Agarose-coated anion exchanger prevents cell-adsorbent interactions

A common problem during recovery of bioproducts by adsorption from particulate broths is fouling of the adsorbent material as a result of the interaction of cells and cell debris, which present negative charges, with the positively charged anion exchangers commonly used in bioprocesses. The effect of shielding an adsorbent with a layer of agarose on reducing the binding of cells while still allowing the low-molecular-mass bioproducts to be adsorbed was studied. Coating the anion-exchange resin Amberlite IRA-400 with agarose followed by cross-linking the agarose layer effectively prevented the binding of Escherichia coli, Saccharomyces cerevisiae, and Lactobacillus casei cells but allowed binding of lactic acid to the adsorbent. The cross-linked agarose layer was stable during recycling of the adsorbent.     

Continuous production of butanol by clostridium acetobutylicum immobilized in a fibrous bed bioreactor

We explored the influence of dilution rate and pH in continuous cultures of Clostridium acetobutylicum. A 200-mL fibrous bed bioreactor was used to produce high cell density and butyrate concentrations at pH 5.4 and 35°C. By feeding glucose and butyrate as a cosubstrate, the fermentation was maintained in the solventogenesis phase, and the optimal butanol productivity of 4.6g/(L h) and a yield of 0.42 g/g were obtained at a dilution rate of 0.9h⁻¹ and pH 4.3. Compared to the conventional acetone-butanol-ethanol fermentation, the new fermentation process greatly improved butanol yield, making butanol production from corn an attractive alternative to ethanol fermentation.     

Enantioseparation of 1-phenyl-1-propanol by supercritical fluid-simulated moving bed chromatography

The enantioseparation of 1-phenyl-1-propanol through the supercritical fluid-simulated moving bed (SF-SMB) process is studied. Non-linear isotherms were measured on an analytical column, and used together with the triangle theory for SMB design to select operating conditions for the SF-SMB. Experiments were carried out on a pilot-scale SF-SMB plant at conditions that corresponded to the non-linear range of the isotherm. Under conditions of low feed concentration, complete separation (extract purity = 99.5%; raffinate purity = 98.4%) was achieved. Under conditions of larger feed concentration, the best separation corresponded to an extract purity of 98.0% and a raffinate purity of 94.0%, and yielded a productivity of 110 g of racemate per kg stationary phase per day.     

Modeling, Simulation and Operation Performance of a Simulated Moving Bed for Enantioseparation of Fluoxetine on New β-Cyclodextrin Columns

A Simulated Moving Bed (SMB) setup, including 8 new -cyclodextrin columns, was used to achieve the enantioseparation of fluoxetine. The effects of feed concentration and feed flowrate on the operation performance parameters: purity, enrichment, recovery and productivity were studied. A simulation approach was applied to simulate the operation and performance of the simulated counter-current system. The model predicted the performance of the transient and cyclic steady state behaviour to a reasonably good extent. The adsorption isotherm and parameters determined by pulse experiments and moment analysis seem to be adequate in simulating both the transient and steady state behaviour. Generally, this model can provide guidance for designing operation condition of the SMB system.     

Gas holdup in three-phase immobilized-cell bioreactors

A number of studies in the published literature deal with gas holdup in three-phase reactors. However, very few address the cases in which the solid density approaches that of the liquid phases and in which low gas velocities are involved. These conditions are commonly encountered in immobilized-cell bubble columns and in fluidized-bed bioreactors. This paper reports the effect of gas and liquid velocity upon gas holdup and bed expansion in fluidized-bed bioreactors. For liquid-fluidization of low-density alginate beads in the absence of gas, the terminal sedimentation velocity (vT) of the particles is a constant, and expansion of the bed follows Richardson and Zaki’s correlation. In the presence of gas, however, the apparent terminal sedimentation velocity value is affected by the velocity of the gas and liquid phases. For gas velocities above a minimum value, the calculated value of vT depends on liquid velocity only, and a constant bed expansion was observed for a range of gas and liquid flow rates. For the gas-liquid interactions, a modified drift-flux model was found to be valid. For superficial gas velocities between 5 and 17 cm/min, the modified drift-flux velocity was observed to be a function of gas velocity, suggesting the prevalence of a coalescence regime.     

CFD Model of Dense Gas-solid Systems in Jetting Fluidized Beds

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Shrinking-bed model for percolation process applied to dilute-acid pretreatment/hydrolysis of cellulosic biomass

For many lignocellulosic substrates, hemicellulose is biphasic upon dilute-acid hydrolysis, which led to a modified percolation process employing simulated two-stage reverse-flow. This process has been proven to attain substantially higher sugar yields and concentrations over the conventional single-stage percolation process. The dilute-acid pretreatment of biomass solubilizes the hemicellulose fraction in the solid biomass, leaving less solid biomass in the reactor and reducing the bed. Therefore, a bed-shrinking mathematic kinetic model was developed to describe the two-stage reverse-flow reactor operated for hydrolyzing biphasic substrates, including hemicellulose, in corn cob/stover mixture (CCSM). The simulation indicates that the shrinking-bed operation increases the sugar yield by about 5%, compared to the nonshrinking bed operation in which 1 reactor volume of liquid passes through the reactor (i.e.,t = 1.0). A simulated optimal run further reveals that the fast portion of hemicellulose is almost completely hydrolyzed in the first stage, and the slow portion of hemicellulose is hydrolyzed in the second stage. Under optimal conditions, the bed shrank 27% (a near-maximum value), and a sugar yield over 95% was attained.     

INVERSE RESPONSE BEHAVIOR OF FIXED-BED REACTOR IN A FISCHER-TROPSCH SYNTHESIS

研究了固定床ＦＴ合成反应器中的动态响应行为。主要研究了当反应器进口气体温度突降后床层中出现的逆响应现象，并探讨了水煤气变换副反应对固定床ＦＴ合成反应器逆响应行为的影响。     

Simulated moving bed technology: old and new

The Simulated Moving Bed (SMB) concept has been applied to the separation of different mixtures as a continuous counter current separation process, avoiding several problems related with solid motion. The aim of this work is to present some relevant examples of SMB separations corresponding to the two major ages in the use of the SMB concept, here named “old” and “new” applications. The “old” applications of SMB technology in the petrochemical industry are still important, with large and highly productive units; and the “new” applications of the second “age” of SMB concept are from the fine chemical, pharmaceutical and biochemistry areas, associated with the demand of high purity products during the last 10 years. Different examples are presented for different ages: a UOP Parex ^® process for the “old”, modelled with the equivalent True Moving Bed (TMB) approach; and a chiral resolution for the “new”, modelled by the real SMB model. Some of the latest developments are also mentioned: the non conventional techniques as the Varicol ^® process, PowerFeed, Modicon, M3C or Enriched Extract-SMB (EE-SMB), MultiFeed (MF), Outlet Streams Swing (OSS) or Pseudo-SMB, involving considerable changes in the SMB concept itself. The use of the last optimization/modelling packages for the development of design techniques, either at the conception stage as well as for performance improvements of existing units is emphasized.     

流化床生物质与煤共气化特性的初步研究

在热天平和流化床实验装置中研究了生物质与煤的共气化特性，采用程序升温热重法对稻秆焦、高粱秆焦、玉米秆焦和神木煤焦以及生物质焦与煤焦混合物进行水蒸气气化研究。结果表明，生物质焦和煤焦的反应活性依次增大，其顺序为高粱焦>稻秆焦>玉米焦>神木煤焦。一定温度下，生物质焦与煤焦混合物的气化碳转化率高于各自气化碳转化率的加和。在流化床气化实验中，比较了单独煤气化与稻秆/煤混合物气化的结果，实验结果表明，混合物气化碳转化率、气体中可燃组分的体积分数均高于单独煤气化，气体中CO2的体积分数低于单独煤气化CO2的体积分数。