| 1. |
- Persson, P, et al.
(författare)
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Aspects of estimating parameter dependencies in a detailed chromatography model based on frontal experiments
- 2006
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Ingår i: Process Biochemistry. - : Elsevier BV. - 1873-3298 .- 1359-5113. ; 41:8, s. 1812-1821
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for estimation of the dependency on flow rate and bead size of the axial dispersion coefficient and the film mass transfer coefficient in a detailed model for chromatographic processes is proposed. The model describes the concentration of the solute in the mobile phase and considers external/internal mass transfer resistance. The flow rate dependency of the mixing effect in the external volume is also considered. The unknown model parameters estimated are the bed void, the axial dispersion coefficient, the liquid film mass transfer coefficient, the effective diffusion coefficient and the apparent bead porosity. All the parameters in the model and the parameter dependencies were subsequently determined in three classes of experiments, i.e. the external mixing behaviour, the mobile phase behaviour and the stationary phase behaviour. The estimates are based on the sum of the least squares of the residuals between the experimental breakthrough curves and the model response. The methodology is exemplified by frontal experiments with blue dextran and bovine serum albumin in a well-defined column set-up. The results show that it is possible to estimate the unknown physical parameters in the detailed model, and their dependencies on flow rate and bead size, using the proposed methodology. (c) 2006 Elsevier Ltd. All rights reserved.
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| 2. |
- Pettersson, Per O., et al.
(författare)
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Modeling simultaneous saccharification and fermentation of softwood
- 2002
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Ingår i: Applied Biochemistry and Biotechnology. - 0273-2289 .- 1559-0291. ; 98-100, s. 733-746
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous saccharification and fermentation (SSF) of wood has been modeled for the past 15-20 years, but the substrates used for model evaluation have so far not included pretreated softwood. In the present study, data from lab-scale batch SSF of SO2-impregnated, steam-pretreated spruce chips were used to evaluate a model found in the literature. The model, which was somewhat modified, consists of a number of nonlinear, coupled ordinary differential equations, which were solved numerically. Some parameter values were fitted to data by use of least-squares minimization. A difficulty in parameter estimation was the lack of cellobiose measurements, something that was relieved by adding assumptions about parameter relations. The simulated concentration profiles agreed well with the measured concentrations of glucose and ethanol. It is therefore concluded that the basic model features apply to softwood SSF. The model predicts rate saturation with respect to enzyme concentration at concentrations above 60 FPU/g cellulose, although this was not observed in the experimental data, which only comprised enzyme concentrations up to 32 FPU/g cellulose.
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| 3. |
- Pettersson, Per O, et al.
(författare)
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Simplistic Modeling approach to heterogeneous dilute-acid hydrolysis of cellulose microcrystallites
- 2003
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Ingår i: Applied Biochemistry and Biotechnology. - 0273-2289 .- 1559-0291. ; 105, s. 451-455
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Tidskriftsartikel (refereegranskat)abstract
- The classic kinetic model for cellulose hydrolysis is often referred to as pseudo-homogeneous, a term revealing the insight that the process is actually heterogeneous. During the past 10-15 yr, the shortcomings of this model have been demonstrated in various studies and the interest in the heterogeneous aspects has increased. The present work presents a simplistic model in which the intrinsic, heterogeneous hydrolysis and transport rates are coupled by the assumption of a constant glucosidic surface concentration. The mechanisms affecting these two rates are largely unknown, but the model serves as a guideline for further exploration of the process.
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| 4. |
- Alkasrawi, Malek, et al.
(författare)
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Recirculation of process streams in fuel ethanol production from softwood based on simultaneous saccharification and fermentation
- 2002
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Ingår i: Applied Biochemistry and Biotechnology. - 0273-2289 .- 1559-0291. ; 98, s. 849-861
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Konferensbidrag (refereegranskat)abstract
- The effect of process stream recirculation on ethanol production from steam- pretreated softwood based on simultaneous saccharification and fermentation (SSF) was investigated for two process configurations. In the first configuration, a part of the stillage stream after distillation was recycled and, in the second configuration, the liquid after SSF was recycled. The aim was to minimize the energy consumption in the distillation of the fermentation broth and in the evaporation of the stillage, as well as the use of fresh water. However, recirculation leads to an increased concentration of nonvolatiles in the first configuration, and of both volatiles and nonvolatiles in the second configuration. These substances might be inhibitory to the enzymes and the yeast in SSF. When 60% of the fresh water was replaced by stillage, the ethanol yield and the productivity were the same as for the configuration without recirculation. The ethanol production cost was reduced by 17%. In the second configuration, up to 40% of the fresh water could be replaced without affecting the final ethanol yield, although the initial ethanol productivity decreased. The ethanol production cost was reduced by 12%. At higher degrees of recirculation,fermentation was clearly inhibited, resulting in a decrease in ethanol yield while hydrolysis seemed unaffected.
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| 5. |
- Andersson, Alexandra, et al.
(författare)
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Comparison of diafiltration and size-exclusion chromatography to recover hemicelluloses from process water from thermomechanical pulping of spruce
- 2007
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Ingår i: Applied Biochemistry and Biotechnology. - : Springer Science and Business Media LLC. - 1559-0291 .- 0273-2289. ; 137:1-12, s. 971-983
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses constitute one of the most abundant renewable resources on earth. To increase their utilization, the isolation of hemicelluloses from industrial biomass side-streams would be beneficial. A method was investigated to isolate hemicelluloses from process water from a thermomechanical pulp mill. The method consists of three steps: removal of solids by microfiltration, preconcentration of the hemicelluloses by ultrafiltration, and purification by either size-exclusion chromatography (SEC) or diafiltration. The purpose of the final purification step is to separate hemicelluloses from small oligosaccharides, monosaccharides, and salts. The ratio between galactose, glucose, and mannose in oligo- and polysaccharides after preconcentration was 0.8: 1: 2.8, which is similar to that found in galactoglucomannan. Continuous diafiltration was performed using a composite fluoro polymer membrane with cutoff of 1000 Da. After diafiltration with four diavolumes the purity of the hemicelluloses was 77% (gram oligo- and polysaccharides/gram total dissolved solids) and the recovery was 87%. Purification by SEC was performed with 5, 20, and 40% sample loadings, respectively and a flow rate of 12 or 25 mL/min (9 or 19 cm/h). The purity of hemicelluloses after SEC was approx 82%, and the recovery was above 99%. The optimal sample load and flow rate were 20% and 25 mL/min, respectively. The process water from thermomechanical pulping of spruce is inexpensive. Thus, the recovery of hemicelluloses is not of main importance. If the purity of 77%, obtained with diafiltration, is sufficient for the utilization of the hemicelluloses, diafiltration probably offers a less expensive alternative in this application.
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| 6. |
- Axelsson, Anders, et al.
(författare)
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Economic evaluation of the hydrolysis of lactose using immobilized beta-galactosidase
- 1990
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 24-5, s. 679-693
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Tidskriftsartikel (refereegranskat)abstract
- A computer program for preliminary cost estimates of free and immobilized enzyme systems has been developed. The cost for the hydrolysis of lactose by β-galactosidase fromAspergillus oryzae has been calculated for a batch tank reactor, with free (BTRF) and immobilized (BTRI) enzymes, a continuously stirred tank reactor (CSTR) and a plug-flow tubular reactor (PFTR), considering the mass transfer behavior and deactivation of the enzyme. Enzyme immobilization is economically feasible, compared with a system with free enzymes, despite a very high cost for the enzyme attachment. At a half-life time of 80 d, the PFTR gives the lowest cost (0.48 SEK/kg lactose), but the cost for the BTRI is just slightly higher (0.66 SEK/kg lactose) and still much lower than the BTRF (2.10 SEK/kg lactose).
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| 7. |
- Bollok, M, et al.
(författare)
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Simultaneous saccharification and fermentation of steam-pretreated spruce to ethanol
- 2000
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 84-6, s. 69-80
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Tidskriftsartikel (refereegranskat)abstract
- Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42 degrees C, using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate, at a cellulase loading of 37 filter paper units/g of cellulose, and a beta-glucosidase loading of 38 IU/ g of cellulose. The detoxification of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37 degrees C, owing to the cessation of ethanol fermentation after the first 10 h.
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| 8. |
- Bondesson, Pia-Maria, et al.
(författare)
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Optimizing Ethanol and Methane Production from Steam-pretreated, Phosphoric Acid-impregnated Corn Stover.
- 2015
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Ingår i: Applied Biochemistry and Biotechnology. - : Springer Science and Business Media LLC. - 1559-0291 .- 0273-2289. ; 175:3, s. 1371-1388
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Tidskriftsartikel (refereegranskat)abstract
- Pretreatment is of vital importance in the production of ethanol and methane from agricultural residues. In this study, the effects of steam pretreatment with phosphoric acid on enzymatic hydrolysis (EH), simultaneous saccharification and fermentation (SSF), anaerobic digestion (AD) and the total energy output at three different temperatures were investigated. The effect of separating the solids for SSF and the liquid for AD was also studied and compared with using the whole slurry first in SSF and then in AD. Furthermore, the phosphoric acid was compared to previous studies using sulphuric acid or no catalyst. Using phosphoric acid resulted in higher yields than when no catalyst was used. However, compared with sulphuric acid, an improved yield was only seen with phosphoric acid in the case of EH. The higher pretreatment temperatures (200 and 210 °C) resulted in the highest yields after EH and SSF, while the highest methane yield was obtained with the lower pretreatment temperature (190 °C). The highest yield in terms of total energy recovery (78 %) was obtained after pretreatment at 190 °C, but a pretreatment temperature of 200 °C is, however, the best alternative since fewer steps are required (whole slurry in SSF and then in AD) and high product yields were obtained (76 %).
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| 9. |
- Ehlde, M, et al.
(författare)
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Influence of experimental errors on the determination of flux control coefficients from transient metabolic concentrations
- 1996
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Ingår i: Biochemical Journal. - 0264-6021. ; 313, s. 721-727
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Tidskriftsartikel (refereegranskat)abstract
- The influence of experimental errors on the determination of flux control coefficients from transient metabolite concentrations with the method proposed by Delgado and Liao [(1992) Biochem. J. 282, 919-927] has been investigated by using Monte Carlo simulations. The method requires least-squares fitting of the transient metabolite concentrations. Three different fitting methods have been evaluated. Simulated metabolite concentrations of a fictive metabolic pathway were scattered randomly, emulating experimental errors, before performing the fits. This was repeated a large number of times; the mean values and standard deviations of the resulting control coefficients are reported. The results show that the proposed method for determining control coefficients is too sensitive to experimental errors to be practicable, with theoretically justified fitting methods. This is in particular due to the high degree of correlation between the concentrations. An alternative ad hoc fitting method produced biased mean values of the estimates of the control coefficients, but with remarkably low standard deviations.
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| 10. |
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