Jun. 23, 2025
Introduction Our Research What Is Pyrolysis? Bio-Oil Researchers
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Biomass
Lignocellulosic biomass is the most abundant renewable carbon source on Earth. Available biomass sources include forest residues, crop residues, purpose grown energy crops (e.g. grasses), animal wastes and food wastes. These materials are the fibrous structural parts of plants and are largely made of cellulose, hemicellulose and lignin. Compared with so called 1st generation bio-feedstocks such as sugars, starches and vegetable oils, nature has made these parts of the plants difficult to deconstruct to chemical building blocks, making utilization of this carbon source a challenge for scientists and engineers. Biorefineries are facilities where biomass is converted to a variety of products. Our target products included advanced hydrocarbon biofuels that are indistinguishable from fossil-based gasoline, diesel or jet fuels along with bio-based chemicals and materials. Technologies need to be developed to more efficiently convert this renewable carbon source so that renewable bio-products from biomass can be made economically competitive with those produced from fossil resources.
Pyrolysis
Pyrolysis is one of the technologies available to convert biomass to an intermediate liquid product that can be refined to drop-in hydrocarbon biofuels, oxygenated fuel additives and petrochemical replacements. Pyrolysis is the heating of an organic material, such as biomass, in the absence of oxygen. Biomass pyrolysis is usually conducted at or above 500 °C, providing enough heat to deconstruct the strong bio-polymers mentioned above. Because no oxygen is present combustion does not occur, rather the biomass thermally decomposes into combustible gases and bio-char. Most of these combustible gases can be condensed into a combustible liquid, called pyrolysis oil (bio-oil), though there are some permanent gases (CO2, CO, H2, light hydrocarbons), some of which can be combusted to provide the heat for the process. Thus, pyrolysis of biomass produces three products: one liquid, bio-oil, one solid, bio-char and one gaseous, syngas. The proportion of these products depends on several factors including the composition of the feedstock and process parameters. However, all things being equal, the yield of bio-oil is optimized when the pyrolysis temperature is around 500 °C and the heating rate is high ( °C/s) fast pyrolysis conditions. Under these conditions, bio-oil yields of 60-70 wt% of can be achieved from a typical biomass feedstock, with 15-25 wt% yields of bio-char. The remaining 10-15 wt% is syngas. Processes that use slower heating rates are called slow pyrolysis and bio-char is usually the major product of such processes. The pyrolysis process can be self-sustained, as combustion of the syngas and a portion of bio-oil or bio-char can provide all the necessary energy to drive the reaction.
Schematic of the Fast Pyrolysis Process.
Bio-oil is a dense complex mixture of oxygenated organic compounds. It has a fuel value that is generally 50 - 70% that of petroleum bases fuels and can be used as boiler fuel or upgraded to renewable transportation fuels. The bio-oil’s composition makes it thermally unstable and therefore difficult to distill or further refine, making additional research on producing higher quality bio-oil necessary. However, its density is > 1 kg L-1, much greater than that of biomass feedstocks, making it more cost effective to transport than biomass. Therefore, it’s is possible to envision a distributed processing model where many small scale pyrolyzers (farm scale) covert biomass to bio-oil which is then transported to a centralized location for refining. To test this hypothesis, our group developed and constructed a mobile one-ton per day pyrolysis demonstration unit based on a reactor design called the combustion reduction integrated pyrolysis system (CRIPS). The CRIPS unit can produce bio-oil on location and can perform fast or catalytic pyrolysis to produce partially deoxygenated bio-oil.
ARS’s Mobile Combustion Reduction Integrated Pyrolysis System (CRIPS)
Furthermore, the bio-char produced can be used on the farm as an excellent soil amender that can sequester carbon. Bio-char is highly absorbent and therefore increases the soil's ability to retain water, nutrients and agricultural chemicals, preventing water contamination and soil erosion. Soil application of bio-char may enhance both soil quality and be an effective means of sequestering large amounts of carbon. Use of bio-char as a soil amendment will offset many of the problems associated with removing crop residues from the land.
Our Project
Our core project at the Eastern Regional Research Center current has four main objectives dedicated to making pyrolysis and biodiesel based biorefineries economically competitive. They include:
Our approach to developing commercially viable pyrolysis based biorefineries is summarized in the Figure above. We are developing catalytic pyrolysis technologies where a catalyst is used to reduce the oxygen content of the bio-oil to produce stable, low or mid-level oxygen content bio-oil that can undergo separation processes such as distillation to sperate fractions to be used for various refining processes to produce renewable chemicals in addition to biofuels. We are also developing replacements for fossil based industrial carbons such as coke and pitch that can be used in heavy carbon emitting industries such as aluminum smelting. Furthermore, we are tackling the plastic waste problem by considering waste plastic, especially the very common polyolefins, as a potential source of cheap hydrogen making up for the inherent hydrogen deficiency in biomass. Our preliminary results indicate that co-pyrolysis of biomass with plastic waste over a catalyst can increase the carbon conversion efficiency to valuable aromatic hydrocarbons.
Pyrolysis is a process involving the separation of covalent bonds in organic matter by thermal decomposition within an inert environment without oxygen.[1][2][3]
The word pyrolysis is coined from the Greek-derived elements pyro- (from Ancient Greek πῦρ : pûr - "fire, heat, fever") and lysis (λύσις : lúsis - "separation, loosening").
Pyrolysis is most commonly used in the treatment of organic materials. It is one of the processes involved in the charring of wood[4] or pyrolysis of biomass. In general, pyrolysis of organic substances produces volatile products and leaves char, a carbon-rich solid residue. Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization. Pyrolysis is considered one of the steps in the processes of gasification or combustion.[5][6] Laypeople often confuse pyrolysis gas with syngas.[why?] Pyrolysis gas has a high percentage of heavy tar fractions, which condense at relatively high temperatures, preventing its direct use in gas burners and internal combustion engines, unlike syngas.
The process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, or to produce coke from coal. It is used also in the conversion of natural gas (primarily methane) into hydrogen gas and solid carbon char, recently introduced on an industrial scale.[7] Aspirational applications of pyrolysis would convert biomass into syngas and biochar, waste plastics back into usable oil, or waste into safely disposable substances.
Pyrolysis is one of the various types of chemical degradation processes that occur at higher temperatures (above the boiling point of water or other solvents). It differs from other processes like combustion and hydrolysis in that it usually does not involve the addition of other reagents such as oxygen (O
2, in combustion) or water (in hydrolysis).[8] Pyrolysis produces solids (char), condensable liquids, (light and heavy oils and tar), and non-condensable gasses.[9][10][11][12]
Pyrolysis is different from gasification. In the chemical process industry, pyrolysis refers to a partial thermal degradation of carbonaceous materials that takes place in an inert (oxygen free) atmosphere and produces both gases, liquids and solids. The pyrolysis can be extended to full gasification that produces mainly gaseous output,[13] often with the addition of e.g. water steam to gasify residual carbonic solids, see Steam reforming.
Specific types of pyrolysis include:
Other pyrolysis types come from a different classification that focuses on the pyrolysis operating conditions and heating system used, which have an impact on the yield of the pyrolysis products.
Pyrolysis has been used for turning wood into charcoal since ancient times. The ancient Egyptians used the liquid fraction obtained from the pyrolysis of cedar wood, in their embalming process.[17]
The dry distillation of wood remained the major source of methanol into the early 20th century.[18] Pyrolysis was instrumental in the discovery of many chemical substances, such as phosphorus from ammonium sodium hydrogen phosphate NH4NaHPO4 in concentrated urine, oxygen from mercuric oxide, and various nitrates.[citation needed]
Pyrolysis generally consists in heating the material above its decomposition temperature, breaking chemical bonds in its molecules. The fragments usually become smaller molecules, but may combine to produce residues with larger molecular mass, even amorphous covalent solids.[citation needed]
In many settings, some amounts of oxygen, water, or other substances may be present, so that combustion, hydrolysis, or other chemical processes may occur besides pyrolysis proper. Sometimes those chemicals are added intentionally, as in the burning of firewood, in the traditional manufacture of charcoal, and in the steam cracking of crude oil.[citation needed]
Conversely, the starting material may be heated in a vacuum or in an inert atmosphere to avoid chemical side reactions (such as combustion or hydrolysis). Pyrolysis in a vacuum also lowers the boiling point of the byproducts, improving their recovery.
When organic matter is heated at increasing temperatures in open containers, the following processes generally occur, in successive or overlapping stages:[citation needed]
Because pyrolysis takes place at high temperatures which exceed the autoignition temperature of the produced gases, an explosion risk exists if oxygen is present. To control the temperature of pyrolysis systems careful temperature control is needed and can be accomplished with an open source pyrolysis controller.[20] Pyrolysis also produces various toxic gases, mainly carbon monoxide. The greatest risk of fire, explosion and release of toxic gases comes when the system is starting up and shutting down, operating intermittently, or during operational upsets.[21]
Inert gas purging is essential to manage inherent explosion risks. The procedure is not trivial and failure to keep oxygen out has led to accidents.[22]
Conversion of CBD to THC can be brought about by pyrolysis.[23][24]
Pyrolysis has many applications in food preparation.[25] Caramelization is the pyrolysis of sugars in food (often after the sugars have been produced by the breakdown of polysaccharides). The food goes brown and changes flavor. The distinctive flavors are used in many dishes; for instance, caramelized onion is used in French onion soup.[26][27] The temperatures needed for caramelization lie above the boiling point of water.[26] Frying oil can easily rise above the boiling point. Putting a lid on the frying pan keeps the water in, and some of it re-condenses, keeping the temperature too cool to brown for longer time.
Pyrolysis of food can also be undesirable, as in the charring of burnt food (at temperatures too low for the oxidative combustion of carbon to produce flames and burn the food to ash).
Carbon and carbon-rich materials have desirable properties but are nonvolatile, even at high temperatures. Consequently, pyrolysis is used to produce many kinds of carbon; these can be used for fuel, as reagents in steelmaking (coke), and as structural materials.
Charcoal is a less smoky fuel than pyrolyzed wood.[28] Some cities ban, or used to ban, wood fires; when residents only use charcoal (and similarly treated rock coal, called coke) air pollution is significantly reduced. In cities where people do not generally cook or heat with fires, this is not needed. In the mid-20th century, "smokeless" legislation in Europe required cleaner-burning techniques, such as coke fuel[29] and smoke-burning incinerators[30] as an effective measure to reduce air pollution[29]
The coke-making or "coking" process consists of heating the material in "coking ovens" to very high temperatures (up to 900 °C or 1,700 °F) so that the molecules are broken down into lighter volatile substances, which leave the vessel, and a porous but hard residue that is mostly carbon and inorganic ash. The amount of volatiles varies with the source material, but is typically 25–30% of it by weight. High temperature pyrolysis is used on an industrial scale to convert coal into coke. This is useful in metallurgy, where the higher temperatures are necessary for many processes, such as steelmaking. Volatile by-products of this process are also often useful, including benzene and pyridine.[31] Coke can also be produced from the solid residue left from petroleum refining.
The original vascular structure of the wood and the pores created by escaping gases combine to produce a light and porous material. By starting with a dense wood-like material, such as nutshells or peach stones, one obtains a form of charcoal with particularly fine pores (and hence a much larger pore surface area), called activated carbon, which is used as an adsorbent for a wide range of chemical substances.
Biochar is the residue of incomplete organic pyrolysis, e.g., from cooking fires. It is a key component of the terra preta soils associated with ancient indigenous communities of the Amazon basin.[32] Terra preta is much sought by local farmers for its superior fertility and capacity to promote and retain an enhanced suite of beneficial microbiota, compared to the typical red soil of the region. Efforts are underway to recreate these soils through biochar, the solid residue of pyrolysis of various materials, mostly organic waste.
Carbon fibers are filaments of carbon that can be used to make very strong yarns and textiles. Carbon fiber items are often produced by spinning and weaving the desired item from fibers of a suitable polymer, and then pyrolyzing the material at a high temperature (from 1,500–3,000 °C or 2,730–5,430 °F). The first carbon fibers were made from rayon, but polyacrylonitrile has become the most common starting material. For their first workable electric lamps, Joseph Wilson Swan and Thomas Edison used carbon filaments made by pyrolysis of cotton yarns and bamboo splinters, respectively.
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Pyrolysis is the reaction used to coat a preformed substrate with a layer of pyrolytic carbon. This is typically done in a fluidized bed reactor heated to 1,000–2,000 °C or 1,830–3,630 °F. Pyrolytic carbon coatings are used in many applications, including artificial heart valves.[33]
Pyrolysis is the basis of several methods for producing fuel from biomass, i.e. lignocellulosic biomass.[34] Crops studied as biomass feedstock for pyrolysis include native North American prairie grasses such as switchgrass and bred versions of other grasses such as Miscantheus giganteus. Other sources of organic matter as feedstock for pyrolysis include greenwaste, sawdust, waste wood, leaves, vegetables, nut shells, straw, cotton trash, rice hulls, and orange peels.[5] Animal waste including poultry litter, dairy manure, and potentially other manures are also under evaluation. Some industrial byproducts are also suitable feedstock including paper sludge, distillers grain,[35] and sewage sludge.[36]
In the biomass components, the pyrolysis of hemicellulose happens between 210 and 310 °C.[5] The pyrolysis of cellulose starts from 300 to 315 °C and ends at 360–380 °C, with a peak at 342–354 °C.[5] Lignin starts to decompose at about 200 °C and continues until °C.[37]
Synthetic diesel fuel by pyrolysis of organic materials is not yet economically competitive.[38] Higher efficiency is sometimes achieved by flash pyrolysis, in which finely divided feedstock is quickly heated to between 350 and 500 °C (660 and 930 °F) for less than two seconds.
Syngas is usually produced by pyrolysis.[25]
The low quality of oils produced through pyrolysis can be improved by physical and chemical processes,[39] which might drive up production costs, but may make sense economically as circumstances change.
There is also the possibility of integrating with other processes such as mechanical biological treatment and anaerobic digestion.[40] Fast pyrolysis is also investigated for biomass conversion.[41] Fuel bio-oil can also be produced by hydrous pyrolysis.
Methane pyrolysis[42] is an industrial process for "turquoise" hydrogen production from methane by removing solid carbon from natural gas.[43] This one-step process produces hydrogen in high volume at low cost (less than steam reforming with carbon sequestration).[44] No greenhouse gas is released. No deep well injection of carbon dioxide is needed. Only water is released when hydrogen is used as the fuel for fuel-cell electric heavy truck transportation, [45][46][47][48][49] gas turbine electric power generation,[50][51] and hydrogen for industrial processes including producing ammonia fertilizer and cement.[52][53] Methane pyrolysis is the process operating around °C for producing hydrogen from natural gas that allows removal of carbon easily (solid carbon is a byproduct of the process).[54][55] The industrial quality solid carbon can then be sold or landfilled and is not released into the atmosphere, avoiding emission of greenhouse gas (GHG) or ground water pollution from a landfill.
In , a company called Monolith Materials built a pilot plant in Redwood City, CA to study scaling Methane Pyrolysis using renewable power in the process.[56] A successful pilot project then led to a larger commercial-scale demonstration plant in Hallam, Nebraska in .[57] As of , this plant is operational and can produce around 14 metric tons of hydrogen per day. In , the US Department of Energy backed Monolith Materials' plans for major expansion with a $1B loan guarantee.[58] The funding will help produce a plant capable of generating 164 metric tons of hydrogen per day by . Pilots with gas utilities and biogas plants are underway with companies like Modern Hydrogen.[59][60] Volume production is also being evaluated in the BASF "methane pyrolysis at scale" pilot plant,[7] the chemical engineering team at University of California - Santa Barbara[61] and in such research laboratories as Karlsruhe Liquid-metal Laboratory (KALLA).[62] Power for process heat consumed is only one-seventh of the power consumed in the water electrolysis method for producing hydrogen.[63]
The Australian company Hazer Group was founded in to commercialise technology originally developed at the University of Western Australia. The company was listed on the ASX in December . It is completing a commercial demonstration project to produce renewable hydrogen and graphite from wastewater and iron ore as a process catalyst use technology created by the University of Western Australia (UWA). The Commercial Demonstration Plant project is an Australian first, and expected to produce around 100 tonnes of fuel-grade hydrogen and 380 tonnes of graphite each year starting in .[citation needed] It was scheduled to commence in . "10 December : Hazer Group (ASX: HZR) regret to advise that there has been a delay to the completion of the fabrication of the reactor for the Hazer Commercial Demonstration Project (CDP). This is expected to delay the planned commissioning of the Hazer CDP, with commissioning now expected to occur after our current target date of 1Q ."[64] The Hazer Group has collaboration agreements with Engie for a facility in France in May ,[65] A Memorandum of Understanding with Chubu Electric & Chiyoda in Japan April [66] and an agreement with Suncor Energy and FortisBC to develop 2,500 tonnes per Annum Burrard-Hazer Hydrogen Production Plant in Canada April [67][68]
The American company C-Zero's technology converts natural gas into hydrogen and solid carbon. The hydrogen provides clean, low-cost energy on demand, while the carbon can be permanently sequestered.[69] C-Zero announced in June that it closed a $34 million financing round led by SK Gas, a subsidiary of South Korea's second-largest conglomerate, the SK Group. SK Gas was joined by two other new investors, Engie New Ventures and Trafigura, one of the world's largest physical commodities trading companies, in addition to participation from existing investors including Breakthrough Energy Ventures, Eni Next, Mitsubishi Heavy Industries, and AP Ventures. Funding was for C-Zero's first pilot plant, which was expected to be online in Q1 . The plant may be capable of producing up to 400 kg of hydrogen per day from natural gas with no CO2 emissions.[70]
One of the world's largest chemical companies, BASF, has been researching hydrogen pyrolysis for more than 10 years.[71]
Pyrolysis is used to produce ethylene, the chemical compound produced on the largest scale industrially (>110 million tons/year in ). In this process, hydrocarbons from petroleum are heated to around 600 °C (1,112 °F) in the presence of steam; this is called steam cracking. The resulting ethylene is used to make antifreeze (ethylene glycol), PVC (via vinyl chloride), and many other polymers, such as polyethylene and polystyrene.[72]
The process of metalorganic vapour-phase epitaxy (MOCVD) entails pyrolysis of volatile organometallic compounds to give semiconductors, hard coatings, and other applicable materials. The reactions entail thermal degradation of precursors, with deposition of the inorganic component and release of the hydrocarbons as gaseous waste. Since it is an atom-by-atom deposition, these atoms organize themselves into crystals to form the bulk semiconductor. Raw polycrystalline silicon is produced by the chemical vapor deposition of silane gases:
Gallium arsenide, another semiconductor, forms upon co-pyrolysis of trimethylgallium and arsine.
Pyrolysis can also be used to treat municipal solid waste and plastic waste.[6][19][73] The main advantage is the reduction in volume of the waste. In principle, pyrolysis will regenerate the monomers (precursors) to the polymers that are treated, but in practice the process is neither a clean nor an economically competitive source of monomers.[74][75][76]
In tire waste management, tire pyrolysis is a well-developed technology.[77] Other products from car tire pyrolysis include steel wires, carbon black and bitumen.[78] The area faces legislative, economic, and marketing obstacles.[79] Oil derived from tire rubber pyrolysis has a high sulfur content, which gives it high potential as a pollutant; consequently it should be desulfurized.[80][81]
Alkaline pyrolysis of sewage sludge at low temperature of 500 °C can enhance H
2 production with in-situ carbon capture. The use of NaOH (sodium hydroxide) has the potential to produce H
2-rich gas that can be used for fuels cells directly.[36][82]
In early November , the U.S. State of Georgia announced a joint effort with Igneo Technologies to build an $85 million large electronics recycling plant in the Port of Savannah. The project will focus on lower-value, plastics-heavy devices in the waste stream using multiple shredders and furnaces using pyrolysis technology.[83]
Waste from pyrolysis itself can also be used for useful products. For example, contaminant-rich retentate from liquid-fed pyrolysis of postconsumer multilayer packaging waste can be used as novel building composite materials, which have higher compression strengths (10-12 MPa) than construction bricks and brickworks (7 MPa), as well as 57% lower density, 0.77 g/cm3 .[84]
Pyrolysis has also been used for trying to mitigate tobacco waste. One method was done where tobacco waste was separated into two categories TLW (Tobacco Leaf Waste) and TSW (Tobacco Stick Waste). TLW was determined to be any waste from cigarettes and TSW was determined to be any waste from electronic cigarettes. Both TLW and TSW were dried at 80 °C for 24 hours and stored in a desiccator.[85] Samples were grounded so that the contents were uniform. Tobacco Waste (TW) also contains inorganic (metal) contents, which was determined using an inductively coupled plasma-optical spectrometer.[85] Thermo-gravimetric analysis was used to thermally degrade four samples (TLW, TSW, glycerol, and guar gum) and monitored under specific dynamic temperature conditions.[85] About one gram of both TLW and TSW were used in the pyrolysis tests. During these analysis tests, CO
2 and N
2 were used as atmospheres inside of a tubular reactor that was built using quartz tubing. For both CO
2 and N
2 atmospheres the flow rate was 100 mL min−1.[85] External heating was created via a tubular furnace. The pyrogenic products were classified into three phases. The first phase was biochar, a solid residue produced by the reactor at 650 °C. The second phase liquid hydrocarbons were collected by a cold solvent trap and sorted by using chromatography. The third and final phase was analyzed using an online micro GC unit and those pyrolysates were gases.
Two different types of experiments were conducted: one-stepwise pyrolysis and two-stepwise pyrolysis. One-stepwise pyrolysis consisted of a constant heating rate (10 °C min−1) from 30 to 720 °C.[85] In the second step of the two-stepwise pyrolysis test the pyrolysates from the one-stepwise pyrolysis were pyrolyzed in the second heating zone which was controlled isothermally at 650 °C.[85] The two-stepwise pyrolysis was used to focus primarily on how well CO
2 affects carbon redistribution when adding heat through the second heating zone.[85]
First noted was the thermolytic behaviors of TLW and TSW in both the CO
2 and N
2 environments. For both TLW and TSW the thermolytic behaviors were identical at less than or equal to 660 °C in the CO
2 and N
2 environments. The differences between the environments start to occur when temperatures increase above 660 °C and the residual mass percentages significantly decrease in the CO
2 environment compared to that in the N
2 environment.[85] This observation is likely due to the Boudouard reaction, where we see spontaneous gasification happening when temperatures exceed 710 °C.[86][87] Although these observations were seen at temperatures lower than 710 °C it is most likely due to the catalytic capabilities of inorganics in TLW.[85] It was further investigated by doing ICP-OES measurements and found that a fifth of the residual mass percentage was Ca species. CaCO
3 is used in cigarette papers and filter material, leading to the explanation that degradation of CaCO
3 causes pure CO
2 reacting with CaO in a dynamic equilibrium state.[85] This being the reason for seeing mass decay between 660 °C and 710 °C. Differences in differential thermogram (DTG) peaks for TLW were compared to TSW. TLW had four distinctive peaks at 87, 195, 265, and 306 °C whereas TSW had two major drop offs at 200 and 306 °C with one spike in between.[85] The four peaks indicated that TLW contains more diverse types of additives than TSW.[85] The residual mass percentage between TLW and TSW was further compared, where the residual mass in TSW was less than that of TLW for both CO
2 and N
2 environments concluding that TSW has higher quantities of additives than TLW.
The one-stepwise pyrolysis experiment showed different results for the CO
2 and N
2 environments. During this process the evolution of 5 different notable gases were observed. Hydrogen, Methane, Ethane, Carbon Dioxide, and Ethylene all are produced when the thermolytic rate of TLW began to be retarded at greater than or equal to 500 °C. Thermolytic rate begins at the same temperatures for both the CO
2 and N
2 environment but there is higher concentration of the production of Hydrogen, Ethane, Ethylene, and Methane in the N
2 environment than that in the CO
2 environment. The concentration of CO in the CO
2 environment is significantly greater as temperatures increase past 600 °C and this is due to CO
2 being liberated from CaCO
3 in TLW.[85] This significant increase in CO concentration is why there is lower concentrations of other gases produced in the CO
2 environment due to a dilution effect.[85] Since pyrolysis is the re-distribution of carbons in carbon substrates into three pyrogenic products.[85] The CO
2 environment is going to be more effective because the CO
2 reduction into CO allows for the oxidation of pyrolysates to form CO. In conclusion the CO
2 environment allows a higher yield of gases than oil and biochar. When the same process is done for TSW the trends are almost identical therefore the same explanations can be applied to the pyrolysis of TSW.[85]
Harmful chemicals were reduced in the CO
2 environment due to CO formation causing tar to be reduced. One-stepwise pyrolysis was not that effective on activating CO
2 on carbon rearrangement due to the high quantities of liquid pyrolysates (tar). Two-stepwise pyrolysis for the CO
2 environment allowed for greater concentrations of gases due to the second heating zone. The second heating zone was at a consistent temperature of 650 °C isothermally.[85] More reactions between CO
2 and gaseous pyrolysates with longer residence time meant that CO
2 could further convert pyrolysates into CO.[85] The results showed that the two-stepwise pyrolysis was an effective way to decrease tar content and increase gas concentration by about 10 wt.% for both TLW (64.20 wt.%) and TSW (73.71%).[85]
Pyrolysis is also used for thermal cleaning, an industrial application to remove organic substances such as polymers, plastics and coatings from parts, products or production components like extruder screws, spinnerets[88] and static mixers. During the thermal cleaning process, at temperatures from 310 to 540 °C (600 to 1,000 °F),[89] organic material is converted by pyrolysis and oxidation into volatile organic compounds, hydrocarbons and carbonized gas.[90] Inorganic elements remain.[91]
Several types of thermal cleaning systems use pyrolysis:
Pyrolysis is used in the production of chemical compounds, mainly, but not only, in the research laboratory.
The area of boron-hydride clusters started with the study of the pyrolysis of diborane (B
2H
6) at ca. 200 °C. Products include the clusters pentaborane and decaborane. These pyrolyses involve not only cracking (to give H
2), but also recondensation.[97]
The synthesis of nanoparticles,[98] zirconia[99] and oxides[100] utilizing an ultrasonic nozzle in a process called ultrasonic spray pyrolysis (USP).
Polycyclic aromatic hydrocarbons (PAHs) can be generated from the pyrolysis of different solid waste fractions,[12] such as hemicellulose, cellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). PS, PVC, and lignin generate significant amount of PAHs. Naphthalene is the most abundant PAH among all the polycyclic aromatic hydrocarbons.[103]
When the temperature is increased from 500 to 900 °C, most PAHs increase. With increasing temperature, the percentage of light PAHs decreases and the percentage of heavy PAHs increases.[104][105]
Thermogravimetric analysis (TGA) is one of the most common techniques to investigate pyrolysis with no limitations of heat and mass transfer. The results can be used to determine mass loss kinetics.[5][19][6][37][73] Activation energies can be calculated using the Kissinger method or peak analysis-least square method (PA-LSM).[6][37]
TGA can couple with Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry. As the temperature increases, the volatiles generated from pyrolysis can be measured.[106][82]
In TGA, the sample is loaded first before the increase of temperature, and the heating rate is low (less than 100 °C min−1). Macro-TGA can use gram-scale samples to investigate the effects of pyrolysis with mass and heat transfer.[6][107]
Pyrolysis mass spectrometry (Py-GC-MS) is an important laboratory procedure to determine the structure of compounds.[108][109]
In recent years, machine learning has attracted significant research interest in predicting yields, optimizing parameters, and monitoring pyrolytic processes.[110][111]
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