Axens’ Portfolio of Selective Hydrogenation Catalysts

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

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Axens’ Portfolio of Selective Hydrogenation Catalysts

Introduction

Selective hydrogenation catalysts are used mainly for the purification of steam-cracker streams although they are also employed to treat FCC effluents. The main objective of a steam-cracker is to produce ethylene, which is accompanied by important co-products such as propylene, butenes, butadiene, and aromatics. Steam cracker feedstocks originate from a wide variety of sources that include ethane, propane, naphtha and gas oils.

The cracked hydrocarbons are recovered in the ethylene plant separation train as different streams that include ethylene, propylene, C4 cuts and pyrolysis gasoline (C5

+). These differ-ent cuts are usually purified by selective hydrogenation to eliminate undesirable by-products or impurities. Selective hydrogenation of FCC C4, C5 and naphtha cuts allows improved downstream plant operations, productivity and product qual-ity. Axens offers a large portfolio (figure 1) of industrially proven, efficient and cost-effective selective hydrogenation catalysts that allow the customers to stay competitive in a rapidly evolving market. These catalysts are perfectly suitable for all types of selective hydrogenation units.

Figure 1 - Axens’ Portfolio of Selective Hydrogenation Catalysts for Steamcrackers Effluents

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Selective Hydrogenation of C2 Cuts Raw C2 cuts contain between 0.5 and 2% acetylene, which inhibits ethylene polymeriza-tion catalysts. The aim of C2 cut selective hy-drogenation is to reduce acetylene content as low as possible while maximizing ethylene yield and minimizing oligomer (green oil) for-mation.

Axens’ catalyst for selective hydrogenation of C2 cuts, LT 279, is a promoted, low palladium catalyst, supported on a special high purity alumina. The highly efficient LT 279 reduces acetylene concentrations to less than 1 ppm at low operating temperatures, providing out-standing ethylene yields, typically superior to 100%. Moreover, it drastically reduces green oil production which results in very long cy-cles. In front-end operations (treatment of C2- cuts), its low tendency towards runaway reac-tions is a further advantage.

Table 1 shows the performance of LT 279 in a typical commercial unit. Ethylene yield is in-creased while acetylene is virtually eliminated.

Low acetylene content

High acetylene content

Acetylene in feed, wt% 0.95 1.28 Acetylene in outlet, ppm

< 1 < 1

Ethylene in feed, wt% 81.4 83.2 Ethylene in outlet, wt% 81.9 83.9 Ethylene yield,% 100.6 100.8

Table 1 - Commercial performance of LT 279

Selective Hydrogenation of C3 Cuts Typical steam cracker C3 cuts contain 90% propylene and 2 to 6% methyl acetylene and propadiene (MAPD) which must be completely removed to meet propylene product specifica-tions. To eliminate MAPD, maximize propylene yield and suppress oligomer (green oil) formation, a selective hydrogenation proc-ess is applied to the C3 cut.

From a process point of view, selective hydro-genation can be carried out in either liquid or vapor phase. Axens has developed a specific catalyst for each option.

Liquid phase hydrogenation

LD 273 catalyst has been developed specifi-cally to obtain high propylene yields. Through optimized chemical and structural characteris-tics, LD 273 achieves efficient MAPD conversion, typically to less than 1 ppm, and propylene yields surpassing 100%, green oil formation is suppressed and over-hydrogenation to propane is minimized.

LD 273’s commercial performance compares well with that of its successful predecessor, LD 265. Both catalysts demonstrate very effi-cient MAPD removal, with effluent concentrations around 1 ppm, with typical MAPD conversions exceeding 99.99%. The catalysts, however, have different palladium (Pd) contents; LD 273 contains less Pd than LD 265 and yet its selectivity is remarkably better as Figure 2 illustrates.

94

96

LD 265 LD 273

Propylene Concentration, %

92Feed

∆ = 1.0%

94.5

95.5

94.0

Reactor Effluent

94

96

LD 265 LD 273

Propylene Concentration, %

92Feed

∆ = 1.0%

94.5

95.5

94.0

Reactor Effluent Figure 2 - Increased propylene concentrations

after 99.996% MAPD conversion The higher propylene concentration in the pro-pylene/propane splitter feed makes the splitter’s task easier. In fact, some customers were even able to shut down their splitter be-cause simple replacement of the existing catalyst by LD 273 was enough to meet the required propylene purity. The comparison given in Figure 3 shows that the propylene yield increases by 1.1% after replacement of LD 265 by LD 273.

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101.0

102.0

LD 265 LD 273

Propylene Yield, %

100.0

100.5

101.6

∆ = 1.1%101.0

102.0

LD 265 LD 273

Propylene Yield, %

100.0

100.5

101.6

∆ = 1.1%

Figure 3 - Increased propylene yield with

LD 273 LD 273 obtains better performance, reducing oligomer and polymer formation by 40%. These materials hinder a reactant’s access to the catalyst’s active sites and stifle the hydro-genation reactions. Also, LD 273 maintains its high performance longer, extending the cycle length.

Vapor phase hydrogenation Axens catalyst for vapor phase processes, LT-279, makes use of promoted Pd on a high purity alumina carrier. LT 279 features highly efficient MA and PD conversion even at low operating temperatures, outstanding propylene selectivity and a drastically reduced green oil formation, which results in very long cycles The following table shows the typical perform-ance of a commercial LT 279 unit for vapor phase hydrogenation of C3 cut.

Feed Product Propylene,% wt 91.2 93.4 Propane,% wt 5.3 6.6 MA, ppm wt 23 000 < 1 PD, ppm wt 12 000 < 10 Propylene yield,% 102.4 MAPD conversion,% 99.97

Table 2 - Commercial performance of LT 279

Selective Hydrogenation of C4 and C5 Cuts There are several processing options for the upgrading of a typical steam-cracker C4 cut containing around 50% butadiene, 25% isobu-tene, 20% butenes and 2% acetylenes, depending on the market for the various C4 components.

In refineries, selective hydrogenation of a FCC C4 cut results in reduced acid consumption in downstream alkylation plants and increased MON of HF alkylate. TAME unit feedstocks, containing essentially C5 compounds, can be upgraded by means of selective hydrogenation, in order to limit gum formation in the down-stream TAME unit and to increase TAME production. Axens has developed optimized catalysts for each processing option.

Selective hydrogenation of acetylene com-pounds in raw C4 cuts for butadiene recovery The selective hydrogenation process to convert vinyl acetylene (VAC) and 1-butyne or ethyl acetylene (ETAC) improves the efficiency and economics of downstream butadiene extraction processes. LD 277 is the ideal catalyst for this application, achieving high acetylenes’ hydrogenation ac-tivities and high butadiene yields as illustrated in Figures 4 and 5. In addition, long catalyst lifetimes are typical. LD 277 is applied in two process configurations, with or without an acetylene removal column in the downstream extraction unit. Figure 4 shows feed and prod-uct butadiene concentrations in a commercial unit having acetylene removal columns.

Butadiene content, %

45

46

47

Feed Effluent Figure 4 - Selective hydrogenation with

acetylene removal columns (LD 277)

If acetylene removal columns are available downstream from the hydrogenation unit, VAC and ETAC conversions can be limited to 50% as shown in Figure 5.

5

0

1.0

2.0

2.5

Feed Effluent

1.5

0.5

VAC Content, %

Figure 5 - VAC conversion for unit configured

with acetylene removal columns (LD 277)

Butadiene Content, %

0

20

40

60

80

100

Feed Product Figure 6 - Butadiene content still remains high without acetylene removal columns (LD 277)

With no acetylene removal columns available, the acetylenes have to be converted more thor-oughly to 100 ppm as seen in Figure 7.

VAC & ETAC Content, %

Feed Effluent0

0.2

0.6

0.8

1

1.2

0.4

100 ppm

Figure 7 - Acetylene conversion in a unit con-

figured with no acetylene removal columns (LD 277)

In either case, LD 277 meets the specified con-version of acetylenes while attaining high butadiene yields, around 101% and 93% re-spectively. Beyond activity and butadiene yield, catalyst stability is a key feature for this kind of appli-cation, since VAC reacts with Pd to form a soluble complex. Conventional Pd catalysts thus rapidly lose their Pd through leaching, resulting in very short lifetimes, typically a few months, and in high costs. LD 277 is a bimetallic catalyst, for which the Pd is stabilized by a dopant that reduces Pd

losses by a factor of ten. Lifetimes of several years can be typically achieved. Moreover, LD 277 tolerates the sulfur compounds that can appear during plant upsets and which act as inhibitors. The initial activity can be recovered simply by restoring the feedstock quality to its original specifications.

Selective catalysts for production of butenes and iso-amylenes

Selective catalyst for 1-butene production

Conventional Pd-only catalysts have poor bu-tene-1 selectivity because they significantly promote 1-butene isomerization to 2-butene. Axens therefore developed LD 271, a special catalyst based on Pd and a promoter on an alumina carrier, endowing the catalyst with very high intrinsic selectivity. Axens’ LD 271 is suitable for the two major processing options concerning 1-butene recovery: - hydrogenation of raw C4 cuts containing

around 50% butadiene, - processing of C4 cuts after butadiene ex-

traction, containing around 1% butadiene.

In both cases the targets are the same: reducing butadiene content to the ppm range, achieving high 1-butene yields, and minimizing 2-butene and butane formation.

Even for a very severe product specification of less than 2 ppm butadiene, about 50% of the butadiene is converted to 1-butene, as shown by the following industrial results for a butadi-ene-rich unit.

Figure 8 shows relatively steady concentrations of butadiene and 1-butene in the feed over a four-year period.

0 500 1000 1500

Days on stream

Concentration in Feed, wt %

1-Butene

Butadiene

0

10

20

30

40

50

60

Figure 8 - Butadiene and 1-butene concentra-tions in feed to hydrogenation unit (LD 271)

Figure 9 shows that, for the same period, the 1-butene concentration after the hydrogenation

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step is generally over 30%, i.e., two or three times the concentration in the feed. The 1-butene increase is around 23% which corre-sponds to about 50% of the butadiene in the feed. Butadiene concentration in the product has remained consistently less than the 2 ppm maximum specification.

0 500 1000 1500

Days on stream

1-Butene

Butadiene

0

10

20

30

40

0

1.0

2.0

3.0

4.0

1-ButeneConcentration, wt %

Butadiene in ButenesProduct, ppm

0 500 1000 1500

Days on stream

1-Butene

Butadiene

0

10

20

30

40

0

1.0

2.0

3.0

4.0

1-ButeneConcentration, wt %

Butadiene in ButenesProduct, ppm

Figure 9 - 1-Butene and butadiene concentra-

tions in butenes after hydrogenation of 1,3-butadiene

Hydroisomerization catalyst for production of 2-butenes

LD 267 R is the catalyst of choice when high 2-butenes yields are essential, for example, upgrading steam-cracker C4s to 2-butene, pre-treatment of HF alkylation unit feedstocks from an FCC unit or pretreatment of feed to an Ax-ens’ Isopure unit. LD 267 R achieves efficient residual butadiene removal with a high isomerization of 1-butene to 2-butene that approaches the thermo-dynamic equilibrium. Over-hydrogenation to butanes is held to a minimum. The catalyst’s selectivity for isomerization and olefin recovery is obtained by a specific pre-treatment step that moderates the catalyst hydrogenation activity. A further advantage of this pretreatment is that the catalyst is delivered in its reduced form. The result is that the acti-vation step during start-up can be performed quickly and easily. Table 3 shows the performance of a typical commercial unit containing LD 267 R catalyst.

Feed Product Butadiene, ppm 650 <10 1-Butene, wt% 22.2 3.2 Trans 2-Butene, wt% 14.1 26.7 cis 2-Butene, wt% 9.3 13.6 i-Butene, wt% 44.8 44.1 n-Butane, wt% 7.5 9.8 i-Butane, wt% 2.1 2.6 Butadiene conversion, % >98.5 Isomerization rate, % 85.6 Olefin yield, % 96.9 i-butene yield, % 98.4

Table 3 - Commercial performance of LD 267 R Catalyst

High sulfur tolerance for butenes and iso-amylenes recovery

FCC C4 cuts often contain sulfur compounds to such an extent that conventional Pd catalysts suffer from severe deactivation, resulting in low butadiene conversion. The consequences can be high acid consumption and equipment fouling in downstream alkylation units, causing operating problems and higher costs. TAME unit feedstocks, containing essentially C5 compounds, can be upgraded by means of selective hydrogenation of C5 diolefins in order to limit gum formation in the TAME unit. Gums cause shorter cycles and product discol-oration. Another benefit of selective hydrogenation is that TAME production in-creases through an increased reactive iso-amylenes yield. In this application too, high sulfur content feedstocks can deactivate con-ventional Pd catalysts. LD 2773 is a promoted Pd catalyst, specially designed for high sulfur feedstocks. The pro-moter confers on LD 2773 an exceptional tolerance towards sulfur compounds contained in C4 and C5 cuts.

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Table 4 shows typical performance obtained by pretreatment with LD 2773 on feed to a com-mercial TAME unit.

Feed Product Sulfur content, ppm wt 90 90 Diolefins,% wt 0.9 0.015 3-methyl-1-butene,% wt 1.7 0.6 2-methyl-1-butene,% wt 9.4 7.1 2-methyl-2-butene,% wt 17.2 20.7 Diolefins conversion,% 98 Reactive amylene yield,% 104.5

Table 4 - Performance obtained with LD 2773 on feedstock to a commercial TAME unit

The results show that LD 2773, despite the high sulfur content, efficiently and selectively hydrogenates the diolefins and increases the overall yield of the two amylene isomers used for TAME production, namely 2-methyl-1-butene and 2-methyl-2-butene.

Total saturation to butanes Taking into account the butadiene surpluses that have arisen in several countries, naphtha cracker operators have to find ways other than butadiene extraction to upgrade their C4 cuts. Total saturation of a C4 olefins cut to a stream containing mainly butanes is one of the op-tions. This stream can then be recycled to the cracking furnaces as its ethylene yield is higher than that of naphtha. Another option is to sell it as LPG. LD 265 is a Pd based catalyst characterized by an efficient hydrogenation activity and high long-term stability. Depending on the process conditions, a wide range of residual olefin con-tents can be attained, from a few ppm to several per cent. Typically, cycle lengths of more than two years are reached.

Selective Hydrogenation of Pygas cuts Pyrolysis gasoline (pygas) cuts are character-ized by high aromatics content and by chemical instability, due to the presence of highly un-saturated compounds such as diolefins and alkenylaromatics. Options for pygas upgrading include preparing it for use as a gasoline pool component or re-covering the aromatics in the pygas for

petrochemical end use. Two process schemes are possible: 1. First stage pygas hydrogenation – This

involves selective hydrogenation of most of the diolefins and alkenylaromatics in or-der to meet gasoline pool stability specifications.

2. Second stage pygas hydrogenation – fol-lowing the first stage hydrogenation, this process removes the remaining diolefins, alkenyl-aromatics and olefins without aro-matics hydrogenation, followed by desulfurization to meet high purity aro-matic product specifications.

The trend toward more stringent environmental regulations concerning gasoline has led to a reduction in the amount of pygas in the gaso-line pool and to an increase in its use as a petrochemical feedstock. Axens offers highly active, selective and stable catalysts for both options.

First stage pygas hydrogenation process Both Pd and nickel (Ni) catalysts are able to carry out the required reactions, i.e., the selec-tive hydrogenation of diolefins and alkenyl-aromatics such as styrene, while minimizing olefin hydrogenation and avoiding aromatics hydrogenation. Nevertheless, the performance of Pd and Ni catalysts differs slightly in several respects:

1. Activity: Pd is intrinsically more active than Ni. High activity catalysts are therefore based on Pd. Switching from a conventional to a highly active catalyst could enable a vari-ety of objectives to be achieved such as more stringent specifications, increased unit throughput, increased catalyst cy-cle-length and lifetime, reduced catalyst inventory provided that unit equipment ca-pacities and reactor hydrodynamics are sufficient.

2. Start-up behavior Fresh nickel catalysts containing insuffi-cient levels of sulfur may be prone runaway reactions during start-up due to the presence of active sites for which the aromatics hydrogenation activity is too high.

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Therefore, nickel catalysts must be inhib-ited prior to start-up, by deposition of a sufficient quantity of sulfur on the most ac-tive sites. This sulfur pretreatment can be carried out either ex situ, making the start-up safe and quick, or in situ. The reliable and efficient ex situ pretreat-ment developed by Axens and Eurecat for nickel catalysts is called ResucatTM. On the other hand, Pd catalysts are intrinsi-cally selective and avoid aromatics hydrogenation.

3. Sensitivity to poisons Nickel catalysts contain 20 to 50 times more active metal atoms than Pd catalysts. For this reason, Ni catalysts are more toler-ant to poisons than Pd catalysts, and therefore they are preferred in case of highly contaminated feedstocks. Arsenic and mercury can be present in pygas mainly when natural gas condensate are used as feeds to steam crackers; such con-tamination occurs more rarely when regular naphtha is processed. Silicon con-tamination is often related to the co-processing of imported feedstock stem-ming from coker or visbreaker units.

4. Sensitivity to sulfur compounds Ni catalysts are more sensitive than Pd catalysts to mercaptans, disulfides and thiophenes contained in feedstocks. For feedstocks with high sulfur content, Pd catalysts are generally preferred.

5. Cost Ni is generally less expensive than Pd. Pd catalysts contain in general between 0.2 - 0.5% wt of the precious metal, whereas Ni catalysts contain between 10 - 20% wt of Ni.

In conclusion, the choice between Pd and Ni catalysts depends on several site-specific con-straints among which are: feedstock characteristics, product specifications, unit characteristics, Pd vs. Ni price differential. A further option is to load the reactor with stacked beds: Pd catalyst on top and Ni catalyst at the bottom of the reactor. The advantage of this option is that it combines the benefit of the Pd catalyst’s higher activity with the above-mentioned advantages of Ni catalysts.

Axens has extensive commercial experience with both Ni and Pd catalysts, including several commercial references of Pd/Ni stacked beds, and was the first catalyst manufacturer to bring both Pd and Ni catalysts to the marketplace for first stage hydrogenation units. LD 265 (based on Pd) and LD 241 (based on Ni) are Axens’ first generation catalysts. They rapidly became the industry benchmarks owing to their successful and dependable operation and their, having achieved consistent customer satisfaction around the world. Based on industrial feedback and extensive research and development efforts, Axens has more recently developed a new generation of catalysts, Pd-based LD 365 and Ni-based LD 341. Through improved physical and chemical characteristics, LD 365 and LD 341 achieve highest of performance levels: - high conversion of diolefins, styrenes and

indenes - no conversion of aromatics - low deactivation rates - long cycles - very good mechanical properties - full regeneration potential

Axens’ portfolio of first stage hydrogenation catalysts is exhibited in Table 5.

Trade name

Metal

Relative activity

per volume

Relative

LHSV

Cycle length,* years

LD 265 Pd 2 1.5 - 2 0.8 - 1.5 LD 365 Pd 3 2.5 - 3 1 - 2 LD 241 Ni 1 1 0.5 LD 341 Ni 2 1.5 - 2 0.8 - 1.5

* Values obtained on full range gasoline i.e., C5-200 °C

Table 5 - First stage hydrogenation catalysts

Commercial experience with LD 365

There are many successful commercial applica-tions of LD 365. A typical example is a pygas unit in Germany designed by others. This unit features a single first stage reactor catalyst bed with no quench and a liquid recycle stream distributed on the top of the bed. Before switching to LD 365, the unit operated using LD 265. The average feedstock characteristics are given in Table 6 and the average first cycle results are compared in Table 7.

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Diene value, g I2/100 g 25 Bromine number, g Br2/100 g 70 Sulfur, ppm 60

Table 6 - Average feedstock characteristics

LD 265 LD 365 Diene value, g I2/100 g 1 0.5 Bromine number, g Br2/100 g 60 60 Aromatics loss,% 0 0 First cycle, days 200 > 300

Table 7 - Effluent characteristics and first cy-cle length for LD 365 compared to LD 265

The specified product Diene Value (DV) of 1.2 g I2 / 100 g was reached in the past without problem with LD 265 catalyst, for a product DV of 1. Switching to LD 365 enabled the DV to be cut in half. The operator now enjoys a substantially longer cycle because the rate of pressure drop increase in the second stage reac-tor is considerably slower. Figure 10 shows the temperature variation at the reactor inlet versus time. The End-of-Run (EOR) temperature limit set by the operator for this unit is 85 °C. With LD 265, this level was reached after 200 days of operation. The first cycle of LD 365 catalyst was terminated after 300 days on stream. This occurred before the EOR limit was reached in order to allow for the steam cracker turnaround. The curve has been extrapolated to show that a cycle of 400 days, twice that which was obtained with LD 265, would have occurred. Further cycles have since confirmed the full regenerability and out-standing stability of LD 365. A unit designed by Axens with a higher EOR temperature stan-dard would have taken even further advantage of the excellent performance of LD 365 cata-lyst.

LD 365Reactor Inlet Temperature

Days on Stream

End of Cycle Due toSteam Cracker Shutdown

LD 265 End of Cycle

Customer’s EOR Criterion

0 100 200 300 400

LD 365Reactor Inlet Temperature

Days on Stream

End of Cycle Due toSteam Cracker Shutdown

LD 265 End of Cycle

Customer’s EOR Criterion

0 100 200 300 400

Figure 10 - Improved stability of LD 365 ver-

sus LD 265

LD 365 was developed not only to improve diolefins hydrogenation activity but also to improve the hydrogenation of styrene con-tained in the pygas. Figure 11 presents commercial results and shows that with LD 365, styrene conversion levels are main-tained between 80 and 90%. These levels are much higher compared to LD 265, for which a maximum 70% styrene conversion was possi-ble. The improved styrene conversion is beneficial for the second stage hydrogenation cycle lengths.

0 50 100 150 200 250 30050

60

70

80

90

100

Days on stream

Styrene Conversion, %

0 50 100 150 200 250 30050

60

70

80

90

100

Days on stream

Styrene Conversion, %

Figure 11 - Commercial performance of

LD 365

Longer cycles with LD 341 The following example concerns a first stage pygas hydrogenation unit that was operated satisfactorily for many years with LD 241, reaching the desired specification. Informed of the new catalyst’s higher activity and resistance to heavily contaminated feeds, the customer decided recently to switch to LD 341. The ob-jectives were to achieve longer cycles and to operate the unit under similar conditions. The objectives set by the customer have been met successfully as depicted in Figure 12. The first cycle reached with LD 341 was nine months, whereas a six-month cycle with LD 241 was typical in the past. This 50% in-crease demonstrates the higher activity and stability of LD 341, resulting lower start-of-run temperatures and lower deactivation slope.

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First Cycle Length, Months

0

2

4

6

8

10

LD 241 LD 341

First Cycle Length, Months

0

2

4

6

8

10

LD 241 LD 341 Figure 12 - LD 341 extends cycle length by

50%

High activity and long cycles even with heavily contaminated feedstocks The high tolerance of LD 341 to catalyst poi-sons was demonstrated recently in a first stage pygas hydrogenation unit processing gasoline containing arsenic in the 50 to 300 ppb concen-tration range. Due to the high arsenic content, the Pd catalyst originally planned for the unit would have experienced very short one-month cycle lengths. In order to reach acceptable cy-cle lengths, LD 341 was installed and the unit has since operated with great success: a first cycle of one year has been reached.

Data shown in Figure 13 for the first six months of the cycle demonstrate the efficient styrene removal capacity of LD 341. The aver-age styrene concentration in the feed was reduced from 3.7% to less than 0.5%.

0

1

2

3

4

0 50 100 150 200

Days on stream

5

Average inlet styrene content

Styrene Concentration,wt%

Styrene Content in Outlet

0

1

2

3

4

0 50 100 150 200

Days on stream

5

Average inlet styrene content

Styrene Concentration,wt%

Styrene Content in Outlet

Figure 13 - Consistent styrene removal effec-

tiveness using LD 341 in a first stage commercial pygas unit

Styrene polymerizing on the catalyst and caus-ing pressure drop is a leading cause for ending the run. Figure 14 presents the pressure drop data for the same time period as represented in Figure 13 and demonstrates that the pressure drop remained stable.

0.00

0.20

0.40

0.60

0.80

0 50 100 150 200

Days on stream

Pressure Drop, bar

0.00

0.20

0.40

0.60

0.80

0 50 100 150 200

Days on stream

Pressure Drop, bar

Figure 14 - Pressure drop in first stage pygas

unit using LD 341

Second stage pygas hydrogenation process The second stage pygas hydrogenation process serves to hydrogenate any traces of diolefins, and the remaining olefins. It also completes the hydrodesulfurization (HDS) process in order to meet aromatics purity specifications. Axens strongly recommends a dual bed for the second stage reactor that has a layer of LD 145, a special NiMo catalyst, placed on top and a layer of HR 406, a CoMo catalyst, placed un-derneath. The purpose of the LD 145 layer is to ensure that all traces of diolefins and a large part of the olefins are converted before the flow reaches the layer of HR 406, a well-proven HDS catalyst that has an acidic alumina sup-port. The acidic function of HR 406, necessary for complete HDS, also accelerates polymeri-zation of unsaturated compounds. The polymerization products (gums) formed would foul the catalyst and cause a rapid increase in pressure drop. Both catalysts are characterized by high activi-ties, low deactivation rates, very good mechanical properties and full regenerability.

Performance of stacked-bed commercial units containing LD 145 and HR 406

The excellent performance of the LD 145 and HR 406 stacked bed system is illustrated by the following commercial data (figure 15, 16 and 17), obtained from a second stage pygas hy-drogenation unit started-up recently and still running as of this date.

Data for the first four months after start-up are reported and the following observations are noted as follows: - no reactor inlet temperature increase has

been necessary during this time

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- pressure drop increase is less than 0.05 bar - very efficient sulfur removal, as shown by

the outlet thiophene content of less than 0.05 ppm wt.

0 500 1000 1500 2000 2500 3000

Hours on stream

Reactor inlet temperature, °C

275

276

277

278

279

280

281

282

0 500 1000 1500 2000 2500 3000

Hours on stream

Reactor inlet temperature, °C

275

276

277

278

279

280

281

282

Figure 15 - Constant activity of LD 145 and

HR 406 in stacked bed reactor system

0.4

0.5

0.6

0.7

0 500 1000 1500 2000 2500 3000

Hours on stream

Pressure drop, bar

0.8

0.4

0.5

0.6

0.7

0 500 1000 1500 2000 2500 3000

Hours on stream

Pressure drop, bar

0.8

Figure 16 - Pressure drop through LD 145 and HR 406 stacked bed reactor system

0

0.02

0.04

0.06

0.08

0.10

0 500 1000 1500 2000 2500 3000

Hours on stream

Thiophene in Outlet,ppm wt.

0

0.02

0.04

0.06

0.08

0.10

0 500 1000 1500 2000 2500 3000

Hours on stream

Thiophene in Outlet,ppm wt.

Figure 17 - Very low thiophene concentration in effluent from LD 145 and HR 406 stacked

bed system

Axens for Advanced Catalytic Solu-tions The catalysts described in this brochure are enjoying considerable commercial success. In fact, over the years Axens has become the world’s leading supplier of hydrogenation processes. There are many reasons for this enviable posi-tion: • State-of-the-art production facilities in

Savannah, Georgia and Salindres, France • R&D support from one of the largest and

most capable organizations in the world • Huge bank of experience and industrial

feedback acquired in a period of over fifty years

• Extensive and responsive worldwide sales network

We are determined to enhance our position by offering our customers continuously improved, reliable, and up-to-date products and services.

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