Biomass gasification is a promising technology for conversion of various biomass feedstocks to producer gas for subsequent production of fuels and chemicals. A dual fluidised bed (DFB) steam gasifier is used in the present research to produce the producer gas for Fischer-Tropsch (FT) liquid fuel synthesis. However, NH3 and H2S gases in the producer gas remain an issue to be resolved because they are poisonous to the catalysts employed in the FT reactor. To remove NH3 and H2S, two methods were investigated in this research: (1) primary measures which were employed in the DFB steam gasifier including process optimisation and application of bed materials for catalytic NH3 decomposition and H2S adsorption; and (2) secondary measures or downstream cleaning methods after the gasifier. The combination of the primary measures and the secondary measures is an effective way to remove the NH3 and H2S in the producer gas from gasification process. Studies on the primary measures were divided into two parts. In the first part, in situ reduction of NH3 and H2S in biomass producer gas from the DFB steam gasifier was performed. The primary measures consisted of optimisation of operation conditions and application of bed materials. The main operation conditions in the DFB steam gasifier studied were gasification temperature, steam to fuel (S/F) ratio, and mean gas residence time (f). The bed materials tested include silica sand, iron sand (ilmenite), and calcined olivine sand. For the second part of the primary measures, an influence of the lignite to fuel (L/F) ratio on NH3 and H2S concentrations and conversions in co-gasification of blended lignite and wood pellets in the DFB steam gasifier was investigated. Experiments were performed in the DFB steam gasifier at 800C with blended lignite and radiata pine wood with the L/F ratio ranging from 0% to 100%. It was found that all of the studied parameters including gasification temperature, S/F ratio, f, bed material, and L/F ratio significantly influenced the NH3 and H2S concentrations and conversions in the producer gas. For the secondary measures, a novel hot catalytic reactor and adsorber was developed in the present research for the simultaneous removal of NH3 and H2S. In a hot gas reactor operated at 500-800C and under atmospheric pressure, titanomagnetite was tested for NH3 and H2S removal by hot catalytic NH3 decomposition and H2S adsorption reactions. Titanomagnetite was tested with three different gas streams including 2,000 ppmv NH3 in Ar, 2,000 ppmv NH3 and 230 ppmv H2S in Ar, and 2,000 ppmv NH3 and 230 ppmv H2S in simulated biomass producer gas. From the experimental results, it was discovered that ferrite (α-Fe) readily formed by the H2 reduction of titanomagnetite has shown almost complete NH3 decomposition (100%) in Ar gas at 700 and 800C. The presence of H2S in the gas mixture of NH3 and Ar slightly reduced the catalytic activity for NH3 decomposition at 700 and 800C (>96%) and H2S adsorption of more than 98% could be achieved at the same temperature range. However, in the test with simulated biomass producer gas, 60% NH3 decomposition and 9% H2S adsorption were obtained at 800C, whereas 40% NH3 decomposition and 80% H2S adsorption were obtained at 500C. The decrease of NH3 decomposition and H2S adsorption at 800C in simulated biomass producer gas could be due to the high content of H2 (45 vol%) in the feed gas that favours the reverse reactions of NH3 decomposition and H2S adsorption, the increased surface coverage of the active α-Fe phase by adsorbed hydrogen, and the competition of α-Fe for the reverse water-gas shift reaction. Besides, it was discovered that the temperature significantly affected the removal of NH3 and H2S in simulated biomass producer gas and thus it needs to be optimised.

No description available.

No description available.

No description available.

No description available.

No description available.

Xylitol is a high value polyalcohol being used in pharmaceutical, hygiene, and food products due to its functional properties such as anticariogenic, antibacterial as well as low calorie and low glycemic properties. An alternative route for xylitol production is the biotechnological method in which microorganisms or enzymes are involved as catalysts to convert xylose into xylitol under mild conditions of pressure and temperature. This method is unlike the conventional chemical method that requires high pressure and temperature and results in low product yield. The goal of this research is to employ an integrated process using all fractions of an agro-industrial biomass (oat hull) for xylitol bioproduction, preferably in a repeated batch bioconversion process, with C. guilliermondii as the biocatalyst. Processes including hydrolysis, biomass delignification, hydrolysate detoxification using adsorption process, and finally free- and immobilized-cell bioconversions were employed in this study. The kinetics of acid-catalyzed hydrolysis of hemicellulose was investigated under mild conditions (temperature: 110ºC to 130ºC and catalyst (H2SO4) concentrations from 0.1 to 0.55 N) to determine the kinetic mechanism and generation of monosaccharides (xylose, glucose, and arabinose) as well as the microbial inhibitors consisting of acetic acid, furfural, and hydroxymethylfurfural (HMF) in the hydrolysate. A maximum recovery of 80% was attained for xylose as the main monosaccharide and the substrate for xylitol; its generation in the hydrolysate followed a single-phase 2-step kinetic mechanism similar to that of the HMF. However, a single-phase mechanism with no decomposition could describe the formation of arabinose, acetic acid, and furfural. Glucose generation followed a biphasic mechanism (fast and slow releasing) apparently with no decomposition. In the alkaline delignification of the hydrolysis byproduct (solid fraction) and the intact (crude) biomass, kinetic models based on biphasic mechanism consisting of bulk and terminal phases gave the best results and fit to the experimental data. In the bulk phase, where the temperature ranged from 30ºC to 100ºC, the reaction rate constant varied from 0.15 to 0.19 1/min for the intact biomass and from 0.25 to 0.55 1/min for the hydrolysis byproduct. According to the models, accelerated lignin removal with the increased operating temperature could be due to the shift of the process from the terminal phase to the bulk phase. The values obtained for the activation energies herein ( 33 kJ/mol) were less than the values reported in the literature for other lignocellulosic materials. The removal or reduction of the microbial inhibitors in the medium was carried out by activated carbon (adsorptive detoxification). According to the results using the Langmuir model with the activated carbon as the adsorbent, the maximum monolayer capacities of 341, 211, and 46 mg/g were obtained, respectively, for phenol, furfural, and acetic acid. Thermodynamic analyses indicated that the adsorption of the three abovementioned chemicals by the activated carbon was exothermic (enthalpy: H0), spontaneous (free energy: G0), and based on the affinity of the solute toward the adsorbent (entropy: S0). In the concentrated hydrolysate, the removal of phenols, as the main inhibitor, was very successful such that by activated carbon doses of 1.25%, 2.5%, and 5% (w/v) they could be reduced to 34%, 13%, and 3% of the initial concentration (8.7 g/l), respectively. During xylitol bioproduction process in the repeated batch mode using C. guilliermondii, variables of pH control, medium supplementation, and cell recycling proved to be more important than medium detoxification. Processes involving pH-controlled condition combined with nitrogen supplementation and a mild detoxification performed very well with consistent conversion parameters in the successive batches; values of over 0.8 g/g, 0.55 g/l/h, and 53 g/l were obtained respectively for xylitol yield, volumetric productivity, and final concentration. On the other hand, in a single-batch bioconversion, there was no need for supplementing the medium with the nitrogen source. Kinetic modeling of the process showed that substrate (xylose) as well as co-substrate (glucose) consumption, product (xylitol) formation, and cell regeneration could be predicted by a diauxic model. In the aerated free-cell and immobilized-cell systems, aeration rates of 1.25 vvm and 1.25-1.5 vvm were required for free-cell and immobilized-cell systems, respectively, to reach the maximum bioconversion performance. In the immobilized-cell system, cell support also played an important role in this biotransformation. Application of the support based on the delignified hydrolysis byproduct resulted in high and consistent bioconversion parameters in all batches comparable to the ones in the free-cell system. However, bioconversions using the lignin-rich material (hydrolysis byproduct) resulted in a lower efficiency in the first batch which could be partly improved in the second batch and almost fully increased in the third batch to nearly reach performance parameters comparable to the ones obtained in the free-cell system. Overall, the integrated process employed in this investigation helps fill in the knowledge gaps existing on the lignocellulosic biomass application for xylitol bioproduction and biorefinery industries.

No description available.

Climate change has become the most important global environmental problem we face today. Agriculture, forestry and the land use sector not only contribute to national economies but also provide a source of greenhouse gas (GHG) emissions as well as a carbon store, contributing approximately 20% but removing about 16%. Energy crops and associated increases in soil carbon sequestration from different ground covers through various land management strategies are examples of approaches that could be adopted to reduce GHG emissions. A number of these options have an associated economic cost to the land manager and it is important to understand what is economically and socially viable by understanding the link between energy crop adoption and a range of socio-economic factors. Agent-based modelling (ABMs) has been identified as providing a promising approach to integrate social, economic and biophysical processes. In the past these areas of research have been mainly studied separately but now there is an urgent need to address these areas in a combined way. Economic rationalisation is fundamental to farmers’ decision-making, although not wholly representative and non-economic factors were identified. The estimated GHG mitigation potential of bioenergy crops at current adoption levels is modest when taking Scotland’s national GHG emissions into account, however, more significant when considering the agricultural sector in isolation. This contribution can only increase with improved management practices and policy designed to encourage adoption and improve energy security. This work will contribute to a greater understanding of bioenergy land use strategies. This project used North East Scotland as the case study, with raw data collated by questionnaire, however, conclusions drawn add to the broader understanding of the link between socio-economic activity, bioenergy adoption and GHG emissions.

The spring application of fertiliser N often fails to stimulate grass growth in improved grass pastures on peaty soils. Fertiliser utilisation efficiencies under these conditions have been found to be low, suggesting that available N is not taken up by the plant. Previous work has suggested that in this type of system, the soil microbial biomass may function as a strong sink for fertiliser N and therefore limit plant growth in the Spring. A series of laboratory based experiments utilising reconstituted and intact cores, and homogenised peat, was set up to identify the factors controlling the competition between N uptake by plants and N immobilisation by soil microorganisms following the addition of fertiliser N to peat. Microbial biomass N concentrations were determined in order to quantify the amount of N present in the microbial pool. The use of 15N labelled fertilisers and selective biocides provides a powerful tool with which to characterise the microbial population responsible for the immobilisation of N under these conditions. Improvement of a grass pasture at Sletill Hill has resulted in the formation of a distinct layer comprised of partially decomposed roots, underneath the surface vegetation and it was within this layer, that microbial immobilisation of fertiliser N was found to occur. Approximately 30% of applied N (equivalent to ca 50 kgN ha-1) was found within the microbial biomass in this layer, 30 days after the addition of fertiliser N. Intact cores were removed from Sletill Hill and maintained under controlled abiotic conditions. Water table level and temperature were found to be important in controlling the extent of microbial immobilisation of applied N. Lowering the water table level increased the quantity of N present in plant and microbial N pools, particularly at lower temperatures (8°C). At higher temperatures (20°C), plant uptake of N tended to be less due to a restriction on plant growth caused by 'droughty' soil conditions.