0071455914_ar014

CHAPTER 2.7UOP TATORAY PROCESS

Antoine Negiz and Thomas J. StoodtUOP LLC

Des Plaines, Illinois

INTRODUCTION

An aromatics complex is a combination of process units which are used to convert petro-leum naphtha and pyrolysis gasoline to the basic petrochemical intermediates: benzene,toluene, and xylenes (BTX). Details of the aromatic complex are discussed in greaterdepth in Chap. 2.1. A fully integrated modern complex designed to produce benzene, para-xylene (PX), and sometimes ortho-xylene includes UOP’s Tatoray process. A simplifiedflow diagram of a typical aromatics complex designed for maximum production of PX isshown in Fig. 2.7.1. The Tatoray process is integrated between the aromatics extractionand xylene recovery sections of the plant (Fig. 2.7.1). Toluene (A7) is fed to the Tatorayunit rather than being blended into the gasoline pool or sold for solvent applications. If thegoal is to maximize the production of PX from the complex, the C9 aromatic (A9) by-prod-uct can also be fed to the Tatoray unit rather than blending it into the gasoline pool.Processing A9-A10 in a Tatoray unit shifts the chemical equilibrium in the unit towarddecreased benzene production and increased production of xylenes.

The Tatoray process provides an ideal way of producing additional mixed xylenes fromlow-value toluene and heavy aromatics. What is seldom recognized, however, is where thexylenes are produced within the complex. For an aromatics complex that includestransalkylation, approximately 50 percent of the xylenes in the complex come from thetransalkylation reaction, that is, the Tatoray process. The reformate provides approximate-ly 45 percent, and 5 percent comes from C8 aromatic isomerization such as the Isomarprocess, via conversion of ethylbenzenes to xylenes. The Tatoray process produces anequilibrium mixture of xylenes plus ethylbenzene. The xylenes are recovered and isomer-ized to PX while the ethylbenzene can also be converted to xylenes. The incorporation ofa Tatoray unit to an aromatics complex can more than double the yield of PX from naph-tha feedstock. It is extremely important, when looking at improving xylene productioneconomics, that one focus not only on the reformer, but also on the transalkylation processand its performance. There are a number of different strategies that producers are pursuingto increase profitability. Two in particular are to reduce feedstock consumption (and theassociated cost) and upgrade by-products to increase their sale value. Transalkylation canplay a key role in both strategies.

2.55

Source: HANDBOOK OF PETROLEUM REFINING PROCESSES

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)Copyright © 2004 The McGraw-Hill Companies. All rights reserved.

Any use is subject to the Terms of Use as given at the website.

PROCESS CHEMISTRY

The two major reactions in the Tatoray process, disproportionation and transalkylation, areillustrated in Fig. 2.7.2. The conversion of toluene alone to an equilibrium mixture of ben-zene and xylenes is called disproportionation. The conversion of a blend of toluene and A9to xylenes through the migration of methyl groups between methyl-substituted aromatics iscalled transalkylation. In general, both reactions proceed toward an equilibrium distributionof benzene and alkyl-substituted aromatics. Methyl groups are stable at Tatoray reaction con-ditions, and thus the reaction equilibrium is easy to estimate when the feed consists of allmethyl-substituted aromatics. The equilibrium distribution is illustrated in Fig. 2.7.3. Thereaction pathways involving A9 for the Tatoray process have also been described elsewhere.1

More complex reaction pathways occur when other alkyl groups are present in the feed.The Tatoray process effectively converts the ethyl, propyl, and higher alkyl group substi-tuted A9-A10 to lighter single-ring aromatics via dealkylation, while preserving the methylgroups. The lighter, mostly methyl-substituted, aromatics proceed with transalkylation toproduce benzene and xylenes in a yield pattern governed by equilibrium. The dealkylationreactions involving propyl and higher substituted groups typically proceed to completion.It is also known that the diffusion coefficients of ethyl and higher alkyl group substitutedrings in some aluminosilicates are much lower than those of the methyl-only substitutedrings.2 The Tatoray catalyst enhances the transport properties of the reactants, therebyincreasing the reaction efficiency.

The TA series of catalysts was first commercialized in 1969. A new generation has beenintroduced, on average, every 6 years. UOP introduced TA-4 in 1988. Tatoray licensees arevery familiar with TA-4 catalyst and have experienced its ruggedness and ability to handlea wide variety of operating conditions while maintaining performance. The catalystdemonstrates superior selectivity and stability over a wide range of feed rates and feedcompositions. High per pass conversion to benzene and mixed xylenes established TA-4as economically attractive.

2.56 BASE AROMATICS PRODUCTION PROCESSES

Platforming

Extraction

NHT

Naphtha

Tatoray

Parex

OXColumn

XyleneSplitter

DeHeptColumn

ortho-xylene

Isomar Light Endspara-xylene

A10+

A9Col

TolCol

BzCol

Benzene

Raffinate

ReformateSplitter

FIGURE 2.7.1 Typical UOP aromatics complex.

UOP TATORAY PROCESS



UOP TATORAY PROCESS 2.57

The most recent Tatoray catalyst to be successfully commercialized is called TA-5.3

This catalyst was designed as a “drop-in” reload catalyst for service in the Tatoray processand was commercialized in October 2000. The stability of TA-5 catalyst is more than dou-ble that of TA-4. This results in improved on-stream efficiency and a reduction in regen-eration frequency. Commercial units have also shown that the activity of TA-5 is at least50 percent better than that of TA-4, allowing users to potentially increase throughput whilemaintaining current cycle lengths. Alternatively, users can use the TA-5 catalyst to processheavier aromatic feeds to produce higher-value benzene and mixed-xylenes products.

Figure 2.7.4 illustrates the relative performance of TA-5 versus TA-4 in terms of activ-ity and stability. This information is based on data from a commercial unit that has beenrunning with TA-5 since October 2000. Prior to the reload of TA-5 catalyst, this unit wasloaded with TA-4. This unit has continuously processed significantly more feed at a sub-stantially lower hydrogen/hydrocarbon mole ratio.

Disproportionation

C

CCC

C C

CCC

2

Toluene Benzene Xylenes

Transalkylation

XylenesC9 AromaticsToluene

+ 2

+

FIGURE 2.7.2 Major Tatoray reactions.

Equ

ilibr

ium

Con

cent

ratio

n, m

ol-%

Methyl/Phenyl Ratio in Feed

1

100

1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8

80

60

40

20

0

Trimethylbenzenes

Benzene

A11+

Xylenes

Tetramethylbenzenes

Toluene

FIGURE 2.7.3 Equilibrium distribution of methyl groups at 700 K.

UOP TATORAY PROCESS



TA-5 catalyst provides significant advantages over other catalysts:

● Higher stability. Figure 2.7.4 clearly illustrates the stability of TA-5 catalyst versus TA-4 catalyst. The slope of the curves shows TA-5 catalyst to be twice as stable as TA-4 cat-alyst. This means a reduction in regeneration frequency that results in improvedon-stream efficiency.

● Higher activity. The 50 percent higher activity translates to increased throughput or low-er hydrogen to hydrocarbon ratios while maintaining the same cycle length.Alternatively, the amount of heavy aromatics charged to the Tatoray unit can beincreased to maximize PX production from the complex while maintaining stability.

● No process modification required. With the same throughput across the reactor, at thesame operating pressure levels and H2/HC ratio as TA-4 catalyst, no process modifica-tions are required to use TA-5 catalyst.

● High conversion and high yield. TA-5 catalyst provides the high conversion and yieldsobtained using TA-4 catalyst.

● Contains no precious metals. The TA-5 catalyst contains no precious metals.● Benzene purity. The quality of the benzene produced depends on the feed composition.

In many applications, TA-5 catalyst delivers high quality benzene product which doesnot require purification by extraction.

● Regenerability. It shows complete recovery of activity, yields, and stability.● UOP’s commercial experience and technical support. UOP’s commercial experience,

comprehensive guarantees, technical service, and state-of-the-art research facilities ensurethat the customer will achieve optimal catalyst performance of the Tatoray process unit.The experience gained from the large installed capacity and the success of the TA seriescatalysts installed in these units help ensure that future reloads will also be a success.

DESCRIPTION OF THE PROCESS FLOW

The Tatoray process uses a very simple flow scheme consisting of a fixed-bed reactor anda product separation section (Fig. 2.7.5). The fresh feed to the Tatoray unit is first com-


Ave

rage

Rx

Bed

Tem

pera

ture

, °C

Catalyst Life (MT of Feed/kg of Catalyst)

Slope = X

Slope = 0.5X

TA-4

TA-5

FIGURE 2.7.4 TA-5 stability and activity.

UOP TATORAY PROCESS



bined with hydrogen-rich recycle gas, preheated by exchange with the hot reactor effluent,and then raised to reaction temperature in a fired heater. The combined feed vapor is thensent to the reactor where it is processed downflow over a fixed bed of catalyst. The reac-tor effluent is then cooled by exchange with the combined feed and a product condenserand is sent to a product separator. Hydrogen-rich gas is taken off the top of the separator,where a small portion of it is purged to remove accumulated light ends from the recyclegas loop. It is then mixed with makeup gas and recycled to the reactor. Liquid from thebottom of the separator is sent to a stripper column. The overhead from the stripper iscooled and separated into gas and liquid products. The stripper overhead gas is exportedto the fuel gas system. The overhead liquid is recycled to the Platforming unit debutaniz-er column so that any benzene in this stream may be recovered to the extraction and or inthe BT separation section of the aromatics complex. The benzene and xylene products,together with the unreacted toluene and C9� aromatics, are taken from the bottom of thestripper and recycled to the BT fractionation section of the aromatics complex.

Because of the dealkylation reaction pathway, the reactor section of the Tatoray processis maintained in a hydrogen atmosphere even though no net hydrogen is consumed in thetransalkylation reactions. In practice, a small amount of hydrogen is always consumed dueto the dealkylation side reactions. Hydrogen consumption increases for heavier feedstockssince these generally contain heavier alkyl groups, typically C3 and C4.

FEEDSTOCK CONSIDERATIONS

The feed to a Tatoray unit is typically a blend of toluene and A9-A10 derived from refor-mate. UOP also has experience with pygas-derived A9-A10 blends with reformate. Figure2.7.6 shows typical yields on fresh feedstocks ranging from 100 wt % toluene to 100 wt% A9. As shown in Fig. 2.7.6, the product composition shifts away from benzene andtoward xylenes as the A9 concentration in the feed increases. Saturates in the feed are gen-erally cracked to propane and butane. For this reason, a limitation on saturates in the feed


Feed SurgeDrum Heater

Reactor

ProductSeparator

Stripper

Purge Gas

OverheadLiquid

To BTFractionation

Section

Recycle Gas

Makeup H2

Toluene

C9Aromatics

Light Ends

FIGURE 2.7.5 Tatoray flow diagram.

UOP TATORAY PROCESS



is usually specified. In general, feed to a Tatoray unit should meet the specifications out-lined in Table 2.7.1.

PROCESS PERFORMANCE

The ability to process A9-A10 in a Tatoray unit can make more feedstock available forxylenes production and dramatically shifts the selectivity of the unit toward decreased ben-zene and increased production of xylenes. A typical aromatics complex without a Tatorayunit can produce approximately 200,000 MTA of PX from 25,000 BPD of Light Arabiannaphtha (160 to 300°F ASTM Distillation). If a toluene-only Tatoray unit is added to thecomplex, the same 25,000 BPD of naphtha can produce 280,000 MTA of PX, an increaseof 40 percent. When an A7/A9-A10 Tatoray unit is added to the complex, the endpoint of thefeed naphtha can be increased from 300 to 340°F in order to maximize the amount of A9-A10 precursors in the feed. If we keep the feed rate to the reformer constant, 25,000 BPDof this heavier naphtha will produce about 420,000 MTA of PX, an increase of 110 per-cent over the base complex (Fig. 2.7.7).

The maximum theoretical conversion per pass is limited by equilibrium and is a functionof the feedstock composition. For example, theoretical conversion for a pure toluene feed isapproximately 59 wt % per pass. Operating at high conversion minimizes the amount ofunconverted material that must be recycled through the BT fractionation section of the com-plex. A smaller recycle stream minimizes the size of the benzene and toluene columns, min-imizes the size of the Tatoray unit, and minimizes the utility consumption in all these units.Tatoray units are designed and operated to provide a range of conversions, depending ondesired production rates, feedstock and utility values, and capital sensitivity.

EQUIPMENT CONSIDERATIONS

Because the Tatoray process uses relatively mild operating conditions, special constructionmaterials are not required. The simplicity of the process design and the use of conventional


Ove

rall

Pro

duct

Yie

ld,

wt-

% o

f Fre

sh F

eed

C9 Aromatics in Fresh Feed, wt-%

0

100

20 40 60 80

80

60

40

20

0

Benzene + Xylenes

Benzene

Xylenes

100

FIGURE 2.7.6 Tatoray yield structure as a function of A9 concentration in feed.

UOP TATORAY PROCESS



metallurgy result in low capital investment and maintenance expenses for the Tatorayprocess. The simple design of the Tatoray process also makes it ideal for the conversion ofexisting reformers, hydrodealkylation units, and hydrotreaters to Tatoray service. To date,two idle reforming units, two hydrodealkylation units, and one hydrodesulfurization unithave been successfully converted to service as Tatoray units.

The charge heater is normally a radiant-convection-type heater. The process stream isheated in the radiant section, and the convection section is used for a hot-oil system or forsteam generation. The heater can be designed to operate on either fuel gas or fuel oil, andeach burner is equipped with a fuel-gas pilot. A temperature controller at the heater outletregulates the flow of fuel to the burners. Radiant-section tubes are constructed of 1.25%Cr and 0.5% Mo. Tubes in the convection section are carbon steel.

The Tatoray process uses a simple downflow, fixed-bed, vapor-phase reactor. The reac-tor is constructed of 1.25% Cr-0.5% Mo.

The purpose of the product separator is to split the condensed reactor effluent into liq-uid product and hydrogen-rich recycle gas. The pressure in the product separator deter-mines the pressure in the reactor. Product separator pressure is regulated by controlling therate of hydrogen makeup flow. Hydrogen purity in the recycle gas is monitored by a hydro-gen analyzer at the recycle gas compressor suction. When hydrogen purity gets too low, asmall purge is taken from the recycle gas. The product separator is constructed of killedcarbon steel.

The recycle gas compressor is usually of the centrifugal type and may be driven by anelectric motor or a steam turbine. The compressor is provided with both a seal-oil andlube-oil circuit and an automatic shutdown system to protect the machine against damage.

The stripper column is used to remove light by-products from the product separator liq-uid. The stripper column usually contains 40 trays and incorporates a thermosiphon reboil-er. Heat is usually supplied by the overhead vapor from the xylene column locatedupstream of the Parex unit. The stripper column is constructed of carbon steel.

The combined feed exchanger is constructed of 1.25% Cr-0.5% Mo. Other heatexchangers are constructed of carbon steel.


FIGURE 2.7.7 Maximum para-xylene yield with Tatoray.

UOP TATORAY PROCESS



CASE STUDY

A summary of the investment cost and utility consumption for a typical Tatoray unit isshown in Table 2.7.2. The basis for this case is a Tatoray unit processing 98.5 MT/h (7,800BPD) of a feed consisting of 60 wt % toluene and 40 wt % A9. This case corresponds tothe case study for an integrated UOP aromatics complex presented in Chap. 2.1. Theinvestment cost is limited to the Tatoray unit and stripper column and does not include fur-ther downstream product fractionation. The estimated erected cost for the Tatoray unitassumes construction on a U.S. Gulf Coast site in 2002. The scope of the estimate includesengineering, procurement, and erection of equipment on the site.

COMMERCIAL EXPERIENCE

UOP has a long tradition of strong commitment to the BTX industry. Since the 1950s,more than 650 aromatics processing units have been licensed for BTX production, includ-ing process technologies for over 15 million MTA of PX production. As a result of thisdedication, UOP has pioneered in all major technology advancements. Employing an inte-grated approach, UOP has focused on improving the economics of aromatics processing.This includes the substantial improvement of yields in the Platformer unit and the efficientconversion and separation of the aromatic rings in the downstream process units that pro-duce the pure BTX products.

Since October 2000, the total TA-5 catalyst installed capacity has reached 120,000BPSD. Every TA-5 installation is operating well and meeting expectations with excep-


TABLE 2.7.1 Tatoray Feedstock Specifications

Contaminant Effect Limit

Nonaromatics Increased cracking, increased H2 consumption,lower benzene purity 2 wt % max.

Water Depresses transalkylation activity; reversible 50 ppm max.Olefins Promotes deposition of coke on catalyst 20 BI* max.Total chloride Promotes cracking of aromatic rings; reversible 1 ppm max.Total nitrogen Neutralizes active catalyst sites; irreversible 0.1 ppm max.Total sulfur Affects quality of the benzene product 1 ppm max.

*Bromine index

TABLE 2.7.2 Investment Cost and UtilityConsumption*

Estimated erected cost million $ U.S. 14.2Utility consumption:

Electric power, kW 780High-pressure steam, MT/h 11Cooling water, m3/h 255Fuel fired, million kcal/h 1.6

*Basis: 98.5 ton/h (7800 BPD) of feedstock. Feed com-position: 60 wt % toluene, 40 wt % C9 aromatics.

Note: MT/h � metric tons per hour.

UOP TATORAY PROCESS



tionally high selectivities to xylenes and benzene. Design feed rates range from 2600 to65,000 BPSD. The market acceptance has been outstanding, making TA-5 catalyst one ofthe most successful products of its kind.

CONCLUSIONS

The transalkylation process plays a key role in the production of xylenes. Improvementsin the Tatoray catalysts have substantially increased the aromatics complex performanceand profitability. The new TA-5 catalyst is now rapidly gaining acceptance in the BTXindustry since its introduction in late 2000. TA-5 catalyst offers the convenience of a drop-in reload, twice the stability, and the same high conversion and selectivity to benzene andC8 aromatics as TA-4 catalyst.

REFERENCES

1. J. R. Mowry, “UOP Aromatics Transalkylation Tatoray Process,” chapter 5.6, in R. A. Meyers, ed.,Handbook of Petroleum Refining Processes, 1st ed., McGraw-Hill, New York, 1986.

2. N. Y. Chen, Stud. Surf. Sci.Catal., vol. 38, p. 153, 1988.

3. A. Negiz, T. J. Stoodt, C. H. Tan, and J. Noe: “UOP’s New Tatoray Catalyst (TA-5) for MaximumYields and Product Quality,” AIChE Spring Conference, Fuels and Petrochemicals Division, NewOrleans, La., March 2002.

4. J. J. Jeanneret, C. D. Low, and V. Zukauskas, “New Strategies Maximize para-Xylene Production,”Hydrocarbon Processing, vol. 6, p. 43, 1994.

5. J. H. D’Auria and T. J. Stoodt, Harts Fuel Technology and Management, vol. 35, 1997.


UOP TATORAY PROCESS



UOP TATORAY PROCESS



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