Laura Azócar

Enzymatic biodiesel production kinetics under previously optimized conditions were investigated. Waste frying oil (WFO) was used as the raw material, Novozym 435 as catalyst, methanol as acyl acceptor and tert-butanol as co-solvent. To investigate pure transesterification kinetics improving product properties, 3 Å molecular sieves were incorporated into the reaction to provide an anhydrous medium avoiding the side reactions of hydrolysis and esterification. The effects of either WFO or methanol on the reaction rate were analyzed separately. The reaction was described by a Ping Pong mechanism and competitive inhibition by methanol. The results obtained in the kinetics study were applied in the operation of a semi-continuous reactor for biodiesel production. The operational conditions of each reaction cycle were: methanol-to-oil ratio 8/1 (mol/mol), 15% (wt) Novozym 435, 0.75% (v/v) of tert-butanol, 44.5 °C, 200 rpm and 4 hours of reaction time. The enzymes were successively reused by...

ABSTRACT Microalgae represent a promising source of biomass for the production of bioproducts and biofuels. However, microalgae cultures are usually diluted. Harvesting processes need then to achieve high levels of volumetric reduction, which is normally energetically demanding. Membrane processes have been recently proposed as an alternative for microalgae concentration. During this research, membrane concentration of non-axenic cultures of saline microalga Nannochloropsis gaditana and freshwater Chlorella sorokiniana was evaluated by a series of batch filtration tests, using tubular ultrafiltration membranes. Theoretical energy demands were determined, based on filtration performance during lab-scale filtration tests. Surface response methodology was also used to determine the effect of cross-flow velocity and biomass concentration over critical flux. Results indicate that exposure of the microalgae culture to cross-flow conditions for long periods may affect suspension properties, decreasing particle size, affecting permeate flux. This would result in high-energy demands when high concentration factors are required, starting from diluted cultures. Moreover, presence of bacteria, resulting from non-sterile conditions, may also determine filtration performance. However, membrane filtration may be an interesting alternative as a post-concentration step for processes normally providing low concentration factors, such as flotation and settling. Short term experiments show that critical fluxes of 50–70 L/m2/h can be achieved, depending on the microalgae, at cross flow velocities in the range of 1.5–2 m/s, when working at 40–50 g/L of VS. Further research would be needed to evaluate if this fluxes can be sustained for long periods.

Biodiesel or fatty acids alkyl esters (FAAE) of long chain are an alternative fuel produced by a transesterification process. The potential production of biodiesel from rapeseed oil in Chile is associated to the solution of economic, environmental and social problems. Experiences ...