2012-08_Reformate

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TECH TALKREFORMATE AND CATALYTIC REFORMING

OIL, GAS AND CHEMICALS SERVICE AUGUST 2012

Introduction

Reformate is a generic term for the product made from catalytic reforming, which is a chemical process usedto convert petroleum refinery naphthas, which typically have low octane ratings, into high-octane liquidcomponents for use in the manufacture or blending of gasoline.

In simple terms, the process re-arranges or re-forms the hydrocarbon molecules in the naphtha feedstocks, aswell as breaking some of the molecules into smaller molecules. The overall effect is that the product reformatecontains hydrocarbons with more complex molecular shapes having higher octane values than thehydrocarbons in the naphtha feedstock. In so doing, the process separates hydrogen atoms from thehydrocarbon molecules and produces very significant amounts of byproduct hydrogen gas for use in a numberof the other processes involved in a modern petroleum refinery. Other byproducts are small amounts ofmethane, ethane, propane, and butanes.

Typical Naphtha Feedstocks

A petroleum refinery includes many unit operations and unit processes. The first unit operation in a refinery isthe continuous distillation of the petroleum crude oil being refined - the straight run. The overhead liquid distillateis called naphtha, which becomes a major component of the refinery's gasoline production. The naphtha is amixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a finalboiling point of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons inthe range from C4 to C11

The naphtha from the crude oil distillation is often further distilled to produce a "light" naphtha containing most(but not all) of the hydrocarbons with 6 or fewer carbon atoms and a "heavy" naphtha containing most (but notall) of the hydrocarbons with more than 6 carbon atoms. The naphthas derived from the distillation of crude oils

are referred to as "straight-run" naphthas.

It is the heavy naphtha (>C6) that is usually processed in a catalytic reformer because the light naphtha (C6 orlower), when reformed, tends to crack into butane and lower molecular weight hydrocarbons which are notuseful as high-octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to formaromatics which are undesirable because governmental environmental regulations in a number of countries limitthe amount of aromatics (most particularly benzene) that gasoline may contain. Heavy naphtha has an initialboiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C

Process Description

One of the most commonly used types of catalytic reforming unit has three reactors, each with a fixed bed ofcatalyst. Such a unit is referred to as a semi-regenerative catalytic reformer (SRR). The process flow diagram

on Page 2 depicts a typical semi-regenerative catalytic reforming unit.

The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5 to 45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowing througha heat exchanger. The preheated feed mixture is then totally vaporized and heated to the reaction temperature(495 to 520 °C) before the vaporized reactants enter the first reactor. As the vaporized reactants flow throughthe fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromaticswhich is highly endothermic and results in a large temperature decrease between the inlet and outlet of thereactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream isreheated in the second fired heater before it flows through the second reactor. The temperature again

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decreases across the second reactor and the vaporized stream must again be reheated in the third fired heaterbefore it flows through the third reactor. As the vaporized stream proceeds through the three reactors, thereaction rates decrease and the reactors therefore become larger. At the same time, the amount of reheatrequired between the reactors becomes smaller. Usually, three reactors are all that is required to provide thedesired performance of the catalytic reforming unit.

The hot reaction products from the third reactor are partially cooled by flowing through the heat exchangerwhere the feed to the first reactor is preheated and then flows through a water-cooled heat exchanger beforeflowing through the pressure controller (PC) into the gas separator.

Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the recycle hydrogen gascompressor and the net production of hydrogen-rich gas from the reforming reactions is exported for use in theother refinery processes that consume hydrogen (such as hydrodesulfurization units and/or a hydrocracker unit).

The liquid from the gas separator vessel is routed into a fractionating column commonly called a stabilizer . Theoverhead offgas product from the stabilizer contains the byproduct methane, ethane, propane and butane gasesproduced by the hydrocracking reactions and it may also contain some small amount of hydrogen. That offgas isrouted to the refinery's central gas processing plant for removal and recovery of propane and butane. Theresidual gas after such processing becomes part of the refinery's fuel gas system.

The liquid product from the stabilizer is the high-octane liquid reformate that will become a component of therefinery's product gasoline.

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CatalystsMost catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina support base, andsome contain both platinum and rhenium. The noble metals (platinum and rhenium) are considered to becatalytic sites for the dehydrogenation reactions and the chlorinated alumina provides the acid sites needed forisomerization, cyclization and hydrocracking reactions.

The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is reduced over timeduring operation by carbonaceous coke deposition and chloride loss. The activity of the catalyst can beperiodically regenerated or restored by in situ high temperature oxidation of the coke followed by chlorination.Semi-regenerative catalytic reformers are regenerated about once per 6 to 24 months. Normally, the catalystcan be regenerated 3 or 4 times before it must be returned to the manufacturer for reclamation of the valuableplatinum and/or rhenium content.

Conclusion

Modern gasoline is a complex product and reformate is a major component of that production; however, theproduction of reformate is not the only catalytic reforming process that takes place in a refinery. It should not beconfused with the catalytic steam reforming used industrially to produce various products such as hydrogen,ammonia, and methanol or with various other catalytic reforming processes that use methanol or biomass-derived feedstocks to produce hydrogen for fuel cells or other uses. While not directly impacting out day to dayinspection activities, the production of reformate and the catalytic reforming process are aspects of our industrythat a well informed inspector should be aware of.

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Minutes of Tech Talk Meeting:

Branch:_______________________________ Divis ion: ______________________________

Person Conducting Meeting:__________________________________________________

At tendees:

Addi tional Items Discussed:

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The original is to be maintained at the Branch forreference and audit purposes. Data from this form isrequired as part of your monthly Global QHS&E reporting

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