Chemical Engineering

The hemicellulose fraction of brewery's spent grain was selectively hydrolyzed by two sequential steps, autohydrolysis and post-hydrolysis (with diluted sulfuric acid), in order to obtain a fermentable hydrolysate. The concentrations of monosaccharides and inhibitory by-products generated by these sequential processes were evaluated and several detoxification methods for inhibitors removal were tested. These methods included pH adjustment to 5.5, overliming, adsorption into activated charcoal and treatment with anion-and cation-exchange resins at different pH. The treatment of the raw hydrolysate with anion-exchange resins without previous pH correction was found to be the method that removed more inhibitory compounds. Detoxification effects in both non-concentrated and concentrated hydrolysates were evaluated for Debaryomyces hansenii biomass and xylitol production, respectively. When supplemented with inorganic salts and vitamins, the detoxified hydrolysates (through anion-exchange resins) showed lower biomass yield and only slightly higher volumetric productivity (11%) compared to the non-detoxified (pH-adjusted) hydrolysates. The best xylitol yields (0.51 and 0.50 g g −1 ) and productivities (0.29 and 0.33 g l −1 h −1 ) were found both in non-detoxified and detoxified with activated charcoal hydrolysates, respectively.

An increasing global demand for a biologically produced energy source has emerged due to the exhausted usage of non-renewable petroleum-derived fuels. Microalgae are a promising feedstock for biofuels because of their capability to produce lipids. In this paper, two operations for biodiesel production were studied from Phaeodactylum Tricornutum microalgae. This marine diatom shows a big potential to produce biodiesel due to its fast growth and lipid accumulation ability. In this research, first the microalgae was harvesting using an inorganic flocculant as copper (II) sulphate (CuSO4). When the dose was 200 mg/L, the microalgae recovery was close 83% in the first five minutes. After that, the microalgal oil was separated by ultrasound extraction process, using ethanol as solvent. This allows to analyze the oil content of the microalgae which is used later in the transesterification. The obtained lipid content was 38% wt. Temperature variations were observed in this process. Finally, a direct transesterification reaction took place with base catalysis by three ways: traditional, microwave assisted and ultrasound assisted. Direct transesterification microwave assisted achieved 52% conversion to biodiesel versus 16% for the traditional method. However, the best performance (90%) was obtained for ultrasound assisted transesterification.

An alternative for biodiesel production is the use of lipids from microalgae. Although all steps to obtain this biofuel are important, harvesting and extraction are the most important. Advances in these areas are necessary in order to obtain third-generation fuels. The purpose of the present study is to compare different methods of lipids extraction and harvesting for freshwater Selenastrum Capricornutum microalgae. The method used for harvesting was flocculation with inorganic agent. Copper (II) Sulphate (CuSO4) was used as flocculant, resulting in the best percentage of recovery (76%) for a dose of 2 g/L. Previously oil extraction, the collected samples were homogenized and their moisture content was analysed obtaining values of 55-96%. Two extraction methods were used: Soxhlet and ultrasound. The use of ultrasound favours cell disruption and increases the extraction yield. In extraction methods, polar, non-polar solvents, and mixes of solvents were used. N-hexane and acetone were used as solvents for Soxhlet extraction, and ethanol, acetone, methanol, chloroform, and a mixture of chloroform and methanol in 1:2 and 2:1 ratios, for extraction ultrasound assisted method. The use of the methanol-assisted ultrasound is the most efficient method for lipids extraction for Selenastrum Capricornutum biomass.

Hydrogen shows very interesting features for its use on-board applications as fuel cell vehicles. This paper presents the modelling of a tank with a metal hydride alloy for on-board applications, which provides good performance under ambient conditions. The metal hydride contained in the tank is Ti0.98Zr0.02V0.43Fe0.09Cr0.05Mn1.5. A two-dimensional model has been performed for the refuelling process (absorption) and the discharge process (desorption). For that, individual models of mass balance, energy balance, reaction kinetics and behaviour of hydrogen gas has been modelled. The model has been developed under Matlab / Simulink© environment. Finally, individual models have been integrated into a global model, and simulated under ambient conditions. With the aim to analyse the temperature influence on the state of charge and filling and emptying time, other simulations were performed at different temperatures. The obtained results allow to conclude that this alloy offers a good behaviour with the discharge process under normal ambient conditions.

This paper presents a toolbox for the simulation of a zero emission urban hybrid bus, which combines batteries and fuel cells. This type of vehicle performs predefined routes with a certain frequency, then they are an ideal option to the replacement of combustion engines with renewable energy systems. The simulation of these vehicles can be made for different standard driving cycles (ECE-15, EUDC, NEDC, SFUDS) or for real routes from GPS device data. This will allow to consider the orography of the route, considering the slope that overcomes the vehicle at each time, generally this parameter is not included in other models, and it could become a determining factor for the applicability of these vehicles on certain specified routes. Moreover, this tool lets to study and to analyse other not easily quantifiable factors, such as the weather or peak-hour traffic. Finally, the performance of an urban hybrid bus was investigated to assess its theoretical range and the technical feasibility of zero-emission vehicles.

The objective of this paper is to study marine macroalgae as an alternative raw material for the biodiesel production. The obtained results show that biodiesel production from oil extracted from marine algae is feasible by transesterification. Oil extraction can be carried out simultaneously with the transesterification. To investigate the optimum reaction conditions, the reaction was carried out at various methanol to oil molar ratios, catalyst concentrations and reaction temperatures. The process yields 1.6-11.5% depending on the reaction conditions. Moreover, the properties of macroalgae transesterification residue after transesterification were analyzed, concluding that it is a suitable material for fuel pellets manufacturing.