SOLID CONSUMABLE REACTION METHOD AND DEVICE FOR IMPLEMENTING SUCH A METHOD

Abstract

The invention relates to a consumable solid reaction process comprising: - feeding a vessel (10) of a reactor (1) with solid particles and at least one liquid suitable for reacting with the particles so as to reduce the size of said particles as the reaction progresses, and stirring said particles suspended in the liquid, and - the continuous discharge of a liquid stream, characterized in that the liquid discharge is achieved by overflow through an outlet orifice (22) arranged in the upper part (21) of an elutriator (2), said elutriator comprising a lower part (20) assembled on the vessel of the reactor (1) and a frustoconical part (23) extending between the lower part (20) and the upper part (21), the upper part having a diameter (Ds) greater than the diameter (De) of the lower part. Figure for the abstract: Fig 1

Description

Title of the invention: CONSUMABLE SOLID REACTION METHOD AND DEVICE FOR IMPLEMENTING SUCH A METHOD technical field

[0001] The invention relates to a continuous consumable solid reaction process, as well as a device for implementing such a process. STATE OF THE ART

[0002] In a consumable solid reaction, solid particles are reacted with a liquid suitable for reacting with the particles in a reactor and the liquid containing the reaction products is continuously withdrawn in solubilized or solid form for further processing.

[0003] As the reaction progresses, the size of the consumable solid particles decreases.

[0004] Below a certain size, solid particles are therefore likely to be carried along by the liquid flow exiting the reactor.

[0005] It is desirable to separate the residence times of the solid and the liquid and to control the size of the consumable solid particles exiting the reactor, in order to prevent excessively large particles from being evacuated from the reactor and to allow the particles introduced into the reactor to be sufficiently consumed before their evacuation. Summary of the invention

[0006] An object of the invention is to develop a continuous consumable solid reaction process in which the management of solid particles is optimized.

[0007] To this end, the invention proposes a consumable solid reaction process comprising:

[0008] - feeding a reactor vessel with solid particles and at least a liquid suitable for reacting with the particles so as to reduce the size of said particles as the reaction progresses, and the agitation of said particles suspended in the liquid, and

[0009] - the continuous evacuation of a liquid flow,

[0010] characterized in that the liquid is evacuated by overflow through an outlet orifice arranged in the upper part of an elutriator, said elutriator comprising a lower part assembled on the reactor vessel and a frustoconical part extending between the lower and upper parts, the upper part having a diameter greater than the diameter of the lower part,

[0011] the diameter of the upper part being chosen according to a maximum size of the solid particles exiting the elutriator,

[0012] the diameter of the lower part being at most equal to the diameter of the reactor vessel and imposing a maximum size of the solid particles entering the elutriator,

[0013] the sedimentation rate of the particles allowing the classification of the particles present in the truncated conical part having a size between the maximum size (Ls) at the outlet and the maximum size at the inlet and the entrainment of the particles having a size less than said maximum size with the flow of liquid evacuated by the outlet orifice.

[0014] Thus, in said process, the liquid carries a first fraction of solid particles out of the reactor and a second controlled fraction, less than the first fraction, out of the elutriator.

[0015] In some embodiments, the reactor is continuously fed with solid particles.

[0016] In other embodiments, the process includes a discontinuous feeding of solid particles into the reactor.

[0017] In a particularly advantageous way, the reaction is carried out at atmospheric pressure.

[0018] Preferably, a height of the frustoconical part of the elutriator is chosen sufficiently large to minimize an accumulation of suspended solid particles and a deposition of solid particles in the lower part.

[0019] A first application of the process described above is a process for depolymerizing polyethylene terephthalate (PET) by methanolysis, in which the consumable solid particles comprise polyethylene terephthalate (PET) and the liquid comprises a catalyst, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH), a reactive solvent, such as methanol (MeOH).

[0020] Another application of said process is a liquid-phase heterogeneous catalytic reaction process, in which the solid particles comprise a catalyst and the liquid comprises at least one reactant.

[0021] Another object relates to a consumable solid reaction device enabling the implementation of the process described above.

[0022] Said device comprises:

[0023] - a reactor adapted to receive solid particles, comprising at least one liquid inlet port,

[0024] - a mixer arranged in the reactor to agitate the solid particles in suspension in the liquid, and

[0025] - an elutriator comprising a lower part assembled on the reactor, a upper part comprising a liquid outlet orifice and a truncated conical part extending between the lower and upper parts, the upper part having a diameter greater than the diameter of the lower part.

[0026] In a particularly advantageous way, the elutriator is mounted removably on the reactor. PRESENTATION OF THE FIGURES

[0027] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying drawings, in which:

[0028] - the [Fig.1] is a schematic diagram of the elutriator reactor according to the invention;

[0029] - [Fig. 2] is a diagram of an installation including such an elutriator reactor for the implementation of a polyethylene terephthalate (PET) depolymerization process by methanolysis. DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0030] The reaction between the solid particles and the liquid is implemented in a reactor.

[0031] In some applications, the liquid comprises at least one reactive solvent suitable for reacting with the consumable solid particles and solubilizing the product. In other applications, the solid particles react with a soluble catalyst and a liquid reagent to which a co-solvent may be added to improve the solubility of the product.

[0032] As the reaction progresses, the size of the consumable solid particles decreases. It is desirable that the consumable solid particles remain in the reactor until they reach a certain size and are not prematurely discharged with the liquid. However, any solid particles produced must be carried away by the liquid.

[0033] For this purpose, an elutriator, from which the liquid flow continuously exits by overflow, is arranged on the reactor.

[0034] Fig. 1 is a schematic diagram of an elutriator reactor according to an embodiment of the invention.

[0035] The reactor 1 is in the form of a tank 10. Preferably, the tank has a generally cylindrical shape with a circular base. Such a geometry of revolution makes it possible to optimize the movement of the liquid within the reactor and to avoid dead zones in which particles would accumulate.

[0036] The reactor advantageously comprises a mixer including a shaft 11 carrying blades 12 arranged in the center of the vessel, movable in rotation about an axis main tank. Tank 10 is advantageously equipped with counter-blades 16 designed to eliminate vortices caused by the mixer.

[0037] The reactor can be maintained at a suitable temperature for the reaction, for example by means of circulating a heat transfer fluid along at least part of the reactor wall. For this purpose, the vessel is at least partially surrounded by a jacket 13 in which the heat transfer fluid circulates between an inlet 131 and an outlet 132, which are connected to a fluid reservoir (not shown) equipped with a means for heating and / or cooling the heat transfer fluid.

[0038] The reactor includes at least one liquid inlet orifice 14, through which the liquid continuously feeds the reactor. The liquid is brought to the orifice 14 by a circuit (not shown in detail) comprising a pump 140. Said circuit may include heating means for raising the liquid to a suitable temperature for the reaction.

[0039] Solid particles can be introduced into the reactor continuously or discontinuously.

[0040] In the case of discontinuous feeding of solid particles, the reactor may include an inlet port separate from the liquid inlet port, for example provided with a trap.

[0041] In the case of a continuous supply of solid particles, said particles can be introduced into the liquid outside the reactor and carried by the liquid so as to enter the reactor through the liquid inlet orifice.

[0042] For example, in the embodiment illustrated in [Fig.1], the solid particles P can be continuously loaded via a screw hopper 141 into the liquid circuit, and carried along with it by means of the pump 140.

[0043] The reactor may optionally include one or more additional liquid inlet ports 15, to introduce one or more other liquids useful to the reaction.

[0044] The inlet flow rates of solid and liquid(s) can be set independently.

[0045] The solids content in the reactor is adjustable and chosen according to requirements. The higher the solids content, the faster the mass flow rate of solids consumption by the reaction.

[0046] The elutriator 2 comprises a lower part 20 assembled on the upper part of the tank 10, and an upper part 21 comprising a liquid outlet 22.

[0047] The lower part 20 of the elutriator has an internal diameter equal to or less than that of the upper part of the reactor vessel.

[0048] In contrast, the upper part 21 of the elutriator has a larger internal diameter than the lower part. To this end, the upper and lower parts of the elutriator are connected by a frustoconical portion 23.

[0049] The elutriator advantageously comprises a central tube 24 adapted for the passage of the shaft of the mixer 11. The remainder of the volume of the elutriator, between said central tube and the side wall of the elutriator, is open to the reactor.

[0050] The circulation of liquid between the reactor inlet 14 and the elutriator outlet 22 results in the formation of a liquid column in the elutriator. This liquid column contains liquid, which includes solubilized solid, and solid particles that are carried along by the liquid.

[0051] The elutriator is designed to avoid the entrainment of consumable solid particles whose size exceeds a predetermined threshold while allowing the exit of the solid particles produced up to a maximum size not to be exceeded.

[0052] The elutriator is therefore designed so that the liquid carries a first fraction of solid particles out of the reactor and a second controlled fraction, smaller than the first fraction, out of the elutriator. These first and second fractions depend on the particle size.

[0053] Let Le be the maximum size of the solid particles entering the elutriator through its lower part 20, and Ls the maximum size of the solid particles exiting the elutriator through the outlet 22 located in its upper part 21. The values ​​of Le and Ls are specific to each of the solids (consumable and product).

[0054] In the elutriator, the solid particles are subjected on the one hand to their apparent weight (which tends to pull them back towards the reactor) and on the other hand to the entrainment caused by the movement of the liquid (which tends to pull them towards the upper part of the elutriator). The solid particles are therefore subject to a competition between their sedimentation velocity (downwards) and the velocity of the liquid (upwards), which allows the particle size distribution of the particles according to their size (elutriation).

[0055] The residence time of the solid particles in the elutriator is at least equal to the consumption time of the solid particles allowing them to decrease to a size smaller than Ls. Depending on their residence time, the particles may have a size smaller than Ls at the outlet or disappear.

[0056] The frustoconical part 23 has a height H and a cone angle a defined by said height and a ratio between the diameters of the lower part and the upper part.

[0057] The height H of the elutriator determines the residence time of the liquid in the elutriation zone. It must be sufficiently large to allow stabilization of the liquid flow, avoid an excessive accumulation of suspended solid particles, which could hinder separation, and ensure a cone angle small enough to limit the deposition of solid particles at the base of the cone.

[0058] The dimensions of the frustoconical section depend on Le, Ls, the sedimentation rate of the particles, and the kinetics of the particle consumption reaction in the elutriator. They are therefore specific to the reaction being carried out. A person skilled in the art is able, for any reaction using a consumable solid, to choose the values ​​of Le and Ls, determine the sedimentation rate, and deduce the appropriate dimensions of the elutriator.

[0059] The size Le is the size below which the particles are carried by the liquid flow exiting the reactor and entering the elutriator at a predetermined velocity. The size Le is determined by the inlet diameter De of the elutriator and the liquid flow rate.

[0060] The size Ls is chosen by a person skilled in the art, based on the maximum permissible size of consumed solid particles and the size of any produced solid particles present in the liquid exiting the elutriator. This choice may depend on the product specifications and the subsequent treatments to which the liquid is subjected.

[0061] The sedimentation rate can be determined experimentally or from the available scientific and technical literature.

[0062] The Reynolds number of grains (particles) of diameter dp (dp = Le or Ls) is:

[0063] o pM (1)

[0064] with: Pf the density, Used the sedimentation rate, and p the experimental viscosity.

[0065] For a laminar flow regime (Stokes regime, Reg < 0.2) and for spherical particles, the sedimentation velocity is written:

[0066] (Ps-P^gdp (2) Used “18 fi

[0067] with: Pu the density of the solid particles and g the acceleration due to gravity.

[0068] For collective sedimentation, the volumetric solids rate must be taken into account according to a law of the form:

[0069] l-ÿ)“ (3)

[0070] with: Used,Coii the collective sedimentation velocity, Used,free the free sedimentation velocity calculated with equation (2), the volume fraction of solid and n an exponent dependent on the Reynolds value.

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080] For non-spherical particles, a correction factor dependent on the particle's sphericity index must be taken into account. Generally speaking, the more a particle's shape deviates from a sphere, the lower its sedimentation rate. The inlet and outlet diameters of the elutriator (denoted De and Ds in [Fig. 1]) are given by the formulas: with: QvL the volumetric flow rate of the liquid, Used,e the sedimentation rate of particles of size Le and Used,s the sedimentation rate of particles of size Ls. The diameters of the lower and upper parts of the elutriator are all the greater when the sedimentation velocities of the solid particles are low (i.e., when the sizes Le and Ls are small). A particularly advantageous feature is that the elutriator is mounted removably on the reactor. It is therefore possible, in a chemical plant, to have several elutriators, each sized for a specific reaction, and to carry out different reactions within the same reactor by installing the appropriate elutriator. EXAMPLES PET depolymerization This example illustrates the use of the invention in a process for depolymerizing polyethylene terephthalate (PET) by methanolysis. This reaction is a consumable solid reaction; the PET particles decrease over time. The procedure used in this example is derived from patent application WO 2020 / 128218A1, the difference being that this earlier document describes a discontinuous process, commonly referred to as a "batch" process. Opaque PET is particularly problematic to recycle because it cannot be recycled in the same recycling stream as other plastics, such as polyethylene (PE) or polypropylene (PP). Recycling by depolymerization allows the recovery of virgin starting monomers, which are terephthalic acid (PTA) or, in its ester form, dimethyl terephthalate (DMT), and ethylene glycol (EG). This method makes it possible to produce new PET with a large number of cycles. This type of continuous process can have numerous applications, particularly in the fields of waste management and sustainable production. Figure [Fig.2] illustrates an installation enabling continuous PET depolymerization using the reactor-elutriator of [Fig.1].

[0081] PET flakes of substantially homogeneous size are introduced into reactor 1 at a flow rate of approximately 1 kg / h. These flakes are typically obtained by grinding waste and have a size of approximately a few cm2.

[0082] A liquid feed of the order of 10 kg / h, composed of a mixture containing methanol (MeOH) (reactive solvent) and a solubilized basic catalyst (for example potassium hydroxide (KOH) or sodium hydroxide (NaOH)), is introduced into the reactor under stirring.

[0083] The reaction takes place at a temperature between 45 and 70°C, at atmospheric pressure (i.e. about 105 Pa). A residence time is defined so that one of the monomers produced, dimethyl terephthalate (DMT), remains substantially below the solubility limit in order not to disrupt the function of the elutriator.

[0084] A 200mm diameter, 5L reactor was used and connected to a truncated conical elutriator as described above.

[0085] The elutriator 2 in this example is sized so that the unreacted PET particles remain in the reactor so that they are not prematurely discharged with the liquid.

[0086] The dimensions of the elutriator were defined to limit the passage of solid particles smaller than 15 pm. In this case, the diameter De of the lower part of the elutriator is 80 mm and the diameter Ds of the upper part of the elutriator is 200 mm.

[0087] Thus the reaction mixture containing the solubilized monomers, the unreacted methanol, the solubilized catalyst as well as the particles smaller than 15 pm can be continuously discharged by an overflow system provided on the elutriator.

[0088] The mixture exiting the elutriator 2 is transferred to a crystallizer 3 under reduced pressure, leading to the crystallization of the solubilized DMT fraction by solvent (MeOH) evaporation. The suspension is then filtered in a filtration device 4. The solid DMT resulting from this filtration is washed in a washing device 5 with the condensed MeOH from the evaporation; the liquid, containing the MEG (Monoethylene Glycol) and the degradation reagents, is treated in a distillation column 6, allowing the MeOH to be isolated at the top of the column, the excess MEG in the middle of the column, and the residual MEG with the reagents at the bottom of the column. The IMP impurities are purged.

[0089] The condensed MeOH, residual MEG and reactants are heated and then recycled into reactor 1.

[0090] The recycling rate makes it possible to control the DMT content at the reactor outlet in order to limit the particle size, on the one hand, and the MEG concentration, on the other hand.

[0091] After depolymerization, the monomers and / or oligomers are purified by vacuum distillation and repolymerized with ethylene glycol to produce PET. The resulting polymer can then be used to manufacture food packaging. The advantage is that it is not necessary to sort the PET before processing, and it is possible to use different grades of PET without affecting the products obtained. Other types of reactions

[0092] The process is applicable to any type of solid-liquid to consumable solid reaction. Non-limiting examples of such reactions include the manufacture of sodium thiosulfate from solid sulfur and sodium sulfite, and any operation involving the dissolution of a solid.

[0093] The said invention can also be used in the context of a heterogeneous catalytic reaction in liquid phase involving one or more liquid reactant(s) and a solid catalyst, the solid catalyst then being considered as the consumable solid.

Claims

Demands

1. A consumable solid reaction process comprising: - feeding a vessel (10) of a reactor (1) with solid particles and at least one liquid suitable for reacting with the particles so as to reduce the size of said particles as the reaction progresses, and stirring said particles suspended in the liquid, and - the continuous discharge of a liquid stream, characterized in that the liquid discharge is carried out by overflow through an outlet orifice (22) arranged in the upper part (21) of an elutriator (2), said elutriator comprising a lower part (20) assembled on the vessel of the reactor (1) and a frustoconical part (23) extending between the lower part (20) and the upper part (21), the upper part having a diameter (Ds) greater than the diameter (De) of the lower part,the diameter (Ds) of the upper part (21) being chosen according to a maximum size (Ls) of the solid particles exiting the elutriator, the diameter (De) of the lower part (20) being at most equal to the diameter of the reactor vessel (1) and imposing a maximum size (Le) of the solid particles entering the elutriator (2), the sedimentation rate of the particles allowing the classification of the particles present in the truncated conical part having a size between the maximum size (Ls) at the outlet and the maximum size (Le) at the inlet and the entrainment of the particles having a size less than said maximum size (Ls) with the liquid flow evacuated by the outlet orifice (22).

2. The method according to claim 1, wherein the liquid carries a first fraction of solid particles out of the reactor (1) and a second controlled fraction, smaller than the first fraction, out of the elutriator (2).

3. A method according to any one of claims 1 or 2, wherein the reactor is continuously fed with solid particles.

4. A method according to any one of claims 1 or 2, comprising a discontinuous feeding of solid particles into the reactor.

5. A method according to any one of claims 1 to 4, wherein the reaction is carried out at atmospheric pressure.

6. A method according to any one of claims 1 to 5, wherein a height (H) of the frustoconical part (23) of the elutriator is chosen sufficiently large to minimize an accumulation of suspended solid particles and a deposition of solid particles in the lower part (20).

7. A process for depolymerizing polyethylene terephthalate (PET) by methanolysis comprising the process according to any one of claims 1 to 6, wherein the consumable solid particles comprise polyethylene terephthalate (PET) and the liquid comprises a catalyst, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH), a reactive solvent, such as methanol (MeOH).

8. A liquid-phase heterogeneous catalytic reaction process comprising the process according to any one of claims 1 to 6, wherein the solid particles comprise a catalyst and the liquid comprises at least one reactant.

Images