Method and apparatus for the continuous recovery of carbon fibers from a hydrogen tank.

Abstract

Method and apparatus for the continuous recovery of carbon fibers from a hydrogen tank. Method for recovering carbon fibers from a used tank for the storage of hydrogen under pressure, said tank comprising an inner and an outer shell formed of a resin composite reinforced by carbon fibers, which are in the form of a strand arranged in a filamentary winding.The process comprises the following steps: placing the used tank from which the carbon fibers are to be recovered in a basic alcoholyse bath in an open reactor (1); conducting the hot basic alcoholyse, causing the depolymerization fragments of the resin to pass into the solvolysis bath and, during this process, providing free access to one end of the strand (8); pulling on said end of the strand (8) to unwind it, which is then brought out at the top of the open reactor (1); cleaning the unwound strand (8); drying the cleaned strand (8); and rewinding the dried strand (8). Figure to be published: Figure 1.

Description

Title of the invention: Method and apparatus for the continuous recovery of carbon fibers from a hydrogen reservoir.

[0001] The present invention relates to a method and apparatus for the continuous recovery of carbon fibers from a hydrogen reservoir.

[0002] With the gradual depletion of fossil fuel sources and an ever-increasing concern to reduce the CO2 impact of our societies, new solutions for the mobility of goods and people are rapidly coming onto the market.

[0003] In addition to electric vehicles, hydrogen vehicles are gradually gaining ground, particularly in the heavy goods transport sector and public transportation. For this technology, the ability to store a large quantity of hydrogen is key to ensuring maximum range. However, hydrogen is a gas that is difficult to liquefy, so most of the storage solutions currently available rely on storage in the form of pressurized gas.

[0004] Among the different types of tanks considered for the storage of hydrogen under pressure, composite tanks, known as type III and IV tanks, particularly type IV, combining carbon fiber and a resin in their external structuring shell - most often an epoxy type resin - are today the only ones to offer the technical performance necessary for large-scale deployment in the field of transport and automotive in particular.

[0005] Thus, with a requirement of approximately 1 kg of carbon fiber per liter of stored hydrogen, the rapid development of hydrogen mobility will contribute to a very sharp increase in the demand for carbon fiber. Furthermore, the 2000 European Directive on end-of-life vehicles requires manufacturers to guarantee that their vehicles are 85% recyclable by mass. This dual constraint—having access to sufficient carbon fiber to meet both the demand from the hydrogen mobility market and more traditional markets, as well as guaranteeing the recyclability of tanks used in vehicle fleets—contributes to strengthening the need for hydrogen tank recycling technologies, particularly those enabling the recovery of high-performance continuous carbon fiber.

[0006] Various recycling technologies have already been tested for the recycling of hydrogen tanks: • a high temperature and high pressure steam approach on a type III tank, which made it possible to produce a new tank with recycled fiber; • an acid solvolysis approach on type IV reservoirs, showing that it It was possible to recover several hundred meters of high-quality fibers; and • an acid solvolysis which made it possible to recover pieces of fibers in order to produce bidirectional composites.

[0007] These approaches are very promising, but all involve reactions at relatively high pressure and are therefore operated in a closed reactor. This necessitates separating the solvolysis operation of the reservoirs from the fiber unwinding operation. This decoupling considerably limits the operation as a whole, but above all creates the risk of fiber entanglement during solvolysis, thus preventing the recovery of a continuous fiber.

[0008] In order to be able to operate solvolysis and unwinding continuously, the Applicant Company has developed an innovative solution based on an alkaline alcoholyse, namely the attack of composite materials by the mixture of an alcohol and a base, having the advantage of allowing work in an open reactor and thus being able to unwind the carbon fiber into strands for recovery and reuse.

[0009] This solution provided by the invention is particularly advantageously applicable to type IV hydrogen tanks. Indeed, these tanks, which have an inner polymer casing, have not yet found a way to be recycled industrially because the classic pyrolysis process - applicable to type III reactors which have an inner metal casing - cannot be applied to type IV reactors because the polymer of the inner casing would collapse during pyrolysis and the fiber would become tangled, making its recovery difficult, or even impossible.

[0010] The present invention allows in all cases an industrial recovery of the entire fiber strand of the reactor without risk of tangling.

[0011] To this end, the present invention relates to a method for recovering carbon fibers from a used tank for the storage of hydrogen under pressure, in particular from a type IV tank, said tank comprising an inner shell intended to receive gaseous hydrogen in a sealed manner and an outer shell or structural casing formed of a resin composite reinforced by carbon fibers, which are in the form of a strand arranged in the resin in a filamentary winding,

[0012] characterized by the fact that it comprises the following steps: • placement of the used tank from which carbon fibers are to be recovered in a basic alcoholyse bath in an open reactor; • conducting the basic hot alcoholyse, bringing the depolymerization fragments of the resin into the solvolysis bath and giving free access to one end of the strand during this process; • pulling on said end of the strand to unwind it, which is brought out in the upper part of the open reactor; • cleaning of the unwound strand; • drying of the cleaned strand; and • rewinding the dried strand.

[0013] The alcoholysis can be carried out at a temperature of 150 to 220°C and a basic alcoholysis bath can be used, composed of at least one alcohol chosen from those having a boiling point higher than the temperature at which the alcoholysis is carried out, such as ethylene glycol and polyethylene glycols, and at least one base chosen from alkali and alkaline earth hydroxides such as NaOH, KOH and Ca(OH)2, the base(s) being present in the bath at a rate of 1 to 5% by mass.

[0014] Alcoholysis can be carried out for a period of 1 to 8 hours.

[0015] The reaction gases that are formed can be advantageously recovered.

[0016] The unwound strand can be cleaned in a water bath.

[0017] The cleaned strand can be dried at a temperature of 50 to 150°C.

[0018] One can carry out sizing of the cleaned and dried strand by passing it through a sizing bath then drying it again before rewinding.

[0019] The process can be carried out continuously, the end of the strand being able to be pulled as soon as access is available to the end of the strand, the alcoholysis reaction continuing in parallel.

[0020] The invention also relates to apparatus for implementing the process according to the invention, characterized in that it comprises: • an open basic alcoholyse reactor, suitable for heating; • a device for pulling, guiding and rewinding the fiber strand released from the resin; • a washing water bath for the strand; • if necessary, a sizing bath of the washed strand; • a device for drying the washed strand and, where applicable, a device for drying the strand coming out of the sizing bath.

[0021] The reactor may include a jacket heated by a fluid such as water vapor, mineral oil, silicone oil.

[0022] The reactor can be equipped with a reaction gas collection system.

[0023] The following examples illustrate the present invention without however limiting its scope.

[0024] The apparatus used for the realization of Examples 2 and 3 is described here schematically with reference to [Fig.1].

[0025] This apparatus comprises an open reactor 1 for basic alcoholysis, the wall of which forms a heating jacket 2 in which a heating fluid 3 can circulate, entering the jacket via a tube 4 and exiting it via a tube 5. The reactor 1 is capped by a reaction gas collection system 6, which can escape at the top through tube 7.

[0026] In reactor 1, a coil 8, simulating a type IV hydrogen reservoir, obtained as shown in Example 3, has been placed. From this coil 8, after the start of solvolysis, the fiber strand 9 can be pulled from its end which becomes accessible due to the decomposition of the resin.

[0027] The strand 9, thus drawn to the upper part of the reactor 1, is brought to pass into a water bath 10, then at the exit of the water bath 10, to pass under a drying device 11, before being wound onto a winder 12. As can be seen in [Fig. 1], the strand 8, in this whole process, advantageously carried out continuously, is guided on different guide rollers 13.

[0028] If desired, the washed and dried fiber strand 9 can be passed through a sizing bath 14, then dried again using a drying device 11' before being rewound onto the winder 12. The apparatus for this embodiment has been shown in [Fig.2], which differs from [Fig.1] by the presence of the sizing bath 14 and the drying device 11', of the same type as the drying device 11, the fiber strand 9 passing over additional guide rollers 13 located above and in the sizing bath 14.

[0029] Example 1: Alkaline alcoholysis of a piece of type IV hydrogen reservoir

[0030] 1.95 g of type IV hydrogen reservoir consisting of 70% by mass of carbon fibers and 30% by mass of epoxy resin was brought into contact with 41 mL of ethylene glycol and 0.87 g of NaOH at 180°C for 1h45.

[0031] At the end of the reaction, the fibers were recovered by filtration and washed with water.

[0032] After drying, thermogravimetric analysis of the fibers showed that they contain less than 1% by mass of residual resin.

[0033] Furthermore, the mechanical analysis of the fibers obtained showed that they retained more than 95% of their mechanical properties: Young's modulus and tensile strength.

[0034] Example 2: Alkaline alcoholysis on a coil simulating a type IV hydrogen tank

[0035] In order to simulate a type IV hydrogen tank, a coil 8 was manufactured by winding 400 meters of carbon fibers pre-impregnated with an epoxy resin precursor onto a polytetrafluoroethylene (PTFE) mandrel, then heating the coil 8 thus obtained to 120°C for 2h to crosslink the epoxy resin.

[0036] After crosslinking, coil 8 weighed 14.0 kg, of which 1.4 kg was epoxy-fiber composite.

[0037] The coil 8 was placed in reactor 1 with 7 kg of ethylene glycol and 120 g of soda. The reactor was heated to 180°C for 5 hours.

[0038] At the end of the reaction, the entire fiber strand was unwound and washed.

[0039] Example 3: Alkaline alcohol on a type IV hydrogen tank

[0040] In the basic alcoholysis reactor 1 of the apparatus in [Fig. 1], a used type IV hydrogen tank with an internal volume of 4 L and a mass of 3.6 kg, of which 2.4 kg was composed of epoxy resin-carbon fiber composite, was placed in place of coil 8 of Example 2, and 12 kg of ethylene glycol and 300 g of sodium hydroxide were introduced. The mixture was heated to 170°C.

[0041] After 1h of reaction, we started to unwind the fiber strand, which we washed with water before drying it and rewinding it onto the reel 12. After 5h of reaction, the entire strand was recovered.

Claims

Claims

1. - Method for recovering carbon fibers from a used tank for storing hydrogen under pressure, in particular a type IV tank, said tank comprising an internal envelope intended to receive the hydrogen gas in a sealed manner and an external envelope or structuring shell formed from a resin composite reinforced by the carbon fibers, which are in the form of a strand arranged in the resin in a filamentary winding, characterized in that it comprises the following steps: • placing the used tank from which the carbon fibers are to be recovered in a basic alcoholysis bath in an open reactor; • carrying out the hot basic alcoholysis, causing the passage of the depolymerization fragments of the resin into the solvolysis bath and giving during the latter free access to one end of the strand;• traction on said end of the strand to unwind it, which is brought out at the top of the open reactor; • cleaning of the unwound strand; • drying of the cleaned strand; and • rewinding of the dried strand.;

2. - Process according to claim 1, characterized in that the alcoholysis is carried out at a temperature of 150 to 220°C, and in that a basic alcoholysis bath is used, composed of at least one alcohol chosen from those having a boiling point higher than the temperature at which the alcoholysis is carried out, such as ethylene glycol and polyethylene glycols, and at least one base chosen from alkali and alkaline-earth hydroxides such as NaOH, KOH and Ca(OH)2, the base(s) being present in the bath at a rate of 1 to 5% by mass.

3. - Method according to one of claims 1 and 2, characterized in that the basic alcoholysis is carried out for a period of 1 to 8 hours.

4. - Method according to one of claims 1 to 3, characterized in that the reaction gases which are formed are recovered.

5. - Method according to one of claims 1 to 4, characterized in that the unwound strand is cleaned in a water bath.

6. - Method according to one of claims 1 to 5, characterized in that the cleaned strand is dried at a temperature of 50 to 150°C.

7. - Method according to one of claims 1 to 6, characterized in that the cleaned and dried strand is sizing by passing it through a sizing bath, then drying it again before rewinding it.

8. - Method according to one of claims 1 to 7, characterized in that the method is carried out continuously, the end of the strand being able to be pulled as soon as access to the end of the strand is gained, the alcoholysis reaction continuing in parallel.

9. - Apparatus for implementing the method according to one of claims 1 to 8, characterized in that it comprises: • an open basic alcoholysis reactor (1), capable of being heated; • a device for pulling, guiding and rewinding the fiber strand (8) freed from the resin; • a water bath (10) for washing the strand (9); • where appropriate, a bath (14) for sizing the washed strand (9); • a device (11) for drying the washed strand (9) and, where appropriate, a device (11') for drying the strand leaving the sizing bath (14).

10. - Apparatus according to claim 9, characterized in that the reactor (1) comprises a casing (2) heated by a fluid such as water vapor, a mineral oil, a silicone oil.

11. - Apparatus according to one of claims 9 and 10, characterized in that the reactor (1) is equipped with a system (6-7) for collecting reaction gases.

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