WO2024069572A1

WO2024069572A1 - An apparatus for thermochemical conversion of a sample comprising rubber or a sample sourced from tyres

Info

Publication number: WO2024069572A1
Application number: PCT/IB2023/059775
Authority: WO
Inventors: Nagar BHAWNA; Oliveira WANDERSON DA SILVA; Hubert Girault
Original assignee: Tyre Recycling Solutions Sa
Priority date: 2022-09-30
Filing date: 2023-09-29
Publication date: 2024-04-04

Abstract

Tyre photo-pyrolysis systems and processes are provided which include feeding tyres, tyre shreds and tyre rubber granules are conveyed to be exposed to a strong illumination from a flash lamp illumination system thereby photo-pyrolysing the tyres, tyre shreds and tyre rubber granules to produce a hydrogen-containing gas stream and porous carbon-containing solids which may contain some oils. A process may also be provided to extract the heat from the flash lamp illumination system, part of it being used to heat the tyres, tyre shreds and/or tyre rubber granules in the anaerobic feeder. A process may still be provided to extract heat from the photo-pyrolysis reactor. Another process may further be provided to extract the solid and liquid products from the photo-pyrolysis reactor while avoiding air entry into the photo-pyrolysis reactor, and where the different components such as porous carbon, metals and oils are separated.

Description

AN APPARATUS FOR THERMOCHEMICAL CONVERSION OF A SAMPLE COMPRISING RUBBER OR A SAMPLE SOURCED FROM TYRES

TECHNICAL DOMAIN

The present invention relates to a pyrolysis apparatus for transforming tyres, tyre shreds or tyre granules or powder to produce hydrogen rich gases, solids containing carbon black particles, metals, and mineral matters as well as oils.

BACKGROUND

Globally approximately one billion waste tyres are generated annually, of which the US and the European Union are the biggest contributors, contributing about 300 and 260 million waste tyres respectively. Out of this, only around 100 million tyres are processed. Millions of these are accumulated in landfills causing land contamination with heavy metals and piling up of these leads to stagnant water and other unhygienic conditions creating a perfect breeding habitat for mosquitoes and other disease-spreading animals.

As per the European Tyre and Rubber Manufacturing Association (ETRMA), 95% of all the end-of-life tyres were collected and treated, out of which 55% were used for material recovery (i.e. recycling) which is majorly granulated and the rest is used for incorporation in cement, sent for pyrolysis for gas and carbon recovery etc. The remaining 40% were used for direct energy recovery through waste tyre rubber (WTR) incineration/ combustion. Different valorisation strategies can be adopted depending on the state of end-of-life tyres. At first, all the worn-out WTR are reused and retreaded if possible and if they can provide equivalent performance. For secondary valorisation, WTR is separated from metal and textile parts and is granulated for repolymerisation/ vulcanisation or as fillers. Tertiary valorisation is the most advantageous option consisting of either pyrolysis in which the tyre rubber is heated to high temperatures in absence of oxygen for obtaining useful oils, gases and carbon or de-vulcanisation for selectively breaking the sulphide bonds to recover the original polymeric backbone i.e. raw materials. The fourth and last valorisation strategy is the most controversial and least favourable - incineration. As tyre rubber has a very high energy content of about 29-39 MJ/ kg, it is an excellent candidate for energy recovery from an economic point of view, however, due to unacceptable amounts of toxic gases emissions (e.g., NOx, SOx, COx, HCN, etc.), it is generally not considered.

Thermal pyrolysis is a well-accomplished and adopted technology wherein the tyres as whole or in the shredded form are exposed to high temperatures in an oxygen deficit environment for converting to oils, gases and solid carbon products. The percentage of different products obtained after pyrolysis at different conditions (time, temperature etc.) is also quite well stated in the literature. The main environmental issue for thermal pyrolysis is that the heat source is more often than not a nonrenewable resource like coal, petroleum and natural gas making it an unsustainable option in the long run. Most of the pyrolysis units utilise more energy than produced. Even with processes that have net zero energy consumption, the problem of postproduction purification steps is a major drawback. The economic and commercial viability of the obtained products is compromised by the cost associated with added processing steps required to attain market purity standards. For instance, tyres consist of up to 30% carbon black, and their recovery is very high in demand, however poor quality due to the presence of volatiles and low yields by pyrolysis renders its commercial feasibility.

European patent application publication number EP0049054A2 discloses a module for a batch type semi-continuous pyrolysis process, wherein shredded tyres are first heated in an oven in an inert atmosphere covered in inclined bins. After heating, the bins are removed and immediately placed in water for cooling as the residual char would burn in presence of air otherwise. To avoid the issue of cooling and removing, United States patent application publication number US5095040A proposes a continuous system where crumbed tyres are fed, by an auger screw, through a furnace. The end of the screw is cold enough to cool down the upcoming tyres from the furnace. Pyrolysing whole tyres or big chunks of tyre presents energy inefficiency issues, as do batch systems in general. The challenge of continuous treatment mode with quality product output has been successfully shown to some extent in United States patent application publication number US20110048916A1, which teaches the use of microwave energy to reduce organic materials, such as tyres, to a high-quality syngas and oils that can be directly used as fuels. In addition, the energy produced in the form of syngas (methane, ethane, propane, butane and carbon monoxide) is shown to be more than sufficient for running the microwave source and other parts of the system. Nonetheless, the system is difficult to realise on an industrial scale since temperatures of around 360°C must be achieved to produce a combination of ethane and methane hydrocarbon vapours and so the system needs immediate cooling to avoid recombination of the gases or repolymerisation. Thus, the process needs to include precise control of cooling temperatures and gas stream pressure as well as exposure times etc. The process relies on the strict control of parameters such as nitrogen gas input and microwave energy etc., which could change the overall economics of the process, making it impractical to realise.

Some of the common major challenges for pyrolysis include i) poor heat conduction of rubber that increases the char accumulation at interfaces causing the need of more energy for longer times ii) the cost of the whole system affected by the relatively high cost of catalysts and the need for additional purification steps and iii) the poor quality of the products recovered (especially carbon black) and lastly iv) the need for a self-sufficient/ self-efficient or self-powered system. As a solution to this problem, United States patent publication number US7329329B2 proposes a process wherein the tyres are first shredded into smaller pieces, or tyre shreds, in order to ease the process as well as to increase energy efficiency (increase the heat transfer effect). However, the techniques disclosed therein increases the capital cost of the process because of the extra machinery and energy which are required. There remains a need for a more advanced pyrolysis process to maximise the production of good quality and high-yield products within a circular economy model. Recognising the aforementioned problems related to the difficulty in recycling used tyres or how to eliminate used tyres without polluting the environment, United States Patent Application Publication No. US 2004/0182001 Al proposes a tyre pyrolysis system for pyrolyzing tyre shreds to produce marketable carbon and fuel products in an economical and commercially viable manner. The pyrolysis system described in the aforementioned patent application however uses a reactor which uses a heating element which provides heat by using sources such as a hydrocarbon or natural fuel (gas, coal, wood), electric heat, hot flue gasses from a high temperature incinerator or the like. Heating rubber to the temperatures required to produce a pyrolytic reaction is highly inefficient as rubber is a poor conductor. The system requires that the tyres be shred into small pieces - it is not possible to process a complete tyre. Furthermore, creating thermochemical reactions by using a heat source, i.e. by colliding gas particles into the sample, tends to create fragments of material in an uncontrolled manner, which may even lead to the production of poisonous gasses.

European patent application publication number EP3527643A1 discloses a plant for carrying out pyrolysis of materials deriving from tyres or bitumen. This document proposes the use of laser radiation focussed on a localised area of the sample for bringing the sample to the required temperature for the pyrolysis to occur. The resulting footprint of the laser on the sample is rather small and there is a need to move the sample around until a sufficient area of the sample has been treated. It is doubtful as to whether such a process would be able to be applied to whole tyres on an industrial scale in a factory line.

Czech patent publication number 292487B6 discloses a process for treating waste tyres by abrasion in a gaseous medium comprising ozone while the tyre is exposed to UV radiation. This system would not be compatible in a situation where the presence of oxygen is to be avoided since there is a high chance of the ozone breaking down into oxygen, or other gasses containing oxygen, in the presence of UV radiation. Flash light photonic surface treatment, or flash light photonic curing, is a known process which can be used to raise the surface of a sample to very high temperatures. The process involves using a flashlamp to illuminate the sample.

The process of using a flashlamp (electric arc lamp, also called flash tube) for producing full spectrum white light is widely employed in printed electronics for rapid curing/ sintering of conductive inks over inexpensive and flexible polymer substrates. Typically, a xenon lamp is used to create flashes of high intensity broad wavelength light for very short durations (< 1ms) over a sample for increasing the temperature locally (due to selective absorption of light by metal precursors and other surrounding materials), causing the non-heat resistant materials such as binders, solvents, resins etc. to heat up and evaporate and the remaining heat resistant materials like metal (nano)particles to sinter and form conductive paths for example in Ag or Cu. Since the temperature is raised locally by radiation, a wide range of low glass transition temperature plastics like PET or PEN or even paper can be used as substrates.

Flash light photonic surface treatment can be used to modify the surface of materials. For example, several reports have shown removal of oxygen functionalities from graphene oxide to form conductive graphene patterns and formation of metal carbide from a metal oxide precursor in solid form.

Flash light photonic surface treatment has also been used to onset surface chemical reactions, such as for the nucleation and growth of metallic nanoparticles from precursor salt solutions or for the synthesis of Prussian Blue.

A novel process for biowaste-to-energy conversion using high powered lights from a xenon flashlamp is described in Chemical Science Volume 13, 2022, at pages 1774 to 1779. The experiments described therein are disclosed as providing for a swift onset of thermochemical reactions as soon as the light impinges on the material surface, rapidly converting bio waste material into combustible gases (syngas) and porous conductive carbon. The document discloses that biomass waste samples such as banana peel, corncob, orange peel, coffee bean and coconut shell can be first dried then ground to form fine powders before exposing them to flashlights with different voltages. A stainless-steel reactor, closed using a quartz glass, having suitably configured gas inlets and outlets for maintaining a desired atmosphere in the reactor, as well as providing for gas collection and analysis is disclosed in the aforementioned document. According to the document, the key advantage of the process described therein, known as photo-pyrolysis, is to circumvent the need for expensive high- temperature ovens by using only a pulsed flash lamp. The document discloses that the conversion time using the process can be reduced significantly, in some cases down to millisecond ranges, while producing higher amounts of hydrogen gas and extremely useful conductive porous carbon compared to conventional thermal pyrolysis techniques. A total of 33wt% solid carbon i.e., biochar was obtained while emitting only 3.8wt% total carbon dioxide. From an energy perspective, a positive energy balance of ~4 MJ/ kg of biomass was calculated (only considering the high heating value of the biomass and converted gases). Amongst the gases obtained, H2 gas constituted 4.4wt% corresponding to ca. 1001 of H2 from 1kg of dried biomass. Successful splitting of biomass into useful end products (combustible gases and conductive carbon) in extremely short exposure times of ~15ms demonstrated the potential for using flash light pyrolysis, or photo-pyrolysis, as an alternative to conventional thermal pyrolysis for biomass materials. However, since biomass contains cellulose, the products of the reaction will invariably include oxygenated products such as carbon monoxide, for example, which is poisonous. It would be desirable to be able to use a thermochemical conversion process which does not generate poisonous gasses or gasses which would cause unwanted combustion.

BRIEF SUMMARY OF THE INVENTION

According to an aspect, provision is made for a system and an apparatus for thermochemical conversion of at least a part of a sample into a plurality of products, the apparatus comprising: a thermal decomposition reaction chamber having at least one chamber wall separating an interior of the reaction chamber from an exterior of the reaction chamber, the reaction chamber configured to receive said sample at least during said thermochemical conversion; a means for heating at least a part of said sample within the reaction chamber to a temperature which is sufficient to bring about said thermochemical conversion; and a purge system configured to produce an inert atmosphere at the interior of said reaction chamber (110) at least during said thermochemical conversion.

Advantageously, said thermochemical conversion is a photo-pyrolysis reaction, said means for heating at least a part of said sample within the reaction chamber being a light source located at the exterior of the reaction chamber and configured to provide light through a light-transparent window in the chamber wall such that at least a part of the light arriving at the sample arrives with sufficient energy to bring about said thermal conversion of at least a part of the sample, the sample comprising rubber. The sample preferably comprises rubber.

Preferably, the system further comprises a sample conveyer system configured to convey the sample from a sample input of the apparatus to a reaction site at the interior of the reaction chamber.

According to an embodiment, the sample is in granular form at least when it reaches the reaction chamber. According to another embodiment, the sample comprises shreds of rubber or material from a tyre, at least when the sample reaches the reaction chamber. The shreds may be as large as several square centimetres in area. For example, the shreds may be up to 5cm² in size. According to an advantageous embodiment, the sample is a complete tyre and the sample conveyor system is configured to hold the tyre and to rotate it around its central axis in the path of the photons from the light source, or source of electromagnetic energy. In a particular embodiment the light source is a Xenon lamp, or a Mercury-Xenon lamp, configured to flash its energy towards the sample. Other optional features of the invention are set out in the dependent claims.

In a preferred embodiment of the system, or apparatus, for performing a thermochemical conversion, the sample conveyor system may be configured to convey the tyre to the interior of the chamber and to rotate the tyre with at least a part of its tread facing the part of the chamber wall which is transparent to said electromagnetic radiation such that during said rotation, said pyrolysis takes place over at least a part of said tread. Preferably, the pyrolysis should take place over a substantial part, if not all, of the tyre, or at least a substantial part of the tread.

The photo-pyrolysis process of the invention operates by light absorption of the tyres, tyre shreds or tyre rubber granules in a wide temperature range and atmospheric pressure. The energy source may be a flash light, which upon absorption by the tyres, tyre shreds or tyre rubber granules, causes a transient temperature rise of the material and of the photo-pyrolysis reactor itself. The transient flash light absorption onsets pyrolysis reaction in the substantially oxygen free, or otherwise oxygen deprived, or inert, atmosphere thereby decomposing at least parts of the tyre, tyre shreds or tyre rubber granules. Surprisingly, a flashlamp can be used to photo- pyrolyse complete tyres and pieces of tyre shreds as large as few centimetres square, for example up to 5cm². The process is suitable to be done on an industrial scale in a continuous production line environment. The products obtained are mainly carbon, syngas, tyre pyrolysis oil (TPO) from the rubber, and steel wires from the tyres and tyre shreds.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a system for photo-pyrolysing at least a part of a tyre or tyre shreds or tyre rubber granules, according to an embodiment of the invention; and

Figure 2 shows a schematic representation of a process for photo-pyrolysing tyres, tyre shreds or tyre rubber granules using the system shown in. Figure 1.

DETAILED DESCRIPTION

Figure 1 shows the schematic of an apparatus or a system according to an embodiment of the present invention. An embodiment of the apparatus may be used to perform photo-pyrolysis of at least a part of a tyre, preferably a used tyre. Another embodiment may be used to perform photo-pyrolysis of tyre shreds. Another embodiment may be used to perform photo-pyrolysis of rubber granules removed from a tyre, for example, preferably a used tyre.

As shown in figure 1, an embodiment of an apparatus for performing a thermochemical conversion of at least a part of a sample into a plurality of products, may comprise a thermal decomposition reaction chamber. Preferably, the reaction chamber is for thermal decomposition by photo-pyrolysis, and as such, the chamber comprises a chamber wall, at least a part of which is configured to let light pass through from the exterior of the chamber to the interior of the chamber where the sample to be converted is placed. Thus, at least a part of the wall of the chamber may comprise a window. Preferably the window should be heat resistant to be able to withstand high temperatures which may be reached within the chamber.

Since pyrolysis takes place in an oxygen-depleted atmosphere, preferably in an inert atmosphere, the apparatus is configured to be able to provide the interior of the chamber with an inert atmosphere. Different ways of achieving this are known by a person having ordinary skill in the art. For example, oxygen may be drawn out from the chamber prior to pyrolysis, or an inert gas may be pumped into the chamber to replace any residual oxygen before the pyrolysis begins. The apparatus may further comprise a system for maintaining the interior of the chamber at a predetermined pressure which is favourable to the conversion reaction.

According to an embodiment, the apparatus comprises a source of electromagnetic energy, positioned at the exterior of the chamber and configured to flash electromagnetic radiation towards a sample in the interior of the chamber through the window in the wall of the chamber. According to a preferred embodiment, the source of electromagnetic energy may be a xenon flash bulb or a mercury-xenon flash bulb or any electromagnetic radiation source capable of emitting photons having wavelengths within a broad range of frequencies, preferably resembling the range of frequencies found in sunlight. According to an embodiment, the frequencies are those corresponding to photons having wavelengths which fall within a range of 200nm to 600nm. As is known in the art, light having wavelengths in the order of 200nm provide enough energy to be able to achieve the breaking of molecular bonds which must take place for the desired photo-pyrolysis to occur. In a preferred embodiment of the invention, a light source is chosen which is capable of providing flashed light having wavelengths of between about 200nm and 350nm. The light source may be located outside of the chamber and configured such that the photons arrive at the sample within the chamber with an intensity which is sufficient to cause at least a part of the sample to undergo a thermal decomposition by pyrolysis.

The apparatus preferably has an inlet through which the sample may pass, and a sample conveyor system configured to convey the sample to the reaction chamber and to position the sample in an appropriate place within the chamber for the pyrolysis to take place when the light source is activated. Consequently, the light source and the sample conveyor system should be mutually arranged within the apparatus such that the photons arrive at the sample with sufficient intensity as described above. According to a first embodiment, the inlet and the sample conveyor system are configured to allow the sample to be transported towards the interior of the reaction chamber when the sample is in the form of granules or powder. According to an embodiment, the apparatus comprises a grinder to grind the sample down to granular or powder form to be transported to the chamber. In such embodiments, the sample conveyor system may be a conveyer belt. The sample conveyor system may comprise a screw mechanism to push the sample towards the chamber. Otherwise, the belt may be on rollers so that the sample may be translated along the conveyer towards the chamber.

According to another embodiment, the inlet and the sample conveyor system may be configured to accept the sample in shredded form, with shreds being as big as several cm squared in area. In a particular embodiment, the apparatus may have a shredder configured to shred parts of the sample from a larger piece of material. Again, in these embodiments, the sample conveyor system may be a conveyer belt or may comprise a screw.

According to yet another embodiment, the inlet is designed to accept a complete tyre. Tyres have treads and beads and have a central axis which coincide with a central axis of a wheel on which the tyre is intended to be mounted. In this embodiment of the system, or apparatus, for performing a thermochemical conversion, the sample conveyor system is designed to hold the sample (in this case the tyre), to convey it to the interior of the reaction chamber, and to turn the tyre about its central axis, with its tread facing the light source though the window in the wall of the chamber so that parts of the tyre undergo the pyrolysis reaction as the tyre spins in front of the flashing electromagnetic energy source.

As such, an apparatus according to embodiment of the invention may comprise a photo-pyrolysis reactor (100) configured to operate in an oxygen impoverished atmosphere, preferably an inert atmosphere, with one inlet (120) through which may be deposited tyres, tyre shreds or tyre rubber granules removed from tyres, onto a sample conveyor system for conveying the tyres, tyre shreds or tyre rubber granules close to a transparent window (140) in a wall of a reaction chamber (110) to be illuminated by a flash lamp illumination system (150). The thus photopyrolysed products may be in gaseous form and so may be extracted by an exhaust system (160) to be further purified or burnt to produce electricity and heat. Other products may be in solid form or in liquid form or both in solid and liquid form and may be collected by a suitable collection system (170).

According to an embodiment, a sample conveyor system is provided for conveying the sample from the inlet (120) of the apparatus to the reaction chamber (110). Parts of the sample conveyor system or parts of the inlet may be heated (180) in order to transfer heat to the sample to pre-heat it to a suitable temperature so that the sample arrives at the reaction chamber at a temperature which allows for an advantageous reaction. Such a heated feeding system, including the inlet and the sample conveyor system, to deliver tyres, preferably used tyres, tyre shreds or rubber granules removed from tyres, preferably from used tyres, may advantageously be associated with a purging gas system to configured to prevent oxygen from entering the reactor and to avoid an oxidation or combustion of the materials within the reaction chamber. The temperature within the feeding system may reach levels as high as 400°C. for example.

A sample conveying system, preferably of a mechanical type, may be used to transport the tyres, tyre shreds or rubber granules removed from tyres from the inlet to an illumination area, or reaction site, which is an area in the reaction chamber where photo-pyrolysis takes place. Different systems can be used depending on the form of the sample materials to be treated. For example, an inclined plate or ramp may be used to roll the tyres to a spinning station, where each tyre may be made to rotate around its central axis in front of the transparent window in the wall of the reaction chamber. A metallic grid conveyor belt, or any other type of conveyor belt (130) can be used to carry the sample towards the heat resistant transparent window, especially when treating tyre shreds or granules. An inclined vibrating plate can be used to carry the sample towards the heat resistant transparent window, especially when treating rubber granules removed from used tyres. Alternatively, a rotating quartz tube can be used as in a kiln, especially for treating small quantities for testing purposes. According to an embodiment, the sample conveyor system, preferably a mechanical conveying system, may be formed by an inclined quartz tube acting as a kiln, where the tyre shreds or the rubber granules removed from used tyres are conveyed by rotation of the quartz tube. Different embodiments may feature different types of mechanical sample conveyor systems depending on the type of sample to be converted.

At least a part of the wall of the chamber is configured to allow light from a flash source outside of the chamber to reach a sample within the chamber. For example, the chamber wall may incorporate a transparent window fixed on to the photo-pyrolysis reactor to enable the illumination of the used tyre shreds or rubber granules removed from used tyres. The window can be easily accessible to allow regular cleaning of possible carbonaceous deposits.

The system or apparatus may further comprise a flashlamp irradiation system comprising a xenon flash lamp or a mercury-xenon flash lamp, a power supply and, optionally, a cooling system.

A gas exhaust may be provided to collect the gases produced by the photopyrolysis reaction. The exhaust may be equipped with a pressure valve to avoid pressure build-up in the photo-pyrolysis reactor. It may comprise a condenser to collect low boiling point gases. It may also be connected to a hydrogen purification unit, where an output of the apparatus provides gasses from the reaction chamber to the hydrogen purification unit for further processing.

The apparatus may further comprise a photo-pyrolysed products collection system for solids, liquids or liquid containing solids. The apparatus may be equipped with air locks to avoid the entry of oxygen in the photo-pyrolysis reactor. It can be equipped with a cooling system to recover heat and to cool the products formed. The products can then be separated and further processed for different applications. In some cases such as dirty raw materials, a portion of the photo-pyrolysed products can be added to the feeding system to enhance the light capture and hence the photopyrolysis process.

According to an embodiment, the apparatus may comprise a heat transfer system for cooling the flash lamp illumination system. Part of the heat can be used to heat the feeding system; the rest being valorised by other processes.

Figure 2 shows a photo-pyrolysis plant process for semi-continuous or continuous processing. The process may be performed by the apparatus or system described in Figure 1. According to an embodiment, the process may include:

(a) Tyres may be received and stored, preferably used tyres or end-of-life tyres;

(b) Optionally, rubber can be removed mechanically from the tyre to provide rubber granules or rubber powder;

(c) Optionally, a shredding unit may be provided to cut the scrap tyre, either completely or after rubber removal in small shreds (for example, shreds measuring a few cm²);

(d) Scrap tyres, tyre shreds or rubber granules are transferred to the inlet part of the feeding system of Figure 1 where they may be heated to more than 150 °C; they may be semi-continuously or continuously transferred to the photopyrolysis reactor of Figure 1 avoiding oxygen entry;

(e) The mechanical conveying system (130) of Figure 1 may carry the tyres, tyre shreds or the rubber granules towards the transparent window of the apparatus shown in Figure 1;

(f) Using the xenon flashlamp of the illumination system of Figure 1, the tyres, tyre shreds or rubber granules are photo-pyrolysed by high power flash light irradiation through the transparent window in few seconds; after irradiation the gas produced are extracted by the exhaust of Figure 1 whilst the solids and liquids are collected through the collection system of Figure 1;

(g) The high-temperature heat from the flash lamp illumination system of Figure 1 may be recovered and part of it may be used to heat the inlet or other parts of the feeding system of Figure 1, such as parts of the sample conveyor system;

(h) metallic wires may be extracted from the solids formed during photopyrolysis. Such extraction may be performed either mechanically in the case of tyres, or by using for example an eddy current separator in the case of tyre shreds;

(i) the carbonaceous and mineral solids may be washed to remove the TPOs, which may then be collected for further processing;

(j) the TPO fraction may be collected for further processing;

(k) the hot gas collected from the photo-pyrolysis reactor may be cooled to condense it to low boiling-point liquids;

(i) the non-condensable fraction that corresponds to syngas (here light hydrocarbons) may be collected;

(m) part of the syngas may be used in an electric power/ heat generator to power the flashlamp illumination system.

Flash light irradiation, according to an exemplary embodiment, may be generated by electric pulses at a voltage of 325 Volt, at a frequency of 45Hz, the pulse duration being 1.5ms and the total process being carried out in 60 seconds. The tyre shreds may be pre-heated. In other embodiments, the tyre shreds need not be preheated. After photo-pyrolysis the carbon particles and metallic wires may be mechanically separated.

According to an embodiment, photo-pyrolysis of rubber granules from used tyres may take place at 325V electric voltage pulse, at a frequency of 45Hz, each pulse lasting 1.5ms during 20 seconds of flash light irradiation, for example. The process may be performed from lOOmg of rubber granules under argon flow in an oxygen free atmosphere for generating hydrogen and methane gases as the main products with a small contribution of carbon monoxide and almost zero CO2.

Some gaseous by-products (H?, CH4, C2H4, H2S, Alkenes, Isoprene) may be generated from the photo-pyrolysis of waste tyres under argon atmosphere performed at 325V-electric voltage pulse, at a frequency of 45Hz, each pulse lasting 1.5ms during 20 seconds of flash light irradiation. The photo-pyrolysis process was carried from lOmg of rubber granules under argon flow of 20mL.min-¹ in Ch-free atmosphere. According to these results H2, CH4 and C2H4 gases are the main gases generated with secondary contribution of H2S, Alkenes and Isoprene. This photopyrolysis process might also generate other gaseous heavy gaseous hydrocarbons.

Graphite produced using an apparatus according to embodiments of the present invention may have a high degree of graphite defects due to the fast photopyrolysis process from strong flash light irradiation (for example for 20 seconds) promoting a fast release of gases and generating a content of microporous carbon. In some embodiments it is possible to perform a complete conversion of the rubber granules into carbon particles and inorganic matter.

Compared to existing thermal pyrolysis systems using ovens to decompose tyres, tyre shreds or tyre rubber granules, the present system relies on a high-power flashlamp illumination system to deliver energy directly. In a classical oven, the tyres, tyre shreds or tyre rubber granules are heated either by heat conduction from the hot oven or from the surrounding gas. As it happens, rubber has a low thermal conductivity (less from O.SW.mAK-¹) being rather an insulator, and hence heating rubber on a hot plate by heat conduction is not an efficient process. Heating by the surrounding gas relies on collisions between rubber and the gas molecules. Indeed, according to the kinetic theory of gases, the temperature in a gas is linked to the energy of molecular collisions. When gas molecules impinge onto a solid material like rubber, the collision energy is given to the material which heats by accumulation of phonons, which are a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter. In the present system, the rubber is heated mainly by radiation where photons are absorbed not only to increase the vibrational energy but also but to disrupt covalent bonds, thereby generating radical reactions. The temperature obtained when irradiating a metal plate with a xenon flashlamp can reach temperature well above 1000°C in a very short time (for example, in less than 1 second). In the case of tyres, tyre shreds or tyre rubber, furthermore loaded with carbon black particles, the high-intensity white light from the xenon lamp is totally absorbed by the material and heat is provided mainly by radiation, rather than by conduction, in a very short time, such that the pyrolysis products are mainly hydrogen rich gases and solid carbonaceous particles with mineral residues. Only a small amount of TPOs is produced compared to thermal pyrolysis processes, as most liquids are vapourised and photo-pyrolysed by the light irradiation

The process described herein is designed to optimise the heat generated with the light illumination system of Figure 1, principally to pre-heat the tyre shreds or the tyre rubber particles in the inlet or elsewhere in the feeding system of Figure 1.

The process described herein is highly efficient at producing hydrogen from waste tyres, which is highly relevant in the context of a circular economy. Such processes feature a near complete absence of both carbon monoxide and carbon dioxide. The process allows more hydrogen production than the convention thermal pyrolysis that can either be sold or utilised to power the photo-pyrolysis system as a part of syngas, thereby enhancing the total calorific value of the syngas. Higher production of hydrogen aids creating an economically efficient process.

Reaching high temperatures in a very short time causes immediate molecule breaking leaving behind solid ash containing carbon black and conductive porous carbon particles. The recovered carbon black (CB) can be re-used in tyres (and plastics) as reinforcements as this is one of the major applications of CB. Other applications include being used as pigments and fillers in printing inks, paints as well as for conductive electrodes for battery applications.

Examples

Example 1. Rubber granules from Truck tyres

The elemental composition of truck tyres was determined by elemental analysis, and the results obtained are summarised in Table 1. They confirm that carbon and hydrogen are the major elements with 83.5wt%, while N, S and O correspond to ca 4.8wt%, the remaining 11.7wt% is attributed to the inorganic matter from fillers and metals. A laboratory photo-pyrolysis experiment was carried out from lOOmg of scrap truck tyre rubber granules (<lgm). Firstly, these tyre rubber granules were spread as a uniform film into a square bench top photo-pyrolysis reactor and then sealed with a quartz window of 3mm thickness and O-ring placed out of the flash light exposition area. Then, before the flash light irradiation, a moderate flow of inert gas (argon) was circulated for 2 minutes to remove the oxygen. Finally, the sample was exposed to multiple flashes of light from a xenon flashlamp pulsed with electric pulses having a voltage of 325V at a frequency of 45Hz, the pulse duration being 1.5ms over a period of 20s, producing gases such as H2, CH4 and C2H4 corresponding to 36% of the weight. A solid fraction of 44wt% corresponding to 32wt% of carbon black and 12wt% of fillers and metals. The remaining 20wt% stems from the TPO fraction obtained in this laboratory scale experiment, started at room temperature. A high temperature (ca 950°C) was reached in a very short time of less than 20 seconds.

Table 1 - Elemental composition of the rubber granules from truck tyres.

Element Mass %

C 76.4

H 7.1

N 0.4 s

o

Inorganic matter*

^'Calculated by difference.

Table 2 - Total solid content of the carbon synthesised by photo-pyrolysis from rubber granules of truck tyres after the flash light pyrolysis.

Weight before photo- Weight after photo- % Total solid (carbonised pyrolysis (mg) pyrolysis (mg) matter)

100 44 44

Example 2: Rubber granules from Car tyres

Firstly lOOmg of scrap car tyre particles (<lpm) were placed and spread as a uniform film into a photo-pyrolysis reactor and purged with argon as presented in example 1. Secondly the car tyre particles were exposed to a high-power flash light irradiation pulsed with electric pulses having a voltage of 325V at a frequency of 45Hz, the pulse duration being 1.5ms over a period of 20s. After this time ca 46wt% of solid matter was recovered, mainly carbon black, the remain content is ascribed to fillers and metals. Syngas was also recovered, where the main gases generated are hydrogen, ethylene and methane.

Example 3: Car tyre shreds

A scrap car tyre was firstly cut in small shreds, then some tyre shreds of a few cm² were selected and transferred to a sealed photo-pyrolysis reactor as presented in example 1. The car tyre shreds were photo-pyrolysed with electric pulses having a voltage of 325V at a frequency of 45Hz, the pulse duration being 1.5ms over a period of 60 seconds of flash light irradiation, after this time carbon and steel wire are separated mechanically and recovered. Therefore, the photo-pyrolysis process can also be applied to pyrolyse the scrap tyre shreds directly, without the grinding process, allowing for the recovery of the carbon, steel wire, TPO and gases in one single and fast step.

Embodiments of the present invention allow for efficient pyrolysis of rubber material to be achieved. When the pyrolysis is performed in an inert atmosphere, the risk of combustion of the products of the reaction is reduced and it is ensured that no poisonous gasses such as CO, CO2 or NOX are produces. The process allows for good quality combustible gasses, carbon, and tyre pyrolysis oil to be produced in an efficient manner, where heat generated during the process can be recirculated, for example for pre-heating the sample as it is being conveyed to the reaction chamber to undergo the pyrolysis. The combustible gasses and the oil have commercial value and so embodiments of the present invention are suited for a circular economy model for treating waste tyre products in an industrial processing line or continuous flow processing environment.

Claims

1. An apparatus (100) for thermochemical conversion of at least a part of a sample into a plurality of products, the apparatus (100) comprising: a thermal decomposition reaction chamber (110) having at least one chamber wall separating an interior of the reaction chamber from an exterior of the reaction chamber, the reaction chamber configured to receive said sample at least during said thermochemical conversion; a means for heating at least a part of said sample within the reaction chamber to a temperature which is sufficient to bring about said thermochemical conversion; and a purge system configured to produce an inert atmosphere at the interior of said reaction chamber (110) at least during said thermochemical conversion; characterised in that: said thermochemical conversion is a photo-pyrolysis reaction, said means for heating at least a part of said sample within the reaction chamber being a light source located at the exterior of the reaction chamber and configured to provide light through a light-transparent window in the chamber wall such that at least a part of the light arriving at the sample arrives with sufficient energy to bring about said thermal conversion of at least a part of the sample, the sample comprising rubber.

2. The apparatus according to claim 1, further comprising a sample conveyor system configured to convey the sample from a sample input (120) of the apparatus (100) to a reaction site at the interior of the reaction chamber (110) where said thermochemical conversion is to occur.

3. The apparatus according to either of claims 1 or 2, wherein said light source is configured to flash light having wavelengths of between 200nm and 350nm through said window in the chamber wall.

4. The apparatus (100) according to any of the preceding claims, said sample conveyor system being configured to convey the sample to the interior of the chamber (110) in granular or powder form.

5. The apparatus (100) according to any of claims 1 to 3, said sample conveyor system being configured to convey the sample to the interior of the chamber (110) in shredded form.

6. The apparatus (100) according to claim 5, wherein the shredded form of the sample comprises sample shreds having a size of up to 5cm².

7. The apparatus (100) according to any of the preceding claims, wherein the sample conveyor system comprises a conveyer belt (130) or a screw mechanism for engendering a translational movement of the sample towards the interior of the reaction chamber (110).

8. The apparatus (100) according to any of claims 1 to 3, wherein the sample is a tyre having a tread for rolling on a road and at least one bead for holding the tyre on a wheel, the wheel having a central axis around which it may rotate, the tyre having a central axis substantially coinciding with the axis of the wheel, the sample conveyor system being configured to grip the tyre in a way which allows the tyre to be rotated about its central axis, the sample conveyor system being further configured to convey the tyre to the interior of the chamber and to rotate the tyre with at least a part of its tread facing the part of the window in the chamber wall (140), said pyrolysis taking place over at least a part of said tread as it passes before the window.

9. The apparatus (100) according to any of the preceding claims, further comprising a temperature management system configured to recover heat from the light source (150).

10. The apparatus (100) according to claim 9, further configured to direct at least a part of said recovered heat towards the sample to pre-heat at least a part of the sample before it reaches the reaction chamber (130).

11. The apparatus (100) according to any of the preceding claims, wherein the light source (150) is a flash light system comprising a Xenon bulb or a Mercury-Xenon bulb, the flash light system being configured to flash the light towards the part of the window in the chamber wall (140).

12. The apparatus (100) according to claim 11, wherein the flash light system (150) further comprises one or more mirrors configured to concentrate the light at or around a predetermined zone at the interior of the reaction chamber (110).

13. The apparatus (100) according to any of the preceding claims, further comprising a gaseous product management system to separate and further process one or more gaseous products (160) of the thermochemical conversion.

14. The apparatus (100) according to any of the preceding claims, further comprising a solid product management system to separate and further process one or more solid products (170) of the thermochemical conversion.

15. The apparatus (100) according to any of claims 10 to 14, further configured to preheat (180) the sample to a temperature of at least 150 degrees Celsius.

16. A method for chemically processing at least part of a sample using an apparatus according to claim 1, the sample comprising a tyre, rubber shreds or rubber granules, the method comprising: loading the sample into the reaction chamber and presenting the sample at the window on the reaction chamber wall; operating the purge system to produce an inert atmosphere within the reaction chamber; operating the light source in a plurality of flashes thus irradiating at least a part of the sample though the window on the reaction chamber wall, thereby producing gaseous and solid reaction products.

17. The method according to claim 16, further comprising: operating the light source to provide a plurality of 1.5ms pulses of light, said pulses being provided at a frequency of 45Hz.

18. The method according to either of claims 16 or 17, wherein the light has a wavelength of between 200nm and 350nm.

19. The method according to any of claims 16 to 18, further comprising either or both of: extracting the gaseous products; extracting the solid products.

20. The method according to any of claims 16 to 19, further comprising: using heat generated by the light source to preheat at least a part of the sample.