Mixed xylenes

Application: To convert C₉⁺ heavy aromatics, alone or in conjunction with toluene or benzene co-feed, primarily to mixed xylenes using ExxonMobil Chemical’s TransPlus process.

Description: Fresh feed, ranging from 100% C₉⁺ aromatics to mixtures of C₉⁺ aromatics with either toluene or benzene, are converted primarily to xylenes in the TransPlus process. Co-boiling C₁₁ aromatics components, up to 435°F NBP, can be included in the C₉⁺ feed. In this process, liquid feed, along with hydrogen-rich recycle gas, are sent to the reactor (2) after being heated to reaction temperature through feed/efﬂ uent heat exchangers (3) and the charge heater (1).

Primary reactions occurring are the dealkylation of alkylaromatics, transalkylation and disproportionation, producing benzene/toluene and C₈ aromatics containing over 95% xylenes. The thermodynamic equilibrium of the resulting product aromatics is mainly dependent on the ratio of methyl groups to aromatic rings in the reactor feed.

Hydrogen-rich gas from the high-pressure separator (5) is recycled back to the reactor with makeup hydrogen (6). Unconverted toluene and C₉⁺ aromatics are recycled to extinction.

The ability of TransPlus to process feeds rich in C₉⁺ aromatics enhances the product slate toward xylenes. Owing to its unique catalyst, long cycle lengths are possible.

Economics: Favorable operating conditions, relative to other alternative technologies, will result in lower capital and operating costs for grassroots units and higher throughput potential in retroﬁ t applications.

Commercial plants: The ﬁ rst commercial unit was started up in Taiwan in 1997. Performance of this unit has been excellent.

Licensor: ExxonMobil Chemical Technology Licensing LLC, (retroﬁ t ap-plications); Axens, Axens NA (grassroots applications).

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Application: To selectively convert toluene to mixed xylene and high-pu-rity benzene using ExxonMobil Chemical’s Toluene DisProportionation 3rd Generation (MTDP-3) process.

Description: Dry toluene feed and up to 25 wt% C₉ aromatics along with hydrogen-rich recycle gas are pumped through feed efﬂ uent heat exchangers and the charge heater into the MTDP-3 reactor (1). Toluene disproportionation occurs in the vapor phase to produce the mixed xy-lene and benzene product. Hydrogen-rich gas from the high-pressure separator (2) is recycled back to the reactor together with makeup hy-drogen. Unconverted toluene is recycled to extinction.

Reactor yields, wt%:

Toluene conversion, wt% 48

Operating conditions: MTDP-3 operates at high space velocity and low H₂ / hydrocarbon mole ratio. These conditions could potentially result in increased throughput without reactor and/or compressor replacement in retroﬁ t applications. The third-generation catalyst offers long operat-ing cycles and is regenerable.

Economics: Estimated onsite battery limit investment for 1997 open shop construction at US Gulf Coast location is $1,860 per bpsd capacity.

Typical utility requirements, per bbl feed converted:

Electricity, kWh 3.0

Fuel, 10³ kcal/hr 87.8

Water, cooling (10°C rise), cm/hr 0.3 Catalyst ﬁ ll, lb/lb feed converted 1.53 10²⁵ Maintenance, per year as % of investment 2.0

Commercial plants: Four MTDP-3 licensees since 1995.

Reference: Oil & Gas Journal, Oct. 12, 1992, pp. 60 – 67.

Licensor: ExxonMobil Chemical Technology Licensing LLC (retroﬁ t ap-plications); Axens, Axens NA (grassroots applications).

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Mixed xylenes

Application: To convert C₉⁺ heavy aromatics, alone or in conjunction with toluene or benzene co-feed, primarily to mixed xylenes using ExxonMobil Chemical’s TransPlus process.

Description: Fresh feed, ranging from 100% C₉⁺ aromatics to mixtures of C₉⁺ aromatics with either toluene or benzene, are converted primarily to xylenes in the TransPlus process. Co-boiling C₁₁ aromatics compo-nents, up to 435°F NBP, can be included in the C₉⁺ feed. In this process, liquid feed along with hydrogen-rich recycle gas, are sent to the reactor (2) after being heated to reaction temperature through feed/efﬂ uent heat exchangers (3) and the charge heater (1).

Hydrogen-rich gas from the high-pressure separator (5) is recycled back to the reactor with make-up hydrogen (6). Unconverted toluene and C₉⁺ aromatics are recycled to extinction.

The ability of TransPlus to process feeds rich in C₉⁺ aromatics enhances the product slate toward xylenes. Owing to its unique catalyst, long cycle lengths are possible.

Commercial plants: The ﬁ rst commercial unit was started up in Taiwan in 1997. There are ﬁ ve TransPlus references.

Licensor: ExxonMobil Chemical, (retroﬁ t applications); Axens, Axens NA (grassroots applications).

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Mixed xylenes

Application: In a modern UOP aromatics complex, the TAC9 process is integrated into the ﬂ ow scheme to selectively convert C₉– C₁₀ aromat-ics into xylenes rather than sending them to the gasoline pool or selling them as a solvent.

Description: The TAC9 process consists of a fi xed-bed reactor and prod-uct separation section. The feed is combined with hydrogen-rich recycle gas, preheated in a combined feed exchanger (1) and heated in a fi red heater (2). The hot feed vapor goes to a reactor (3). The reactor effl uent is cooled in a combined feed exchanger and sent to a product separa-tor (4). Hydrogen-rich gas is taken off the top of the separasepara-tor, mixed with makeup hydrogen gas, and recycled back to the reactor. Liquid from the bottom of the separator is sent to a stripper column (5). The stripper overhead gas is exported to the fuel gas system. The overhead liquid may be sent to a debutanizer column or a stabilizer. The stabilized product is sent to the product fractionation section of the UOP aromat-ics complex.

Economics: The current generation of TAC9 catalyst has demonstrated the ability to operate for several years without regeneration. ISBL costs based on a unit processing 306,400 mtpy of feed consisting of 100 wt% C₉– C₁₀ (US Gulf Coast site in 2003):

Investment, US$ million 11.6

Utilities (per mt of feed)

Electricity, kWh 3.1

Steam, mt 0.07

Water, cooling, m³ 1.6

Fuel, MMkcal 0.13

Commercial plants: Three commercial units have been brought on-stream, with feed rates ranging from 210,000 mtpy to 850,000 mtpy.

Licensor: UOP LLC.

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Mixed xylenes

Application: The Tatoray process produces mixed xylenes and petro-chemical grade benzene by disproportionation of toluene and transalk-lyation of toluene and C₉+ aromatics.

Description: The Tatoray process consists of a fi xed-bed reactor and product separation section. The fresh feed is combined with hydrogen-rich recycle gas, preheated in a combined feed exchanger (1) and heated in a fi red heater (2). The hot feed vapor goes to the reactor (3). The reactor effl uent is cooled in a combined feed exchanger and sent to a product separator (4).

Hydrogen-rich gas is taken off the top of the separator, mixed with makeup hydrogen gas and recycled back to the reactor. Liquid from the bottom of the separator is sent to a stripper column (5). The stripper overhead gas is exported to the fuel gas system. The overhead liquid may be sent to a debutanizer column. The products from the bottom of the stripper are recycled back to the BT fractionation section of the aromatics complex.

The Tatoray process unit is capable of processing feedstocks ranging from 100 wt% toluene to 100 wt% A ₉⁺. The optimal concentration of A ₉⁺ in the feed is typically 40 – 60 wt%. The Tatoray process provides an ideal way to produce additional mixed xylenes from toluene and heavy aromatics.

Economics: The process is designed to function at a much higher level of conversion per pass. This high conversion minimizes the size of the BT columns, and the size of Tatoray process unit, as well as the utility consumption of all of these units. Estimated ISBL costs based on a unit processing feed capacity of 355,000 mtpy (US Gulf Coast site in 2003):

Investment, US$ million 11.3

Utilities (per mt of feed)

Electricity, kWh 17.5

Steam, mt 0.11

Water, cooling, M³ 2.5

Fuel, MMkcal 0.04

Commercial plants: UOP has licensed a total of 44 Tatoray units; 40 of these units are in operation and 4 are in various stages of construction.

Licensor: UOP LLC.

m-Xylene

Application: The MX Sorbex process recovers meta-xylene (m-xylene) from mixed xylenes. UOP’s innovative Sorbex technology uses adsorp-tive separation for highly efﬁ cient and selecadsorp-tive recovery, at high purity, of molecular species that cannot be separated by conventional frac-tionation.

Description: The process simulates a moving bed of adsorbent with con-tinuous counter-current ﬂ ow of liquid feed over a solid bed of adsor-bent. Feed and products enter and leave the adsorbent bed continuous-ly, at nearly constant compositions. A rotary valve is used to periodically switch the positions of the feed-entry and product-withdrawal points as the composition proﬁ le moves down the adsorbent bed.

The fresh feed is pumped to the adsorbent chamber (2) via the ro-tary valve (1). M-xylene is separated from the feed in the adsorbent chamber and leaves via the rotary valve to the extract column (3). The dilute extract is then fractionated to produce 99.5 wt% m-xylene as a bottoms product. The desorbent is taken from the overhead and recircu-lated back to the adsorbent chamber. All the other components present in the feed are rejected in the adsorbent chamber and removed via the rotary valve to the rafﬁ nate column (4). The dilute rafﬁ nate is then frac-tionated to recover desorbent as the overhead product and recirculated back to the adsorbent chamber.

Economics: The MX Sorbex process has been developed to meet in-creased demand for puriﬁ ed isophthalic acid (PIA). The growth in de-mand for PIA is linked to the copolymer requirement for PET bottle resin applications, a market that continues to rapidly expand. The process has become the new industry standard due to its superior environmental safety and lower cost materials of construction. Estimated ISBL costs based on unit production of 50,000 mtpy of m-xylene (US Gulf Coast site in 2003).

Investment, US$ million 30.0 Utilities (per mt of m-xylene produced)

Electricity, kWh 87

Steam, mt 4.0

Water, cooling, m³ 3.8

Commercial plants: Five MX Sorbex units are currently in operation and another unit is in design. These units represent an aggregate production of 335,000 mtpy of m-xylene.

Licensor: UOP LLC.

Octenes

Application: The Dimersol-X process transforms butenes to octenes, which are ultimately used in the manufacture of plasticizers via iso-nonanol (isononyl alcohol) and diisononyl phthalate units.

Description: Butenes enter the Dimersol-X process, which comprises three sections. In the reactor section, dimerization takes place in multiple liquid-phase reactors (1) using homogeneous catalysis and an efﬁ cient recycle mixing system. The catalyst is generated in situ by the reaction of components injected in the recycle loop. The catalyst in the reactor efﬂ uent is deactivated in the neutralization section and separated (2).

The stabilization section (3) separates unreacted oleﬁ n monomer and saturates from product dimers while the second column (4) separates the octenes. A third column can be added to separate dodecenes.

Yields: Nearly 80% conversion of n-butenes can be attained and se-lectivities toward octenes are about 85%. The typical C₈ product is a mixture having a minimum of 98.5% octene isomers with the following distribution:

n-Octenes 7%

Methyl-heptenes 58%

Dimethyl-hexenes 35%

Dimersol-X octenes exhibit a low degree of branching resulting in higher downstream oxonation reaction yields and rates, and better plasticizer quality.

Economics: Basis: ISBL 2004 for a Gulf Coast location using 50,000 tpy of a rafﬁ nate - 2 C₄ cut containing 75% n-butenes.

Investment, US$ million 6

Typical operating cost, US$ 60 per metric ton of octenes Commercial plants: Thirty-ﬁ ve Dimersol units treating various oleﬁ nic C₃ and C₄ cuts have been licensed. Typical octenes production capacities range from 20,000 tpy up to 90,000 tpy.

Reference: Convers, A., D. Commereuc, and B. Torck, “Homogeneous Catalysis,” IFP Conference.

Licensor: Axens, Axens NA.

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Olefins—progressive separation for

In document HP's Petrochemical Processes 2005 (Page 110-117)