One of the most promising renewable fuels proposed as an alternative to fossil diesel is biodiesel. The competitive potential of biodiesel is limited by the price of vegetable oils, which strongly influences the final price of this biofuel. On the other hand, extensive use of vegetable oils may cause other significant problems such as starvation in developing countries. Appropriately planning and designing the whole production process, from the seed to the biodiesel end-product, is essential to contain the influence of energy inefficiencies on the high price of the end-product. The present study reviews the technologies currently used in the production of biodiesel. We first discuss the technologies for extracting the vegetable oil from the seed, and its subsequent refining and conversion into biodiesel. This study focuses on the characteristics of the production processes currently used in the sector, illustrating the technological options and emphasizing the drawbacks of certain practices and the best choices available. The vegetable oils tend to be processed using procedures that are well established, but oriented more towards obtaining products suitable for the foodstuffs industry, and that consequently use technologies that are sometimes excessive for energetic purposes. The processes for extracting the vegetable oil from the seed generally include a set of steps, the complexity of which depends on the raw material. Basically, the two extraction technologies involved rely on the use of pressure or solvents. In practice, the two systems are often combined. Using the vegetable oils as a source of energy makes some of these steps superfluous and enables technologies to be used that would be unsuitable for foodstuffs production. This study focuses on feasible technological improvements that would give rise to oil that is still suitable for use as a source of energy, but at a lower cost. The refined vegetable oil can subsequently be converted into biodiesel by means of a great variety of technologies, many of which are still not suitable for applications on an industrial scale. The solution that has met with the greatest favor is homogeneous alkaline transesterification with KOH and methanol. Even when dealing with this type of conversion alone, it is impossible to establish a universal schema to describe the conversion or purification stages because there are numerous possible different solutions. When we then look more closely at the state of the art in industrial biodiesel production plants, we encounter the potential problems introduced by the type and characteristics of the original raw material. Comparing some of the reference solutions that have inspired numerous installations, a sensitivity analysis is conducted on the main elements involved in the process, focusing on their behavior in different working conditions to obtain products with the characteristics required by the international standards (EN 14214:2008, ASTM D 6751 07b). © 2011 Elsevier Ltd

The vapor pressure data of 2,3,3,3-Tetrafluoroprop-1-ene (CF 3 CF=CH 2 , HFO-1234yf) were measured using a constant volume apparatus. Measurements were carried out in a wide temperature range, from (224 to 366) K, and at pressures from (39 to 3218) kPa. A total of 35 experimental points were obtained. The measurements were fitted to the Wagner equation with an absolute deviation of 0.35 %. To our knowledge, no other experimental results have been published in the open literature on the properties studied here; for this reason our experimental results were compared with a preliminary equation of state.

A novel process is presented to generate electricity from low-grade heat by combining a Reverse Electrodialysis membrane with an Adsorption desalinator in a closed-loop system. A Reverse Electrodialysis membrane generates electricity by controlled mixing of two salt solutions of different concentrations. An Adsorption desalinator restores the initial salt gradient by utilising low-grade heat for the separation. In this study the process is designed from optimising the salt and material selection to the development of the real system application. Energy and exergy efficiencies of the proposed system show the potential of this novel renewable energy technology. The efficiencies of 227 salts with a range of different valences and 10 adsorption materials have been investigated over a large number of system parameters. The results show that the optimised system can achieve an exergy efficiency of up to 30 %. Moreover, high salt concentrations do not significantly increase the specific energy consumption of the Adsorption desalinator, which allows operating the Reverse Electrodialysis membrane at the optimal salt concentrations.

The P-V-T properties of 2,3,3,3-Tetrafluoroprop-1-ene (CF 3 CF=CH 2 , HFO-1234yf), an environment friendly refrigerant, were measured using a constant volume apparatus. Measurements were carried out at temperatures from (243 to 373) K and at pressures from (84 to 3716) kPa. A total of 136 experimental points, taken along 12 isochores, were obtained. Our experimental results were compared with a preliminary equation of state. The measurements were also regressed to the Martin-Hou equation of state. No any other data on this fluid were found in the literature for the superheated region.

The composite material 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid in Syloid AL-1FP silica shows unprecedented water vapor sorption equilibrium properties. Equilibrium data were recorded at different loads of ionic liquid in the silica support (from 1.8%w to 60%w). At loadings >1.8%w, all the composites show type 3 isotherm, therefore conserving the vapor-liquid equilibrium of the bulk ionic liquid/water binary system but with increased dependence between temperature and water adsorbed. This feature makes this composite material particularly suitable for thermally-driven technologies. The composite 60%w 1-ethyl-3methylimidazolium methanesulfonate ionic liquid in 40%w Syloid AL-1FP silica shifts the performance of sorption desalination and drying processes at the unprecedented working capacity of 0.46 gwater/gsorbent (desalination) and 0.82 gwater/gsorbent (drying).

Adsorption heat transformers use low-grade heat to produce potable water and provide cooling at the same time. In this study, we present a comprehensive performance analysis for an experimental system featuring the world's smallest design using silica gel, which is commonly used as benchmarking material. We analyse the system performance in a thorough cycle analysis that quantifies the influence of isosteric heating times and cycle times onto the adsorption working capacity. In addition, the performance is assessed through common performance indicators for desalination as well as cooling. We found that the system achieved a Specific Daily Water Production of up to 10.9 kg w /(kg sg d) at 80°C. The combination of cooling and desalination is discussed highlighting advantages as well as disadvantages, which are often neglected. The results show that silica gel has a high performance in desalination, which decreases by more than 60 % if cooling is desired as well.

Closed-loop Reverse Electrodialysis is a novel technology to directly convert low-grade heat into electricity. It consists of a reverse electrodialysis (RED) unit where electricity is produced exploiting the salinity gradient between two saltwater solutions, coupled with a regeneration unit where waste-heat is used to treat the solutions exiting from the RED unit and restore their initial composition. One of the most important advantages of closed-loop systems compared to the open systems is the possibility to select ad-hoc salt solutions to achieve high efficiencies. Therefore, the properties of the salt solutions are essential to assess the performance of the energy generation and solution regeneration processes. The aim of this study is to analyse the influence of thermodynamic properties of non-conventional salt solutions (i.e. other than NaCl-aqueous solutions) and their influence on the operation of the closed-loop RED. New data for caesium and potassium acetate salts, i.e. osmotic and activity coefficients in aqueous solutions, at temperature between 20 and 90°C are reported as a function of molality. The data are correlated using Pitzer's model, which is then used to assess the theoretical performance of the whole closed-loop RED system considering both single and multi-stage regeneration units. Results indicate that KAc, CsAc and LiCl are the most promising salts among those screened.

The current concentration of carbon dioxide in the atmosphere demands for development of negative emission solutions such as direct carbon dioxide removal from the atmosphere (air capture). Many well-established processes can remove carbon dioxide from the atmosphere but the real technological challenge consists of concentrating and compressing carbon dioxide at the conditions for long term geological storage, with efficient use of non-fossil energy sources. A thermally-driven, negative-carbon adsorption process for capture, purification and compression of carbon dioxide from air is proposed. The process is based on a series of batch adsorption compressors of decreasing size to deliver a compressed carbon dioxide stream to a final storage. Thermodynamic analysis of the process shows that, by exploiting the equilibrium properties of commercial and non-commercial materials, carbon dioxide can be produced at specifications appropriate for geological storage. By operating the process with zeolite 13X at regeneration temperature of 95°C, a final storage vessel can be pressurized with carbon dioxide at purities >0.95 mole fraction and specific energy consumption <2.2 MJth molCO2-1. Tailored materials provide a step-change in performance. When the process operates with zeolite NaETS-4, carbon dioxide can be purified at values >0.97 mole fraction.