Pyrolysis oil, sometimes also known as biocrude or bio-oil, is a

synthetic fuel Synthetic fuel or synfuel is a liquid fuel, or sometimes Fuel gas, gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by ...

with few industrial applications and under investigation as substitute for

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

. It is obtained by heating dried

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

without

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

in a reactor at a temperature of about with subsequent cooling, separation from the aqueous phase and other processes. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

. This high oxygen content results in non-volatility, corrosiveness, partial miscibility with

fossil fuels A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...

, thermal instability, and a tendency to

polymerize In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many form ...

when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.

Standards

There are few standards for pyrolysis oil because of few efforts to produce it. One is from

ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

Feedstock decomposition

Pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

is a well established technique for

decomposition Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ess ...

organic material Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

at elevated temperatures in the absence of

into oil and other constituents. In second-generation biofuel applications—forest and agricultural residues, waste wood, yard waste, and energy crops can be used as feedstock.

Wood

When wood is heated above it begins a process of decomposition called

carbonization Carbonization or carbonisation is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation. Complexity in carbonization Carbonization is a pyrolytic reaction, therefore, is considered a ...

. In the absence of oxygen, the final product is

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ca ...

. If sufficient oxygen is present, the wood will burn when it reaches a temperature of about leaving

wood ash Wood ash is the powder (substance), powdery residue remaining after the combustion of wood, such as burning wood in a fireplace, bonfire, or an industrial power plant. It is largely composed of calcium compounds, along with other non-combustible ...

behind. If wood is heated away from air, the moisture is first driven off and until this is complete, the wood temperature remains at about . When the wood is dry its temperature rises, and at about it begins to spontaneously decompose and generate heat. This is the well known exothermic reaction which takes place in the burning of charcoal. At this stage evolution of carbonization by-products starts. These substances are given off gradually as the temperature rises and at about the evolution is complete. The solid residue, charcoal, is mainly carbon (about 70%), with the remainder being tar-like substances which can be driven off or decomposed completely only by raising the temperature to above about 600 °C to produce

Biochar Biochar is a form of charcoal, sometimes modified, that is intended for organic use, as in soil. It is the lightweight black remnants remaining after the pyrolysis of biomass, consisting of carbon and ashes. Despite its name, biochar is steril ...

, a high-carbon, fine-grained residue that today is produced through modern

pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

processes, which is the direct

thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic ...

of biomass in the absence of oxygen, which prevents

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...

, to obtain an array of solid (biochar), liquid—Pyrolysis oil (bio-oil/pyrolysis-oil), and gas (

syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as ...

) products. The specific yield from the pyrolysis is dependent on process conditions. such as temperature, and can be optimized to produce either energy or biochar. Temperatures of produce more char, while temperatures above favor the yield of liquid and gaseous fuel components. (See Table 1 for differences in output for Fast, Intermediate, Slow, and Gasification). Pyrolysis occurs more quickly at higher temperatures, typically requiring seconds instead of hours. High temperature pyrolysis is also known as

gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...

, and produces primarily syngas. Typical yields are 60% bio-oil, 20% biochar, and 20% syngas. By comparison, slow pyrolysis can produce substantially more char (~50%). For typical inputs, the energy required to run a “fast” pyrolyzer is approximately 15% of the energy that it outputs. Modern pyrolysis plants can use the syngas created by the pyrolysis process and output 3–9 times the amount of energy required to run.

Algae

Algae may be subjected to high temperatures (~500 °C) and normal atmospheric pressures. The resultant products include oil and nutrients such as nitrogen, phosphorus, and potassium.

There are numerous papers on the pyrolysis of lignocellulosic biomass. However, very few reports are available for algal bio-oil production via pyrolysis. Miao et al. (2004b) performed fast pyrolysis of Chllorella protothecoides and Microcystis areuginosa at 500 °C, and bio-oil yields of 18% and 24% were obtained, respectively. The bio-oil exhibited a higher carbon and nitrogen content, lower oxygen content than wood bio-oil. When Chlorella protothecoides was cultivated heterotrophically, bio-oil yield increased to 57.9% with a heating value of 41 MJ/kg (Miao et al., 2004a). Recently when microalgae become a hot research topic as the third generation of biofuel, pyrolysis has drawn more attention as a potential conversion method for algal biofuel production. Pan et al. (2010) investigated slow pyrolysis of Nannochloropsis sp. residue with and without the presence of HZSM-5 catalyst and obtained bio-oil rich in aromatic hydrocarbons from catalytic pyrolysis. Algal pyrolytic liquids separate into two phases with the top phase called bio-oil (Campanella et al., 2012; Jena et al., 2011a). The higher heating values (HHV) of algal bio-oil are in the range of 31−36 MJ/kg, generally higher than those of lignocellulosic feedstocks. Pyrolytic bio-oil consists of compounds with lower mean molecular weights and contains more low boiling compounds than bio-oil produced by hydrothermal liquefaction. These properties are similar to those of Illinois shale oil (Jena et al., 2011a; Vardon et al., 2012), which may indicate that pyrolytic bio-oil is suited for replacing petroleum. In addition, the high protein content in microalgae led to a high N content in the bio-oil, resulting in undesirable NOx emissions during combustion and deactivation of acidic catalysts when co-processed in existing 10 crude oil refineries. Algal bio-oil had better qualities in many aspects than those produced from lignocellulosic biomass. For example, algal bio-oil has a higher heating value, a lower oxygen content and a greater than 7 pH value. However, upgrading towards the removal of nitrogen and oxygen in the bio-oil is still necessary before it can be used as drop-in fuels.

Hydrothermal liquefaction

Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet

into an oil—sometimes referred to as bio-oil or biocrude—under a moderate temperature and high pressure of 350 °C (662 °F) and 3,000 pounds per square inch (21,000 kPa). The crude-like oil (or bio-oil) has high energy density with a lower heating value of 33.8-36.9 MJ/kg and 5-20 wt% oxygen and renewable chemicals. The HTL process differs from pyrolysis as it can process wet biomass and produce a bio-oil that contains approximately twice the energy density of pyrolysis oil. Pyrolysis is a related process to HTL, but biomass must be processed and dried in order to increase the yield. The presence of water in pyrolysis drastically increases the heat of vaporization of the organic material, increasing the energy required to decompose the biomass. Typical pyrolysis processes require a water content of less than 40% to suitably convert the biomass to bio-oil. This requires considerable pretreatment of wet biomass such as tropical grasses, which contain a water content as high as 80-85%, and even further treatment for aquatic species, which can contain higher than 90% water content. The properties of the resulting bio-oil are affected by temperature, reaction time, algae species, algae concentration, reaction atmosphere, and catalysts, in subcritical water reaction conditions.

Biocrude

Bio-oil typically requires significant additional treatment to render it suitable as a refinery feedstock to replace crude oil derived from

, coal-oil, or coal-tar. Tar is a black mixture of

hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic; their odor is usually faint, and may b ...

and free carbon obtained from a wide variety of

s through

destructive distillation Destructive distillation is a chemical process in which decomposition of unprocessed material is achieved by heating it to a high temperature; the term generally applies to processing of organic material in the absence of air or in the presence o ...

. Tar can be produced from

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

, or

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

. * Pine tar is a sticky material produced by the high temperature carbonization of

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...

wood in

anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...

conditions (dry distillation or destructive distillation). The wood is rapidly decomposed by applying heat and pressure in a closed container; the primary resulting products are charcoal and pine tar. Pine tar consists primarily of aromatic hydrocarbons, tar acids and tar bases. Components of tar vary according to the pyrolytic process (e.g. method, duration, temperature) and origin of the wood (e.g. age of pine trees, type of soil and moisture conditions during tree growth). * Birch tar is a substance (liquid when heated) derived from the

dry distillation Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids). The method may involve pyrolysis or thermolysis, or it may not (for instance, a simple mixture of ice and glass could be ...

of the bark of the

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' contains 3 ...

tree. It is compounded of

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (− O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds ar ...

such as guaiacol,

cresol Cresols (also known as hydroxytoluene, toluenol, benzol or cresylic acid) are a group of aromatic organic compounds. They are widely-occurring phenols (sometimes called ''phenolics'') which may be either natural or manufactured. They are also c ...

xylenol Xylenols are organic compounds with the formula (CH3)2C6H3OH. They are volatile colorless solids or oily liquids. They are derivatives of phenol with two methyl groups at various positions relative to the hydroxyl group. Six isomers exist, of whi ...

and creosol (not to be confused with

). Wood-tar

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types w ...

is a colourless to yellowish greasy liquid with a smoky odor, produces a sooty flame when burned, and has a burned taste. It is non-buoyant in water, with a

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at . When transparent, it is in its purest form. Dissolution in water requires up to 200 times the amount of water as the base creosote. The creosote is a combination of natural phenols: primarily guaiacol and creosol (4-methylguaiacol), which will typically constitute 50% of the oil; second in prevalence, cresol and

; the rest being a combination of monophenols and

polyphenol Polyphenols () are a large family of naturally occurring phenols. They are abundant in plants and structurally diverse. Polyphenols include phenolic acids, flavonoids, tannic acid, and ellagitannin, some of which have been used historically as ...

s. Pitch is a name for any of a number of

viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both Viscosity, viscous and Elasticity (physics), elastic characteristics when undergoing deformation (engineering), deformation. Viscous mate ...

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s. Pitch can be natural or manufactured, derived from petroleum,

coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoria ...

or plants. Black liquor and Tall oil is a viscous liquid by-product of wood pulp manufacturing. Rubber oil is the product of the pyrolysis method for recycling used tires.

Biofuel

Biofuel Biofuel is a fuel that is produced over a short time span from Biomass (energy), biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricu ...

s are synthesized from intermediary products such as syngas using methods that are identical in processes involving conventional feedstocks, first generation and second generation biofuels. The distinguishing feature is the technology involved in producing the intermediary product, rather than the ultimate off-take. A

Biorefinery A biorefinery is a refinery that converts biomass to energy and other beneficial byproducts (such as chemicals). The International Energy Agency Bioenergy Task 42 defined biorefining as "the sustainable processing of biomass into a spectrum of bi ...

is a facility that integrates biomass conversion processes and equipment to produce fuels, power, heat, and value-added chemicals from

. The biorefinery concept is analogous to today's petroleum refinery, which produce multiple fuels and products from petroleum. *

Biodiesel Biodiesel is a renewable biofuel, a form of diesel fuel, derived from biological sources like vegetable oils, animal fats, or recycled greases, and consisting of long-chain fatty acid esters. It is typically made from fats. The roots of bi ...

is a diesel fuel derived from animal or plant lipids (oils and fats). A variety of oils can be used as biodiesel

feedstock A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials/Intermediate goods that are feedstock for future finishe ...

. * Wood diesel. A new biofuel was developed by the

University of Georgia The University of Georgia (UGA or Georgia) is a Public university, public Land-grant university, land-grant research university with its main campus in Athens, Georgia, United States. Chartered in 1785, it is the oldest public university in th ...

from

woodchips Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, Tree stump, stumps, roots, and wood waste. Woodchips may be used as a biomass solid fuel and are r ...

. The oil is extracted and then added to unmodified diesel engines. Either new plants are used or planted to replace the old plants. The charcoal byproduct is put back into the soil as a fertilizer. This biofuel can actually be carbon negative not just carbon neutral. Carbon negative processes decrease carbon dioxide in the air reversing the

greenhouse effect The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source (as in the case of Jupiter) or ...

not just reducing it. *

Algae fuel Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that use algae as the source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made fro ...

s, can be produced from various types of

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

, and are dependent on the technique and the part of the cells used, some species of algae can produce 50% or more of their dry weight in the form of oil. The

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

, or oily part of the algae biomass can be extracted and converted into biodiesel through a process similar to that used for any other vegetable oil, or converted in a refinery into "drop-in" replacements for petroleum-based fuels. Algaculture can use waste materials such as sewage and without displacing land currently used for food production.

Atmospheric carbon dioxide removal

Bio-oil is a recent contender technique for carbon sequestration. Corn stalks are converted by pyrolysis into bio-oil, which is then pumped underground.

Industrial applications

Currently, bio-oil has few industrial uses. A reported application is in the production of

zinc oxide Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, Zinc metabolism, food supplements, rubbe ...

as thermal source. In this use, the fuel has substituted heavy fuel oils as a biogenic source of heat. The bio-oil is used in the kiln burners as a direct substitute with little to no change in the operational results. The fuel has higher water and oxygen content which makes a higher volumetric flow for the same heat capacity.

References

{{Reflist

External links

Pyrolysis Oil: An Innovative Liquid Biofuel for Heating

PyroKnown
website is dedicated to sharing knowledge and learning about biomass fast pyrolysis.

* ttps://www.nrel.gov/docs/fy07osti/37779.pdf Large-Scale Pyrolysis Oil Production: A Technology Assessment and Economic Analysis Synthetic fuels Biofuels Pyrolysis