Reaction Kinetics and Intermediate Determination of Solid Acid Catalysed Liquid-phase Hydrolysis Reactions: A Real-time in situ ATR FT-IR Study

The appearance of catalyst–reactant interactions observed in on-line ATR FT-IR spectra of Nafion/silica catalysed esterification and etherification reactions of 1-octanol was investigated. It was assessed by variation of catalyst and solvent that the catalyst–reactant band is a result of the reaction of silica with 1-octanol, yields Si–O–R functionalities. Based on off-line TPD-MS and TGA characterisation of the used solid catalyst powder, the formation of Si–O–R linkages on the SiO₂ surface was confirmed. This demonstrates conclusively that in specific liquid-phase reactions, on-line analysis of intermediate species adsorbed on heterogeneous catalysts is possible. Using on-line particle analyzers, it was assessed that the absorptions were not the result of severe attrition of the catalyst particles in the course of the reaction, but apparently the result of apolar interactions of the particles with the diamond crystal.     

ORGANIC - INORGANIC INTERACTIONS IN OILFIELD SANDSTONES: EXAMPLES FROM TURBIDITE RESERVOIRS IN THE CAMPOS BASIN, OFFSHORE EASTERN BRAZIL

Turbidite sandstone reservoir rocks in the Campos Basin, offshore eastern Brazil, show evidence of a number of interactions among organic and mineral phases during diagenesis. These include extensive dissolution of plagioclase, precipitation of kaolinite into intergranular and intragranular pores, dissolution of carbonate cements and grains, as well as selective deposition of organic films on kaolinite aggregates, dissolved plagioclase and carbonate grains. These processes are connected with the biodegradation of hydrocarbons within the reservoir, related to the influx of meteoric fluids possibly during sea-level lowstands, through major stratigraphic sequence boundaries and large-scale faults. Oil biodegradation generated organic solvents responsible for mineral alteration, as well as heavy oils rich in asphaltenes. The action of organic solvents in the reservoirs is indicated by the extensive dissolution of feldspars, quartz, garnets and kaolinite, and the negative mass balance between dissolved feldspar and precipitated kaolinite, indicating aluminum mobilization. Asphaltene films and coatings may affect the wettability of the reservoir rocks and the evaluation of hydrocarbon saturation in the reservoirs by resistivity logs.
These various inorganic and organic processes are apparently interrelated in the diagenesis of the Campos Basin turbidite reservoir sandstones. These interactions should be considered in future models of the basin and its petroleum system, as well as for the creation of geochemical models capable of predicting the quality of the reservoirs and the occurrence of degraded heavy oils.     

Influence of the Hopping Technology on the Storage‐induced Appearance of Staling Aldehydes in Beer

In this paper, the involvement of iso‐α‐acids in the appearance of stale flavour in beer during storage was examined. Flavour instability upon storage, by far the most important quality problem of beer, may be caused by a multitude of reactions, in particular, the degradation of trans‐iso‐α‐acids is pivotal. In order to gain improved understanding of the beer ageing process, the behaviour of the stereoisomers of the bitter acids was studied for the first time in pilot beers at particularly high and low proportions of the trans‐iso‐α‐acids concentration relative to the cis‐iso‐α‐acids concentration. Therefore, pure trans‐ respectively cis‐isomers were required and obtained on a pilot scale by the separation of trans‐iso‐α‐acids as β‐cyclodextrin inclusion complexes from a commercial isomerised hop extract, permitting the quantitative dosage to beer in mg/L amounts. The relationship between the storage‐induced degradation of these iso‐α‐acids in authentic beer samples and the increase in staling aldehydes, especially 2‐methylpropanal, 2‐methylbutanal and 3‐methylbutanal, is the subject of further investigations. A remarkable increase in the relative concentration of cis‐iso‐α‐acids was observed in the beers bittered with purified trans‐iso‐α‐acids, which may be ascribed to partial conversion, i.e., reverse isomerisation, of trans‐iso‐α‐acids via α‐acids into cis‐iso‐α‐acids. In spite of the trans‐specific degradation observed during ageing, the decomposition of these bitter acids leading to volatile carbonyl compounds is of minor importance. Aldehyde formation as a function of forced ageing was irrespective of the mode of bittering, emphasising that malt quality and the brewing process itself are probably the most important factors regarding the flavour instability of beer.     

Capacity bounds of deployment concepts for Wireless Mesh Networks

Local area wireless networks are like cellular systems: Stations associate to one out of several access points (APs), which connect to a wired backbone. Due to signal attenuation and transmission power limitations, radio connectivity is available only sufficiently close to an AP. In scenarios with a dense deployment of APs the wired backbone causes unprofitably high costs.A Wireless Mesh Network (WMN) serves to extend the coverage of APs by means of Mesh Points (MPs) that forward data between a station and an AP. This concept reduces deployment costs, but reduces also network capacity, owing to multiple transmissions of the same data packet on its multi-hop route.This paper analyzes how the capacity of cost-limited WMNs can be optimized. A layered model of a WMN specifying the typical characteristics of the network is used to calculate the upper capacity bound. Based on the heuristics developed, networks of more than 150 nodes (APs, MPs and stations) can be handled.We apply the method to investigate the combination of three measures for improving the WMN capacity: (i) concurrent scheduling of transmissions, (ii) application of directional antennas and (iii) variable number of MPs per AP. The capacity bounds for different combinations of the measures mentioned is computed and compared. Combined with a simple cost model, these results are useful to provide insight into the economical feasibility of WMNs for wireless Internet access.     

Non-uniform triggering of gg-nMOSt investigated by combined emission microscopy and transmission line pulsing

The triggering of grounded-gate nMOS transistors and field-oxide devices, essential for optimized protection design, is addressed by transmission line pulser (TLP)-pulsed emission microscopy. Current non-uniformity and instability effects in snapback operation under DC and TLP conditions are demonstrated. The comprehensive correlation of emission and electrical behavior allows an improved interpretation of device operation. Technological influences on the trigger uniformity are discussed.     

Steam pretreatment of dilute H2SO4-impregnated wheat straw and SSF with low yeast and enzyme loadings for bioethanol production

Conversion of lignocellulosic material to monomeric sugars and finally ethanol must be performed at low cost, i.e. with limited consumption of chemicals, yeast and enzymes while still reaching high yields, if it is to compete with other fuel conversion processes. The objective of this study was thus to investigate ethanol production from steam-pretreated wheat straw by simultaneous saccharification and fermentation (SSF). The concentration of sulphuric acid in the impregnation liquid prior to pretreatment was kept low, 0.2%, and SSF was performed at low enzyme loadings, 3–14 FPU g⁻¹ water-insoluble solids (WIS), and a low yeast concentration, 2 g L⁻¹. The pretreatment conditions were optimised to give the highest overall glucose and xylose recovery after enzymatic hydrolysis of the residual WIS. The highest recovery of glucose (102%) and xylose (96%) was obtained after pretreatment at 190 °C for 10 min. Achieving high yields of glucose and xylose with the same pretreatment conditions is unusual and makes wheat straw a highly suitable raw material for bioethanol production. SSF was performed on whole slurry from straw pretreated under the optimal conditions. A high overall ethanol yield, 67% of the theoretical based on glucose in the raw material, was obtained.     

Effect of a phase-transfer catalyst on the chemical modification of poly(vinyl chloride) by substitution with thiocyanate as a nucleophile

This study examined the effect of the phase-transfer catalysts tetrabutylammonium bromide (TBAB) and tetrabutylammonium hydrogen sulfate (TBAHS) on the chemical modification of poly(vinyl chloride) (PVC) by substitution with thiocyanate as a nucleophile. TBAB accelerated the dechlorination of PVC in SCN/ethylene glycol (EG) solution. Furthermore, the addition of TBAB to SCN/EG solution improved the substitution of the Cl in PVC with SCN in solution. The addition of TBAB or TBAHS to SCN/H₂O solution promoted the dechlorination of PVC, whereas dechlorination did not occur without the catalyst. The catalysts preferred substitution to the elimination of HCl in SCN/H₂O solution, and TBAB was slightly superior to TBAHS in terms of the degree and selectivity of the substitution. The addition of nitrobenzene to SCN/H₂O solution with TBAB increased the degree of substitution. Consequently, phase-transfer catalysts, particularly TBAB, were very effective at promoting the substitution of Cl in PVC with SCN in solution.     

A vibrotactile approach to tactile rendering

While moving our fingertip over a fine surface we experience a sensation that gives us an idea of its properties. A satisfactory simulation of this feeling is still an unsolved problem. In this paper, we describe a rendering strategy based on vibrations that play an important role in the tactile exploration of fine surfaces. To produce appropriate excitation patterns we use an array of vibrating contactor pins. Similar to the colour model in computer graphics, we simulate arbitrary vibrations as a superposition of only two sinewaves. Each sinewave is intended for the excitation of a specific population of mechanoreceptors. We carried out first tests of our rendering strategy on Brownian surfaces of different fractal dimensions.