FR3128717A1 - Process for processing polymeric materials - Google Patents

Abstract

Process for the treatment of polymeric materials, preferably polyolefinic, in which (a) the polymeric materials are subjected to a depolymerization treatment comprising at least one treatment with hydrogen, so as to form at least a first fraction comprising liquid alkanes or solids and a second fraction comprising at least hydrocarbons, preferably gaseous and; (b) the hydrocarbons contained in the second fraction are introduced into a stage of catalytic decomposition of the hydrocarbons into hydrogen and carbon.

Description

Process for processing polymeric materials

The present invention relates to a method for treating polyolefinic waste. It also relates to a process for the co-production of liquid and/or solid alkanes, hydrogen and carbon.

The world market for polyolefins (polyethylene, polypropylene, polystyrene) represents in 2020 more than 200 million tons. About 50% of the polyethylene is used in the form of films, the rest in the form of injected products, cables, pipes, etc. As far as polypropylene is concerned, most of the uses concern injected products such as packaging, toys, automotive products and the rest in the form of films, pipes, fibers, etc. The recovery of end-of-life products, therefore also after physical recycling operations (less than 15% of polyolefins in 2020) is therefore a major societal issue.

Generally, the chemical recycling of polymers by depolymerization today represents less than 5% of world production, and forecasts count on 20-25% in 2030. In this evolution, the share of polyolefins is low, which is a a natural consequence of the difficulty in breaking C-C bonds at low temperatures.

It has been proposed to convert polyolefinic waste into liquid alkanes which can be used, for example, as lubricants see for example EP-A-620264 and WO-A-2010/136850. This process consumes a lot of energy and hydrogen. Also, it produces fractions of gaseous alkanes which are greenhouse gases.

Another process is described in WO-A-2019/234408 according to which polymeric waste is decomposed into hydrogen and carbon with an iron-based catalyst or iron oxide under electromagnetic radiation. This process is difficult to implement on an industrial scale given the large investments required to make microwaves available to treat large volumes of waste. Also, this process continues to produce substantial quantities of harmful gaseous fractions, containing alkanes, CO2 and toxic CO.

The invention provides an improved and more environmentally friendly process for the treatment of polymeric materials, in particular polyolefinic waste, allowing better recovery of the polyolefinic waste.

The invention therefore relates to a method for treating polymeric materials, preferably polyolefinic materials, in which
(a) the polymeric materials are subjected to a depolymerization treatment comprising at least one treatment with hydrogen, so as to form at least a first fraction comprising liquid and/or solid alkanes and a second fraction comprising at least hydrocarbons , preferably gaseous and;
(b) the hydrocarbons contained in the second fraction are introduced into a stage of catalytic decomposition of the hydrocarbons into hydrogen and carbon.

Surprisingly, the process according to the invention allows a net production of hydrogen and a high yield of liquid or solid alkanes while avoiding the co-production of substantial quantities of greenhouse or toxic gases. It has been found that the hydrocarbon fractions and in particular the methane contained in these fractions is of sufficient quality to supply a stage of catalytic cracking with hydrogen and carbon. It has been found that the depolymerization process can produce hydrocarbon fractions, preferably in the gaseous state, in sufficient quantity, which can be converted, in an environmentally friendly manner, into hydrogen for the needs of the depolymerization or even produce a substantial excess of hydrogen.

For the purposes of the present invention, the terms “solid”, “liquid” and “gaseous” refer to the state of a material under normal conditions, namely a temperature of 25°C and an atmospheric pressure of 101325 Pascal ( 1 atmosphere).

The polymeric materials used in the process according to the invention can be, for example, polymers containing heteroatoms, such as polyesters, polyamides or polyurethanes. Preferably, the polymeric materials include polyolefins. Examples of preferred polyolefins are chosen from polyethylene, polypropylene and polystyrene.

The process according to the invention can be applied to pure polymers and to polymer blends. A particularly advantageous case is the treatment by the method according to the invention of polymeric waste.

The depolymerization step can for example comprise
(i) a stage of thermal cracking of the polymeric materials, preferably carried out at a temperature of 350° C. to 600° C. and at least one fraction comprising hydrocarbons, preferably in the gaseous state, is withdrawn;
(ii) optionally carrying out a hydrotreatment of at least part of the polymeric fraction resulting from step (i);
(iii) at least part of the polymeric fraction resulting from step (i) or (ii) is treated with hydrogen in the presence of a catalyst, preferably at a temperature of 270° C. to 400° C. , and at least one fraction comprising liquid and/or solid alkanes is recovered

Illustrations of the principle of this step can be found for example in the references EP-A-620264 and WO-A-2010/136850.

It has now been found that depolymerization can be effected in synergistic combination with catalytic decomposition of hydrocarbons to hydrogen and carbon, provided it is conducted to produce a gaseous hydrocarbon fraction which can serve as the decomposition feed. catalyst, in considerable quantities, in particular sufficient or even greater than what is necessary to meet its own hydrogen needs. Contrary to the state of the art which considers the gaseous hydrocarbon fractions as problematic, the present invention seeks to maximize them with respect to an optimum production of liquid and/or solid alkanes.

In the process according to the invention, at least a first fraction is formed comprising liquid and/or solid alkanes

In the process according to the invention, the depolymerization treatment generally has a selectivity for alkanes whose number of carbon atoms is greater than 6 at least equal to 90% by weight, preferably at least equal to 95% by weight per relative to the weight of the polymeric materials treated.

In this case, the molar mass of the products resulting from the reaction can be between 16 g/mol and 478 g/mol.

In the process according to the invention, at least one second fraction comprising gaseous hydrocarbons is formed. These gaseous hydrocarbons are chosen, for example, from alkanes and olefins. Specific examples are chosen from alkanes having 1 to 5 carbon atoms and olefins having 2 to 5 carbon atoms. Preferably the second fraction comprises alkanes having 1, 2, 3 or 4 carbon atoms, more particularly methane.

In the process according to the invention, the depolymerization treatment generally has a selectivity of at least 0.05 mol methane per mole of carbon contained in the polymer waste.

The second fraction can optionally be subjected to one or more separation treatments. For example, a fraction enriched in methane can be separated from other components of the second fraction, for example by a membrane separation operation. In this case, the methane content in the fraction enriched in methane is generally at least 50% molar, preferably it is at least 95% molar. The methane-enriched fraction is preferred for feeding step (b) of the process according to the invention.

The second fraction can also be introduced into step (b) of the process according to the invention without separation treatment.

In step (b) of the process according to the invention, the hydrocarbons contained in the second fraction as described above are introduced into a step of catalytic decomposition of the hydrocarbons into hydrogen and carbon. More specifically, hydrocarbons, preferably comprising methane, can be introduced into a decomposition stage in the presence of a catalyst, preferably iron-based, at a temperature of 400° C. to 1000° C. and hydrogen and carbon. An illustration of the decomposition of hydrocarbons into carbon and hydrogen can be found for example in the reference US-B-10179326.

In a preferred aspect of the process according to the invention, the depolymerization treatment is fed with hydrogen coming at least partially from step (b).

In a preferred embodiment, the hydrocarbon decomposition step (b) produces more hydrogen than the depolymerization process consumes.

There illustrates a preferred scheme of the process according to the invention:

A supply (1) of polyolefin waste from the depolymerization stage (2) comprising at least one treatment with hydrogen is carried out, the first fraction comprising liquid or solid alkanes is drawn off (3), the second fraction comprising at least gaseous hydrocarbons, optionally, a fraction enriched in methane is separated (5) from other components of the second fraction and a fraction enriched in other components is withdrawn (6), methane is introduced (7) contained in the second fraction in the step (9) of catalytic decomposition of methane into hydrogen and carbon, optionally, a step (9) of catalytic decomposition of methane into hydrogen and carbon into methane not originating from the depolymerization stage (2) comprising at least one treatment with hydrogen, carbon is recovered (11), a gaseous fraction comprising hydrogen and optionally unreacted methane is withdrawn (12) and said fraction is introduced , if necessary, in a step (13) for separating hydrogen and methane so as to form a fraction enriched in methane which is recycled (15) to step (9) of catalytic decomposition and a first fraction of hydrogen which is introduced (16) into step (2) of depolymerization comprising at least one treatment with hydrogen and a second fraction of hydrogen is recovered (14).

The supply (10) of gaseous hydrocarbons, in particular methane, not originating from step (2) of depolymerization is particularly advantageous for starting the process according to the invention.

The invention also relates to a process for the co-production of hydrogen, carbon and solid and/or liquid alkanes comprising the treatment process as described in the present description.

The example below is intended to illustrate the invention without however limiting it.

Example

A depolymerization stage is fed with 100,000 tons per year of polyethylene with a degree of polymerization of 500,000 (flow 1). The selectivity of the catalytic depolymerization process is 15% (number of carbon atoms transformed into methane / number of carbon atoms initially present in the fed polyethylene). The additional methane supply (10) is deactivated. The depolymerization process (2) converts the polyethylene, by adding hydrogen from the methane cracking step (9), into a mixture of alkanes with the average molecular formula C20H42, and methane.

The annual production of the entire process consists of:
85,607 t/year of mixture of alkanes with average molecular formula C20H42
1,536 t/year of dihydrogen H2
12,857 t/year of solid carbon

Claims (10)

Process for the treatment of polymeric materials, preferably polyolefinic, in which
(a) the polymeric materials are subjected to a depolymerization treatment comprising at least one treatment with hydrogen, so as to form at least a first fraction comprising liquid or solid alkanes and a second fraction comprising at least hydrocarbons, preferably carbonated and;
(b) the hydrocarbons contained in the second fraction are introduced into a stage of catalytic decomposition of the hydrocarbons into hydrogen and carbon. Process according to Claim 1, in which the depolymerization treatment is supplied with hydrogen originating at least partially from stage (b). Process according to claim 1 or 2, in which the depolymerization treatment has a selectivity of at least 0.05 mol methane per mole of carbon contained in the polymeric waste. Process according to any one of Claims 1 to 3, in which the depolymerization treatment has a selectivity for alkanes whose number of carbon atoms is greater than 6 at least equal to 95% by weight relative to the weight of the polymeric materials treated . Process according to Claim 4, in which the molar mass of the products resulting from the reaction is between 16 g/mol and 478 g/mol. A process according to any one of claims 2 to 5, wherein step (b) of decomposing hydrocarbons produces more hydrogen than is consumed by the depolymerization treatment. A method according to any of claims 2 to 6, wherein the depolymerization step comprises
(i) a stage of thermal cracking of the polymeric materials, preferably carried out at a temperature of 350° C. to 600° C. and at least one fraction comprising hydrocarbons, preferably in the gaseous state, is withdrawn;
(ii) optionally carrying out a hydrotreatment of at least part of the polymeric fraction resulting from step (i);
(iii) at least part of the polymeric fraction resulting from step (i) or (ii) is treated with hydrogen in the presence of a catalyst, preferably at a temperature of 270° C. to 400° C. , and at least one fraction comprising liquid and/or solid alkanes is recovered Process according to any one of Claims 2 to 7, in which hydrocarbons, preferably comprising methane, are introduced into a decomposition stage in the presence of a catalyst, preferably based on iron, at a temperature of 400° C to 1000° C. and hydrogen and carbon are recovered. Process for the co-production of hydrogen, carbon and solid and/or liquid alkanes comprising the process according to any one of claims 6 to 8. Process according to claim 9, in which a supply (1) of polyolefin waste from the depolymerization stage (2) comprising at least one treatment with hydrogen is carried out, the first fraction comprising liquid alkanes is withdrawn (3) or solids, the second fraction comprising at least hydrocarbons is drawn off (4), preferably in the gaseous state, optionally, a fraction enriched in methane is separated (5) from other components of the second fraction and drawn off (6 ) a fraction enriched in other components, methane contained in the second fraction is introduced (7) into stage (9) of catalytic decomposition of the methane into hydrogen and carbon, optionally, a stage (9) of catalytic decomposition of methane into hydrogen and carbon into methane not originating from the depolymerization step (2) comprising at least one treatment with hydrogen, carbon is recovered (11), a gaseous fraction comprising hydrogen and optionally unreacted methane and said fraction is introduced, if necessary, into a stage (13) for separating hydrogen and methane so as to form a fraction enriched in methane which is recycled (15 ) to stage (9) of catalytic decomposition and a first fraction of hydrogen which is introduced (16) into stage (2) of depolymerization comprising at least one treatment with hydrogen and is recovered (14) a second fraction of hydrogen.