Design and Optimization of Hybrid Separation Processes for the Dehydration of 2-Propanol and Other Organics

Abstract

The dehydration and recycling of industrial solvents often requires complex processes due to azeotropes and pronounced pinch-points. Combined processes consisting of distillation and pervaporation/vapor permeation might overcome these thermodynamic limitations and offer economically attractive alternatives by simplifying process structure, reducing energy consumption, and avoiding entrainers. The technical and economical feasibility of organic solvent dehydration by pervaporation and vapor permeation with inorganic membranes was evaluated. A survey of the process industry revealed the most attractive applications. The separation of 2-propanol and water was studied in detail. For all process calculations the commercial software Aspen Plus was used. Compatible Fortran routines were developed to incorporate membrane units into the program. Different process configurations to integrate pervaporation and vapor permeation with distillation are compared to conventional separation by extractive distillation. A hybrid process design should take advantage of the specific benefits of both separation methods. Often, savings in energy consumption of up to 85% are possible. Investment and operation costs can be reduced by more than 40% in comparison to conventional processes. The most attractive design is distillation and further purification of the top stream by a membrane unit. Here, the economical benefits increase from adiabatic pervaporation over isothermal pervaporation to vapor permeation. A sensitivity analysis of various parameters affecting the operating costs of the plant was carried out.

Study of the Dehydration of Isopropanol by a Pervaporation‐Based Hybrid Process

“…They carried out an economic comparison between the traditional azeotropic distillation process and different hybrid configurations. A similar study was also performed by Sommer and Melin [8]. In both cases it was concluded that the hybrid process combining distillation followed by pervaporation is the most economical option, leading to savings of about 50 % compared to the azeotropic distillation process.…”

“…To obtain an isopropanol concentration higher than 99.9 wt % nearly twice the membrane area would be required. Sommer and Melin [8] proposed that the separation of the isopropanol/ water azeotrope by a pervaporation unit located between two distillation columns can become more economically when the desired water content in isopropanol should be in the region of a few ppm, since the driving force for the permeation process becomes extremely low for the removal of the remaining water traces.…”

“…Pervaporation can be used for the purification of the azeotropic distillate stream up to the desired isopropanol purity [7]. Recently, Sommer and Melin [8] and Van Hoof et al [9] compared different process configurations for the dehydration of isopropanol. They compared the conventional extractive and azeotropic distillation process using ethylene glycol [8] and benzene [9] as entrainers with different distillationpervaporation hybrid processes.…”

Separation technologies for the recovery and dehydration of alcohols from fermentation broths

“…However, most cost and energy comparisons of this type have been made for isopropanol dehydration. [292][293][294] Nevertheless, in most cases, the membrane processes were reported to require less energy than a molecular sieve system. Th e sum of engineering capital and operating costs was also found to be lower for the membrane processes with reduced operating costs more than compensating for increased capital costs.…”

A hybrid distillation–pervaporation system in a single unit for breaking distillation boundaries in multicomponent mixtures

“…Otherwise, it can be used as a final treatment stage. Applications for binary mixtures 7,9,10 and multicomponent mixtures 11,12 can be found in literature, where the effect of the membrane properties and operating variables on the hybrid process performance have been discussed. It has been shown that a retentate stream composed of a mixture of liquid and vapour can reduce the membrane area requirements compared to conventional pervaporation units and membrane savings higher than 40 % can be achieved 13,14 .…”