Patent Application
20230331991
The present invention relates to a process for converting used tires by thermal decomposition.
Processes for converting used tires by thermal decomposition are generally directed toward producing gaseous, liquid and solid fractions. The tire is generally initially ground to obtain either ground tire material still containing a portion of the textile fibers or metal wires contained in the tire (typically pieces of 1 to 10 cm) or granules (generally less than 6 mm in size) free of textile fibers or metal wires. It is possible to react these feedstocks thus prepared by exposing them to heat to decompose the used tire and to recover a gaseous fraction, a liquid fraction and a solid fraction. To succeed in decomposing the tire, it is generally necessary to expose the tire to a quite high temperature, generally between 300° C. and 900° C. for reaction times ranging from 30 minutes to several hours.
Numerous technologies exist for performing these reactions. For example, the tires may be subjected to high temperatures in rotating furnaces (Lewandowski et al., Journal of Analytical and Applied Pyrolysis, 140, 2019, 25-53), or in moving beds (EP2661475). These technologies are robust, but generally require working at quite high temperatures, generally on average above 500° C. In these processes, the carbon black generally present in the feedstock in a proportion of 25-40% by weight and originally consisting of very fine sub-micrometric or micrometric particles/agglomerates, tends to agglomerate in the presence of the decomposed rubber which forms a coke binding these structures at various scales, the solid often leaving the reactor in the form of blocks of several millimeters/centimeters which then need to be finely ground in order to reuse this solid as carbon black, which requires substantial energy expenditure. In these processes, the temperature conditions are high and essentially gaseous and solid fractions are found in the reactor. The liquids produced then result from condensation of the gaseous products downstream of the reactor. These high temperature conditions moreover tend to promote polycondensation and coking reactions to form polyaromatic structures via cyclization reactions involving the aromatic and olefinic structures present (M.F. Laresgoiti, B.M. Caballero, I. de Marco, A. Torres, M.A. Cabrero, M.J. Chomón. J. Anal. Appl. Pyrolysis 71 (2004) 917-934) or coke. The higher the temperature, the greater the contents of polyaromatic structures formed and of coke formed. Now, while aromatic molecules are, firstly, good solvents and, secondly, find numerous applications, notably as petrochemical bases, polyaromatic structures are, on the other hand, prejudicial to the quality of the liquid formed and very difficult to refine or to convert. Furthermore, they are coke precursors. There is thus every interest in seeking to minimize polycondensation reactions in order to produce a minimum of polyaromatic structures while preserving the monoaromatic structures present.
To improve the quality of the solid phase and to limit the formation of coke on carbon black, it is possible to lower the partial pressure of hydrocarbons by injecting steam during the cracking reactions which nevertheless require a high temperature above 500° C. to perform the cracking under essentially gas-solid conditions (US 2016/0083657). These gas-solid processes generally lead to productions of noncondensable gases under the atmospheric conditions, these productions being very high and between 10% and 25% by weight relative to the tire feedstock entering the reactor. However, upgrading of reaction gases is locally complex. These gases are thus generally used to produce the heat required to perform the reactions, but this is done at the expense of the amount of readily upgradable liquid products, which is then limited. These liquid fractions are, specifically, subsequently optionally upgraded to produce new hydrocarbon cuts (naphtha, gasoline, kerosene, gas oil, vacuum distillate, residues) used in a refinery to produce fuels or in petrochemistry to produce bases subsequently used for the production of plastics. It is nevertheless necessary to refine these cuts in order to bring them to the desired specifications. The more numerous the polyaromatic structures, the more complex the refining.
An alternative route consists in placing the tire feedstocks in contact with a liquid, raising the temperature of this liquid and dissolving and converting the tires into a homogeneous liquid phase in which the tire feedstock is stirred and gradually disappears. An example of this implementation is given in US 3 978 199 and US 3 704 108. This type of process makes it possible to recover carbon black in the liquid phase after filtration without these particles having undergone agglomeration or deposition of coke at their surface, as is the case in the reactions operating in the gas-solid phase. Implementation under temperature conditions below 450° C. moreover limits the polycondensation reactions of the aromatics, the formation of coke at the surface of the carbon black particles and the formation of gases, which is generally between 1% and 7% by weight of the entering feedstock. The use of a solvent containing aromatic fractions, preferentially monoaromatic fractions, is favorable and enables better dissolution of the feedstock in the reactor. As tires are, naturally, composed of various rubbers including large amounts of synthetic rubber composed of styrene-butadiene rubbers (SBR), the liquid fractions produced contain large amounts of aromatics and it may be advantageous to separate and recycle a portion of the liquid formed during the reaction to use it as solvent, while the liquid fraction that is not recycled may be sent to a refinery to be refined and then upgraded as a hydrocarbon cut to feed the product pools or petrochemistry. By way of example, in document US 3,978,199, the heavy fraction of the filtrate obtained after distillation, comprising aromatic compounds, is heated and then recycled to the reactor as liquid solvent. However, depending on the composition of the heavy fraction used to dissolve the solid feedstock, and also the recycle ratio of the heavy fraction relative to the solid feedstock, the filtration time of the carbon black can vary considerably. The applicant has developed a new process for converting used tires that makes it possible to prevent the abovementioned drawbacks by optimizing the existing process as described in document US 3,978,199.
One subject of the present invention is a process for converting used tyres to obtain carbon black, comprising at least the following steps:
The applicant has surprisingly discovered that the use of such a recycled hydrocarbon cut as a liquid solvent in the used tire conversion zone, comprising a content rich in aromatic compounds, low in C40+ compounds (vacuum residues), and a content of C5-C10 hydrocarbon compounds (gasoline) that is not too high, with a specific solvent/solid feedstock weight ratio, synergistically allows better dissolution and decomposition of the solid feedstock thus maximizing the production of carbon black.
In one embodiment according to the invention, before step a) of said process, said solid feedstock is sent to a pretreatment unit to at least partly remove the textile fibers and metal wires contained in said solid feedstock.
In one embodiment according to the invention, step a) comprises the following substeps:
In one embodiment according to the invention, the content of aromatic compounds in the hydrocarbon cut is greater than 40% by weight relative to the total weight of said cut.
In one embodiment according to the invention, the content of C5-C10 hydrocarbon compounds in the hydrocarbon cut is less than 10% by weight relative to the total weight of said cut.
In one embodiment according to the invention, the content of C40+ hydrocarbon compounds in the hydrocarbon cut is less than 3% by weight relative to the total weight of said cut.
In one embodiment according to the invention, the weight ratio between said liquid solvent and the solid feedstock is greater than 3 weight/weight.
In one embodiment according to the invention, the viscosity of the second liquid effluent at 100° C. is less than 10 cP as measured according to the standard ASTM D3236.
In one embodiment according to the invention, in step c) of said process, a light cut is also obtained, the final boiling point of which is preferentially between 250° C. and 325° C.
In one embodiment according to the invention, the light cut is sent at least in part upstream to a distillation column to obtain at least one light cut, the final boiling point of which is below or equal to 200° C.
In one embodiment according to the invention, said light cut, the final boiling point of which is below or equal to 200° C., is sent at least in part to the filtration/washing zone as washing solvent according to step b) of said process.
In one embodiment according to the invention, step b) comprises the following substeps:
Preferably, the washing stream is sent to an intermediate fractionation unit to obtain a cut which is recycled at least in part upstream of the washing and filtration device as washing solvent.
Advantageously, the hydrocarbon cut has a content of C10-C20 hydrocarbon compounds of between 20% and 65% by weight relative to the total weight of the hydrocarbon cut. Advantageously, the hydrocarbon cut has a content of C20-C40 hydrocarbon compounds of between 30% and 80% by weight relative to the total weight of the hydrocarbon cut.
Advantageously, the hydrocarbon cut has an initial boiling point of between 50° C. and 325° C. and a final boiling point of between 350° C. and 520° C.
Cn hydrocarbon cut is understood to mean a cut comprising hydrocarbons having n carbon atoms.
Cn+ cut is understood to mean a cut comprising hydrocarbons having at least n carbon atoms.
With reference to
The solid feedstock 100 used in the context of the present invention is advantageously based on tires resulting from the processing of used tires which may originate from any source, for instance light vehicles (LV) or heavy goods vehicles (HGV). Said solid feedstock may advantageously be in the form of tyre granules, i.e. in the form of particles less than 6 mm in size. Preferably, said solid feedstock 100 is substantially free of textile fibers and metal wires, and/or of ground tyre materials, i.e. pieces of ground tyres, with a characteristic size generally between 1 cm and 20 cm. Thus, according to a preferred embodiment according to the invention, the solid feedstock 100 is sent to a pretreatment unit 10 in order to remove textile fibers and metal wires 110 from the solid feedstock 100. Such a pretreatment unit is well known to those skilled in the art and can consist of grinders of various types (i.e. a rotary shear, a shredder, a granulator, a rechipper), a magnetic separator, or else a vibrating screen, a separation table.
According to step a) of the conversion process, the rubber which is contained in the solid feedstock 100 is dissolved in contact with the liquid solvent 760 and then is thermally decomposed. The origin and composition of the liquid solvent 760 will be described in detail below. Step a) is preferably carried out at a temperature below or equal to 425° C., preferably at a temperature of between 375° C. and 425° C., and at a pressure of less than 1.5 Mpa, preferably between 0.8 MPa and 1.2 MPa. At the end of step a), the at least one gaseous effluent 310 is obtained and the first liquid effluent 320 comprising carbon black, and optionally solids 210 contained in the used tires, such as metal wires or textile fibers, which are released and separated from the liquid effluent 320 obtained at the end of this step.
The first liquid effluent 320 comprising the carbon black is then sent to the filtration and washing zone 40 (i.e. step b) of the preparation process according to the invention) in order to recover the filtered and washed carbon black cake 430 and the second liquid effluent 410. In one embodiment according to the invention, the viscosity of the second liquid effluent 410 measured at 100° C. is less than 10 cP, preferentially less than 5 cP, more preferentially less than 3 cP, as measured according to the standard ASTM D3236.
The filtration and washing unit can comprise any device allowing the filtration of the carbon black particles contained in the first liquid effluent 320. Such a device may for example be in the form of a rotary filter operating preferentially at a temperature between 50° C. and 200° C. During step b), the carbon black cake is washed using a washing solvent.
In one embodiment according to the invention, the washing solvent used during step b) is a solvent external to the process 800, as shown in
In another embodiment according to the invention, the washing solvent used during step b) is composed, at least partly, of a light cut 720 obtained at the end of step c). More particularly, with reference to
The filtered and washed carbon black cake 430 is sent to a drying unit 50 operating at a temperature of between 50° C. and 200° C., preferably between 50° C. and 150° C. in order to recover the carbon black 520 (i.e. step e) of the process according to the invention). Advantageously, the vapor effluent 510 from the drying unit 50 comprising the washing solvent is recycled to the washing/filtration unit 40.
According to an essential feature of the conversion process according to the invention, the gaseous effluent 310 obtained at the end of step a) and the second liquid effluent 410 obtained at the end of step b) are sent to the fractionation unit 70 (i.e. step c) of the process according to the invention) to produce at least one hydrocarbon cut 730 comprising a content of aromatic compounds of greater than 30% by weight relative to the total weight of said hydrocarbon fraction 730, and further comprising at least:
Advantageously, the hydrocarbon cut 730 also has a content of C10-C20 hydrocarbon compounds of between 20% and 65% by weight relative to the total weight of the hydrocarbon cut, preferably between 30% and 65% by weight, and even more preferentially between 45% and 65% by weight.
Advantageously, the hydrocarbon cut 730 also has a content of C20-C40 hydrocarbon compounds of between 30% and 80% by weight relative to the total weight of the hydrocarbon cut, preferably between 30% and 70% by weight, and even more preferentially between 30% and 55% by weight.
Advantageously, the hydrocarbon cut 730 has an initial boiling point of between 50° C. and 325° C., preferably between 50° C. and 250° C., and a final boiling point of between 350° C. and 520° C., preferably between 350° C. and 450° C.
Specifically, the applicant has observed that the use of such a recycled hydrocarbon cut as a liquid solvent 760 of the reaction zone 80 (i.e. step d) of the process according to the invention), with a content rich in aromatic compounds, low in C40+ compounds (vacuum residues), and a content of C5-C10 hydrocarbon compounds (gasoline) that is not too high, and using a solvent/solid feedstock weight ratio of greater than 3 weight/weight, preferably between 3 and 10 weight/weight, more preferentially between 4 and 7 weight/weight, synergistically allows better dissolution and decomposition of the solid feedstock 100 thus maximizing the production of carbon black. This results notably in a shorter filtration time of the carbon black in the washing/filtration zone 40.
Advantageously, the fractionation zone 70 also makes it possible to obtain noncondensable gases 710, light cut 720, the final boiling point of which is preferentially between 250° C. and 325° C., and a heavy cut 740, the initial boiling point of which is preferentially between 350° C. and 450° C. Advantageously, the light cut 720 can be sent, at least in part, as washing solvent to the washing and filtration zone 40 to obtain the filtered and washed carbon black cake 430. Advantageously, the light cut 720 has a content of C10- hydrocarbon compounds of greater than 60% by weight relative to the total weight of the light cut 720.
Advantageously, the heavy cut 740 has a content of C40+ hydrocarbon compounds of greater than 60% by weight relative to the total weight of the heavy cut 740.
According to the invention, a fraction of the hydrocarbon cut 730 is sent, at least in part, to the reaction zone 80 of step a) as liquid solvent 760, the other part 750 being advantageously sent out of the process according to the invention as an upgradable product. The weight ratio between the liquid solvent 760 and the flow of the solid feedstock 100 injected into the reaction zone 80 is greater than 3 weight/weight (w/w), preferably between 3 and 10 weight/weight, more preferentially between 4 and 7 weight/weight. Specifically, one of the features of the liquid solvent 760 is that it contains a content of aromatics of greater than 30% by weight relative to the total weight of said liquid solvent 760, making it possible to effectively dissolve the solid feedstock 100 and to effectively reduce the viscosity of the reaction medium in the reaction zone 80. Another advantage of the process according to the invention is that the use of such a solvent makes it possible to remain in liquid form while limiting the pressure in the reactors to a level below 1.5 MPa given the limited production of gas and light hydrocarbons in the reaction zone 80 and the low content of C10- hydrocarbon compounds in the hydrocarbon cut 730.
In order to better understand the invention, the description given below as an application example relates to a process for converting used tyres which makes it possible to maximize the the recovery of carbon black. With reference to
At the end of the reaction in the second stirred reactor 30, the first liquid effluent 320 containing the carbon black particles in suspension and the gaseous effluent 310 are obtained. The first liquid effluent 320 is then sent to the filtration and washing zone 40, comprising a rotary filter 41 and an intermediate fractionation unit 42 (cf.
The gaseous effluent 310 leaving the reaction zone 80 via the second reactor 30, and the second liquid effluent 410 from the washing/filtration zone 40 are then sent to the fractionation zone 70. The fractionation zone 70 may consist of heat exchangers, gas-liquid separator drums, a distillation column containing a top take-off, a bottom take-off and a side take-off, or a sequence of several distillation columns, such as a sequence of a distillation column at atmospheric pressure operating with a top take-off and a bottom take-off, followed by a distillation column operating under a low vacuum. This fractionation zone 70 makes it possible in particular to produce the hydrocarbon cut 730 comprising a content of aromatic compounds of greater than 30% by weight relative to the total weight of said hydrocarbon cut 730, preferentially greater than 40% by weight, and further having:
This fractionation zone 70 also makes it possible to obtain noncondensable gases 710, the light cut 720, the final boiling point of which is preferentially between 250° C. and 325° C., and the heavy cut 740, the initial boiling point of which is preferentially between 350° C. and 450° C. Advantageously, the light cut 720 can be sent, at least in part, as washing solvent to the washing and filtration device 41 of the washing and filtration zone 40 to obtain the filtered and washed carbon black cake 430.
During the start-up of the facility, in the absence of production of a stabilized intermediate cut, i.e. the hydrocarbon cut 730, it is possible temporarily to use an imported solvent which will preferentially be constituted of a content of aromatic molecules of greater than 40% by weight relative to the total weight of the cut. This cut may thus be constituted, for example, of conversion effluents from the process of fluid catalytic cracking (FCC) of middle distillate (light cycle oil (LCO)) or of heavy distillate (heavy cycle oil (HCO)), for example.
The examples that follow illustrate preferential embodiments of the process according to the present invention without, however, limiting the scope thereof. The process used for illustrating the invention is in accordance with that described in
In a first example, in accordance with the invention, use is made of used tire granules (solid feedstock), produced by granulators using grinders, which originate from heavy goods vehicle tires and the grains resulting from the grinding have a size close to 2 millimeters. The tire granules result from a pretreatment unit 10 and are free of textile and metal fibers. The granules are then sent continuously to a dissolution reactor where they are mixed with the liquid solvent resulting from the recycling of the hydrocarbon cut 730 from the fractionation zone 70. A portion of the hydrocarbon cut 730 is used as liquid solvent 760, the composition of which is shown in table 1 below. The amount of solid feedstock treated is 100 kg/h. The amount of solvent that is recycled to the reactor 20 is 500 kg/h, corresponding to a solvent/granule weight ratio equal to 5 w/w. In the reactor 20, the temperature is maintained equal to 290° C., which makes it possible to dissolve the granules. The liquid fractions and the carbon black in suspension are then sent to the reactor 30 where the temperature is maintained equal to 400° C. for one hour. At the outlet of the reactor 30, a first liquid effluent 320 and a gaseous effluent 310 are recovered, the latter being sent entirely to the fractionation zone 70. The first liquid effluent 320 is sent to a rotary filter 41 operating at 140° C. The filtered carbon black is washed with toluene. The second liquid effluent 410 collected at the outlet of the washing and filtration zone 40 is sent in its entirety to the fractionation zone 70. The filtered and washed carbon black 430 is sent to a drying unit 50 operating at 150° C. for 24 hours to recover the filtered, washed and dried carbon black 520.
In examples 2 to 5, not in accordance with the invention, the steps of the conversion process and the operating conditions are identical to those of example 1, except for the following features:
By comparing the results in terms of carbon black filtration time relative to example 1 according to the invention, it is found that when the content of C40+ hydrocarbon compounds (vacuum residue) is 8% by weight in the hydrocarbon cut 730 relative to the total weight of said cut (example 2), the carbon black filtration time is 4 times longer, or even 8 times longer when the content of C40+ hydrocarbon compounds is 20% by weight (example 3). Furthermore, when the content of C5-C10 hydrocarbon compounds (gasoline) is 26% by weight in the hydrocarbon cut 730, the carbon black filtration time is 4 times longer (example 4). Finally, a liquid solvent 760 / solid feedstock 100 weight ratio that is not optimized significantly lengthens the carbon black filtration time (example 5).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009912 | Sep 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/075670 | 9/17/2021 | WO |
