Polymerisation of olefins catalysed by a palladium complex in supercritical carbon dioxide

A late transition metal catalyst has been used to polymerise hex-1-ene and ethene in supercritical carbon dioxide, yielding high molecular weight polymers; a comparison with polymerisations in CH2Cl2 reveal that polymers with identical molecular weight and polydispersity are formed

Polymerisation of olefins catalysed by a palladium complex in supercritical carbon dioxide

A late transition metal catalyst has been used to polymerise hex-1-ene and ethene in supercritical carbon dioxide, yielding high molecular weight polymers; a comparison with polymerisations in CH2Cl2 reveal that polymers with identical molecular weight and polydispersity are formed

Solute rejection in the presence of a deposited layer during ultrafiltration

During ultrafiltration deposited layers are often formed on the membrane surface. These layers not only reduce the volumetric flux through the membrane, but also may influence the rejection of other solutes in the feed. In the present paper we will show that besides an increase in the rejection, a decrease in rejection may also occur, which can completely alter the aimed selectivity of the separation process. The influence of deposited layers has been studied experimentally by two types of depositing components: silica sol and the protein BSA. In the presence of a relatively open silica deposit a strong drop in the rejection of PEG and dextran was found compared to the rejection on a clean membrane. For thick deposit layers the rejection even decreased to zero, thus resulting in a total permeation of a normally partially rejected solute. On the other hand an increase in PEG rejection occurred in the presence of a BSA deposit. Due to the compressibility of the protein deposit the highest rejections were measured at the highest pressures. The effects were the most pronounced at the isoelectric point of BSA. A model is presented to describe the underlying phenomena

Validated numerical analysis of CaSO4 fouling

In scaling experiments, the formation of fouling layers on heat transfer surfaces usually proceeds in a non-uniform manner. The result is a non-uniform layer, and hence a varying thermal resistance over the area covered with scale. Consequently, a non-uniform heat flux distribution results over the heat transfer surface. To evaluate the changes in the heat flow distribution resulting from a non-uniform scale layer, numerical calculations have been performed using a case where CaSO4 scales form on a heated copper plate subjected to a shear flow. The calculated heat flux is used to calculate fouling resistances from measured temperatures. The results of the numerical calculations confirm that a non-uniform heat flux distribution occurs over the surface when the plate is partially covered with scale. Further, it is seen that the heat flux, the surface temperature, and the driving force all decrease with increase in scale accumulation

Influence of particles on scaling in industrial heat exchangers : preliminary studies

Scale formation in industrial heat exchangers is a big problem in cane sugar factories resulting in various operational problems. Process fluids flowing in heat exchangers of these factories contain various org. and inorg. salts and suspended particles. A cane sugar factory in Zambia is studied and the main operational problems encountered are presented. Further scale deposits forming on syrup heater surfaces are analyzed to det. their constituents. Gypsum is the dominant compd. in the scale layer. Also obsd. are foreign particles imbedded in the scale layer. Results from preliminary expts. show that particles suspended in the fluid may have an effect on the scaling process. These findings provide motivation to study the effect of particles on the scaling proces

Hollow fibre microporous silica membranes for gas separation and pervaporation : synthesis, performance and stability

Thin microporous silica membranes were prepared on the outer surface of hollow fibre ceramic substrates. In principle this enables relatively fast and inexpensive production of large membrane surface area, combined with a low support resistance and a high membrane surface area/module volume ratio (>1000 m2 m-3) compared to tubular membranes. Membranes were analysed using SEM, SNMS, single gas permeance and pervaporation. High He permeance (1.1–2.9 × 10-6 mol m-2 s-1 Pa-1), high He/N2 permselectivity (100–1000) and Arrhenius type temperature dependence of gas permeance indicate that the membranes are microporous and possess a low number of defects. The contribution of the hollow fibre substrate to the overall mass transport resistance is found to be small, even for fast permeating gases like helium. Hence, the small dimensions of the substrate enable further improvement of the silica layer without the support resistance becoming significant. In the dehydration of n-butanol (80 °C, 5 wt.% water) initially a high flux and selectivity were observed (2.9 kg m-2 h-1 and 1200, respectively). A similar behaviour was found for the dehydration of DMF. For most of the membranes the water permeance finally reaches a steady value of 1 kg m-2 h-1 bar-1 with selectivities between 5 and 25. The good performance of the hollow fibre membranes, combined with their advantages compared to other support geometries, makes them interesting candidates for a variety of applications