• Energy Research

Higher alcohols such as butanol isomers have received remarkable attention as alternative fuels for compression ignition engines because of their great potential as blending components in mixtures with biodiesel and diesel resulting in significant reduction in greenhouse gases and harmful pollutants. In this context, the influence of temperature and pressure on the density of used cooking oil biodiesel, 1-butanol, isobutanol, and biodiesel mixtures with different levels of isobutanol (0.0500, 0.0941, and 0.1397 by mass) was assessed over the temperature range of 298–343 K and pressures up to 30 MPa. For this purpose, a vibrating tube densimeter was calibrated using water and n -octane. The average expanded uncertainty of measured density at a confidence level of 0.95 ( k = 2) was estimated to be 0.80 kg m –3 . The densities of all the systems were represented by the Tait equation of state with AARD % (0.01–0.035%) including the results for the new Tait equation for the biodiesel + isobutanol blends. When isobutanol is added to biodiesel to form a 14% by mass of alcohol, the density of mixture decreases 11 kg.m –3 . Thermal expansivity and isothermal compressibility increase with maximum deviations of 9.6 % and 7.8 % at 343 K and atmospheric pressure.

Carbon nanotubes (CNTs) – perhaps the most enticing class of nano-materials, can be added in small volume fractions to enhance the thermal properties of fluids when process intensification or even device miniaturization is required. This work reports on the results obtained when measuring viscosity, and thermal conductivity of homogenous CNTs – water based nanofluids. The influence of CNTs volume concentration on the nanofluid thermo-physical properties is studied and measurements are undertaken at different temperatures, ranging from 283.15 K to 333.15 K. The nanofluids have been prepared by adding different volume concentrations of treated CNTs to water. The latter has been then sonicated for one hour and the colloidal stability monitored via UV – vis spectrophotometer. The absorbance of the nanofluid was observed at 263 nm, and the average concentration of CNTs was maintained at 9.35 mg/l, even after 200 hours, over 97% when compared with the initial concentration. The viscosity was measured using a controlled stress rheometer, and the measurements were performed in the shear rate ranging from 0 to 600 sec-1. At the same shear rate and temperature, the viscosity was observed to rise with increasing CNTs volume concentration. In what concerns thermal conductivity, it was assessed with a KD2 pro thermal property tester from Decagon Devices and the results clearly show that thermal conductivity rises with CNTs volume fraction, reaching its maximum at 2.5%vol where it represents more than 100% enhancement when the comparison is established with the corresponding value for the base fluid, at the same temperature conditions (i.e. 283.15 – 303.15 K). Furthermore, at higher temperatures (i.e. 313.15 – 333.15 K), the latter, for up to 1%vol concentration represents a 70% enhancement in thermal conductivity.

Abstract Fuel viscosity is an important property that has a significant effect in fuel injection, spray development and combustion in Compression Ignition (CI) engines. Current and future injector designs of diesel engines (such as rail injection systems) work at high pressures (>100 MPa), meaning that fuel viscosity increases substantially over the atmospheric values. The estimation of biodiesel (BD) viscosity based on the knowledge of its composition would be of great potential in the optimization of biodiesel production processes, particularly in the blending of raw materials and refined products. In this work, comprehensive data sets were chosen from literature regarding several BD classes, in order to establish new correlations and new predictive methods of viscosity. The proposed methodologies were validated using available viscosity data of BDs having different chemical compositions in wide ranges of temperature and pressure. The new methods developed at atmospheric pressure for predicting BD viscosity were found to have better predictive ability than those commonly used in literature. In particular, the models developed with the Lewis and Squires equation fitted to biodiesel feedstock (LSDB model) and the same equation using the predicted degree of unsaturation (DU) (LSDU1 model) presented a very good performance with average relative deviation (ARD)

The viscosities of cottonseed oil (CSO) and cottonseed biodiesel (CSB) were measured at atmospheric pressure and temperatures from (293 to 373) K and (303 to 348) K, respectively. The Vogel–Fulcher–Tammann (VFT) and Mauro (MYEGA) equations were selected to represent the temperature dependence of the experimental data, giving deviations within the experimental uncertainties. These equations allowed estimating the glass transition temperatures, which were compared with available values from literature. For viscosity prediction, the group contribution method proposed by Ceriani was compared with the fragment approach given by Zong for CSO. For CSB the Grunberg–Nissan equation coupled with Ceriani and Yuan models was applied, and the influence of the interaction parameter (Gij) is highlighted.

Abstract This study focuses on the mineral carbonation to capture CO2 using an alkaline industrial waste, the grits, formed during the kraft pulp production process. An indirect mineral carbonation route was adopted, composed by two steps: first the extraction of calcium from the grits and second the precipitation of calcium carbonate. Firstly, four solvents were analyzed (HNO3, CH3COOH, NaOH and NH4Cl). Only HNO3 and CH3COOH have shown significant extraction efficiencies of 79.4 and 73.2 %, respectively, after 2 h at 30 °C. Kinetic tests demonstrated that equilibrium conditions are reached after 60 min. Since the nitric acid is a corrosive acid and with high associated costs, the acetic acid was selected for the dissolution of grits and extraction of calcium. The optimal conditions determined were an acetic acid concentration of 2 M, solid/liquid ratio of 30 g/L and temperature of 45 °C with an efficiency approximately of 77 %. In the second step, carbonation experiments were performed contacting the Ca-rich liquor, obtained from the extraction step, with a flux of pure CO2 gaseous in a stainless inox reactor. The optimal conditions determined were 30 °C and 30 bar, reaching a carbonation efficiency of 74 %, corresponding a CO2 sequestration capacity of 460 kg CO2/ton of grits.

This review article presents the state-of-the-art on the catalytic oxidative steam reforming (OSR) of glycerol to produce syngas. Concerning the different technologies proposed for the catalytic OSR of glycerol, the following key points can be highlighted: (1) the robustness is much higher than other reforming technologies, (2) several catalysts can work with low deactivation, some of which can recover almost full activity by suitable regeneration, (3) syngas production by catalytic OSR of glycerin is higher than with concurrent technologies, (4) their scaling-up remains an unrealized task, (5) the thermodynamics of the process has been sufficiently covered in the literature, (6) there is a significant lack of kinetic and mechanistic studies that could help gaining deeper insight on the process, (7) novel concepts and reactor designs must be proposed for their development at larger scales, (8) new catalyst formulations must be developed for attaining higher resistance against oxidation and (9) process intensification could help developing them at larger scales. António Portugal and Rui Moreira are grateful to the Portuguese Foundation for Science and Technology (FCT) and the European Development Regional Fund (ERDF) for funding under the scope of the MultiBiorefinery project (POCI-01-0145-FEDER-016403). Luis M. Gandía thanks Banco de Santander and Universidad Pública de Navarra for their financial support under the 'Programa de Intensificación de la Investigación 2018' initiative. Fernando Bimbela and Luis M. Gandía wish to thank financial support from Spanish Ministerio de Ciencia, Innovación y Universidades , and the European Regional Development Fund ( ERDF / FEDER ) (grant RTI2018-096294-B-C31). José Luis Sánchez expresses his gratitude to Aragón Government (Ref. T22_20R), co-funded by FEDER 2014–2020 'Construyendo Europa desde Aragón' for providing frame support for this work.