Slags from the production of high‐alloyed steel contain both chemically bound chromium (mainly as Cr2O3) in the mineral fraction and elemental chromium in the metallic remainders. Thermochemical post treatment of the slag in an electric arc furnace under reducing conditions enables the nearly complete recovery of the total amount of chromium in form of a metallic alloy. The best results were achieved by resistance melting (submerged electrodes) with addition of a reducing agent into the melt. The efficiencies of the reducing agents carbon, aluminium, silicon (as ferrosilicon) and silicon carbide were investigated and compared. As aluminium is the strongest reducing agent, it is less selective and reduces much more SiO2 than Cr2O3. While SiC shows only low reactivity because of its high thermal resistance, carbon and silicon had the highest reducing potentials: More than 97% of the chemically bound chromium can be recovered by application of these reducing agents. Due to the high temperature required for the reduction of the chromium compounds, the reduction of SiO2 as an undesired side reaction cannot be avoided. However, compared with mechanical procedures that are limited to the recovery of the metallic remainders, the total chromium recovery can be significantly increased by the described reductive melting procedure.
The feasibility of using native lipase A from Candida antarctica (CAL-A) to esterify fatty acids with water-insoluble alcohols in the presence of excess water was investigated in stirred-tank reactors. For high reaction rates, a ratio of water:substrates of 0.6-1.4:1 (v/v) was required. CAL-A showed higher substrate selectivity for the esterification of saturated palmitic acid with branched-chain 2-ethyl-1-hexanol than for unsaturated oleic acid with linear alcohol (1-decanol). After 18 h at 70 °C in a 1.5 l bulk stirred-tank reactor, an 2-ethyl-1-hexyl palmitic acid ester was obtained near 100 % yield [molar ratio palmitic acid:2-ethyl-1-hexanol ~1:1.25, with 1.11 % (w/w) Novocor ADL (based on palmitic acid weight)].
Commercial native lipase A from Candida antarctica was used to produce alkyl esters through the alcoholysis of (waste) fats with 2-ethyl-1-hexanol. The process was carried out in batch stirred tank reactors (from 100 mL up to 3000 L).The content of alkyl esters in reaction mixtures was determined by gradient HPLC using an evaporative light scattering detector and the reaction progress was controlled by determining the ratio of the palmitic acid ester peak area to the oleic acid ester peak area in HPLC chromatograms.The results show that alcoholysis is the favoured reaction in presence of excess water and water-insoluble alcohols in comparison with hydrolysis (fatty acid content ,5%). The optimum amount of water for the alcoholysis was found to be 80-100% of the amount of fat. In the presence of low quantities of water both alcoholysis and hydrolysis are slow.Conversion rate increases with increasing temperature to 65-70 7C.Based on these results a large-scale test to produce 3000 L of alkyl ester (to be used as lubricant coolant) was carried out. The experiments have proved that alcoholysis is completed after about 7-10 h depending on temperature.
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