Alkaline folates in water, with or without added NaCl, form columnar mesophases; the columns are composed of a stacked array of folate tetramers held together by Hoogsteen-type hydrogen bonds and stacking interactions. There is a considerable difference in both the liquid crystalline polymorphism and the columnar characteristics in pure water and those in 1 mol L-1 NaCl solutions. In pure water, the tetramer-tetramer interaction is weak, the columnar length changes slowly with the folate concentration, and only the hexagonal mesophase is observed. In 1 mol L-1 NaCl, the tetramer-tetramer interaction is stronger, a cholesteric mesophase is observed, and, even at relatively low folate concentration, the length of the columns is significant (ca. 20 disks at the isotropic-to-cholesteric transition). In both cases, the columns are finite at all concentrations investigated. The formation of a cholesteric mesophase with a pitch of ca. 14 pm indicates that the tetramers do not pile up in register but are rotated one with respect to the other to give a chiral column similar both to the four-stranded helix of poly(G) and to thecolumnar aggregates formed by homoguanylic oligodeoxynucleotides.

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.

This paper is a review of the available literature on the main features of 11 of the most widely adopted oxygenated additives to base gasoline and diesel, focusing particularly on the emissions from the oxygenates considered as additives. The oxygenated additives studied are methyl tert-butyl ether, ethyl tertiary butyl ether, tert-amyl ethyl ether, tertiary amyl methyl ether, isopropyl ether, dimethyl carbonate, dimethoxymethane, dibutyl ether, diglycol methyl ether, diethyl carbonate, and 2-methoxyethyl acetate.

No abstract