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CHAPTER 1.3UOP ALKYLENE™ PROCESS

FOR MOTOR FUEL ALKYLATION

Cara RoeselerUOP LLC

Des Plaines, Illinois

INTRODUCTION

The UOP Alkylene process is a competitive and commercially available alternative to liq-uid acid technologies for alkylation of light olefins and isobutane. Alkylate is a key blend-ing component for gasoline having high octane, low Reid vapor pressure (RVP), lowsulfur, and low volatility. It is composed of primarily highly branched paraffinic hydro-carbons. Changing gasoline specifications in response to legislation will increase theimportance of alkylate, making it an ideal “clean fuels” blend stock. Existing liquid acidtechnologies, while well proven and reliable, are increasingly under political and regula-tory pressure to reduce environmental and safety risks through increased monitoring andrisk mitigation. A competitive solid catalyst alkylation technology, such as the Alkyleneprocess, would be an attractive alternative to liquid acid technologies.

UOP developed the Alkylene process during the late 1990s, in response to the indus-try’s need for an alternative to liquid acid technologies. Early attempts with solid acid cat-alysts found some to have good alkylation properties, but the catalysts also had short life,on the order of hours. In addition, these materials could not be regenerated easily, requir-ing a carbon burn step. Catalysts with acid incorporated on a porous support had beeninvestigated but not commercialized. UOP invented the novel HAL-100 catalyst that hashigh alkylation activity and long catalyst stability and easily regenerates without a high-temperature carbon burn. Selectivity of the HAL-100 is excellent, and product quality iscomparable to that of the product obtained from liquid acid technologies.

ALKYLENE PROCESS

Olefins react with isobutane on the surface of the HAL-100 catalyst to form a complexmixture of isoalkanes called alkylate. The major constituents of alkylate are highlybranched trimethylpentanes (TMP) that have high-octane blend values of approximately

1.25

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100. Dimethyl hexanes (DMH) have lower-octane blend values and are present in alkylateat varying levels.

Alkylation proceeds via a carbenium ion mechanism, as shown in Fig. 1.3.1. The com-plex reaction paths include an initiation step, a propagation step, and hydrogen transfer.Secondary reactions include polymerization, isomerization, and cracking to produce otherisoalkanes including those with carbon numbers which are not multiples of 4. The primaryreaction products are formed via simple addition of isobutane to an olefin such as propy-lene, butenes, and amylenes. The key reaction step is the protonation of a light olefin onthe solid catalyst surface followed by alkylation of an olefin on the C4 carbocation, form-ing the C8 carbocation. Hydride transfer from another isobutane molecule forms the C8paraffin product. Secondary reactions result in less desirable products, both lighter andheavier than the high-octane C8 products. Polymerization to acid-soluble oil (ASO) isfound in liquid acid technologies and results in additional catalyst consumption and yieldloss. The Alkylene process does not produce acid-soluble oil. The Alkylene process alsohas minimal polymerization, and the alkylate has lighter distillation properties than alky-late from HF or H2SO4 liquid acid technologies.

Alkylation conditions that favor the desired high-octane trimethylpentane include lowprocess temperature, high localized isobutane/olefin ratios, and short contact time betweenthe reactant and catalyst. The Alkylene process is designed to promote quick, intimate con-tact of short duration between hydrocarbon and catalyst for octane product, high yield, andefficient separation of alkylate from the catalyst to minimize undesirable secondary reac-tions. Alkylate produced from the Alkylene process is comparable to alkylate producedfrom traditional liquid acid technologies without the production of heavy acid-soluble oil.The catalyst is similar to other hydroprocessing and conversion catalysts used in a typicalrefinery. Process conditions are mild and do not require expensive or exotic metallurgy.

1.26 ALKYLATION AND POLYMERIZATION

High

Low

Isobutane/OlefinRatio

C4 =

C4 =

C4

i-C4

i-C4C12 – C20 C12 – C20

90 RON

C5 – C7Cracked Products

60-93 RON

+

C8 C8TMP

100 RON

Isomerized C8DMH

60 RON

+

++

Low HighTemperature

Low HighContact Time

Min

or

Minor

Min

or

FIGURE 1.3.1 Reaction mechanism.

UOP ALKYLENE™ PROCESS FOR MOTOR FUEL ALKYLATION



UOP ALKYLENE™ PROCESS FOR MOTOR FUEL ALKYLATION 1.27

Reactor temperature, isobutene/olefin ratio, contact time, and catalyst/olefin ratios are thekey operating parameters.

Feeds to the Alkylene unit are dried and treated to move impurities and contaminantssuch as diolefins, oxygenates, nitrogen, and sulfur. These contaminants also cause higheracid consumption, higher acid-soluble oil formation, and lower acid strength in liquid acidtechnologies. Diolefin saturation technology, such as the Huels Selective HydrogenationProcess technology licensed by UOP LLC, saturates diolefins to the correspondingmonoolefin and isomerizes the 1-butene to 2-butene. The alkylate formed by alkylatingisobutane with 2-butene is the preferred 2,2,3-TMP compared to the 2,2-DMH formed byalkylating isobutane with 1-butene.

The olefin and isobutane (Fig. 1.3.2) are combined and injected into a carbon-steel ris-er reactor with continuous catalyst reactivation (Fig. 1.3.3) to maintain a constant catalystactivity and minimize catalyst inventory. This provides constant product quality, highyield, and high on-stream efficiency. Liquid-phase hydrocarbon reactants transport the cat-alyst around the reactor circuit where velocities are low relative to those of other movingcatalyst processes. The reaction time is on the order of minutes for the completion of theprimary reactions and to minimize secondary reactions. The catalyst and hydrocarbon areintimately mixed during the reaction, and the catalyst is easily disengaged from the hydro-carbon product at the top of the reactor. The catalyst is reactivated by a simple hydro-genation of the heavier alkylate on the catalyst in the reactivation wash zone. Hydrogenconsumption is minimal as the quantity of heavy alkylate on the HAL-100 catalyst is verysmall. The reactivation process is highly effective, restoring the activity of the catalyst tonearly 100 percent of fresh. The liquid-phase operation of the Alkylene process results inless abrasion than in other catalyst circulation processes due to the lubricating effect of theliquid. Furthermore, the catalyst and hydrocarbon velocities are low relative to those inother moving catalyst processes. This minimizes the catalyst replacement requirements.Catalyst circulation is maintained to target catalyst/olefin ratios. A small catalyst slip-stream flows into a separate vessel for reactivation in vapor phase with relatively mild con-ditions to remove any last traces of heavy material and return the catalyst activity toessentially the activity of fresh catalyst.

Alkylate from the reactor is sent to a downstream fractionation section, which is simi-lar to fractionation sections in liquid acid process flow schemes. The fractionation sectionrecycles the unconverted isobutane back to the reactor and separates out the final alkylateproduct.

FeedPretreatment

ReactorSection

FractionationSection

Butamer Unit

Propane

n-Butane

Alkylate

H2 H2ButaneFeed

ButaneFeed

Light EndsLight Ends

IsobutaneRecycle

OlefinFeed

optional

FIGURE 1.3.2 Alkylene process flow scheme.




ALKYLENE PERFORMANCE

HAL-100, the Alkylene process catalyst, has high acidity to promote desirable alkylationreactions. It has optimum particle size and pore distribution to allow for good mass transferof reactants and products into and out of the catalyst. The catalyst has been commerciallyproduced and demonstrates high physical strength and very low attrition rates in extensivephysical testing. Catalyst attrition rates are several orders of magnitude lower than thoseexperienced in other moving-bed regeneration processes in the refining industry.

HAL-100 has been demonstrated in a stability test of 9 months with full isobutane recy-cle and showed excellent alkylate product qualities as well as catalyst stability.Performance responses to process parameters such as isobutane/olefin ratio, catalyst/olefinratio, and process temperature were measured. Optimization for high performance, cata-lyst stability, and economic impact results in a process technology competitive with tradi-tional liquid acid technologies (Fig. 1.3.4).

Typical light olefin feedstock compositions including propylene, butylenes, andamylenes were also studied. The primary temporary deactivation mechanism is the block-age of the active sites by heavy hydrocarbons. These heavy hydrocarbons are significant-ly lower in molecular weight than acid-soluble oil that is typical of liquid acidtechnologies. These heavy hydrocarbons are easily removed by contacting the catalystwith hydrogen and isobutane to strip them from the catalyst surface. These heavy hydro-carbons are combined in the total alkylate product pool and are accounted for in the alky-late properties from the Alkylene process.

The buildup of heavy hydrocarbons on the catalyst surface is a function of the operat-ing severity and the feedstock composition. The reactivation conditions and the frequencyof vapor reactivation are optimized in order to achieve good catalyst stability as well ascommercially economical conditions.


FeedPretreatment

Section

OlefinFeed

IsobutaneRecycle

Alkylate

LightEnds

LPG

ReactivationWash Zone

i-C4 / H2

AlkyleneReactor

ReactivationVessel

FractionationSection

H2

FIGURE 1.3.3 Alkylene process flow diagram.




ENGINEERING DESIGN AND OPTIMIZATION

The liquid transport reactor for the Alkylene process was developed by UOP based onextensive UOP experience in fluid catalytic cracking (FCC) and continuous catalyst regen-eration (CCR) technologies. Novel engineering design concepts were incorporated.Extensive physical modeling and computational fluid dynamics modeling were used toverify key engineering design details. More than 32 patents have been issued for theAlkylene process technology.

The reactor is designed to ensure excellent mixing of catalyst and hydrocarbon with lit-tle axial dispersion as the mixture moves up the riser. This ensures sufficient contact timeand reaction time for alkylation. Olefin injection nozzles have been engineered to mini-mize high olefin concentration at the feed inlet to the riser. The catalyst is quickly sepa-rated from the hydrocarbon at the top of the riser and falls by gravity into the reactivationzone. The catalyst settles into a packed bed that flows slowly downward in the upper sec-tion of the vessel, where it is contacted with low-temperature hydrogen saturated isobutanerecycle. The heavy hydrocarbons are hydrogenated and desorbed from the catalyst. Thereactivated catalyst flows down standpipes and back into the bottom of the riser. The reac-tor section includes separate vessels for reactivating a slipstream of catalyst at a highertemperature to completely remove trace amounts of heavy hydrocarbons. By returningfreshly reactivated catalyst to the riser continuously, catalyst activity is maintained for con-sistent performance.

The UOP Butamer process catalytically converts normal butane to isobutane with highselectivity, minimum hydrogen consumption, and excellent catalyst stability. When theButamer process is combined with the Alkylene process, n-butane in the feed can be react-ed to extinction, thereby reducing the fresh feed saturate requirements. In addition, the


C5

C6-C7

C8

C9+

Prod

uct D

istr

ibut

ion,

LV

-%

0

20

40

60

80

100

HF H2SO4 Alkylene

RON 95.7 96.6 97.0MON 94.2 93.6 94.2Temp, °F 100 50 77Temp, °C 38 10 25

FIGURE 1.3.4 Catalyst comparison: mixed 4 olefin feed.




increased isobutane concentration in the isostripper reduces the size of the isostripper andallows for a reduction in utilities consumption. A novel flow scheme for the optimal inte-gration of the Butamer process into the Alkylene process was developed. The two units canshare common fractionation and feed pretreatment equipment. Synergy of the two unitsreduces the capital cost requirement for the addition of the Butamer process and reducesthe operating cost. Table 1.3.1 illustrates the maximum utilization of the makeup C4 paraf-fin stream and the utilities savings.

ALKYLENE PROCESS ECONOMICS

The product research octane number can be varied according to the reaction temperatureand the isobutane/olefin ratio. Additional refrigeration duty can be justified by higherproduct octane, depending on the needs of the individual refiner. Higher isobutane/olefinratio requires higher capital and utilities. Mixed propylene and butylene feedstocks canalso be processed with less dependence on operating temperature. However, the alkylateproduct octane is typically lower from mixed propylene and butylene feed than from buty-lene-only feed. Processing some amylenes with the butylenes will result in slightly loweroctane. Most refiners have blended the C5 stream in the gasoline pool. However, withincreasing restrictions on Reid vapor pressure, refiners are pulling C5 out of the gasolinepool and processing some portion in alkylation units.

The three cases shown in Table 1.3.2 compare the economics of the Alkylene processwith those of conventional liquid acid alkylation. The basis is 8000 BPSD of alkylate prod-uct from the Alkylene process. Case 1 is the Alkylene process, case 2 is an HF alkylationunit, and case 3 is a sulfuric acid unit with on-site acid regeneration. All cases include aButamer process to maximize feed utilization.

The Alkylene process has a yield advantage over liquid acid alkylation technologiesand does not produce acid-soluble oil (ASO) by-products. In addition, the capital cost ofthe Alkylene process is competitive compared with existing technologies, and maintenancecosts are lower. The HF alkylation unit requires HF mitigation capital and operating costs.The sulfuric acid alkylation unit requires regeneration or transport of large volumes ofacid. Overall, the Alkylene process is a safe and competitive option for today’s refiner.

SUMMARY

Future gasoline specifications will require refiners to maximize the use of assets and rebal-ance refinery gasoline pools. The potential phase-out of MTBE will create the need for


TABLE 1.3.1 Alkyene Process Capital Costs

Alkylene Alkylene � Butamer

Total feed from FCC, BPSD 7064 7064C4 paraffin makeup 9194 2844C5� alkylate, BPSD 8000 8000C5� alkylate RONC 95.0 95.0USGC EEC, million $ 43.0 43.7Utilities Base 0.96*Base




clean, high-octane blending components, such as alkylate, to allow refiners to meet poolrequirements without adding aromatics, olefins, or RVP. Alkylate from the Alkyleneprocess has excellent alkylate properties equivalent to those of HF acid technology, doesnot generate ASO, has better alkylate yield, and is a safe alternative to liquid acid tech-nologies. Recent developments propel the Alkylene process technology into the market-place as a viable option with technical and economic benefits.

As the demand for alkylate continues to grow, new alkylation units will help refinersmeet the volume and octane requirements of their gasoline pools. The Alkylene processwas developed as a safe alternative to commercial liquid acid alkylation technologies.

BIBLIOGRAPHY

Cara M. Roeseler, Steve M. Black, Dale J. Shields, and Chris D. Gosling, “Improved Solid CatalystAlkylation Technology for Clean Fuels: The Alkylene Process,” NPRA Annual Meeting, SanAntonio, March 2002.


TABLE 1.3.2 Comparison of Alkylation Options

Alkylene � HF � On-site regenerationButamer Butamer H2SO4 � Butamer

Total feed from FCC, BPSD 7064 7064 7064C5� alkylate, BPSD 8000 7990 7619C5� alkylate

RONC 95.0 95.2 95.0MONC 92.9 93.3 92.2(R � M) / 2 94.0 94.3 93.6

C5� alkylate D-86, °F50% 213 225 2190% 270 290 29

Utilities, $/bbl C5 � alkylate 174 0.70 1.32Acid cost, $/bbl — 0.08 0.01Catalyst cost, $/bbl 0.60 0.02 0.02Metals recovery, $/bbl 0.03 0.00 0.00Chemical cost, $/bbl 0.03 0.02 0.02Variable cost of production, $/bbl 2.39 0.82 1.37Fixed cost, $/bbl 1.97 2.43 3.53Total cost of production, $/bbl 4.37 3.25 4.90Estimated erected cost, million $ 43.5 40.5 63.3







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