Energy content of biofuel explained

The energy content of biofuel is the chemical energy contained in a given biofuel, measured per unit mass of that fuel, as specific energy, or per unit of volume of the fuel, as energy density.A biofuel is a fuel produced from recently living organisms. Biofuels include bioethanol, an alcohol made by fermentation—often used as a gasoline additive, and biodiesel, which is usually used as a diesel additive. Specific energy is energy per unit mass, which is used to describe the chemical energy content of a fuel, expressed in SI units as joule per kilogram (J/kg) or equivalent units.^[1] Energy density is the amount of chemical energy per unit volume of the fuel, expressed in SI units as joule per litre (J/L) or equivalent units.^[2]

Energy and CO₂ output of common biofuels

See also: Orders of magnitude (specific energy density). The table below includes entries for popular substances already used for their energy, or being discussed for such use.

The second column shows specific energy, the energy content in megajoules per unit of mass in kilograms, useful in understanding the energy that can be extracted from the fuel.

The third column in the table lists energy density, the energy content per liter of volume, which is useful for understanding the space needed for storing the fuel.

The final two columns deal with the carbon footprint of the fuel. The fourth column contains the proportion of CO₂ released when the fuel is converted for energy, with respect to its starting mass, and the fifth column lists the energy produced per kilogram of CO₂ produced. As a guideline, a higher number in this column is better for the environment. But these numbers do not account for other green house gases released during burning, production, storage, or shipping. For example, methane may have hidden environmental costs that are not reflected in the table. https://web.archive.org/web/20070922180338/http://www.cypenv.org/worldenv/files/methane.htm

Fuel Type	Specific energy (MJ/kg)	Energy Density (MJ/L)	CO2 Gas made from Fuel Used (kg/kg)	Energy per CO2 (MJ/kg)
Solid Fuels
	Bagasse (Cane Stalks)	9.6		~+40%(C6H10O5)n+15% (C26H42O21)n+15% (C9H10O2)n1.30	7.41
	Chaff (Seed Casings)	14.6		[Please insert average composition here]
	Animal Dung/Manure	http://www.humanitarianinfo.org/darfur/uploads/idp/Cooking%20fuel%20-%20helpdoc%20by%20UNJLC.pdf 10–https://web.archive.org/web/20101126092443/http://home.hccnet.nl/david.dirkse/math/energy.html 15		[Please insert average composition here]
	Dried plants (C6H10O5)n	10–16	1.6–16.64	IF 50%(C6H10O5)n+25% (C26H42O21)n+25% (C10H12O3)n1.84	5.44-8.70
	Wood fuel (C6H10O5)n	16–21	http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch03.pdf 2.56–21.84	IF 45%(C6H10O5)n+25% (C26H42O21)n+30% (C10H12O3)n1.88	8.51–11.17
	Charcoal	30	5.4–6.6	85–98% Carbon+VOC+Ash 3.63	8.27
Liquid Fuels
	Pyrolysis oil	17.5	21.35	varies	varies
	Methanol (CH3-OH)	19.9–22.7	15.9	1.37	14.49–16.53
	Ethanol (CH3-CH2-OH)	23.4–26.8	18.4–21.2	1.91	12.25–14.03
	Ecalene	28.4	22.7	75%C2H6O+9%C3H8O+7%C4H10O+5%C5H12O+4%Hx 2.03	14.02
	Butanol (CH3-(CH2)3-OH)	36	29.2	2.37	15.16
	Fat	37.656	31.68	C55H104O6
	Biodiesel	37.8	33.3–35.7	~2.85	~13.26
	Sunflower oil (C18H32O2)	https://web.archive.org/web/20070927065241/http://www.pttplc.com/en/document/pdf/biofuel_en.pdf 39.49	33.18	(12% (C16H32O2)+16% (C18H34O2)+71% (LA)+1% (ALA))2.81	14.04
	Castor oil (C18H34O3)	https://web.archive.org/web/20111113061656/http://www.castoroil.in/uses/fuel/castor_oil_fuel.html 39.5	33.21	(1% PA+1% SA+89.5% ROA+3% OA+4.2% LA+0.3% ALA)2.67	14.80
	Olive oil (C18H34O2)	39.25–39.82	33–33.48	(15% (C16H32O2)+75% (C18H34O2)+9% (LA)+1% (ALA))2.80	14.03
Gaseous Fuels
	Methane (CH4)	55–55.7	(Liquefied) 23.0–23.3	(Methane leak exerts 23 × greenhouse effect of CO2) 2.74	20.05–20.30
	Hydrogen (H2)	120–142	(Liquefied) 8.5–10.1	(Hydrogen leak slightly catalyzes ozone depletion) 0.0
Fossil Fuels (comparison)
	Coal	29.3–33.5	39.85–74.43	(Not Counting: CO, NOx, Sulfates & Particulates) ~3.59	~8.16–9.33
	Crude Oil	41.868	28–31.4	(Not Counting: CO, NOx, Sulfates & Particulates) ~3.4	~12.31
	Gasoline	45–48.3	32–34.8	(Not Counting: CO, NOx, Sulfates & Particulates) ~3.30	~13.64–14.64
	Diesel	48.1	40.3	(Not Counting: CO, NOx, Sulfates & Particulates) ~3.4	~14.15
	Natural Gas	38–50	(Liquefied) 25.5–28.7	(Ethane, Propane & Butane Not Counting: CO, NOx & Sulfates) ~3.00	~12.67–16.67
	Ethane (CH3-CH3)	51.9	(Liquefied) ~24.0	2.93	17.71
Nuclear fuels (comparison)
	Uranium -235 (^235U)	77,000,000	(Pure)1,470,700,000	[Greater for lower [[Uraninite|ore]] conc.(Mining, Refining, Moving)] 0.0	~55 – ~90
	Nuclear fusion (^2H -^3H)	300,000,000	(Liquefied)53,414,377.6	(Sea-Bed Hydrogen-Isotope Mining-Method Dependent) 0.0
Fuel Cell Energy Storage (comparison)
	Direct Methanol	4.5466	http://uk.computers.toshiba-europe.com/cgi-bin/ToshibaCSG/news_article.jsp?service=UK&ID=0000005758 3.6	~1.37	~3.31
	Proton-Exchange (R&D)	up to 5.68	up to 4.5	(IFF Fuel is recycled) 0.0
	Sodium Hydride (R&D)	up to 11.13	up to 10.24	(Bladder for Sodium Oxide Recycling) 0.0
Battery Energy Storage (comparison)
	Lead–acid battery	0.108	~0.1	(200–600 Deep-Cycle Tolerance) 0.0
	Nickel–iron battery	https://web.archive.org/web/20061213172224/http://www.beutilityfree.com/batterynife/Flyer.pdf 0.0487–0.1127	0.0658–0.1772	(<40y Life)(2k–3k Cycle Tolerance IF no Memory effect) 0.0
	Nickel–cadmium battery	0.162–0.288	~0.24	(1k–1.5k Cycle Tolerance IF no Memory effect) 0.0
	Nickel–metal hydride	0.22–0.324	0.36	(300–500 Cycle Tolerance IF no Memory effect) 0.0
	Super-iron battery	0.33	http://dataweek.co.za/news.aspx?pklNewsID=597&amp;pklCategoryID=31&amp;pklIssueID=40 (1.5 * NiMH) 0.54	http://www.sciencenews.org/articles/20040320/fob6.asp (~300 Deep-Cycle Tolerance) 0.0
	Zinc–air battery	0.396–0.72	https://web.archive.org/web/20060812091528/http://www.electric-fuel.com/evtech/index.shtml 0.5924–0.8442	(Recyclable by Smelting & Remixing, not Recharging) 0.0
	Lithium-ion battery	0.54–0.72	0.9–1.9	(3–5 y Life) (500-1k Deep-Cycle Tolerance) 0.0
	Lithium-Ion-Polymer	0.65–0.87	(1.2 * Li-Ion)1.08–2.28	(3–5 y Life) (300–500 Deep-Cycle Tolerance) 0.0
	Lithium iron phosphate battery
	DURACELL Zinc–Air	1.0584–1.5912	5.148–6.3216	(1–3 y Shelf-life) (Recyclable not Rechargeable) 0.0
	Aluminium battery	1.8–4.788	7.56	(10–30 y Life) (3k+ Deep-Cycle Tolerance) 0.0
	PolyPlusBC Li-Aircell	3.6–32.4	3.6–17.64	(May be Rechargeable)(Might leak sulfates) 0.0

Notes

Yields of common crops associated with biofuels production

Crop	Oil (kg/ha)	Oil (L/ha)	Oil (lb/acre)	Oil (US gal/acre)	Oil per seeds (kg/100 kg)	Melting Range (°C)			Iodine number	Cetane number
						Oil / Fat	Methyl Ester	Ethyl Ester
	Groundnut					(Kernel)42
	Copra					62
	Tallow						35–42	16	12	40–60	75
	Lard						32–36	14	10	60–70	65
	Corn (maize)	145	172	129	18		-5	-10	-12	115–124	53
	Cashew nut	148	176	132	19
	Oats	183	217	163	23
	Lupine	195	232	175	25
	Kenaf	230	273	205	29
	Calendula	256	305	229	33
	Cotton	273	325	244	35	(Seed)13	-1 – 0	-5	-8	100–115	55
	Hemp	305	363	272	39
	Soybean	375	446	335	48	14	-16 – -12	-10	-12	125–140	53
	Coffee	386	459	345	49
	Linseed (flax)	402	478	359	51		-24			178
	Hazelnuts	405	482	362	51
	Euphorbia	440	524	393	56
	Pumpkin seed	449	534	401	57
	Coriander	450	536	402	57
	Mustard seed	481	572	430	61	35
	Camelina	490	583	438	62
	Sesame	585	696	522	74	50
	Safflower	655	779	585	83
	Rice	696	828	622	88
	Tung oil tree	790	940	705	100		-2.5			168
	Sunflowers	800	952	714	102	32	-18 – -17	-12	-14	125–135	52
	Cocoa (cacao)	863	1,026	771	110
	Peanuts	890	1,059	795	113		3			93
	Opium poppy	978	1,163	873	124
	Rapeseed	1,000	1,190	893	127	37	-10–5	-10–0	-12 – -2	97–115	55–58
	Olives	1,019	1,212	910	129		-12 – -6	-6	-8	77–94	60
	Castor beans	1,188	1,413	1,061	151	(Seed)50	-18			85
	Pecan nuts	1,505	1,791	1,344	191
	Jojoba	1,528	1,818	1,365	194
	Jatropha	1,590	1,892	1,420	202
	Macadamia nuts	1,887	2,246	1,685	240
	Brazil nuts	2,010	2,392	1,795	255
	Avocado	2,217	2,638	1,980	282
	Coconut	2,260	2,689	2,018	287		20–25	-9	-6	8–10	70
	Chinese Tallow		4,700		500
	Oil palm	5,000	5,950	4,465	635	20–(Kernal)36	20–40	-8–21	-8–18	12–95	65–85
	Algae		95,000		10,000
Crop	Oil (kg/ha)	Oil (L/ha)	Oil (lb/acre)	Oil (US gal/acre)	Oil per seeds (kg/100 kg)	Melting Range (°C)			Iodine number	Cetane number
						Oil / Fat	Methyl Ester	Ethyl Ester

Notes

See also

• Eichhornia crassipes#Bioenergy
• Syngas
• Conversion of units
• Energy density
• Heat of combustion

Notes and References

1. Kenneth E. Heselton (2004), "Boiler Operator's Handbook". Fairmont Press, 405 pages.
2. Web site: The Two cap of SI Units and the SI Prefixes . NIST Guide to the SI . 2012-01-25.