Energy content of biofuel

Extraction of energy from substances

Different substances contain different amounts of potential energy, that is, the ability to do work.

To extract energy from a substance, a process must convert the substance into another state, releasing the potential energy as kinetic energy in the process, usually in the form of heat. Most man-made machines for harnessing this energy then convert the heat released into mechanical energy (such as a spinning turbine), then finally into electrical energy if needed, using a generator.

These machines vary in their effectiveness at capturing and harnessing the energy released. The proportion of energy usefully captured and converted into mechanical or electrical form is called its efficiency. No machines are 100% efficient. Thus the amount of useful work actually performed by these substances upon processing will never equal their potential energy content.

Furthermore, the mass and volume of a substance contributes to overhead energy costs for producing, processing, shipping, and storing of the substance required to utilize it as a fuel. When calculating economic or environmental impact of a particular fuel, all of these factors must be considered holistically.

Energy and CO₂ output of common fuels

The table below includes entries for popular substances already used for their energy, or being discussed for such use.

The second column shows the energy content in kilojoules per unit of mass in kilograms, useful in understanding the energy needed to ship the fuel, which takes away from its net energy contribution.

The third column in the table lists 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. [1]

Fuel Type	Specific Energy Density (MJ/kg)	Volumetric 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	[2] 10-[3] 15		[Please insert average composition here]
Dried plants (C6H10O5)n	10 – 16	1.6 - 16.64	IF50%(C6H10O5)n+25%(C26H42O21)n+25%(C10H12O3)n1.84	5.44-8.70
Wood fuel (C6H10O5)n	16 – 21	[4] 2.56 - 21.84	IF45%(C6H10O5)n+25%(C26H42O21)n+30%(C10H12O3)n1.88	8.51-11.17
Charcoal	30		85-98% Carbon+VOC+Ash 3.63	8.27
Liquid Fuels
Pyrolysis oil	17.5	21.35	(Assumption Of Fuel: Carbon Content = 23% w/w) 0.84	20.77
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
EcaleneTM	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	[Please insert average composition here]
Biodiesel	37.8	33.3 – 35.7	~2.85	~13.26
Sunflower oil (C18H32O2)	[5] 39.49	33.18	(12%(C16H32O2)+16%(C18H34O2)+71%(LA)+1%(ALA))2.81	14.04
Castor oil (C18H34O3)	[6] 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	(Liquified) 23.0 – 23.3	(Methane leak exerts 23 × greenhouse effect of CO2) 2.74	20.05-20.30
Hydrogen (H2)	120 – 142	(Liquified) 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	(Liquified) 25.5 – 28.7	(Ethane, Propane & Butane N/C:CO,NOx & Sulfates) ~3.00	~12.67-16.67
Ethane (CH3-CH3)	51.9	(Liquified) ~24.0	2.93	17.71
Nuclear fuels (comparison)
Uranium-235 (235U)	77,000,000	(Pure)1,470,700,000	[Greater for lower ore conc.(Mining, Refining, Moving)] 0.0	~55 - ~90
Nuclear fusion (2H-3H)	300,000,000	(Liquified)53,414,377.6	(Sea-Bed Hydrogen-Isotope Mining-Method Dependent) 0.0
Fuel Cell Energy Storage (comparison)
Direct-Methanol	4.5466	[7] 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	[8] 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	[9] (1.5 * NiMH) 0.54	[10] (~300 Deep-Cycle Tolerance) 0.0
Zinc-air battery	0.396 - 0.72	[11] 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

• While all CO₂ gas output ratios are calculated to within a less than 1% margin of error(assuming total oxidation of the carbon content of fuel), ratios preceded by a Tilde (~) indicate a margin of error of up to (but no greater than) 9%. Ratios listed do not include emissions from fuel plant cultivation/Mining, purification/refining and transportation. Fuel availability is typically 74–-84.3% NET from source Energy Balance.
• While Uranium-235 (²³⁵U) fission produces no CO₂ gas directly, the indirect fossil fuel burning processes of Mining, Milling, Refining, Moving & Radioactive waste disposal, etc. of intermediate to low-grade uranium ore concentrations produces some amount of carbon dioxide. Studies vary as to how much carbon dioxide is emitted. The United Nations Intergovernmental Panel on Climate Change reports that nuclear produces approximately 40 g of CO₂ per kilowatt hour (11 g/MJ, equivalent to 90 MJ/kg CO₂e). A meta-analysis of a number of studies of nuclear CO₂ lifecycle emissions by academic Benjamin K. Sovacool finds nuclear on average produces 66 g of CO₂ per kilowatt hour (18.3 g/MJ, equivalent to 55 MJ/kg CO₂e). One Australian professor claims that nuclear power produces the equivalent CO₂ gas emissions per MJ of net-output-energy of a Natural Gas fired power station. Prof.Mark Diesendorf, Inst. of Environmental Studies, UNSW.

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

Oil per seeds = Typical oil extraction from 100 kg of oil seeds
- Note: Chinese Tallow (Sapium sebiferum, or Tradica Sebifera) is also known as the "Popcorn Tree".
Source: Used with permission from The Global Petroleum Club

See also

• Syngas
• Conversion of units
• Energy density
• Heat of combustion