Consumable solid reaction method

Abstract

The invention relates to a consumable solid reaction method comprising: - supplying 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 the particles as the reaction progresses, and stirring the particles in suspension in the liquid; and - continuously discharging a stream of liquid, characterised in that the discharge of the liquid is carried out via overflow through an outlet port (22) arranged in the upper portion (21) of an elutriator (2), and wherein the elutriator comprises a lower portion (20) connected to the vessel of the reactor (1) and a frustoconical portion (23) extending between the lower portion (20) and the upper portion (21), and wherein the upper portion has a diameter (Ds) greater than the diameter (De) of the lower portion.

Description

[0001] CONSUMABLE SOLID REACTION PROCESS

[0002] TECHNICAL FIELD

[0003] The invention relates to a continuously operating consumable solid reaction process.

[0004] STATE OF THE ART

[0005] In a solid-state reaction, solid particles are reacted with a liquid suitable for reacting with the particles in a reactor and the liquid containing the reaction products in the solubilized or solid state is continuously withdrawn for further processing.

[0006] As the reaction proceeds, the size of the edible solid particles decreases.

[0007] Below a certain size, solid particles are therefore likely to be carried away by the flow of liquid leaving the reactor.

[0008] It is desirable to separate the residence times of the solid and the liquid and to control the size of the particles of consumable solid leaving the reactor, in order to avoid particles of too large a size being evacuated from the reactor and to allow the particles introduced into the reactor to be sufficiently consumed before their evacuation.

[0009] SUMMARY OF THE INVENTION

[0010] One aim of the invention is to develop a continuous solid-consumable reaction process in which the management of solid particles is optimized.

[0011] To this end, the invention proposes a consumable solid reaction process comprising:

[0012] - feeding a reactor vessel 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

[0013] - the continuous evacuation of a liquid flow, characterized in that the evacuation of the liquid is carried out 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 part and the upper part, the upper part having a diameter greater than the diameter of the lower part, the diameter of the upper part being chosen according to a maximum size of the solid particles leaving the elutriator, 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,the sedimentation rate of the particles allowing the classification of the particles present in the truncated cone-shaped 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 through 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, lower 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 method comprises a discontinuous feeding of solid particles into the reactor.

[0017] Particularly advantageously, the reaction is carried out at atmospheric pressure.

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

[0019] A first application of the process described above is a process for depolymerizing polyethylene terephthalate (PET) by methanolysis, 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).

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

[0021] A consumable solid reaction device allowing the implementation of the method described above comprises:

[0022] - a reactor adapted to receive solid particles, comprising at least one liquid inlet orifice,

[0023] - a mixer arranged in the reactor to stir the solid particles suspended in the liquid, and

[0024] - an elutriator comprising a lower part assembled on the reactor, an upper part comprising a liquid outlet orifice and a frustoconical part extending between the lower part and the upper part, the upper part having a diameter greater than the diameter of the lower part.

[0025] Particularly advantageously, the elutriator is removably mounted on the reactor. PRESENTATION OF THE FIGURES

[0026] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0027] - figure 1 is a schematic diagram of the elutriator reactor according to the invention;

[0028] - Figure 2 is a diagram of an installation including such an elutriator reactor for the implementation of a process for depolymerizing polyethylene terephthalate (PET) by methanolysis.

[0029] DETAILED DESCRIPTION OF EMBODIMENTS

[0030] The reaction between solid particles and liquid is carried out in a reactor.

[0031] In some applications, the liquid comprises at least one reactive solvent adapted to react with the consumable solid particles and solubilize the product. In other applications, the solid particles react with a soluble catalyst and a liquid reagent to which a co-solvent is optionally 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 not be prematurely removed with the liquid. However, any solid particles produced must be entrained by the liquid.

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

[0034] Figure 1 is a schematic diagram of an elutriator reactor according to one 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 comprising a shaft 11 carrying blades 12 arranged in the center of the tank, movable in rotation around a main axis of the tank. The tank 10 is advantageously provided with counter-blades 16 intended to eliminate the vortices caused by the mixer.

[0037] The reactor can be maintained at a temperature suitable for the reaction, for example by means of a circulation of a heat transfer fluid along at least a portion of the wall of the reactor. 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) provided with a means for heating and / or cooling the heat transfer fluid. The reactor comprises 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 comprise heating means for bringing the liquid to a temperature suitable for the reaction.

[0038] Solid particles can be introduced into the reactor continuously or discontinuously.

[0039] In the case of a discontinuous supply of solid particles, the reactor may comprise an inlet orifice separate from the liquid inlet orifice, for example provided with a hatch.

[0040] In the case of a continuous supply of solid particles, said particles may be introduced into the liquid outside the reactor and entrained by the liquid so as to enter the reactor through the liquid inlet.

[0041] For example, in the embodiment illustrated in Figure 1, the solid particles P can be continuously loaded via a screw hopper 141 into the liquid circuit, and driven therewith by means of the pump 140.

[0042] The reactor may optionally comprise one or more additional liquid inlet ports 15, for introducing one or more other liquids useful for the reaction.

[0043] The solid and liquid inlet flow rates can be adjusted independently.

[0044] The solids content in the reactor is adjustable and chosen according to needs. The higher the solids content, the faster the mass flow rate of solid consumption by the reaction.

[0045] 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 orifice 22.

[0046] The lower portion 20 of the elutriator has an internal diameter equal to or less than that of the upper portion of the reactor vessel.

[0047] On the other hand, the upper part 21 of the elutriator has an internal diameter greater than that of the lower part. For this purpose, the upper part and the lower part of the elutriator are connected by a truncated cone part 23.

[0048] The elutriator advantageously comprises a central tube 24 adapted for the passage of the mixer shaft 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.

[0049] The circulation of liquid between the inlet 14 of the reactor and the outlet 22 of the elutriator results in the formation of a liquid column in the elutriator. Said liquid column contains liquid, which includes solubilized solid, and solid particles which are entrained by the liquid.

[0050] The elutriator is designed to prevent the entrainment of consumable solid particles whose size is greater than a predetermined threshold while allowing the exit of solid particles produced up to a maximum size not to be exceeded. The elutriator is therefore designed so that the liquid entrains a first fraction of solid particles at the outlet of the reactor and a second controlled fraction, smaller than the first fraction, at the outlet of the elutriator. These first and second fractions depend on the size of the particles.

[0051] We note: Le, the maximum size of the solid particles at the entrance to the elutriator, through the lower part 20 of the latter, and Ls, the maximum size of the solid particles at the exit of the elutriator, through the outlet orifice 22 located in the upper part 21 of the elutriator. The values ​​of Le and Ls are specific to each of the solids (consumable and product).

[0052] In the elutriator, the solid particles are subjected on the one hand to their apparent weight (which tends to bring them back towards the reactor) and to the entrainment caused by the movement of liquid (which tends to carry them towards the upper part of the elutriator). The solid particles are therefore subjected to a competition between their sedimentation speed (downwards) and the speed of the liquid (upwards), which allows the granulometric classification of the particles according to their size (elutriation).

[0053] 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 pass 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.

[0054] The truncated cone-shaped 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.

[0055] The height H of the elutriator determines the residence time of the liquid in the elutriation zone. It must be large enough to allow the liquid flow to stabilize, avoid 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.

[0056] The dimensions of the truncated part 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 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, to determine the sedimentation rate and to deduce the appropriate dimensions of the elutriator.

[0057] The size Le is the size below which particles are entrained by the liquid flow leaving the reactor and entering the elutriator at a given speed. The size Le is imposed by the inlet diameter De of the elutriator and the liquid flow rate.

[0058] The size Ls is chosen by the person skilled in the art, depending on the maximum tolerated particle size of solid consumed and the size of the particles of solid produced possibly present in the liquid leaving the elutriator. This choice may depend on the specifications concerning the product and the treatments to which said liquid is subsequently subjected. The sedimentation rate can be determined experimentally or by available scientific and technical literature.

[0059] The Reynolds number of grains (particles) of diameter d p (d p = The or Ls) is:

[0060] ( 1 ) with: the density, Used the sedimentation rate, and p the experimental viscosity.

[0061] For a laminar flow regime (Stockes regime, Re g < 0.2) and for spherical particles, the sedimentation velocity is written: with: p sthe density of solid particles and g the acceleration of gravity.

[0062] For collective sedimentation, the solid volume rate must be taken into account with a law of the form: sed, coll Used,lib re (.^ P) (3) with: U S ed,coii the collective sedimentation velocity, Used, libre the free sedimentation velocity calculated with equation (2), p the volume fraction of solid and n an exponent depending on the Reynolds value.

[0063] For non-spherical particles, a correction factor depending on the particle sphericity index must be taken into account. Generally speaking, the more the particle has a shape other than a sphere, the lower the sedimentation velocity.

[0064] The inlet and outlet diameters of the elutriator (denoted De and Ds in figure 1) are given by the formulas: with: Q VL the volume flow rate of the liquid, U se d, e the sedimentation velocity of particles of size Le and Used, s the sedimentation velocity of particles of size Ls.

[0065] The diameters of the lower and upper parts of the elutriator are all the larger as the sedimentation speeds of the solid particles are low (therefore the sizes Le and Ls are low).

[0066] Particularly advantageously, the elutriator is removably mounted on the reactor.

[0067] It is thus possible, in a chemical installation, to have several elutriators, each sized for a respective reaction, and to implement different reactions within the same reactor by installing the appropriate elutriator.

[0068] EXAMPLES

[0069] Depolymerization of PET

[0070] This example illustrates the use of the invention in a process for depolymerizing polyethylene terephthalate (PET) by methanolysis. This reaction is a solid-based reaction, the PET particles decreasing over time. The procedure used in this example is taken from patent application WO 2020 / 128218A1, with the difference that this prior document relates to a discontinuous process, commonly called “batch”.

[0071] Opaque PETs are particularly problematic to recycle because they cannot be recycled in the same recycling chain as other plastics, such as polyethylene (PE) or polypropylene (PP). Recycling by depolymerization allows the recovery of the virgin starting monomers, which are terephthalic acid (PTA) or in its ester form dimethyl terephthalate (DMT) and ethylene glycol (EG). This route 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.

[0072] Figure 2 illustrates an installation allowing the continuous depolymerization of PET using the reactor-elutriator of Figure 1.

[0073] PET flakes of approximately uniform size are introduced into reactor 1 at a flow rate of around 1 kg / h. These flakes are typically obtained by grinding waste and have a size of around a few cm2.

[0074] A liquid feed of the order of 10 kg / h, composed of a mixture containing methanol (MeOH) (reactive solvent) as well as a solubilized basic catalyst (for example potassium hydroxide (KOH) or sodium hydroxide (NaOH)), is introduced into the reactor with stirring.

[0075] The reaction takes place at a temperature between 45 and 70°C, at atmospheric pressure (i.e. approximately 10 5 Pa). A residence time is defined so that one of the monomers produced, dimethyl terephthalate (DMT), remains significantly below the solubility limit so as not to disrupt the function of the elutriator.

[0076] A 200mm diameter 5L reactor was used and connected to a truncated cone elutriator as described above.

[0077] Elutriator 2 in this example is sized so that unreacted PET particles remain in the reactor so that they are not prematurely discharged with the liquid.

[0078] 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.

[0079] 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 evacuated by an overflow system provided on the elutriator.

[0080] The mixture leaving the elutriator 2 is transferred to a crystallizer 3 under reduced pressure, leading to the crystallization of the DMT portion solubilized by evaporation of solvent (MeOH). The suspension is then filtered in a filtration device 4. The solid DMT resulting from this filtration is washed in a washing device 5 by the condensed MeOH from the evaporation; for its part, the liquid, containing the MEG (MonoEthyleneGlycol) and the degradation reagents, is treated in a distillation column 6 allowing the isolation of the MeOH 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.

[0081] The condensed MeOH, residual MEG and reagents are reheated and then recycled to reactor 1.

[0082] 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.

[0083] 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 this having any influence on the resulting products.

[0084] Other types of reactions

[0085] The process is usable for 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.

[0086] 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

CLAIMS 1. Consumable solid reaction process comprising: - feeding a tank (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 evacuation of a liquid flow, characterized in that the evacuation of the liquid 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 reactor vessel (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 as a function of a maximum size (Ls) of the solid particles leaving 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 speed of the particles allowing the classification of the particles present in the truncated cone-shaped 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 flow of liquid evacuated through the outlet orifice (22)., 2. Method according to claim 1, in which the liquid carries a first fraction of solid particles at the outlet of the reactor (1) and a second controlled fraction, less than the first fraction, at the outlet of the elutriator (2).

3. Method according to one of claims 1 or 2, in which the reactor is continuously supplied with solid particles.

4. Method according to one of claims 1 or 2, comprising a discontinuous supply of solid particles into the reactor.

5. Method according to one of claims 1 to 4, in which the reaction is carried out at atmospheric pressure.

6. Method according to one of claims 1 to 5, in which a height (H) of the truncated part (23) of the elutriator is chosen to be sufficiently large to minimize a accumulation of suspended solid particles and deposition of solid particles in the lower part (20).

7. A process for depolymerizing polyethylene terephthalate (PET) by methanolysis comprising the process according to 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 process for a heterogeneous catalytic reaction in the liquid phase comprising the process according to one of claims 1 to 6, wherein the solid particles comprise a catalyst and the liquid comprises at least one reagent.

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