Augmenting Distillation by Membranes: Developments and Prospects

The growing consciousness for sustainable industrial processes has resulted in industrially developed countries in supporting research efforts toward thorough evaluation of possibilities for improving efficiency of energy intensive separations implying also significant reduction of related carbon dioxide emissions. Being inherently thermodynamically inefficient, distillation, which is by far the most widely utilised and energy intensive separation technology in chemical process industries, has become primary target of energy conservation projects in refining, petrochemical and chemical industries. Improvement is an ongoing activity, replacing still beyond comprehension and a great deal of academic effort is oriented towards augmenting distillation by combining it, where appropriate, with membranes, i.e. pervaporation or vapour permeation, which in conjunction with polymeric membranes proved to be an industrially viable alternative to conventional processes for dehydration of alcohols. Present paper addresses recent developments along this line striving for larger fluxes in alcohol dehydrations by utilising ceramic membranes, with focus on vapour permeation, as well as the potential for the recovery of organic solvents and reactants forming azeotropes with other organics

Pervaporation and vapour permeation of methanol and MTBE through a microporous methylated silica membrane

The combination of conventional unit operations with pervaporation or vapour permeation membrane separation processes offers opportunities for process intensification in terms of augmenting capacity and decreasing energy consumption of conventional unit operations. The MTBE production process is an often studied example of a so-called hybrid process in which distillation is combined with pervaporation or vapour permeation. In this work transport of pure methanol through and separation of methanol from MTBE by a supported microporous methylated membrane (developed by the Energy research Centre of the Netherlands) is studied. Several aspects of modelling of transport through the support layers and the selective layer are addressed, thereby comparing the Maxwell-Stefan equations for pure methanol transport with a practical engineering model. From experiments performed at temperatures up to 140°C it appeared that both the selectivity towards methanol and flux of the membrane are high. The thesis ends with a study comparing pervaporation and vapour permeation on laboratory scale as well as on large scale by simulations.Applied Science

Validation of the Danckwerts-plot technique by simultaneous chemical absorption of CO2 and physical desorption of O2

The Danckwerts-plot technique [Danckwerts et al., 1963. Chemical Engineering Science 18, 63–72] is used in chemical engineering to simultaneously obtain the mass transfer parameters, kL and a, from mass transfer experiments. This method requires variation of the reaction kinetics by adding different amounts of catalyst. Although the method is known for several decades, it was never verified that the variation of the amount of catalyst does not affect the hydrodynamics of the system under investigation. To study this, absorption of CO2 in a carbonate/bicarbonate buffer solution was performed simultaneously with desorption of oxygen from this solution, after verification that absorption and desorption are processes, taken place at identical rates, but in a different direction. It was shown that the addition of catalyst did not affect the desorption rate of oxygen. The obtained kLa for oxygen was, however, 64% higher compared to the kLa of carbon dioxide. This was probably due to a lower effective interfacial area, caused by the complete depletion of small bubbles containing CO2. Mass transfer experiments with oxygen, with a low gas phase conversion, are therefore to be preferred, as the measured mass transfer parameters are less affected by the gas phase RTD and the shape of the bubble size distribution

Saccular Abdominal Aortic Aneurysms Patient Characteristics, Clinical Presentation, Treatment, and Outcomes in the Netherlands

Objective: The aim of this was to analyze differences between saccularshaped abdominal aortic aneurysms (SaAAAs) and fusiform abdominal aortic aneurysms (FuAAAs) regarding patient characteristics, treatment, and outcome, to advise a threshold for intervention for SaAAAs.Background: Based on the assumption that SaAAAs are more prone to rupture, guidelines suggest early elective treatment. However, little is known about the natural history of SaAAAs and the threshold for intervention is not substantiated.Methods: Observational study including primary repairs of degenerative AAAs in the Netherlands between 2016 and 2018 in which the shape was registered, registered in the Dutch Surgical Aneurysm Audit (DSAA). Patients were stratified by urgency of surgery; elective versus acute (symptomatic/ruptured). Patient characteristics, treatment, and outcome were compared between SaAAAs and FuAAAs.Results: A total of 7659 primary AAA-patients were included, 6.1% (n = 471) SaAAAs and 93.9% (n = 7188) FuAAAs. There were 5945 elective patients (6.5% SaAAA) and 1714 acute (4.8% SaAAA). Acute SaAAApatients were more often female (28.9% vs 17.2%, P = 0.007) compared with acute FuAAA-patients. SaAAAs had smaller diameters than FuAAAs, in elective (53.0mm vs 61 mm, P = 0.000) and acute (68mm vs 75 mm, P = 0.002) patients, even after adjusting for sex. In addition, 25.2% of acute SaAAA-patients presented with diameters <55mm and 8.4% <45 mm, versus 8.1% and 0.6% of acute FuAAA-patients (P = 0.000). Postoperative outcomes did not significantly differ between shapes in both elective and acute patients.Conclusions: SaAAAs become acute at smaller diameters than FuAAAs in DSAA patients. This study therefore supports the current idea that SaAAAs should be electively treated at smaller diameters than FuAAAs. The exact diameter threshold for elective treatment of SaAAAs is difficult to determine, but a diameter of 45mm seems to be an acceptable threshold.Vascular Surger