ABSTRACTthe overall liquid yield and easing the conditions of operation.The process is based on the separation of n-paraffins fromheavy naphtha by adsorption, then processing n-paraffins in adedicated C7+ isomerization unit and non-paraffinic heavynaphtha in a reformer.

In a C7+ isomerization unit, n-paraffins will be isomerized atoptimum operating conditions, and the isomerate producedcan be sent directly to the gasoline pool. The reformer unitwith non-paraffinic feed will be operated at mild operatingconditions, and the products can be blended into the gasolinepool as required or can be used for petrochemicals. The absenceof n-paraffins in the feed will allow operating the reformer atmild operating conditions, which is expected to increase theliquid yield up to 10 wt%, substantially improve catalyst lifeand increase hydrogen production. Additionally, the separa-tion of aromatics and the purification of hydrogen from theconcentrated reformer effluents will be easier and cheaper.

INTRODUCTION

Gasoline is a complex mixture of hydrocarbons containing car-bon atoms — 5 to 12 — and having a boiling point range of40 °C to 190 °C. Modern reformulated gasoline is a blend ofseveral refining streams, which fulfills certain specificationsdictated by both performance requirements and governmentregulations. Typical gasoline blending streams are presented inTable 11-3.

Gasoline is a complex mixture of hydrocarbons containing 5to 12 carbon atoms and having a boiling point range of 40 °Cto 190 °C. It is a blending of many streams from various refin-ing processes, which fulfills certain specifications dictated byboth performance requirements and government regulations.Reformate makes up approximately one-third of the gasolinepool, and with its 60 vol% to 70 vol% aromatic content, ithas been the main octane source for gasoline over the years.Gasoline specifications have been gradually changing in pastyears due to the regulations dictated by safety and environ-mental concerns. With the decrease of aromatics in gasoline,the role of reformate as the main octane source is expected toshrink. Based on this trend and the restriction on aromaticcontent, it is believed that future gasoline will be mostlybranched paraffins.

The reduction of aromatics in gasoline will create a big oc-tane gap, and refineries will have to find economic solutions toclose the octane gap and prepare for the future. Isomerizationof gasoline range n-paraffins, C7-C12, is one of the more eco-nomical and environmentally acceptable ways to address thearomatic issue and ease the octane gap. The novel process pro-posed here is a step in the direction of helping refineries in thissearch. The process, which involves the parallel operation of aC7+ paraffin isomerization unit with a reformer, will also cre-ate additional benefits for refineries by substantially increasing

A New Refining Process for EfficientNaphtha Utilization: Parallel Operationof a C7+ Isomerization Unit with aReformer Authors: Dr. Cemal Ercan, Dr. Yuguo Wang and Dr. Rashid M. Othman

Blending Compound Gasoline (vol%) Comments

Desired Gasoline Specifi cations

Specifi cations Range

FCC Naphtha 30 – 50 Has ~30 vol% aromatics and 20 to 30 vol% olefi ns Octane number 90 – 95

LSR Gasoline (Naphtha) 2 – 5 Sulfur (max) 10 – 15 ppm

Reformate 20 – 40 Has ~60 to 65 vol% aromatics Aromatics (max) 25 – 30 vol%

Alkylate 10 – 15 Benzene (max) < 1 vol%

Isomerate (C5/C6) 5 – 10 Olefi ns (max) 10 – 18 vol%

Oxygenate (MTBE) 10 – 15 Oxygen (max) 2 – 2.7 wt%

Butanes < 5 Vapor Pressure (max) 7 – 8 psia

Table 1. Gasoline blending streams of modern refinery with typical compositions and properties

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aromatics. Since the aromatics are the principal source of oc-tane, decreasing the aromatic level will create an octane gap inthe gasoline pool. As such, octane maintenance will continueto be a challenge for refineries.

The trends in changing gasoline specifications can be sum-marized as follows:

• A high octane number will still be required — ~95Research Octane Number (RON) — which means thatthe demand for high performance will stay or evenincrease.

• The aromatic content will continue to be reduced,dropping below 35 vol%. The U.S. has already loweredit below 30 vol%.

• The benzene content will be lowered to < 1.0 vol%. It isexpected eventually to be phased out.

• The sulfur content will be reduced to ~10 ppm and isexpected to be reduced further.

• The olefin content will continue to be reduced,dropping below 10 vol%.

• Vapor pressure will be low, around 7.0 psi.Reformulated gasoline specifications after January 1,1998, introduced a major reduction in the distillationrange. New specifications will completely eliminate lightproducts, such as C4.

• The optimal oxygen content will be maintained — max2.7 wt%.

As the aromatic content of gasoline goes down, the portionof reformate in the gasoline pool has to go down, too, since re-formate is the main source of aromatics. Therefore, refineriescan no longer heavily rely on reformate — or aromatics — asan octane source, and alternative octane sources are needed.An ecologically sound way of closing the octane gap due to the

Fluid catalytic cracking (FCC) naphtha and reformate makeup approximately two-thirds of the volume of gasoline. Sinceboth FCC naphtha and reformate contain high levels of aro-matics and olefins, they are also the major octane source forgasoline. Figure 1 summarizes the octane values of various refining streams.

Over the years, safety and environmental concerns havecaused gasoline specifications to change, and as a result, re-fineries have changed their operations and gasoline composi-tions accordingly. As an example, the evolution of Europeangasoline specifications over the years is presented in Table 2,which shows a gradual change of the gasoline specificationsfrom 1994 to 2010. A more or less similar trend is observed inother parts of the world1.

Table 2 also shows a gradual decrease in aromatic, olefinand benzene levels while the octane value remains high. TheU.S. already requires aromatic levels of less than 30 vol%,with benzene levels limited to 0.8%. Furthermore, the aro-matic level limit in gasoline will soon fall even lower; particu-larly as distillation end points (usually characterized as the90% distillation temperature) are lowered, thereby disallowingthe high boiling point portion of gasoline — which is largely

European

1994 1995 2000 2005 2010

Sulfur, wt ppm max 1,000 500 150 50/10 < 10

Aromatics, vol% max — — 42 35 < 35

Olefi ns, vol% max — — 18 18 <10

Oxygen, wt% max — 2.7 2.7 2.7 —

Benzene, vol% max 5.0 — 1.0 1.0 < 1.0

RVP, psi max 5.8 – 10.2 — 6.5 – 8.7 6.5 – 8.7 6.5 – 8.7

Distilled at 100 °C (min), v/v% 54 – 65 — 46 – 71 46 – 71 46 – 71

Distilled at 150 °C (min), v/v% — — 75 75 75

RON/MON (min) — — 95/85 95/85 95/85

Table 2. European gasoline specifications

Fig. 1. Octane values of various refinery streams.

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conventional feed to a reformer, e.g., heavy naphtha, containsmostly C7-C12 paraffins, naphthenes and aromatics. The pur-pose of reforming is to produce aromatics from naphthenesand paraffins for use in various applications. Among the groupof chemicals, aromatics go through the reforming reactor asthey are; naphthenic dehydrogenation to aromatics is rapidand efficient. So, naphthene conversion — dehydrogenation —goes almost to completion at the initial part of the reactor orin the first reactor of a multi-reactor reforming unit (the latterrequiring an even less severe operation) at a mild temperature.

Paraffins are very difficult to convert, however, and requirea higher temperature and longer residence time in the reformer.Some conversion of the paraffins occurs toward the end of thereactor system at highly severe operating conditions, wheremost of the paraffins undergo cracking into light gases. There-fore, to increase the paraffin conversion, highly severe opera-tion conditions are needed, which decreases liquid yield due toexcessive cracking. The cracking of paraffins also decreases thehydrogen yield. As shown in Fig. 3, although the octane num-ber increases due to the concentrated aromatic content, a sub-stantial liquid yield loss is observed.

Therefore, in a conventional reformer, aromatics are prima-rily made via the dehydrogenation of naphthenes, and paraf-fins are considered to be the main source of liquid loss due tocracking. Hydrogen is also produced primarily by naphthenedehydrogenation4, 5.

Heavy naphtha, which is normally fed into a reformer, con-tains paraffins, naphthenes and aromatics. According to itsparaffin content, heavy naphtha is classified as lean or richnaphtha. The naphtha with a high concentration of paraffins isreferred to as lean naphtha. Lean naphtha is difficult toprocess and typically produces too much light — cracked —products, so has a low liquid yield. In comparison, rich naph-tha makes the reforming unit’s operation much easier andmore efficient, so it is more desirable as a reformer feed thanlean naphtha. The rich naphtha is relatively easier to processand has a higher liquid yield. Figure 4 schematically illustratesthe typical conversions of lean and rich naphthas at typical re-former operating conditions, and also indicates that for this

reduction of aromatics is by increasing the concentration ofthe branched alkanes at the expense of normal paraffins. Con-sequently, an increase in iso-alkanes with a high octane num-ber is desirable.

The novel refining process described here is intended to address the octane gap generated as a result of aromatic reduc-tion in gasoline. The new process will also provide a substantialimprovement in the performance of the reformer.

PROCESS

The novel process for refining naphtha proposed4 here beginswith first separating a naphtha feed into light naphtha —C5/C6 paraffins — and heavy naphtha. Second, introducinglight naphtha to the first isomerization unit — C5/C6 isomer-ization — under usual isomerization conditions will produce alight isomerate, separating the heavy naphtha into a heavy n-paraffin — C7+ n-paraffins — and a heavy non-paraffinicnaphtha. Third, introducing the heavy n-paraffins to the sec-ond isomerization unit — C7+ isomerization unit — under dif-ferent isomerization operating conditions will produce a heavyisomerate. Fourth, introducing the heavy non-paraffinic naph-tha to a reforming unit under milder reforming conditions willproduce reformate. Finally, combining at least a portion ofeach of the light isomerates, the heavy isomerate and the refor-mate will form a gasoline blend. Figure 2 is the process flowdiagram of the proposed novel process.

In this process, the initial steps — separating a naphtha feedinto light naphtha and heavy naphtha, and processing the lightnaphtha in the C5/C6 isomerization unit — is a standard refin-ing process, and nothing is new about it. Novelty comes afterthat, i.e., separating the heavy naphtha into heavy n-paraffins,C7 – C12, and heavy non-paraffinic fractions, then processingthese fractions in C7 – C12 isomerization and reforming units,respectively. To understand the advantages of this novelprocess, the chemistry going on inside the reformer first needsto be reviewed in detail.

As previously mentioned, the reformate with high aromaticcontent is typically the main octane source for gasoline. The

Fig. 2. Process flow diagram of the proposed novel process for naphtha processing4. Fig. 3. Reformate yields and aromatic content of a typical reformer.

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typical case, the reformate produced using a rich naphtha hasa liquid yield of approximately 10 wt% greater than the refor-mate produced using a lean naphtha — basically due to thepresence of low levels of paraffins.

Therefore, paraffin conversion in a reformer is consideredslow, inefficient and unable to produce the desired products.The most desirable reaction in the reformer is dehydrogenationof naphtha to aromatics, which also produces 3 moles of hy-drogen per mole of naphtha dehydrogenated. Because isomer-ization is an equilibrium reaction where low temperaturefavors isomerization to normal, the reformer temperature istoo high for a quantifiable amount of paraffin isomerization tooccur. Similarly, hydro-cyclization of paraffins does not occurin an appreciable amount in the reformer. So, in a conven-tional reformer, naphthene dehydrogenation to aromatics isthe main aromatic — octane — maker, with hydrogen produc-tion an added result of this reaction.

To summarize, paraffins in a reformer mostly undergocracking, thereby reducing the liquid yield, and require other-wise unnecessarily severe operating conditions and a longerresidence time (or more reactors). The separation of n-paraf-fins from heavy naphtha with a known method, such as ad-sorption, therefore produces a much more desirable feedstock— one with negligible n-paraffin content — for the reformer.With this kind of feedstock, reformer performance is expectedto be improved, as will be discussed next.

Typically, heavy naphtha feed contains around 10% to 40%of n-paraffins. Separating the n-paraffins from heavy naphthawith adsorption produces two feedstocks, namely heavy n-paraffins, C7+, and heavy naphtha without n-paraffins, or non-paraffinic heavy naphtha. Non-paraffinic heavy naphtha is afeedstock ideal for a reformer — due to its negligible paraffiniccontent. With the reduction of paraffins within the heavy non-paraffin naphtha, the naphthene and aromatic content in-creases, and the feedstock becomes rich naphtha. Theprocessing of this feedstock in a reformer is easier, and the performance of the reforming unit improves substantially; ahigher liquid yield is achieved at a lower reactor temperature,

which means a longer catalyst life. Figure 5 shows the expected increase in liquid yield and the

decrease in operating temperature as a function of naphtheneplus aromatics in the feedstock5. The points in Fig. 5 show ex-perimental data for the operating temperature and liquid yield,C5+ liquid product, as a function of the total percentage ofnapthene plus aromatics in the reformer feed. As seen, with thereduction of paraffins within the heavy naphtha, the naph-thene plus aromatics content of the feed increases. As thenaphthene plus aromatics content increases, the C5+ liquidyield increases, and the reaction temperature decreases. There-fore, the performance of the reformer improves substantially— providing a higher liquid yield due to less cracking and alonger catalyst life due to lower reactor temperature. The ex-pected increase in liquid yield and decrease in operating tem-perature can be estimated from Fig. 5.

The next question is: What to do with the heavy n-paraf-fins? Although the heavy n-paraffins, as they are, present a desirable feedstock for a steam cracker to produce lightolefins, the proposed process uses a dedicated C7+ isomeriza-tion unit to produce branched paraffins, which can be blendedinto gasoline. As previously mentioned, the operating tempera-ture of a reformer is not suitable for isomerization. On theother hand, a dedicated C7+ isomerization unit operating atoptimum temperature will substantially improve isomerizationwhile also minimizing cracking. The following example clearlyillustrates the benefits of the proposed process.

Assume that 100 kg of heavy naphtha — of which 60 wt%are paraffins, 27.5 wt% are naphthenes, and 12.5 wt% arearomatics — is sent to a reformer under typical reforming con-ditions. The resulting reformates would include 20.4 kg ofnon-aromatics and 47.6 kg of aromatics, thereby yielding a total liquid yield of 68 kg, or 68 wt% of the original feed.

Now, assume that the same amount of naphtha, which hasthe same composition, is used as a feedstream. But, beforesending the heavy naphtha to the reformer, approximately 40kg of paraffins, about 67%, are extracted from it and sent to

Fig. 5. Reactor temperature and reformate yield a function of naphthene plusaromatics (N+A) value; reaction conditions: 100 RON, p = 30 bar, WHSV = 2.0 h-1,and H2/HC = 4.5.

Fig. 4. Schematics of typical conversion of lean and rich naphthas in a reformer: A =aromatics, N = naphthenes, and P = paraffins.

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the C7+ isomerization unit. The remaining 60 kg of heavynaphtha is sent to a reformer, which can operate at a mildercondition due to the lower paraffin content — including at alower temperature of approximately 10 °C to 20 °C. The re-sulting reformate includes 13.4 kg of non-aromatics and 40.6kg of aromatics, for a total liquid yield of about 54 kg, whichis about 90 wt% of the reformer feed. Meanwhile, the secondisomerization unit has produced a total liquid yield from theextracted paraffins of approximately 95 wt% — 38 kg out of40 kg. Therefore, the overall total liquid yield for both the iso-merization unit and the reformer is approximately 92 wt%.So, a net increase in liquid is 24 wt%. The summary of the results for both cases is presented in Table 3.

CONCLUSIONS

A new process for the efficient processing of naphtha, which is based on separating C7+ n-paraffins from heavy naphtha,processing non-paraffinic heavy naphtha in a reformer andprocessing C7+ n-paraffins in a C7+ isomerization unit, is pro-posed. This unique process, using the parallel operation of areformer and a C7+ isomerization unit, produces branched C7+

paraffins to be used in gasoline, concentrated reformate for usein gasoline as needed as well as in petrochemicals, and hydro-gen, also for various uses. The absence of n-paraffins in the reformer feed allows the operating of the reformer at milderconditions with a substantial improvement in liquid yield. Thebenefits of this new process can be summarized as follows:

• Improved reformer performance: Higher liquid yield —minimum 10 wt% higher than yields from aconventional reformer — and hydrogen production.

• Milder operating conditions: ~10 °C lower temperature,which has a positive effect on catalyst life.

• Shorter residence time in the reformer or a reducednumber of reformer reactors.

• Reformate with a high aromatic content, making thearomatic separation for petrochemical use easier.

• Higher hydrogen concentration in the off-gas due to lesscracking, making hydrogen purification also easier.

• An octane booster: Dedicated C7+ isomerization atoptimum operating conditions will provide thenecessary branched paraffins.

• The ability to revamp existing extra reformers toisomerization.

• Flexibility in blending streams at the desired levels forgasoline.

ACKNOWLEDGMENTS

The authors would like to thank the management of SaudiAramco for their support and permission to publish this article.

REFERENCES

1. Ercan, C., Dossary, M. and Wang, Y.: “GasolineSpecifications: Historical Trend & the Future,” Focus, Fall2009, pp. 12.

2. Ercan, C.: “C7 – C10 n-Paraffin Isomerization,”presentation at R&DC, Saudi Aramco, May 28, 2011.

3. Wang, Y., Dossary, M., Sameer, G. and Ercan, C.: “Review

The fi rst isomerization (C5/C6 Isomerization) is not included because its performance is the same in both cases.

Case I Case II-A Case II-B

Reformate Feed Reformate Feed C7+ Isomerization

Feedstock (units) 100 60 40

C5+ Yield (wt%) 68 90 95

Heavy Naphtha wt% wt%

Paraffi ns 60 33.33 100

Naphthenes 27.5 Non-aromatics 29.96 45.83 24.77 100

Aromatics 12.5 Aromatics 70.04 20.83 75.23

Total 100 Total 100 100 100

N+A 40 RON 100 105 +20

Total Liquid Yield (wt%) 68 54 38

Case I: Reformer runs at typical operating conditions to obtain RON of 100.Case II: Reformer runs at milder conditions and C7+ Isomerization runs at temperature lower than 300 °C.

Table 3. Comparison of performance of stand-alone reformer (Case I) and parallel operation of a reformer and a C7+ isomerization unit

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of C7 – C10 Paraffin Isomerization,” Proceedings of theFuture Challenge for Catalysis Workshop, King FahdUniversity of Petroleum and Minerals, Dhahran, SaudiArabia, May 2009.

4. Ercan, C., Wang, Y., Dossary, M. and Othman, R.M.:“Process Development by Parallel Operation of ParaffinIsomerization Unit with Reformer,” U.S. Patent 8,808,534B2, August 19, 2014.

5. Antos, G.J. and Aitani, A.M. (editors): Catalytic NaphthaReforming, CRC Press, Boca Raton, Florida, 2004, 624 p.

BIOGRAPHIES

Dr. Cemal Ercan joined SaudiAramco’s Research & DevelopmentCenter in 2005 and is now a memberof the Oil & Gas Treatment R&DDivision of the R&D Center. He hasmore than 25 years of experience inthe oil and gas, and petrochemicals

industries.Prior to joining the company, Cemal had worked for

ABB Lummus Global, Bloomfield, NJ, as a Senior &Principal Process Development Engineer; for theSyntroleum Corporation in Tulsa, OK, as a TechnicalManager; and for ConocoPhillips as a Chief Engineer.

He received his B.S. and M.S. degrees from Middle EastTechnical University, Ankara, Turkey, and his Ph.D. degreefrom McGill University, Montreal, Quebec, Canada, all inChemical Engineering.

Dr. Yuguo Wang joined SaudiAramco’s Research & DevelopmentCenter in 2006 and is now a memberof the Oil & Gas Treatment R&DDivision of the R&D Center.Previously, he had worked for theCenter for Applied Energy Research

and Fossil Fuel Science at the University of Kentucky,Lexington, KY, and as a Modeling Engineer at CypressSemiconductors.

Yuguo has more than 15 years of experience in the coal,and oil and gas industries.

He received his B.S. degree in Physics from ShandongUniversity, Shandong, China, and his Ph.D. degree inChemistry from the University of Kentucky, Lexington, KY.

Dr. Rashid M. Al-Othman is a ScienceConsultant in the Oil & GasTreatment R&D Division of SaudiAramco’s Research & DevelopmentCenter. He has 30 years of experiencewith Saudi Aramco, during which hehas completed internal assignments in

both the Ras Tanura Refinery and Shedgum Gas Plant andan external assignment at the French Institute forPetroleum.

Rashid received his B.S. degree from Seattle University,Seattle, WA, and M.S. and Ph.D. degrees from theUniversity of Washington, Seattle, WA, all in Chemistry.

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