Gas handling for plastics liquefaction

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...

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Details

521 405, C08J 1110, C08J 1114, B01D 5314

Patent

active

061213349

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a method for removing high molecular weight low melting point hydrocarbon vapors from an offgas stream produced during liquefaction of a waste plastic material, and more particularly for utilizing the offgas vapor stream as a heater fuel for the liquefaction process.
2. Description of the Prior Art
Diminishing natural resources as well as economic considerations have led to the increasing use of organic feedstocks from impure sources, such as scrap or waste plastic materials.
Waste or scrap plastic materials often comprise at least one solid carbonaceous thermoplastic and/or thermosetting material which may or may not contain associated inorganic matter, such as fillers and reinforcement material. Such materials may be derived from obsolete equipment, household containers, packaging, industrial sources, recycling centers and discarded automobiles. Scrap plastic comprises solid organic polymers derived from sheets, films, extruded shapes, moldings, reinforced plastics, laminates and foamed plastics. The mixture of scrap plastics varies with the source and with the presence of non-combustible inorganic matter incorporated in the plastic as fillers, catalysts, pigments and reinforcing agents.
It is desirable to convert particulate scrap plastic into a liquid hydrocarbonaceous feedstock for a partial oxidation reaction to produce gas mixtures of hydrogen and carbon monoxide, referred to as synthesis gas, or simply "syngas." Syngas can be used to make other useful organic compounds or as a fuel to produce power.
The partial oxidation reaction can be conducted in a free-flow unpacked noncatalytic quench gasifier. The reaction temperature varies about 1800.degree. F. to about 3000.degree. F. and the reaction pressure is about 1 to about 100 atmospheres, preferably about 30 to about 80 atmospheres.


SUMMARY OF THE INVENTION

The present invention relates to a method for removing high molecular weight high melting point hydrocarbon vapors from a hydrocarbon vapor offgas stream produced during the liquefaction of a solid waste plastic material to produce an oil that serves as a liquid feedstock for a partial oxidation reaction. The hydrocarbon vapor offgas stream is directly contacted with a water spray at a condensation temperature above the melting point of the high molecular weight hydrocarbons contained in the offgas. This results in the condensation and convenient removal of the high melting point hydrocarbons, referred to as "waxes." One or more subsequent condensation steps can be conducted at lower condensation temperatures to remove the lower temperature condensible hydrocarbons. The remaining uncondensed vapors are then recycled to serve as a heater fuel for the liquefaction of the waste plastic material.


BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is a simplified diagrammatic representation of the offgas condensation operation.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

Particulate waste plastic materials, even those containing halogens can be converted by thermal cracking to an oil composition suitable as a feedstock for a partial oxidation reaction in a quench gasifier to produce a synthesis gas.
The liquefaction of the particulate waste plastic materials, particularly bulk waste plastic materials involves melting the waste plastic material by direct contact with a hot oil melting medium to produce a molten viscous mixture of the waste plastic materials in the hot oil melting medium. The melting of the waste plastic material also produces an offgas vapor which includes hydrocarbon vapors of varying molecular weights, carbon dioxide and water vapor. Depending upon the nature of the waste plastic material, acid halides and halohydrocarbons can also be contained in the offgas vapor.
An important aspect of this invention is the treatment of the offgases generated during the liquefaction of the particulate waste plastic material to recover condensible hydrocarbons and to use uncondensed hydrocarbon vapors to f

REFERENCES:
patent: 4072604 (1978-02-01), Ward
patent: 4401561 (1983-08-01), Thompson et al.
patent: 4810267 (1989-03-01), Landeck
patent: 5837037 (1998-11-01), Winter

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