Using static mixers to intensify the removal of organics from industrial effluents.

摘要

iquid-liquid contacting is an important operation that is encountered in a wide range of chemical, petroleum processing operations (e.g. desulphurisation of diesel, metal recovery from dilute solutions, nitrification,).and in petrochemical operations (e.g. chemical reactions, preparation of emulsions, reactive extraction, extractive separation, and the reduction or elimination of unwanted by-products). It is also used an effective means for removing hazardous soluble components from industrial effluents and waste management sites.;To achieve aforementioned objectives, the experiments are conducted within a pilot-scale unit 770 mm long, 6.35 mm ID that is equipped with 24 stainless steel screen elements and placed in a vertical orientation. Proponic acid was selected as the solute which is transferred between the two immiscible phases and the two solvents tested are 1-Hexanol/ and 2-Octanol.;The results obtained show that, overall volumetric mass transfer coefficients as high as 27.0 s-1 can be achieved. This is 100→3,000 times higher than the values reported for other liquid-liquid contactors. These high inter-phase mass transfer coefficients, combined with the plug flow characteristics of this contactor, resulted in mass transfer efficiencies as high as 99% being achieved within residence times shorter than 1 s with specific energy consumption rates that are much smaller than those required by conventional contactors.;The high mass transfer coefficients that can be achieved allow for the use of smaller contactors/reactors and significantly enhance the selectivity and yield of mass transfer controlled chemical operations. It also enhances the inherent safety of the operations and significantly reduces the capital and operating costs.;Obtaining high volumetric mass transfer coefficient, Ka, in such operations allows for the use of smaller and safer contactors and can significantly enhance the selectivity and yield of mass transfer controlled chemical operations. This investigation was therefore, undertaken with the objective of developing a better understanding of the factors that influence inter-phase mass transfer in liquid-liquid contacting and how the hydrodynamic conditions affect the mass transfer performance of screen type static mixer. This information is to be used to assess the potential for applying this contactor to intensify selected multi-phase operations in the petrochemical industry and to understand the factors affecting the continuous-phase mass transfer coefficient.;The correlations between mass transfer performance indicator (i.e., superficial velocity, dispersed phase holdup, and energy dissipation rate), volumetric mass transfer coefficient, and the continuous phase mass transfer coefficient were developed.;The results obtained in the present investigation were used as a case study to assess the possibility of using solvent extraction to recover Ethanol from the aqueous effluents emanating from an Acetic acid plant (600 m3/day). It was found that: (1) Small inexpensive contactors can be used for that purpose (e.g. 5 stages, D=180mm, L=2,200mm) results in low capital costs. (2) The specific power consumption (4 ≤ E ≤ 7 kWh/m 3 or 0.16 ≤