Dongming Xie

Effect of electrolytic systems on electrochemical hydrogenation of mesophase coal tar pitch

Abstract A mid-temperature coal tar pitch (CP) was extracted by pyridine and heat-treated to obtain a mesophase coal tar pitch (MCP). The microstructures of refined coal tar pitch (RCP) and MCP were observed, and the properties of MCP were improved by electrochemical hydrogenation. Electrolytic systems, such as electrolytic cells, electrolytic solvents, supporting electrolytes, and cathode materials, used for electrochemical hydrogenation of MCP are discussed. The results showed that the hydrogen content (H%) and ratio of hydrogen to carbon (H/C) of hydrogenated MCP (HMCP) were increased, and the softening point (SP) was decreased in comparison with untreated MCP. IR and 1 H-NMR spectra established that –CH 3 and –CH 2 had appeared in HMCP, and the ratio of aromatic hydrogen to aliphatic hydrogen of HMCP was decreased.

Modeling of glycerol production by fermentation in different reactor states

A kinetic model of glycerol production by fermentation with the osmophilic yeast Candida krusei was studied firstly by analogies to published works. Considering that the glycerol produced competes with glucose, as a second carbon source for energy maintenance, mathematical models of glucose utilization and glycerol accumulation were modified further. By adjusting only two variable macrokinetic parameters, K-S and beta, the model simulations could fit experimental data well when the reactor was changed from Airlift Loop Reactor in different scale or airlift mode to Stirred Vessel. To avoid a significant reduction in glycerol production in the latter fermentation stage, the final condition of the fermentation, determined by the concentration ratio of glycerol to glucose, was also investigated in four different Reactor States. The kinetic models and simulation results can provide certain reference for scale up of glycerol production by fermentation

Critical influence of osmotic pressure on continuous production of glycerol by an osmophilic strain of Candida krusei in a multistage cascade bioreactor

The effects of osmotic pressure and dilution rate were investigated on the continuous production of glycerol in a multistage cascade bioreactor. The results showed that high osmotic pressure could improve fermentation performance significantly. At a dilution rate of 0.050 h?1 and feeding 400 g l?1 glucose solution, a glycerol yield of 25.0% based on glucose consumed and a maximum productivity of 19.4 g l?1 per day were obtained, respectively, in a six-stage cascade bioreactor. When the dilution rate was increased from 0.023 to 0.085 h?1, the glycerol yield, based on biomass, remained constant, but specific productivity increased by 94.7%. Productivity increased by only 46.6% due to low biomass concentration in the bioreactor at the higher dilution rates.

Glycerol production by Candida krusei employing NaCl as an osmoregulator in batch and continuous fermentations

Addition of 40 g NaCl l−1 to a chemically defined medium containing 140 g glucose l−1 in shake-flask culture improved glycerol production by Candida krusei from 16.5 g l−1 to 47.7 g l−1. With 40 g NaCl l−1 at a dilution rate of 0.065 h−1, glycerol concentration, glycerol yield (based on glucose consumed), and productivity in a four-stage cascade bioreactor were higher by 240%, 27% and 28%, respectively, than in a single-stage continuous culture system.

Production of glycerol by fermentation using osmophilic yeast Candida krusei with different starchy substrates

An osmophilic yeast, Candida Krusei, was used for glycerol production with various starchy substrates. The results showed that cassava starch and corn starch were easily liquefied and saccharified compared with corn meal and sweet potato meal. The optimal concentrations of corn steep liquor (CSL) added to the liquefied and saccharified media from corn meal, sweet potato meal, cassava starch, and corn starch were 0, 0, 0.15%, and 0.1%, respectively. Correspondingly, the maximal glycerol productions were 3.8%, 3.5%, 5.5%, and 7.1%, respectively. Furthermore, it was found that glycerol produced was utilized as the second carbon source at 24 h, 24 h, 72 h, and 84 h, respectively, in addition, accompanying the lower rate of glycerol production (RGP), the maximal glycerol production (GP) and glycerol yield (GY) were reached when corn starch was selected as starchy substrate. in the case of corn meal and sweet potato used as starchy substrates, biomass increased rapidly and residual glucose decreased quickly, compared with corn starch and cassava starch.

Improvement of glycerol production by Candida krusei in batch and continuous cultures using corn steep liquor

No fermentation parameter was affected at phosphate concentration above 0.4 g l−1 when KH2PO4 was used as phosphate source and the glucose consumption rate was difficult to control when corn steep liquor (CSL) was adopted as the phosphate source. However, if CSL was supplemented as a source of growth factors instead of as the phosphate source, not only glucose uptake and glycerol was improved, but also fermentation became easy to control and a steady state of continuous culture was easily obtained.

Model-based optimization of temperature and feed control strategies for glycerol production by fed-batch culture of osmophilic yeast Candida krusei

In this study, the optimization of temperature and feed control strategies for glycerol production by fed-batch culture of osmophilic yeast Candida krusei was investigated to maximize the final yield whilst to control the residual glucose at a low concentration. For the purposes of convenient control performance and easy numerical solution, the entire fermentation process was proposed being divided into multi-subintervals. In each subinterval, temperature was controlled constantly; while glucose and corn steep liquor were fed in pulse form at each start. Both piecewise-constant temperature (PCT) and discrete-pulse feed (DPF) control strategies were optimized by the complex method of Box based on previous macro-kinetic model and verified experimentally in a 600 ml airlift loop reactor. It was found that, by model-based optimization of only DPF control strategies, the final glycerol yield were significantly improved compared with those by previous empirical strategies. The yield could be improved further by optimization of both PCT and DPF control strategies and by selecting the first half of the whole fermentation process as the control emphasis. The optimization approach proposed appeared promising to solve the multivariable control problem in many fermentation processes.

Effects of phosphorus and nitrogen limitations on continuous production of glycerol in a multistage cascade bioreactor by Candida krusei

A multistage cascade culture was used for the continuous production of glycerol by an osmophilic yeast Candida krusei. The effects of phosphorus and nitrogen limitations on glycerol production were investigated. The results showed that the fermentation performance was improved under either phosphorus or nitrogen limitation. A maximum glycerol yield of 24.7% based on the glucose consumed and a maximum glycerol yield of 7.1 g g(-1) based on the biomass were achieved under the optimum nitrogen limitation. The maximum productivity for the whole system under the optimum phosphorus limitation was 11.3% higher than that under the optimum nitrogen limitation. This indicated that the nitrogen limitation benefited the improvement of glycerol yield based on the glucose consumed and the production ability of glycerol per unit biomass but the phosphorus limitation favored the increase of productivity. The glycerol/glucose yield and the glycerol/biomass yield could be further improved under the dual limitations of phosphorus and nitrogen, but the biomass yield and the productivity were reduced

Multipulse feed strategy for glycerol fed-batch fermentation: a steady-state nonlinear optimization approach.

During glycerol fed-batch fermentation, the process could be divided into multiple equal subintervals, and the feed operation was performed in pulse form at the start of each subinterval. Based on the macrokinetic models, the multipulse feed strategy for both glucose and corn steep slurry was determined by a general nonlinear optimization approach to maximize the final glycerol productivity and still control the residual glucose at a low concentration. The experimental results in a 600-mL Airlift Loop Reactor showed that the tested data with this strategy agreed well with the corresponding model prediction, and that the feed mode with nonlinear optimization could improve the glycerol productivity significantly compared with those determined just by limited experimental optimization in previous studies.

Optimization of glycerol fed-batch fermentation in different reactor states: a variable kinetic parameter approach.

To optimize the fed-batch processes of glycerol fermentation in different reactor states, typical bioreactors including 500-mL shaking flask, 600-mL and 15-L airlift loop reactor, and 5-L stirred vessel were investigated. It was found that by reestimating the values of only two variable kinetic parameters associated with physical transport phenomena in a reactor, the macrokinetic model of glycerol fermentation proposed in previous work could describe well the batch processes in different reactor states. This variable kinetic parameter (VKP) approach was further applied to model-based optimization of discrete-pulse feed (DPF) strategies of both glucose and corn steep slurry for glycerol fed-batch fermentation. The experimental results showed that, compared with the feed strategies determined just by limited experimental optimization in previous work, the DPF strategies with VKPs adjusted could improve glycerol productivity at least by 27% in the scale-down and scale-up reactor states. The approach proposed appeared promising for further modeling and optimization of glycerol fermentation or the similar bioprocesses in larger scales.