Coking: Difference between revisions
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{{related|[[Coke (fuel)]], a carbon-rich solid obtained by coal pyrolysis}} |
{{related|[[Coke (fuel)]], a carbon-rich solid obtained by coal pyrolysis}} |
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'''Coking''' is the heating of [[coal]] in the absence of air (oxygen) to a temperature above 600 |
'''Coking''' is the heating of [[coal]] in the absence of air (oxygen) to a temperature above 600 °C, to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content, called "[[Coke (fuel)|coke]]". Coke consists almost entirely of [[hydrocarbons]]. The porousity gives it a high surface area, which makes it burn faster (as does a sheet of paper versus a wooden log). When a kilogram of coke is burned it releases more heat than a kilogram of the original coal. |
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Coke is strong enough to be used as the fuel in a [[blast furnace]]. In a |
Coke is strong enough to be used as the fuel in a [[blast furnace]]. In a continuous process, coke, iron ore, and limestone are mixed together, and placed in the top of the blast furnace, and at the bottom liquid iron, and waste slag, are removed. The raw materials continuously move down the blast furnace. During this continuous process more raw materials are placed at the top, and the coke must withstand the ever-increasing weight of the raw materials above it. It is the ability to withstand this crushing force, in addition to its high energy content and rapid combustion, that makes coke ideal for use in blast furnaces. |
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==Petroleum coking== |
==Petroleum coking== |
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“Coking is a refinery unit operation that upgrades material called bottoms from the atmospheric or vacuum distillation column into higher-value products and produces petroleum coke—a coal-like material.” |
“Coking is a refinery unit operation that upgrades material called bottoms from the atmospheric or vacuum distillation column into higher-value products and produces petroleum coke—a coal-like material.”.<ref>{{cite website=|title=U.S. Energy Information Administration|title= “Coking is a Refinery Process that Produces 19% of Finished Petroleum Product Exports”|https://www.eia.gov/todayinenergy/detail.php?id=9731}}</ref> In [[heterogeneous catalysis]], the process is undesirable because the [[Clinker (waste)|clinker]] blocks the catalytic sites. Coking is characteristic of high temperature reactions involving hydrocarbons feedstocks. Typically coking is reversed by combustion, provided that the catalyst will tolerate such.<ref>{{cite journal|title="Coking" of zeolites during methanol conversion: Basic reactions of the MTO-, MTP- and MTG processes|journal=Catalysis Today|volume=154|pages=183–194|doi=10.1016/j.cattod.2010.05.012|author=H. Schultz}}</ref> |
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A simplified equation for coking is shown in the case of [[ethylene]]: |
A simplified equation for coking is shown in the case of [[ethylene]]: |
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A more realistic but complex view involves the [[alkylation]] of an aromatic ring of a coke nucleus. [[solid acid|Acidic]] catalysts are thus especially prone to coking because they are effective at generating [[carbocation]]s (i.e., alkylating agents). |
A more realistic but complex view involves the [[alkylation]] of an aromatic ring of a coke nucleus. [[solid acid|Acidic]] catalysts are thus especially prone to coking because they are effective at generating [[carbocation]]s (i.e., alkylating agents). |
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Coking is one of several mechanisms for the deactivation of a [[heterogeneous catalyst]]. Other mechanisms include [[sintering]], [[catalyst poisoning|poisoning]], and [[Phase transition|solid-state transformation]] of the catalyst.<ref>{{cite journal|title=Catalyst Deactivation|authors=Forzatti, P.; Lietti, L.|journal=Catalysis Today|year=1999|volume=52|pages= |
Coking is one of several mechanisms for the deactivation of a [[heterogeneous catalyst]]. Other mechanisms include [[sintering]], [[catalyst poisoning|poisoning]], and [[Phase transition|solid-state transformation]] of the catalyst.<ref>{{cite journal|title=Catalyst Deactivation|authors=Forzatti, P.; Lietti, L.|journal=Catalysis Today|year=1999|volume=52|pages=165–181|doi=10.1016/S0920-5861(99)00074-7}}</ref><ref>{{cite journal|last1=Bartholomew|first1=Calvin H|title=Mechanisms of Catalyst Deactivation|journal=Applied Catalysis A: General|volume=212|issue=1–2|pages=17–60|doi=10.1016/S0926-860X(00)00843-7|year=2001}}</ref> |
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==References== |
==References== |
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Revision as of 01:38, 3 November 2019
Coking is the heating of coal in the absence of air (oxygen) to a temperature above 600 °C, to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content, called "coke". Coke consists almost entirely of hydrocarbons. The porousity gives it a high surface area, which makes it burn faster (as does a sheet of paper versus a wooden log). When a kilogram of coke is burned it releases more heat than a kilogram of the original coal.
Coke is strong enough to be used as the fuel in a blast furnace. In a continuous process, coke, iron ore, and limestone are mixed together, and placed in the top of the blast furnace, and at the bottom liquid iron, and waste slag, are removed. The raw materials continuously move down the blast furnace. During this continuous process more raw materials are placed at the top, and the coke must withstand the ever-increasing weight of the raw materials above it. It is the ability to withstand this crushing force, in addition to its high energy content and rapid combustion, that makes coke ideal for use in blast furnaces.
Petroleum coking
“Coking is a refinery unit operation that upgrades material called bottoms from the atmospheric or vacuum distillation column into higher-value products and produces petroleum coke—a coal-like material.”.[1] In heterogeneous catalysis, the process is undesirable because the clinker blocks the catalytic sites. Coking is characteristic of high temperature reactions involving hydrocarbons feedstocks. Typically coking is reversed by combustion, provided that the catalyst will tolerate such.[2]
A simplified equation for coking is shown in the case of ethylene:
- 3 C2H4 → 2 C ("coke") + 2 C2H6
A more realistic but complex view involves the alkylation of an aromatic ring of a coke nucleus. Acidic catalysts are thus especially prone to coking because they are effective at generating carbocations (i.e., alkylating agents).
Coking is one of several mechanisms for the deactivation of a heterogeneous catalyst. Other mechanisms include sintering, poisoning, and solid-state transformation of the catalyst.[3][4]
References
- ^ Template:Cite website=
- ^ H. Schultz. ""Coking" of zeolites during methanol conversion: Basic reactions of the MTO-, MTP- and MTG processes". Catalysis Today. 154: 183–194. doi:10.1016/j.cattod.2010.05.012.
- ^ "Catalyst Deactivation". Catalysis Today. 52: 165–181. 1999. doi:10.1016/S0920-5861(99)00074-7.
{{cite journal}}: Unknown parameter|authors=ignored (help) - ^ Bartholomew, Calvin H (2001). "Mechanisms of Catalyst Deactivation". Applied Catalysis A: General. 212 (1–2): 17–60. doi:10.1016/S0926-860X(00)00843-7.