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'''Naphtha''' is an intermediate hydrocarbon liquid stream derived from the [[Petroleum refining processes|refining]] of [[crude oil]].<ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref><ref name=Leffler>{{cite book|author=Leffler, W.L. |title=Petroleum refining for the nontechnical person|edition=2nd Edition|publisher=PennWell Books|year=1985|id=ISBN 0-87814-280-0}}</ref>  It is most usually [[Hydrodesulfurization|desulfurized]] and then [[Catalytic reforming|catalytically reformed]], which re-arranges or re-structures the [[hydrocarbon]] [[molecules]] in the naphtha as well as breaking some of the molecules into smaller molecules to produce a high-[[octane]] component of [[gasoline]] (or [[petrol]]).


Some refineries also produce a small amount of specialty naphthas for use as solvents and those specialty naphthas are subjected to purification processes other than catalytic reforming.
== Where the naptha is obtained ==
The first unit process in a petroleum refinery is the [[Petroleum refining processes#The crude oil distillation unit|crude oil distillation unit]]. The overhead liquid distillate from that unit is called ''virgin'' or ''straight-run'' naphtha and that distillate is the largest source of naphtha in most petroleum refineries.  The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial [[boiling point]] of about 35 °C and a final boiling point of about 200 °C, and it contains [[paraffin]], [[naphthene]] (cyclic paraffins) and [[aromatic]] hydrocarbons ranging from those containing 4 [[carbon]] [[atom]]s to those containing about 10 or 11 carbon atoms.
The virgin naphtha is often further distilled to produce a ''light'' naphtha containing most (but not all) of the hydrocarbons with 6 or less [[carbon]] [[atoms]] and a ''heavy'' naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C.
It is the virgin heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high-octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics (most particularly [[benzene]]) that gasoline may contain.<ref>[http://www.ec.gc.ca/CEPARegistry/regulations/detailReg.cfm?intReg=1 Canadian regulations on benzene in gasoline]</ref><ref>[http://www.ukpia.com/industry_issues/environment_air_quality_health_safety/benzene_in_petrol.aspx United Kingdom regulations on benzene in gasoline]</ref><ref>[http://www.washingtonpost.com/wp-dyn/content/article/2006/03/01/AR2006030102113.html USA regulations on benzene in gasoline]</ref>
== Types of virgin naphthas ==
It should be noted that there are a great many petroleum crude oil sources worldwide and each crude oil has its own unique composition or [[assay]]. Also, not all refineries process the same crude oils and each refinery produces its own virgin naphthas with their own unique initial and final boiling points. In other words, naphtha is a generic term rather than a specific term.
The table just below lists some fairly typical virgin heavy naphthas, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:
{| class="wikitable"
|+ Typical Heavy Naphthas
|-
! Crude oil name <math>\Rightarrow</math><br>Location <math>\Rightarrow</math>
! Barrow Island<br>Australia<ref>[http://www.santos.com/library/barrow_crude.pdf Barrow Island crude oil assay]</ref>
! Mutineer-Exeter<br>Australia<ref>[http://www.santos.com/library/refining_characteristics.pdf Mutineer-Exeter crude oil assay]</ref>
! CPC Blend<br>Kazakhstan<ref>[http://crudemarketing.chevron.com/overview.asp?cpc CPC Blend crude oil assay]</ref>
! Draugen<br>North Sea<ref>[http://www.statoil.com/STATOILCOM/crude/svg02659.nsf/UNID/C9AC3EF9CE76B0DFC1256B5600528D6D/$FILE/Dra4kv02.pdf Draugen crude oil assay]</ref>
|-
| Initial boiling point, °C ||align=center|149||align=center|140||align=center|149||align=center|150
|-
| Final boiling point, °C ||align=center|204||align=center|190||align=center|204||align=center|180
|-
| Paraffins, liquid volume % ||align=center|46||align=center|62||align=center|57||align=center|38
|-
| Naphthenes, liquid volume % ||align=center|42||align=center|32||align=center|27||align=center|45
|-
| Aromatics, liquid volume % ||align=center|12||align=center|6||align=center|16||align=center|17
|}
== Cracked naphthas ==
Some refinery naphthas also contain some [[Olefin|olefinic]] hydrocarbons, such as naphthas derived from the [[fluid catalytic cracking]], [[visbreaker]]s and [[coking]] processes used in many refineries. Those olefin-containing naphthas are often referred to as ''cracked'' naphthas.
In some (but not all) petroleum refineries, the cracked naphthas are desulfurized and catalytically reformed (as are the virgin naphthas) to produce additional high-octane gasoline components.
== References ==
{{reflist}}

Revision as of 23:34, 31 January 2008

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