Oxygen transfer in three-phase airlift and stirred tank reactors using silicone oil as transfer vector

The use of organic liquids as vectors to enhance mass transfer has been applied since the 1970s. However, mass transfer in three-phase reactors is only partially understood. This paper aimed to characterize oxygen transfer in three-phase reactors containing air as gas, silicone oil as vector and water as aqueous phase. A mass transfer model that considers separately air/vector, vector/water and air/water oxygen transfers was developed. The model was used to describe oxygen transfer in airlift and stirred tank reactors containing from 0 to 50% of silicone oil. Under the experimental conditions, silicone oil had a positive effect on the overall oxygen transfer. In both reactor designs, the maximum overall oxygen transfer was observed with 10% silicone oil which was increased by 65 and 84% in the airlift and stirred reactor, respectively, compared to reactors operated without silicone oil. The overall transfer increase was mainly due to an enhanced air/water transfer. With 10% silicone oil, the air/water contribution to the overall oxygen transfer was 94.7 and 93.0% for the airlift and stirred reactor, respectively.     

Production of biofuel from waste cooking palm oil using nanocrystalline zeolite as catalyst: process optimization studies

The catalytic cracking of waste cooking palm oil to biofuel was studied over different types of nano-crystalline zeolite catalysts in a fixed bed reactor. The effect of reaction temperature (400-500 °C), catalyst-to-oil ratio (6-14) and catalyst pore size of different nanocrystalline zeolites (0.54-0.80 nm) were studied over the conversion of waste cooking palm oil, yields of Organic Liquid Product (OLP) and gasoline fraction in the OLP following central composite design (CCD). The response surface methodology was used to determine the optimum value of the operating variables for maximum conversion as well as maximum yield of OLP and gasoline fraction, respectively. The optimum reaction temperature of 458 °C with oil/catalyst ratio=6 over the nanocrystalline zeolite Y with pore size of 0.67 nm gave 86.4 wt% oil conversion, 46.5 wt% OLP yield and 33.5 wt% gasoline fraction yield, respectively. The experimental results were in agreement with the simulated values within an experimental error of less than 5%.     

Continuous biosynthesis of biodiesel from waste cooking palm oil in a packed bed reactor: optimization using response surface methodology (RSM) and mass transfer studies

This study aimed to develop an optimal continuous procedure of lipase-catalyzes transesterification of waste cooking palm oil in a packed bed reactor to investigate the possibility of large scale production further. Response surface methodology (RSM) based on central composite rotatable design (CCRD) was used to optimize the two important reaction variables packed bed height (cm) and substrate flow rate(ml/min) for the transesterification of waste cooking palm oil in a continuous packed bed reactor. The optimum condition for the transesterification of waste cooking palm oil was as follows: 10.53 cm packed bed height and 0.57 ml/min substrate flow rate. The optimum predicted fatty acid methyl ester (FAME) yield was 80.3% and the actual value was 79%. The above results shows that the RSM study based on CCRD is adaptable for FAME yield studied for the current transesterification system. The effect of mass transfer in the packed bed reactor has also been studied. Models for FAME yield have been developed for cases of reaction control and mass transfer control. The results showed very good agreement compatibility between mass transfer model and the experimental results obtained from immobilized lipase packed bed reactor operation, showing that in this case the FAME yield was mass transfer controlled.     

Kinetics of olive oil hydrolysis in an enzyme membrane reactor. Bond graph network model of reactor performance (part 1)

Hydrolyses of olive oil were performed in a reactor with lipase immobilized on a laboratory ultrafiltration poliamide-6 membrane. The reactor consisted of two circulating phases of olive oil and buffer solution. For the characterization of the reactor performance, a model of the hydrolysis process was developed. It was created by means of thermodynamic network representation of both the chemical processes and the transport of the reactants. According to an estimated bond graph network, the model is represented quantatively by a set of thirty-three differential equations representing the time derivatives of the particular species concentration. The parameters of the model were estimated based on experimental data and/or literature notations. Close agreement of numerical estimations of the product concentrations with experimental data was gained. The model enabled an extended analysis of the influence of different reaction parameters, enzyme inhibition and concentration of the reactants on reactor performance.     

Integrated biodiesel production: a comparison of different homogeneous catalysts systems

The most common catalysts for biodiesel production are homogeneous basic catalysts. In the present paper, a comparison is made of different basic catalysts (sodium methoxide, potassium methoxide, sodium hydroxide and potassium hydroxide) for methanolysis of sunflower oil. All the reactions were carried out under the same experimental conditions in a batch stirred reactor and the subsequent separation and purification stages in a decanter. The analytical methods included gas chromatography and the determination of fat and oil conventional parameters. The biodiesel purity was near 100 wt.% for all catalysts. However, near 100 wt.% biodiesel yields were only obtained with the methoxide catalysts. According to the material balance of the process, yield losses were due to triglyceride saponification and methyl ester dissolution in glycerol. Obtained biodiesel met the measured specifications, except for the iodine value, according to the German and EU draft standards. Although all the transesterification reactions were quite rapid and the biodiesel layers achieved nearly 100% methyl ester concentrations, the reactions using sodium hydroxide turned out the fastest.     

Mathematical modeling of diffusion and reaction in the hydrolysis of vegetable protein in an immobilized enzyme recycle reactor

Experimental investigation is by far the most effective approach for studying the behavior of physical systems. However, an enzymatic solubilization of vegetable protein is a complex combination of intrinsic problems, of which many are not easily adaptable to experimental investigation. Experimental designs to study enzyme vegetable protein reactions yield data which describe the extramembraneous activity of the immobilized enzyme. In a continuous recycle immobilized enzyme reactor, the microenvironment concentration of the substrate or product in the membrane phase, or the concentrations along the reactor axial length in the bulk phase are not discernible to the experimenter. However, the knowledge of such concentration profiles is important in weighing the significance of such factors as intermembrane diffusion, enzyme loading, wet membrane size, and the mode of operation of the reactor. The simulation of mathematical models, which describe the physical system within the constraints imposed, yields information which is vital to the understanding of the process occurring in the reactor. The kinetics and diffusion of an immobilized thermophilic Penicillium duponti enzyme at pH 3.4-3.7 and 50 degrees C was modeled mathematically. The kinetic parameters were evaluated by fitting a model to experimental data using nonlinear regression analysis. Simulation profiles of the effects of reactor geometry, substrate concentration, membrane thickness, and enzyme leading on the hydrolysis rate are presented. From the profiles generated by the mathematical model, the best operational reactor strategy is recommended.     

Design,Construction, and Operation of a Fast Pyrolysis Plant for Biomass

A continuous fluidized‐bed plant (PDU‐scale) for fast pyrolysis of lingnocellulosic biomass gives rise to bio‐oil yields of 65 wt.‐%. The average reactor gas residence time was 1.2 s only. The gas and charcoal yields were 15–20 wt.‐%, respectively. The bio oils were chemically characterized. The main monomeric products of the thermal degradation of carbohydrates are acetic acid, hydroxyacetaldehyde, hydroxypropanone, and levoglucosan. The process described in this paper can also be used for disposal of inorganic‐, metal‐organic‐, and chlorine‐organic contaminated waste‐wood. Inorganic compounds of wood preservatives are concentrated in the charcoal fraction and can be separated easily. Chlorine‐organic wood preservatives are mostly degraded. The process has been positively tested as a technique for disposal, recycling, and exploitation of industrial biomass waste (wood waste, grinding grit, fibre sludge, cocoa shell and modern composites like HPL). Bio oil from fast pyrolysis can be used for the production of energy and chemical feedstock. Research for these purposes is ongoing.     

Correlation between the release of sugars and uronic acid and free oil recovery following enzymatic digestion of oil seed cell walls

Aqueous extraction of sunflower seeds and rapeseeds with mixtures of hydrolytic enzymes were carried out in 2-L reactor and uronic acid and reducing sugar concentrations were measured during digestion. The goal of the study was to determine if a correlation between those concentrations and free oil exists that would allow predicting free oil release from aqueous solution measurements. Similar concentrations of 4.5 and 4.7 g/L of reducing sugars and 43 and 55 g/L of uronic acid were found for sunflower and rapeseeds, respectively. The corresponding yields of free oil from the two seeds were 83% and 16% of total oil, and this difference was due to the formation of an emulsion in the rapeseed dispersion. Therefore, measurement of reducing sugars or uronic acid concentrations are not sufficient to predict a release of free oil from all oil seeds.     

Hydrothermal conversion of municipal organic waste into resources

Sub- and supercritical water have been focused on as an environmentally attractive reaction media where organic materials can be decomposed into smaller molecules. We applied a hydrothermal reaction in subcritical water to the treatment of rabbit food as a model municipal solid waste. The reaction was carried out in a batch reactor at the temperature range of 473-623 K or in a semi-continuous reactor with the temperature profile from 473 to 573 K. The liquid reaction products were separated into water-soluble and water-insoluble parts. The water-soluble part was analyzed in terms of glucose and organic acids. For the batch reactor, the largest amount of water-soluble component was approximately 50%. Major organic acids detected were acetic acid and lactic acid. The largest yields were 2.6% for acetic acid and 3.2% for lactic acid. The largest yield of glucose was 33% at 523 K. For the semi-continuous reactor, the glucose yields were 11.5%, 3.9% and 8.7% in each fraction obtained at 473, 523, and 573 K, respectively.     

Enzymatic production of biodiesel from cotton seed oil using t-butanol as a solvent

The enzymatic production of biodiesel by methanolysis of cottonseed oil was studied using immobilized Candida antarctica lipase as catalyst in t-butanol solvent. Methyl ester production and triacylglycerol disappearance were followed by HPLC chromatography. It was found, using a batch system, that enzyme inhibition caused by undissolved methanol was eliminated by adding t-butanol to the reaction medium, which also gave a noticeable increase of reaction rate and ester yield. The effect of t-butanol, methanol concentration and temperature on this system was determined. A methanolysis yield of 97% was observed after 24h at 50 degrees C with a reaction mixture containing 32.5% t-butanol, 13.5% methanol, 54% oil and 0.017 g enzyme (g oil)(-1). With the same mixture, a 95% ester yield was obtained using a one step fixed bed continuous reactor with a flow rate of 9.6 mlh(-1) (g enzyme)(-1). Experiments with the continuous reactor over 500 h did not show any appreciable decrease in ester yields.     

Product and Economic Analysis of Direct Liquefaction of Swine Manure

Direct hydrothermal liquefaction of biomass is a technology that has shown promising results in treating waste and producing oil. A batch hydrothermal liquefaction system was used to treat swine manure, and it successfully converted up to 70% of swine manure volatile solids into oil and reduced manure chemical oxygen demand by up to 75% (He et al., Trans ASAE 43(6):1827?C1833, 2000). A continuous-flow reactor was developed and resulted in similar conversion rates to the batch process, indicating the potential for scale-up (Ocfemia, 2005). This study investigates the hydrothermal process in relation to a livestock system to determine the impact on oil yields and fertilizer values that might be realized in a farm-scale application. Oil products from the hydrothermal process are maximized using manure containing around 20% solids, but typical swine confinement facilities contain wetter manure slurries. A preliminary investigation of liquid?Csolid separation methods was conducted to determine the resultant oil yields and the effects of the hydrothermal process on fertilizer values in the wastewater as compared to the unprocessed manure. Energy and economic analyses of the liquid?Csolid separation and hydrothermal liquefaction processes were also conducted. The hydrothermal process results in an oil product as well as a fertilizer product that retains the majority of its nitrogen value with a reduced level of phosphorus (as compared to the unprocessed swine manure). The economic analyses indicate feasibility for several different liquid?Csolid separation methods, dependent on the equipment and maintenance costs assumed for each method. Conveyor-belt manure collection systems in conjunction with hydrothermal liquefaction are especially promising.     

Continuous enzymatic biodiesel production from coconut oil in two-stage packed-bed reactor incorporating an extracting column to remove glycerol formed as by-product

The transesterification of coconut oil with ethanol catalyzed by Burkholderia cepacia lipase immobilized on polysiloxane–polyvinyl alcohol was performed in a continuous flow. The experimental design consisted of a two-stage packed-bed reactor incorporating a column with cationic resin (Lewatit GF 202) to remove the glycerol formed as by-product and the reactor performance was quantified for three different flow rates corresponding to space-times from 10 to 14 h. The influence of space-time on the ethyl ester (FAEE) concentrations, yields and productivities was determined. The reactor operation was demonstrated for space-time of 14 h attaining FAEE concentrations of 58.5 ± 0.87 wt%, FAEE yields of 97.3 ± 1.9 % and productivities of 41.6  ± 1.0 mg_ester g _medium ^?1  h^?1. Biodiesel purified samples showed average kinematic viscosity values of 5.5 ± 0.3 mm² s^?1 that meet the criteria established by the American National Standard ASTM (D6751). The immobilized lipase was found to be stable regarding its morphological and catalytic characteristics, showing half-life time (t _1/2) around 1540 h. The continuous packed-bed reactor connected in series with simultaneous glycerol removal has a great potential to attain high level of transesterification yields, raising biodiesel productivity.     

Enhanced synthesis of isoamyl acetate using liquid-gas biphasic system by the transesterification reaction of isoamyl alcohol obtained from fusel oil

In this work, the transesterification reaction of isoamyl alcohol obtained from fusel oil and leading to the synthesis of isoamyl acetate was conducted simultaneously with in situ ethanol removal, which allows to shift the reaction equilibrium toward ester synthesis. The extracellular Aspergillus oryzae lipase was immobilized into calcium alginate. Effects of immobilization conditions on the loading efficiency and on the specific activity of entrapped lipase were investigated. The kinetic transfer of volatile reactants from the reactor was investigated using an experimentally first order kinetic model, in order to approve the feasibility of the liquid-gas system with continuous ethanol removal in the ester synthesis. The effects of the most influent parameters affecting the reaction have been also investigated using a Doehlert matrix design. The better operating conditions for isoamyl acetate synthesis were: a temperature of 68.5°C and a respective isoamyl alcohol and A. oryzae lipase concentration of 0.72 M and 2.39 g/L. At these conditions, the resulting reaction conversion and ethanol extraction yields were of 89.55 and 69.60%, respectively. The use of the fluidized bed reactor with continuous ethanol removal has allowed to improve the reaction conversion which was two times than the conversion higher obtained in batch reactor. Furthermore, under the optimized conditions in the fluidized bed reactor, the reaction conversion and the ethanol extraction yields were increased by 44.8 and 36.2%, respectively.     

Sunflower shells utilization for energetic purposes in an integrated approach of energy crops: laboratory study pyrolysis and kinetics

Sunflower is a traditional crop which can be used for the production of bioenergy and liquid biofuels. A study of the pyrolytic behaviour of sunflower residues at temperatures from 300 to 600 degrees C has been carried out. The experiments were performed in a captive sample reactor under atmospheric pressure and helium as sweeping gas. The yields of the derived pyrolysis products were determined in relation to temperature, with constant sweeping gas flow of 50 cm3 min(-1) and heating rate of 40 degrees Cs(-1). The maximum gas yield of around 53 wt.% was obtained at 500 degrees C, whereas maximum oil yield of about 21 wt.% was obtained at 400 degrees C. A simple first order kinetic model has been applied for the devolatilization of biomass. Kinetic constants have been estimated: E=78.15 kJ mol(-1); k(0)=1.03 x 10(3)s(-1).     

Pyridine biodegradation in a novel rotating rope bioreactor

A novel immobilised bioreactor has been developed especially for the treatment of pollutants characterized by high volatility along with high water solubility and low microbial yields. The new bioreactor referred to as the rotating rope bioreactor (RRB) provides higher interfacial area (per unit reactor liquid volume) along with high oxygen mass transfer rate, greater microbial culture stability; and consequently higher substrate loadings and removal rates in comparison to other conventional rectors for the treatment of volatile compounds. Pyridine was used as a model compound to demonstrate the enhanced performance with RRB, when compared to that reported with other conventional bioreactors. The experimental results indicate that the novel RRB system is able to degrade pyridine with removal efficiency of more than 85% at higher pyridine concentration (up to 1000 mg/l) and loading [up to 400 mg/m(2)/h (66.86 g/m(3)/h)], with a shorter hydraulic retention time (9-18 h). The reactor has been in operation for the past 15 months and no loss of activity has been observed.     

Mechanistic modeling of biodiesel production using a liquid lipase formulation

In this article, a kinetic model for the enzymatic transesterification of rapeseed oil with methanol using Callera? Trans L (a liquid formulation of a modified Thermomyces lanuginosus lipase) was developed from first principles. We base the model formulation on a Ping‐Pong Bi‐Bi mechanism. Methanol inhibition, along with the interfacial and bulk concentrations of the enzyme was also modeled. The model was developed to describe the effect of different oil compositions, as well as different water, enzyme, and methanol concentrations, which are relevant conditions needed for process evaluation, with respect to the industrial production of biodiesel. The developed kinetic model, coupled with a mass balance of the system, was fitted to and validated on experimental results for the fed‐batch transesterification of rapeseed oil. The confidence intervals of the parameter estimates, along with the identifiability of the model parameters were presented. The predictive capability of the model was tested for a case using 0.5% (wt. Enzyme/wt. Oil), 0.5% (wt. Water /wt. Oil) and feeding 1.5 times the stoichiometric amount of methanol in total over 24 h. For this case, an optimized methanol feeding profile that constrains the amount of methanol in the reactor was computed and the predictions experimentally validated. Monte‐Carlo simulations were then used to characterize the effect of the parameter uncertainty on the model outputs, giving a biodiesel yield, based on the mass of oil, of 90.8 ± 0.55 mass %. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1277–1290, 2014     

Evaluation of biological nutrient removal from wastewater by Twin Circulating Fluidized Bed Bioreactor (TCFBBR) using a predictive fluidization model and AQUIFAS APP

A two-phase and three-phase predictive fluidization model based on the characteristics of a system such as media type and size, flow rates, and reactor cross sectional area was proposed to calculate bed expansion, solid, liquid and gas hold up and specific surface area (SSA) of the biofilm particles. The model was subsequently linked to 1d AQUIFAS APP software (Aquaregen) to model biological nutrient removal in two phase (anoxic) and three phase (aerobic) fluidized bed bioreactors. The credibility of the proposed model for biological nutrient removal was investigated using the experimental data from a Twin Circulating Fluidized Bed Bioreactors (TCFBBR) treating synthetic and municipal wastewater.The SSA of bio-particles and volume of the expanded bed were simulated as a function of operational parameters. Two-sided t-tests demonstrated that simulated SCOD, NH₄-N, NO₃-N, TN, VSS and biomass yields agreed with the experimental values at the 95% confidence level.     

Production of biodiesel by lipase-catalyzed transesterification of vegetable oils: a kinetics study

Kinetics of production of biodiesel by enzymatic methanolysis of vegetable oils using lipase has been investigated. A mathematical model taking into account the mechanism of the methanolysis reaction starting from the vegetable oil as substrate, rather than the free fatty acids, has been developed. The kinetic parameters were estimated by fitting the experimental data of the enzymatic reaction of sunflower oil by two types of lipases, namely, Rhizomucor miehei lipase (RM) immobilized on ion-exchange resins and Thermomyces lanuginosa lipase (TL) immobilized on silica gel. There was a good agreement between the experimental results of the initial rate of reaction and those predicted by the proposed model equations, for both enzymes. From the proposed model equations, the regions where the effect of alcohol inhibition fades, at different substrate concentrations, were identified. The proposed model equation can be used to predict the rate of methanolysis of vegetable oils in a batch or a continuous reactor and to determine the optimal conditions for biodiesel production.     

Northwestern Argentina: A Center of Genetic Diversity of Lemon Verbena (Aloysia citriodora Paláu,Verbenaceae)

The aerial parts of lemon verbena (Aloysia citriodora Paláu ) are worldwide used due to their medicinal and aromatic properties. The essential‐oil and acteoside contents have been proposed as the main quality markers for their pharmacological and organoleptic features. The northwestern region of Argentina has been repeatedly proposed as the place of origin for this species. For this reason, the essential‐oil yields and chemical compositions of leaves of 25 populations of lemon verbena from both wild collections and experimental crops from this region were studied. Plants from six different collections were subsequently grown on the same experimental parcel located at Cerrillos, Salta province, during more than seven years. In addition, the acteoside contents determined in all the samples collected in 2010 showed significant variations (from 0.5 to 4.0%). Large differences were observed in the essential‐oil composition and yields, which ranged from 0.4 to 2.1% (v/w). Nevertheless, most of the samples complied with the European Pharmacopoeia specifications. A remarkable chemical diversity with at least four clearly defined chemotypes was detected in this region. Therefore, it would be urgent to encourage actions to protect these genotypes of lemon verbena in the northwestern Argentina.     

The effect of bovine serum albumin on batch and continuous enzymatic cellulose hydrolysis mixed by stirring or shaking

Bovine serum albumin (BSA) was applied as a model non-catalytic protein to enzymatic hydrolysis of Avicel and dilute acid pretreated corn stover at different reaction conditions to improve the understanding of its ability to enhance cellulose hydrolysis. Addition of BSA improved the 72 h hydrolysis yields in shake flasks by up to 26% for both substrates by reducing de-activation of the exoglucanases and by facilitating reductions in particle size and crystallinity during a magnetically stirred pre-incubation step. The enzyme stabilizing effect of BSA addition was most striking for batch hydrolysis in a stirred tank reactor, with glucose yields increasing by 76% after 72 h for Avicel and by 40% after 145 h for corn stover. Application of BSA to continuous hydrolysis for a mean residence time of 24h gave 33% and 40% higher glucose yields for corn stover and Avicel compared to the controls.