Mercedes Martínez

Application of the factorial design of experiments and response surface methodology to optimize biodiesel production

The production of fatty acid methyl esters, to be used as a diesel substitute (biodiesel), has been studied. The reaction of refined sunflower oil and methanol was carried out over different types (acid and basic, homogeneous and heterogeneous) of catalysts. The catalyst that led to largest conversions was sodium hydroxide. No methyl esters were detected when zirconium-based catalysts and an immobilized lipase were used. The process of biodiesel production was optimized by application of the factorial design and response surface methodology. Temperature and catalyst concentration were found to have a positive influence on conversion, concentration effect being larger than temperature effect. A second-order model was obtained to predict conversions as a function of temperature and catalyst concentration. Optimum conditions for the production of methyl esters were found to be mild temperatures (20‐50°C) and large catalyst concentrations (1.3%).

Production of biodiesel from bioethanol and Brassica carinata oil: oxidation stability study.

In the present work the synthesis from bioethanol and Brassica carinata, as alternative vegetable oil, using KOH as catalyst, has been developed and optimized by application of the factorial design and response surface methodology (RSM). Temperature and catalyst concentration were found to have significant influence on conversion. A second-order model was obtained to predict conversions as a function of temperature and catalyst concentration. The maximum yield of ester (98.04%) was obtained working with an initial concentration of catalyst (1.5%) and an operation temperature of (35 degrees C). Results show that the acid value, peroxide value, and viscosity, increased while the iodine value decreased with increasing storage time of the biodiesel sample. Fatty acid ethyl esters (biodiesel) from B. carinata oil were very stable because they did not demonstrate rapid increase in peroxide value, acid value, and viscosity with increasing storage time to a period of 12 months.

Enzymatic synthesis of fatty esters. Part I. Kinetic approach

A kinetic study of palmitic acid esterification reaction catalyzed by immobilized lipase Novozym 435 (from Candida antarctica) has been made in a range of 65–75°C temperature and 3–7% of initial catalyst concentration and atmospheric pressure. Influence of operating variables also was studied. Different values of temperature, initial lipase concentration, acid/alcohol molar ratio, and products concentrations were tested. Experiments were carried out in a stirred batch reactor equipped with adequate control systems. Evolution of concentration of the species involved was found by using gas-liquid chromatography. The kinetic characteristics observed in the esterification reaction with isopropanol were found to follow an ordered bi-bi mechanism with competitive inhibition by reactants and products. According to the mechanism maximum reaction rate, Michaelis–Menten constants and inhibition constants were determined. A good quality of fit was observed by fitting experimental rate data to the kinetic model with an average error beneath the 15%. Kinetic constants, as well as enthalpy and entropy values, have been determined for the model proposed for the esterification reaction within the experimental range studied.

Kinetic model for the esterification of oleic acid and cetyl alcohol using an immobilized lipase as catalyst

A kinetic model has been developed for the enzymatic esterification of oleic acid with cetyl alcohol catalyzed by a Candida antarctica immobilized lipase. The model is based on an ordered reaction mechanism with two reactants and two products. The reaction mechanism includes two groups of steps. The first group consists of reaction steps, while the second is formed by the inhibition steps involving enzymatic complexes or free lipase. The reaction has been carried out at a laboratory scale in a stirred tank reactor. The operating conditions have been fixed so that the system operates in liquid phase and can be considered as pseudohomogeneous with regard to the flow conditions. Depending on the pressure level, the reaction can be considered reversible or irreversible. In both cases the kinetic model has been proposed to cover a range of temperatures between 70 and 80°C, an initial concentration of immobilized lipase between 3 and 7 wt%, and considering different molar ratios of reactants. Parameter estimation was carried out by using computer programmes based on numerical calculation algorithms. Discrimination of parameters was carried out by considering their physical meaning and the adequate prediction of the experimental results. Finally, the validity of the proposed models was quantified by means of residual analysis and simulation experiments.

Formation of a jojoba oil analog by esterification of oleic acid using zeolites as catalyst

An analog of Jojoba oil has been obtained by esterification of oleic acid with oleic alcohol, using ultrastable Y zeolites as catalysts. A maximum in activity is observed at 30–40 and ≈ 10 Al/u.c. for steam and SiCl4-dealuminated samples, respectively. Ultrastable zeolites do not catalyze the formation of esters with 38 or more carbon atoms, but are very active and selective for those with 32–34 and 36 carbon atoms. The reaction takes place on an outer shell of the crystallites, the crystallite size and surface composition being important parameters for controlling both activity and selectivity.

Enhancement of lipid accumulation in Scenedesmus obliquus by Optimizing CO2 and Fe3+ levels for biodiesel production

The effects of cultivation of Scenedesmus obliquus in nutrient medium supplemented with 0.03%, 3, 9% and 12% CO(2) or 2.5-20 mg L(-1) of Fe(3+) on dry weight of biomass (DW), total lipid accumulation (TL contents) and total lipid productivity (TLP) were evaluated under indoor conditions. The accumulation of TL and TLP showed an increasing trend with increasing of CO(2) or Fe(3+) levels. In cultures with 12% CO(2) or 20mg/L Fe(3+), maximum TL contents of 33.14% and 28.12%, respectively were obtained. These lipids displayed a fatty acid profile which is suitable for biodiesel production as the most abundant compounds were oleic (32.19-34.44%), palmitic (29.54-25.12%) and stearic (12.26-16.58% of total FAMEs) acids. The properties of biodiesel obtained from S. obliquus, were the same with those specification for biodiesel standards including ASTM D 6751 (American Society for Testing Material) and the European Standard En 14214. Thus, S. obliquus biomass could be used as suitable feedstock for biodiesel production.

Enzymatic synthesis of fatty esters : Part II. optimization studies☆

The synthesis of isopropyl palmitate over an enzymatic catalyst has been developed and optimized following the Factorial Design and Response Surface Methodology. A full two-factorial design has proved effective in the study of the influence of the variables (selected for the present study temperature and enzyme concentration) on the process. The range studied was 62.9°C and 77°C for temperature, and 2.2%wt and 7.83%wt for the catalyst concentration. Catalyst concentration has been found to be the most significant factor on the esterification process and its influence is positive. The Response Surface model obtained, representing the yield on ester, has been found to describe adequately the experimental results obtained.

Kinetic modelling of esterification reactions catalysed by immobilized lipases

The kinetics of the synthesis of several esters of different chain length and physical properties was studied. A commercial Candida antarctica lipase was used as catalyst for the synthesis of oleyl oleate, isopropyl oleate, isopropyl palmitate, myristyl myristate, cetyl oleate, and oleyl 2-methylbutyrate. A general kinetic model was derived and tested experimentally for the synthesis of the above esters. The general kinetic model took a different shape for each particular esterification reaction, depending on the significance of the different terms. The corresponding parameters were calculated by non-linear regression. The kinetic models were found to describe the experimental values adequately.

Process Optimization for Biodiesel Production from Corn Oil and Its Oxidative Stability

Response surface methodology (RSM) based on central composite design (CCD) was used to optimize biodiesel production process from corn oil. The process variables, temperature and catalyst concentration were found to have significant influence on biodiesel yield. The optimum combination derived via RSM for high corn oil methyl ester yield (99.48%) was found to be 1.18% wt catalyst concentration at a reaction temperature of C. To determine how long biodiesel can safely be stored, it is desirable to have a measurement for the stability of the biodiesel against such oxidation. Storage time and oxygen availability have been considered as possible factors influencing oxidative instability. Biodiesel from corn oil was stored for a period of 30 months, and the physico-chemical parameters of samples were measured at regular interval of time. Results show that the acid value (AV), peroxide value (PV), and viscosity () increased while the iodine value (IV) decreased. These parameters changed very significantly when the sample was stored under normal oxygen atmosphere. However, the , AV, and IV of the biodiesel sample which was stored under argon atmosphere were within the limit by the European specifications (EN 14214).

Biorefinery approach for coconut oil valorisation: a statistical study.

The biorefinery approach, consisting in transesterification using methanol and potassium hydroxide as catalyst, has been used to assess coconut oil valorisation. Due to the fatty acid composition of coconut oil, low (LMWME) and high (HMWME) molecular weight fatty acid methyl esters were obtained. Methyl laurate (78.30 wt.%) is the major component of the low molecular weight fraction. The influence of variables such as temperature and catalyst concentration on the production of both fractions has been studied and optimized by means of factorial design and response surface methodology (RSM). Two separate optimum conditions were found to be a catalyst concentration of 0.9% and 1% and an operation temperature of 42.5 degrees C and 57 degrees C for LMWME and HMWME, respectively, obtaining conversion rates of 77.54% and 25.41%. The valuable components of LMWME may be recovered for sale as biolubricants or biosolvents, the remaining fraction could be used as biodiesel, matching the corresponding European Standard.