Process for controlled degradation of hydrocarbon polymers

Details Process for controlled degradation of hydrocarbon polymers Process for controlled degradation of hydrocarbon polymers

1998-01-12

2001-01-09

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Cracking

C208S111010, C208S111050, C208S111200, C208S111250, C208S111300, C208S108000, C208S109000, C208S111150, C585S241000

Reexamination Certificate

active

06171475

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel catalytic process leading to the controlled degradation of heavy hydrocarbons under the effect of hydrogen into upgradeable products such as methane and lower alkanes, higher alkanes or any type of hydrocarbon, or oligomers or polymers of the lower variety covering a very wide range of molecular weights.
BACKGROUND OF THE INVENTION
Heavy hydrocarbons which may be degraded by this novel process are in particular waxes. Such waxes are hydrocarbons in C
12
to C
50
which generally are saturated. However, they can be sometimes unsaturated. They can be derived from processes of synthesis like Fischer-Tropsch. In fact, their structure is very similar to the structure of oligomers based on low molecular weight polyethylene.
Polymers which may be degraded by this novel process are polymers having chains with carbon—carbon bonding, for example polyethylene, polypropylene or polystyrene.
Among the fields of application of the invention, mention may be made of environmental protection or the polymer production industry, in particular appertaining to polymers with controlled molecular mass, petrochemical products, fuels (hydrocarbon fractions), lubricants or alternatively energy.
The invention is in particular advantageous in the field of fuel for obtaining hydrocarbon fractions like diesel, which is constituted of hydrocarbons in C
12
to C
20
, from waxes derived from Fischer-Tropsh's synthesis. As these waxes are solid at room temperature, their conversion needs very high temperatures with conventional catalysts. According to the present invention this conversion can be achieved by reacting waxes with hydrogen in less severe conditions.
The invention can also find applications in the food packaging industry, or that appertaining to any other type of packaging where the polymer waste produced during manufacture cannot be reused.
Heightened environmental protection requires the implementation of reliable new techniques for processing the polymer waste commonly referred to as plastics. Among the various methods envisaged for the reuse or disposal of used polymers, energy and/or chemical recycling may afford satisfactory solutions complementary to material recycling.
Among the solutions relating to plastics waste, incineration with or without energy recovery constitutes one possible way, but the temperatures needed for this type of processing are very high, of the order of 400 to 700° C. However, this type of process can only lead to energy recovery from polymers, and has the drawback of being unecological because it would increase the greenhouse effect.
Chemical recycling is starting to attract great interest. This technique consists in chemically decomposing the macromolecules with a view to obtaining molecules which have low molecular masses and can be reused with regard to their physical or chemical or energy (fuel) properties. In general, catalytic degradation (cracking or hydrocracking) of polyolefins makes it possible to improve the selectivity of this type of reaction in comparison with purely chemical and thermal processes, and consequently to obtain directly hydrocarbon fractions which are easier to upgrade. The catalysts for cracking and hydrocracking polypropylene or polyethylene are generally silicas, silica/aluminas, zeolites or catalysts based on cobalt and molybdenum which operate at elevated temperature, typically between 200 and 600° C. and most often towards 400° C. and under high hydrogen pressure. These techniques are described, in particular, by BELTRAME et al., in Polymer degradation and stability, 26, (1989) 29-220., HIROTA et al., in Makromol. Chem. Macromol. Symp. 57, 161-173 (1992), Y. ISHIRA et al., Fuel, 69, 978, (1990), I. KORFF et al., in Erdol Erdgas 105, (1989) 223.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel catalytic process for hydrocracking waxes or polymers of the polyolefin type, which can be employed in less severe conditions than the processes known hitherto, with the purpose of using simplified equipment to easily and efficiently produce upgradeable products with a variety of applications according to their molecular mass.
The present invention thus relates to a process for the conversion of a wax or a polymer or an oligomer, said oligomer or said polymer deriving from an ethylenically unsaturated monomer, into alkanes or a hydrocarbon fraction or an oligomer fraction of the lower variety by controlled hydrocracking, characterized in that it comprises the steps consisting in:
bringing the said wax or polymer or oligomer into the presence of a catalyst based on a metal hydride or an organometallic complex supported on an inorganic support, the said complex including at least one hydrocarbon ligand, and optionally at least one hydride ligand, then
reacting this mixture with hydrogen, thus catalytically hydrocracking the said polymer or oligomer.
According to the present invention, the expression “alkanes or a hydrocarbon fraction or an oligomer fraction of the lower variety” means hydrocarbon compounds whose chain includes a number of carbon atoms lower than the number of carbon atoms in the initial polymer or oligomer or wax.
Using a very high-performance catalyst, it is possible according to the invention to hydrocrack polyolefins such as polyethylene, polypropylene, polystyrene or polyisoprene, in temperature and pressure conditions which are remarkably low compared to those customarily required in the prior art for reactions employing macromolecular solid material, in which low conditions conventional hydrocracking catalysts (silica, silica/alumina, zeolites) are inactive. The process can thus be employed with simplified apparatus in improved safety conditions. However, the originality of the present invention resides primarily in the great versatility of the operating conditions of the process, and these will be described below, making it possible to set the selectivity appertaining to the formation of certain degradation products, that is to say to carry out controlled degradation of the macromolecules.
As regard waxes, they are saturated or optionally olefinic hydrocarbons in C
12
to C
50
. They can be derived from Fischer-Tropsch's synthesis.
As regards polymers, the present invention permits, in particular, controlled degradation of polyolefins in order to give polymers with specific properties that are more beneficial owing to the molecular mass modification. This controlled degradation can also be carried out during the polymerization process, but more generally after polymerization, that is to say when forming the polymer.
More generally, the polymers that can be degraded according to the invention may derive from monomers having a single polycondensable ethylenic unsaturation, either of the olefinic type, such as ethylene, propylene, isobutylene, methylpentene, hexene, or of the aromatic alkenyl type, such as styrene, the vinylpyridines or vinylnaphthalenes, and/or monomers having a plurality of polycondensable ethylenic unsaturations, such as butadiene, isoprene, piperylene, methylpentadiene, phenylbutadiene, dimethylhexadienes, dimethyloctadienes.
The process according to the invention applies more advantageously to waxes or polymers whose hydrocarbon skeleton is a saturated polyolefin, optionally substituted, which derive from one or more monomers including a single ethylenic unsaturation.
These polymers, such as polyethylene or polypropylene, are known for their exemplary thermal and chemical stability. It is this extraordinary chemical stability which has made them successful. Unfortunately, it is this thermal and chemical stability which makes it particularly difficult to solve the ecological problem posed by the waste produced by these polymers. The invention described here gives particularly spectacular results as regards the conditions for hydrocracking saturated polyolefins, in particular polypropylene and polyethylene.
The invention also applies to polymers whose hydrocarbon skeleton, optionally substituted, incl

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