A liquid-liquid extraction of nitrobenzene (NB) in impinging stream-rotating packed bed (IS-RPB) was proposed using cyclohexane as an extractant, presented for its improvement of micromixing and mass transfer performance. The effects of pH, phase ratio (the flow rate of organic phase/aqueous phase) and rotating speed of IS-RPB on removal efficiency and extraction stage efficiency of NB were investigated experimentally in IS-RPB. The experimental result showed that the removal rate of NB reached 94.93%, and extraction stage efficiency was 99.99% in IS-RPB, respectively, under the following experimental conditions including: a pH of 6.4, a temperature of 25 °C, a phase ratio of 1:1, a liquid flow rate of 50 L/h, a rotating speed for IS-RPB of 400 r/min, and an initial impinging velocity of 7.88 m/s. Besides, IS, RPB and IS-RPB were compared based on the removal rate of NB and extraction stage efficiency in the same experimental conditions. Compared with other mixing devices, IS-RPB has better extraction stage efficiency and shorter extraction time than other extraction devices, proving that high gravity technology can be utilized to effectively improve the extraction stage efficiency and has a good application prospect.

Extraction of nitrobenzene from aqueous solution in impinging stream-rotating packed bed

Oxidative desulfurization (ODS) is an attractive complementary or alternative process for the hydrodesulfurization (HDS) process due to advantages such as mild operating conditions. In the ODS process, the sulfur-containing compounds are oxidized first to polar sulfoxide and sulfone products and then these polar compounds are separated using solvent extraction or an adsorption process. In the present study, the separation of oxidized sulfur-containing compounds of diesel as a real fuel has been investigated using extraction in a single drop column. The oxidation system was hydrogen peroxide/formic acid. The selected solvent for the extraction of oxidized sulfur-containing compounds was dimethylformamide (DMF). In single drop tests, the effect of various parameters including the drop size (1.70-4.60 mm) and column height (228-550 mm) on the different parameters such as drop velocity and sulfur concentration in the dispersed and continuous phases has been investigated. The outcome of this study provides valuable insights for designing the extraction column for separation of oxidized sulfur-containing compounds from middle distillate fuels in an ODS process.

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Separation of sulfur-containing compounds from diesel by oxidation followed by solvent extraction in a single drop column

The possibility of regenerating the solvent of extraction units by cyclic adsorption was analyzed. This combination seems convenient when extraction is performed with a high solvent-to-impurity ratio, making other choices of solvent regeneration, typically distillation, unattractive. To our knowledge, the proposed regeneration scheme has not been considered before in the open literature. Basic relations were developed for continuous and discontinuous extraction/adsorption combinations. One example, deacidification of plant oil with alcohol, was studied in detail using separate experiments for measuring process parameters and simulation for predicting performance at different conditions. An activated carbon adsorbent was regenerated by thermal swing, making cyclic operation possible. When extracting the acid with methanol in a spray column, feed = 4 L min−1, solvent = 80 L min−1, feed impurity level 140 mmol L−1, and extract concentration 7.6 mmol L−1, the raffinate reaches a purity of 1.2 mmol L−1, the solvent being regenerated cyclically in the adsorber (364 kg) to an average of 0.7 mmol L−1. Regeneration of the solvent by cyclic adsorption had a low heat duty. Values of 174 kJ per litre of solvent compared well with the high values for vaporization of the whole extract phase (1011 kJ L−1).

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Coupling Solvent Extraction Units to Cyclic Adsorption Units

Terminal velocity and mass transfer of rising drops in a stagnant liquid were experimentally measured. The chemical system included the toluene drops whose acetic acid content was transferred to the surrounding water. Three sets of structured packing were used in the column to investigate the impact of packing at different heights of 10, 25 and 40 cm. The effects of flow rate (Q), drop size (d), inverse viscosity (N f ), Eotvos number (Eo), and Reynolds number (Re) on terminal velocity, u t , and Froude number, Fr, were investigated. The critical points of d = 3.4 mm, Eo = 0.5 and N f  = 200 were found at which two regions of circulating and oscillating drops were separated, and the Fr was constant within each region. The effect of packing height on Fr and Sherwood number against Reynolds number was also investigated. Compared to the non-packed column it was revealed that a 30% increase in Sherwood number could be achieved using a packing with 40 cm in height. Moreover, it was found that simultaneous increase of packing height and the flow rate consistently enhanced the mass transfer coefficient. Finally, a correlation was proposed which permitted the prediction of Sherwood number versus the dimensionless numbers of Reynolds, Weber and the packing height ratio.

Packing effect on mass transfer and hydrodynamics of rising toluene drops in stagnant liquid

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Biphasic Cellulose Acetate/Rtil Membranes And Functionalized Graphene Adsorbents For Natural Gas Processing: Experimental And Molecular Simulation Studies

The effects of holdup on Sauter mean drop diameter, D32, and dispersed phase mass transfer coefficient have been studied in the spray and packed extraction columns. For both columns, two well-defined regions for the dependence of D32 on holdup were observed. D32 increased and decreased with an increase in holdup at low and high levels of holdup, respectively. Changes in dispersed phase mass transfer coefficient against holdup were shown to be similar to D32 for both columns. Moreover, empirical correlations have been derived to predict D32 and dispersed phase mass transfer coefficient for both columns. It has been shown that the derived correlations are in a good agreement with the experimental data. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Zohreh Kheirjooy

Papers

Spray and packed liquid–liquid extraction columns: drop size and dispersed phase mass transfer