Hydrous pyrolysis
Encyclopedia
Hydrous pyrolysis
refers to the thermal decomposition which takes place when organic compounds are heated to high temperatures in the presence of water
.
Steam cracking is used in the petroleum
industry to produce the lighter alkene
s. Steam cracking uses water in the gas
phase, whereas many hydrous pyrolysis processes use superheated water
in the liquid phase.
Hydrous pyrolysis may be a significant process in the creation of fossil fuel
s. Simple heating without water, anhydrous pyrolysis
has long been considered to take place naturally during the catagenesis
of kerogen
s to fossil fuels. In recent decades it has been found that water under pressure causes more efficient breakdown of kerogens at lower temperatures than without it. The carbon isotope
ratio of natural gas
also suggests that hydrogen
from water has been added during creation of the gas.
U.S. patent 2,177,557, describes a two-stage process in which a mixture of water, wood chips, and calcium hydroxide is heated in the first stage at temperatures in a range of 220 to 360 °C (428 to 680 F), with the pressure "higher than that of saturated steam at the temperature used." This produces "oils and alcohols" which are collected. The materials are then subjected in a second stage to what is called "dry distillation", which produces "oils and ketones". Temperatures and pressures for this Second stage are not disclosed.
Zhang et al., at the University of Illinois, report on a hydrous pyrolysis process in which swine manure is converted to oil by heating the swine manure and water in the presence of carbon monoxide in a closed container. For that process they report that a temperatures of at least 275 °C (527 °F) is required to convert the swine manure to oil, and temperatures above about 335 °C (635 °F) reduces the amount of oil produced. The Zhang et al. process produces pressures of about 7 to 18 Mpa
(1000 to 2600 psi
- 69 to 178 atm
), with higher temperatures producing higher pressures. Zhang et al. used a retention time of 120 minutes for the reported study, but report at higher temperatures a time of less than 30 minutes results in significant production of oil.
A commercialized process using hydrous pyrolysis (see the article Thermal depolymerization
) used by Changing World Technologies, Inc. (CWT) and its subsidiary Renewable Environmental Solutions, LLC (RES) to convert turkey offal reported by Adams et al. as a two-stage process, the first stage to convert the turkey offal to hydrocarbons at a temperature of 200 to 300 °C (392 to 572 F) and a second stage to crack the oil into light hydrocarbons at a temperature of near 500 °C (932 °F). Adams et al. report only that the first stage heating is "under pressure"; Lemley, in a non-technical article on the CWT process, reports that for the first stage (for conversion) a temperature of about 260 °C (500 °F) and a pressure of about 600 psi, with a time for the conversion of "usually about 15 minutes". For the second stage (cracking), Lemley reports a temperature of about 480 °C (896 °F).
The EROEI [Energy Returned On Energy Invested] of these processes is uncertain and/or has not been measured.
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...
refers to the thermal decomposition which takes place when organic compounds are heated to high temperatures in the presence of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
.
Steam cracking is used in the 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...
industry to produce the lighter alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s. Steam cracking uses water in the gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
phase, whereas many hydrous pyrolysis processes use superheated water
Superheated water
Superheated water is liquid water under pressure at temperatures between the usual boiling point and the critical temperature . It is also known as subcritical water and pressurized hot water...
in the liquid phase.
Hydrous pyrolysis may be a significant process in the creation of fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s. Simple heating without water, anhydrous 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...
has long been considered to take place naturally during the catagenesis
Catagenesis (geology)
Catagenesis is a term used in petroleum geology to describe the cracking process which results in the conversion of organic kerogens into hydrocarbons.-Theoretical reaction:...
of kerogen
Kerogen
Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the huge molecular weight of its component compounds. The soluble portion is known as bitumen. When heated to the right...
s to fossil fuels. In recent decades it has been found that water under pressure causes more efficient breakdown of kerogens at lower temperatures than without it. The carbon isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
ratio of natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
also suggests that 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...
from water has been added during creation of the gas.
U.S. patent 2,177,557, describes a two-stage process in which a mixture of water, wood chips, and calcium hydroxide is heated in the first stage at temperatures in a range of 220 to 360 °C (428 to 680 F), with the pressure "higher than that of saturated steam at the temperature used." This produces "oils and alcohols" which are collected. The materials are then subjected in a second stage to what is called "dry distillation", which produces "oils and ketones". Temperatures and pressures for this Second stage are not disclosed.
Zhang et al., at the University of Illinois, report on a hydrous pyrolysis process in which swine manure is converted to oil by heating the swine manure and water in the presence of carbon monoxide in a closed container. For that process they report that a temperatures of at least 275 °C (527 °F) is required to convert the swine manure to oil, and temperatures above about 335 °C (635 °F) reduces the amount of oil produced. The Zhang et al. process produces pressures of about 7 to 18 Mpa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(1000 to 2600 psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
- 69 to 178 atm
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
), with higher temperatures producing higher pressures. Zhang et al. used a retention time of 120 minutes for the reported study, but report at higher temperatures a time of less than 30 minutes results in significant production of oil.
A commercialized process using hydrous pyrolysis (see the article Thermal depolymerization
Thermal depolymerization
Thermal depolymerization is a depolymerization process using hydrous pyrolysis for the reduction of complex organic materials into light crude oil. It mimics the natural geological processes thought to be involved in the production of fossil fuels...
) used by Changing World Technologies, Inc. (CWT) and its subsidiary Renewable Environmental Solutions, LLC (RES) to convert turkey offal reported by Adams et al. as a two-stage process, the first stage to convert the turkey offal to hydrocarbons at a temperature of 200 to 300 °C (392 to 572 F) and a second stage to crack the oil into light hydrocarbons at a temperature of near 500 °C (932 °F). Adams et al. report only that the first stage heating is "under pressure"; Lemley, in a non-technical article on the CWT process, reports that for the first stage (for conversion) a temperature of about 260 °C (500 °F) and a pressure of about 600 psi, with a time for the conversion of "usually about 15 minutes". For the second stage (cracking), Lemley reports a temperature of about 480 °C (896 °F).
The EROEI [Energy Returned On Energy Invested] of these processes is uncertain and/or has not been measured.
External links
- A Possible Deep-Basin High-Rank Gas Machine Via Water Organic-Matter Redox Reactions, Leigh C. Price
- Surreptitiously converting dead matter into oil and coal - Water, Water Everywhere, Science News, February 20, 1993, Elizabeth Pennisi
- Hydrogen isotope systematics of thermally generated natural gases, Chris Clayton