Ayla Çalimli

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.

Adsorption of o-, m- and p-nitrophenols onto organically modified bentonites

Experiments were conducted on the adsorption characteristics of o-, m- and p-nitrophenols by organically modified bentonites at different temperatures. Two organobentonites (HDTMA-B and PEG-B) were synthesized using hexadecyltrimethylammonium bromide (HDTMABr) and poly(ethylene glycol) butyl ether (PEG). Synthesized HDTMA-B and PEG-B were characterized by XRD, FTIR and DTA-TG analyses and their specific surface area, particle size and pore size distributions were determined. BET surface areas and basal spacings (d(001)) of the HDTMA-B and PEG-B were found to be 38.71 m(2)g(-1), 69.04 m(2)g(-1) and 21.96 Å, 15.17 Å, respectively. Increased adsorption with temperature indicates that the process is endothermic for o-nitrophenol. On the other hand m- and p-nitrophenols exhibited lower rates of adsorption at higher temperatures suggesting a regular exothermic process taking place. Results were analyzed according to the Langmuir, Freundlich and Dubinin-Redushkevich (D-R) isotherm equations using linearized correlation coefficient at different temperatures. R(L) separation factors for Langmuir and the n values for Freundlich isotherms showed that m- and p-nitrophenols are favorably adsorbed by HDTMA-B and, p-nitrophenol is favored by PEG-B. Adsorption of o-, m- and p-nitrophenols as single components or from their binary mixtures on HDTMA-B and, p-nitrophenol on PEG-B are all defined to be physical in nature.

Aromatic products of 340 °C supercritical-toluene extraction of two Turkish lignites: an n.m.r. study

Abstract Fractions of Elbistan and Seyitomer (Turkish) lignites, extracted with supercritical toluene at 340 °C and 8 MPa, have been separated by solvent extraction and silica-gel chromatography. Analyses by n.m.r. and i.r. spectroscopies and other methods have been combined in structural-analysis schemes to yield information about the average molecule in aromatic extracts. Carbon aromaticities, f a , derived from 22.63 MHz 1 H-decoupled pulse Fourier-transform (PFT) 13 C-n.m.r. are more widely spread for Elbistan (0.34–0.56) than for Seyitomer (0.40–0.43), and are lower than for supercritical-gas (SCG) products from bituminous coals. 13 C-n.m.r. also reveals the presence of aromatic ether-O in polar fractions. Narrow aromatic signals in 100 MHz 1 H-n.m.r. spectra suggest the presence of single-aromatic-ring average structures. In the hexane-soluble aromatics, 27% (Elbistan) and 29% (Seyitomer) of the available sites are substituted by alkyI groups, some of which are at least eight carbon atoms long; the hexane-soluble polar and asphaltene/asphaltol fractions contain fewer such groups.

Effect of inert solid particles at low concentrations on gas–liquid mass transfer in mechanically agitated reactors

Abstract Volume referred mass transfer coefficients k L a were determined for the slurries of 6 solids in water and n -butanol in a mechanically agitatted reactor of standard configuration. The measurements were carried out under variation of power input, gas flow rate, and solids concentration. It is observed that inert solid particles used increased by a drastically compared to the case with pure water only. On the other hand, the same inert solid particles with the same solid volume, exhibited conflicting behaviour in suspensions of n -butanol.

The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

The effect of the Na2CO3 activation on the rheological properties of a bentonite from Kutahya (Turkey) was investigated. The bentonite was activated with Na2CO3 at different dosages (1–15 g Na2CO3/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na2CO3/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na2CO3 (bentonite concentrations 2–6% w/w). At 2.5 g Na2CO3/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l−1. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.

Modification of rheology and permeability of Turkish ceramic clays using sodium silicate

Abstract Rheological properties of two ceramic clays (Sindirgi and Kure) having different chemical and mineral compositions were determined. The variation in viscosity for suspensions having 50%, 55% and 60% (w/w) clay was measured as a function of initial loading of sodium silicate. The relationship between shear rate (0–120 s −1 ) and shear stress (0–350 Pa) was determined for these suspensions in the presence of various amounts of sodium silicate. The effect of the amount of clay on the suspension thixotropy properties was investigated for original and treated suspensions. Slip viscosities of 1500, 500 and 100 cP were evaluated and the suspensions were filtered to obtain cakes. From rheological measurements, thixotropy properties changes were correlated with increased solid and electrolyte in the suspension and the clay mineral type. In addition, results showed that the permeability, the porosity and the casting rate increase with the viscosity in the clay suspensions and the permeability decreases with decreasing porosity. When the clay ratio in the suspensions is 50% (w/w) and the viscosity 1500 cP, the porosity and the permeability values obtained in each sample are higher than the others.

Microporous Scaffolds from Poly(Lactide-Co-∊-Caprolactone) Composites with Hydroxyapatite and Tricalcium Phosphates Using Supercritical CO2 for Bone Tissue Engineering

A copolymer of L-lactide and ∊-caprolactone (M n: 73,523, M w: 127,990 and PI: 1.74) was synthesized by ring-opening polymerization and confirmed by FTIR, 1 H-NMR and DSC. The copolymer ratio of L-lactide to ∊-caprolactone, determined by 1H-NMR, was 89/11. Specific amounts of hydroxyapatite or tricalcium phosphate were blended in the copolymer matrix to form new composites. Films were made by solvent casting the copolymer and the composite materials. The films were subjected to supercritical CO2 at 3300psi and 70°C to create porous structures. The pore sizes were in the range of 40–80 μm. The porous films (both copolymer and composite) degraded in Ringer solutions much faster than corresponding untreated non-porous films.

Desorption of Salicylic Acid from Modified Bentonite by Using Supercritical Fluids in Packed Bed Column

ABSTRACT Desorption of salicylic acid from organically modified bentonite by using supercritical fluids (SCFs) was studied. The parameters, such as pressure, temperature, SCF flow rate, and cosolvent (entraîner) concentration, were investigated. A desorption yield of 40 wt% salicylic acid was obtained by using supercritical CO2 by operating at low pressure (300 bar), low temperature (40°C), and 2 mL CO2/min, it reached up to 77 wt% in the presence of ethanol as cosolvent 10 vol%. Similarly, a maximum desorption yield of 76wt% salicylic acid was obtained by using supercritical C02 by operating at high pressure (500 bar), high temperature (80°C), and 2 mL SC CO2/min, it reached up to 98 wt% in the presence of ethanol as cosolvent 10vol%. Hence, it was concluded that the mean contents in the desorbed solute are approximately 1.5-2-fold higher by addition of 10vol% ethanol than only supercritical CO2 desorption process.

Supercritical Dioxane Extraction of Spruce Wood and of Dioxane-Lignin and Comparison of the Extracts with the Pyrolysis Products

Abstract Samples of spruce wood and of dioxane-lignin prepared from spruce wood were subjected to supercritical dioxane extraction at 330 C. To compare the yield and the nature of the compounds present in distillate obtained upon pyrolysis to those of supercritical gas extract, the same samples were pyrolysed at 340°C. The extracts and distillates were separated into three fractions by solvent fractionation using hexane and benzene successively. The simpler compounds were identified by GC/MS and the yields of phenols were compared. More complex compounds insoluble both in hexane and benzene have been characterized by 1H NMR spectrometry. It was found that the supercritical extracts and the pyrolysis distillates contained similar compounds; however, demethoxylation during pyrolysis was extensive compared to supercritical gas extraction which occurred under rather mild conditions.

Sulphuric Acid Activation of a Calcium Bentonite

The objective of this work was to determine the changes of thermal and surface properties of a bentonite from Çankιrι after activation using different concentrations of H2SO4 solutions (0.5–4 M). XRD, FTIR, DTA, and TG analyses of the samples were performed to examine the structural changes of the bentonite before and after acid activation. DTA peaks showed an exothermic change in the temperature region 900–1000°C. Changes at low acid concentrations resulted from cation exchange (exchangeable cations with H ions) and removal of impurities from the bentonite. Differences of surface properties and thermal properties at higher acid concentrations (2–4 M H2SO4) were caused by structural changes and partial decomposition of the samples. Surface area measurements showed that with the increase of concentration of H2SO4 solution the total BET surface area increased, while the maximum value of specific surface area (240.9 m2/g) was attained by the sample activated with 2 M H2SO4. Activation with higher concentrations (3–4 M) caused a decrease in the surface area. The particle size distributions of the original and acid-activated samples showed that the acid activation strongly affected the particle sizes of the particles. While 97.8% of the original bentonite sample is less than 10 µm in size, 97.8% of the activated samples with 0.5 M acid and 92% of the activated sample with 4 M acid are less than 28.25 µm in size.