Hydrolysis characteristics and kinetics of waste hay biomass as a potential energy crop for fermentable sugars production using autoclave parr reactor system

The use of the organic fraction of municipal solid waste crops has received considerable attention as a sustainable feedstock that can replace fossil fuels for the production of renewable energy. Therefore, municipal bin-waste in the form of hay was investigated as a potential energy crop for fermentable sugars production. Hydrolysis of hay by dilute phosphoric acid was carried out in autoclave parr reactor, where reactor temperature (135-200 degrees c) and acid concentration (2.5-10% (w/w)) were examined. Analysis of the decomposition rate of hemicellulosic biomass was undertaken using HPLC of the reaction products. Xylose production reached a maximum value of 13.5 g/100 g dry mass corresponding to a yield of 67% at the best identified conditions of 2.5 wt% H3PO4, 175 degrees C, 10 min reaction time, and at 5 wt% H3PO4, 150 degrees C, and 5 min reaction time. For glucose, an average yield of 25% was obtained at 5 wt% H3PO4, 175 degrees C and 30 min. Glucose degradation to HMF was achieved at 10 wt% H3PO4 and 200 degrees C. The maximum yield for produced arabinose was an average of 3 g/100 g dry. mass corresponding to 100% of the total possible arabinose. The kinetic study of the acid hydrolysis was also carried out using the Saeman and the Two-fraction models. It was found for both models that the kinetic constants (k) depend on the acid concentration and temperature. For xylose and arabinose it was found that the rate of formation was more favoured than the rate of degradation. By contrast, for glucose it was found that glucose degradation was occurring faster than glucose formation. It can be concluded that dilute phosphoric acid hydrolysis of hay crop is feasible for the production of fermentable sugars which are essential for bioethanol synthesis. 

Kinetics of the photocatalysed oxidation of NO in the ISO 22197 reactor

The photocatalytic reactor described in the NOx removal ISO 22197-1:2007 is used to study the kinetics of the process, using a film of P25 TiO2 which has either been conventionally pre-irradiated in a stream of air, or unconventionally in a stream of NO (1 ppmv). In the former case it is shown that the system does not achieve steady state exit levels of NO, probably due to the gradual accumulation of HNO3 on the surface of the photocatalyst. The NO-preconditioned TiO2 film demonstrated excellent steady-state levels when monitored as a function of NO concentration, [NO] and UV irradiance, ρ. However, in this case the photocatalytic reaction under study is NOT NOx removal, but the conversion of NO to NO2. It is shown that the kinetics of this steady state process fit very well to a kinetic expression based on a disrupted adsorption reaction mechanism, which has also been used by others to fit their observed (non-steady state) kinetics for NOx removal on conventionally-(air) preconditioned films of P25. The appropriateness of this model for either system is questioned, since in both systems the kinetics appear to have a significant mass transport element. These findings suggest that mass transport and non-steady-state kinetics are likely to be significant features for most active photocatalytic samples, where the %NO conversion is >7%, and so limits the usefulness of the NOx removal ISO 22197-1:2007.

Dilute acid hydrolysis of cellulose and cellulosic bio-waste using a microwave reactor system

The dilute acid hydrolysis of grass and cellulose with phosphoric acid was undertaken in a microwave reactor system. The experimental data and reaction kinetic analysis indicate that this is a potential process for cellulose and hemi-cellulose hydrolysis, due to a rapid hydrolysis reaction at moderate temperatures. The optimum conditions for grass hydrolysis were found to be 2.5% phosphoric acid at a temperature of 175 degrees C. It was found that sugar degradation occurred at acid concentrations greater than 2.5% (v/v) and temperatures greater than 175 degrees C. In a further series of experiments, the kinetics of dilute acid hydrolysis of cellulose was investigated varying phosphoric acid concentration and reaction temperatures. The experimental data indicate that the use of microwave technology can successfully facilitate dilute acid hydrolysis of cellulose allowing high yields of glucose in short reaction times. The optimum conditions gave a yield of 90% glucose. A pseudo-homogeneous consecutive first order reaction was assumed and the reaction rate constants were calculated as: k(1) = 0.0813 s(-1); k(2) = 0.0075 s(-1), which compare favourably with reaction rate constants found in conventional non-microwave reaction systems. The kinetic analysis would indicate that the primary advantages of employing microwave heating were to: achieve a high rate constant at moderate temperatures: and to prevent 'hot spot' formation within the reactor, which would have cause localised degradation of glucose.

A kinetic study of ammonia oxidation on a Pt catalyst in the explosive region in a microstructured reactor/heat-exchanger

The application of an aluminum-based microstructured reactor/heat-exchanger for measuring reaction kinetics in the explosive region is presented. Platinum-catalyzed ammonia oxidation was chosen as a test reaction to demonstrate the feasibility of the method. The reaction kinetics was investigated in a wide range of conditions [NH3 partial pressure: 0.03-0.20 atm, O-2 partial pressure: 0.10-0.88atm; reactant flow 2000-3000 cm(3) min(-1) (STP); temperature 240-360degreesC] over a supported Pt/Al2O3 catalyst (mass of Al2O3 layer in the reactor, 1.95 mg; Pt/Al molar ratio, 0.71; Pt dispersion, 20%). The maximum temperature non-uniformity in the microstructured reactor was ca. 5degreesC, even at conditions corresponding to an adiabatic temperature rise of 1400degreesC. Based on the data obtained, a previous kinetic model for ammonia oxidation was extended. The modified 13-step model describes the data in a considerably wider range of conditions including those with high ammonia loadings and high reaction temperatures. The results indicate the large potential of microstructured devices as reliable tools for kinetic research of highly exothermic reactions.

A Monte Carlo model of DNA double-strand break clustering and rejoining kinetics for the analysis of pulsed-field gel electrophoresis data

In studies of radiation-induced DNA fragmentation and repair, analytical models may provide rapid and easy-to-use methods to test simple hypotheses regarding the breakage and rejoining mechanisms involved. The random breakage model, according to which lesions are distributed uniformly and independently of each other along the DNA, has been the model most used to describe spatial distribution of radiation-induced DNA damage. Recently several mechanistic approaches have been proposed that model clustered damage to DNA. In general, such approaches focus on the study of initial radiation-induced DNA damage and repair, without considering the effects of additional (unwanted and unavoidable) fragmentation that may take place during the experimental procedures. While most approaches, including measurement of total DNA mass below a specified value, allow for the occurrence of background experimental damage by means of simple subtractive procedures, a more detailed analysis of DNA fragmentation necessitates a more accurate treatment. We have developed a new, relatively simple model of DNA breakage and the resulting rejoining kinetics of broken fragments. Initial radiation-induced DNA damage is simulated using a clustered breakage approach, with three free parameters: the number of independently located clusters, each containing several DNA double-strand breaks (DSBs), the average number of DSBs within a cluster (multiplicity of the cluster), and the maximum allowed radius within which DSBs belonging to the same cluster are distributed. Random breakage is simulated as a special case of the DSB clustering procedure. When the model is applied to the analysis of DNA fragmentation as measured with pulsed-field gel electrophoresis (PFGE), the hypothesis that DSBs in proximity rejoin at a different rate from that of sparse isolated breaks can be tested, since the kinetics of rejoining of fragments of varying size may be followed by means of computer simulations. The problem of how to account for background damage from experimental handling is also carefully considered. We have shown that the conventional procedure of subtracting the background damage from the experimental data may lead to erroneous conclusions during the analysis of both initial fragmentation and DSB rejoining. Despite its relative simplicity, the method presented allows both the quantitative and qualitative description of radiation-induced DNA fragmentation and subsequent rejoining of double-stranded DNA fragments. (C) 2004 by Radiation Research Society.

Evidence for complexity at the nanometer scale of radiation-induced DNA DSBs as a determinant of rejoining kinetics

The rejoining kinetics of double-stranded DNA fragments, along with measurements of residual damage after postirradiation incubation, are often used as indicators of the biological relevance of the damage induced by ionizing radiation of different qualities. Although it is widely accepted that high-LET radiation-induced double-strand breaks (DSBs) tend to rejoin with kinetics slower than low-LET radiation-induced DSBs, possibly due to the complexity of the DSB itself, the nature of a slowly rejoining DSB-containing DNA lesion remains unknown. Using an approach that combines pulsed-field gel electrophoresis (PFGE) of fragmented DNA from human skin fibroblasts and a recently developed Monte Carlo simulation of radiation-induced DNA breakage and rejoining kinetics, we have tested the role of DSB-containing DNA lesions in the 8-kbp-5.7-Mbp fragment size range in determining the DSB rejoining kinetics. It is found that with low-LET X rays or high LET alpha particles, DSB rejoining kinetics data obtained with PFGE can be computer-simulated assuming that DSB rejoining kinetics does not depend on spacing of breaks along the chromosomes. After analysis of DNA fragmentation profiles, the rejoining kinetics of X-ray-induced DSBs could be fitted by two components: a fast component with a half-life of 0.9 +/- 0.5 h and a slow component with a half-life of 16 +/- 9 h. For a particles, a fast component with a half-life of 0.7 +/- 0.4 h and a slow component with a half-life of 12 5 h along with a residual fraction of unrepaired breaks accounting for 8% of the initial damage were observed. In summary, it is shown that genomic proximity of breaks along a chromosome does not determine the rejoining kinetics, so the slowly rejoining breaks induced with higher frequencies after exposure to high-LET radiation (0.37 +/- 0.12) relative to low-LET radiation (0.22 +/- 0.07) can be explained on the basis of lesion complexity at the nanometer scale, known as locally multiply damaged sites. (c) 2005 by Radiation Research Society.

Integrating intrinsic and global kinetics as a dual kinetic model for automotive catalysis

The majority of the kinetic models employed in catalytic after-treatment of exhaust emissions use a global kinetic approach owing to the simplicity because one expression can account for all the steps in a reaction. The major drawback of this approach is the limited predictive capabilities of the models. The intrinsic kinetic approach offers much more information about the processes occurring within the catalytic converter; however, it is significantly more complex and time consuming to develop. In the present work, a methodology which allows accessing a model that combines the simplicity of the global kinetic approach and the accuracy of the intrinsic kinetic approach is reported. To assess the performance of this new approach, the oxidation of carbon monoxide in the presence of nitric oxide as well as a driving cycle was investigated. The modelling of carbon monoxide oxidation with oxygen which utilised the intrinsic kinetic approach with the global kinetic approach was used for the carbon monoxide + nitric oxide reaction (and all remaining reactions for the driving cycle). The comparison of the model results for the dual intrinsic + global kinetic approach with the experimental data obtained for both the reactor and the driving cycle indicate that the dual approach is promising with results significantly better than those obtained with only the global kinetics approach.

Development of a slurry continuous flow reactor for photocatalytic treatment of industrial waste water

The water treatment capability of a novel photocatalytic slurry reactor was investigated using methylene blue (MB) as a model pollutant in an aqueous suspension. A pellet TiO ₂ catalyst was employed and this freed the system from the need of filtration of catalyst following photocatalysis. This configuration combines the high surface area contact of catalyst with pollutant of the slurry reactor and also offers a high illumination of catalyst by its unique array of weir-like baffles. In this work, the batch adsorption of MB from aqueous solution (10μM) onto the TiO ₂ catalyst was studied, adsorption isotherms and kinetics were determined from the experimental data. Complete degradation of MB was achieved within 60 min illumination with various loadings of catalyst (30-200 g L ^-1). A modest catalyst loading (30 g L ^-1) achieved 98% degradation within 60 min of irradiation. Experimental results indicate that this novel reactor configuration has a high effective mass transfer rate and UV light penetration characteristics. 

The nitric oxide ISO photocatalytic reactor system: Measurement of NOx removal activity and capacity

Although the NO removal-based air-purification ISO method ISO 22197-1:2007 is well established, its preconditioning requirements mean that only the initial activity of the photocatalyst under test is measured owing to the often-reported, gradual alteration of the surface kinetics for NO oxidation by air through the accumulation of surface HNO3. Herein, we compare the photocatalytic NO removal abilities of a number of different, common TiO2 materials, surface-saturated with photogenerated HNO3, with their behaviours observed during the typical 5 h-long ISO standard test. It is found that all the TiO2 materials studied eventually become largely NO to NO2 converters after sufficient exposure to NO under irradiation (>5 h) due to the accumulation of surface HNO3. The UV exposure time, t*, necessary to reach this HNO3 saturated condition is different for each different catalyst. As a consequence, an alternative preconditioning process for the ISO method is proposed which can be used to provide a more realistic measure of the photocatalytic activity of the underlying material and provide a measure of the NOx removing capacity of the photocatalytic material under test.

TAP Reactor Development and Application in the Kinetic Characterization of Catalysts for Heterogeneously Catalyzed Gas Phase Reactions

This manuscript describes the application and further development of the TAP technique in kinetic characterization of heterogeneous catalysis. The major application of TAP systems is to study mechanisms, kinetics and transport phenomena in heterogeneous catalysis, all of which is made possible by the sub-millisecond time resolution. Furthermore, the kinetic information obtained can be used to gain an insight into the mechanism occurring over the catalyst system. This is advantageous as heterogeneous catalysts with an improved efficiency can be developed as a result. TAP kinetic studies are carried out at low pressure (~1x10-7 mbar) and TAP pulses are sufficiently small (1013-1015 molecules) so as to maintain this low pressure. The use of a small number of molecules in comparison to the total number of active sites means the state of the catalyst remains relatively unchanged. The use of the low intensity pulses also makes the pressure gradient negligible and so allows the TAP reactor system to operate in the Knudsen Diffusion regime, where gas-gas reactions are eliminated. Hence only gas-catalyst reactions are investigated and, by the use of moment analysis of observed exit flow, rate constants of elementary steps of the reaction can be obtained.

In this manuscript, two attempts to further the TAP technique are reported. Firstly, the work undertaken at QUB to attempt to control the number of molecules of condensable reagents that can be pulsed during a TAP pulse experiment is disclosed. Secondly, a collaborative project with SAI Ltd Manchester is discussed in a separate chapter, where technical details and validation of a customised time of flight mass spectrometer (ToF MS) for the QUB TAP-1 system are reported. A collaborative project with Cardiff Catalysis Institute focusing on the study of CO oxidation over hopcalite catalysts is also reported. The analysis of the experimental results has provided an insight into the possible mechanism of the oxidation of CO over these catalysts. A correction function has also been derived which accounts for the adsorption of reactant molecules over inert materials that are used for the reactor packing in TAP experiments. This function was then applied to the selective reduction of O2 in a H2 rich ethene feed, so that more accurate TAP moment based analysis could be conducted.