1,3-Propanediol and 2,3-butanediol are two promising chemicals which have a wide range of applications and can be biologically produced. The separation of these diols from fermentation broth makes more than 50% of the total costs in their microbial production. This review summarizes the present state of methods studied for the recovery and purification of biologically produced diols, with particular emphasis on 1,3-propoanediol. Previous studies on the separation of 1,3-propanediol primarily include evaporation, distillation, membrane filtration, pervaporation, ion exchange chromatography, liquid-liquid extraction, and reactive extraction. Main methods for the recovery of 2,3-butanediol include steam stripping, pervaporation, and solvent extraction. No single method has proved to be simple and efficient, and improvements are especially needed with regard to yield, purity, and energy consumption. Perspectives for an improved downstream processing of biologically produced diols, especially 1,3-propanediol are discussed based on our own experience and recent work. It is argued that separation technologies such as aqueous two-phase extraction with short chain alcohols, pervaporation, reverse osmosis, and in situ extractive or pervaporative fermentations deserve more attention in the future.

Many networks are characterized by highly heterogeneous distributions of links, which are called scale-free networks and the degree distributions follow p(k) ∼ ck −α . We study the robustness of scale-free networks to random failures from the character of their heterogeneity. Entropy of the degree distribution can be an average measure of a network's heterogeneity. Optimization of scale-free network robustness to random failures with average connectivity constant is equivalent to maximize the entropy of the degree distribution. By examining the relationship of the entropy of the degree distribution, scaling exponent and the minimal connectivity, we get the optimal design of scale-free network to random failures. We conclude that the entropy of the degree distribution is an effective measure of network's resilience to random failures.

1,3-Propanediol (1,3-PD) was produced by Klebsiella pneumoniae using crude glycerol obtained from biodiesel production. The 1,3-PD concentration of 51.3 g/l(-1) on crude glycerol from alkali-catalyzed methanolysis of soybean oil was comparable to that of 53 g/l(-1) on crude glycerol derived from a lipase-catalyzed process. The productivities of 1.7 g l(-1) h(-1) on crude glycerol were comparable to that of 2 g l(-1) h(-1) on pure glycerol. It could be concluded that the crude glycerol could be directly converted to 1,3-PD without any prior purification.