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Antje C. Spiess - One of the best experts on this subject based on the ideXlab platform.

  • Factors influencing the operational stability of NADPH-dependent alcohol dehydrogenase and an NADH-dependent variant thereof in gas/solid Reactors
    Journal of Molecular Catalysis B-enzymatic, 2010
    Co-Authors: Liliya Kulishova, Kerasina Dimoula, Max Jordan, Astrid Wirtz, Diana Hofmann, Beatrix Santiago-schübel, Jörg Fitter, Martina Pohl, Antje C. Spiess
    Abstract:

    Abstract The continuous enzymatic gas/solid bio-Reactor serves both for the production of volatile fine chemicals and flavors on an industrial scale and for thermodynamically controlled investigation of substrate and water effects on enzyme preparations for research purposes. Here, we comparatively investigated the molecular effects on the operational stability of NADPH-dependent Lactobacillus brevis alcohol dehydrogenase and an NADH-dependent variant thereof, Lb ADH G37D, in the gas/solid bioReactor. The reference reaction is the reduction of acetophenone to ( R )-1-phenylethanol with concomitant oxidation of 2-propanol to acetone for the purpose of regeneration of the redox cofactor. It could be clearly shown that not the thermostability of the cofactor, but the thermostability of the proteins in the solid dry state govern the order of magnitude of the operational stability of both purified enzymes in the gas/solid Reactor at low thermodynamic activity of water and substrate. However, at higher thermodynamic activity the operational stability in the gas/solid Reactor is overlaid by stabilizing and destabilizing effects of the substrates that require further investigation. We demonstrated first evidence that the substrate affinity of the two variants in the gas/solid Reactor is similar to the affinity in aqueous medium. We could also show that partial unfolding of the proteins with subsequent aggregation are the factors governing protein thermo-in-stability both in the dissolved and in the dry state. Thus, stability investigations of enzymes in the dry state are suggested to predict their basal level of operational stability in gas/solid reactions.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology Journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at aw=0.9. Significant hysteresis during water desorption is identified, resulting g in up to 0.6 mgwater/mgprotein, for lyophilized enzyme preparation and up to 10 mgwater/mgprotein for deposited enzyme preparation The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mgprotein, at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at water activity of 0.9. Significant hysteresis during water desorption is identified, resulting in up to 0.6 mg(water)/mg(protein), for lyophilized enzyme preparation and up to 10 mg(water)/mg(protein) for deposited enzyme preparation. The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mg(protein), at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

Kerasina Dimoula - One of the best experts on this subject based on the ideXlab platform.

  • Factors influencing the operational stability of NADPH-dependent alcohol dehydrogenase and an NADH-dependent variant thereof in gas/solid Reactors
    Journal of Molecular Catalysis B-enzymatic, 2010
    Co-Authors: Liliya Kulishova, Kerasina Dimoula, Max Jordan, Astrid Wirtz, Diana Hofmann, Beatrix Santiago-schübel, Jörg Fitter, Martina Pohl, Antje C. Spiess
    Abstract:

    Abstract The continuous enzymatic gas/solid bio-Reactor serves both for the production of volatile fine chemicals and flavors on an industrial scale and for thermodynamically controlled investigation of substrate and water effects on enzyme preparations for research purposes. Here, we comparatively investigated the molecular effects on the operational stability of NADPH-dependent Lactobacillus brevis alcohol dehydrogenase and an NADH-dependent variant thereof, Lb ADH G37D, in the gas/solid bioReactor. The reference reaction is the reduction of acetophenone to ( R )-1-phenylethanol with concomitant oxidation of 2-propanol to acetone for the purpose of regeneration of the redox cofactor. It could be clearly shown that not the thermostability of the cofactor, but the thermostability of the proteins in the solid dry state govern the order of magnitude of the operational stability of both purified enzymes in the gas/solid Reactor at low thermodynamic activity of water and substrate. However, at higher thermodynamic activity the operational stability in the gas/solid Reactor is overlaid by stabilizing and destabilizing effects of the substrates that require further investigation. We demonstrated first evidence that the substrate affinity of the two variants in the gas/solid Reactor is similar to the affinity in aqueous medium. We could also show that partial unfolding of the proteins with subsequent aggregation are the factors governing protein thermo-in-stability both in the dissolved and in the dry state. Thus, stability investigations of enzymes in the dry state are suggested to predict their basal level of operational stability in gas/solid reactions.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology Journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at aw=0.9. Significant hysteresis during water desorption is identified, resulting g in up to 0.6 mgwater/mgprotein, for lyophilized enzyme preparation and up to 10 mgwater/mgprotein for deposited enzyme preparation The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mgprotein, at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at water activity of 0.9. Significant hysteresis during water desorption is identified, resulting in up to 0.6 mg(water)/mg(protein), for lyophilized enzyme preparation and up to 10 mg(water)/mg(protein) for deposited enzyme preparation. The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mg(protein), at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

Martina Pohl - One of the best experts on this subject based on the ideXlab platform.

  • Factors influencing the operational stability of NADPH-dependent alcohol dehydrogenase and an NADH-dependent variant thereof in gas/solid Reactors
    Journal of Molecular Catalysis B-enzymatic, 2010
    Co-Authors: Liliya Kulishova, Kerasina Dimoula, Max Jordan, Astrid Wirtz, Diana Hofmann, Beatrix Santiago-schübel, Jörg Fitter, Martina Pohl, Antje C. Spiess
    Abstract:

    Abstract The continuous enzymatic gas/solid bio-Reactor serves both for the production of volatile fine chemicals and flavors on an industrial scale and for thermodynamically controlled investigation of substrate and water effects on enzyme preparations for research purposes. Here, we comparatively investigated the molecular effects on the operational stability of NADPH-dependent Lactobacillus brevis alcohol dehydrogenase and an NADH-dependent variant thereof, Lb ADH G37D, in the gas/solid bioReactor. The reference reaction is the reduction of acetophenone to ( R )-1-phenylethanol with concomitant oxidation of 2-propanol to acetone for the purpose of regeneration of the redox cofactor. It could be clearly shown that not the thermostability of the cofactor, but the thermostability of the proteins in the solid dry state govern the order of magnitude of the operational stability of both purified enzymes in the gas/solid Reactor at low thermodynamic activity of water and substrate. However, at higher thermodynamic activity the operational stability in the gas/solid Reactor is overlaid by stabilizing and destabilizing effects of the substrates that require further investigation. We demonstrated first evidence that the substrate affinity of the two variants in the gas/solid Reactor is similar to the affinity in aqueous medium. We could also show that partial unfolding of the proteins with subsequent aggregation are the factors governing protein thermo-in-stability both in the dissolved and in the dry state. Thus, stability investigations of enzymes in the dry state are suggested to predict their basal level of operational stability in gas/solid reactions.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology Journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at aw=0.9. Significant hysteresis during water desorption is identified, resulting g in up to 0.6 mgwater/mgprotein, for lyophilized enzyme preparation and up to 10 mgwater/mgprotein for deposited enzyme preparation The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mgprotein, at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

  • Substrate and water adsorption phenomena in a gas/solid enzymatic Reactor
    Biotechnology journal, 2009
    Co-Authors: Kerasina Dimoula, Martina Pohl, Jochen Büchs, Antje C. Spiess
    Abstract:

    The adsorption of water and substrates to dry deposited alcohol dehydrogenase from Lactobacillus brevis (LBADH) is studied in a continuous enzymatic gas/solid Reactor. This work is aiming at obtaining a deeper and more thorough understanding of the enzyme microenvironment in the gas/solid system of acetophenone reduction with concomitant oxidation of 2-propanol. Extensive water adsorption studies showed that the effect of sucrose in the enzyme preparation on the water adsorption isotherm is significant for water activities exceeding 0.5 and reaches a factor 2 with respect to bead mass at water activity of 0.9. Significant hysteresis during water desorption is identified, resulting in up to 0.6 mg(water)/mg(protein), for lyophilized enzyme preparation and up to 10 mg(water)/mg(protein) for deposited enzyme preparation. The adsorption of the substrates is quantified here for the first time. Whereas the adsorption of the main substrate, acetophenone, may reach a significant level of up to 6 mg/mg(protein), at an acetophenone activity of 0.32, the secondary substrate, 2-propanol is not adsorbed at a detectable degree. The presence of water leads to a decrease of the adsorbed amount of acetophenone, by approximately 25%, at a water activity of 0.54.

Gernot Krammer - One of the best experts on this subject based on the ideXlab platform.

  • Jet pulsed filters as chemical gas/solid Reactors—Experiment and model prediction
    Chemical Engineering and Processing: Process Intensification, 2005
    Co-Authors: A. Kavouras, Gernot Krammer
    Abstract:

    Abstract A recently introduced generations filter model [A. Kavouras, G. Krammer, Distributions of age, thickness and gas velocity in the cake of jet pulsed filters—application and validation of a generations filter model, Chem. Eng. Sci. 58 (2003) 223–238] allows one to determine from macroscopic experimental data the distribution of cake thickness versus filter area and in consequence the complete filter behaviour. Based on a simplified assumption this generations filter model is employed in a predictive way to estimate operating points of imperfectly cleaned filters. However, filter behaviour in terms of the fraction of the filter area cleaned when jet pulsed cannot be predicted yet without experimental data. This is due to the variable cleaning properties of the cake, which are dependent on the filter operating parameters. Combining the predictive filter model and a model for the chemical reactions in the fixed bed of the filter cake [A. Kavouras, B. Breitschaedel, G. Krammer, A. Garea, J.A. Marques, A. Irabien, SO 2 removal in the filter cake of a jet pulsed filter: a combined filter and fixed bed reaction model, Ind. Eng. Chem. Res. 41 (2002) 5459–5469], the filter performance as a gas/solid Reactor can also be simulated in a predictive way. It is found that the pressure drop across the filter has a weak influence on filter performance as a gas/solid Reactor.

  • Deriving cake detachment versus cake area load in a jet pulsed filter by a mechanistic model
    Powder Technology, 2003
    Co-Authors: Andreas Kavouras, Gernot Krammer
    Abstract:

    Abstract Dust particles in gas streams are frequently removed through cake filtration on rigid or flexible filter media. The cake is mostly removed by jet pulses. There patchy cleaning is a typical phenomenon, which means that a patch of a filter cake is torn off by the pressure pulse completely whereas the rest of the cake remains intact on the filter. Pilot plant and large-scale filters are usually divided in compartments where only one compartment is cleaned at a time. Often only some of the compartments, i.e. only part of the total filter area is cleaned at the end of one filter cycle. In this study, a model is proposed that mirrors this behaviour from the start up of the filtration process with a clean filter medium through division of the filter in model areas. Each model area represents one cake of uniform thickness and a fraction of this cake is removed altogether at the end of a filter cycle, provided this cake is exposed to a jet pulse. In order to gain a true detachment function of the pulsed cake (i.e. the removed cake fraction versus cake thickness), the single compartments are treated separately in this study, so that an intrinsic detachment function of the filter cake can be decided from pilot plant filter experiments. These genuine cake detachment functions are typical of one filter operating point only, although the pulse reservoir pressure, the duration of a pulse and the cleaning system are identical. This implies that the cleaning effect of a jet pulse on the filter depends on the cake mass and its distribution on the filter but also cake compaction and cohesive effects could be liable for the discrepancies in the cake detachment functions determined. A by-product of the model application is an estimate of the total solid hold up on the filter cloth, which is in excellent agreement with the experiments presented here. Also the distribution of the solid load and gas velocity over the filter area are decided as well as the residence time distribution of the solid in the filter cake. These are key factors for modelling the filter as a chemical gas solid Reactor. The model application can give an estimate, to which extent the solid concentration in the gas of jet pulsed filters is increased during filter cleaning due to disintegration of removed cake. This phenomenon is known as redeposition or reentrainment of detached cake.

Stein O. Wasbø - One of the best experts on this subject based on the ideXlab platform.

  • An integration scheme for stiff solid-gas Reactor models
    Modeling Identification and Control: A Norwegian Research Bulletin, 2001
    Co-Authors: Bjarne A. Foss, Stein O. Wasbø
    Abstract:

    Many dynamic models encounter numerical integration problems because of a large span in the dynamic modes. In this paper we develop a numerical integration scheme for systems that include a gas phase, and solid and liquid phases, such as a Gas-Solid Reactor. The method is based on neglecting fast dynamic modes and exploiting the structure of the algebraic equations. The integration method is suitable for a large class of industrially relevant systems. The methodology has proven remarkably efficient. It has in practice performed excellent and been a key factor for the success of the industrial simulator for electrochemical furnaces for ferro-alloy production

  • An integration scheme for stiff solid–gas Reactor models
    Computer Methods in Applied Mechanics and Engineering, 2001
    Co-Authors: Bjarne A. Foss, Stein O. Wasbø
    Abstract:

    Abstract Many dynamic models encounter numerical integration problems because of a large span in the dynamic modes. In this paper we develop a numerical integration scheme for systems that include a gas phase, and solid and liquid phases, such as a gas–solid Reactor. The method is based on neglecting fast dynamic modes and exploiting the structure of the algebraic equations. The integration method is suitable for a large class of industrially relevant systems. The methodology has proven remarkably efficient. It has in practice performed excellently and been a key factor for the success of the industrial simulator for electrochemical furnaces for ferro-alloy production.