Anestis Vlysidis

Succinic acid fermentation in a stationary-basket bioreactor with a packed bed of immobilized Actinobacillus succinogenes: 1. Influence of internal diffusion on substrate mass transfer and consumption rate

This paper is dedicated to the study on external and internal mass transfers of glucose for succinic fermentation under substrate and product inhibitions using a bioreactor with a stationary basket bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the Jerusalimsky kinetic model including both inhibitory effects, specific mathematical expressions have been developed for describing the profiles of the substrate concentrations and mass flows in the outer and inner regions of biocatalyst particles, as well as for estimating the influence of internal diffusion on glucose consumption rate. The results indicated that very low values of internal mass flow could be reached in the particles center. The corresponding region was considered biologically inactive, with its extent varying from 0.24% to 44% from the overall volume of each biocatalyst. By immobilization of bacterial cells and use of a basket bed, the rate of glucose consumption is reduced up to 200 times compared with the succinic fermentation system containing free cells.

Utilisation of glycerol to platform chemicals within the biorefinery concept: A case for succinate production

In this study, a biorefinery concept is introduced for the production of platform chemicals by utilising the by-products of the biodiesel industry. An unstructured kinetic model for the bacterial growth of Actinobacillus succinogenes, which is our chosen biocatalyst, is proposed. The model describes cell growth and considers both substrate and product inhibition. The main product chosen here is succinic acid and by-products like acetate, formate and ethanol have insignificant low concentrations. Experiments on different initial glycerol concentrations at the same environmental conditions are carried out and simulation studies are conducted using the proposed model. Parametric values are estimated based on experimental results. Prior to that, the main environmental factors that affect the bioprocess are examined and beneficial conditions in terms of yield, final succinic acid concentration and productivity are assessed by a factorial experimental procedure.

Fractionation of Carboxylic Acids Mixture Obtained by Succinic Fermentation using Reactive Extraction

Formic, acetic, and succinic acids have been selectively separated from their mixture obtained by A. succinogenes fermentation using reactive extraction with tri-n-octylamine (TOA) dissolved in three solvents with different polarities (n-heptane, butyl acetate, and dichloromethane) without and with 1-octanol addition. This technique allows recovering formic and acetic acids from the mixture, the raffinate containing only succinic acid. The extractant concentration and organic phase polarity control the selectivity of acids extraction. Thus, at pH = 1, the selectivity factor increased from 92, in the absence of 1-octanol; to 148, in the presence of this alcohol in organic phase. The corresponding optimum concentrations of TOA in the solvent were 30 and 50 g/l, respectively. The total separation of monocarboxylic acids from the mixture with succinic acid is possible by a multi-stage extraction process, adjusting the extractant concentration in each stage to that stoechiometrically needed for reactions with formic and acetic acids only. The addition of 1-octanol reduces the number of required extraction stages.

Integrated Biodiesel Plants: Options and Perspectives

In this study, we investigate the upgrading of biodiesel plants into integrated biorefineries. Economic analysis and a life cycle assessment studies have been implemented for an integrated biodiesel biorefmery using its side-product (glycerol) to produce succinic acid (SA), a value-added chemical. Four process scenarios considering different uses of glycerol are simulated in Aspen Plus and Mat Lab and compared in this study. We examine simple utilisation methods of this side-product such as the disposal, distillation (80 %) and purification (95 %) of glycerol and we compare them in terms of economic and environmental impact with an integrated approach that produces SA via fermentation. For the latter case, we have incorporated into the overall process a batch fermenter to convert glycerol into succinate followed by a purification/recovery process to produce pure SA crystals. Furthermore, we have performed optimisation studies to compute the maximum profit and simultaneously to reduce the environmental impact. Profitability indicators are used to compare the developed biorefmery cases while environmental impact is calculated based on the CO2 emissions for each scenario. Copyright ?? 2011, AIDIC Servizi S.r.l.

An integrated biorefinery framework for the coproduction of biofuels and chemicals: Experimental analysis, detailed modelling, optimization and life cycle analysis

In this work, a novel integrated biorefinery framework is introduced. A ?cradle to grave? analysis is developed by adding novel steps into a basic biodiesel process involving the valorization of waste streams to value-added chemicals. Insights are given towards a new bioconversion route of glycerol to succinic acid. An unstructured model of batch experiments at different conditions is constructed. Experimental results at the bench scale are used to estimate kinetic parameters and to validate model predictions. The developed model is used in optimization studies to compute the best initial conditions for batch as well as the optimal feeding profiles for fed-batch processes to maximize succinic acid productivity. Finally, the above process is incorporated into a biorefinery scheme. Simulation and optimization in conjunction with life cycle analysis (LCA) is performed to simultaneously improve its sustainability and its economics.

Sampling with poling-based flux balance analysis: optimal versus sub-optimal flux space analysis of Actinobacillus succinogenes

BackgroundFlux balance analysis is traditionally implemented to identify the maximum theoretical flux for some specified reaction and a single distribution of flux values for all the reactions present which achieve this maximum value. However it is well known that the uncertainty in reaction networks due to branches, cycles and experimental errors results in a large number of combinations of internal reaction fluxes which can achieve the same optimal flux value.ResultsIn this work, we have modified the applied linear objective of flux balance analysis to include a poling penalty function, which pushes each new set of reaction fluxes away from previous solutions generated. Repeated poling-based flux balance analysis generates a sample of different solutions (a characteristic set), which represents all the possible functionality of the reaction network. Compared to existing sampling methods, for the purpose of generating a relatively “small” characteristic set, our new method is shown to obtain a higher coverage than competing methods under most conditions.The influence of the linear objective function on the sampling (the linear bias) constrains optimisation results to a subspace of optimal solutions all producing the same maximal fluxes. Visualisation of reaction fluxes plotted against each other in 2 dimensions with and without the linear bias indicates the existence of correlations between fluxes. This method of sampling is applied to the organism Actinobacillus succinogenes for the production of succinic acid from glycerol.ConclusionsA new method of sampling for the generation of different flux distributions (sets of individual fluxes satisfying constraints on the steady-state mass balances of intermediates) has been developed using a relatively simple modification of flux balance analysis to include a poling penalty function inside the resulting optimisation objective function. This new methodology can achieve a high coverage of the possible flux space and can be used with and without linear bias to show optimal versus sub-optimal solution spaces. Basic analysis of the Actinobacillus succinogenes system using sampling shows that in order to achieve the maximal succinic acid production CO2 must be taken into the system. Solutions involving release of CO2 all give sub-optimal succinic acid production.

Glycerol metabolic conversion to succinic acid using Actinobacillus succinogenes. a metabolic network-based analysis

Glycerol is produced in large quantities by the growing biodiesel industry (approximately 100kg per ton of biodiesel). Hence there is a growing demand for processes converting glycerol into useful valuable chemicals. Here we consider the conversion of glycerol into the commodity chemical succinic acid (SA) throughfermentation with the organism Actinobacillus succinogenes. Metabolic control analysis is applied, using knowledge of the structure, the fluxes generated through flux balance analysis and elasticities, which are modelled using random sampling to account for their uncertainty. The results of this analysis give ranges of control coefficients, summarised with a novel parameter we have called the control bias. We have found that the step having the greatest positive effect on SA production is the glycerol uptake and that the enzymes from malate to SA, and from pyruvate to malate are important steps with positive control. A less obvious step identified is the uptake of CO2. Steps having negative control are the ones leading to byproducts such as formic acid. ?? 2011 Elsevier B.V.

Chapter 5:Assessment of Economic and Environmental Cost-benefits of Developed Biorefinery Schemes

In this work modelling and optimisation studies for the evaluation and improvement of several biorefinery schemes were performed. Economic and environmental objectives were considered with the aim to find configurations that maximise profits while minimising the environmental impact. Biorefineries were modelled using a commercial simulator (Aspen Plus) combined with calculations in MatLab. Optimisation studies (including multi-objective optimisation) were carried out using both stochastic (simulated annealing) and deterministic (sequential-quadratic-programming based) approaches. The results show that for a number of schemes improved profits can be found including biodiesel and biogas production in addition to supercritical CO2 extraction from wheat straws. An oil-to-methanol ratio of around 1:13 to 1:14 was found to be optimal for the biodiesel-producing transesterification reaction. The optimum conditions for the biogas case involved recycling most of the digestate, which leads to a high productivity of biogas. Supercritical CO2 extraction was found to be most profitable at around 36,000 tons per year capacity. Multi-objective optimisation was also performed in order to find how the optimal profits change when different constraints are placed on the emissions from each process. For the biodiesel cases these constraints reduced the profits by up to €10 per ton of feed. For biogas production reducing the emissions meant using more of the digestate as fertiliser. For supercritical CO2 extraction reducing emissions requires reducing the yearly capacity, which in turn reduces the profits by €63 per ton. Comparisons of the different schemes are performed using calculations of profits and emissions ‘per ton of feed’ in order to give a fair comparison of biorefinery processes operating at different scales. These comparisons showed that the most profitable schemes were those with the lowest capacity. These lower capacity schemes could be very profitable if they can be scaled up and if there is sufficient feedstock available. Comparison of the emissions for these cases showed that the most profitable schemes also have the highest emissions. This is because these cases involve either high-energy usage (usually with larger quantities of electricity) or combustion.

Implementation of heat integration to improve the sustainability of an integrated biodiesel biorefinery

Recently, a great research effort has been dedicated in order to establish integrated biorefineries as the next generation plants for the production of fuels, energy and chemicals. In this work, heat integration techniques are applied to an integrated biodiesel biorefinery that as well as biodiesel it also produces succinic acid through a fermentation process in order to improve its economic efficiency. Initially, heat integration options are identified by extracting the thermodynamic results of the overall biorefinery from simulations carried out in Aspen Plus 2006.5. By implementing pinch analysis and stochastic optimisation techniques, we determine a new heat exchanger network (HEN) that shows a minimum total annualised cost (TAC) of the overall HEN. The optimisation of the HEN results in a 17.2 % reduction in the TAC and 62.3 % and 64.2 % reduction in the hot and cold utilities, respectively, compared to the initial plant.