Aromatics Recovery via Extraction and Extractive Distillation
The process allows the user to take maximum advantage of the highly effective sulfolane solvent to extract high-purity BTX aromatics from catalytic reformate, hydrotreated pyrolysis gasoline, Coke Oven Light Oils (COLO), and other refinery streams. The sulfolane recovery process has been licensed for commercial use since the mid-’60 at refinery and petrochemical processing sites in North and South America, the Middle East and the Far East. Start-up and continued operation has been trouble-free and solvent losses are held to very low levels.
Hydrodealkylation (HDA)
The thermal process uses a plug flow reactor for the production of benzene and naphthalene. Nearly theoretical yields of benzene are obtained because of the inherent nature of the thermal process and the novel feature of recycling diphenyls to establish a dynamic equilibrium. The control of residence distribution in the HDA process reduces the amount of benzene and toluene that are reacted to heavy aromatics. HDA process investment per unit of benzene produced has been found to be lower than competing process because:
(a) operations are conducted at relatively low H2 to aromatics ratios
(b) benzene yields are high because of recycling diphenyls
(c) the conversion of toluene per pass is higher
(d) there is no catalyst cost
(e) operating efficiency is higher because there is no downtime associated with catalyst regeneration or changes.
Paraxylene Crystallization
The unique two-stage or single-stage process is using cold-temperature crystallizers to freeze paraxylene and centrifugal separation of the paraxylene rich solids from the remaining liquid. The freezing point of paraxylene is significantly higher than that of the other isomers, allowing paraxylene to be frozen, and recovered in crystal form, at a temperature at which the other isomers are still in the liquid phase. The wash system (with paraxylene or toluene) enables extremely high-purity paraxylene to be recovered from residual xylenes at a cost lower than that of the other process.
EB conversion/Xylenes Isomerization (Octafining)
The process uses a noble metal catalyst to restore to near-equilibrium concentrations, C8 aromatic streams deficient in one or more of the xylene isomers. In conjunction with an appropriate process any of the xylene isomers can be produced by recycling to extinction the other less marketable xylene isomers and ethylbenzene. Feedstocks containing over 30% EB have been successfully processed. Ultimate catalyst life of greater than 3 years has been achieved commercially. The catalyst is regenerable in situ with no additional mechanical equipment being required. The recycle gas compressor is used to circulate nitrogen into which controlled quantities of plant air are added. A complete regeneration cycle from “feed out” to “feed in” can generally be completed in less than 3 days. Commercial experience has led to optimization of catalyst performance characteristics and process designs such that ultimate xylene yields have increased too greater than 90 wt. % of feed.
C7/C9 Disproportionation/Transalkylation (XylenesPlus)
The process combines in a single unit the capability to perform toluene disproportionation to xylenes and benzene and C7/C9 transalkylation to produce xylenes. The catalyst used is very stable and inexpensive non-precious metal catalyst and is subjected to continuous regeneration within the system, thus maintaining constant activity and controlled selectivity. Hydrogen is not required in XylenesPlus so that the expensive compression costs are not incurred. In addition, liquid yields are in the order of 97 vol % since methyl groups are not lost to light hydrocarbons. Also, essentially no toluene is converted to EB (ethylbenzene). Typically, the C8 aromatics produced in the XylenesPlus process contain 26% paraxylene, 24% orthoxylene, and 50% metaxylene.
Benzene to Cyclohexane
The process is a commercially proven method for producing cyclohexane from benzene in a single reactor system. The special design of the reactor efficiently controls the highly exothermic reaction while generating high-pressure steam. A specific catalyst is used to maintain high hydrogenation activity at low operating temperatures and to completely inhibit the formation of methylcyclopentane (MCP). This combination of unique design and specific catalyst results in a highly efficient, long onstream-time process. In addition to cyclohexane, the unit can be used for producing aliphatic solvents, smokeless jet fuels, and refined lubricants.
Orthoxylene / EB Fractionation (OX-FRAC)
The process requires superfractionation in the production of high-purity orthoxylene or ethylbenzene. A highly efficient control system is included in the fractionation system.
COLO Hydrotreating (COLO)
Coke Oven Light Oil (COLO) is a by-product of coke manufacture from coal. The oil derived is a foul smelling amber liquid composed of mononuclear aromatic hydrocarbons, olefins, styrene, sulfur, and nitrogen compounds, etc. The process requires: (1) two-stage hydrotreating reaction, which saturates of diolefins, styrene, mono-olefins and converts sulfur nitrogen compounds to H2S, NH3 respectively. (2) Fractionation removes light ends, produces a concentrated aromatics stream for downstream aromatics extraction. This unique process operates at lower temperature and pressure than competitors and recovers the maximum possible quantity of benzene from COLO, with minimum aromatics loss due to saturation.