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Open Chemistry
|
2007
|
vol. 5
|
issue 4
1124-1147
EN
Hybrid separation processes are becoming more and more important in the practice if membrane technologies are also involved. In this work, a systematic investigation is completed for three sequence alternatives of distillation and pervaporation. These are the following: pervaporation followed with distillation (PV+D), distillation followed with pervaporation (D+PV), two distillation columns and a pervaporation unit between them (D+PV+D). The hybrid separation process alternatives are evaluated with rigorous modelling tools, but first, a rigorous simulation algorithm is determined for the pervaporation. The three hybrid separation processes are rigorously modelled with CHEMCAD, and optimized with the dynamic programming optimization method for the case of the separation of ethanol-water mixture. The objective function is the total annual cost (TAC). The energy consumption is also investigated. The selection of the ethanol-water mixture has two motivations: (i) it is quite often studied and well known, and (ii) to make biofuel (ethanol) production more economical, membrane technologies might also be applied. The results are compared with each other and with the classical separation completed with heteroazeotropic distillation. The optimized TAC shows that the distillation column followed with pervaporation is the most economical hybrid separation process alternative. Its TAC is about 66% of that of the classical separation. [...]
EN
The sustainable development and consumption need more efficient use of natural resources. As a consequence, the use of industrial solvents demands their recovery instead of end-of-pipe treatment. It is not always clear, however, which treatment alternative should be applied. Based on an industrial case study, the environmental and economic evaluation and comparison of the treatment alternatives of a non-ideal solvent mixture containing azeotropes is investigated for determining the preferable option. For the recovery of the industrial solvent mixture, two different separation alternatives are evaluated: a less effective alternative and a novel design based on hybrid separation tools. An end-of-pipe treatment alternative, incineration, is also considered and the split of the solvent mixtures between recovery and incineration is investigated. The environmental evaluation of the alternatives is carried out using ‘Eco-indicator 99 life-cycle impact assessment methodology’. Economic investigation is also accomplished. The economic features clearly favour the total recovery, however, the environmental evaluation detects that if a recovery process of low efficiency is applied, its environmental burden can be similar or even higher than that of the incineration. This motivates engineers to design more effective recovery processes and reconsider the evaluation of process alternatives at environmental decision making.
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EN
The soy bean process water that is a by-product of soy processing technology can be utilized with a hybrid separation system recommended and investigated in this work. The aims of the soy bean water processing are to i.) concentrate the valuable components of the soy process water and ii.) reuse its water content. Two hybrid separation systems are considered and investigated: ultrafiltration followed by nanofiltration and centrifugal separation followed by nanofiltration. These hybrid separation systems are new in the area of their current application. Experiments verify that centrifugal separation is a more appropriate pre-treatment method for the removal of suspended solids and for the preservation of the sucrose content of the soy bean process water than ultrafiltration. Total sucrose can be rejected by nanofiltration membrane forming a sugar-rich retentate that contains other valuable components, too. Both tested hybrid processes result in clear and reusable permeates with low chemical oxygen demand that can be recycled to the production process reducing its water consumption and improving its sustainability. The recommended new hybrid separation system, centrifugal separation followed by nanofiltration, proves to be successful in this area of the biochemical industry.
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