Pyrolysis

Pyrolysis (/paɪˈrɒlɪsɪs/; ; from Ancient Greek πῦρ (pûr) 'fire' and λύσις (lúsis) 'separation') is a process involving the separation of covalent bonds in organic matter by thermal decomposition within a chemically inert environment without oxygen.

Quotes

Methane has not been generally used as a feedstock in simple thermal cracking... because the decomposition temperature is too high and yield of useful products too low. Nevertheless... pyrolysis of methane has been used for the production of acetylene and carbon black... Diamonds can be formed... under suitable conditions... [E]arly stages of...decomposition are... well understood... but... details of later stages are not... clear... All oxidation reactions, including oxidative pyrolysis, have been excluded.
- Margaret H. Back & Robert A. Back, "Thermal Decomposition and Reactions of Methane" (1983) Ch.1 Pyrolysis: Theory and Industrial Practice ed., Lyle F. Albright, Billy L. Crynes, William H. Corcoran, pp. 1-2.

[A]n overall model for the simulation of pyrolysis reactors should... include the heat, momentum, mass-balances differential equations, physicochemical properties (specific heats, enthalpies, thermal conductivities, etc.) firing-box patterns, and sometimes fluid dynamic characterization (as in advanced cracking reactors).
- Mario Dente, Eliseo M. Ranzi, "Mathematical Modeling of Hydrocarbon Pyrolysis Reactions" (1983) Ch.7 Pyrolysis: Theory and Industrial Practice ed., Lyle F. Albright, Billy L. Crynes, William H. Corcoran, p. 135.

Flash pyrolysis has the potential of producing maximum yields of gases and liquids from coal and organic solid wastes such as municipal refuse, tree bark, cow manure, rice hulls and grass straw using simple process equipment. The main features of the process are near ambient pressure, no requirement for added chemicals, low capital investment, high feed throughput flexibility of feedstock, variability of temperature, and minimum feed pretreatment.
- James R. Loganbach, Fred Bauer, Fuels and Chemicals by Pyrolysis (1976) Ch. 27, Industrial and Laboratory Pyrolyses: Symposiums p. 476.

The pyrolysis of ethane and propane is often the process of choice for the production of ethylene. ...Marketing of the products of from ethane pyrolysis is greatly simplified by the low yield of by-products. ...Pyrolysis of ethane and propane produces the lowest yield of byproducts, which... minimizes the size of downstream units... as the depropanizer, debutanizer, and compressors.
- Christopher F. McConnell, Billy D. Head, "Pyrolysis of Ethane and Propane" (1983) Ch.2 Pyrolysis: Theory and Industrial Practice ed., Lyle F. Albright, Billy L. Crynes, William H. Corcoran, pp. 26-27.

The Pyrolysis of Carbon Compounds (1929)

by Charles Dewitt Hurd. A Source.

Fire, as the agent for destructive distillation, was a favorite tool of the alchemist. Although the general prevalence... of pyrolysis has long been recognized... in the last six decades... the subject has assumed a scientific basis. Since many... data on thermal decompositions have been incidental observations... the information is widely scattered... [T]hat ...records of many melting-point determinations are accompanied by ..."It melts with decomposition" is ...evidence ...the subject ...has ...an unorganized past.

The transformation of a compound into another substance, or... substances, through... heat alone is... pyrolysis.

Frequently, pyrolyses are thermal decompositions, but... "Pyrolysis" is... broader... [and] more concise. In "decompositions", there is... formation of at least two simpler substances. In pyrolyses... not always... [R]earrangements may be caused by heat alone. ...[F]ormation of large molecules ...is often effected by heat. Both ...are pyrolytic ...but it would be awkward to classify them as decompositions.

Some compounds decompose at the temperature of boiling water... others require red heat. ...[C]ompounds may be stable at -40° but not at 0°. All... if caused by temperature alone, are... pyrolysis.

[T]he great majority of pyrolyses occur at "high" temperatures, but this only means... familiarity with compounds which cannot exist at ordinary temperatures is... extremely limited.

Occasionally... it will be helpful to note the effect of catalysts... Frequently in thermal decompositions, it is difficult to distinguish between the catalytic and the non-catalytic. ...Glass, quartz or porcelain surfaces are the ones which are most used in laboratory pyrolyses. Their catalytic action is, at the best, very slight.
- Ref: Paul Sabatier, Catalysis in Organic Chemistry (1922) Tr. E. Emmet Reid, D. Van Nostrand Co.

In larger scale work... metallic surfaces [are usually necessary]. Wilson and Bahlke... reported that in cracking stills... chromium-steels ("stainless" steels) [are best], or aluminum or calorized iron. Copper and some bronzes are not satisfactory, neither... [is] monel... These authors were interested in corrosion...
- Ref: Robert E. Wilson and W.H. Bahlke, "Special Corrosion Problems in Oil Refining" Ind. Eng. Chem. 17, 355 (1925)

Franz Fischer... performed... pyrogenic experiments in a tinned-iron tube, which would have failed in an iron tube because of carbon deposition or other causes. ...[He] has shown that a ferrous sulfide inner lining [formed by passing hydrogen sulfide through] in an iron tube also prevents carbon deposit[s] ...
- Ref: 1) Fischer, Chem. Abstracts 15, 590, 886 (1921); Brit. Pat. 152.960. 2) Fischer and Zerbe, Brennstof-Chem. 4, 309 (1923); Chem. Abstracts 18, 674 (1924)

The subject of wood distillation has... been treated in... this series. ...[W]ood is not a compound.
- Ref: 1) Hawley, "Wood Distillation," New York, Chemical Catalog Co. (1923) 2) Hawley and Wise, "The Chemistry of Wood," ibid. (1926)

[S]ubstances... identified among... products of wood distillation may be arranged... in a few groups of related compounds. Much of the accurate knowledge... is due to the work of Klason.
- Ref: 1) Klason, vom Heidenstam and Norlin, Arkiv Kemi. Mineral. Geol. 3, 1-34 (1908); 2 & 3) Z. angew. Chem. 25, 1205 (1909); 27, 1252 (1910). 4) Klason, J. prakt. Chem. [2] 90, 413 (1914)

The groups from [wood distillation] are
1. Acids; formic to caproic, especially acetic acid. Also, furoic, angelic, lignoceric acids, and valerolactone. For different woods, the total acid, calculated as acetic acid, varies between 4.3 and 6.8[%]... In vacuum distillation... formic acid may be... as high as 35[%] of the acetic acid, but in ordinary distillation at atmospheric pressure, it varies from 10-20[%] of the acetic acid. Only these two acids appear to be formed in appreciable amounts. 2. Alcohols; especially methanol and allyl alcohol, but also isoamyl and isobutyl alcohols, and buten-3-ol-2. The methanol content is usually... 1.3-2[%]. 3. Esters; formed by interaction of the above acids and alcohols. 4. Ketones; acetone... and... its homologs... [plus] small quantities of cyclopentanone, methyl cyclopentanone, and diacetyl. The acetone is not a primary [distillation] product... but is formed secondarily from the acetic acid... homologs of acetone have a similar history. 5. Aldehydes; formaldehyde, acetaldehyde, methylal and dimethyl acetal, valeric aldehyde, furfural and methyl furfural. The pentosans are... the source of the furfural and other... homologs of furan... 6. Phenols and phenol methyl ethers [only about 1 percent of the wood distilled], mostly methyl ethers of di- and triphenols. ...These substances come largely from the lignin. 7. [< 0.2 percent of the total] Ammonia, methyl amine, pyridine and methyl pyridine... 8. Toluene, m-xylene, melene, etc. 9. Gases; the yields of carbon dioxide, carbon monoxide and methane vary with the maximum temperature of distillation, but at 350-400° the yields from hardwoods are about 8, 4 and 1.5[%], respectively. 10. Water; the yield... varies... 22.3-27.8[%]. 11. Charcoal. ...30-45[%] ...depending on the wood, and on the maximum temperature.

Pyrolytic Methods in Organic Chemistry (1980)

by Roger F.C. Brown

The destructive distillation of mineral or organic material was one of the few preparative methods available to the alchemists and the first chemists. That materials could undergo profound changes at high temperatures became a well-recognized principle... emphasized by... landmarks as the formation of sulfuric acid by heating ferrous sulfate (copperas) described by Basil Valentine... Brandt's discovery of phosphorus in 1669 by destructive distillation of residues from urine... isolation of benzene from oil gas by Faraday in 1825 and of pyrrole from bone oil by Runge in 1834.
- Note: See Benzene#Discovery

Mineral acids, alkalis, and many other inorganic reagents were available... in the early nineteenth century... [T]heir use often added to... descriptive organic chemistry... without clarifying structural relationships. ...[V]igorous pyrolysis of organic compounds, involving no addition of further groups, remained a common technique until about the end of the nineteenth century. ...[M]any high-temperature reactions are fragmentations which produce simple products ...[D]irect decarboxylation of ...carboxylic acids and ...similar decomposition of carboxylic salts by heating with lime or soda lime are... examples.

Mitscherlich prepared benzene as early as 1834 by vigorous distillation of benzoic acid and lime.

Coal pyrolysis (1982)

by George R. Gavalas, Coal Science and Technology Vol. 4.

Prompted by the need of non-petroleum-based fuels, coal research has reemerged... Pyrolysis research... has gained... momentum because of its close connection to combustion, hydropyrolysis and liquification. Spectroscopic and other instrumental techniques are... producing... information about coal structure and pyrolysis mechanisms, while modeling efforts are breaking new ground in sorting out chemical and physical phenomena... [P]ostulates and assumptions of current work provide a meaningful starting point in... theoretical descriptions of greater validity and applicability.

[T]he survey of experimental results will be confined to flash pyrolysis at the exclusion of slow pyrolysis or carbonization.

Flash pyrolysis poses three experimental difficulties..: (i) control and measurement of the temperature-time history of the coal particles (ii) suppression of secondary reactions (iii) quantitative collection of products.

[M]easurement of the coal particles' temperature is not trivial. In many cases the temperature... must be calculated from a heat transfer model. The other two experimental problems, the suppression of secondary reactions and the collection of products, depend on the reactor geometry and flow pattern...

[P]roduct distribution is the most essential information relative to the commercial utilization of pyrolysis and... sheds considerable light on reaction mechanisms.

[P]roducts can be classified into two groups relative to the temperature dependence of the yields. Tar, water and carbon dioxide evolve at lower temperatures with ultimate yields that are essentially independent of temperature above 700°C. The second group... of gaseous hydrocarbons, carbon monoxide and hydrogen evolve at higher temperatures. The ultimate yield of these... continues increasing... up to 1,000°C or higher.

In bituminous coals, tar makes up 50-80% of the weight loss, the remaining consisting of hydrocarbon gases, water and carbon dioxide.

We are... concerned with the evolution of tar and gases during the plastic state of coal. In this... mass transfer consists of two processes in series: diffusion through the molten coal to some internal surface, that of a bubble or a pore; and transport with the bubble or through the pore to the surface of the particle. The role of preexisting pores is not well understood. ...[A] certain fraction of preexisting pores (< 60 Å) collapse during pyrolysis perhaps due to surface tension effects. Pores... 60-300 Å were preserved... but one could not distinguish preexisting pores and pores generated by the evolution of bubbles. It appears likely... the major... mass transfer occurs via bubbles while preexisting bubbles play a... minor role.

Fast pyrolysis of biomass (1999)

: A Handbook Abstract & Introduction by A. V. Bridgewater.

Fast pyrolysis is a new technology that shows... potential for producing... liquid... for fuel applications or as a source for... chemicals.

Wood and biomass can be used in a variety of ways to provide energy:
• by direct combustion... for... heating.., steam production and hence electricity generation.
• by gasification to provide fuel gas... for heat, or in an engine or turbine for electricity generation.
• by fast pyrolysis to provide a liquid fuel... for fuel oil in... static heating or electricity generation... [and] to produce... chemicals.

Fast pyrolysis is a high temperature process in which biomass is rapidly heated in the absence of oxygen. ...[I]t decomposes to generate mostly vapours... aerosols and some charcoal. After cooling and condensation, a... liquid is formed which has a heating value about half... conventional fuel oil. ...Fast pyrolysis ...is carefully controlled to give high yields ...

[E]ssential features...
• high heating and heat transfer rates... usually requires finely ground biomass feed
• carefully controlled... reaction temperature... [~]500C... vapour phase... short vapour residence typically [<]2 sec...
• rapid cooling of pyrolysis vapours to give... bio-oil product.

[M]ain product, bio-oil... in yields up to 80%... with byproduct char and gas... used within... process so no waste...

Chemistry of Fossil Fuels and Biofuels (2013)

by Harold H. Schobert

Pitch is a highly viscous residue remaining from wood pyrolysis... In the days of sailing ships, pitch was extremely valuable to seal the wood planking and for... where a tightly sticking, water-resistant material was needed.

Eventually it was understood that the charcoal residue from a fire came from... insufficient oxygen (air) to consume the wood completely. From that... came... recognition of making charcoal deliberately by heating wood in the absence of air, or burning under severely air-limited conditions. ...[I]t was [later] realized ...volatile materials "cooked" out ...during conversion... also had valuable uses.

Production of charcoal... with [other] chemical products... involves pyrolysis, i.e. decomposition of compounds through application of heat.

Because pyrolysis converts wood to highly carbonaceous... charcoal... [it] is also known as carbonization. Since volatile compounds are driven off, but... residual non-volatile[s are] altered.., another name... is destructive distillation.

[T]hermal decomposition of wood begins [≈]250°C. Industrial carbonization... at ≈500°C.

Carbonization drives off moisture... with... low molecular weight organic compounds... from extractives and... pyrolysis of ... biopolymers. Condensing vapors from carbonization produces... pyroligneous acid... a dilute solution of up to 50 small, polar (...[i.e.] water soluble) organic compounds. ...[M]ost important ...are acetic acid, acetone, and methanol.

Condensable non-aqueous ...wood tars ...[are] produced by pyrolysis and destructive distillation. Tars can be fractionated into [1] light oils, boiling below 200°C... [2] heavy tars, boiling above that... and [3] pitch. Light tars tend to be mixtures of aldehydes, carboxylic acids, esters, and ketones. Heavy oil contains... phenol derivatives; one of its uses... a wood preservative... wood tar creosote...

In fuel chemistry... we deal with several kinds of bond, and mixtures of... different compounds. At temperatures high enough to drive pyrolysis of... one kind of bond... other kinds... break... [I]mmediate products may undergo... subsequent reactions. As a result, pyrolysis... give[s] complex mixtures of products... of little utility if the intent is to produce a single product...

With... peat... sealed within layers of inorganic sediment... long... geological processes can operate. Assuming typical geothermal gradients... [b]urial to 10 km would be equivalent to... 100-300°C. These... seem too low to drive... pyrolysis reactions... significant at... [≈]350°C. But... time is on our side... in geological time, tens of millions of years for catagenesis of humic kerogen.

Like their aliphatic counterparts, the smaller phenols are also water-soluble. Phenol... has... solubility...[≈]82 g/kg water. ...Phenols are produced in coal and wood pyrolysis. Any water used in such processes becomes contaminated with phenols (as well as other compounds) and requires processing before being released... into the environment.

The organic material in oil shales requires pyrolysis to force the catagenesis of kerogen... This can be done above ground in kilns, or underground with the shale still in place.

Gasification of coal... [goes] back to the 1790s at least. Before World War II, the United States... had... [≈20,000] small coal gassifiers... a popular fuel gas until... the interstate natural gas pipeline network... after World War II. Many... were simple pyrolysis or steam-carbon reactions in... crude equipment having serious environmental problems.

Groundwater could become contaminated by organic compounds during coal pyrolysis, and by various inorganic compounds liberated as the coal is consumed. Some... pose problems for environmental quality or human health.

To a large extent, biomass gasification resembles coal gasification, with some distinctions... The kinds... considered... include wood, wood wastes (e.g. sawdust), and municipal solid wastes. Some... grass, such as switchgrass... grown as energy crops might also serve... [R]elative to coal, biomass usually has lower calorific value... and sulfur... higher moisture, higher... hydrogen and oxygen, and produces a higher yield of volatiles on pyrolysis. ...Generally biomass chars are more reactive than coal chars, so... may[be]... less steam and oxygen are needed for... [its] gasification.

[L]iquids can be produced from coal by... pyrolysis... by dissolution... [i.e.] solvent extraction... or by reaction of coal with hydrogen or with solvents... donating hydrogen (hydroliquification). All... constitute... coal-to-liquids (CTL) technology.

Pyrolysis of biomass, heavy petroleum fractions, oil sands, oil shale, and coal usually produces some amount of liquid product. Pyrolysis... without an externally added... hydrogen [source] is constrained... Pyrolysis produces liquids, but leaves a residue of carbonaceous char or coke. Usually... gases also form. The... proportions of solid, liquid, and gas depend on the... feedstock and... reaction conditions.

[L]arge particles may not be heated uniformly... consequently pyrolysis yields are less. Heating rate is also important. During slow heat-up as... in simple... kilns most coals begin to decompose [≈]350-400°C. ...[L]iquid and gaseous products ...peak ...[≈]425-475°C. This phase of pyrolysis ends ...[≈]500-550°C. ...[V]ery rapid heating [e.g.] in entrained flow gasifiers ...quickly by-passes this stage, so... evolution of liquids is nil.

Coal pyrolysis is... complicated... by the fact... primary pyrolysis products... are... able to react among themselves... with steam... from the moisture in the coal... with char or coke, or... several of these. The products... often called secondary... may differ... from the primary... Primary products can be studied... if... quench[ed]... rapidly or... [fed] directly into a suitable... instrument... [e.g.] a gas chromatograph.

In industrial practice... design of the pyrolysis reactor affects... composition of liquid products, because... [it] determines how long... primary products are exposed to pyrolysis temperatures...

Commercial... applications of pyrolysis have been to produce... a gaseous fuel... or a char... Liquids... directly are unsuitable... as fuels... Some... downstream operations would be required... Nevertheless, low-temperature tars can be refined... into gasoline or diesel fuel.

Possibly, future events on the world energy scene will revive interest... Pyrolysis offers... simplicity of process and equipment design relative to gasification and hydroliquification. ...[But] competing technologies usually provide high yields of a single type... gas, liquid or solid... which may offset the added complexity and cost...

[R]ules change when an external supply of hydrogen is... available. Hydropyrolysis, i.e. pyrolizing coal in a hydrogen atmosphere, increases the yields of liquids and gases... [H]ydrogen... stabilizes radicals by hydrogen capping before... termination by recombination reactions that... lead to char... Despite this advantage... hydropyrolysis has never been commercialized.

[S]tories... about "free oil" from coal pyrolysis, often in reference to a low-temperature carbonization... by Lewis Karrick... [≈]80 years ago. Many... accompanied by... conspiracy theories... The Karrick process, and similar carbonization processes... produce a liquid. Presumably, a... clever accountant could figure out how this... could be "free," provided... markets existed for... large amounts of char and gas produced at the same time, and... could be sold... high enough to compensate for giving away the liquid. Then there's the cost of refining the low-temperature tar into specification-grade marketable fuel...

Often... terms carbonization and pyrolysis are used almost interchangeably. Pyrolysis has the broader meaning: breaking... molecules by... heat or thermal energy. ...[P]yrolysis ...could be run to make gases and liquids rather than solids as the primary product. Carbonization... narrowly defined, refers to conversion of a starting material into carbon, or a carbon-rich solid. ...[One can] pyrolyze a hydrocarbon feedstock for the purpose of carbonization, but carbonization is not... pyrolysis by another name. Carbonization can be effected without heat as... primary driving force... Carbonization driven by thermal energy usually requires >500°C.

Pyrolysis of an oil product or natural gas leads to thermal blacks. ...Acetylene black is made by thermal decomposition of acetylene. ...[P]reheated to 800°C ...acetylene is introduced and... because the pyrolysis is exothermic, the temperature... reaches ~2500°C. Carbon black formation takes place... [800°C-~]2000°C. ...2000-2500°C induces partial graphitization of the carbon black. Due to... partial graphitic nature, acelylene blacks have... applications where good [electrical and thermal] conductivity... or... very low chemical reactivity is desirable.

Almost all pyrolysis reactions are endothermic because they involve breaking bonds in stable compounds.

Pyrolysis of fossil or biofuels... is... accompanied by char formation. In some cases, this is the point... charcoal being an example. ...[I]f pyrolysis were ...done to make gaseous or liquid fuels, and no... market existed for the char, it would be possible to... bury the char... [which] would sequester carbon...

[P]yrolysis of biomass to produce char for carbon sequestration has multiple benefits... The product... is... called biochar or Agri-char, sometimes terra preta (dark earth)... Trials in Australia have produced a doubling... or tripling of crop production... [C]har is likely to retain some... nitrogen, phosphorus, and pottasium... Biochars are very porous... taking up and holding moisture. ...By ...stimulating plant growth, biochar has a double impact... First, it... sequesters carbon. Second... increased growth of plants removes CO, from the atmosphere...

Annual production of agricultural waste worldwide amounts to some four gigatonnes. A pyrolysis... that yielded only ten percent biochar could produce enough to fertilize some forty million hectares...

Kilns are... ancient technology. Biomass pyrolysis would be "low tech." Farmers could build and install their own... Alternatively, a biochar kiln could be mounted on... a truck... and taken from farm to farm...

A comprehensive biofuel program..: harvesting and shipping biomass to a centralized biomass or biodiesel plant within the economically limiting radius, and beyond... converting biomass to biochar in small, decentralized units.

External links

Wikipedia

Wikipedia has an article about:

Pyrolysis

In-Situ Catalytic Fast Pyrolysis Technology (Mar 31, 2013) by Mary J. Biddy, Abhijit Dutta, Susanne B. Jones, Aye Meyer, @UNT (University of Texas) Digital Library

YouTube videos
- 10 years designing top-of-the-line Pyrolysis Technology Biomass pyrolysis @ARTI channel.
- Process of Pyrolysis @Biofuels Edu channel.
- Technology of vortex processing of pyrolysis process from biomass @Garik Donagafonovich channel