Ülkü Mehmetoğlu

Modeling of extraction of β-carotene from apricot bagasse using supercritical CO2 in packed bed extractor

This work investigates the modeling of β-carotene extraction from industrial waste product of apricot bagasse at the production of fruit juice. Shrinking core model was selected as the best mathematical model, which characterize the extraction process, after take into consideration of mass transfer mechanisms such as adsorption, diffusion, solubility, and desorption. Effect of main separation parameters such as pressure, temperature, CO2 flow rate, and particle size on the extraction yields were researched at the supercritical fluid extraction system of laboratory scale and the results were compared with the results obtained from the solution of mathematical model.

Investigation of extractive citric acid fermentation using response-surface methodology

Extractive citric acid fermentation with Aspergillus niger microoganism was investigated in the presence of corn oil and Hostarex A327 in oleyl alcohol. In the extractive fermentation, production and separation phases are achieved simultaneously. Before Response Surface Methodology (RSM) was applied,the effect of potassium ferrocyanide (K4Fe(CN)6) concentration on citric acid production and the prevention of solvent toxicity using corn oil were investigated. Citric acid concentration increased with increasing K4Fe(CN)6 concentration. Solvent toxicity was reduced using corn oil in the extractive citric fermentation. In the RSM, the potassium ferrocyanide concentration, (0.02–0.10%, w/v), the ratio of organic phase volume to the aqueous phase volume, Vor/Vaq, (0.5–1.5), the corn oil concentration (0–20%, by volume) and the Hostarex A327 content in oleyl alcohol (10–50%, by volume) were the critical components. Optimum citric acid concentration was obtained as 5.70 g/l with employing the following predicted optimum extraction conditions: K4Fe(CN)6 of 0.06% (w/v), Vor/Vaq of 1.25, corn oil concentration of 13.7% (by volume) and Hostarex A327 content in oleyl alcohol of 33% (by volume). Citric acid production by extractive fermentation was increased approximately 40% with respect to the control run (4.10 g/l).

Substrate interactions during the biodegradation of benzene, toluene and phenol mixtures

Abstract Benzene, toluene and phenol were degraded completely at high initial concentrations by Pseudomonas putida F1 ATCC 700007. Two hundred and fifty milligram per litre benzene, 225 mg/l toluene and 200 mg/l phenol were degraded individually in 19, 14 and 35 h, respectively. The biodegradation times increased on increasing the substrate concentration. The maximum biodegradation rates were 149 mg benzene/g dry cellxa0h for 60 mg/l benzene, 44 mg toluene/g dry cellxa0h for 110 mg/l toluene and 102 mg phenol/g dry cellxa0h for 100 mg/l phenol. The specific growth rates were 0.530/h for 30 mg/l benzene, 0.410/h for 28 mg/l toluene and 0.037/h for 50 mg/l phenol and decreased on increasing the concentration of these compounds. Cell growth using toluene and benzene as carbon source was better and faster than growth in phenol. These substrates were also biodegraded as binary and tertiary mixtures. The presence of toluene, phenol and toluene–phenol binary mixture increased the biodegradation time of 60 mg/l benzene from 6 to 8, 11 and 8 h respectively. The presence of benzene and/or phenol did not affect significantly the biodegradation time of 55 mg/l toluene. The presence of benzene, toluene and benzene–toluene binary mixture decreased the biodegradation time of 200 mg/l phenol from 35 to 18, 15 and 16 h, respectively.

Biotransformation of 2-phenylethanol to phenylacetaldehyde in a two-phase fed-batch system

Abstract Phenylacetaldehyde (PA) can be produced by the oxidation of 2-phenylethanol (PE) through biotransformation. In order to prevent substrate and product inhibitions and the transformation of the PA to phenylacetic acid (PAA), utilization of a two-phase system is very attractive. Gluconobacter oxydans B-72 was used as the microorganism and iso-octane as the solvent. The effect of initial substrate concentration on the PA production was investigated in single- and two-phase systems. In the single-phase system, substrate inhibition occurred above 5xa0g/l, and in the two-phase system, above 7.5xa0g/l. Substrate inhibition kinetics were also studied in the two-phase system and kinetic constants were determined as rmax=0.64xa0g/lxa0min, KM=8.15xa0g/l, KPA=2.5xa0g/l. Because it was observed that two-phase system is insufficient to remove the substrate inhibition effect, fed-batch operation was utilised in this study. For 7.5xa0g/l of PE, 1.65, 3.85, and 7.35xa0g/l of PA were obtained in the single-phase, two-phase, and two-phase three fed-batch systems, respectively. Effect of biotransformation time, initial substrate concentration, agitation speed, and fed-batch number on the PA production was investigated in a two-phase fed-batch system by the response surface methodology (RSM). The optimum values were found as 3 fed-batch number, 2.75xa0g/l initial substrate concentration, 150xa0rpm agitation speed, and 65xa0min of one batch biotransformation time. In order to verify these results, an experiment was performed at these optimum conditions and 7.10xa0g/l of PA concentration was obtained.

Production of Citric Acid Using Immobilized Conidia of Aspergillus niger

Conidia of Aspergillus niger were immobilized in calcium alginate gel for the production of citric acid. First, the type of the preactivation medium, together with the preactivation period, was investigated. It was found that A. niger requires a 2-d preactivation period at a 0.05 g/L NH4NO3 concentration. Second, preactivated cells were used to determine the effects of nitrogen concentration and the flow rate of oxygen and air on the production of citric acid. Maximum citric acid production was attained with medium containing 0.01 g/L of NH4NO3. The rate of citric acid production in the nitrogenous medium was 33% higher when oxygen was used instead of air during the production phase. This corresponds to an increase of 85% when compared to production when neither oxygen nor air was fed into the system. In the nonnitrogenous medium citric acid concentration remained similar regardless of the use of air or oxygen. However, in the nonnitrogenous production medium, citric acid production was not influenced considerably when oxygen was used instead of air. The advantage of using immobilized cells is that production is achieved easily in the continuous system. Therefore, citric acid production was also tested using a packed-bed bioreactor, and an increase in productivity by a factor of 22 was achieved compared to the batch system.

Effective diffusion coefficient of sucrose in calcium alginate gel

The effective diffusion coefficient of sucrose in 5% calcium alginate gel containing 41.6 g.d.c. l-1. Saccharomyces cerevisiae was investigated. Both free and immobilized S. cerevisiae in 0.175 cm and 0.3 cm diameter particles were used and the reactions were achieved in a medium containing 100 g l-1 sucrose and 0.05 M CaCl2. With the assumption that the microorganisms did not grow or die in this medium, the results were analyzed according to Michaelis-Menten kinetics and the values of the parameters were determined as: Vm = 0.256 g ml-1 gel h-1, Km0 = 0.097 g ml-1, Km1 = 0.125 g ml-1, and Km2 = 0.165 g ml-1. Using these values, effectiveness factors were calculated as eta 1 = 0.89 and eta 2 = 0.76, and effective diffusion coefficients for sucrose in calcium alginate gel were determined as De1 = 4.1 X 10(-6) cm2 s-1 and De2 = 4.0 X 10(-6) cm2 s-1, for the particle size involved.

REACTIVE EXTRACTION OF ORGANIC ACIDS BY SUPERCRITICAL CO2

Reactive extraction of citric acid and acetic acid from their aqueous solutions by supercritical (SC) CO2 was studied. Since organic acids are polar compounds which can hardly be extracted by SC CO2, reactants which increase the solubility of the acid by a chemical reaction are used. Alamine 336 and Hostarex A 327 were used as reactants and oleyl alcohol was selected as an active diluent, i.e., a solvent containing functional groups that interact strongly with the acid-amine complex. For this purpose, the solubilities of synthetic citric and acetic acid solutions, amines and acid-amine complexes in SC CO2 were examined. The extraction experiments were carried out at 313 K, 100 atm and S ml/min CO2 feed rate in a system which is continuous in terms of CO2. The solubilities of the acids in SC CO2 were very low; however, the solubilities of the amines in SC CO2 were higher than those of the acids. The acid-amine complexes were extracted more than the amines and the acids alone under the given conditions. Among the tertiary amines studied, Alamine 336 indicates better results than Hostarex A 327 for the extraction of both acids.

SUPERCRITICAL CO2 EXTRACTION OF ETHANOL FROM FERMENTATION BROTH IN A SEMICONTINUOUS SYSTEM

Abstract Extraction of ethanol from fermentation broth was investigated under different operating conditions (313xa0K, 100–140xa0atm, 0.5–7.5xa0ml feed CO2xa0min−1), in a system which is continuous in terms of CO2, and batch in terms of fermentation broth. The experimental system consists of mainly four parts: the CO2 storage system, the high pressure liquid pump, the extractor and the product collection unit. Samples were analysed by a gas chromatograph. The main objective of the extraction experiments was to explore the effects of CO2 feed rate, extraction time and pressure on the extraction yield. Experiments that were carried out at 313xa0K, under 100xa0atm pressure and at seven different CO2 feed rates demonstrated that the extraction yield is closely related to the CO2 feed rate. While 13% of the initial ethanol load was extracted at 0.75xa0mlxa0min−1 CO2 feed rate after 5xa0h, 72% extraction was accomplished at 7.5xa0mlxa0min−1 and at the same extraction time. It was also observed that extraction yield is a close function of extraction time. The effect of pressure on the extraction yield was investigated at 313xa0K under 100, 120 and 140xa0atm pressures. Although a pressure effect has not been established yet, there is some evidence that the increased pressures help to achieve higher yields.

THE EFFECTS OF BIOPROCESS PARAMETERS ON THE YIELD IN EXTRACTIVE ETHANOL FERMENTATION

A mathematical model was described and solved for extractive fermentation in a continuous stirred tank bioreactor. The effects of bioprocess parameters on the classical and the extractive ethanol fermentations using decanol as a solvent were investigated. The maximum ethanol yields in the classical and the extractive fermentations for the initial substrate concentration, 200 g/1 were obtained as 7.73 g/l-h and 26.24 g/l-h, respectively. When the initial substrate concentration was increased from 100 g/1 to 600 g/1, ethanol yield increased from 12.43 g/l-h to 57.23 g/l-h in the extractive fermentation. When another process parameter, i.e., solvent dilution rate, increased from 0.5 h to 5.0 h~, the value of total ethanol yield increased from 6.07 g/l-h to 22.63 g/l-h.