Search

In commercial slabstock foaming, liquid CO2 technology is increasingly applied to replace previously used liquid auxiliary blowing agents like CFCs and methylene chloride. Knowledge of physical properties of mixtures which are used in liquidCO2 foaming may contribute to the further development of the liquid CO2 technology. Equations have been determined which do predict, for specific operational conditions and formulations, the pressures which are required in commercial foam operation to keep theCO2 dissolved both in the polyol/CO2 and in the foaming mixture/CO2 solutions. The evident dependence on temperature ofCO2 solubility, established for both polyol and foaming mixtures, strongly supports tight temperature control of the feedstocks in slabstock liquid CO2 foaming. The solubility of CO2 in polyol was found to increase with the EO content of the polyol where the effect of molecular weight was found to be negligible. It was established that small amounts of water and surfactant lower the CO2 solubility, and it is predicted that the commonly used levels of TDI do the same. Based on this information, it is advisable to conduct the mixing of TDI and auxiliary components at pressures a fraction higher than the saturation pressure of the liquid CO2 polyol mixture. A significant decrease of both viscosity and surface tension is quantified for polyol and model foaming systems at increasing liquidCO2 concentration. These decreases may explain why very small cell sizes can be obtained with liquid CO2 foaming, as the nucleation process takes place at high liquid CO2 concentration. The rise in viscosity upon evaporation ofCO2 into the froth may explain the relative stability of the unreacted froth. A cooling capacity of about 1°C per part of CO2 per hundred parts of polyol is determined from two independent experiments. However, for safety reasons, it is advisable to keep the current assumption of 0°C per part of CO2 per hundred parts of polyol in commercial foaming until a further study on the temperature evolution of liquidCO2 blown foaming under practical conditions is conducted.

Homogeneous thin films of zinc titanate have been successfully prepared on Si(100) wafers by depositing a film of zinc and titanium oxides (ZnO-TiO2) by low-pressure metalorganic chemical vapor deposition (MOCVD), followed by an annealing treatment. The precursors used for the deposition were diethylzinc (DEZ), tetraisopropoxide titanium (TPT), and water. By performing the deposition at temperatures between 140 and 350C, the stoichiometry of the as-deposited films could be effectively controlled over Zn/Ti ratios between 0.5 and 2.5, which cover the composition of various zinc titanate phases identified in the literature. The as-deposited ZnO-TiO2 films are amorphous, and possess a fairly smooth surface. XPS and SIMS analysis showed that the composition of these films is uniform over the wafer as well as through the films bulk. An annealing treatment of the as-deposited films at high temperature

An extensive study has been executed to understand the mechanism of calcite scale deposition occurring in the main heat exchanger at the MPP (main production platform) facilities at SVSA. The deposit necessitated a change out of the internals of the heat exchanger, which caused production deferment and capital expenditures. The conclusion of this investigation was that the mechanism for accelerated calcite scale build-up in the HX heat exchanger is driven by the considerably high skin temperature (above 120 °C at normal heating conditions) in a high pH environment. This latter is caused by the triazine, which is part of the H2S scavenger package (used to remove H2S from some of the sour gas production), and by-products originating from the reaction of triazine (an amine) with H2S. The CaCO3 scaling tendencies and indices as calculated by scaling software (ScaleChem, StreamAnalyzer) predict the adverse impact of the high temperature and alkalinity conditions encountered in the heat exchanger. Several technical options to mitigate the effects of the scavenger were considered from an economic and operational perspective. The most effective of the options was the injection of an appropriate scale inhibitor at a suitable dosage upstream of the heat exchanger.