Читать книгу Biodiesel Production - Группа авторов - Страница 31

Biodiesel can be produced from various feedstock, which are broadly classified according to type such as edible oils, nonedible oils, animal fats, and other miscellaneous sources as shown in Table 2.1. The use of edible oils has been discontinued since the growing population needs oil crops for sustenance, and this helps avoid the food vs. fuel dispute [2]. The use of nonedible oil crops is being thoroughly investigated by researchers worldwide, with quite a few crops such as jatropha, castor, karanja, etc. being used for small‐scale commercial production [3–6]. However, most of these crops are available in the tropical and subtropical belt, and, as such, these belts exhibit quite the diversity in flora. They can also be classified according to different generations described as follows:

Table 2.1 Feedstock for biodiesel classified according to type.

Edible oils	Nonedible oils	Animal fats	Other sources
Sunflower	Tobacco seed	Poultry fat	Switchgrass
Soybean	Rubber seed	Pork lard	Spent coffee grounds
Sesame	Neem	Fish oil	Poplar
Safflower	Nag champa	Chicken fat	Olive stones
Rice bran	Mahua	Beef tallow	Miscanthus
Rapeseed	Krating oil		Microalgae
Peanut	Karanja		Fungi
Palm	Jojoba		Cyanobacteria
Mustard	Jatropha curcas		Calophyllum inophyllum
Groundnut	Croton megalocarpus
Corn	Cotton seed
Coconut	Castor
Canola	Camelina sativa
Barley

 The earliest oil crops used for fuel synthesis have been designated as the first‐generation feedstock. Including mostly edible oils such as palm, rapeseed, sunflower, soybean, etc. [7–10], these are easy to convert due to their simple fatty acid composition. However, growing concerns over food security inhibit the use of these oils in fuel synthesis.

 With advantages ranging from being nonedible to having the potential of growing in harsh and arid climates as well as being useful as decorative plants, feedstock designated as second generation includes both these nonedible oil crops and waste oils or fats such as waste cooking oil (WCO), brown and yellow grease, and animal tallow. The fuel yield is analogous to that obtained from edible oilseeds and hence is a much better alternative, provided that the chosen feedstock is sufficiently available to sustain commercial scale production.

 Using plant‐based oils usually means that the oil produced per kilogram biomass is far less lucrative in terms of net energy benefits. Also plants tend to have long growth cycles with typically one harvest per year, which is a setback in terms of annual oil yield and fuel production. This is where lipid accumulating microalgae, designated as third‐generation feedstock, are beneficial since (i) they do not need arable land [11]; (ii) algae show rapid growth rates and can accumulate biomass indefinitely without nutrient constraints [2]; (iii) they have high oil to biomass ratio; (iv) genetic manipulation on individual strains is easy; and (v) they can be engineered for high oil yield and for improved carbon capture and biomass accumulation. However, genetic modifications are often associated with very low success rates, and extensive screening is required. Also the culture medium must be properly aerated for CO2 solubilization, as well as to eliminate local accumulation of formed by‐products.