Encyclopedia of Renewable Energy. James G. Speight
Читать онлайн книгу.
an animal feed called distillers’ dried grain with soluble matter.
Corn wet milling is the process of separating the corn kernel into starch, protein, germ, and fiber in an aqueous medium prior to fermentation. The primary products of wet milling include starch and starch-derived products (e.g., high fructose corn syrup and ethanol), corn oil, and corn gluten.
Ethanol can also be produced from other forms of biomass that do not fall under the nomenclature of food crops. One set of production processes is applicable to what is known as cellulosic biomass, including fast-growing fuel crops, agricultural waste such as bagasse and corn stover, and forest and wood processing waste, while a second set of techniques can make use of practically any form of inexpensive biomass including the cellulosic sort as well as the black liquor produced by paper mills, animal wastes, and some types of landfill wastes.
Ethanol can be readily produced by fermentation of simple sugars that are converted from starch crops. Feedstocks for such fermentation ethanol include corn, barley, potato, rice, and wheat. This type of ethanol may be called grain ethanol, whereas ethanol produced from cellulose biomass such as trees and grasses is called bioethanol or biomass ethanol.” Both grain ethanol and bioethanol are produced via biochemical processes, while chemical ethanol is synthesized by chemical synthesis routes that do not involve fermentation.
Cellulosic biofuels, such as cellulosic ethanol, began to be produced in commercial-scale plants in 2013. These fuels are made from cellulose-containing organic material. Cellulose forms the primary structural component of green plants and is by far the most abundant organic (carbon-containing) compound on Earth. The primary cell wall of green plants is made primarily of cellulose; the secondary wall contains cellulose with variable amounts of lignin. Lignin and cellulose, considered together, are termed lignocellulose, which (as wood) is the most common biopolymer on Earth. Cellulosic biomass, derived from non-food sources, such as trees and grasses, is also being developed as a feedstock for ethanol production. Even dry ethanol has roughly one-third lower energy content per unit of volume compared to gasoline, so larger (and therefore heavier) fuel tanks are required to travel the same distance, or more fuel stops are required.
Ethanol may also be used as a fuel, most often in combination with gasoline. For the most part, it is used in a 9:1 ratio of gasoline to ethanol to reduce the negative environmental effects of gasoline. There is increasing interest in the use of a blend of 85% fuel ethanol blended with 15% gasoline. This fuel blend, called E85, has a higher fuel octane than premium gasoline, allowing in properly optimized engine increases in both power and fuel economy over gasoline.
Biopropanol
Propanol (propyl alcohol, C3H7OH) is the next member of the alcohol series followed by butanol (butyl alcohol, C4H9OH). Both alcohols may be used as a fuel with the normal combustion engine. The advantages of propanol and butanol are the high octane rating (over 100) and high energy content, only approximately 10% lower than gasoline, and subsequently more energy-dense than methanol and ethanol. The major disadvantage of propanol and butanol as fuels for the internal combustion engine is the relative high flashpoint of these alcohols.
Biobutanol
Butanol can be produced from biomass (as biobutanol) as well as fossil fuels, but biobutanol and crude oil-derived butanol (sometimes referred to as petro-butanol) have the same chemical properties. Butanol may be used as a fuel in an internal combustion engine. Because its longer hydrocarbon chain causes it to be fairly non-polar, it is more similar to gasoline than it is to ethanol. Butanol has been demonstrated to work in vehicles designed for use with gasoline without modification, and is thus often claimed to provide a direct replacement for gasoline (in a similar way to biodiesel in diesel engines). Biobutanol has the advantage in combustion engines in that its energy density is closer to gasoline than the simpler alcohols (while still retaining over 25% higher octane rating); however, biobutanol is currently more difficult to produce than ethanol or methanol.
See also: Biodiesel, Biofuels, Biogas, Vegetable Oil.
Biocatalysts
A biocatalyst is a catalyst (such as, for example, an enzyme) that is of biological origin. Thus, biocatalysis is the use of natural catalysts, such as protein enzymes, to perform chemical transformations on organic compounds. Both enzymes that have been more or less isolated and enzymes still residing inside living cells are employed for this task. More than one hundred years ago, biocatalysis was employed to achieve chemical transformations on non-natural man-made organic compounds, and the last 30 years have seen a substantial increase in the application of biocatalysis to produce fine chemicals, especially for the pharmaceutical industry.
Biocatalysts are living (biological) systems that increase the rate of chemical reactions. In biocatalytic processes, natural catalysts, such as enzymes, perform chemical transformations of organic compounds. In fact, enzymes that have been isolated as separate molecular entities as well as enzymes still remain inside living cells are employed as catalysts that can catalyze novel small molecule transformations that may be difficult or impossible using classical synthetic organic chemistry. In addition, enzymes are environmentally benign insofar as they can be completely degraded in the environment.
Biocatalysts do not operate by different scientific principles from organic catalysts. The existence of a multitude of enzyme models including oligopeptide or polypeptide catalysts proves that all enzyme action can be explained by rational chemical and physical principles. However, enzymes can create unusual and superior reaction conditions such as extremely low pKa values or a high positive potential for a redox metal ion. Enzymes have increasingly been found to catalyze almost any reaction of organic chemistry. Moreover, the notion that biocatalysts are slow catalysts is false and optimized syntheses not only produce high selectivity or total turnover numbers but also satisfactory-to-high yields of products.
See also: Enzymes.
Biochar
Biochar is organic matter that has undergone combustion under low to no oxygen conditions (such as during pyrolysis) resulting in a recalcitrant, high carbon material specifically for use as a soil amendment. Recently, fervent interest in the production of biochar to address issues of fertility, water-holding capacity, remediation, climate change mitigation, etc., led to a much greater understanding of the complexities of this potential amendment in altering soil biological, chemical, and physical properties. Rather than assume the benefit of any biochar created from any feedstock added to any soil ecosystem, concepts of matching appropriate feedstock and pyrolysis condition to soil type to achieve specific goals associated with remediation, increasing yields, decreasing greenhouse gas emission, and/or climate change mitigation emerged.
This porous sponge-like property of biochar makes it useful for many things such as the production of activated carbon filters used to purify water. Industrial production of biochar employs pyrolysis, a means of combustion without much air or oxygen and that is more efficient in that it produces little ash.
The production of biochar is a sustainable option for waste management since the char contains 50% of the original carbon which is highly recalcitrant in nature; therefore, its production helps in carbon sequestration by locking the carbon present in the plant biomass. The elemental composition and structural configuration of biochar is strongly correlated with temperature, heating rate, and residence time maintained during its production. Along with the biochar, some amount of bio-oil and gases are also produced which can be used for generation of energy and various chemicals.
Soil pH and electrical conductivity (EC) increase in soil incorporated with biochar which may be due to the presence of ash residue that is dominated by carbonates of alkali and alkaline earth metals, and some amount of silica, heavy metals, and organic and inorganic nitrogen. With its large surface area, biochar helps in increasing water holding capacity, cation exchange capacity (CEC), and microbial activity (act as its habitat) and also reduces leaching of nutrient by providing nutrient binding sites. This reduces the total fertilizer requirement of biochar-amended