Reaction of lipids containing hydroxy groups with trimethylsulfonium hydroxide: Formation ofO-methyl derivatives

Base-catalyzed transesterification of acyl lipids with trimethylsulfonium hydroxide (TMSH) is an easy and convenient method for the preparation of fatty acid methyl esters (FAME) for gas chromatography (GC) analyses. We have found, however, that lipids containing hydroxy groups are partially converted to the correspondingO-methyl ether derivatives which may interfere with FAME in GC separations. For example, long-chain alcohols are found to be converted to alkyl methyl ethers,rac-1-O-alkylglycerols to the corresponding 2-O-and 3-O-monomethyl ethers, as well as 2,3-di-O-methyl ethers, hydroxy fatty acids to methoxy FAME, and cholesterol to cholesteryl 3β-methyl ether. From our results, it is obvious that TMSH derivatization method is not recommended without limitation for lipids containing hydroxy groups; it may be, however, of some diagnostic value for the analysis of such lipids by GC/mass spectrometry.     

Plant optimisation by retrofitting using a hierarchical method: Entrainer selection,recycling and heat integration

Systematic procedures for reducing wastes in complex chemical plants are needed to allow efficient optimisation. Here, a hierarchical procedure was applied to the optimisation of a real industrial plant to reduce wastes as well as energy and raw material consumption. In the case studied, the continuous production of methyl-butynol (MBI), acetylene reacts with acetone. The solvent ammonia and acetylene are recycled to the reactor. Unreacted substrates and by-products are separated from the product stream by distillation. Part of the unreacted acetone can be reused for other purposes after distillation. A substantial part of the unreacted substrates and by-products is delivered to a wastewater treatment plant. These waste streams constitute a substantial problem for the operation of this plant. First, waste streams were characterised and tracked back to their origin. Following the hierarchical design procedure, the overall input–output structure was fixed. The entrainer in the present process was critically examined and options were suggested. Then various recycle schemes were considered for later detailed study. The existing plant was simulated using ASPENPLUS. After adjusting the model to all important aspects of the real process scheme, excellent agreement between actual process performance data and simulation was obtained. The various process schemes were simulated and assessed for their economic and ecological performance. The objective functions used included utility, substrate and catalyst costs, as well as costs for wastewater treatment. Additionally, the environmental burden related to energy supply was accounted for by a carbon dioxide tax as suggested by the Nordic countries. The process changes included separation of unreacted acetone from the product stream and recycling to the reactor. By-products were converted back to substrates in an additional reactor separation system and recycled. In various simulated process configurations and operational schemes substantial economic and ecologic improvements were achieved. This study demonstrates the usefulness of hierarchical approaches combined with process simulation for plant optimisation. ©1997 SCI     

Lithium diffusion in aluminum-lithium alloy 2090 clad with 7072

The loss of lithium during solution heat treatment of alloy 2090 clad with approximately 100 μm of 7072 was investigated. Lithium concentration profiles in the alloy were measured using a nuclear reaction analysis technique after samples had been subjected to various solution heat treatments. The results showed that the cladding-base metal interface provided no impediment to lithium diffusion and that the rate of lithium diffusion in the cladding was similar to its rate of diffusion in the base metal. A lithium-rich oxide was formed on the external surface, but the concentration profiles showed that the effective lithium concentration at the surface was near zero. Thus, lithium in the bulk experienced a maximum concentration gradient and diffused to the surface as rapidly as possible. Despite the absence of any lithium diffusion barrier in the cladding, the initial rate of lithium loss is much less than in bare material. The cladding provides effective protection from lithium loss, and the rate of loss in clad materials only approaches that of bare materials after approximately 4 hours.     

Moderne Verfahren zur Berechnung des Strahlungsaustausches in brennstoffbeheizten Röhrenöfen

Modern procedures for calculation of radiational heat transfer in fueled tubular furnaces . The zone method due to Hottel, the Monte-Carlo method and the flux method are of great importance for the calculation of radiational heat transfer in combustion chambers, along with simple zero- to two-dimensional models. Only the first three methods can be used for three-dimensional problems. The zone method and the Monte-Carlo method are mathematically exact, while the flux method gives only approximate values. The radiational heat transfer to the pipes of a cracking furnace is calculated by a simple zero-dimensional zone method to show, for example, that simple models often also give reasonable results.