The objective of this work was to assess some of the points that need to be elucidated in order to define the economic viability of the noncatalytic supercritical biodiesel process. Net yield of the supercritical process, consumption of methanol, and the quality of the fuel issuing from the reactor were studied. Biodiesel was prepared by reacting refined soy oil with supercritical methanol at T ) 280 °C and methanol-to-oil molar ratios of 15 and 20. After the reaction, unreacted methanol, water, and other volatile compounds were removed from the product by stripping with nitrogen at 110 °C. Biodiesel production by the reaction of oils in supercritical methanol under the conditions used in this work produces practically no glycerol byproduct. This fact simplifies the downstream refining of the produced biodiesel. Glycerol is transformed into products of smaller molecular size and water. At first this water reacts with the triglycerides of the reacting mixture to form free fatty acids (FFA), thus increasing the acidity of the product. At longer reaction times the acids are converted into methyl esters again. Glycerol methanolysis reactions increase the methanol consumption. The small amount of glycerides and FFA contaminants in the biodiesel product makes a final step of refining by silica adsorption convenient. No liquid effluents are issued with such a refining step. After the FFA and glycerides are recycled, the yield of the process is 94-96%.

No abstract

No abstract

Discarded carrots are a valuable source of biomass amenable for valorization. Their use as raw material for ethanol production by fermentation, using yeasts immobilized in Calcium alginate, was proposed. The biocatalyst immobilization method, the existence of internal and external mass transfer limitations, the effect of the initial pH and the reuse of immobilized yeasts were particularly evaluated. Results indicate that beads made with a 2 % solution of Sodium alginate and a 30 % solution of Saccharomyces cerevisiae were strong enough to allow an efficient nutrient transfer into the matrix and to prevent cell leaking. A stirring rate of 200 rpm was needed to avoid external mass transfer limitations. These beads were used in three successive fermentations. An initial pH of 5.5 reached the best fermentation parameters. Non-enriched, non-sterile carrot must was fermented through immobilized yeasts; and values of ethanol concentration (29.9 g L-1), Y p/s (0.409 g g-1), and productivity (7.45 g L-1 h-1) were obtained. These values were similar to those registered when free cells were used.

No abstract

The present work studies the catalytic hydrogenation of the (À)-menthone fraction existing in a dementholized peppermint oil, subproduct of the low-temperature crystallization process of the Arvensis peppermint oil. The aim is to obtain a liquid menthol composition for commercial use that replacing the crystal form. Pt/Al 2 O 3 catalysts with different metal content (1 and 4% Pt) were used and the effect of several operating variables is analyzed: H 2 pressure, reaction temperature, and reactant mass/catalyst mass ratio. Total conversion values ((À)-menthone + (+)-isomenthone) in the order of 95% on the fresh catalyst after 4 h on-stream were obtained for 4%Pt/Al 2 O 3 . These conversion values decrease when the catalyst is reused, which is indicative of deactivation. When the Pt content is reduced, the total conversion values fall drastically. The (À)-menthone to (À)-menthol selectivity values are higher than 90% in every case. #

BACKGROUND Hydrogenolysis of glycerol to glycols in continuous flow three phase reactors is of practical importance due to the need to give value to huge amounts of surplus glycerol. Thermodynamic and kinetic aspects must be revised for a proper design. The system was studied in a trickle‐bed reactor using copper chromite and Cu/Al2O3 as catalysts. RESULTS Phase equilibrium and flow pattern were verified. Solid, liquid and gas phases were present, with the liquid phase in ‘trickling’ flow. Catalysts were characterized by inductively coupled plasma (ICP), nitrogen sortometry, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), temperature programmed reduction (TPR) and pyridine thermal programmed desorption (TPD). The average reaction rate was found to be practically constant under different process conditions. A theoretical analysis indicated that the resistance to the transfer of hydrogen from the gas to the liquid phase dominated the overall kinetics. Selectivity to 1,2‐propanediol varied with temperature, with a maximum at 230 °C (97%). Selectivity was a function of the catalyst acidity. When the pressure was increased the selectivity to 1,2‐propanediol was increased, up to 97% at 14 bar. Higher pressures did not modify this value. CONCLUSIONS Optimum reaction conditions for maximum selectivity to 1,2‐propanediol with Cu‐based catalysts are 230 °C and 14 bar. System kinetics are, however, dominated by the gas–liquid mass transfer resistance. © 2017 Society of Chemical Industry

The elimination of free fatty acids (FFAs) and water from biodiesel is usually performed in industrial practice using different units for neutralization with caustic, washing, and drying of the fuel. Adjustment of the acidity, however, can be performed in only one operation using bleaching tanks and commercial adsorbents. The current article explores the use of several adsorbents (TriSyl commercial silicas, diatomaceous earth, impregnated activated carbon) and varying process conditions (temperatures, vacuum levels, residence times) for the removal of FFAs from commercial biodiesel fuel. It was found that silica TriSyl 3000 was the best performing adsorbent, with a capacity for the removal of FFAs of about 1 g g −1 at high values of biodiesel acidity. The two factors influencing the capacity for FFA adsorption are the temperature and the silica residual water content. The latter depends on both the temperature and especially the vacuum level of the pretreatment step. The FFA uptakes over TriSyl silicas in a vacuum were 3−4 times larger than that obtained at atmospheric pressure. The adsorption curves were linear in the range of interest (0−2% acidity), and hence, Henry's law could be used. Values of the Henry's constant of 30.0−47.6 (dimensionless) were measured for TriSyl 3000 silica, along with a heat of adsorption of −5.7 kcal mol −1 . From the kinetic point of view, FFA adsorption is rather slow despite the small diameter of the particles used. The system was found to be highly constrained either by intrinsic slow kinetics or by intraparticle mass-transfer resistance. An unfavorable adsorption equilibrium leading to high adsorbent consumption in one-bleacher operation suggested the use of a countercurrent liquid−solid mode of operation with multiple bleachers. Simulation of two and three serial bleachers working in countercurrent mode revealed that savings greater than 60% can be obtained by using three bleachers operating in countercurrent flow.