Chayanoot Sangwichien

Density functional theory predictions of adsorption isotherms with hysteresis loops

Abstract Adsorption equilibrium is calculated for slit-like pores of various sizes using lattice density functional theory (LDFT). It is shown that LDFT can predict adsorption isotherms with hysteresis loops and that different types of hysteresis loops can be obtained by varying energies of adsorbate–adsorbate and adsorbate–adsorbent interactions for different widths and lengths of slit-like pores. LDFT also predicts hysteresis loops with multiple steps. Though such behavior has not been part of the characterization of isotherms with hysteresis loops, there are experimental data that exhibit steps within hysteresis loops.

Pilot-scale steam explosion for xylose production from oil palm empty fruit bunches and the use of xylose for ethanol production.

Pilot-scale steam explosion equipments were designed and constructed, to experimentally solubilize xylose from oil palm empty fruit bunches (OPEFB) and also to enhance an enzyme accessibility of the residual cellulose pulp. The OPEFB was chemically pretreated prior to steam explosion at saturated steam (SS) and superheated steam (SHS) conditions. The acid pretreated OPEFB gave the highest xylose recovery of 87.58 ± 0.21 g/kg dried OPEFB in the liquid fraction after explosion at SHS condition. These conditions also gave the residual cellulose pulp with high enzymatic accessibility of 73.54 ± 0.41%, which is approximately threefold that of untreated OPEFB. This study has shown that the acid pretreatment prior to SHS explosion is an effective method to enhance both xylose extraction and enzyme accessibility of the exploded OPEFB. Moreover, the xylose solution obtained in this manner could directly be fermented by Candida shehatae TISTR 5843 giving high ethanol yield of 0.30 ± 0.08 g/g xylose.

Optimizing Alkali Pretreatment of Oil Palm Empty Fruit Bunch for Ethanol Production by Application of Response Surface Methodology

Oil palm empty fruit bunch (OPEFB) is a potential source of cellulose which can serve as a promising raw material for the production of ethanol. The increasing interest on use of lignocellulosic waste for bioconversion to fuels and chemicals are justifiable as these materials are low cost, renewable and widespread sources of sugars. The objective of the present study was to determine the effect of NaOH concentration, reaction temperature and reaction time for alkali pretreatment to increase the amount of cellulose for hydrolysis to achieve high glucose yield. Batch reactions were carried out under various reaction temperature, reaction time and NaOH concentration. Response Surface Methodology (RSM) was followed to optimize the alkali pretreatment in order to obtain high amount of cellulose (%). The optimum reaction temperature, reaction time and NaOH concentration were found to be 130 ˚c, 40 min and 15% (w/v), respectively. The maximum value of cellulose was obtained 68.8% by using the above condition. 19.96 g/L glucose was achieved when reaction was carried out at 130 ˚c for time period of 90 min when 6% (w/v) of H2SO4 concentration maintained.

Optimization Studies on Acid Hydrolysis of Pretreated Oil Palm Empty Fruit Bunch for Production of Xylose by Application of Response Surface Methodology

Oil palm empty fruit bunch is a lignocellulosic material from palm oil plantations. It is a potential source of xylose which can be used as a raw material for production of xylitol. Using of lignocellulosic waste for bioconversion to fuels and chemicals is justifiable as these materials are low cost, renewable and widespread sources of sugars. The objective of the present study was to determine the effect of H2SO4 concentration, reaction temperature and reaction time for acid hydrolysis of pretreated OPEFB, pretreated OPEFB with reaction temperature, reaction time and NaOH concentration were 130 °C, 40 min and 15% (w/v), respectively to achieve high xylose yield. Batch reactions were carried out under various reaction temperature, reaction time and H2SO4 concentration. Response Surface Methodology (RSM) was followed to optimize acid hydrolysis in order to obtain high yield of xylose. The optimum reaction temperature, reaction time and H2SO4 concentration were found to be 140 °C, 90 min and 7% (w/v), respectively. The maximum value of xylose was obtained 56.39 g/l by using the above condition. The best result of xylose yield obtained was 126%.

Pattern of adsorption isotherms in Ono-Kondo coordinates.

The Ono-Kondo lattice density functional theory is used to analyze adsorbate-adsorbate interactions for supercritical systems. In prior work, this approach has been used to study intermolecular interactions in subcritical adsorbed phases, and this has included the study of adsorbate-adsorbate repulsions in the regime of adsorption compression. In this paper, we present the general pattern of adsorption isotherms in Ono-Kondo coordinates; this has not been done in the past. For this purpose, experimental isotherms for adsorption of supercritical fluids (including nitrogen, methane, and carbon dioxide) are plotted in Ono-Kondo coordinates. In addition, we performed Grand Canonical Monte Carlo simulations of adsorption for Lennard-Jones molecules and plotted isotherms in Ono-Kondo coordinates. Our results indicate a pattern of isotherms with regimes of adsorbate-adsorbate attractions at low surface coverage and adsorbate-adsorbate repulsions at high surface coverage. When the generalized Ono-Kondo model is used over a wide range of pressures - from low pressures of the Henrys law regime to supercritical pressures - the slope of the isotherm varies from positive at low pressures to negative at high pressures. The linear sections of these graphs show when the adsorbate-adsorbate interaction energies are approximately constant. When these linear sections have negative slopes, it indicates that the system is in a state of adsorption compression.

Precipitated Silica Derived from Palm Oil Mill Fly Ash: Kinetics and Characterization

The silica extraction from palm oil mill fly ash (POMFA) using sodium hydroxide as one of viable processes for obtaining silica from agricultural waste was investigated. The effects of extraction time and temperature were closely examined to study the kinetics of the process. The fixed variables used in the present work were mass of POMFA 468.2 gram; the POMFA mass to NaOH volume ratio 0.2341 g/cm3; the concentration of NaOH 1.4 N and the stirring speed of 1065 RPM. The levels of temperature employed were 348 K, 358 K, 368 K and 378 K for different time durations up to 60 min. The mechanical fragmentation process was applied to obtain precipitated silica from the extracted silica. The precipitation conditions were: stirring speed of 1160 RPM, pH of 8.75, temperature of 303 K and precipitation time of 100 min. The shrinking core model (SCM) with intra-particle diffusion controlled mechanism and the Jander equation can satisfactorily represent the extraction process. The activation energy for silica extraction was 58.20 kJ/mol for the SCM with intra-particle diffusion and 62.22 kJ/mol for the Jander equation respectively. The precipitated silica agglomerate obtained at the time of 100 min has the median-weighed volume particle size distribution of 114.07 μm. The chemical composition and physical characteristic of precipitated silica which were analyzed with LPSA, XRF, XRD, FTIR and SEM are similar to the precipitated silica from the references.

Enhanced Alkali Pretreatment of Narrow Leaves Cattail by Response Surface Methodology

The purpose of this work is to develop a pretreatment process of lingo-cellulosic ethanol production from narrow leaves cattail (Typha angustifolia) by using alkali catalysis with the response surface methodology (RSM) as a central composite design (CCD). The first step, LiOH, NaOH, and KOH were used as catalytic alkali for preliminary test. Second, the suitable alkali from first step was selected to optimize of pretreatment condition of three independent variables (alkali concentration, temperature, and residence time) that varies at CCD five codes (-2, -1, 0, 1, 2). Sodium hydroxide (NaOH) is the proper alkali because it could increase cellulose more than KOH and nearby LiOH while it is cheapest. RSM result shows the optimized pretreatment condition based on cellulose increased which obtained from this study that is NaOH 5 % w/v at 100 °C and residence time for 120 min. Beside, this condition was analyzed using an ANOVA with a second order polynomial equation after eliminated non-significant terms. At the optimized conditions, cellulose increased, hemicellulose decreased and weight recovery were achieved 77.81%, 80.59, and 41.65%, respectively. Moreover, the model was reasonable to predict the response of strength with less than 5% error.