Biofuels Distillation

Bioethanol is the largest biofuel today and is used in low 5%—10% blends with gasoline (E5, E10), but also as E85 in flexible-fuel vehicles. Conventional production is a well known process, based on the enzymatic conversion of starchy biomass (cereals) into sugars, and fermentation of 6-carbon sugars with final distillation of ethanol to fuel grade. 

Biofuels are obtained from renewable sources and, when they are combusted, generate only as much CO2 as withdrawn form atmosphere by photosynthesis. Less carbon dioxide is formed in the course of combustion than by the equivalent amount of crude oil distillate fuel, for example diesel fuel. In addition, very little sulfur dioxide is formed. Of course, biofuels are biodegradable. 

During the global transition from the present oil-based economy to a clean and inexhaustible energy economy, the importance of distillation will increase because biofuel production also involves distillation and because... 

Production of ethanol via yeast-catalyzed fermentation of plant carbohydrates is an ancient process. Professor John Thompson (Lane Community College, Eugene, Oregon, USA) has developed an interesting variant of this process using molasses as the feedstock. We use this experiment to introduce the ideas of catalysis (yeast enzymes), azeotropes, density, and biofuels, as well as the technique of simple distillation of ethanol using 19/22 glassware (5). 

Ethanol is the most successful biofuel and, for example, already supplies 40% of Brazil s transportation fuel needs. Its main advantage is that there is a well-established infrastructure for its production and use. Techniques for its production by the fermentation of sucrose are in place, large-scale distillation technologies have been developed, and it can be used in so-called flexible-fuel vehicles. In addition, the logistics for its distribution are well-established. Every gas station in Brazil supplies it, with gasoline being provided in a commercial blend containing up to 24% ethanol. 

An area of current interest is the purification of biofuels produced from biomass. The fermentation of sugar from starch or cellulose typically produces an aqueous mixture of 6-8% ethanol by weight. Other low molecular alcohols (e.g., butanol) may be produced at concentrations as low as 1% and the use of alcohol-resistant yeast can allow fermentation up to a concentration of 15%. Currently, fuel grade alcohol is produced by distillation of the aqueous mixture. However, membrane pervaporation [63], vapor permeation [64], and hybrid processes offer the potential for significant energy and cost savings. 

The competition between distillation and membranes for biofuel purification is strikingly similar to that for desalination. The current state for biofuel purification corresponds to the state of desalination 40 years ago when membrane processes first appeared - membrane processes show potential and start-up companies are touting products but acceptance is low due to concerns over cost and reliability. However, experiences with desalination may dramatically reduce the time required for membrane processes to become as competitive in the biofuel industry as they are in desalination. 

Economic studies on the production of biobutanol from corn determined that distillation recovery of butanol from the dilute ABE fermentation broth is not economical comparing to the butanol production from the current petrochemical route (Ezeji et al., 2007c). However, the life-cycle analysis on the corn-based butanol production indicated that the use of corn-based butanol as a biofuel can lead to substantial fossil energy savings relative to the use of conventional petroleum gasoline, and it can also avoid a large amount of GHG emission burdens (Wu et al., 2008). 

Bio-oil, a kind of biofuel, could be obtained by flash pyrolysis of biomass. Because bio-oil is a type of complex mixture, some researches about bio-oil separation have been conducted in the recent years. Xianwei Zheng et al. have successfully separated flash pyrolysis oil into four kinds of substances by united extraction and distillation. Garcia-Perez et al. have provided an efficient separation method by using five kinds of solvent extraction, and bio-oil was separated into six kinds of substances. 

Enzymes can convert lignocellulosic biomass into a suitable fermentation feed-stock for biofuel production. Different yeast strains are used for ethanol production, such as S. diastaticus, Candida sp., S. cerevisiae and K. marxianus, as well as different bacteria such as Zymomonas mobilis. The employment of distillation is desirable for food grade purity of applications other than that of biofuel. In fact, batch fermentation was coupled with a membrane distillation process developed with the application of a membrane distillation bioreactor for ethanol production. Meanwhile,... 

The interest in w-butanol as a biofuel has increased in recent years owing to its superior fuel qualities compared to ethanol. These include a higher octane number, lower heat of vaporization, higher energy density (energy/volume), and lower vapor pressure. However, in the traditional ABE (acetone-butanol-ethanol) fermentation process, the concentration of n-butanol coming from the fermenter is lower than that achieved in ethanol fermentation. In addition, acetone and ethanol are also produced. Recent studies to improve yield and increase w-butanol concentration have explored fed-batch systems with stripping, adsorption, liquid-liquid extraction, distillation, and/or pervaporation to recover products. 

Short path and molecular distillation always apply in case a gentle treatment of the material is a must, for example in the chemical industry, in the production of pharmaceuticals and of food ingredients or in bio technology. The number of applications in the production of polymers, special chemicals, biofuels and in the recovery of valuables from wastes is increasing. 

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