Prime-G+TM: Commercial Performance

of FCC Naphtha Desulfurization

Technology

Axens 89, bd Franklin Roosevelt - BP 50802 92508 Rueil Malmaison Cedex -France Tel.: + 33 1 47 14 21 00 Fax: + 33 1 47 14 25 00 www.axens.net

Axens North America, Inc Houston Office 1800 St. James Place, Suite 500 Houston, TX 77056 - USA Tel.: + 1 713 552 9666 Fax: + 1 713 552 1007

Q. Debuisschert, J.L. Nocca

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Prime-G+™ Commercial Performance of FCC Naphtha Desulfurization Technology

Quentin Debuisschert Jean-Luc Nocca Axens Axens North America, Inc. 89, Bd Franklin Roosevelt- BP 50802 92508 Rueil-Malmaison Cedex 1800 St James, Suite 500 France Houston, TX 77056, USA e-mail: quentin.debuisschert@axens.net e-mail: jnocca@axensna.com Tel: 33 1 47 14 25 30 Tel: (1-713) 552-9666

www.axens.net

Introduction The last two decades have produced a significant demand increase for automotive fuels. Although fuel qualit ies (fuel reformulation) and engine efficiencies have constantly been improved, the increase in overall fuel consumption has resulted in an increase in overall emissions. Progressively stronger regulations have been enacted by most industrialized countries to reduce emissions from transportation engines. In particular, gasoline and diesel sulfur specifications are being tightened to allow advances in engine and catalytic converter technologies to be implemented to further reduce emissions. To meet the ultra-low vehicle emission specifications, the automotive industry has requested the introduction of sulfur-free fuels (i.e., sulfur < 10 ppm) as outlined in the Worldwide Fuel Charter. In the U.S., Tier II regulations call for an average gasoline sulfur level of 30 ppm in 2006 with a gradual phase-in starting in 2004. In most of Europe, gasoline sulfur will be capped at 50 ppm in 2005. However, a tax incentive policy, adopted by a number of countries, has resulted in an earlier introduction of low and ultra-low sulfur fuels. Germany has led Europe in this tax incentive policy introducing fuels containing less than 50 ppm sulfur in 2001 and less than 10 ppm in 2003. The European Union is now in the process of finalizing regulations limiting sulfur to 10 ppm in 2009. It is anticipated that most Western European refiners will be positioned to produce 10 wppm sulfur gasoline by 2005, well ahead of specified mandates. This article will focus on solutions provided by Axens, a company formed two years ago through the merger of IFP’s licensing division with Procatalyse Catalysts & Adsorbents, to meet the low sulfur gasoline regulations. Industrial results from the world leading technology, Prime-G+, are supplied for both European and North American refineries. Another route to ultra-low sulfur gasoline is described in this article. The OATS process, initially developed by BP and exclusively licensed by Axens, operates under mild conditions and requires neither fired heater nor compressor as it requires no hydrogen. Gasoline Sulfur Control Meeting gasoline regulations does not only imply severely limiting sulfur in FCC gasoline, the main sulfur contributor to the pool, but also in other streams, such as light straight run naphtha, thermally or steam cracked naphthas and butane streams. There are two methods for reducing

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FCC naphtha sulfur: FCC feed hydrotreating (pretreatment) or FCC naphtha desulfurization (post-treatment). Despite the numerous technical merits of FCC feed hydrotreating, the post-treatment route has been the method of choice due to its lower capital cost and lower hydrogen consumption.

Table 1 – Typical sulfur distribution in the US gasoline pool

Source Vol% of Pool Sulfur, ppm Sulfur Contribution,%

FCC Naphtha 35 1000 98

Others 65 10 2

Total 100 357 100

Gasoline desulfurization units must show good octane and gasoline yield retention to be economically viable. Other important factors include the ability to co-process, in the FCC naphtha hydrodesulfurization unit, other sulfur-containing gasoline streams and the ability to meet more drastic sulfur reductions with limited additional investment. Finally, having the flexibility to reduce olefins is also of potential interest to some refiners. Because gasoline production has become very complex due to the number of gasoline streams, specific country regulations, octane and/or hydrogen demand, types of crudes processed and requirements for gasoline or diesel maximization, there is no single solution to meet future regulations. However, such requirements can usually be met with the Prime-G+ and OATS technologies. Prime-G+ Prime-G+ is a commercially proven selective hydrodesulfurization technology for cracked naphtha. In addition to treating FCC naphtha, it offers the flexibility to co-process steam-cracker, light straight-run, and coker/VB naphthas. The Prime-G+ technology stems from extensive experience acquired by Axens in the field hydrodesulfurization of cracked naphtha and selective hydrogenation of LPG and gasoline streams. The increased requirement for high selectivity in HDS units has led to a refinement of the previous generation, non-selective, Prime-G process, and to the development of the dual catalyst concept of the Prime-G+ HDS process. Two main challenges must be addressed by a selective gasoline HDS technology: • Meet a long catalyst cycle, i.e., equivalent to the FCC turnaround (3-5 years) • Minimize octane loss at ultra-low product sulfur level. The required unit cycles are met not only by selecting adequate operating conditions and catalysts, to reduce catalyst deactivation, but also by minimizing polymerization reactions. Polymer formation is a major cause for unit shutdowns when processing cracked naphtha. The polymerization reaction rates increase with the diolefin concentration in FCC gasoline. Faced with the high number of compounds encountered in cracked naphtha, gas chromatography

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cannot identify all diolefins and severely underestimates their content in these streams. Diolefins are better estimated by Diene Value (DV) or Maleic Anhydride Value (MAV) measurements. Depending on FCC riser temperature, the quality of termination devices and FCC feed quality, typical diolefin content in full range FCC naphtha ranges from 0.5 to 2%. Such diolefin levels will, in most cases, prevent the attainment of long catalyst cycles due to pressure drop build-up in the HDS unit. Axens’ extensive experience has shown that proper engineering guidelines for HDS reaction section design coupled with a selective hydrogenation reactor upstream are keys in achieving the long operating cycle requirements. FCC Naphtha Splitting Typical olefin and sulfur distributions in the three main FCC naphtha distillation cuts are shown below in Figure 1.

0

10

20

30

40

50

60

Per Centof FCCN

Volume Olefin Contribution Sulfur Contribution

LightNaphtha

Mid-CutNaphtha

HeavyNaphtha

Figure 1 – FCC naphtha cut volumes, sulfur and olefin distributions

Olefins concentrate in the light cracked naphtha (LCN) fraction of FCC naphtha while sulfur concentrates in the heavy cracked naphtha (HCN) fraction. Since most of the sulfur found in the LCN cut can be removed by caustic extraction, an LCN/HCN splitter is effective in reducing octane loss and hydrogen consumption. In addition, installation of the splitter minimizes the size of the selective HCN HDS unit. However, for low-sulfur feeds and/or modest HDS requirements, the full range gasoline may be sent directly to the selective HDS section. The decision to install or not to install the naphtha splitter will be the result of economic calculations taking into account the cost of steam, octane, hydrogen and the extent of olefin control required. FCC Naphtha Selective Hydrogenation (Prime-G+ SHU) Depending on processing schemes, the selective hydrogenation reactor may be either installed in series with the HDS reaction section or installed upstream of a naphtha splitter separating an olefin rich LCN from a sulfur rich HCN. In the selective hydrogenation reactor, the following reactions take place: • Diolefin hydrogenation

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• External olefins isomerization to internal olefins (double-bond isomerization) • Conversion of light mercaptans and light sulfides to heavier sulfur species. The combination of the selective hydrogenation unit (SHU) and splitter is referred to as Prime-G+ 1st step. This processing arrangement provides a number of significant benefits as outlined below. • Production of a low-sulfur, mercaptan-free LCN stream. Since this stream has a low diolefin

concentration, it may be further processed, after additional fractionation if required, in an etherification or alkylation unit. The LCN stream produced by the Prime-G+ 1st step has a lower sulfur content than that which may be achieved with a conventional mercaptan extraction process. This is due to the higher degree of mercaptan conversion (particularly ethyl through butyl mercaptans), the conversion of light sulfides (not removed by extractive sweetening) and the absence of re-entry disulfides usually encountered in extractive sweetening units. The absence of caustic use and associated spent caustic disposal problems is an additional benefit.

• Protection of the HCN HDS section by hydrogenation of the diolefins normally encountered

in the HCN stream. These diolefins, if untreated, are the cause of increased pressure drop and reduced catalyst cycle time.

• The Prime-G+ 1st step may be used to co-process other streams and to desulfurize them

without additional hydrotreating. This may be the case when co-processing highly olefinic and mercaptans-rich light coker naphtha. Mercaptans and sulfides from the light coker naphtha are converted to heavy sulfur compounds in the SHU and most of the light desulfurized coker naphtha is recovered in the splitter overhead. This sulfur shift is achieved with no octane loss and minimal hydrogen consumption. Light straight-run naphthas and butane-rich streams are also good candidates for co-processing in the Prime-G+ 1st step. Examples of the Prime-G+ 1st step effectiveness are shown in Tables 2 and 3 below.

Table 2 – Prime-G+ 1st step feed blend: 70% FRCN and 30% light straight run naphtha.

SHU Feed SHU Effluent LCN LCN / HCN Cut Point,°F 170 S, ppm 850 850 50 C1 to C4 RSH, ppm 34 0 < 1 Light Sulfides, ppm 27 1 Br. No., g/100g 60 59 Diolefins, wt.% 1.3 < 0.2 (R+M)/2 82.8 83.0

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Table 3 – Prime-G+ 1st step feed blend: 91% FRCN and 9% light delayed coker naphtha

SHU Feed SHU Effluent LCN LCN / HCN Cut Point,°F 150 S, ppm 950 950 50 C1 to C4 RSH, ppm 220 0 1 Light Sulfides, ppm 43 1 Diolefins, wt.% 1.2 < 0.2 (R+M)/2 85.3 85.5

It is important to understand that the SHU reactor is not intended to desulfurize the cracked naphtha, but simply to promote a light sulfur shift to heavier sulfur. Therefore, there is no production of H2S in the SHU reactor. In both cases, one can note the nearly complete conversion of light mercaptans and light sulfides. The LCN stream produced after fractionation is sweet and contains sulfur only in the form of thiophene. Further reduction of LCN sulfur via lower thiophene concentration is possible by cutting back the LCN draw and improving the fractionation operation. The selectivity of the SHU reactor is evidenced by the bromine number and octane retention between the SHU feed and effluent. In most cases, an octane boost, resulting from the olefin double bond isomerization reactions in the SHU reactor, can be measured. For the two examples provided above, the conversion of light sulfides is extremely important to ensure the production of a low sulfur LCN stream. Without light sulfide (carbon disulfide, dimethyl sulfide, ethyl-methyl sulfide) conversion, these compounds would concentrate in the LCN stream resulting in sulfur contents well in excess of 100 ppm even with complete mercaptan removal. As sulfur regulations are becoming increasingly stringent, the ability to produce ultra-low sulfur LCN becomes extremely important. A number of refiners already equipped with an HCN HDS unit are installing a Prime-G+ 1st step to meet future sulfur regulations. The SHU is a low cost unit as it operates under mild conditions and requires only carbon steel equipment. Its hydrogen consumption is low, typically in the range of 20 standard cubic feet per barrel of feed. Several SHU units have been installed and have demonstrated excellent catalyst stability, allowing the HCN HDS unit to meet long catalyst cycles (equivalent to the FCC turnaround cycle). The Prime-G+ 1st step is the world-leading technology for LCN desulfurization. FCC Naphtha Selective Hydrodesulfurization (Prime-G+ HDS) The full Prime-G+ process generally consists of the Prime-G+ 1st step followed by a selective HDS of the HCN stream (i.e., splitter bottoms stream). A schematic of the typical Prime-G+ scheme is shown in Figure 2.

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Splitter

HCN

H2 Make-up

FRCN

Prime-G+Selective

Hydrogenation

LCN to Pool, TAME or Alky. Unit

Ultra-LowSulfur

Gasoline

Prime-G+Dual Catalyst

Reactor System

Figure 2: Prime-G+ Schematic

The selective HCN HDS unit employs operating conditions and catalysts tailored to maximize selectivity, that is, minimize olefins saturation while deeply desulfurizing. The low degree of olefins saturation, coupled with the absence of aromatics saturation and cracking reactions, results in relatively low hydrogen consumption. The distillation curve and vapor pressure of the desulfurized gasoline are similar to that of the fresh feed. The Prime-G+ process is the result of industrial experience in the Prime-G process, a deep understanding of the chemical reactions involved and extensive pilot work. The increase in selectivity as compared to a conventional hydrotreating catalyst is illustrated in Figure 3.

OlefinSaturation

Conventional

Prime-G+

4-8 PointRoad Octane

Difference

Extent of HDS

Figure 3 – Prime-G+ Performance as compared to Conventional HDS

Optimization of operating conditions and catalyst attributes are essential to solving the two main product quality challenges of selective cracked naphtha desulfurization: • Olefin saturation control at high HDS level • Minimization of recombinant mercaptans.

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Two catalysts were developed to tackle this problem. The lead catalyst, which achieves the bulk of the desulfurization reactions, has been tailored to minimize olefin saturation reactions while having sufficient activity to desulfurize the most refractory sulfur species encountered in the gasoline boiling range. The finishing material is a polishing catalyst exhibiting practically no olefin saturation activity, but able to achieve the last increment of the desulfurization requirement while reducing product mercaptans. As a result, extremely low product sulfur levels can be achieved in a single-stage unit with excellent octane retention and low product mercaptans. The start-ups of the first, two Prime-G+ units in Germany have demonstrated the ability to reduce sulfur in the cracked gasoline below 10 ppm with low product mercaptans.

Prime-G/Prime-G+ References

As of January 2003, sixty five (65) Prime-G/Prime-G+ units had been licensed with thirteen (13) units in commercial operation. The total licensed capacity exceeds 1,700,000 BPSD making Prime-G+ the leading technology for cracked naphtha desulfurization. The following shows the wide range of application of this technology:

• Feed capacity ranging from 2,500 BPD to 100,000+ BPD (feed to SHU) • Sulfur level ranging from 30 ppm to 4,000+ ppm • Olefin concentration ranging from 15% to 55% • Co-processing of FCC C4 cuts • Product sulfur below 10 ppm. The selective HCN HDS flow-scheme is quite similar to that of a conventional hydrotreater. In many cases, retrofitting an idle hydrotreater or semi-regenerative reformer may be possible. Axens has already performed several (15) revamps of such units to Prime-G/Prime-G+ applications. The technology is particularly versatile and can be implemented stepwise (SHU and/or splitter and/or selective HDS) depending upon local refinery configurations and constraints.

Prime-G+: European Commercial Experience

Though mid-term specifications for ultra low sulfur gasoline (ULSG) have not yet been finalized in the European Union - 10 wppm sulfur being likely for 2009, a majority of refiners will have processing facilities in place to produce 100% of their pool at 10 wppm sulfur by 2005. Tax incentives proposed in Germany in 2001 (50 wppm) and 2003 (10 wppm) have led to a wave of investments in this country and also in surrounding areas.

Within the last 16 months, the first four Prime-G+ units producing ULSG were successfully started up in Western Europe. These are believed to be the only refineries currently in position to produce 100% of their gasoline pool at the 10 wppm sulfur level, well ahead of regulations.

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All projects share the following characteristics:

• Ultra low sulfur in the pool (less than 10 wppm)

• Ultra high HDS (97.5% up to 99.5%) achieved by Prime-G+ technology

• Technology selection was made after pilot testing

• Fast implementation (from eighteen months to two years between the initiation of Axens’ basic engineering package and unit oil-in)

• Complete offer of Axens services: basic engineering, assistance during detailed engineering, catalyst supply, precommissioning, commissioning, start-up and operational tech service

• All licensor guarantees have been systematically met.

Start-up of the First Two Prime-G+ Selective HDS Units (10 wppm sulfur in product)

Two German refineries have pioneered the implementation of the ULSG desulfurization technology to meet future sulfur regulations. The process had to be installed very rapidly to take advantage of the fall 2001 tax incentive (50 ppm sulfur). The selected technology also had to be able to reduce sulfur to less than 10 ppm, as this level was necessary in Germany starting in 2003, to continue to take advantage of the tax incentives. Both refineries evaluated a number of selective and non-selective naphtha desulfurization technologies and both selected Prime-G+.

Refinery “A” installed a grassroots unit with the flexibility to co-process steam-cracker naphtha from nearby plants in addition to its FCC naphtha. The plant had existing depentanizing facilities in place. The Prime-G+ unit therefore processes a C6-410 °F (210 °C) stream with a selective hydrogenation reactor installed in series with the HDS reaction section train. It has a capacity of 18,000 BPD and is designed to reduce sulfur from 550 ppm to 10 ppm. Only 22 months elapsed between the project kick-off meeting and the unit start-up. The short project execution time was the result of excellent cooperation between the refinery, the detailed engineering company and Axens. The start-up went very smoothly and on-spec gasoline was produced one day after oil-in. Since start-up, the unit has been operating at a level of 10 ppm sulfur in the product with conventional control.

Refinery “B” employed a revamp of an existing hydrotreater and processes 21,500 BPD of C6+

FCC naphtha containing 400 ppm sulfur. To maximize the use of existing equipment, the plant is operated at very low hydrogen-to-oil ratios. Like unit A, the Prime-G+ B unit started-up less than two years after the technology award. Similarly, on-specification product with very low mercaptan content was achieved very shortly after oil-in. After start-up in summer 2001, this refinery tuned sulfur in the product from 50 down to 10 ppm to meet market demand, and currently operates its Prime-G+ continuously at 10 ppm sulfur taking full advantage of the German ULSG tax incentives.

Start-up of the First Two Full Prime-G+ Schemes

Two other units started-up in Western Europe in March 2002. The process configuration of these units is similar to that shown in Figure 2. Like the German units, the desulfurization requirement is extremely high (97.5% and 99.5%) and is achieved with low octane loss.

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Of particular interest is that both units have demonstrated the efficiency of the Prime-G+ 1st step for light mercaptans removal and sulfides conversion. Despite light mercaptan contents in the full range naphtha of approximately 100 wppm, the LCN recovered at the splitter overhead contains less than 2 wppm mercaptans and can be sent directly to gasoline storage without sweetening. Partial conversion of light sulfides has also been demonstrated.

Commercial European Data Summary All four operating units illustrate the extensive capabilities of the Prime-G+ technology:

§ Octane retention (Figure 4)

Even at extremely high HDS levels (over 98%), the degree of octane retention satisfies all licensees.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

9998979695

Sulfur conversion as a per cent of sulfur contentin feed to Prime-G+ Unit

Octane Loss

Delta MONDelta (R+M)/2

Figure 4: Octane retention at very high (>98%) HDS levels in a European Prime-G+ unit

§ Consistent production of less than 10 ppm product sulfur

Figure 5 depicts the ability of the technology to attain less than 10 ppm sulfur gasoline over long periods of time with conventional control.

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Product SulfurConcentration, ppm

0

200

400

600

0 50 100 150 200 250 300 350 400 450 5000

20

40

60

Feed Sulfur Concentration, ppm

Days on Stream Figure 5. Stability of Prime-G+ catalysts

(feed sulfur = left axis; product sulfur = right axis)

§ Mercaptan Control

The effectiveness of mercaptan control in the hydrodesulfurized effluent using the dual catalytic system is illustrated in Figure 6.

Sulfur & Mercaptansin Product,

wt ppm

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400 450

Days on Stream

Total sulfur in productMercaptans in product

Figure 6. Mercaptans are controlled at low levels.

§ Flexibility to accept wide sulfur fluctuations in the feed

High fluctuations in sulfur content in the FCC feed due to changes in crude supply can be easily handled by the unit as shown in Figure 7.

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Feed and ProductSulfur Contents, ppm

Days of Operation0 5 10 15 20 25 30

0

400

800

1200

1600

Sulfur in Feed

Sulfur in Product

Figure 7. Product sulfur content is consistently low despite wide

fluctuations in feed sulfur content.

§ Catalyst Stability

High catalyst stability is ensured, based on the experience acquired over the last ten years, sound catalyst manufacturing methods, and unit design. Extremely low deactivation has been observed after a year and a half of operation, Figure 8. The cycles are expected to be at least equivalent to those attained on previous generation catalysts, i.e. more than four years.

HDSCatalystWABT

0 100 200 300 400 500

Days on Stream Figure 8. Weighted average bed temperature remains close to that of start-of-run.

§ Pressure Drop Management

Sound design and efficient removal of diolefins upstream of the HDS catalytic section result in efficient pressure drop management. Through these features, Prime-G+ avoids pressure drop build-up on the catalysts, thus ensuring that the gasoline desulfurization cycle length will not be a constraint for the FCC operation, see Figure 9.

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0 100 200 300 400 500

Normalized Pressure Drop,∆P

(Flow Rate)2

Days on Stream

in HDS Reactorin SHU Reactor

Figure 9 By removing diolefins, pressure drop build-up is virtually eliminated.

§ Prime-G+ SHU Effectiveness

Axens’ Prime-G+ SHU has commercially confirmed its performance in terms of octane balance and desulfurization/sweetening of the LCN stream.

Table 4 – Prime-G+ 1st Step – 100 % FRCN

SHU Feed SHU Effluent LCN LCN / HCN Cut Point,°F 140 Sulfur, ppm 1950 1950 < 10 C1 to C4 RSH Sulfur, ppm 100 < 0.5 < 2 MAV 11 < 1.5 RON 94.0 94.3 MON 82.0 82.3

Prime-G+: North American Commercial Experience

In order to meet the U.S. Tier II and Canadian regulations, a large number of North American refiners have selected the Prime-G+ technology to meet gasoline sulfur regulations. Due to the extensive conversion facilities in North American refineries and because gasoline is the main refinery product, a number of Prime-G+ feeds include co-processing of light coker naphtha and/or light straight run gasoline. The first two, North American, full Prime-G+ units successfully started up in December 2002 and several other units are expected be on stream before the presentation of this article.

Unit “E” was designed to process FCC gasoline with a wide feed sulfur range (800 to 2,000+ ppm). The unit has demonstrated capabilities to produce low product sulfur with moderate octane loss as illustrated in Figure 10.

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0.00.51.01.52.02.53.03.54.0

0 10 20 30 40 50

Recombined Product Sulfur, ppm

Overall Octane Loss

Figure 10 – Unit E - Octane loss versus product sulfur

Unit “F” processes a 70:30 blend of FCC naphtha and light straight run naphtha (LSRN). Pilot tests performed during technology evaluation had shown that the LSRN contained significant concentrations of light sulfides (refer to Table 2). The ability of the Prime-G+ 1st step, to convert not only light mercaptans but also light sulfides, was critical to achieving low gasoline sulfur. Figures 11 and 12 show (1) the ability of the Prime-G+ 1st step in producing a low-sulfur light gasoline and (2) the low recombined product sulfur achieved while processing this gasoline blend.

0

10

20

30

40

Run Days

LCN S, ppm

25%

30%

35%

40%

45%

LCN/Feed, vol. %

LCN S

LCN/Feed

Figure 11. – Unit F – Prime-G+ 1st Step effectiveness

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300

500

700

900

1100

1300

Run Days

Feed S, ppm

0

20

40

60

80

100

Product S, ppm

Feed SProduct S

Figure 12 – Unit F – feed & product sulfur

Both units are now optimizing product sulfur to current requirements by increasing the LCN draw in the splitter overhead and/or decreasing the selective HDS severity. As with the European units, these two North American startups demonstrate the ability of Prime-G+ to produce low sulfur gasoline with moderate octane loss and confirm the possibility of reducing sulfur in light gasoline to very low levels without using caustic treatment.

OATS Technology In addition to the Prime-G+ technology, the OATS (Olefins Alkylation of thiophenic Sulfur) process is also exclusively offered for license by Axens. This technology, initially developed by BP, converts the light sulfur species to heavier sulfur components. Of particular interest is the very high conversion of thiophene to alkyl thiophene by alkylation reactions with light olefins. As a result, a very low sulfur, low-RVP LCN stream can be produced after fractionation of the OATS effluent. Because of the high degree of thiophene conversion, the LCN can have an end-point as high as 210°F (100 °C) while still containing a very low sulfur level.

0

100

200

300

Oats Product

Oats Feed

0 20 40 60 80 100

Cumulative Sulfur, wt%

TBP Cut Point, °C

Figure 13 – OATS Sulfur Shift

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Thiophene and methyl-thiophenes typically represent 5-25% of the total FCC naphtha sulfur. These sulfur compounds boil in the intermediate catalytic naphtha (ICN) distillation range (150 - 250°F, 65 - 120 °C). In this portion of the FCC naphtha, the olefin content is still very high (typically 30-45%). Since thiophenic sulfur cannot be extracted by caustic wash, low product sulfur requires sending the 150°F+ (65 °C+) material to an HDS unit. By alkylating thiophenes with olefins, the sulfur species boiling in the 150-250°F (65 – 120 °C) range are transformed to heavier sulfur species. As a result, the light intermediate cracked naphtha (Lt ICN) becomes practically sulfur free and does not need to be sent to an HDS plant. Since the HDS unit will process a feed with lower olefin content, the octane retention will be improved while hydrogen consumption will be reduced. The OATS process operates under mild conditions in the absence of hydrogen. It does not require the installation of compressors or fired heaters. The unit usually comprises a feed/effluent exchanger, steam-preheater and two reactors in series typically followed by fractionation. The operation, with two interchangeable lead/lag reactors, ensures non-stop operation. Since its solid acid catalyst is sensitive to basic compounds, feed pretreatment, such as a water-wash, may be required in some instances to increase catalyst life. The catalyst also promotes olefin oligomerization reactions. These reactions produce branched olefins, which exhibit better octane retention than linear olefins during hydrogenation. These reactions also result in reduced product vapor pressure. Several processing schemes involving OATS units are possible; the basic scheme is shown in Figure 14. For refiners which require that only a portion of their gasoline meet the ULSG requirement, an OATS step followed by fractionation enables a significant portion of the FCC gasoline to be included in the ULSG pool. This is achieved with no hydrogen consumption and with a low capital cost. The fractionator bottoms may be sent to a catalytic reformer HDT unit, to an existing HDS unit or to the conventional MoGas pool. A selective HDS unit processing this stream may also be erected at a later date.

High S to HDS

Feed

ReactionSection

ULS Product

Figure 14 - Stand-alone OATS unit

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For refiners having an installed Prime-G+ unit or a selective HCN HDS unit, further sulfur reduction with minimum octane loss may be achieved by implementation of an OATS unit on the intermediate catalytic naphtha (ICN) stream (Figure 15).

H2 Make-up

FRCN

Ultra LowSulfur HCN

Prime-G+Sel. HDS

OATS

ULS LCN

ULS ICN (EP: 210°F)

Prime-G+1st Step

ICN Splitter (optional)

HCN

Figure 15 – Prime-G+ / OATS Integration

As light olefins are oligomerized in the OATS process, the operating conditions may be adjusted to reduce the RVP of LCN by dimerizing C5 olefins. Although this alternative reduces gasoline production due to the volume shrinkage associated with the oligomerization reactions, it is a significantly less expensive route than C5 alkylation. Two OATS units began operating in Germany in 2001 and 2002 and another plant has successfully started up in Northern Europe at the end of January 2003. The OATS process meets expectations and allows recovery of ultra low sulfur LCN streams by cutting the light gasoline at 212 °F (100 °C).

0 200 400 600 800 1000 1200 1400

Thiophene conversion, %

0

40

80

120

160

200

S in splitter overhead, ppm

Thiophene conversionS in OVHD

LCN/HCNcut point = 110 °C

LCN/HCNcut point = 100 °C

0.00

20.00

40.00

60.00

80.00

100.00

Figure 16- Commercial OATS unit performance

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Conclusion The introduction of ULSG began in Europe through a program of tax incentives. A majority of European refineries will be equipped to produce most of their gasoline pool at 10 ppm sulfur levels by 2005, well ahead of legislation (2009). Low sulfur fuels are already produced in California and will be gradually introduced starting end of 2003 throughout the US and Canada. Sulfur regulations are expected to be implemented throughout most of the industrialized countries in a manner similar to the progressive lead phased out. The Prime-G+ and OATS processes, offered by Axens for ULSG production, have been successfully put into commercial operation. Prime-G+ has demonstrated its ability to reduce FCC naphtha sulfur to below 10 ppm with very low octane loss. These are believed to be the world’s first large-scale commercial units producing ULSG at this level. The first two North American Prime-G+ units also were successfully streamed at the end of 2002 and several others are expected to be on stream at the time of this presentation. Axens, the world leader in the field of cracked gasoline desulfurization, is committed to further improve its Prime-G+ technology through advances in processing schemes and catalyst improvements. In addition, an extensive cooperation program between BP and Axens is being pursued to take full advantage of the OATS chemistry and provide the most efficient and cost-competitive technologies in the market.