Pyrolysis oil
Encyclopedia
Pyrolysis oil is a synthetic fuel
under investigation as substitute for petroleum
. It is extracted by biomass to liquid
technology of destructive distillation
from dried biomass
in a reactor
at temperature of about 500°C with subsequent cooling. Pyrolytic oil (or bio-oil) is a kind of tar
and normally contains too high levels of oxygen to be a hydrocarbon
. As such it is distinctly different from similar petroleum products.
pyrolysis
). The solid component, charcoal
, may be used for heating the process, a soil additive (biochar
), or as activated carbon
in absorption processes. The non-condensable gaseous component, consisting of hydrogen
(H2), carbon monoxide
(CO), carbon dioxide
(CO2) and methane
(CH4), may be burned. The condensible gases, however, may be rapidly cooled to form condensate droplets, which can then be separated from the non-condensable gases due to the substantial difference in density of each fraction. The condensate may be reignited similar to #2 fossil fuel. The heating value is 15-22 MJ/kg.
of 1.5-3.8 (2.8). The acidity may be lessened by the addition of readily-available base compounds. Little work has been done on the stability of bio oil acidity that has been altered with base compounds. While the exact composition of bio-oil depends on the biomass source and processing conditions, a typical composition is as follows: Water 20-28 %; Suspended solids and pyrolitic lignin 22-36 %; Hydroxyacetaldehyde 8-12%; Levoglucosan
3-8 %; Acetic acid
4-8 %; Acetol 3-6 %; Cellubiosan 1-2 %; Glyoxal
1-2 %; Formaldehyde
3-4 %; Formic Acid
3-6%. .
The water molecules are split during pyrolysis and held separately in other compounds within the complex pyrolysis liquid. This distinction is significant, as the "water" in pyrolysis oil does not separate like standard fossil fuels. The density is approximately 1.2-1.3 (1.22) kg/l or 10.01-10.85 (10.18) lbs/gallon, which is much higher than that of diesel. The oxygen content is 40-50% (mostly from the "water" content) and no sulfur
may be detected normally. The lower heating value is approximately 16-21 (17.5) MJ/kg. The pour point is -12°C to -33°C, and no cloud point
could be observed until -21°C. The carbon residue is 17-23 % wt (0.13% ash
). The flash point is 40-100°C, and the pyrolysis oil is not auto-igniting in a diesel engine
. The cetane number
is only 10. The viscosity
increases to a maximum in period of 12 months due to polymerization
. The pyrolysis oil is not stable reacting with air and degasing
. Pyrolysis oil cannot be blended with diesel .
It may be very attractive, from an economic standpoint, to first recover valuable bio-chemicals from the bio-oil. The remainder of the bio-oil can then be combusted to generate electricity or converted to a syngas
, from which chemicals and clean fuels can be synthesized .
Synthetic fuel
Synthetic fuel or synfuel is a liquid fuel obtained from coal, natural gas, oil shale, or biomass. It may also refer to fuels derived from other solids such as plastics or rubber waste. It may also refer to gaseous fuels produced in a similar way...
under investigation as substitute for petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
. It is extracted by biomass to liquid
Biomass to liquid
Biomass to Liquid or BMtL is a multi-step process which produces liquid biofuels from biomass:The process uses the whole plant to improve the carbon dioxide balance and increase yield....
technology of destructive distillation
Destructive distillation
Destructive distillation is the chemical process involving the decomposition of feedstock by heating to a high temperature; the term generally applies to processing of organic material in the absence of air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents,...
from dried biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
in a reactor
Chemical reactor
In chemical engineering, chemical reactors are vessels designed to contain chemical reactions. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction...
at temperature of about 500°C with subsequent cooling. Pyrolytic oil (or bio-oil) is a kind of tar
Tar
Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...
and normally contains too high levels of oxygen to be a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
. As such it is distinctly different from similar petroleum products.
Process
Biomass is split into solid and gaseous components under the influence of heat only (anhydrousAnhydrous
As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
). The solid component, charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
, may be used for heating the process, a soil additive (biochar
Biochar
Biochar or terra preta is charcoal created by pyrolysis of biomass. Biochar is under investigation as an approach to carbon sequestration via bio-energy with carbon capture and storage. Biochar thus has the potential to help mitigate climate change, via carbon sequestration...
), or as activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
in absorption processes. The non-condensable gaseous component, consisting of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
(H2), carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
(CO), carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
(CH4), may be burned. The condensible gases, however, may be rapidly cooled to form condensate droplets, which can then be separated from the non-condensable gases due to the substantial difference in density of each fraction. The condensate may be reignited similar to #2 fossil fuel. The heating value is 15-22 MJ/kg.
Fuel oil characteristics
The oil produced in a pyrolysis process (bio-oil) is acidic, with a pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of 1.5-3.8 (2.8). The acidity may be lessened by the addition of readily-available base compounds. Little work has been done on the stability of bio oil acidity that has been altered with base compounds. While the exact composition of bio-oil depends on the biomass source and processing conditions, a typical composition is as follows: Water 20-28 %; Suspended solids and pyrolitic lignin 22-36 %; Hydroxyacetaldehyde 8-12%; Levoglucosan
Levoglucosan
Levoglucosan is an organic compound with six carbon ring structure formed from the pyrolysis of carbohydrates, such as starch and cellulose...
3-8 %; Acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
4-8 %; Acetol 3-6 %; Cellubiosan 1-2 %; Glyoxal
Glyoxal
Glyoxal is an organic compound with the formula OCHCHO. This yellow colored liquid is the smallest dialdehyde . Its tautomer acetylenediol is unstable.-Production:...
1-2 %; Formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
3-4 %; Formic Acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
3-6%. .
The water molecules are split during pyrolysis and held separately in other compounds within the complex pyrolysis liquid. This distinction is significant, as the "water" in pyrolysis oil does not separate like standard fossil fuels. The density is approximately 1.2-1.3 (1.22) kg/l or 10.01-10.85 (10.18) lbs/gallon, which is much higher than that of diesel. The oxygen content is 40-50% (mostly from the "water" content) and no sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
may be detected normally. The lower heating value is approximately 16-21 (17.5) MJ/kg. The pour point is -12°C to -33°C, and no cloud point
Cloud point
The cloud point of a fluid is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance...
could be observed until -21°C. The carbon residue is 17-23 % wt (0.13% ash
Ash (analytical chemistry)
In analytical chemistry, ashing is the process of mineralization for preconcentration of trace substances prior to chemical analysis. Ash is the name given to all non-aqueous residue that remains after a sample is burned, and consist mostly of metal oxides....
). The flash point is 40-100°C, and the pyrolysis oil is not auto-igniting in a diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
. The cetane number
Cetane number
Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality.- Definition :...
is only 10. The viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
increases to a maximum in period of 12 months due to polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
. The pyrolysis oil is not stable reacting with air and degasing
Degasification
Degasification is the removal of dissolved gases from liquids, especially water or aqueous solutions, in the fields of science and engineering. There are numerous possible methods for such removal of gases from solids....
. Pyrolysis oil cannot be blended with diesel .
It may be very attractive, from an economic standpoint, to first recover valuable bio-chemicals from the bio-oil. The remainder of the bio-oil can then be combusted to generate electricity or converted to a syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
, from which chemicals and clean fuels can be synthesized .