Xylitol production by liquid emulsion membrane encapsulated yeast cells

BACKGROUND: Liquid emulsion membrane (LEM)‐encapsulated live cells can be used to produce various products. This work reports on LEM‐encapsulated cells for producing xylitol and models the production process. RESULTS: Encapsulated cells of Candida mogii ATCC 18364 were used to produce xylitol from xylose. Soybean oil LEM consisting of 5% (w/v) lanolin and microwaxes was found most suitable for this process. The LEM‐encapsulated cells were immobilized in a tubular biocatalytic loop. Xylitol was produced under oxygen‐limited and aerobic conditions. Xylitol productivity and yield were 0.005 g L^?1 h^?1 and 0.52 g g^?1, respectively, for oxygen‐limited operation. Under aerobic conditions, xylitol productivity increased greatly to 0.022 g L^?1 h^?1, but yield on xylose declined to 0.49 g g^?1. A mathematical model successfully described substrate consumption and product formation in the LEM‐immobilized cell system. CONCLUSION: Potentially, immobilized cell LEM systems are useful for certain fermentations and they can be successfully modeled, as shown by the example of xylitol from xylose process. Copyright © 2009 Society of Chemical Industry     

Gas Chromatographic Enantioseparation of Fluorinated Anesthetics: Single‐Column Performance and Scale‐up Estimation

Results of a study devoted to provide the pure enantiomers of isoflurane and desflurane from racemic mixtures using gas chromatography are presented. For that purpose, a cyclodextrin‐based selector described in earlier work was immobilized on porous glass beads. The adsorption isotherms were determined and applied to predict operating parameters which provide the highest possible productivity of the separation. The analysis included evaluation of the performance of larger columns applying simplifying scale‐up considerations. Using repetitive batches, the method can provide per day with a laboratory scale column approximately 1 g pure enantiomer. Selected model predictions were validated experimentally.     

Performance and Energy Consumption of Membrane‐Distillation Hybrid Systems for Olefin‐Paraffin Separation

Light olefin and paraffin are commonly separated by energy‐intensive cryogenic distillation. Membrane/distillation hybrid systems constitute an economical alternative separation process. Different configurations of this hybrid system are studied for olefin‐paraffin separation with emphasis on C₃ separation. An approach based on the McCabe‐Thiele method is applied to analyze different process configurations. A facilitated transport membrane is considered as membrane type. Both new column design and augmentation of an existing distillation column by a membrane module are considered. Numerical examples are considered for the separation of propane from propylene through different hybridization shapes with facilitated transport membranes. The energy requirement can be halved using hybrid systems.     

Biporous polymeric microspheres coupled with mercaptopyridine for rapid chromatographic purification of plasmid DNA

A biporous absorbent coupled with mercaptopyridine was synthesized for the purification of plasmid DNA. Analyses by scanning electron microscopy and mercury intrusion porosimetry revealed that the matrix contained two families of pores, i.e., micropores and superpores. The superpores provided not only convective flow channels for the mobile phase, but also a large surface for biomacromolecules binding. So the chromatographic process can be operated at high flow rate with high column efficiency and low backpressure as identified on a 2‐mL column. When 10 mL crude feedstock containing 3 mg of plasmid (5.4 kb pcDNA3) was loaded at a flow rate as high as 20 cm/min, the separation was finished in 10 min, and the plasmid was completely recovered with undetectable impurities of nucleic acids and proteins. The productivity was determined to be 9.0 g/L h, comparable to the pDNA productivity obtained using the commercial column. These results indicate that the biporous medium is promising for high‐throughput purification of plasmid DNA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2205–2211, 2007     

Analysis of energetics and economics of sub-ambient hybrid post-combustion carbon dioxide capture

Adsorption of CO₂ from post-combustion flue gas is one of the leading candidates for globally impactful carbon capture systems. This work focused on understanding the opportunities and limitations of sub-ambient CO₂ capture processes utilizing a multistage separation process. A hybrid process design using a combination of pressure-driven separation of CO₂ from flue gas (e.g., adsorption- or membrane-based separation) followed by CO₂-rich product liquefaction to produce high-purity (>99%) CO₂ at pipeline conditions is considered. The operating pressure of the separation unit is a key cost parameter and also an important process variable that regulates the available heat removal necessary to reach the sub-ambient operating conditions. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management was found to be most influenced by the productivity of the adsorption system, with productivities as high as 0.015 /kg_sorb⁻¹ sec⁻¹ being required to reduce costs of capture below $60/ton CO₂ captured. This analysis was carried out using a simplified two-bed process, and thus there is opportunity for further cost reduction with exploration of more complex cycle designs. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeolite 13X) were considered for application in the sub-ambient process of PSA unit. Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures as compared to sub-ambient. MIL-101(Cr) and UiO-66 fiber composites had improved purity, recovery, and productivity at colder temperatures reducing costs of capture as low as $61/ton CO₂. Future economic improvement could be achieved by reducing the required operating pressure of the PSA unit and pushing the Pareto frontier closer to the final pipeline requirement via a combination of PSA cycle design and material selection.     

Intensified process for aromatics separation powered by Kaibel and dividing-wall columns

Process intensification in distillation led to major developments, such as reactive distillation, heat-integrated distillation, cyclic distillation, as well as Kaibel and dividing-wall column. Still, the separation of aromatics at industrial scale is carried out typically in a series of conventional distillation columns, with severe penalties on the associated plant footprint, investment and operating costs. To solve this problem, this study investigates novel separation alternatives powered by dividing-wall column (DWC) and Kaibel distillation column. The new sequences using process intensification are able to separate five products (lights, benzene, toluene, xylene and heavies) at high purity levels, in only two distillation columns.AspenTech Aspen Plus^® was used as a computer aided process engineering tool to perform the rigorous simulation and optimization of the new separation alternatives, applied to a simplified industrial case study. In order to allow a fair comparison, all design alternatives were optimized using the sequential quadratic programming (SQP) method.Notably, the novel design with two consecutive DWC units reduces the energy demand by 14%, while the alternative combining a conventional stripper with a Kaibel column leads to over 17% energy savings as compared to the conventional direct distillation sequence. Moreover, the new separation schemes require less equipment and a reduced plant footprint.     

Integrated adsorbent‐process optimization for carbon capture and concentration using vacuum swing adsorption cycles

A novel approach for integrated adsorbent and process design is proposed. The traditional pressure or vacuum swing adsorption (PSA) / vacuum swing adsorption (VSA) process optimization for chosen objectives, where operating conditions are the decision variables, and CO₂ purity and recovery are constraints, is expanded to include adsorbent isotherm characteristics as additional decision variables. Two VSA cycles, namely a four‐step process¹, currently known to have the lowest energy consumption for CO₂ capture and concentration (CCC), and a six‐step process², recently proven to have a wider operating window for the evacuation pressure, have been investigated in the current study. The integrated optimization results simultaneously provide the lower bound of minimum energy and upper bound of maximum productivity for CCC achievable from the two VSA processes along with the operating conditions and the corresponding isotherm shapes necessary to achieve them. It may be viewed as an enabler for adsorbent design or expedient adsorbent search by process inversion. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2987–2995, 2017     

Optimisation of a continuous flash fermentation for butanol production using the response surface methodology

Factorial design and response surface techniques were used in combination with mathematical modelling and computational simulation to optimise an innovative industrial bioprocess, the production of biobutanol employing the flash fermentation technology. A parametric analysis performed by means of a full factorial design at two levels determined the influence of operating variables on butanol yield and productivity. A second set of simulations were carried out based on the central composite rotatable design. This procedure generated simplified statistical models that describe butanol yield and productivity as functions of the significant operating variables. From these models, response surfaces were obtained and used to optimise the process. For a range of substrate concentration from 130 to 180 g/l, the optimum operating ranges ensure butanol productivity between 7.0 and 8.0 g/l h, butanol yield between 19 and 22%, substrate conversion above 90% and final butanol concentration around 25 g/l.     

Modeling,Characteristic Analysis and Optimization of an Improved Heat‐Integrated Air Separation Column

Cryogenic air separation as the most important part of an integrated gasification combined cycle is a widely used operation unit for producing large quantities of high‐purity oxygen and nitrogen. However, cryogenic distillation requires a large amount of energy due to the work needed to compress the air feed. An improved heat‐integrated air separation column (HIASC) is proposed. The requirements of high‐purity separation in the industrial cryogenic air separation process are achieved. An optimization model of the heat transfer coefficient (UA), a key parameter in column structure design and operation, is presented. The optimized UA value is obtained within the accepted value range reported in the international open literature, which ensures the practicability of the improved HIASC.     

常压反应-减压精馏耦合生产氯化苄的工艺优化设计

采用常压反应-减压精馏耦合装置应用于甲苯氯化体系生产氯化苄。为了找到集成装置的最佳结构参数,建立了以独立反应量为基础的模型方程,并开发了基于Powell法的多层优化设计法。结果表明,在塔釜上升蒸汽量一定的情况下,增加精馏塔分离段塔板数、反应器台数、相邻反应器间间隔塔板数,反应能力有所增加,然而当其超过一定值后,反应能力增加的趋势不明显;在优化得到的结构操作参数下,反应能力与分离能力达到最佳匹配。     

A methodology for the graphical determination of operating conditions of chromatographic sequences incorporating the trade‐offs between purity and yield

Multiple‐step chromatography sequences are necessary in biopharmaceutical downstream processing to achieve the desired levels of purity for products such as therapeutic proteins. Traditional methods of process design deal with each step individually, but this can result in a sequence that does not achieve best overall performance. This paper proposes a graphical methodology for the identification of operating conditions for a two‐step chromatography sequence. The method uses windows of operation to incorporate the trade‐offs between yield, purity and productivity. A tie‐line procedure is developed that separates the window of operation for the first chromatographic step into two zones. One zone contains those operating conditions that combine to produce a material which can be purified successfully by the second step to produce a product that meets the desired specifications. The second zone consists of operating conditions which will not yield a material that can be adequately purified by a second chromatographic stage to yield a product of the predetermined specifications. The methodology is valuable in that it helps in achieving the rapid design of a two‐step chromatography sequence, and aids in choosing the optimum operating conditions for the first step that are highly dependent upon the operation and specifications of the second chromatographic step. Simulations carried out using a software package based on the general rate model depict the construction and use of the method applied to a sequence of ion exchange and hydrophobic interaction chromatography separating a three‐component protein mixture. Copyright © 2006 Society of Chemical Industry     

Systematic controllability analysis for chemical processes

Modern chemical industrial processes are becoming more and more integrated and consist of multiple interconnected nonlinear process units. These strong interactions profoundly complicate a system's inherent properties and further alter the plant‐wide process dynamics. This may lead to a poor control performance and cause plant‐wide operability problems. To ensure entire processes run robustly and safely, with considerable profitability, it is crucial to recognize the inherent characteristics that can jeopardize controllability and process behavior at the early design stage. With a focus on inherently safer designs, from a plant‐wide perspective, a systematic method for chemical processes controllability analysis is addressed in this study. In the proposed framework, based on open‐loop stability/instability and minimum/nonminimum‐phase behavior, the entire operating zone of the process can be categorized into distinct subregions with different inherent properties. Variations in the inherent characteristics of a plant‐wide process with the operation and design conditions, over the feasible operation region, can be probed and analyzed. An attempt of this framework is made to illustrate how to clarify the roots of the poor controllability that arise in the design and operation of a large scale chemical process, and the results can provide guidance for both deciding the optimal operation conditions and selecting the most suitable control structure. Singularity theory is also applied in the framework to improve the computational efficiency. The framework is illustrated with two case studies. One involves a reactor‐external heat exchanger network and the other a more complex plant‐wide process, comprising a reactor, an extractor, and a distillation column. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3096–3109, 2012     

Continuous perfusion culture of encapsulated hybridoma cells

BACKGROUND: The production of Monoclonal antibodies (mAbs) is often performed in batch or fed‐batch operations where low cell densities and low volumetric productivities are achieved. The main bottleneck of both processes is the short operating time with productive cells at maximum cell concentration. RESULTS: The process studied in this work is based on a fluidized‐bed bioreactor culture of encapsulated KB26.5 cells in a liquid core of calcium alginate microcapsules as a culture strategy to produce IgG₃. First, DMEM medium was modified in order to protect the microcapsules from degradation, and later, the optimal operating conditions were set. Under these conditions encapsulated KB26.5 cells reached cell densities of 1.05 × 10⁸cells mL^?1 or 9.8 × 10⁶ cells mL^?1 (referred to the inner capsule volume or total bioreactor volume, respectively), and a mAb volumetric productivity of 2.75 µg mL^?1 h^?1. CONCLUSIONS: The productivity of encapsulated KB26.5 cells in perfusion culture was enhanced significantly in comparison with batch and fed‐batch processes. Continuous operation of the perfusion culture for periods longer than 35 days, represented a volumetric productivity about five‐fold higher than conventional operations. However, the fluidized‐bed also showed limitations such as low cell viability at high cell densities due to the mass transfer limitations of large molecules inside the microcapsules. Copyright © 2011 Society of Chemical Industry     

Reactive distillation for biodiesel production from soybean oil

Biodiesel, which is regarded as a promising alternative to a conventional petroleum-based diesel fuel, can be produced from transesterification of vegetable oils and alcohol in conventional batch and continuous reactors. Since the transesterification is an equilibrium-limited reaction, a large excess of reactants is usually used to increase the production of biodiesel, thereby requiring more expensive separation of unreacted raw materials. This study proposed the use of a reactive distillation for transesterification of soybean oil and methanol catalyzed by sodium hydroxide to produce biodiesel. The simulation results showed that a suitable configuration of the reactive distillation column consists of three reactive stages. The optimal conditions for the reactive distillation operation are at the molar feed ratio of methanol and oil at 4.5: 1, reflux ratio of 3, and reboiler duty of 1.6×10⁷ kJ h⁻¹. Methanol and soybean oil should be fed into the column at the first stage. The effect of important operating and design parameters on the performance of reactive distillation was also presented.     

Treatment of Liming Effluent from Tannery using Membrane Separation Processes

Abstract

A treatment method of liming effluent of a tannery is tested using hybrid membrane separation processes. The effluent after gravity settling and alum coagulation is subjected to ultrafiltration followed by nanofiltration. The optimum alum dose is obtained by analyzing the effluent using various concentrations of alum. The membrane separation processes are conducted in a continuous cross flow mode. The effects of operating conditions e.g., transmembrane pressure difference, and cross flow velocity (Reynolds number) on the permeate flux are analyzed. Effects of change in hydrodynamic conditions in various flow regimes, e.g., laminar, laminar with turbulent promoter, and turbulent flow on flux improvement have been studied. A resistance‐in‐series model for flux decline during the filtration process is proposed. COD, BOD, TDS, TS, pH, Ca²⁺ concentration, Cl^? concentration and conductivity are measured before and after each operation. The potential of the dried sludge as organic fertilizer is also explored.     

The effects of dilution rate and glucose concentration on continuous acetone–butanol–ethanol fermentation by Clostridium acetobutylicum immobilized on bricks

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of butanol through biological routes has attracted increasing attention. However, low butanol productivity severely impedes its potential industrial production. It is known that the immobilization of whole cells can enhance productivity in the acetone‐butanol‐ethanol (ABE) continuous fermentation process. Therefore, the objective of this study was to develop a low‐cost continuous operation for butanol production. RESULTS: Bricks were chosen as cell support because of their low cost and ease of use for immobilization. The solvent productivity for the bricks with immobilized cells was 0.7 g L^?1 h^?1, 1.89 times that of free cells (0.37 g L^?1 h^?1) at a dilution rate of 0.054 h^?1. The productivity improvement can contribute to greater retention of biomass inside the reactor due to immobilization. The increase in glucose feed concentration raised total solvent production. However, it resulted in a decrease in yield (grams of solvents produced per gram of glucose introduced). Continuous operation with immobilized cells at a dilution rate of 0.107 h^?1 resulted in a solvent productivity of 1.21 g L^?1 h^?1, 2.1 times that of the operation at 0.027 h^?1. However, the yield (butanol produced per glucose consumed) was decreased to 0.19 from 0.29 under the same glucose feeding condition of 60 g L^?1. CONCLUSION: The increase in dilution rate and feed glucose concentration enhanced productivity, but decreased the utilization of substrates and the final solvent concentration. Therefore, a balance between productivity and glucose utilization is required to ensure continuous process operation. Copyright © 2011 Society of Chemical Industry     

Process integration technology review: background and applications in the chemical process industry

Process integration is a holistic approach to process design and operation which emphasizes the unity of the process. Process integration design tools have been developed over the past two decades to achieve process improvement, productivity enhancement, conservation in mass and energy resources, and reductions in the operating and capital costs of chemical processes. The primary applications of these integrated tools have focused on resource conservation, pollution prevention and energy management. Specifically, the past two decades have seen the development and/or application of process integration design tools for heat exchange networks (HENs), wastewater reduction and water conservation networks, mass exchange networks (MENs), heat‐ and energy‐induced separation networks (HISENs and EISENs), waste interception networks (WINs) and heat‐ and energy‐induced waste minimization networks (HIWAMINs and EIWAMINs), to name a few. This paper provides an overview of some of these developments and outlines major driving forces and hurdles. The fundamental aspects of this approach along with their incorporation in an overall design methodology will be discussed. The paper also highlights several recent applications of process integration to industrial processes. Copyright © 2003 Society of Chemical Industry     

Recycle optimization in non-linear productive chromatography—I Mixing recycle with fresh feed

This paper examines the chromatographic separation of two solutes interacting non-linearly with the sorbent, when only partial separation is achieved at the column outlet, and an intermediate cut of the effluent is recycled. It is shown that, for given feed composition and column size, there is an optimum of the amount of fresh feed injected per cycle; alternately, for given feed composition and amount treated per cycle, there is an optimal column length. This optimum is such that interferences of concentration fronts are minimized in the column. The process is analysed using the “equilibrium theory”, which neglects hydrodynamic dispersion and mass-transfer resistances. Complete analytical solutions are given in the optimal situation, for the case of mass-action law equilibria with unity exponents (Langmuir type equilibrium).The theoretical predictions are compared to experimental results for the separation of Na⁺ from K⁺ by H⁺ eluent in chloride solutions, on a commercial cation-exchanger. The results are also compared to “classical” chromatography (without recycle), and to “two-way” chromatography, presented in a previous paper[1]. With respect to “classical chromatography”, for a given product purity, the optimal recycle process is shown to improve product richness (i.e. concentration of product with respect to solvent) and all performance criteria (eluent consumption, sorbent immobilization, productivity). With respect to “two-way” chromatography, it improves sorbent immobilization and productivity, but yields a poorer Na⁺ product, thus uses more eluent.     

Selection and optimisation of macroporous resin for separation of stilbene glycoside from Polygonum multiflorum Thunb.

BACKGROUND: 2,3,5,4′‐Tetrahydroxystilbene‐2‐O‐β‐glucopyranoside (SG; a stilbene glycoside) is a major bioactive component of Polygonum multiflorum Thunb. (PM), a popular traditional Chinese herb. In this study a method was developed for the separation of SG from PM on macroporous resins. These were selected and optimised using the linear correlation coefficients of the Langmuir and Freundlich isotherms and a pseudo‐first‐order model to explain the kinetic results. Then dynamic adsorption and desorption experiments were carried out on a column packed with the chosen resin to optimise the separation process. RESULTS: HPD100 resin gave the best performance in the separation of SG from PM. The optimal parameters were a sample concentration in solution of 3.5 g mL^?1, a pH of 4.8, a flow rate of 1.5 mL min^?1 and an elution solvent of 40% (v/v) ethanol. Using this scaled‐up column, a product with a final SG content of 819 mg g^?1 and a recovery yield of 74.7% was achieved. In addition, pure acicular crystals of SG could be obtained from this product. CONCLUSION The results showed that HPD100 was the most efficient resin for the separation of SG, which may provide a scientific basis for larger‐scale stilbene glycoside production from PM and other plant extracts. Copyright © 2008 Society of Chemical Industry     

Ceramic Oxygen Generators with Thin-Film Zirconia Electrolytes

Ceramic oxygen generators (COGs) based on stabilized zirconia electrolytes are being developed for oxygen generation from air and other gases, e.g., carbon dioxide. In zirconia-based COG cells, it is desirable to use thin-film electrolytes to minimize ohmic resistance losses, thus permitting reduced operating temperatures (600°–800°C vs 900°–1000°C). The tape calendering process developed by Honeywell is a simple, cost-effective process for fabrication of thin-film electrolytes supported on a substrate electrode. In combination with optimized electrodes, thin-film electrolytes allow significantly high performance in COG cells. Performance characteristics of COG cells and stacks made by tape calendering for oxygen generation from air and CO₂ are discussed.