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  • 1.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Computational Studies of Metal Clusters and Carbon Nanotubes2008Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Carbon nanotubes constitute a promising candidate material in the realisation of nanoscaled electronics. This requires the ability for systematic production of carbon nanotubes with certain properties. This is called selective carbon nanotube growth. Two important aspects related to carbon nanotube growth are investigated in order to shed some light on this issue. First the melting behaviour of nanometer sized iron particles is investigated using molec- ular dynamics simulations. The iron nanoparticles studied are mounted on a porous Al2 O3 substrate in order to mimic the experimental situation during nanotube growth with the chemical vapour deposition method. This showed that the melting temperature of a cluster on a porous substrate may be lower than the melting temperature of a cluster on a flat sub- strate. This means that the catalyst particles used for nanotube growth may be liquid. In association with these studies the role of surface curvature to melting behaviour is explored further. The second presented study concerns the docking of nickel clusters to open single wall carbon nanotube ends. The motivation for this study was the possibility to continue growth of a carbon nanotube by docking of catalyst particles to its end. This work may also be of importance for the creation of electric junctions between carbon nanotubes and metal elec- trodes. This study showed that independent of whether the metal was gently put on the nanotube end or brutally forced to the end, it is the metal that adapts to the nanotube and not vice versa. For forced docking it was seen that carbon might dissolve in to the metal. This was not seen for the gently docked clusters. Carbon dissolution might affect the electronic properties of the metal (carbide) and nanotube-metal junction.

  • 2.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    First Principles Studies of the Effect of Nickel Carbide Catalyst Composition on Carbon Nanotube Growth2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 42, p. 18045-18050Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations were used to investigate the stability of single-walled carbon nanotubes (CNTs) attached to nanoparticles. The total energies and the adhesion energies between the CNTs and the nanoparticles were calculated for systems where the nanoparticles were either pure Ni or Ni carbide. It was found that the adhesion between the CNT and a pure Ni cluster is stronger than between the same CNT and a Ni carbide cluster although the energy difference was small compared to the total adhesion energies. This adhesion strength implies that CNTs are likely to remain attached to both pure Ni and Ni carbide clusters and that either pure Ni or Ni carbide clusters may be docked onto the open CNT ends to achieve continued growth or electronic contacts between CNTs and electrode materials. The system with a CNT attached to a pure Ni cluster was found to be energetically favored compared to a system containing the same CNT attached to a Ni carbide. The difference in total energy implies that a CNT should act as a sink for C atoms dissolved in the Ni carbide cluster, which means that the dissolved C atoms will be drained from the cluster, yielding a pure metal in the zero Kelvin thermodynamic limit. It is argued that this draining procedure is likely to occur even if carbon is added to the cluster at a proper rate, for example, during CNT growth.

  • 3.
    Ferreira, Jorge A.
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Lennartsson, Patrik R.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    Airlift bioreactors for fish feed fungal biomass production using edible filamentous fungi2017Conference paper (Refereed)
    Abstract [en]

    Airlift bioreactors are generally considered to be better alternatives for cultivation of filamentous fungi in comparison to stirred-tank bioreactors or bubble columns bioreactors. The reason for the former includes fungal growth around all internal parts including impellers, baffles or pH, temperature and oxygen probes limiting mass transfer, whereas the latter is limited by air flow rates that can be applied before the system provides deficient mixing and so mass transfer rates. Spent sulphite liquor, a by-product from the paper pulp industry, was used for cultivation of edible Rhizopus sp., a strain isolated from Indonesian tempeh used as human food, using a 26 L airlift bioreactor. Increasing the aeration rate from 0.15 to 1 vvm led to increased biomass production (1 vs 7 g/L). The aeration rate was also found to influence fungal morphology and metabolite production during batch cultivation. Rhizopus sp. shifted from mycelial suspensions at 0.15 and 0.5 vvm to small compact pellets of regular size at 1 vvm. The production of ethanol and lactic acid, a proof of sub-optimal aeration conditions, was also reduced when increasing the aeration rate from 0.15 to 1 vvm. The produced biomass was found to be composed, on a dry weight basis, of 30-50% protein, 2-7% lipids, and 3-9% glucosamine. Considering the edible character of the fungus used as well as its biomass nutritional characteristics, there is a potential for its use as fishmeal replacement within the increasing aquaculture sector.

  • 4.
    Ishola, Mofoluwake M.
    University of Borås, School of Engineering.
    Novel application of membrane bioreactors in lignocellulosic ethanol production: simultaneous saccharification, filtration and fermentation (SSFF)2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biofuels production and utilisation can reduce the emission of greenhouse gases, dependence on fossil fuels and also improve energy security. Ethanol is the most important biofuel in the transportation sector; however, its production from lignocelluloses faces some challenges. Conventionally, lignocellulosic hydrolysis and fermentation has mostly been performed by separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). SHF results in product inhibition during enzymatic hydrolysis and increased contamination risk. During SSF, suboptimal conditions are used and the fermenting organism cannot be reused. Bacterial contamination is another major concern in ethanol production, which usually results in low ethanol yield. In these studies, the above-mentioned challenges have been addressed. A novel method for lignocellulosic ethanol production ‘Simultaneous saccharification filtration and fermentation (SSFF)’ was developed. It circumvents the disadvantages of SSF and SHF; specifically, it uses a membrane for filtration and allows both the hydrolysis and fermentation to be carried out at different optimum conditions. SSFF also offers the possibility of cell reuse for several cultivations. The method was initially applied to pretreated spruce, with a flocculating strain of yeast Saccharomyces cerevisiae. SSFF was further developed and applied to pretreated wheat straw, a xylose rich lignocellulosic material, using encapsulated xylose fermenting strain of S. cerevisiae. High solids loading of 12% suspended solids (SS) was used to combat bacterial contamination and improve ethanol yield. Oil palm empty fruit bunch (OPEFB) was pretreated with fungal and phosphoric acid in order to improve its ethanol yield. An evaluation of biofuel production in Nigeria was also carried out. SSFF resulted in ethanol yield of 85% of the theoretical yield from pretreated spruce with the flocculating strain. Combination of SSFF with encapsulated xylose fermenting strain facilitated simultaneous glucose and xylose utilisation when applied to pretreated wheat straw; this resulted in complete glucose consumption and 80% xylose utilisation and consequently, 90% ethanol yield of the theoretical level. High solids loading of 12% SS of pretreated birch resulted in 47.2 g/L ethanol concentration and kept bacterial infection under control; only 2.9 g/L of lactic acid was produced at the end of fermentation, which lasted for 160 h while high lactic acid concentrations of 42.6 g/L and 35.5 g/L were produced from 10% SS and 8% SS, respectively. Phosphoric acid pretreatment as well as combination of fungal and phosphoric pretreatment improved the ethanol yield of raw OPEFB from 15% to 89% and 63% of the theoretical value, respectively. In conclusion, these studies show that SSFF can potentially replace the conventional methods of lignocellulosic ethanol production and that high solids loading can be used to suppress bacterial infections during ethanol productions, as well as that phosphoric acid pretreatment can improve ethanol yield from lignocellulosic biomass.

  • 5.
    Ishola, Mofoluwake M.
    et al.
    University of Borås, School of Engineering.
    Brandberg, Tomas
    University of Borås, School of Engineering.
    Taherzadeh, Mohammad J
    University of Borås, School of Engineering.
    Minimization of Bacterial Contamination with High Solid Loading during Ethanol Production from Lignocellulosic Materials2014Conference paper (Refereed)
    Abstract [en]

    Ethanol is the most important renewable fuel in the transportation sector. Its production from lignocellulosic materials, commonly referred to as second generation ethanol, is considered more attractive than production from starch and sugar crops. Bacterial contamination by lactic acid-producing bacteria is still a major problem during ethanol production processes. Bacteria compete with the yeast by consuming the sugars and the nutrients required by the yeast for efficient ethanol production. This often causes substantial economic losses at industrial fermentations. In this study, without any sterilization of the substrate, simultaneous saccharification and fermentation (SSF) was performed using cellulase Cellic® Ctec2 enzyme for hydrolysis and Baker’s yeast, Saccharomyces cerevisiae, was used as the fermenting organism with different loads of suspended solids - 8%, 10% and 12%. With8%and 10% SS, there was a significant contamination, which caused consumption of both hexoses pentose sugars in the fermentation medium, this resulted in lactic acid concentrations of 43 g/L and 36 g/L from 10% SS and 8% SS respectively. In contrast, only 2.9 g/L lactic acid was observed with 12% SS. An ethanol concentration of 47 g/L was produced from high solid loading of 12% SS while just 26 g/L and 23 g/L were produced from 10% and 8% SS respectively. Our results show that SSF with 12% SS has an increased concentration of inhibitors, particularly acetic acid which selectively inhibited the bacterial growth without affecting the metabolic activities of the yeast during the fermentation.

  • 6.
    Moradian, Farzad
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    A. Tchoffor, Placid
    SP Technical Research Institute of Sweden.
    O. Davidsson, Kent
    SP Technical Research Institute of Sweden.
    Pettersson, Anita
    University of Borås, Faculty of Textiles, Engineering and Business.
    Backman, Rainer
    Umeå University.
    Thermodynamic equilibrium prediction of bed agglomeration tendency in dual fluidized-bed gasification of forest residues2016In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 154Article in journal (Refereed)
    Abstract [en]

    Dual fluidized-bed (DFB) gasification is one of the recently developed technologies for production of heat, power, transportation fuels and synthetic chemicals through steam gasification of biomass. Bed agglomeration is a serious ash-related problem that should be taken into account when biomass-based fuels are selected for fluidized-bed gasification and combustion. This study developed a thermodynamic equilibrium model to assess the risk of bed agglomeration in gasification and combustion reactors of a DFB gasifier using biomass (forest residues) as feedstock. The modelling approach combined thermodynamic equilibrium calculations with chemical fractionation technique to predict the composition and melting behaviour of the fuel-derived ash as well as bed particles coating layer in the gasification and combustion reactors. FactSage was employed for the thermodynamic equilibrium calculations. The modelling results were then compared with experimental data obtained from a full-scale DFB gasifier to estimate the reliability and validity of the predictive model. In general, a good agreement was found between the modelling results and experimental observations. For the forest residues as feedstock and olivine as bed material, the modelling results indicate a low risk of bed agglomeration in the DFB gasifier, as long as the dominant temperature in the combustion zone is below 1020 °C. In contrast, quartz as bed material in the DFB gasifier was shown to significantly increase the risk of bed agglomeration through coating-induced agglomeration mechanism. © 2016 Elsevier B.V.

  • 7.
    Morshed, Mohammad Neaz
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business. University of Boras.
    Bouazizi, Nabil
    Behary, Nemeshwaree
    Guan, Jinping
    College of Textile and Clothing Engineering, Soochow University.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Stabilization of zero valent iron (Fe0) on plasma/dendrimer functionalizedpolyester fabrics for Fenton-like removal of hazardous water pollutants2019In: Chemical Engineering Journal, ISSN 1385-8947, Vol. 374, p. 658-673Article in journal (Refereed)
    Abstract [en]

    This study reports the synthesis, immobilization and stabilization of multiscale zero valent iron (Fe0=ZVI)particles on fibrous polyester (PET) nonwoven membrane for heterogeneous Fenton-like removal of hazardouspollutants in water. Activation of PET fiber surface by air atmospheric plasma with or without a consecutivegrafting of hyperbranched poly-(ethylene glycol)-pseudo generation 5 dendrimer having hydroxyl (-OH) endgroup functionality created polar reactive functional groups allowing immobilization and stabilization of ZVIparticles. Synthesis of ZVI was carried out through chemical reduction of ferric ions, either through a single stepin-situ, or a two-step ex-situ reduction-immobilization method. The nonwovens were characterized usingwettability, Fourier transform infrared spectroscopy (FTIR), optical microscopy, scanning electron microscopy(SEM), X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and thermo-gravimetric analysis(TGA). Results confirmed the formation and immobilization of nano to sub-micronic multi-scale ZVI particles.The particle size, distribution and stability of ZVI were found to be influenced by the methods of ZVI synthesisand PET surface activation used. The ZVI particles initially formed, quasi-instantaneously turned to yellowishbrown indicating the formation of oxide layer, except in the case of dendrimer grafted PET, where higher content(22.30%) and stability of ZVI was detected. All ZVI immobilized nonwovens exhibited high effectiveness towardsFenton-like degradation of malachite green dye (20 ppm), with fastest color removal (98% in 20 min) achievedby dendrimer/ex-situ nonwoven. This nonwoven could be used up to eight repeated cycles providing low TDS (52 ppm) and high COD reduction (66.23%). Combined use of eco-friendly plasma and dendrimer grafting,provides efficient fibrous textile base heterogeneous catalysis.

  • 8.
    Morshed, Mohammad Neaz
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Bouazizi, Nabil
    Behary, Nemeshwaree
    Vieillard, Julien
    Thoumire, Olivier
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Azzouz, Abdelkrim
    Iron-loaded amine/thiol functionalized polyester fibers with high catalyticactivities: Comparative study2019In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234Article in journal (Refereed)
    Abstract [en]

    Dispersion of iron nanoparticles (Fe-NPs) was achieved on polyester fabrics (PET) beforeand after incorporation of dendrimers (PAMAN), 3-(aminopropyl) triethoxysilane (APTES) orthioglycerol (SH). The catalytic activity of the resulting materials (PET-Fe, PET-PAMAM-Fe,PET-APTES-Fe and PET-SH-FE) was comparatively investigated in the degradation of 4-nitrophenol(4-NP) and methylene-blue (MB. Full characterization through diverse instrumentalmethods allowed correlating the type of the organic moiety incorporated to the Fe content,catalytic properties and stability. The highest 4-NP degradation yield reached 99.6 % in 12 minsfor PET-SH-Fe. The catalytic activity was explained in terms of reactant interaction with Fe-NPs. The 1st order reaction kinetics and pseudo-1st order adsorption kinetics provide evidenceof the key-role of reactant adsorption. These findings allow envisaging the preparation of fiberbasedcatalysts for potential uses in environmental and green chemistry.

  • 9.
    Nair, Ramkumar B
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Kalif, Mahdi
    University of Borås, Faculty of Textiles, Engineering and Business.
    Ferreira, Jorge A.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    Lennartsson, Patrik R.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Mild-temperature dilute acid pretreatment for integration of first and second generation ethanol processes2017In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 245, p. 145-151Article in journal (Refereed)
    Abstract [en]

    The use of hot-water (100 °C) from the 1st generation ethanol plants for mild-temperature lignocellulose pretreatment can possibly cut down the operational (energy) cost of 2nd generation ethanol process, in an integrated model. Dilute-sulfuric and -phosphoric acid pretreatment at 100 °C was carried out for wheat bran and whole-stillage fibers. Pretreatment time and acid type influenced the release of sugars from wheat bran, while acid-concentration was found significant for whole-stillage fibers. Pretreatment led up-to 300% improvement in the glucose yield compared to only-enzymatically treated substrates. The pretreated substrates were 191–344% and 115–300% richer in lignin and glucan, respectively. Fermentation using Neurospora intermedia, showed 81% and 91% ethanol yields from wheat bran and stillage-fibers, respectively. Sawdust proved to be a highly recalcitrant substrate for mild-temperature pretreatment with only 22% glucose yield. Both wheat bran and whole-stillage are potential substrates for pretreatment using waste heat from the 1st generation process for 2nd generation ethanol.

  • 10.
    Nair, Ramkumar B
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Ravula, Vamsikrishna
    University of Borås, Faculty of Textiles, Engineering and Business.
    Lennartsson, Patrik R.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    Neurospora intermedia pellets for enhanced ethanol and fungal biomass production from wheat straw2017In: Proceedings of 39th Symposium on Biotechnology for Fuels and Chemicals, 2017Conference paper (Refereed)
    Abstract [en]

    Recent studies at our research group have described an ‘integrated-biorefinery’ model for the existing 1st generation wheat-based ethanol facilities, by using edible filamentous fungus, Neurospora intermedia. The process focuses on the production of 2nd generation ethanol together with fungal biomass (for animal or aquaculture feed applications) from wheat straw. A final ethanol yield of 94% (theoretical maximum based on substrate glucan content) was obtained with N. intermedia fermentation in dilute phosphoric acid pretreated (0.7%w/v acid, 7min at 201±4°C) and enzymatically hydrolyzed (10FPU cellulase/g substrate) straw. Fungal cultivation in liquid straw hydrolysate resulted in a maximum of 3.71±0.11g/L dry fungal biomass. Considering the industrial significance of the fungal process, attempts were made to manipulate N. intermedia to grow as pellet forms in the straw hydrolysate, for the first time. Of the various culture conditions screened, stable pellet morphology was obtained at pH 3.0 to 5.5, resulting in uniform pellets with size ranging from 2.5 to 4.25mm. Fermentation using N. intermedia pellets in the liquid straw hydrolysate, resulted in about 31% increase in the ethanol yield, with an improved glucose assimilation by the pellets (82% reduction) as opposed to filamentous forms (51% reduction), at similar culture conditions. The growth of fungal pellets in presence of inhibitors (at different concentrations of acetic acid and furfural) resulted in about 11% to 45% increase in ethanol production as compared to filamentous forms, at similar growth conditions in the liquid straw hydrolysate. Detailed results on N. intermedia pelletization in liquid straw hydrolysate will be discussed in this presentation.

  • 11.
    Olsson, Johanna
    University of Borås, School of Engineering.
    Fuel dispersion and bubble flow distribution in fluidized beds2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Fluidized bed technology is used for thermal conversion of solid fuels (combustion and gasification) and is especially suitable for conversion of low-rank fuels such as biomass and waste. The performance of fluidized bed units depends on the fuel mixing and fuel-gas contact. Thus, it is important to understand these two phenomena in order to develop models for reliable design and scale up of fluidized bed units. This work investigates, under conditions representative for industrial fluidized bed units, the lateral fuel mixing (in a unit with a cross section of 1.44 m2 both at hot and cold conditions) and the bubble flow distribution (in a 1.2 m-wide 2-dimensional unit). The work confirms previous findings on the formation of preferred bubble paths and shows that these bubble paths are enhanced by lowering the fluidization velocity, increasing the dense bed height and reducing the pressure drop across the gas distributor. From the fuel mixing experiments, an estimation of the lateral effective dispersion coefficient to values in the order of 10-3 m2/s is obtained under both hot and cold conditions. The experiments under cold conditions give additional qualitative information on the fuel mixing patterns such as flotsam/jetsam tendencies. The camera probe developed for fuel tracking under hot conditions enables to study the fuel dispersion under real operation at relevant industrial scales. Based on the characteristics of the bubble path flow, a model for the horizontal fuel dispersion on a macroscopic scale is formulated and shown to be able to give a good description of the experimental data. As opposed to the commonly applied diffusion-type modeling of the lateral solids dispersion, the proposed model facilitates integration with models of the bubble flow. Thus, the present modeling work is a first step to provide a modeling of the fuel dispersion, which uses as inputs only the main operational parameters of the fluidized bed.

  • 12.
    Osadolor, Osagie Alex
    University of Borås, Faculty of Textiles, Engineering and Business.
    Nair, Ramkumar B
    University of Borås, Faculty of Textiles, Engineering and Business.
    Lennartsson, Patrik R.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    Effect of media rheology and bioreactor hydrodynamics on filamentous fungi fermentation of lignocellulosic and starch-based substrates under pseudoplastic flow conditions2018In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 263, p. 250-257Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to study how media rheology and bioreactor hydrodynamics would influence fermentation of lignocellulosic and starch-based substrates under pseudoplastic flow conditions. This was investigated using hydrolyzed wheat straw, wheat-based thin stillage and filamentous fungi as inoculum in bubble column, airlift and horizontal hybrid tubular/bubble column (textile bioreactor) bioreactors. The rheological models showed that the consistency index was dependent on biomass growth (R2 0.99) while the flow behavior index depended on biomass growth and suspended solid (R2 0.99). Oxygen transfer rate above 0.356 mmol-O2/L/h was needed for growing fungi with a cube-root growth rate constant of 0.03 g1/3/L1/3/h. At 1.4 VVM aeration the textile bioreactor performed better than others with minimal foaming, yields of 0.22 ± 0.01 g/g and 0.47 ± 0.01 g/g for ethanol and biomass, substrate consumption rate of 0.38 g/L/h. Operating the bioreactors with air-flowrate to cross-sectional area ratio of 8.75 × 10−3 (m3/s/m2) or more led to sustained foaming.

  • 13.
    Pourbafrani, Mohammad
    University of Borås, School of Engineering.
    Citrus Waste Biorefinery: Process Development, Simulation and Economic Analysis2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The production of ethanol and other sustainable products including methane, limonene and pectin from citrus wastes (CWs) was studied in the present thesis. In the first part of the work, the CWs were hydrolyzed using enzymes – pectinase, cellulase and β-glucosidase – and the hydrolyzate was fermented using encapsulated yeasts in the presence of the inhibitor compound ‘limonene’. However, the application of encapsulated cells may be hampered by the high price of encapsulation, enzymes and the low stability of capsules’ membrane at high shear stresses. Therefore, a process based on dilute-acid hydrolysis of CWs was developed. The limonene of the CWs was effectively removed through flashing of the hydrolyzate into an expansion tank. The sugars present in the hydrolyzate were converted to ethanol using a flocculating yeast strain. Then ethanol was distilled and the stillage and the remaining solid materials of the hydrolyzed CWs were anaerobically digested to obtain methane. The soluble pectin content of hydrolyzate can be precipitated using the produced ethanol. One ton of CWs with 20% dry weight resulted in 39.64 l ethanol, 45 m3 methane, 8.9 l limonene, and 38.8 kg pectin. The feasibility of the process depends on the transportation cost and the capacity of CW. For example, the total cost of ethanol with a capacity of 100,000 tons CW/year was 0.91 USD/L, assuming 10 USD/ton handling and transportation cost of CW to the plant. Changing the plant capacity from 25,000 to 400,000 tons CW per year results in reducing ethanol costs from 2.55 to 0.46 USD/L in an economically feasible process. Since this process employs a flocculating yeast strain, the major concern in design of the bioreactor is the sedimentation of yeast flocs. The size of flocs is a function of sugar concentration, time and flow. A CFD model of bioreactor was developed to predict the sedimentation of flocs and the effect of flow on distribution of flocs. The CFD model predicted that the flocs sediment when they are larger than 180 micrometer. The developed CFD model can be used in design and scale-up of the bioreactor. For the plants with low CW capacity, a steam explosion process was employed to eliminate limonene and the treated CW was used in a digestion plant to produce methane. The required cost of this pretreatment was about 0.90 million dollars for 10,000 tons/year of CWs.

  • 14.
    Purwadi, Ronny
    University of Borås, School of Engineering.
    Continuous ethanol production from dilute-acid hydrolyzates: detoxification and fermentation strategy2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The production of fuel ethanol from cellulosic biomass is of growing interest around the world. Lignocellulosic residuals can be used to produce transportation fuel, with the overall process having little net production of greenhouse gases. Lignocellulosic materials are available as a by-product of many industrial processes and agricultural materials, or can potentially be produced from dedicated energy crops. The production of ethanol from lignocellulosic materials includes hydrolysis which breaks the cellulose and hemicellulose polymers to fermentable sugars, followed by cultivation which converts the sugars into ethanol, and finally a separation process where ethanol purification is carried out to produce fuel ethanol. However, some byproducts such as furan compounds are released during chemical hydrolysis and inhibit the yeast during cultivation. This work contributes a solution to overcome these problems especially for a continuous process which is economically superior. Hydrolyzate detoxification using lime (â overlimingâ ) in concert with the capability of yeast to carry out in-situ detoxification is focused upon in the work. The kinetics of the overliming process were studied, where both sugars and furan compounds are degraded through a formation of complex ion. The sudden addition of lime in a batch process shows severe degradation of sugars together with furan compounds. This knowledge leads to development of a continuous detoxification process where gradual addition of lime can save 25% of the initial sugar with similar detoxification effects under certain conditions. Cell immobilization and cell flocculation have been studied to develop a high cell density system. High cell density is effective in carrying out in-situ detoxification. This study shows a good combination of continuous detoxification and cell immobilization where continuous ethanol production of 5.14 g/L·h can be carried out at a high feeding rate of 0.648 h-1. In addition, the application of a serial bioreactor has been found to increase the utilization of substrates. A gain in substrate assimilation of 11.6% has been achieved when using a serial bioreactor at residence time of 2.32 h. Furthermore, a cell flocculating system has been studied and developed. In a steady-state condition, the cell flocculation system could cultivate fresh hydrolyzates at a high feeding rate of 0.52 h-1 without any additional chemical detoxification, while sugar assimilation and ethanol productivity were 96% and 7.4 g/L·h respectively. In conclusion, this study proposes a concept of rapid continuous production of ethanol where inhibitory obstacles can be overcome by chemical detoxification and/or in-situ detoxification by yeast.

  • 15. Samadikhah, Kaveh
    et al.
    Larsson, Ragnar
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Continuum-molecular modelling of graphene2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 53, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

    membranes using a hierarchical modeling strategy to bridge the scales required to describe and understand the material. Quantum Mechanical (QM) and optimized Molecular Mechanical (MM) models are used to describe details on the nanoscale, while a multiscale continuum mechanical method is used to model the graphene response at the device or micrometer scale. The complete method is obtained on the basis of the Cauchy Born Rule (CBR), where the continuum model is coupled to the atomic field via the CBR and a local discrete fluctuation field. The MM method, often used to model carbon structures, involves the Tersoff--Brenner (TB) potential; however, when applying this potential to graphene with standard parameters one obtains material stress behavior much weaker than experiments. On the other hand, the more fundamental Hartree Fock and Density Functional Theory (DFT) methods are computationally too expensive and very limited in terms of their applicability to model the geometric scale at the device level. In this contribution a simple calibration of some of the TB parameters is proposed in order to reproduce the results obtained from QM calculations. Subsequently, the fine-tuned TB--potential is used for the multiscale modeling of a nano indentation sample, where experimental data are available. Effects of the mechanical response due the calibration are demonstrated.

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  • asciidoc
  • rtf