Process energy efficiency in pervaporative and vacuum membrane distillation separation of 2,3-butanediol†

This work focused on the energy aspects of the pervaporative separation of 1-butanol/2,3-butanediol. A numeric model was developed to simulate the mass and energy balance of the pervaporation process. It was found that the distribution of evaporation heat requirement over the membrane area is asymmetric, and more than 85% of the heat was consumed in the 60% of the membrane area. It was also revealed that recycling the permeate having higher than 5% w/w 2,3-butanediol can improve the recovery of 2,3-butanediol, and thus enhance the process energy efficiency. Two recycling strategies (the single or multiple point admission of permeate to the retentate flow) were explored. The specific energy requirement (the heat required by generating 1 kg 99.5% w/w 2,3-butanediol as product) was proposed to evaluate the process energy efficiency of both the pervaporation and vacuum membrane distillation, and it was shown that pervaporation can bring about nearly four times energy savings over the vacuum membrane distillation. Ce travail etait axe sur les aspects energetiques de la separation pervaporative de 1-butanol/2,3-butanediol. Un modele numerique a ete cree pour simuler le bilan massique et energetique du processus de pervaporation. On a decouvert que la distribution de la consommation calorifique de l'evaporation sur la surface de la membrane est asymetrique et plus de 85% de la chaleur etait consommee dans les 60% de la surface de la membrane. On a egalement revele que le recyclage du permeat superieur a 5% p/p 2,3-butanediol peut ameliorer la recuperation de 2,3-butanediol et ainsi accroitre l'efficacite energetique du processus. Deux strategies de recyclage (l'admission unique ou multiple du permeat au flux de retentat) ont ete explorees. Le besoin energetique particulier (la chaleur requise par la production de 1 kg 99,5% p/p 2,3-butanediol comme produit) a ete propose pour evaluer l'efficacite energetique du processus a la fois de la pervaporation et de la distillation de membrane sous vide et il a ete demontre que la pervaporation peut occasionner presque quatre fois les economies d'energie par rapport a la distillation de membrane sous vide.