Netzer

BENZENE SUPPLY TRENDS AND PROPOSED METHOD FOR
ENHANCED RECOVERY
David Netzer
Consulting Chemical Engineer
Houston, Texas, U.S.A.
Presented to
2005 World Petrochemical Conference
March 29-31, 2005
Houston, Texas, U.S.A.
ABSTRACT
This paper focuses on the two traditional sources for petrochemical benzene, which are catalyticnaphtha reforming from petroleum refining and steam cracking of petroleum liquids. These sourcesyield 27,300 KT/Y (560,000 bpsd) or 75% of the global benzene supply for the petrochemical industry.
An additional 6,000 KT/Y (123,000 bpsd) of benzene is produced by toluene conversion processing,and most of this toluene is captive to reforming and steam cracking sources.
In the U.S., catalytic reforming of naphtha accounts for about 38% of benzene production. Benzeneis an incidental product from reforming during the manufacture of high-octane blending components(HOBC) used in gasoline blending. A further 28% of benzene is attributed to pyrolysis gasolinefrom steam cracking sources where the benzene is an incidental product during the production ofethylene and propylene. In Europe, the ratio is about reversed where steam cracking accounts fornearly 52% of benzene while catalytic reforming accounts for about 30%.
Benzene costs rose to about 2.9 times the cost of crude oil in 2004 as compared to an average of 1.9times crude oil from 2000-2003, despite the dramatic increase in price of crude oil. This 50% increasein cost ratio, and nearly 200% increase in total cost has caused the petrochemical industry to reviewmarket factors causing the supply/demand imbalance and look for more cost effective ways of buyingand using benzene in their processes.
This presentation tries to identify the root cause of market supply trend, review alternate approachesand to propose at least a partial solution that will alleviate the imbalance in the market. The fall out ofthis approach would be; improving the environmental impact by removing benzene from the gasolinepool and also substantially elevating the octane of the gasoline pool and reducing vapor pressure.
Future anticipated regulations for benzene reduction in the gasoline pool would be extremely synergisticwith the proposed concept.
One concept that could further benefit the industry is use of lower purity benzene (97-98 wt%)
instead of the traditional high purity stock (99.5-99.9 wt%). The concept has previously been discussed
in the NPRA paper AM-03-10 presentation on March 2003, Hydrocarbon Processing April 2002,
Hydrocarbon Engineering Nov. 2003 and U.S. Patent 6,677,496, (www.petrochemicals.dnetzer.net)
showing a typical economic advantage of 30-40%. The concept involves fractionation of dilute
benzene streams (8-25 vol% benzene) from catalytic reforming in petroleum refining. This dilute
benzene is used as feed or partial feed to steam cracking producing olefins and shifting the benzene
recovery from the refining operation to the petrochemical operation.
Benzene Supply Sources and Market Trend
On a global basis, catalytic reforming accounts for some 55% of benzene production includingassociated toluene conversion. Steam cracking and associated toluene conversion accounts for nearly40% of benzene production.
A typical benzene yield from steam cracking could be as follows.
• Cracking naphtha, 4.5-6.5 wt%, depending on feedstock and cracking severity.
• Cracking of gas oil, 4.5-6.5 wt%, depending on feedstock and cracking severity.
• Cracking of propane and butane, 2.5-3.0 wt% benzene depending on severity.
• Cracking of ethane 0.6-1.0 wt% depending on pressure and ethane conversion.
On a global basis, about 50% of ethylene is produced via naphtha cracking at an average yield ofabout 31-35%. About 6% of ethylene is produced via cracking of gas oil at an average cracking yieldof 25-28%. The balance of the ethylene, about 44%, is produced via gas cracking: about 14% bycracking C3/C4 at about 38-44% cracking yield and 30% from cracking ethane at about 76-81%average cracking yield.
Production of ethylene from ethane, aside from low benzene yield has very limited co-production ofpropylene. Since the recent trend in the olefin market is focused on propylene, the propylene productionbrings new issues affecting benzene production. Traditionally, about 60-65% of propylene has beenattributed to steam cracking while nearly all the balance is attributed to FCC (fluid catalytic cracking)gasoline production in petroleum refining. About 2% of propylene production is attributed todehydrogenation of propane.
The Benzene Attributed to Steam Cracking is Captive to the Following Sources:
0.070 ton benzene per ton of ethylene.
0.010 ton benzene per ton of ethylene.
The average global benzene production from steam cracking sources is 0.12 ton benzene per ton ofethylene produced at B/L and associated toluene conversion by hydrodealkylation could account foradditional 0.01 ton of benzene per ton of ethylene, thus resulting in a total of 0.130 ton benzene perton of ethylene on a total global basis.
Recent trends in steam cracking have been to increase propylene market share in relationship toethylene, as high as 0.65 ton of propylene per ton of ethylene at OBL of liquid crackers as opposed tohigher severity P/E=0.50 as the more traditional average. The low severity operation, driven bypropylene market results in reduction of benzene make for most full range naphtha feeds by about15-20% or more, thus further disturbing the benzene supply situation. As discussed later, the emergenceof high severity FCC as driven by the propylene market, co-produces substantially higher benzeneyield, thus potentially creating a niche market opportunity for additional benzene production in situationswhere VGO (vacuum gas oil) is attractively priced; however, at this point it represents a very minorshare of the benzene market and is exclusive to China.
The following twenty olefin projects are officially in advanced planning or invitation to bid to majorcontractors, or are under construction, and scheduled for operation by year 2009. About 17,520 KT/Y ethylene will be produced if all these projects are materialized, and as shown 9,115 KT/Y (52%) inthe Middle East and 6,240 KT/Y in China(36%). It would be a reasonable assumption that not allthese projects materialize for typical business reasons; however, it is reasonable also to assume thatsome additional projects in FSU, Mexico, India, Venezuela, and perhaps even the U.S., Canada andEurope are yet to be announced.
Based on the data in the table below, the estimated benzene to be co-produced will be 1,600 KT/Y,340 KT/Y (21%) in the Middle East and 1080 KT/Y (68%) in China. The total benzene productionis estimated at 1,730 KT/Y after assumed hydrodealkylation of toluene, 0.098 ton benzene per ton ofethylene about 75% of current global average.
MAJOR ETHYLENE EXPANSIONS (2005 - 2009)
LOCATION FEEDSTOCK
CAPACITY TIMING
On this basis for an ethylene growth rate of 4.0% per year, including ethylene conversion to propylene,the growth in benzene from steam cracking sources would be only 3.0% per year.
Industry search for alternate feedstock for steam cracking is well underway. For example, it wasrecently announced that Dow’s joint venture in China and others are studying the option of methanolto ethylene, producing methanol via coal gasification. (http://www.dow.com/dow_news/corporate/2004/20041220a.htm) The methanol product will be used for MTO (methanol to olefins) producingolefins. Regardless of the final results of the studies, based on a currently known technology, see SRIreport PEP 111-A, no appreciable co-production of benzene is anticipated. The same is the caseconverting methanol to propylene; see SRI report PEP Review 98-13 and methanol to gasoline,(MTG) see SRI report PEP-191.
The growth of new refining capacity in the U.S., Europe and Japan has been nearly stagnant over thepast two decades. As a matter of fact, according to ExxonMobil, (see Hydrocarbon Processing Jan.
2005) gasoline consumption in Europe is expected to decline by about 0.9% per year through 2020while motor fuel demand is shifting toward diesel. The growth of refining capacity in China, India,and the Middle East has involved adding relatively smaller reforming capacity compared to the U.S.
because the domestic fuel product slate in these regions of the world is geared more toward diesel andfuel oil rather than high octane gasoline. For example, the published reforming capacity in China isunder 7% and India 5% of crude oil fractionation capacity, as opposed to 21% in the U.S., 17% inMexico, and about 15% in the European Union and Japan and about 11% in the Middle East. Needlessto say, this lack of growth further contributes to the imbalance in supply/demand of benzene.
Traditionally, as a rule of thumb, the sale price of benzene (SG=0.88/ 30 API gravity) has been 1.75-1.90 times the cost on weight basis of crude oil. Recent market trend has brought the cost of benzeneto a historic high of 3.6 times crude oil, and a recent decline has stabilized the cost at 2.5-2.9 times thecost of crude oil. Given the new processing trend of steam cracking it appears a reasonable assumptionas any, that the near future cost ratio of benzene to crude oil price could remain at this level. The keyto these issues is the growth rate in benzene consumption in China.
The growth of benzene derivatives has been on the order of 4.0% per year, mostly into styrene,cumene and cyclohexane, which has created a supply demand imbalance that is the current focusissue of the petrochemical industry.
Potential Added Benzene Recovery
In some twenty one (21) known refineries, including twelve (12) refineries in California, one (1) inthe state of Washington, two (2) in Eastern Canada and the balance in Europe and Australia, wherebenzene is being produced in reforming that potentially could be recovered, it is being hydrotreated tomeet environmental specifications of benzene in the gasoline pool. The current benzene specificationsare limited to 1.0 vol% in much of the U.S., European and Japanese markets, and further reductionscan be anticipated in the future.
The currently practiced hydrotreating ( http://www.uop.com/objects/Bensat.pdf) of benzene, asideof significant hydrogen consumption, approximately 40-60 Scf/bbl (0.5 kg/ton) on the total average gasoline pool, amounts to about $0.1/bbl ($0.85 per ton) gasoline depending on the value of hydrogen.
Benzene saturation also reduces the octane of the typical gasoline pool by 0.20-0.25 RON. Thisoctane penalty by itself accounts for about $0.10-0.15/bbl ($0.85-1.30/ton) gasoline. EliminatingMTBE from California gasoline blend has even further aggravated the octane issue, and blending ofethanol has its own limitations especially higher RVP (Reid Vapor Pressure).
In the state of California, or gasoline dedicated for marketing in the state of California, the hydrotreatedbenzene concentrate is very good molecular composition in terms of meeting the T-50 (mid boilingpoint) and olefins of CARB gasoline. The added value of CARB gasoline, probably $0.06-0.08/gallon over a conventional regular gasoline could provide an incentive to the current hydrotreatingpractice of benzene. A major project recently completed in a refinery in the U.S. northwest wasfocused on avoiding export of benzene concentrate to the Gulf Coast and hydrotreating andisomerization of C5/C6 cuts, thus producing a good blend for CARB gasoline for the Californiamarket. Nevertheless, this practice should be assessed against the changing market values of benzenevs. the market for CARB gasoline. Further, unlike isomerization of pre-fractionated C5/C6 fromreformer feed, the isomerization of C5/C6 from unconverted naphtha results in very marginal boost inoctane.
In this context it should be noted that the gasoline’s end point, which is one of the key attributes ofCARB gasoline, is not affected by the proposed removal of the dilute benzene cut and the effect onaverage olefin content, another attribute to CARB gasoline, is very small, (see CARB model http://www.arb.ca.gov/fuels/gasoline/premodel/premodel.htm).
The assumed legal obstacles or perceptions of legal obstacles in liability of handling dilute benzene
could be a factor as well. It is assessed that the estimated increase in octane of about 1.8-2.0 RON
resulting from removal of dilute benzene and reduction in RVP, probably by far will out weigh the
issues of olefins, T-50 and perceptions of liability. At the end, based on regulatory development in
other states and Europe, it is assessed that the probability of adopting some of the CARB gasoline
specifications like the T-50 is very small.
The Following Sources of Benzene Could Be Considered
• Benzene recovery from reformers which are not practicing benzene recovery.
• Benzene recovery from High Severity FCC gasoline, 570-600 C reaction. .
• Benzene recovery from tar sand processing, mostly in western Canada.
• Benzene production from LPG such as Cyclar process in Saudi Arabia.
High Severity FCC ( http://www.uop.com/objects/PetroFCC.pdf )
The high severity FCC projects are driven mostly by the increase in demand for propylene. A typical
propylene yield of 17-20 wt% and about 3 wt% ethylene was reported from severely hydrotreated
VGO (vacuum gas oils) using 0.015-0.020 ton of hydrogen per ton of VGO, as opposed to 4-5 wt %
propylene and 0.8-1.0 wt% ethylene yields in conventional FCC. The benzene production in HS
FCC is 3.0 to 3.5 higher than “normal” FCC, and the assumed benzene recovery would become
economically more viable after disproportionation of toluene to additional benzene and xylene,
probably for downstream production of paraxylene. Therefore, benzene recovery is almost incidental
to paraxylene production, and the overall economics of HS- FCC is governed by the assumed values
of VGO as well as values of propylene and paraxylene. Nevertheless, at the end, the key to the
relative economics of high severity FCC as a route for aromatics and propylene is the value assigned
to VGO, vacuum gas oil. It is speculated that for projects of high severity FCC, mostly in China and
a recent project in the Middle East, the assigned values of VGO are considerably lower than the
known market rates as posted. Once advantageous pricing for VGO is achieved, the option of
conventional steam cracking of hydrotreated VGO also deserves a consideration.
Benzene From Oil Sand
Not much has been reported on benzene recovery from tar sand or shale oil. Alberta Energy Research,the province of Alberta, Canada, has sponsored with interested parties a number of studies related tothe added value of petrochemicals production from synthetic crude oil. The estimated investment inan assumed typical complex could be on the order of $5,000 MM U.S. producing clean fuels, olefinsand co-producing paraxylene and some 500 KT/Y of benzene. High severity FCC is likely to be acore unit in the petrochemical operation along with delayed coking, coke gasification for hydrogenproduction and hydrocracking for producing premium products, including CARB gasoline.
The overall added economic value of the assumed petrochemical operation will likely be indexed totwo major factors: • Cost of synthetic crude, mostly capital charges • Relative competition of natural gas, as indexed to the U.S. market.
At the moment, all olefins production in western Canada is based on ethane which of course isderived from natural gas, mostly exported to the U.S. Massive imports of LNG to the U.S., particularlyto California or Baja California, Mexico, could indirectly reduce the overall incentive of petrochemicalsfrom oil sand. On the other hand, these tar sand upgrading units are expected to utilize very significanthydrocracking capacity and hydrocracked gasoline, low in olefins and sulfur is more compatible withCARB gasoline and exporting this gasoline blend to California could result in higher margin.
Nevertheless, regardless of the final economic case, given the order of capital investment and thelocation, it seems that for benzene production, this oil sand option presents a niche market at best.
LPG to Benzene
A single commercial Cyclar plant, benzene from LPG was built in 1991 in Saudi Arabia. Noadditional second plant was ever built, while benzene has been imported to Saudi Arabia. This leadsone to speculate that alternate methods of producing benzene have proven more economical thanCyclar.
Benzene From Catalytic Reforming
Reforming OverviewMost reformers built in the past generation, about 35% of global reforming capacity, are of CCR type.
Reformate comprises about 30% of U.S. gasoline and about 43% of European gasoline pools. On a global basis, reformates are being produced in 450 refineries, including 120 refineries in the U.S.,twenty (20) in Canada and six (6) large refineries in Mexico. A typical reforming capacity couldrange in volumetric capacity between 10-30% of the input to the crude oil distillation unit and itsvolumetric yield between 75-82 vol%. The octane of reformates typically ranges from 94 RON to102 RON, where 97-100 RON would be a reasonable range for a modern CCR.
A good measure for naphtha reforming quality is N+2A, which is volumetric percentage of naphthenecontent + twice the percentage of aromatics content. An N+2A of over 50 would represent a goodreforming feedstock and N+2A=70 would represent an excellent feedstock. Highly paraffinic naphtha,typically from the Middle East, may have N+2A content around 40, and is thus good for olefins viasteam cracking but traditionally less advantageous for reforming as compared with naphtha fromcrude oils such as Brent North Sea, N+2A=72, light Louisiana crude and Alaska North SlopeN+2A=60, Isthmus (Mexico) N+2A=52, Dura ( Indonesia) and West African N+2A=78-80 .
In any of the above methods, additional benzene could be produced by hydrodealkylation of toluene,HDA. Since most toluene is produced in catalytic reforming, most of the benzene production byconversion of toluene is accounted as a portion of global benzene share as captive to catalytic reformingand amounts to 6% of global benzene production. The economics of converting toluene and in rarecases xylene to benzene by HDA, is a function of relative values of benzene to toluene as well as costof hydrogen and value of fuel gas. The basic benzene yield of HDA is about 80% and in today’smarket this operation is justified, however, the relative merit of HDA is very cyclic. The conversion oftoluene to benzene and xylene by disproportionation would be driven by the economics of paraxylene.
Based on all the above, the presentation will focus on an improved method of benzene recovery fromHOBC which is in most cases more economical than the alternate methods. In this context it shouldbe noted that higher yield of benzene by CCR (continuous catalytic reforming) could be achieved ascompared with the older semi-regenerative reforming technology.
Reverting reformer operations to pre 1990 Clean Air Act, standards could significantly increase
the benzene yield, and in most cases with relatively small capital investment. However, in some cases,
the added isomerization capacity is so integrated with reforming operation that reverting to pre 1990
Clean Air Act standards could become a complex issue, complex but not impossible. Needless to say,
the installation of new reforming capacity would be more ideally suited for the proposed production
of dilute benzene.
As said, it is anticipated that future regulations will call for further benzene reduction as opposed tothe current 1.0 vol%. All present methods of reconfiguring the reformers for minimum benzeneproduction have nearly reached their practical limits, thus the only known methods of eliminatingbenzene are by either hydrogenation of benzene concentrate heart cut, as currently being practiced, oralkylation with light olefins. In either case, fractionation of benzene concentrate heart cut will berequired thus diversion of dilute benzene to OBL steam cracking could be a fall out. In about four (4)U.S. refineries, two in the Gulf Coast and two in the North East, two (2) Canadian refineries andprobably several European refineries, C6/C7 heart cut benzene concentrate from reforming is beingrecovered. However, rather than being hydrotreated such as in California it is sold for benzeneextraction, and in case of eastern Canada and one U.S. North East refinery, the benzene concentrateis shipped to the U.S. Gulf Coast.
On average, at least in the U.S. and Europe, benzene attributed to reforming represents 70-80% oftotal benzene in gasoline, while the balance 20-30% of the benzene is essentially in the FCC gasoline.
Therefore, eliminating this benzene from reformate streams as discussed later, would present the mostviable approach for meeting future environmental regulations, while simultaneously recovering valuablepetrochemical product. Further, removing benzene from FCC gasoline, typically 0.5 vol%, wouldpresent a very uneconomical operation.
Illustrative Refinery Configuration With Typical Catalytic Reforming
The following diagram, Generic Refinery Configuration, represents a conventional high conversion200,000 bpsd 31.5 API crude input refinery, including 50 vol% Mid East paraffinic crude. The refineryconfiguration includes 34,000 bpsd, continuous catalytic reforming CCR of naphtha, N+2A=50 toproduce 28,000 bpsd HOBC (high octane blending component) RON=98.5 and 50 MM scfd ofhydrogen at 87 mol% purity. The atmospheric fractionation in a crude unit is producing: • Naphtha cut 350 F end point 38,000 bpsd • Kerosene cut 550 F end point 20,000 bpsd • Diesel cut 700 F end point 25,000 bpsd • Atmospheric gas oil, AGO, 750 F cut point 15,000 bpsd The atmospheric residue proceeds to vacuum distillation and produces the following cuts: • Vacuum gas oil, VGO, 650-950 F boiling range 60,000 bpsd The vacuum bottom proceeds to delayed coking to produce: • 2,000 stpd petroleum coke, 4.0 wt% sulfur, 15.000 btu/lb • 5,000 bpsd coker naphtha, relatively high in sulfur olefins and benzene.
• 2,000 bpsd LPG- to Merox ( Mercaptan oxidation) • 10,000 bpsd coker diesel - to hydrotreating • 11,000 bpsd coker gas oil- to FCC.
The combined atmospheric, vacuum and coker gas oils 86,000 bpsd is feeding a conventional FCCunit and producing: • 49,000 bpsd gasoline, end point 430 F, benzene content 0.6 vol%.
• Light cycle oil, aromatic diesel material, 15,000 bpsd • Slurry oil , heavy fuel oil 3,000 bpsd • Propylene 6,500 bpsd (185 KT/Y) for petrochemical recovery • Fuel gas CH4 /C2/H2, containing about 13 mol% ethylene.
The C4 mix along with some 4,000 bpsd imported isobutane is feeding a 9,000 bpsd alkylation unit.
The alkylate RON=95 MON=92 is blended to the gasoline pool.
The coker naphtha rich inolefins and di-olefins and Generic Refinery Configuration
Hydrogen
Gas Plant
LPG – 2000 BPSD
Reforming
Fraction
Treating
38.000 BPSD
Kerosene
Diesel
AGO
Isomerization
15.000 BPSD
9300 BPSD
100.000 BPSD
81 octane
Propylene
60.000 BPSD
C4 Olefins
Gasoline
40.000 BPSD
Naphtha Hydro
Cycle Oil
Treating
Slurry Oil
Coker Gas Oil
A light reformate dilute benzene cut, 7,500 bpsd RON=70, MON=58 is fractionated and sent as afeed to steam cracking. An optional fractionation of 3,300 bpsd C5-i C6 is possible along withsending this stream to isomerization for further octane enhancement.
Under the first scenario the net gasoline make is 87,000 bpsd and 7,500 bpsd of steam crackingfeedstock containing 13.3 vol% benzene. In the alternate case 90,300 bpsd gasoline is produced and4,200 bpsd C6/C7 petrochemical feedstock containing 24 vol% benzene is feeding the steam cracking.
In the first case the RON of the gasoline is elevated from 92.0 to 93.9. The impact on the MON(Motor Octane), is even higher, thus the actual octane revenue could increase by about $70,000-80,000 per day ($25 MM per year) and let alone the 0.4 psi reduction in RVP. This reduction in RVPwill allow blending of some 400 bpsd of N-butane.
If as discussed later, if 20% added reforming capacity can be made available, about 7,000 bpsd ofnaphtha dedicated to steam cracking or an alternate source can be partially swapped with 9,000 bpsddilute benzene to be fractionated while co-producing an additional 10 MM scfd of hydrogen and anadditional 500 bpsd (15 KT/Y) of LPG. The total gasoline make under this scenario will be 92,600bpsd and RON= 94.2.
Once dilute benzene recovery is in place, or for that matter even conventional recovery by extraction,more precursors of benzene could be introduced to the reformer thus increasing benzene make bysome 25-50% depending on particular naphtha analysis and process limitations of the reformer. Addingprecursors of benzene to reformer feed may increase the firing duty of the first heater by some 10%.
Inexpensive ceramic coating,say an investment of Generic Catalytic Reforming Process
$500,000, could alleviate thispotential bottleneck if existing represents a simplifiedscheme of continuouscatalytic reforming. Naphthafeed is being prefractionated naphtha. The heavy C7-360F naphtha is being ppm, and nitrogen.
Hydrotreated naphtha is entering a three to four stage reformer operating at nominal 5 bars-g and 450-500 C reforming initial temperatures and pressure. Reformer hydrogen rich product gas is beingrecycled at a ratio of 5-6 to 1 to the feed on a molar basis. Heat is recovered from the flue gas ofinterheaters producing steam at 40 bar-g and 400 C. This steam is used as motive power source in therefinery and a steam turbine for the reformer recycle compressor would be an ideal user. The reformateis under going stabilization by separating C3/C4 LPG product and hydrogen rich by-product 50 MMscfd of contained hydrogen as 87-90 vol% is proceeding to OBL, probably 38 MM Scfd to dieselhydrotreating and about 12 MM scfd for naphtha hydrotreating. The hydrotreater off-gas, mostlyH2S, is routed to a sulfurrecovery unit.
Conventional Benzene Recovery by
Extraction
to Isomar Parex
P-xylene
Recovery
reforming sources 4-9 wt%(3.5.-8 vol%) benzene in Reformate
Reformate
Splitter
Benzene Toluene
reformate streams usingextraction such as the Fractionation
Depentanizer
Benzene - Toluene
Sulfolane
Extraction
reformate streams. To the
C / C Raffinate
contrary, in order to
minimize benzene in the
gasoline pool, at least in the U.S., Canada, Australia, West Europe and Japan, benzene and precursors
of benzene such as cyclohexane and methylcyclopentane are pre-fractionated prior to reforming thus
meeting benzene specification in the gasoline pool and not necessarily presenting an optimal gasoline
production scheme had the benzene limitation not been an issue like pre-1990 Clean Air Act. Thus,
the refinery operation is driven not by gasoline economy as prior to the Clean Air Act, but rather
environmental considerations. Recovery of dilute benzene for steam cracking as would be suggested,
will allow many U.S. and West European refineries to revert to the old operation while increasing
benzene production by some 30% and possibly 50% in some cases and yet meet all environmental
limitations. Refineries in Mexico, East Europe and Asia could avoid all together this benzene control
modification as already being practiced in the U.S., Canada, Australia, Europe and Japan.
As shown, in the conventional scheme reformate is under going reformate splitting C8+ as heavy
reformate and C5-C7 including toluene is light cut, and this fractionation uses about 70 trays. The
light cut proceeds to a depentanizer, followed by aromatic extraction. Benzene and toluene is being
extracted as a BT mix and undergoing post fractionation for benzene recovery and incidental pure
toluene recovery. The C6/C7 raffinate RON=55-60 could be reblended in the gasoline pool, or it
could more likely go as a feed to steam cracking.
Recovery of benzene from pyrolisis gasoline sources in steam cracking, say 35-50 wt %, lent it selfmore in favor of extractive distillation such as Uhde’s Morphylane, Lurgi’s Distapex or GTCTechnology, rather than conventional typical Solfulane extraction.
New Method of Benzene Recovery From HOBC Catalytic Reforming Sources
Reformate, RON=94-102 is being fractionated in a simple 75 tray low pressure column to producelight cut unconverted naphtha mostly C5-C7 paraffin containing all the produced benzene 200 F cutpoint. This low octane, about20-25 vol% of the reformate Modified Catalytic Reforming Process
containing 10-20 vol%
benzene and essentially no
toluene has a typical octane
RON=68-72 thusrepresenting a bad blend to a gasoline pool with RON=92.
This material is used as a feed, fractionation of C5 and light C6 and returning it to the gasoline pool. The assumed benzene cut to thesteam cracker would represent 5-9 vol% of the typical gasoline pool in the U.S. and 7-11 vol% inEurope depending on specific refinery configuration.
It should be noted that by removing benzene from gasoline, aside from the removal of a known toxicmaterial from the gasoline pool, the benzene as a gasoline blend represents the highest relativecontributor to greenhouse gas emission because of the higher ratio of carbon to hydrogen. Steamcracking of dilute benzene tends to increase propylene yield, which is well synchronized with currentmarket trends.
Naphtha Dilute Benzene Swap to Improve the Above Method.
It has been discovered by my own personal survey with 35 U.S. and Canadian refineries that in about65-70% of reformers in the U.S., 15-20% additional reforming capacity could be achieved withrelatively small capital investment and in some cases no investment at all. As a good rule of thumb, itcould be said that in 65-70% of U.S. reformers, an additional 15-20% capacity could be achievedwith an investment of 3-5% of the cost of a new reformer at the same capacity. For example theinvestment in a 35,000 bpsd reformer including OBL could be on the order of $150 MM U.S., whilefor $6.0 MM it may be debottlnecked to 42,000 bpsd and preserving the original octane. A typicaldebottlenecking may involve replacing the feed effluent exchanger with a plate type exchanger suchas Packinox, ceramic coating of the tubes in the heaters and other mechanical revamps as applicableon a case-by-base basis.
Under the above scenario, naphtha from OBL dedicated to steam cracking is swapped with unconvertednaphtha dilute benzene cut. Application of this concept is likely to elevate the RON of the gasolinepool by 1.8-2.5, will increase hydrogen and LPG production, eliminate benzene in the gasoline pooland will reduce RVP by 0.3-0.5 psi. For California refineries or refineries dedicating their product tothe state of California, it would be a prudent idea to run the CARB model for T-50 (mid boiling point)driveability index etc. These issues could affect some of the design considerations. It should be notedthat typical naphtha dedicated to steam cracking tends to be paraffinic, in order to achieve maximumolefin yield, while reformer naphtha is on the naphthenic/aromatic side in order to achieve highoctane. Therefore, this issue of feed swap should be viewed with caution and on a case-by-base basis.
Steam Cracking of Dilute Benzene
Dilute benzene stream C5-C7 cut or in an alternate case C6-C7 cut can be introduced as an exclusivefeed to a cracking furnace, and in most cases as a partial feed after being mixed with naphtha. It hasbeen determined that the impact of benzene on the cracker in terms of operability or process limitationsis rather small, and actually in most cases, likely to be negligible. The resulting pyrolysis gasolineinstead of being comprised of 35-50 wt% benzene would comprise 70-85 wt% benzene. Thusdownstream recovery of benzene from 35-85 wt% benzene concentration would be far moreeconomical than benzene recovery from a reformate stream comprising 4-9 wt% benzene. Further,producing pyrolysis gasoline with 70-85 wt% benzene will allow conventional fractionation of benzeneto 97-98 wt% or more at much lower capital cost and utilities than the common extractive distillation,and let alone conventional extraction from reformate streams. To a degree the benzene concentration would be a function ofcracking severity, and higher Steam Cracking Dilute Benzene
Steam 100 Bar 500° C
Recovery
Ethane Recycle
Hydrogen
Nevertheless, the crackingseverity at the most is a very Ethylene
from Refinery
Dilute Benzene
8 Furnaces &
Quench Water
Cracked Gas
Compressor &
Steam Cracking
Lower Purity Benzene
Refinery
Cold Fractionation
Demethanizer
Deethanizer
Ethylene Frac
Refrigeration
Propylene
Propylene
Fractionation
Pygas Hydro-
Treater Benzene
C Fractionation
Recovery
Propylene
Benzene 98.0 wt%
benzene purity has no
impact on the alkylation or
transalkylation catalysts.
As for alkylation, catalyst issues have been fully resolved by ExxonMobil and Atofina. The non-aromatics in the benzene feed with some residual benzene would be purged to steam cracking, thusall the benzene is ultimately recovered and the impurities are converted to additional olefins. Lowerpurity benzene will not affect the purity of ethylbenzene or downstream production of styrene monomer.
The initial research by UOP, ExxonMobil, Chevron and Atofina, U.S. 6,002,057, U.S. 5,750,814,U.S. 5,273,644, U.S. 5,083,990, U.S. 4,209,383 on alkylating dilute benzene streams was motivatedoriginally by the desire to alkylate benzene concentrate from gasoline, say 30 wt% benzene heart cutfrom reformate with ethylenefrom FCC off-gases. This was New Concept - Dilute Benzene
Production
Disproportion
Isomar-Parex
Fractionation
to P-xylene
Modified
Optional
Reformate
Splitter
Purification
Ethylene
C – C /Benzene
Propylene
Cracking
Treating
Fractionation
C4 Olefins
Further, it was also discovered that for cyclohexane oxidation to adipic acid as a precursor to nylon6,6, benzene purity of 97-98 wt%, where the balance is C6/C7 non-aromatics containingmethylcyclopentane, that resulted in lower purity cyclohexane is more than adequate. A recentevaluation in pilot plant operation by a nylon 6,6 producer has demonstrated that lower puritycyclohexane containing some 3,000 ppm methylcyclopentane is not an issue. For adipic acid nylon6,6, some minor process modifications are needed to solve new issues associated with the downstreamcyclohexane oxidation process. The common industry specifications of cyclohexane are 99.85%purity and not to exceed 200 ppm methylcyclopentane and 50 ppm aromatics, but these were drivenby caprolactam producers. However, new testing for adipic acid nylon 6,6 which is about 33% ofglobal and 60% of the U.S. nylon market, have shown that common specifications for cyclohexanewith the exception of aromatics may have run their “useful life” and new specifications could beadopted.
The following benzene concentrations could be achieved by conventional double column fractionations; • Benzene from pygas of dilute benzene feed- Recovery of toluene, 92-95 wt% and 5-8 wt% C7-C8 non aromatics will require an additional column.
This toluene would be suitable for HDA with higher hydrogen consumption.
The final concentration of benzene is simply a function of the ratio of benzene to C6/C7 co-boilers,which needs to be determined on a case-by-case basis and related to feed composition and severity ofcracking.
For the very conservative operator producing ethylbenzene by liquid phase or mixed phase, and
concerned by benzene purity, the 97-98 wt% benzene produced by conventional fractionation of
pyrolysis gasoline, could be further purified to 99.9 wt% at a capital cost of about 50% of “normal”
extractive distillation of pyrolysis gasoline and considerable less utilities, mostly 17 bar steam.
Nevertheless, the “conservative” operators can also easily test the benzene purity concept by injecting
2-3 wt% impurities, cyclohexane, methylcyclopentane, N-hexane dimethylpentane methylcyclohexane
into the benzene stream and reaching their own conclusions. As said, conventional fractionation of
benzene from reformate stream HOBC may reach a limit of 20-40 wt%, thus benzene extraction or
extractive distillation of reformate is the only way for benzene recovery from reformate streams.
Total Global Opportunity
The bottom line is very simple: a technical survey of some 35 best candidate refineries in the U.S. and
Canada alone, show that about 1,700 KT/Y of benzene that could be easily recovered as dilute
benzene and logistically located near waterways or in close proximity to the market, is left unconverted
in the gasoline pool or hydrotreated. An additional 400 KT/Y could be recovered from reformer
gasoline in Mexico, and probably some 1,500 KT/Y in the European Union, with additional substantial
recovery in the FSU, Japan, Venezuela, Algeria, Australia and India.
Business Cases
Two business cases are analyzed; producing styrene monomer in a generic emerging market andproducing low purity cyclohexane in the U.S. Gulf Coast. The modified oxidation process ofcyclohexane is third party confidential information.
Ethylbenzene Styrene production
1. The Base Case represents a conventional steam cracking of light naphtha, mostly C5/C6 from natural gas condensate. The assumed project produces 1,000 KT/Y ethylene, 500 KT/Ypropylene and 500 KT/Y styrene monomer. Ethylene and propylene are polymerized in downstream operation. About 160 KT/Y benzene is produced by extractive distillation ofhydrotreated pyrolysis gasoline and an additional 70 KT/Y benzene is produced byhydrodealkylation of toluene and xylene. The balance of the benzene, 160 KT/Y, is importedfrom OBL.
2. In the alternate Case, about 19,000 bpsd iso-C6 Octane =75 RON is being fractionated from the 80,000 bpsd condensate. The iso-C6 and 3,000 bpsd of C4 olefin mix is being exchangedwith 21,000 bpsd dilute benzene stream from two refineries and 1,000 bpsd n-butane purgefrom alkylation. Based on this scheme the gasoline production rate, the octane and the Reid Olefins/Aromatics Petrochemical
Configuration (Base Case)
Olefins/Aromatics Petrochemical
Configuration (Alternate Case)
Vapor Pressure (RVP) and all other gasoline qualities remain the same or slightly improved.
About 160 KT/Y benzene is removed from the gasoline pool, and the petrochemical complexbecomes self sufficient in benzene. Additional advantages are obtained by using dilute ethylenealkylation using 10 vol% ethylene from the demethanization zone operating at about 30 bars.
Benzene at 97 wt% purity is produced thus avoiding aromatic extraction.
3. The economic diagram as shown in the slides represent the two cases. Product and feedsock values of October 2004 show the net benefit of the Alternate Case is $130 MM U.S. per year.
The total cost of feedstock was estimated at $1,200 MM per year. The total value of productswas estimated at $2,000 MM U.S. per year. Thus the added benefit represents 11% of thefeedstock and 27% of the margin.
Olefins/Aromatics Petrochemical
Configuration (Base/Alternative Cases)
ETHYLENE 101.5 / 101
BUTADIENE 20.0 / 20.0
PROPYLENE 59.5 / 59.5
FUEL OIL 31.0 / 31.0
HYDROGEN 1.8 / 1.0
FUEL GAS 13.0 / 12.0
BUTENE-1 0.0 / 0.0
STEAM 40 BAR G 0.0 / 60.0
C4 MIX 36.0 / 36.0
PY-GAS 53.0 / 71.0
0.0 / 267.0
18.0 / 0.0
DILUTE BENEZENE 0 / 100.0
C4 OLEFINS 16.0 / 16.0
BENZENE 30.5 / 48.5
17.5 / 18.0
0.0 / 81.0
0.0 / 348.0
FUEL OIL 1.0 / 1.0
348.0 / 0.0 CONDENSATE FEED FROM BL
STYRENE 59.5 / 59.5
348.0 / 348.0
N-BUTANE TO MAH 3.0 / 3.0
Cyclohexane Case
A gas cracker in U.S. Gulf Coast cracking ethane and propane has the capability to accept up to24,000 bpsd of liquids, in this case about 22,000 bpsd of dilute benzene and 2,000 bpsd of hydrotreatedpyrolysis gasoline recycle. The dilute benzene will probably come from three (3) refineries and willbe cracked with 35-40% of furnace capacity. Benzene is recovered from hydrotreated pygas byconventional fractionation as 97-98 wt% benzene and balance of C6/C7 non- aromatics includingsome 3,000 ppm methylcyclopentane. The benzene would be dedicated for on-site conversion tocyclohexane using hydrogen as produced by the cracker. The lower purity cyclohexane is moved off-site for air oxidation followed by oxidation with nitric acid to adipic acid. The oxidation was recentlytested in a pilot plant and all necessary modifications to the existing system have been identified. Assaid, the nature of the modification remains a third party confidential.
1. The diagram above represents the configuration of the steam cracker prior to the revamp. This operation calls for five (5) furnaces operating on propane net feed of 29 tons per hour eachplus 6.5 tons per hour propane recycle. Also three (3) furnaces on ethane 16 ton per hour net Benzene to Nylon 6,6
Hydrogen
Dilution steam at 5 bar-g, about 0.35 ton per Cyclohexane
Cyclohexane
Oxidation
extracted from the mainsteam turbine driver.
Cyclohexanol
Nitric Acid
Nylon 6.6
Oxidation
the diagram on theprevious pagerepresents therevamped operation.
Two stages pygas C5-C8 hydrotreating have been added. The first stage converts di-olefins to olefins while thesecond stage saturates the olefins and removes sulfur compounds which could be critical tothe cyclohexane oxidation process. A new cyclohexane 220 KT/Y is added that is exporting26 tons per hour steam at 5.5 bar-g to the steam cracker dilution steam system thus reducingdilution steam make by about one-third. The hydrotreated pygas, 2,000 bpsd 9.0 tons perhour mostly C5 is recycled to 3 cracking furnaces along with the dilute benzene feed 22,000bpsd, 110 tons per hour.
3. As said the lower purity cyclohexane is moved to the OBL oxidation facility using proprietary process as well as proprietary modification to handle the impurities.
The reduction in cost of cyclohexane would be very much a site specific analysis. Early analysis of lowerpurity benzene production NPRA 2003 AM-10 has shown 30% cost advantage for producing ethylbenzenestyrene. Nevertheless, the introduction of dilute benzene feed changes the product slate. For ex-ample, it increases propylene yield, very substantially increasing benzene yield and C4 mix yield.
Cost of dilute benzene feedstock, value of by-products, and the overall business model will greatlyaffect the value of cyclohexane.
It is our opinion that with the exception of niche market situations and advantageous pricing of
feedstock, benzene production via the conventional route as co-product to gasoline production is the
more economical route. Further, the production of new molecules of benzene at least on the short
term is not necessary. The molecules of benzene, as said over 3,500 KT/Y are here now and being
blended to gasoline while the refining industry is facing investments to reduce this carcinogenic
material in gasoline. It is estimated that close to 50,000 b/d of benzene have disappeared from the U.S
gasoline pool since 1990.
It is thought by reverting to pre 1990 Clean Air Act and the appropriate European and Japanese
regulation could further alleviate the shortage of benzene for petrochemical industries by increasing
the availability of benzene to 5,000 KT/Y.
Recovery of benzene as dilute benzene feedstock to steam cracking and downstream benzene recov-ery from pyrolysis gasoline is by far more economical than conventional extraction of benzene fromreformate streams.
Recovery of benzene as impure material, 97-98 wt% will fit to over 60% of market need. Once vaporphase alkylation for production of EB-styrene is replaced by liquid phase or mixed phase, which isindustry trend, well over 80% of the market for benzene derivatives will fit to the lower purity mode.
The mixed phase alkylation, is attributed to dilute ethylene alkylation and well described in NPRApaper AM-03-10.
Based on all the above, and given the fact the relative reforming capacity in the Middle East is limited,the naphtha is paraffinic (lean), and all steam crackers are gas crackers, mostly ethane crackers, theproduction of benzene and derivatives in Middle East locations does not offer an advantage overother global locations such as the U.S. and Europe with high reforming capacity using rich naphthafeeds and steam cracking capacity of liquid feedstock. Low cost dilute ethylene or lower puritypropylene, from steam cracking sources could further enhance the relative economics of benzenederivatives of non Middle East locations. (ECN, Dec. 6th 2004) The final cost of benzene and derivatives should be analyzed on a case-by-case situation, subject to
cost of feedstock, by-products and business model. Prior case analysis in NPRA -03-10 suggested
savings of over 30% and no new information suggests the reversal of this prior assessment.

Source: http://w.eni-italy.info/ENI_Web/Data/PDFs/BENZENE%20SUPPLY%20TRENDS%20AND%20PROPOSED%20METHOD.pdf