WO2023073129A1

WO2023073129A1 - Process for the treatment of polymeric materials

Info

Publication number: WO2023073129A1
Application number: PCT/EP2022/080129
Authority: WO
Inventors: Jean-Marie Basset; André GORIUS
Original assignee: Jmb Sas
Priority date: 2021-10-29
Filing date: 2022-10-27
Publication date: 2023-05-04
Also published as: FR3128717A1; TW202330799A

Abstract

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

Description

Process for the treatment of polymeric materials

The present patent application claims priority to French patent application FR2111580 the entire contents of which is incorporated by reference into the present application. The present invention concerns a process for the treatment of polyolefins waste. The invention also concerns a process of co-producing liquid and/or solid alkanes, hydrogen and carbon. The worldwide polyolefins market (ie polyethylene, polypropylene, polystyrene) represents in 2020 more than 200 million tons. About 50% of the polyethylene is used under the form of film, as injected products, cables or pipes etc. Concerning the polypropylene, the essential uses concern injected, particularly injection molded, products such as packaging, toys, automotive products and to a lesser extent under the form of films, pipes, fibers etc.

The valorization, of end-of-life products, even after operating mechanical recycling ( less than 15% of the polyolefins in 2020) is therefore a major societal issue at stake. Generally, the chemical recycling of polymers by depolymerization, today represents less than 5% of the worldwide production, and the forecasts estimate 20-25% in 2030. In this evolution, the part of polyolefins is weak, what is a natural result of the difficulty of breaking C-C bonds at low temperature.

It has been proposed to convert polyolefin waste into liquid alkanes that can be used, for example, as lubricants, see for instance EP-A-620264 and WO-A-2010/136850. Said process consumes lots of energy and hydrogen. Also, it produces gaseous alkane fractions which are greenhouse gasses. Another process is described in WO-A-2019/234408 wherein polymeric waste is decomposed into hydrogen and carbon in presence of an iron-based catalyst or iron oxide under electromagnetic radiation. This process is difficult to implement at an industrial scale in view of the significant investments necessary to make available microwaves treating high volumes of waste. Also, this process still produces significant amounts of harmful gaseous fractions containing alkanes, CO2 and toxic CO. US-B-6171475 (counterpart of FR2736646) discloses a method for converting a polymer or oligomer derived from an ethylenically unsaturated monomer into alkanes or into a hydrocarbon fraction or a lower oligomer fraction by controlled hydrocracking.

The invention makes available a process, which is improved and more respectful of the environment, for the treatment of polymeric materials, in particular of polyolefinic waste materials thereby allowing a better valorization of the polyolefins waste.

The invention concerns a process for the treatment of polymeric materials, preferably polyolefins, wherein (a) the polymeric materials are submitted to a depolymerization treatment comprising at least a 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, preferably gaseous, hydrocarbons and; (b) hydrocarbons contained in the second fraction are introduced into a step of catalytic decomposition of hydrocarbons into hydrogen and carbon.

Surprisingly, the process according to the invention allows a net hydrogen production and a high yield of liquid or solid alkanes while avoiding co-producing a substantial amount of greenhouse or toxic gases. It has been found that the quality of hydrocarbons and notably of methane contained in those fractions is sufficient for feeding a step of catalytic cracking into hydrogen and carbon. It has been found that the depolymerization process may produce a sufficient amount of hydrocarbon fractions, preferably in a gaseous state, that can be converted into hydrogen in an environmentally-friendly manner for the needs of the depolymerization, or even may produce a substantial excess of hydrogen.

As used in the present invention, the terms “solid”, “liquid” and “gaseous” refer to the state of matter in usual conditions, namely at a temperature of 25°C and an atmospheric pressure of 101325 Pascal (1 atmosphere).

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

In one particular aspect, the polymeric materials comprise aliphatic polyolefins. In this particular aspect wherein the polymeric materials submitted to the depolymerization treatment comprise usually at least 90% by weight, preferably at least 95% by weight of aliphatic polyolefins, in particular polyethylene and/or polypropylene, relative to the total weight of polymeric materials submitted to the depolymerization treatment.

Such aliphatic polyolefins can be, for example, homopolymers of aliphatic olefinic monomers such as ethylene, propylene, 1-butene, 2-butene, isobutene, butadiene, 1-pentene, 2-pentene, amylene, isoprene, 1-hexene, 2-hexene, 1,3-hexadiene, 1,4-hexadiene and 1,5-hexadiene. Such aliphatic polyolefins can also be, for example, copolymers. One example are copolymers between ethylene and propylene. Another example are copolymers of ethylene and/or propylene with at least one other aliphatic olefinic monomer selected from 1-butene, 2-butene, isobutene, butadiene, 1-pentene, 2-pentene, amylene, isoprene, 1-hexene, 2-hexene, 1,3-hexadiene, 1,4-hexadiene and 1,5-hexadiene. Another example are copolymers of ethylene and/or propylene with at least one alicyclic olefinic monomer selected from cyclopentene, cyclopentadiene, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene and cycloheptene. Still another example are copolymers of ethylene and/or propylene with at least one functionalized olefinic monomer such as vinyl acetate. However, aliphatic polyolefins based on monomers consisting of carbon and hydrogen, especially the aforementioned monomers are preferred.

In a preferred aspect, the polymeric material comprises polyethylene and/or polypropylene.

When the polymeric material comprises polyethylene, it often comprises at least one polyethylene selected from linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium density polyethylene (MDPE), high-density polyethylene (HDPE) and cross-linked polyethylene (XLPE).

When the polymeric material comprises polypropylene, it often comprises at least one polypropylene selected from isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene and polpropylene-ethylene random copolymer, preferably an isotactic polypropylene.

The process of the present invention may be applied to pure polymers and to mixtures of polymers. A particularly advantageous embodiment is the treatment of polymeric waste with the process according to the present invention. In that case, the polymeric materials which are submitted to the depolymerization treatment generally consist or consist essentially of polymeric waste. Generally, waste polymeric materials used in the present invention comprise end-of-life polymeric articles in particular polyethylene articles such as films and bags, injected products such as cables or pipes and/or end-of-life polypropylene articles in particular injection molded products such as packaging, toys, automotive products, films, pipes and fibers.

The depolymerization step may for instance comprise (i) a thermal cracking step of the polymeric materials, in particular polymeric materials as described here before, more particularly polymeric waste, carried out preferably at a temperature from 350°C to 600°C and withdrawing at least a fraction comprising gaseous hydrocarbons; (ii) optionally hydrotreating at least a part of the polymeric fraction formed in step (i); (iii) treating at least a part of the polymeric fraction formed in step (i) or (ii) with hydrogen in the presence of a catalyst, preferably at a temperature from 270°C to 400°C, and recovering at least a fraction comprising liquid and/or solid alkanes.

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

In the process according to the invention the hydrogen pressure applied in step (a) is generally equal to or higher than 2 bar abs., often this pressure is equal to or higher than 4 bar abs.. In the process according to the invention the hydrogen pressure applied in step (a) is generally equal to or lower than 10 bar abs. In the process according to the invention the hydrogen pressure applied in step (a) is preferably about 5 bar abs.

It has now been found that the depolymerization may be carried out in synergistic combination with a catalytic decomposition of hydrocarbons into hydrogen and carbon, provided that it is conducted so as to produce a gaseous hydrocarbon fraction which can be used as feedstock for the catalytic decomposition, in a significant amount, notably in an amount sufficient or even more than what is necessary to ensure its own hydrogen supply. Unlike the prior art which considers gaseous hydrocarbon fractions as problematic, the present invention aims at maximizing 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 comprising liquid and/or solid alkanes is formed. The aforesaid first fraction generally comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 10 and 40. n may be an integer or a decimal number.

In a first particular embodiment, the first fraction comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 10 and 16. More preferably n is about 12. The alkanes in accordance with this embodiment are preferably linear. They are useful, for example, as fuel for diesel engines.

In a second particular embodiment, the first fraction comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 18 and 40. More preferably n is equal to or about 20. The alkanes in accordance with this embodiment are preferably linear. They are useful, for example, as lubricants. In one aspect of this embodiment, the alkane mixture is suitable as an oil lubricant. In another aspect of this embodiment, the alkane mixture is suitable as a grease lubricant.

In the process according to the invention and in the two particular embodiments described here before, the first fraction generally comprises at least 90% by weight of said alkane mixture, more particularly the first fraction may consist or consist essentially of said alkane mixture.

In the process according to the invention and in the two particular embodiments described here before, the first fraction generally consists of fully saturated alkanes. However, in certain aspects, a low amount of unsaturated hydrocarbons, typically less than 1% by weight relative to the total weight of the first fraction, may be present.

In the process according to the invention, the first fraction can be withdrawn directly from the reaction medium. The constituents of the first fraction can also be withdrawn along with other components from the reaction medium and the first fraction is subsequently separated from its mixture with other components by suitable separation techniques such as e.g. solvent extraction or preferably distillation. In a particular aspect, the first fraction is withdrawn from step (a) as a liquid phase, notably a melt.

In the process according to the invention, the depolymerization treatment generally has a selectivity to alkanes having more than 6 carbon atoms of at least 90% by weight with respect to the weight of the treated polymeric materials.

In the process according to the invention, at least a second fraction comprising preferably gaseous hydrocarbons is formed. These gaseous hydrocarbons are selected, for example, from alkanes and olefins. Particular examples are selected from alkanes having a number of carbon atoms ranging from 1 to 5 and olefins having a number of carbon atoms ranging from 2 to 5. 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 second fraction often comprises at least 90 mol% of hydrocarbons which are in gaseous state at a temperature of 25°C and an atmospheric pressure of 101325 Pascal (1 atmosphere).

In the process according the invention the second fraction can be suitably withdrawn from step (a) as a stream, which is gaseous under the conditions of step (a). It is advantageous to withdraw said gaseous stream of second fraction directly from the reaction medium of step (a). Alternatively, such gaseous stream can suitably be withdrawn, for example, from a separation step such as described above for the first fraction.

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

The second fraction may be eventually submitted to one or more separation treatments.

For instance, a methane enriched fraction can be separated from other components of the second fraction, for example by a membrane separation operation. In this case, the methane content of the methane enriched fraction is generally at least 50 % molar, preferably, it is at least 95 % molar. In this aspect, the second fraction can consist of methane or of equal to or less than 98% molar of methane.

Preferably, the second fraction can be treated by pressure swing adsorption to produce a methane enriched fraction, in particular as described here before.

The methane enriched fraction is preferred for feeding step (b) of the process according to the invention.

In another aspect, the process according to the invention further comprises subjecting gaseous hydrocarbons from the second fraction to a deacidification step prior to the introduction into step (b).

The second fraction may also be introduced into step (b) of the process according to the invention without separation treatment. In a particular embodiment, the stream of second fraction withdrawn from step (a), in particular as described above, is fed directly, after optional pre-heating, into step (b).

In the process according to the invention, heat contained in a gaseous stream produced by step (b) can suitably be used to heat said hydrocarbons contained in the second fraction, prior to introduction into step (b). Gaseous streams produced by step (b) include in particular streams comprising hydrogen gas and optionally hydrocarbons, as described below.

In an advantageous embodiment, step (b) is operated at a higher temperature than the step (a). In that case, hydrocarbons contained in the second fraction can suitably be pre-heated by a fraction comprising hydrogen gas and optionally hydrocarbons withdrawn from step (b) to facilitate said hydrocarbons reaching the reaction temperature of step (b) while the fraction comprising hydrogen gas and optionally hydrocarbons from step (b) are cooled to facilitate said fraction reaching the reaction temperature of the treatment with hydrogen of step (a).

The process according to the invention therefore also allows to realize synergies in terms of the overall energy consumption of the process.

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

Reference US-A-2021-A-0114003 discloses a method of using a treated iron ore catalyst comprising contacting a feed gas with a treated iron ore catalyst to produce hydrogen and graphene.

The form under which carbon is recovered from step (b), the catalytic decomposition of hydrocarbons into hydrogen and carbon, is readily apparent to the skilled person. Usually, solid carbon is recovered from step (b). In that case, the solid carbon is generally selected from graphene, fullerenes, carbon nanotubes, amorphous carbon, graphite and graphitic carbon.

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

In a preferred embodiment, step (b) of decomposing hydrocarbons produces more hydrogen than the depolymerization treatment consumes. In that case, the ratio of hydrogen produced in step (b) to hydrogen consumed in step (a) is generally equal to or greater than 1.1, preferably equal to or greater than 1.5, more preferably equal to or greater than 2.0. The ratio of hydrogen produced in step (b) to hydrogen consumed in step (a) is generally at most 5.0.

In a particular embodiment of the process according to the invention,  (i) a fraction comprising hydrogen gas and optionally hydrocarbons is withdrawn from step (b)  (ii) if appropriate, hydrocarbons are separated from said fraction and recycled to step (b) and a fraction, enriched in hydrogen gas, is recovered and  (iii) at least part of said fraction comprising hydrogen gas is fed into step (a).

The fraction comprising hydrogen gas, if appropriate after separation from hydrocarbons comprises generally at least 80% molar, preferably at least 95% molar and even 99% molar of hydrogen gas. This fraction can consist of hydrogen gas. It has however been found that it can be advantageous to feed a fraction comprising the above contents of hydrogen gas along with unreacted hydrocarbons and optional inert gases such as for example nitrogen gas and noble gases into step (a). In fact this embodiment allows the depolymerization to proceed while minimizing separation operations and optimizing heat recovery. In that case, the fraction comprising hydrogen gas generally contains equal to or greater than 1 mole% more particularly 5 mole% of unreacted hydrocarbons, in particular methane, and optional inert gases. The fraction comprising hydrogen gas generally contains equal to or less than 20 mole% of unreacted hydrocarbons, in particular methane, and optional inert gases.

In a particular aspect of this embodiment, the process further comprises treating said fraction comprising hydrogen gas to remove impurities such as, for example, traces of water.

illustrates a preferred schematic diagram of the process according to the invention:

Feeding (1) of polyolefin waste materials to the depolymerization step (2) comprising at least a treatment with hydrogen is carried out the first fraction comprising liquid or solid alkanes is withdrawn (3), the second fraction comprising at least gaseous hydrocarbons is withdrawn (4), optionally, a methane enriched fraction is separated (5) from other components of the second fraction and a fraction enriched with other components is withdrawn (6), methane contained in the second fraction is introduced (7) in the catalytic decomposition step (9) of methane into hydrogen and carbon, optionally, a catalytic decomposition step (9) of methane into hydrogen and carbon is fed (10) with methane not stemming from the depolymerization step (2) comprising at least a treatment with hydrogen, carbon is recovered (11), a gaseous fraction comprising hydrogen and eventually unreacted methane is withdrawn (12) and, optionally, said fraction is introduced in a step (13) of separating hydrogen and methane so as to form a methane enriched fraction that is recycled (15) to the catalytic decomposition step (9) and a first hydrogen fraction that is introduced (16) into the depolymerization step (2) comprising at least a treatment with hydrogen and a second hydrogen fraction is recovered (14).

Feeding (10) with gaseous hydrocarbons, with methane in particular, not stemming from the depolymerization step (2) is particularly advantageous for starting the process according to the invention.

The invention also concerns a plant suitable for practicing the process according to the invention, in particular in accordance with .

The invention concerns also a process of co-producing hydrogen, carbon and solid and/or liquid alkanes said process comprising the treatment process as described in the present specification.

The following example intends to illustrate the invention without however limiting it.

Example

A depolymerization step is fed with 100,000 tons per year of polyethylene having a degree of polymerization 500000 (flow 1). The selectivity of the catalytic depolymerization process is 15% (number of carbon atoms converted / number of carbon atoms present in the initially fed polyethylene). The additional feeding with methane (10) is deactivated. The depolymerization process (2) converts the polyethylene, by addition of hydrogen generated by the step of methane cracking (9), into a mixture of alkanes having an average chemical formula C₂₀H₄₂ and methane.

The annual production of the whole process is composed of: 85,607 t/year of alkanes mixtures of average chemical formula C₂₀H₄₂

1,536 t/year of dihydrogen H₂

12,857 t/year of solid carbon

Claims

Process for the treatment of, preferably polyolefinic, polymeric materials, wherein
(a) the polymeric materials are submitted to a depolymerization treatment comprising at least a treatment with hydrogen, so as to form at least a first fraction comprising liquid or solid alkanes and a second fraction comprising at least, preferably gaseous, hydrocarbons and;
(b) hydrocarbons contained in the second fraction are introduced into a step of catalytic decomposition of hydrocarbons into hydrogen and carbon.
Process according to claim 1, wherein the polymeric materials comprise an aliphatic polyolefin.
Process according to claim 1 or 2, wherein the polymeric materials comprise polyethylene and/or polypropylene.
Process according to claim 3, wherein the polyethylene comprises at least one polyethylene selected from linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium density polyethylene (MDPE), high-density polyethylene (HDPE) and cross-linked polyethylene (XLPE).
Process according to claim 3, wherein the polypropylene comprises at least one polypropylene selected from isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene and polypropylene-ethylene random copolymer, preferably an isotactic polypropylene.
Process according to anyone of claims 1 to 5, wherein the polymeric materials submitted to the depolymerization treatment comprise at least 90% by weight, preferably at least 95% by weight of aliphatic polyolefins, relative to the total weight of polymeric materials submitted to the depolymerization treatment.
Process according to anyone of claims 1 to 6, wherein the polymeric materials which are submitted to the depolymerization treatment consist or consist essentially of polymeric waste.
Process according to anyone of claims 1 to 7, wherein the depolymerization treatment is fed with hydrogen at least partially stemming from step (b).
Process according to anyone of claims 1 to 8, wherein the hydrogen pressure used in step (a) is from 2 to 10 bar abs, preferably about 5 bar abs.
Process according to anyone of claims 1 to 9, wherein the depolymerization treatment has a selectivity to alkanes having more than 6 carbon atoms of at least 90%, preferably at least 95% by weight by weight with respect to the weight of the treated polymeric materials.
Process according to anyone of claims 1 to 10 wherein the molar mass of the products generated by the depolymerization treatment ranges from 16 g/mol to 478 g/mol.
Process according to anyone of claims 1 to 11 wherein the first fraction comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 10 and 40.
Process according to anyone of claims 1 to 12 wherein the first fraction comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 10 and 16.
Process according to anyone of claims 1 to 12 wherein the first fraction comprises an alkane mixture having an average molecular formula of CnH2n+2 with n being comprised between 18 and 40.
Process according to anyone of claims 12 to 14, wherein the first fraction comprises at least 90% by weight of said alkane mixture.
Process according to claim 15, wherein the first fraction consists or consists essentially of said alkane mixture.
Process according to anyone of claims 1 to 16 wherein the first fraction is withdrawn from step (a) as a melt.
Process according to anyone of claims 1 to 17, wherein the depolymerization treatment presents a selectivity of at least 0.05 mol methane per mol of carbon contained in the polymeric materials, preferably the polymeric waste.
Process according to anyone of claims 1 to 18 wherein the second fraction is withdrawn from step (a) as a stream, which is gaseous under the conditions of step (a).
Process according to anyone of claims 1 to 19 wherein the second fraction comprises at least 90 % molar of hydrocarbons which are in gaseous state at a temperature of 25°C and an atmospheric pressure of 101325 Pascal (1 atmosphere).
Process according to anyone of claims 1 to 207 wherein the second fraction comprises alkanes having a number of carbon atoms ranging from 1 to 5 and olefins having a number of carbon atoms ranging from 2 to 5, preferably alkanes having 1, 2, 3 or 4 carbon atoms, more particularly methane.
Process according to anyone of claims 1 to 21 wherein the second fraction comprises at least 50 % molar, preferably at least 95% molar of methane.
Process according to claim 22, wherein the second fraction has been treated with a membrane or by pressure swing adsorption to produce a methane enriched fraction.
Process according to anyone of claims 1 to 23 which further comprises subjecting gaseous hydrocarbons from the second fraction to a deacidification step prior to the introduction into step (b).
Process according to anyone of claims 19 to 22, wherein the stream of second f raction withdrawn from step (a) is fed directly, after optional pre-heating, into step (b).
Process according to anyone of claims 1 to 25 wherein heat contained in a gaseous stream produced by step (b) is used to heat said hydrocarbons contained in the second fraction prior to introduction into step (b).
Process according to anyone of claims 8 to 26, wherein step (b) of decomposing hydrocarbons produces more hydrogen than the depolymerization treatment consumes.
Process according to claim 27, wherein the ratio of hydrogen produced in step (b) to hydrogen consumed in step (a) is equal to or greater than 1.1, preferably equal to or greater than 1.5, more preferably equal to or greater than 2.0, generally at most 5.0.
Process according to anyone of claims 1 to 28, wherein (i) a fraction comprising hydrogen gas and optionally hydrocarbons is withdrawn from step (b) (ii) if appropriate, hydrocarbons are separated from said fraction and recycled to step (b) and a fraction, enriched in hydrogen gas, is recovered and (iii) at least part of said fraction comprising hydrogen gas is fed into step (a).
Process according to claim 29, wherein the fraction comprising hydrogen gas, if appropriate after separation from hydrocarbons comprises at least 80%, preferably at least 95% molar of hydrogen gas.
Process according to claim 29 or 30, which further comprises treating said fraction comprising hydrogen gas to remove impurities.
Process according to anyone of claims 29 to 31, wherein the part of the fraction comprising hydrogen gas which is fed into step (a) comprises at least 80% molar of hydrogen and at most 20% molar unreacted hydrocarbons, preferably methane, and optional inert gases.
Process according to anyone of claims 1 to 32 wherein solid carbon is recovered from step (b).
Process according to claim 33 wherein the solid carbon is selected from graphene, fullerenes, carbon nanotubes, amorphous carbon, graphite and graphitic carbon.
Process according to anyone of claims 1 to 34, wherein the depolymerization step comprises
(i) a thermal cracking step of polymeric materials preferably at a temperature from 350°C to 600°C and at least a fraction comprising, preferably gaseous, hydrocarbons, is withdrawn;
(ii) optionally a hydrotreatment of at least a part of the polymeric fraction formed in step (i) is carried out;
(iii) treating at least a part of the polymeric fraction formed in step (i) or (ii) with hydrogen in the presence of a catalyst, preferably at a temperature from 270°C to 400°C, and recovering at least a fraction comprising liquid and/or solid alkanes.
Process according to any of claims 1 to 35, wherein hydrocarbons, preferably comprising methane, are introduced in a decomposition step in the presence of a catalyst, preferably an iron-based catalyst, at a temperature ranging from 400°C to 1000°C and hydrogen and carbon are recovered.
Process of co-producing hydrogen, carbon and liquid and/or solid alkanes comprising the process according to any of claims 1 to 36.
Process according to claim 37, wherein feeding (1) of polyolefin waste materials into the depolymerization step (2) comprising at least a treatment with hydrogen is carried out, the first fraction comprising liquid or solid alkanes is withdrawn (3), the second fraction comprising at least gaseous hydrocarbons is withdrawn (4), optionally, a methane enriched fraction is separated (5) from other components of the second fraction and a fraction enriched with other components is withdrawn (6), methane contained in the second fraction is introduced (7) in the catalytic decomposition step (9) of methane into hydrogen and carbon, optionally, a catalytic decomposition step (9) of methane into hydrogen and carbon is fed (10) with methane not stemming from the depolymerization step (2) comprising at least a treatment with hydrogen, carbon is recovered (11), a gaseous fraction comprising hydrogen and optionally unreacted methane is withdrawn (12) and, if appropriate, said fraction is introduced in a step (13) of separating hydrogen and methane so as to form a methane enriched fraction that is recycled (15) to the catalytic decomposition step (9) and a first hydrogen fraction that is introduced (16) into the depolymerization step (2) comprising at least a treatment with hydrogen and a second hydrogen fraction is recovered (14).