Reactive flash volatilization

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Reactive flash volatilization (RFV) is a chemical process that rapidly converts nonvolatile solids and liquids to volatile compounds by thermal decomposition for integration with catalytic chemistries.

Contents

Chemistry

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The utilization of heavy fossil fuels or biomass rich in carbohydrates, (C6H10O5)n, for fuels or chemicals requires an initial thermochemical process called pyrolysis which fractures large polymers to mixtures of small volatile organic compounds (VOCs). A specific method of pyrolysis of biomass, termed "fast pyrolysis," converts particles of biomass to about 10% carbon-rich solid called char, about 15% gases such as carbon dioxide, and about 70% a mixture of organic compounds commonly referred to as "bio-oil" at 500 °C in 1–2 seconds. [ dead link ]

Pyrolysis: Biomass + Heat → 0.70VOCs + 0.10Char + 0.15Gases

The volatile organics can be collected as a brown, highly acidic liquid for further thermochemical conversion by traditional processes such as steam reforming, gasification, catalytic partial oxidation, catalytic cracking, combustion, or hydrotreating.

Catalytic steam reforming: VOCs + H2O + Heat + Catalyst → H2 + CO + Catalyst
Catalytic partial oxidation: VOCs + O2 + Catalyst → H2 + CO + Heat + Catalyst
Catalytic combustion: VOCs + O2 + Catalyst → CO2 + H2O + Heat + Catalyst

These two sets of chemistries, pyrolysis and catalytic processing, are combined to form the reactive flash volatilization process. Solid hydrocarbons or biomass are contacted with high temperature (500–900 °C) catalysts to generate gases and volatile organic compounds. [1] The volatile species flow into the catalyst with a reactant (H2, O2, or H2O) to convert to desirable products (H2, CO, H2O, CO2, or VOCs).

RFV: Biomass + heat + Reactant + Catalyst → Gases + VOCs + Reactant + Catalyst → Products + Catalyst

Discovery

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Reactive flash volatilization was demonstrated in 2006 in the journal Science by the high temperature (700–800 °C) conversion of soybean oil (triglycerides) and sugar (D-(+)-glucose) to synthesis gas (H2 + CO) and olefins (ethylene and propylene). [2] Complete, continuous catalytic conversion of heavy fuels was surprising, because the initial pyrolytic chemistry has been shown to generate significant amounts of solid residue called "char" which was expected to block the necessary interaction between the reactant compounds and the solid metal catalyst. [ dead link ]

The process has been described, "The low volatility of these biofuel feedstocks not only leads to soot production when they are used directly in internal combustion engines but also causes them to coat industrial catalysts with a deactivating layer of carbon, thus hindering their conversion to lighter products. James Richard Salge and colleagues show that if heavy fuels such as soybean oil or biodiesel are sprayed onto hot rhodium-cerium catalysts as fine droplets in the presence of oxygen, the fuels can self-heat and fully react to form hydrogen without carbon formation and catalyst deactivation." [3] RFV: Triglyceride + O2 + Catalyst → Ethylene + Propylene + CO2 + H2O + Catalyst

The process converted 70% of the atomic hydrogen in soy-oil triglycerides to molecular H2, and 60% of atomic carbon to carbon monoxide on a Rh-based catalyst with Cerium supported on alpha-alumina. [4] Under different operating conditions, the process can produce a significant amount of ethylene and propylene. [5]

The first demonstration of reactive flash volatilization occurred by a series of experimental steps: [6]

  1. The researchers start with either pure soybean oil or a thick sugar syrup.
  2. The reactor consists of an automotive fuel injector, used to spray the oil or syrup as fine droplets through a tube. Sitting like a plug in the tube is a porous ceramic disk made of a rhodium-cerium catalyst material.
  3. As the droplets hit the disk-whose surface temperature is 1,000 °C-the heat and oxygen break apart the molecules of oil or sugar.
  4. The catalyst guides the breakdown toward the production of syngas rather than toward water vapor and carbon.
  5. The syngas passes through the porous disk and is collected downstream in the tube.
  6. No external heating is needed because the chemical reactions release enough heat to break up molecules of oil or sugar following in their wake.

An initial supply of heat is necessary to achieve temperatures of 300 °C, after which the reaction initiates, or "lights off," and quickly rises to temperatures of 700–800 °C. Under steady conditions, the reaction generates sufficient heat to maintain the high temperature, extremely fast chemistry. [7] The total time for conversion of heavy, nonvolatile compounds to volatile or gaseous species occurs in milliseconds (or thousandths of a second).

Application to Solid Biomass

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Reactive flash volatilization of solid particles composed of cellulose, starch, lignin, Quaking Aspen ( Populus tremuloides ) wood chips, and polyethylene was demonstrated in 2007 in the scientific journal Angewandte Chemie . [8] Particles of cellulose were completely converted to syngas (H2 and CO) and combustion products (H2O and CO2) in as little as 30 milliseconds. Catalytic reforming of all materials occurred without the requirement of an external heat source while operating at 500–900 °C. Under optimal conditions, 50% of all atomic hydrogen and 50% of all atomic carbon can be converted to molecular H2 and carbon monoxide in as little time as 30 milliseconds. Reaction chemistry was demonstrated on both a Rh-Ce/alumina catalyst and a Ni-Ce/alumina catalyst. [8]

A publication in the scientific journal Green Chemistry demonstrated that the process of reactive flash volatilization can be considered a combination of several other global chemistries occurring through thermal and chemical integration. [9] As shown in the diagram at the right, the initial pyrolysis chemistry occurs when the biomass particle (green) physically contacts the hot catalyst (orange). Volatile organic compounds (VOCs) flow into the catalyst with oxygen, adsorb on Rh atoms, and react to form combustion products (H2O and CO2) and syngas (H2 and CO). After this initial chemistry, three main global reactions occur. Combustion products react catalytically with syngas by the water-gas shift reaction. Also, volatile organics react catalytically with steam (H2O) to form new combustion products and syngas. Finally, the volatile organics can crack homogeneously in the gas phase to form smaller volatile organics. [8]

The operating temperature has been shown to vary within the catalyst length while also being a strong function of the biomass-to-oxygen ratio. An experimental examination has shown that the heat required to thermally fracture biomass was generated within the catalyst bed by surface oxidation reactions. The temperature profile (and reaction temperature) was shown to be extremely important to prevent the formation of carbon at equilibrium. [9] Very fast conversion has been attributed to high operating temperatures, but the maximum cellulose processing rate has not been determined. [10] However, catalytic partial oxidation of volatile organic compounds has shown that complete conversion can occur in less than 10 milliseconds. [11]

Related Research Articles

Hydrocarbon Organic compound consisting entirely of hydrogen and carbon

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 with only weak odours. Because of their diverse molecular structures, it is difficult to generalize further. Most anthropogenic emissions of hydrocarbons are from the burning of fossil fuels including fuel production and combustion. Natural sources of hydrocarbons such as ethylene, isoprene, and monoterpenes come from the emissions of vegetation.

Syngas Fossil fuel derived from other hydrocarbon sources

Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. The name comes from its use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas is usually a product of coal gasification and the main application is electricity generation. Syngas is combustible and can be used as a fuel of internal combustion engines. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII. However, it has less than half the energy density of natural gas.

Pyrolysis Thermal decomposition of materials at elevated temperatures in an inert atmosphere

The pyrolysis process is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".

Gasification Form of energy conversion

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 (CO
2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

Cracking (chemistry) Process whereby complex organic molecules are broken down into simpler molecules

In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of a large alkane into smaller, more useful alkenes. Simply put, hydrocarbon cracking is the process of breaking a long chain of hydrocarbons into short ones. This process requires high temperatures.

Propene, also known as propylene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like odor.

The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen or water gas into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The process was first developed by Franz Fischer and Hans Tropsch at the Kaiser-Wilhelm-Institut für Kohlenforschung in Mülheim an der Ruhr, Germany, in 1925.

Steam reforming or steam methane reforming is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:

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 of limited amounts of oxygen or other reagents, catalysts, or solvents, such as steam or phenols. It is an application of pyrolysis. The process breaks up or 'cracks' large molecules. Coke, coal gas, gaseous carbon, coal tar, ammonia liquor, and coal oil are examples of commercial products historically produced by the destructive distillation of coal.

Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most common process chain is "Coal to Liquid Fuels" (CTL).

Charring is a chemical process of incomplete combustion of certain solids when subjected to high heat. Heat distillation removes water vapour and volatile organic compounds (syngas) from the matrix. The residual black carbon material is char, as distinguished from the lighter colored ash. By the action of heat, charring removes hydrogen and oxygen from the solid, so that the remaining char is composed primarily of carbon. Polymers like thermoset, or most solid organic compounds like wood or biological tissue, exhibit charring behaviour.

Biomass to liquid is a multi-step process of producing synthetic hydrocarbon fuels made from biomass via a thermochemical route.

Pyrolysis oil, sometimes also known as bio-crude or bio-oil, is a synthetic fuel under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C with subsequent cooling. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, immiscibility with fossil fuels, thermal instability, and a tendency to polymerize 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.

Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas, partial oxidation of methane, and coal gasification. Other methods of hydrogen production include biomass gasification, no CO2 emissions methane pyrolysis, and electrolysis of water. The latter processes, methane pyrolysis as well as water electrolysis can be done directly with any source of electricity, such as solar power.

Thermal oxidizer

A thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.

Lanny D. Schmidt American physical chemist

Lanny D. Schmidt was an American chemist, inventor, author, and Regents Professor of Chemical Engineering and Materials Science at the University of Minnesota. He is well known for his extensive work in surface science, detailed chemistry (microkinetics), chemical reaction engineering, catalysis, and renewable energy. He is also well known for mentoring over a hundred graduate students and his work on millisecond reactors and reactive flash volatilization.

Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet biomass, and other macromolecules, into crude-like oil under moderate temperature and high pressure. The crude-like 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.

Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.

Paul Dauenhauer, a chemical engineer and MacArthur Fellow, is the Lanny Schmidt Honorary Professor at the University of Minnesota (UMN). He is recognized for his research in catalysis science and engineering, especially, his contributions to the understanding of the catalytic breakdown of cellulose to renewable chemicals, the invention of oleo-furan surfactants, and the development of catalytic resonance theory.

References

  1. ↑ Van Noorden, Richard (2006-11-02). "How best to use biomass?". Chemistry World. Royal Society of Chemistry.
  2. ↑ Salge, JR; Dreyer, BJ; Dauenhauer, PJ; Schmidt, LD (2006). "Renewable Hydrogen from Nonvolatile Fuels by Reactive Flash Volatilization". Science. 314 (5800): 801–804. Bibcode:2006Sci...314..801S. doi:10.1126/science.1131244. PMID   17082454. S2CID   24891756.
  3. ↑ Bitterman, Mark (2006-11-07). "Vegetable oil or Nuclear fission". Cleantech Blog. Cleantech.org. Archived from the original on 2012-07-22.
  4. ↑ Gates, Bruce C.; George W. Huber; Christopher L. Marshall; Phillip N. Ross; Jeffrey Siirola; Yong Wang (April 2008). "Catalysts for Emerging Energy Applications". MRS Bulletin. 33 (4): 429–435. doi: 10.1557/mrs2008.85 .
  5. ↑ USapplication 20080237542,Lanny D. Schmidt, Paul J. Dauenhauer, Bradon J. Dreyer, James R. Salge, David Rennard,"Reactive Flash Volatilization of Fluid Fuels"
  6. ↑ "Flash volatilization: a new biomass-to-liquids process". Biopact. 2006-11-04.
  7. ↑ Curtin, Ciara (2006-11-03). "Biofuels Discovery Promises to End Dependence on Natural Gas". Scientific American.
  8. 1 2 3 Dauenhauer, Paul J.; Dreyer, Bradon J.; Degenstein, Nick J.; Schmidt, Lanny D. (2007). "Millisecond Reforming of Solid Biomass for Sustainable Fuels". Angewandte Chemie International Edition. 46 (31): 5864–7. CiteSeerX   10.1.1.614.932 . doi:10.1002/ange.200701238. PMID   17610233.
  9. 1 2 Colby, Joshua L.; Paul J. Dauenhauer; Lanny D. Schmidt (2008). "Millisecond Authothermal Steam Reforming of Cellulose for Synthetic Fuels by Reactive Flash Volatilization". Green Chemistry. 10 (7): 773–783. CiteSeerX   10.1.1.1007.860 . doi:10.1039/b804691c.
  10. ↑ George W. Huber, ed. (2008). "Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels: Next Generation Hydrocarbon Biorefineries" (PDF). National Science Foundation.Cite journal requires |journal= (help)
  11. ↑ Dauenhauer, P.; Salge, J.; Schmidt, L. (2006). "Renewable Hydrogen by Autothermal Steam Reforming of Volatile Carbohydrates". Journal of Catalysis. 24 (2): 238. doi:10.1016/j.jcat.2006.09.011.
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