An alcohol molecule is a nucleophile by virtue of the dense electron cloud on its O atom, which results in a partial negative charge there. As soon as it gets within striking distance of the target molecule the electron cloud bulges out towards the positively charged C atom and forms a carbon–oxygen bond. At about the same time, the alcohol molecule shrugs off the H atom (as a proton) that it brought with it; that proton is picked up by a nearby water molecule, which becomes an H3O+ ion. A proton has been restored to the medium: one was used to prepare the target and now one has been returned. That marriage-broker-like action of the proton, its role in bringing about reaction but its release for involvement elsewhere after its work has been done, is the central nature of catalytic action.
Peter Atkins, Reactions: The Private Life of Atoms (2011), p. 122
As long as the starting material is grown on farmland, Searchinger says, biofuels will be bad for the planet. But Alex Farrell at Berkeley sees a way out of this. He says the focus of the biofuels industry needs a rapid change of direction, away from using cropland — which is where most U.S. biofuels come from today — and toward other sources of starting material. "We could replace all of the ethanol that we consume in California just using waste that goes to the landfill today, and turning that into ethanol," Farrell says. Environmentally friendly biofuels could also be made from agricultural waste or grasses grown on land that's not suitable for crops. The biofuels industry is heading in that direction, but the technology to make use of fuels other than corn and soy is still in its infancy.
Biofuels have grabbed the attention of engineresearchers ever since the oil-crisis and escalating costs of petro-chemicals cropped up in the ׳70s. Ethanol and methanol were the most widely researched alcohols in IC engines. However, the last decade has witnessed significant amount of research in higher alcohols due to the development of modern fermentation processes using engineeredmicro-organisms that improved yield. Higher alcohols are attractive second/third generation biofuels that can be produced from sugary, starchy and ligno-cellulosic biomass feedstocks using sustainable pathways. The present work reviews the current literature concerning the effects of using higher alcohols ranging from 3-carbon propanol to 20-carbon phytol on combustion, performance and emission characteristics of a wide range of diesel engines under various test conditions. The literature is abound with evidence that higher alcohols reduce carcinogenicparticulateemissions that are prevalent in diesel engines.
It can be concluded that higher alcohols reduce smoke emissions with their fuel-borne oxygen; enhance air/fuel mixing by offering long ignition delay and eventually replace fossildiesel (partially or wholly) to enable a clean and efficient combustion in compression-ignition engines. The chief thrust areas include developing mutant strains with higher yield, higher tolerance to toxic inhibition and low-cost substrates for fermentation. Further work is required in stipulating optimum blend-fuel characteristics and ensuring the long-term durability of the engines using these fuels.
