Abstract In the production of chemicals from fermentation, the cost of downstream purification constitutes the major portion of the total production cost. Since the bioprocess generally contains a large amount of biochemical separation units, its flowsheets are complex. How to generate the rigorous superstructure of the downstream bioprocess is a primary problem and key step. In this work, a robust combined approach based on the P-graph was proposed to generate the rigorous superstructure of the downstream process of fermentation. This method integrates the hierarchical decomposition of the heuristics with P-graph-based algorithm MSG with the advantages including: (1) Different design flowsheets could be evaluated simultaneously; (2) An unique bipartite graph, P-graph, was introduced, which could represent the maximum structure clearly and intuitively; (3) The rigorous superstructure could be automatically generated. The validity of the present method was verified with two practical bioprocesses. Results show that the effective processes and the adequate operation units could be determined in the beginning stage of the design, and the tedious reforming steps during process synthesis could be avoided.

Gas absorption accompanied by an instantaneous irreversible chemical reaction in bubble columns has been analyzed theoretically. A mass transfer model based on the Dankwerts surface-renewal model as well as the penetration theory for surface stretch proposed by Angelo et al. was developed, in which the effects of bulk motion and turbulence on mass transfer were taken into account. The analytical expressions for the time-average mass transfer coefficient and the enhancement factor have been obtained. The fast reactive absorption of SO2 from gas mixtures into aqueous NH4HCO3 solution was investigated experimentally in a bubble column reactor to validate the mass transfer model, and the results calculated by the present model agree well with the experimental results.

The viscosity distribution of the liquid around a rising bubble in carboxymethyl cellulose (CMC) aqueous solutions was measured experimentally by particle image velocimetry (PIV). The effect of the concentration of CMC solutions on the viscosity distribution around a bubble and the coupling relations between the viscosity field, flow field and shear stress field were also studied. Results indicated that the specific viscosity (non-dimensionalized by η0) decreases with the increase in CMC solution concentration due to a shear thinning effect. Within the experimental range, similar viscosity distributions of liquids around a rising bubble were found: a hollow cylindrical low viscosity region around the bubble wake and a high viscosity region in the central bubble wake.