffusivities in water of large organic ions such as biomolecules are not readily available. There is a need for adequate measurement and estimation methods. In this work, a rapid method is presented for the determination of diffusivities of ionic species in aqueous systems, based on steady state conductivity measurements. As transient composition gradients are essentially absent in our proposed method, an important source of errors in the form of poorly controlled gradients in thermodynamic non-ideality is eliminated. Ionic transport is described with the generalized Maxwell-Stefan model, taking friction between solvent and ionic solutes, and between the moving ionic species into account. Ion-water diffusivities could be correlated satisfactorily for a wide range of organic ions, zwitterions and neutral species with the Wilke-Chang relation, and to a lesser extent with a modified Stokes-Einstein relation. Furthermore, the model describes ionic fluxes over a large range of concentrations when corrected for concentration and temperature dependent viscosity effects, by using a modified Stokes-Einstein relation.

Centrifugal partition chromatographic reaction for the production of chiral amino acids

The use of a centrifugal partition chromatographic reactor is investigated for the production of chiral amino acids from racemic mixtures. Chirally selective enzymatic hydrolysis of N-acetyl-L-methionine into acetic acid and L-methionine was carried out in the chromatographic reactor to demonstrate the concept of integrated reaction and separation in centrifugal partition chromatography (CPC). The products L-methionine and acetic acid, as well as the unconverted substrate, N-acetyl-D-methionine are obtained separately. An aqueous two-phase system, consisting of PEG 600, potassium phosphate and water was successfully applied as liquid-liquid two-phase system in CPC. A model is presented, which describes the reaction chromatograms on the basis of the independently measured partition and mass transfer coefficients of the individual (reacting) components. The model appears to be a valuable tool for optimizing the reaction-separation process.

Continuous enzymatic penicillin G hydrolysis in countercurrent water–butyl acetate biphasic systems

Abstract Penicillin G (Pen G) was continuously hydrolyzed into phenylacetic acid (PAA) and aminopenicillanic acid (APA) by penicillin acylase in countercurrently contacted water–butyl acetate biphasic systems. A set of three mixer–settlers was used to establish countercurrent contact of the two immiscible liquid phases. The enzymatic reaction was catalyzed by immobilized penicillin acylase. Pen G was fed in the central mixer. APA continuously left the system with the aqueous exit stream and PAA with the organic exit stream. The conversion in the countercurrently contacted biphasic system was significantly higher than the conversion that can be achieved in an equivalent batch system. A mathematical model, which is based on partition and reaction equilibria, was used to predict the concentrations and pH along the countercurrent reactor. Provided that no APA crystallization occurs, the mathematical model predicted the conversion and the pH profile in the mixer–settler cascade accurately.

Integration of bioconversion and continuous product separation by means of countercurrent adsorption

Abstract Selective product removal from the reaction zone by means of adsorption is advantageous in case of unfavourable thermodynamic equilibria as can be encountered for enzymatic conversions. The application of a multi-stage fluid bed contactor as a continuous device for adsorptive bioconversion is investigated as a possible solution. In this reactor-adsorber, two solid flows (adsorbent and immobilized biocatalyst) can be controlled independently. As a first step in the process design a mathematical model describing the steady state performance of the reactor is developed. The design and construction of a laboratory scale multi-stage fluid bed reactor-adsorber is illustrated for the reversible first order glucose-fructose isomerization with a zeolitic adsorbent as model system. This proved the reactor-adsorber to be an useful tool in the design of (bio-)conversion processes.

Techno-economic evaluation of an inclusion body solubilization and recombinant protein refolding process

Expression of recombinant proteins in Escherichia coli is normally accompanied by the formation of inclusion bodies (IBs). To obtain the protein product in an active (native) soluble form, the IBs must be first solubilized, and thereafter, the soluble, often denatured and reduced protein must be refolded. Several technically feasible alternatives to conduct IBs solubilization and on‐column refolding have been proposed in recent years. However, rarely these on‐column refolding alternatives have been evaluated from an economical point of view, questioning the feasibility of their implementation at a preparative scale. The presented study assesses the economic performance of four distinct process alternatives that include pH induced IBs solubilization and protein refolding (pH_IndSR); IBs solubilization using urea, dithiothreitol (DTT), and alkaline pH followed by batch size‐exclusion protein refolding; inclusion bodies (IBs) solubilization using urea, DTT, and alkaline pH followed by simulated moving bed (SMB) size‐exclusion protein refolding, and IBs solubilization using urea, DTT and alkaline pH followed by batch dilution protein refolding. The economic performance was judged on the basis of the direct fixed capital, and the production cost per unit of product (PC). This work shows that (1) pH_IndSR system is a relatively economical process, because of the low IBs solubilization cost; (2) substituting β‐mercaptoethanol for dithiothreithol is an attractive alternative, as it significantly decreases the product cost contribution from the IBs solubilization; and (3) protein refolding by size‐exclusion chromatography becomes economically attractive by changing the mode of operation of the chromatographic reactor from batch to continuous using SMB technology.

Dynamics of precipitation of casein with carbon dioxide

Abstract Carbon dioxide is a green alternative for mineral acids (e.g., sulphuric acid) in protein precipitation. The precipitation using a gaseous precipitant differs from the conventional precipitation in the way and the rate at which the precipitant can be applied to the aqueous solution. In this paper, the consequences of using carbon dioxide were investigated for the precipitation of the milk protein casein. Product properties, such as particle size, solids content and calcium release were investigated in a batch system at various mixing conditions and gas addition rates. In addition, mass transfer coefficients were determined from pH response data. The experiments revealed a strong influence of stirring rate and gas flow rate on the particle size. The main effect of varying the gas flow was through the change of acidification rate, much alike precipitation with sulphuric acid. At high acidification rates, the particle size of casein precipitated with carbon dioxide was smaller than with sulphuric acid.