Simulated dynamics and control of an extractive alcoholic fermentation

In this study, we investigated the dynamics of a computer simulation of a continuous alcoholic fermentation process combined with a flash column under vacuum. The alcohol was partially extracted in order to maintain its concentration at about 40 kg/m³ in the fermentor. The mathematical model of the fermentation was developed for industrial conditions and considers the effect of the temperature on the kinetic parameters. The performance of the dynamic matrix control algorithm, single input single output and multiple input multiple output, for the control of the extractive process was studied. The concepts of factorial design were used in a simulation study to determine the best control structures for the process.     

Optimization Strategies Based on Sequential Quadratic Programming Applied for a Fermentation Process for Butanol Production

In this work, the mathematical optimization of a continuous flash fermentation process for the production of biobutanol was studied. The process consists of three interconnected units, as follows: fermentor, cell-retention system (tangential microfiltration), and vacuum flash vessel (responsible for the continuous recovery of butanol from the broth). The objective of the optimization was to maximize butanol productivity for a desired substrate conversion. Two strategies were compared for the optimization of the process. In one of them, the process was represented by a deterministic model with kinetic parameters determined experimentally and, in the other, by a statistical model obtained using the factorial design technique combined with simulation. For both strategies, the problem was written as a nonlinear programming problem and was solved with the sequential quadratic programming technique. The results showed that despite the very similar solutions obtained with both strategies, the problems found with the strategy using the deterministic model, such as lack of convergence and high computational time, make the use of the optimization strategy with the statistical model, which showed to be robust and fast, more suitable for the flash fermentation process, being recommended for real-time applications coupling optimization and control.     

Robust stabilization of a chemical reactor

Robust static output feedback control was applied to a continuous stirred tank reactor with parametric uncertainty and multiple steady states in which exothermic reaction takes place. The problem of robust controller design was converted to a solution of linear matrix inequalities and a computationally simple non-iterative algorithm is presented. The possibility of using robust static output feedback for stabilization of reactors with uncertainty and comparison of robust P and PI controllers with an optimal controller is demonstrated by simulation results.     

Model predictive control-based robust stabilization of a chemical reactor

The paper addresses an approach to robust stabilization of chemical continuous stirred tank reactors. State feedback was used for the stabilization and the feedback controller was designed using the robust model-based predictive control algorithm in which the symmetric constraints on input and output variables are taken into account. The known strategy was modified by adding integral action to the controller. Parameters of robust feedback controllers with and without integral action were found as solutions of a constrained optimization problem solved on the infinite prediction horizon. The possibility to stabilize chemical reactors with uncertainty using the robust model-based predictive control has been verified by simulations and compared with the optimal linear quadratic control and the model-based predictive control. The obtained results confirm that the robust model-based predictive control provides better results than other approaches.     

A simple model for the continuous production of butanol by immobilized clostridia: I: Clostridium beyerinckii on glucose

A simple model has been developed to describe the continuous production of butanol and isopropanol from glucose by Clostridium beyerinckii cells immobilized in calcium alginate beads. The model contains linear butanol inhibition kinetics and assumes the biomass to be homogeneously distributed throughout the alginate beads. For design purposes this model, containing five parameters, satisfactorily predicts the values of three output variables (the concentrations of glucose, butanol and isopropanol) as a function of three input variables (the glucose feed concentration, the dilution rate and the fraction of beads in the reactor). For process design a high bead fraction and well mixed conditions seem advantageous.     

Redox potential in acetone-butanol fermentations

In batch and continuous cultivations ofClostridium acetobutylicum ATCC 824 on lactose, a strong relationship was observed between redox potential of broth and the cellular metabolism. The specific productivity of butanol as well as of butyric acid was found to be maximum at a redox potential of -250 mV. The specific production rate of butyric acid decreased rapidly at redox potentials. For butanol, however, it achieved a lower but stable value. This was true for dynamic as well as steady states. The continuous fermentations involving lactose exhibited sustained oscillations at low dilution rates. These oscillations appear to be related to butanol toxicity to the growth of cells. At higher dilution rates where butanol concentrations were relatively low, no such oscillations were observed. It can be concluded that broth redox potential is an excellent indicator of the resulting fermentation product partitioning.     

Design and Evaluation of an Optimal Controller for Simultaneous Saccharification and Fermentation Process

Ethanol from corn is produced using dry grind corn process in which simultaneous saccharification and fermentation (SSF) is one of the most critical unit operations. In this work an optimal controller based on a previously validated SSF model was developed by formulating the SSF process as a Bolza problem and using gradient descent methods. Validation experiments were performed to evaluate the performance of optimal controller under different process disturbances that are likely to occur in practice. Use of optimal control algorithm for the SSF process resulted in lower peak glucose concentration, similar ethanol yields (13.38±0.36% v/v and 13.50±0.15% v/v for optimally controlled and baseline experiments, respectively). Optimal controller improved final ethanol concentrations as compared to process without optimal controller under conditions of temperature (13.35±1.28 and 12.52±1.19% v/v for optimal and no optimal control, respectively) and pH disturbances (12.65±0.74 and 11.86±0.49% v/v for optimal and no optimal control, respectively). Cost savings due to lower enzyme usage and reduced cooling requirement were estimated to be up to $1 million for a 151 million L/yr (40 million gal/yr) dry grind plant.     

Mechanism of nitromethane liquid membrane oscillator containing sodium oleate

The oscillatory behavior of a liquid membrane oscillator with anionic surfactant was investigated in order to understand the oscillation mechanism at the molecular level. As a theoretical framework, an approach based on chemical kinetics laws has been used. The chosen system involved nitromethane with 2,2(')-bipyridine as liquid membrane. The aqueous donor phase contained sodium oleate and butanol, while sodium chloride was added to the aqueous acceptor phase. It was established that the oscillations take place exclusively at the aqueous acceptor phase/membrane interface. Therefore, liquid membrane oscillators with anionic surfactants behave the same way as oscillators with cationic surfactants as to the location of oscillations. An oscillation mechanism involving three stages is proposed and confirmed by numerical simulations. The oscillations of electrical potential differences between the two aqueous phases are produced by sudden adsorption and desorption of anionic surfactant in solvated form and butanol at the acceptor/membrane interface. The whole process is controlled by the slow diffusion of these species across the liquid membrane. The chaotic character of the oscillations was demonstrated by Lyapunov exponents obtained from the strange attractor of the system.     

Modeling and simulation of butanol separation from aqueous solutions using pervaporation

A study was conducted to separate butanol from an aqueous solution using pervaporation. A specially designed and manufactured cell was used to separate the butanol from butanol/water solutions of different butanol concentrations (6-8-11-16-20-50) g/l. A 250 cm³ butanol mixture at 33 °C was used to feed the cell, while the pressure of permeation side was about 0 bar. Results revealed that butanol concentration changes non-linearly during the first 3 h, and then proceeds linearly. The percentage of butanol removal increases with increasing feed concentration. The permeability of the used membrane was determined experimentally. A resistance in series model was used to simulate the pervaporation step. The butanol concentration in the feed during the pervaporation step was predicted by using the developed model. There is a fair agreement between butanol concentration in feeding tank of pervaporation cell both experimentally and predicted from the developed model.     

Self-pulsing at an oil/water interface in the presence of phospholipid

Irregular electrical potential oscillations and interfacial tension were observed in an oil/water system consisting of nitrobenzene and an aqueous solution of 5 vol% butanol. When phospholipid, dipalmitoylphosphatidylethanolamine (DPPE), was added to the aqueous phase in this system, rhythmic oscillations were generated. The molecular mechanism for the oscillations has been interpreted with the aid of computer simulation based on a set of nonlinear differential rate-equations.     

Effects of multiple-stage membrane process designs on the achievable performance of automatic control

There is limited information from literature on the dynamic operability of membrane processes with multiple stages or loops. Such information is useful for assessing the performance achievable by an automatic controller proposed for a process design before the actual controller is implemented. Based on dynamic modeling of an industrial whey ultrafiltration process with an increasing number of stages up to a maximum of 12, the dynamic responses of the flowrate and concentration of the retentate were obtained. Features of the dynamic responses were used to determine the performance, in terms of quality and speed, that can be achieved by automatic controllers. In particular, limitations on the performance are indicated by features of dynamic responses such as effective time delay and inverse responses. Changes in effective time delay and inverse responses with the number of stages in the whey ultrafiltration process demonstrate a trade-off between process performance and control performance. This trade-off should be considered during process and controller design to maximize the economic return from the production of whey protein concentrates.     

A smart gelator as a chemosensor: application to integrated logic gates in solution, gel, and film

A gelator that consisted of one benzimidazole moiety and four amide units was used as a chemosensor. We found that its absorption and emission spectra in solution were sensitive to two complementary chemical stimuli: protons and anions. Thus, YES and INH logic gates were obtained when absorbance was defined as an output. A combination gate of XNOR and AND with an emission output was also obtained. Moreover, wet gels in two solvents were used to construct two more-complicated three-input-three-output gates, owing to the existence of the gel phase as an additional output. Finally, in xerogel films that were formed from two kinds of wet gels, reversible changes in their emission spectra were observed when they were sequentially exposed to volatile acid and NH(3). Another combination two-output logic gate was obtained for xerogel films. Finally, three states of the gelator were used to construct not only basic logic gate, but also some combination gates because of their response to multiple chemical stimuli and their multiple output signals, in which one chemical input could erase the effect of another chemical input.     

Dynamical Regime of the Phloroglucinol‐Based Chemical Oscillator in the Presence of Alcohols: Rebirth of Oscillations after an Inhibition Time

This study pertains to the dynamic evolution of the Belousov–Zhabotinsky (BZ) chemical oscillator upon the addition of different aliphatic alcohols (methanol, ethanol, n‐propanol, iso‐propanol, n‐butanol, sec‐butanol, iso‐butanol, and tert‐butanol) at 30°C in a stirred batch reactor. The oscillations are monitored potentiometrically. The experimental findings reveal that the course of the BZ reaction is significantly altered depending on the concentration of the alcohol and the type of the carbon chain present. The mechanism of the alcohol perturbation has been interpreted on account of the experimental results. Besides the qualitative study, a new approach for monitoring the analytical concentration of these alcohols using the BZ oscillatory regime has been explored and it has been found that the alcohol perturbation is directly related to the concentration of the alcohol added, which in turn depends on the inhibition time for the rebirth of oscillatory regime.     

A Simple Substrate Feeding Strategy using a pH Control Trigger in Fed-Batch Fermentation

A simple automated glucose feeding strategy based on pH control was developed to produce high-cell-density fed-batch fermentation. In this strategy, the pH control scheme utilized an acidified concentrated glucose solution to lower the pH. The frequency of glucose addition to the fermentor is determined by the culture’s growth kinetics. To demonstrate the effectiveness of the coupled pH and glucose control strategy in biomass and/or secondary metabolite production, several fed-batch fermentations of indigenous Escherichia coli and recombinant E. coli were carried out. Both strains produced biomass with optical density of greater than 40 at 600 nm. We also tested the glucose control strategy using two types of pH controller: a less sophisticated portable pH controller and a more sophisticated online proportional-integral-derivative (PID) controller. Our control strategy was successfully applied with both controllers, although better control was observed using the PID controller. We have successfully demonstrated that a glucose feeding strategy based on a simple pH control scheme to indirectly control the glucose concentration can be easily achieved and adapted to conventional bioreactors in the absence of online glucose measurement and control.     

Bifurcation Analysis of the Bulk Propylene Polymerization in the LIPP Process

Summary: A dynamic model is built to describe the bulk propylene polymerization in stirred tank reactors (LIPP process), assuming that catalyst deactivation takes place and that the reactor temperature must be controlled with the help of reflux condensers and external heat exchangers. Simulation results show that the dynamic behavior of the LIPP process can be much more complex than described previously, when catalyst deactivation and the performance of the real temperature controller are taken into consideration. Particularly, it is shown that chaotic behavior can be observed in very wide ranges of operation conditions when the more realistic operation conditions are considered.     

Bioethanol Production Optimization: A Thermodynamic Analysis

In this work, the phase equilibrium of binary mixtures for bioethanol production by continuous extractive process was studied. The process is composed of four interlinked units: fermentor, centrifuge, cell treatment unit, and flash vessel (ethanol-congener separation unit). A proposal for modeling the vapor–liquid equilibrium in binary mixtures found in the flash vessel has been considered. This approach uses the Predictive Soave–Redlich–Kwong equation of state, with original and modified molecular parameters. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. The results show that the introduction of new molecular parameters r and q in the UNIFAC model gives more accurate predictions for the concentration of the congener in the gas phase for binary and ternary systems.     

在Matlab/Simulink仿真平台上演示和模拟高分子的粘弹性

设计了基于Matlab／Simulink的高分子粘弹性计算机辅助教学（CAI）软件。计算机程序由各种功能模块根据聚合物的粘弹性原理连接组合而成,通过点击模块可以输入和修改实验数据和模拟参数,运行后可以从虚拟的“示波器”、“数字显示屏”和“XY记录仪”上显示模拟结果。该软件可演示和模拟高分子材料的静态和动态粘弹性行为,如形变的滞后效应、动态力学损耗、Boltzmann叠加和自由振动衰减曲线等。该软件不仅可用于高分子物理课程的教学演示,也能够应用于高分子材料的设计和研究。     

Intermittent Chaos in the Bray–Liebhafsky Oscillator. Dependence of Dynamic States on the Iodate Concentration

Chaotic dynamic states with intermittent oscillations were generated in a Bray–Liebhafsky (BL) oscillatory reaction in an isothermal open reactor i.e., in the continuously-fed well-stirred tank reactor (CSTR) when the inflow concentration of potassium iodate was the control parameter. They are found between periodic oscillations obtained when [KIO₃]₀ < 3.00 × 10^–2 M and stable steady states when [KIO₃]₀ > 4.10 × 10^–2 M. It was shown that the most chaotic states obtained experimentally somewhere in the middle of this region are in high correlation with results obtained by means of largest Lyapunov exponents and phenomenological analysis based on the quantitative characteristics of intermittent oscillations.     

A fast event processor for counting loss-corrected gamma-spectrometry

The design of a fast microprogrammed direct memory access processor for a PDP-11/34 is described. The controller is able to address a storage area of 128K-16 bit words, enabling us to record several conventional spectra and loss-corrected spectra of 4096 channels in three byte precision simultaneously and in short temporal succession. Beyond it, the interface contains: a) system timing controller for multisource multiscaling; b) two d/A-converters for general purposes; c) display generator with gray scale control for an external oscilloscope; d) two 16-bit parallel input/output ports, which provide interfacing beetween peripheral devices and the minicumputer.     

Conversion of municipal solid waste into carboxylic acids by anaerobic countercurrent fermentation

Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations were performed under anaerobic conditions at 40°C. Calcium carbonate was added to neutralize the carboxylic acids and to control the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and 17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor 3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation.