Polibutenos Argentinos S.A. plans to more than double its polymer capacity with the installation of a 40,000 mt/y isobutane dehydrogenation unit at its Ensenada, Argentina, plant.
The plant, located 37 miles southeast of Buenos Aires, produces synthetic hydrocarbon polymers for uses ranging from oil additives to electrical cable insulation. Polibutenos exports 70% of its production.
To provide the additional isobutylene feedstock needed to double production, Polibutenos is constructing a STAR (steam active reforming) unit, designed by Phillips Petroleum Co., Bartlesville, Okla. Start-up of the unit is scheduled for July.
PROJECT
Polibutenos is boosting isobutylene capacity from 14,000 mt/y to 30,000 mt/y for its own use. An additional 10,000 mt/y will be produced for sale to other petrochemical manufacturers.
"To reach the total production level of 40,000 mt/v, it is necessary to incorporate a dehydrogenation unit, since isobutylene--the plant's current raw material--is limited in supply in the area," said plant manager Nilo A. Michetti.
Polibutenos evaluated several dehydrogenation processes, Michetti said, but chose this one for its higher selectivity, longer process cycles, less severe pressure and temperature conditions, and noncarcinogenic catalyst. Plus, it handles feeds containing olefins.
John Brown Engineering & Construction provided basic engineering for the unit. Financing and much of the equipment will come from Spain, says Phillips.
Polibutenos' operators will be trained at Phillips units in Bartlesville and at a field installation.
CATALYST
Key to the process is a proprietary, promoted, noble-metal catalyst. The catalyst dehydrogenates light paraffins at near-equilibrium conversions, with high selectivity and essentially no structural isomerization, says Phillips.
In normal operation, the catalyst has an expected life of at least 1-2 years. When no longer regenerable, the catalyst's valuable metals can be reclaimed and the residual base material disposed of.
PROCESS
The fixed-bed reactor system operates at a slight positive pressure and moderate temperature. Positive-pressure operation means lower downstream compression ratios, requiring less horsepower for product recovery, compared to vacuum and hydrogen-dilution dehydrogenation processes. The scheme also increases safety by avoiding potentially hazardous air leaks.
Vaporized hydrocarbon is diluted with steam and superheated to reaction temperature (flow diagram). The hot stream is then distributed to several catalyst-filled tubes in a down-fired furnace at a liquid hourly space velocity of 0.5-10, thus dehydrogenating the feedstock.
Steam dilution, at 2-10 moles steam/mole feed, increases product conversion by lowering the partial pressures in the reactor. Steam also suppresses coke formation and provides an additional heat sink, which facilitates transfer of the endothermic heat of reaction.
The required process steam is generated within the unit's battery limits. After effluent heat recovery, the process steam is condensed, treated, and recycled to the process.
The dehydrogenation reaction occurs at 210-620 C. (420-1,148 F.). Firing the tubes from the outside provides heat for the endothermic reaction at optimum isothermal conditions, thus avoiding the equilibrium shift associated with adiabatic reactors.
A typical STAR reactor operates on an 8-hr cycle--7 hr for processing and 1 hr for catalyst regeneration. In situ regeneration completely restores catalytic activity by removing the carbon deposited during processing.
The unit is a net exporter of energy, which can be used for reboiling fractionators or generating steam. After recovering most of the contained heat, reactor effluent is further cooled to condense process steam.
The effluent is then compressed and, after additional condensate recovery, passed to the separation section. The product is stabilized in a fractionator, where light components are sent to fuel.
Produced hydrogen is recovered by either cryogenic, membrane, or pressure swing adsorption systems, depending on plant size. The hydrogen-rich stream (90+ mole % hydrogen) can be used as fuel or further purified.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
