Isomerisation of cresols over zeolites HZSM5, HBeta and HMordenite

Includes bibliographical references (leaves 92-94)In the natural (phenolic material obtained from coal) phenolics industry two problems are experienced with regards to cresol isomers. Firstly, insufficient quantities are recovered from natural sources such as coal tar and refinery caustics and secondly the isomer distribution is inflexible and does not always meet market demand. Thus, having technology which provides alternative routes to certain cresol isomers is of utmost importance to natural cresol producers. The isomerisation of one cresol isomer into one or more of the others would enable a producer to swing (to a limited extent) the distribution of isomers to suite the demand of customers. For this study, the isomerisation and disproportionation of the three cresol isomers were investigated over three types of zeolites under liquid as well as vapour phase (only o-cresol isomer) reaction conditions. The best activity for o-cresol isomerisation, in the liquid phase, was initially HMordenite but because the catalyst deactivates so quickly, HZSM5 was thus regarded as the best catalyst. HZSM5 gave the best activity for both m-and p-cresol isomerisation in the liquid phase. The activity over HBeta was between that of HZSM5 and HMordenite for all the cresol isomer conversions. Expected from the shape selectivity of the zeolite, the best isomerisation selectivity (>86.0%) was obtained with HZSM5. HBeta gave both isomerisation and disproportionation but the favored pathway is disproportionation, while HMordenite, due to the deactivation, proved to be suitable for neither isomerisation nor disproportionation. It can thus be concluded that HZSM5 gave the best conversion for 0-, m-and p-cresol in terms of the desired isomerised products and that it is the preferred catalyst for isomerisation in the liquid phase. The average activity for o-cresol conversion in the vapour phase followed the order HZSM5 > HBeta = HMordenite. HZSM5 proved to be the best isomerisation catalyst for o-cresol and high selectivity (>95%) and stability was obtained over five days on stream, while HBeta showed a gradual decline in isomerisation selectivity and stability. A rapid decrease was noticeable over HMordenite in terms of selectivity and stability. The activity, stability and isomerisation selectivity data obtained, is therefore conclusive with regards to HZSM5 being the preferred zeolite for isomerisation of o-cresol. Further work could entail optimisation of the p-selectivity, from o-cresol and m-cresol transformation, and lifetime studies of the preferred zeolite HZSM5. It is thus recommended to investigate CVD (chemical vapour deposition) to deactivate the external surface of the catalyst as well as noble metal impregnation and/or the use of hydrogen as a carrier gas

Driving forces in free visual search : An ethology

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FIFE data analysis: Testing BIOME-BGC predictions for grasslands

The First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) was conducted in a 15 km by 15 km research area located 8 km south of Manhattan, Kansas. The site consists primarily of native tallgrass prairie mixed with gallery oak forests and croplands. The objectives of FIFE are to better understand the role of biology in controlling the interactions between the land and the atmosphere, and to determine the value of remotely sensed data for estimating climatological parameters. The goals of FIFE are twofold: the upscale integration of models, and algorithm development for satellite remote sensing. The specific objectives of the field campaigns carried out in 1987 and 1989 were the simultaneous acquisition of satellite, atmospheric, and surface data; and the understanding of the processes controlling surface energy and mass exchange. Collected data were used to study the dynamics of various ecosystem processes (photosynthesis, evaporation and transpiration, autotrophic and heterotrophic respiration, etc.). Modelling terrestrial ecosystems at scales larger than that of a homogeneous plot led to the development of simple, generalized models of biogeochemical cycles that can be accurately applied to different biomes through the use of remotely sensed data. A model was developed called BIOME-BGC (for BioGeochemical Cycles) from a coniferous forest ecosystem model, FOREST-BGC, where a biome is considered a combination of a life forms in a specified climate. A predominately C4-photosynthetic grassland is probably the most different from a coniferous forest possible, hence the FIFE site was an excellent study area for testing BIOME-BGC. The transition from an essentially one-dimensional calculation to three-dimensional, landscape scale simulations requires the introduction of such factors as meteorology, climatology, and geomorphology. By using remotely sensed geographic information data for important model inputs, process-based ecosystem simulations at a variety of scales are possible. The second objective of this study is concerned with determining the accuracy of the estimated fluxes from BIOME-BGC, when extrapolated spatially over the entire 15-km by 15-km FIFE site. To accomplish this objective, a topographically distributed map of soil depth at the FIFE site was developed. These spatially-distributed fluxes were then tested with data from aircraft by eddy-flux correlation obtained during the FIFE experiment

A daily soil temperature model based on air temperature and precipitation for continental applications

Soil temperature is a necessary component for estimating below-ground processes for continental and global carbon budgets; however, there are an insufficient number of climatic stations monitoring soil temperature. We used an 11-day running average of daily mean air temperature to estimate daily mean soil temperature at a depth of 10 cm using linear regression. This model was tested using data from 6 climate regions across the United States. Frequency analyses for 17 of 19 data sets showed that the number of days which were within a +/-3.5 degree C range centered on the measured soil temperature varied from 77 to 96%. The values of R2 between observed and final predicted soil temperatures ranged from 0.85 to 0.96 with standard errors from 1.5 to 2.9 degrees C for all 19 simulations. Changes of soil temperature under snow cover were smaller than those without snow cover. Soil temperature under vegetation cover was also simulated assuming the rate of soil warming under vegetation cover would be reduced with increasing leaf area index according to the Beer-Lambert Law. Annual soil respiration can be estimated from the predicted soil temperature with reasonable accuracy. Daily soil temperature may be predicted from daily air temperature once regional equations have been established, because weather stations in the United States can be generalized into a few regions and sites within each region may use the same equation

Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost

<b>Aim</b><p></p> The energy efficiency of FES-cycling in spinal cord injured subjects is very much lower than that of normal cycling, and efficiency is dependent upon the parameters of muscle stimulation. We investigated measures which can be used to evaluate the effect on cycling performance of changes in stimulation parameters, and which might therefore be used to optimise them. We aimed to determine whether oxygen cost and stimulation cost measurements are sensitive enough to allow discrimination between the efficacy of different activation ranges for stimulation of each muscle group during constant-power cycling. <p></p> <b>Methods</b><p></p> We employed a custom FES-cycling ergometer system, with accurate control of cadence and stimulated exercise workrate. Two sets of muscle activation angles (“stimulation patterns”), denoted “P1” and “P2”, were applied repeatedly (eight times each) during constant-power cycling, in a repeated measures design with a single paraplegic subject. Pulmonary oxygen uptake was measured in real time and used to determine the oxygen cost of the exercise. A new measure of stimulation cost of the exercise is proposed, which represents the total rate of stimulation charge applied to the stimulated muscle groups during cycling. A number of energy-efficiency measures were also estimated. <p></p> <b>Results</b><p></p> Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired <i>t</i>-test, <i>p</i> < 0.05): oxygen costs were 0.56 ± 0.03 l min<sup>−1</sup> and 0.61 ± 0.04 l min<sup>−1</sup>(mean ± S.D.), respectively; stimulation costs were 74.91 ± 12.15 mC min<sup>−1</sup> and 100.30 ± 14.78 mC min<sup>−1</sup> (mean ± S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2. <p></p> <b>Conclusion</b><p></p> Oxygen cost and stimulation cost measures both allow discrimination between the efficacy of different muscle activation patterns during constant-power FES-cycling. However, stimulation cost is more easily determined in real time, and responds more rapidly and with greatly improved signal-to-noise properties than the ventilatory oxygen uptake measurements required for estimation of oxygen cost. These measures may find utility in the adjustment of stimulation patterns for achievement of optimal cycling performance. <p></p&gt