Penex
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The Penex process is a continuous catalytic process used in the
refining Refining is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum w ...
of
crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...
. It isomerizes light
naphtha Naphtha (, recorded as less common or nonstandard in all dictionaries: ) is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it can also be produced from natural-gas condensates, petroleum distillates, and ...
(C5/C6) into higher-octane, branched C5/C6
molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s. It also reduces the concentration of benzene in the gasoline pool. It was first used commercially in 1958. Ideally, the isomerization catalyst converts normal pentane (nC5) to isopentane (iC5) and normal hexane (nC6) to 2,2- and 2,3-dimethylbutane. The thermodynamic equilibrium is more favorable at low temperature.


Background

In the
petroleum industry The petroleum industry, also known as the oil industry, includes the global processes of hydrocarbon exploration, exploration, extraction of petroleum, extraction, oil refinery, refining, Petroleum transport, transportation (often by oil tankers ...
, much research has been done on the upgrading of light
hydrocarbons 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; their odor is usually faint, and may b ...
. The realisation that normal pentane is one of the most important remaining components of naphtha that can be easily upgraded prompted Phillips Petroleum to investigate the various processes for converting normal (linear) pentane into (branched) isopentane. The decisive factor in the isomerisation of normal pentane is an increase in the total octane number. This improvement in quality makes the result more valuable for blending with today's high-octane fuels. In addition, like other isoparaffins, isopentane has a low sensitivity (research octane minus engine octane) which means improved performance at street octane. Increasing the octane number also allows larger quantities of pentanes to be blended into premium petrol. In a refinery, light naphtha can come from the distillation column ("straight-run naphtha") or from other processes, for example the cracking units.


Process

During isomerisation, the low-octane normal hydrocarbons are converted into their higher-octane isomers. For this purpose, the feed material is passed over a fixed bed catalyst in the presence of hydrogen. The hydrogen is continuously circulated in the reactor circuit. The Penex process uses fixed-bed
catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s containing chlorides. As this is an equilibrium reaction, 100% conversion of the normal isomers is not achieved. The maximum octane number of the product is achieved by separating the unconverted normals using a
molecular sieve A molecular sieve is a material with pores of uniform size comparable to that of individual molecules, linking the interior of the solid to its exterior. These materials embody the molecular sieve effect, in which molecules larger than the pore ...
(Molex technology) and returning them to the reactor.


Results

A single pass of feedstock with an
octane rating An octane rating, or octane number, is a standard measure of a liquid fuel, fuel's ability to withstand Compression ratio, compression in an internal combustion engine without causing engine knocking. The higher the octane number, the more compres ...
of 50-60 through such a bed typically produces an end product rated at 82-86. If the feedstock is subsequently passed through a DIH (deisohexanizer) column, the end product typically has an octane rating of 87-90.5. If the feedstock is subsequently passed through a Molex-technology column, the end product typically has an octane rating of 88-91. If the feedstock is first passed through a DIP (deisopentanizer) column to remove iso-pentanes, then through the Penex bed, and subsequently through the DIH column, the end product typically has an octane rating of 91-93.


Field use

The Penex Process is licensed by the UOP corporation and currently utilized at more than 120 units at
petroleum refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petr ...
and
natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
liquids plants throughout the world.


References


External links


UOP's Website on C5/C6 Penex Process
Chemical processes Oil refining {{petroleum-stub