Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/48—Separation; Purification; Stabilisation; Use of additives
  • C07C67/56—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
  • B01D15/08—Selective adsorption, e.g. chromatography
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/005—Selection of auxiliary, e.g. for control of crystallisation nuclei, of crystal growth, of adherence to walls; Arrangements for introduction thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/03—Preparation of carboxylic acid esters by reacting an ester group with a hydroxy group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/48—Separation; Purification; Stabilisation; Use of additives
  • C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/76—Esters of carboxylic acids having a carboxyl group bound to a carbon atom of a six-membered aromatic ring
  • C07C69/80—Phthalic acid esters
  • C07C69/82—Terephthalic acid esters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D2009/0086—Processes or apparatus therefor
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
  • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
  • C08J11/24—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds containing hydroxyl groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds

Definitions

• the invention relates to a method for purifying a diester monomer, in particular a diester terephthalate monomer, and in particular bis-(2-hydroxyethyl) terephthalate (BHET), by adsorption. More particularly, the invention relates to a method for purifying a crude diester monomer feed, in particular comprising a diester terephthalate monomer and in particular bis-(2-hydroxyethyl) terephthalate (BHET), by adsorption of a mixture of said feed. with an aqueous solvent by at least one adsorbent, to obtain a purified and decolorized diester monomer effluent.
• the raw diester monomer filler can be obtained, for example, by depolymerizing a polyester filler consisting in particular of polyester waste and post-consumer plastic materials.
• polyester in particular polyethylene terephthalate (PET)
• PET polyethylene terephthalate
• polyesters come from material collection and sorting circuits.
• the polyester in particular the PET, can come from the collection of bottles, trays, films, resins and/or fibers composed of polyester (such as, for example, textile fibers, tire fibers). Polyester from collection and sorting channels is called recycled polyester.
• PET for recycling can be classified into four main categories:
• - clear PET consisting mainly of colorless transparent PET (generally at least 60% by weight) and azure colored transparent PET, which does not contain pigments and can be used in mechanical recycling processes,
• PET green, red, etc.
• green, red, etc. which can generally contain up to 0.1% by weight of dyes or pigments but remains transparent or translucent;
• Opaque PET is increasingly used, for example, for the manufacture of food containers, such as milk bottles, in the composition of cosmetic, phytosanitary or dye bottles;
• Multilayer PET which comprises layers of polymers other than PET or a layer of recycled PET between layers of virgin PET (i.e. PET not having undergone recycling), or an aluminum film for example.
• Multilayer PET is used after thermoforming to make packaging such as trays.
• the recycling of these streams generally consists of a first conditioning stage during which bales of raw packaging are washed, purified and sorted, crushed and then purified and sorted again to produce a flow of flakes generally containing less than 1% by mass of "macroscopic” impurities (glass, metals, other plastics, wood, cardboard, mineral elements), preferably less than 0.2% of "macroscopic” impurities and even more preferably less than 0.05%.
• "macroscopic" impurities glass, metals, other plastics, wood, cardboard, mineral elements
• the clear PET flakes can then undergo an extrusion-filtration step to produce extrudates which are then reusable when mixed with virgin PET to make new products (bottles, fibres, films).
• a solid state vacuum polymerization step (known by the acronym SSP for Solid State Polymerization according to the English term) is often necessary for food uses. This type of recycling is called mechanical recycling.
• the dyes are natural or synthetic substances, soluble in particular in the polyester material and used to color the material in which they are introduced.
• the dyes generally used are of different natures and often contain heteroatoms of O and N type, and conjugated unsaturations, such as for example quinone, methine, azo functions, or molecules such as pyrazolone and quinophthalone.
• Pigments are finely divided substances, insoluble in particular in polyester material, used to color and/or opacify the material in which they are introduced.
• the main pigments used to color and/or opacify polyesters, in particular PET are metal oxides such as T1O 2 , C0Al 2 O 4 , Fe 2 O 3 , silicates, polysulphides, and carbon black.
• Pigments are particles with a size generally between 0.1 and 10 ⁇ m, and mostly between 0.4 and 0.8 ⁇ m. The total elimination of these pigments, necessary to envisage a recycling of opaque PET, by filtration is technically difficult because they are extremely clogging.
• Patent application US 2006/0074136 describes a process for depolymerization by glycolysis of colored PET, in particular resulting from the recovery of green colored PET bottles.
• the PET filler treated by this process is brought into contact with ethylene glycol at a temperature between 180 and 280°C for several hours.
• the glycolysis product obtained at the end of the depolymerization stage is, directly or after filtration, purified on activated carbon at a temperature above 170° C. then by extraction of the residual dyes, in particular yellow dyes, by a solvent which may be an alcohol, such as methanol, or a glycol, such as ethylene glycol, and crystallization of the BHET in the extraction solvent by lowering the temperature.
• the BHET is then separated by filtration.
• post-consumer PET comprising a mixture of different PETs, such as clear PET and colored PETs such as blue PET, green PET and/or amber PET, is depolymerized by glycolysis in the presence of ethylene glycol and an amine catalyst and alcohol, in a reactor at 150-250° C., in batch mode.
• the diester monomer then obtained is purified by direct filtration, then by adsorption on activated carbon and finally by passage through an ion exchange resin, in particular at a temperature of 80-90°C, before being crystallized and recovered by filtration.
• Patent application US 2015/0105532 discloses another mode of purification of the diester monomer obtained by short path distillation at 200°C.
• US Patent 6,642,350 describes the purification of a solution of crude BHET dissolved in methanol or ethylene glycol, comprising at least a succession of bringing said solution into contact with an activated carbon, an exchange resin of anions and a cation exchange resin, at a temperature between 40 and 120°C, in particular equal to 60°C, 65°C or 80°C.
• This patent indeed shows that bringing it into contact only with activated carbon under the conditions described above is not sufficient in particular to discolor completely the solution since a residual color, in particular yellow, persists while the yellow color no longer appears with a succession of passages on activated carbon and anion and cation exchange resins.
• the process comprises the steps of depolymerizing colored polyester, for example green PET, in the presence of a diol, in particular ethylene glycol, in a reactor at a temperature between 180 and 240°C, optionally evaporation in a scraped film evaporator (thin film evaporator according to the English term), dissolution in a hot solvent and a filtration stage to separate the insoluble impurities of size greater than 50 ⁇ m.
• a diol in particular ethylene glycol
• a scraped film evaporator thin film evaporator according to the English term
• Patent JP3715812 describes obtaining refined BHET from PET.
• the process comprises: the glycolysis of PET flakes, previously pretreated by washing with water in solid form, in the presence of ethylene glycol and a catalyst in a stirred reactor, at 180°C then at 195-200°C ; followed by a pre-purification step by cooling, filtration, adsorption and treatment on an ion exchange resin.
• This pre-purification step is presented as important and carried out before the evaporation of the glycol and the purification of the BHET to avoid the re-polymerization of the BHET in the subsequent purification steps.
• going through a stage of filtration and ion exchange resin can be extremely problematic when the load includes a large amount of very small solid particles such as pigments.
• patent application FR 3053691 describes a process for depolymerizing a polyester filler comprising opaque PET and in particular 0.1 to 10% by weight of pigments, by glycolysis in the presence of ethylene glycol.
• a purified bis-(2-hydroxyethyl) terephthalate (BHET) effluent is obtained after specific stages of separation and purification by adsorption.
• the BHET effluent obtained by the depolymerization process described in application FR 3053691 may have imperfections: the BHET effluent obtained is colored in particular rapidly despite passing through an adsorbent column.
• the present invention seeks to improve the purification of a crude diester monomer, and in particular the purification step of the processes of the state of the art, such as those mentioned above, in order to improve the discoloration of a monomer.
• diester in particular of BHET monomer, in particular obtained after depolymerization of a polyester filler comprising PET.
• the object of the invention is in fact to obtain a diester monomer, in particular a BHET monomer, of high purity and discolored, from a crude diester monomer charge, in particular resulting from a depolymerization reaction by glycolysis of polyester waste and in particular of PET waste.
• the subject of the invention is therefore a method for purifying a crude diester monomer charge, the method comprising: a) a mixing step supplied with the crude diester monomer charge and an aqueous solvent, and carried out at a temperature between 60 and 150 ° C, to obtain an aqueous mixture of diester monomer, the amount of aqueous solvent introduced being adjusted so that the crude diester monomer charge represents between 20 and 90% by weight of the total weight of the aqueous mixture of diester monomer; b) an adsorption step carried out by contact of the aqueous mixture of diester monomer with at least one adsorbent, at a temperature between 60 and 150° C. and at a pressure between 0.1 and 1.0 MPa, to obtain an effluent purified monomer.
• An advantage of the present invention lies in obtaining, from a crude diester monomer feed, in particular a crude BHET feed, a purified and decolorized diester monomer effluent, in particular a BHET effluent.
• a purified and decolorized diester monomer effluent in particular a BHET effluent.
• the purified diester monomer effluent obtained at the end of the process according to the invention is advantageously colorless or almost colorless to the eye; when treated to obtain an effluent in solid form, the purified diester monomer effluent in solid form is a white solid, to the eye.
• the method according to the invention makes it possible to obtain a purified diester monomer effluent having no significant absorption band (that is to say, which cannot be distinguished from the background noise) in the range of lengths d visible wave, that is to say between 400 and 800 nm when characterized by UV-visible spectrometry.
• the purified diester monomer effluent, obtained at the end of the process according to the invention has, preferably in solid form, color parameters expressed in the CIE 1976 L * a * b * reference system, determined by colorimetry (according to the ASTM D6290 2019 method), preferably with:
• An advantage of the invention is therefore to be able to obtain a purified and decolorized diester monomer effluent from a raw diester monomer stream, resulting in particular from a process for depolymerization by glycolysis of polyester waste which typically comprises colored, opaque, or even multi-layers and therefore therefore pigments and dyes.
• the process according to the invention thus makes it possible to remove residual impurities, such as dyes and/or organic or inorganic salts, which would not have been removed during separation steps downstream of the depolymerization of the polyester.
• Such a diester monomer can then be then (re)polymerized into a polyester polymer which has no difference with a virgin polyester, in particular a virgin PET, thus authorizing all the uses of virgin PET.
• the process according to the invention is very flexible and can easily be integrated downstream of any process for the depolymerization, in particular by glycolysis, of polyester, such as PET and in particular opaque and/or colored PET, as a step for purifying the diester monomer effluent obtained directly by the depolymerization reaction or after stages of separation of the diol introduced in excess for the glycolysis or generated during the depolymerization and/or heavy impurities such as the oligomers not entirely converted and the pigments.
• the method according to the invention can easily be integrated instead of the bleaching step of the method described in patent application FR 3053691.
• Figure 1 shows the UV-visible spectra obtained between 550 nm and 700 nm, for the effluents produced by the processes described in examples 1, 2 and 3.
• Figure 2 shows the UV-visible spectrum obtained between 350 nm and 850 nm, for the effluent produced by the process described in Example 1.
• polyethylene terephthalate or poly(ethylene terephthalate), also simply called PET has an elementary unit comprising a terephthalic acid diester, of repetition of formula:
• PET is obtained by polycondensation of terephthalic acid (PTA), or dimethyl terephthalate (DMT), with ethylene glycol.
• the term “monomer” or “diester monomer” advantageously designates the repeating unit of a polyester polymer, and defines a diester of a dicarboxylic acid, preferably of an aromatic dicarboxylic acid and preferentially of the terephthalic acid, and a diol preferably comprising between 2 and 12 carbon atoms, preferably between 2 and 4 carbon atoms, the preferred diol being ethylene glycol. More particularly, the “monomer” or “diester monomer” corresponds to the product targeted by the process according to the invention.
• the term "monomer” or “diester monomer” denotes bis(2-hydroxyethyl) terephthalate (BHET) of chemical formula H0C 2 H 4 -C0 2 -(C 6 H 4 )-C0 2 -C 2 H 4 OH, in which -(C 6 H 4 )- represents an aromatic ring.
• BHET bis(2-hydroxyethyl) terephthalate
• oligomer typically denotes a polymer of small size, generally consisting of 2 to 20 elementary repeating units.
• ester oligomer or “BHET oligomer” designates a terephthalate ester oligomer, comprising between 2 and 20, preferably between 2 and 5, elementary repeating units of formula -[0- C0-(C 6 H 4 )-C0-0-C 2 H 4 ]-, with -(C 6 H 4 )- an aromatic ring.
• diol and “glycol” are used interchangeably and correspond to compounds comprising 2 hydroxyl —OH groups, and preferably comprising between 2 and 12 carbon atoms, preferably between 2 and 4 carbon atoms.
• the preferred diol is ethylene glycol, also called mono-ethylene glycol or MEG.
• diol streams or diol effluent optionally used in the steps of the process of the invention, thus preferably comprise ethylene glycol (or MEG) in an amount greater than 40% by weight, preferably greater than 50% by weight , preferably greater than or equal to 60% by weight, of the total weight of the diol stream or diol effluent.
• MEG ethylene glycol
• the term "dye” defines a substance soluble in the polyester material and used to color it.
• the dye can be of natural or synthetic origin.
• the term "pigment”, more particularly coloring and/or opacifying pigment, defines a finely divided substance, insoluble in particular in the polyester material.
• the pigments are in the form of solid particles, with a size generally between 0.1 and 10 ⁇ m, and mostly between 0.4 and 0.8 ⁇ m. They are often mineral in nature.
• the pigments generally used, in particular for opacification are metal oxides such as Ti0 2 , C0Al2O4 , Fe 2 0 3 , silicates, polysulphides, and carbon black.
• the expressions "between ... and ! and "between ... and " are equivalent and mean that the limit values of the interval are included in the range of values described. If such were not the case and the limit values were not included in the range described, such precision will be provided by the present invention.
• the different ranges of parameters for a given step can be used alone or in combination.
• a range of preferred pressure values can be combined with a range of more preferred temperature values.
• upstream and downstream are to be understood according to the general flow of the flux in the process.
• the pressures are absolute pressures and are given in MPa or MPa absolute (or MPa abs.).
• the process according to the invention is fed with a crude diester monomer charge.
• Said crude diester monomer charge advantageously comprises at least 70.0% by weight, preferably at least 85.0% by weight, preferably at least 95.0% by weight, more preferably at least 99.0% by weight and very preferably at least 99.9% by weight, of a diester monomer, preferably bis-(2-hydroxyethyl) terephthalate (or BHET), 100.0% by weight representing the maximum of diester monomer in the charge.
• the raw diester monomer charge can also comprise impurities, preferably soluble in the diester monomer. These impurities can also be called residual impurities.
• dyes typically used to color the polyester polymeric material, organic or inorganic salts, or compounds of the ester type of a dicarboxylic acid, preferably of an aromatic dicarboxylic acid and preferentially of terephthalic acid, and at least one diol dimer or trimer (said diol being that which makes up the targeted diester monomer) preferably comprising between 4 and 36 carbon atoms, preferentially between 4 and 8 carbon atoms, for example diethylene glycol (such impurity is for example 2-(2-hydrohyetoxy)ethyl 2-hydroxyethyl terephthalate, which is an ester of terephthalic acid with ethylene glycol and diethylene glycol).
• diethylene glycol such impurity is for example 2-(2-hydrohyetoxy)ethyl 2-hydroxyethyl terephthalate, which is an ester of terephthalic acid with ethylene glycol and diethylene glycol.
• dye-type impurities can represent up to 1% weight (that is to say less than 1% by weight), preferably up to 0.1% by weight, preferably up to 0.05% by weight, of the total weight of the crude diester monomer charge, and in particular at least 1 ppmw of the total weight of crude diester monomer feed.
• the other impurities in particular of dicarboxylic acid ester type and of at least one diol dimer or trimer, may represent a total of up to 15.0% by weight, preferably up to 10.0% by weight, preferably up to to 5.0% by weight, of the total weight of the crude diester monomer charge, and in particular at least 10 ppm by weight of the total weight of the crude diester monomer charge.
• the crude diester monomer charge may also optionally comprise a solvent, such as a mono-alcohol, in particular methanol or ethanol, or a diol, more particularly ethylene glycol.
• the crude diester monomer charge may in particular comprise up to 30.0% by weight, preferably up to 15.0% by weight, preferably up to 5.0% by weight, preferably up to 1.0% by weight. and very preferably up to 0.1% by weight of solvent, and more particularly of diol such as ethylene glycol, or only traces of solvent and in particular less than 500 ppm by weight of solvent, preferably of diol and in particular ethylene glycol.
• the crude diester monomer charge may also not include a solvent.
• the raw diester monomer feed is obtained from a process for the depolymerization by glycolysis of a polyester feed, in particular a waste polyester feed which typically comprises colored PETs and/or opaque, and possibly multi-layered PETs.
• the crude diester monomer filler can be derived directly or indirectly from the depolymerization in the presence of diol, preferably ethylene glycol, of a polyester filler comprising colored and/or opaque PET, "indirectly derived” meaning that the depolymerization process comprises stages of pre-purification of the reaction effluent obtained by the depolymerization reaction in the presence of diol, such as for example a stage of separation of the diol used in excess for the glycolysis or generated during the depolymerization and/or a step for separating heavy impurities such as the oligomers not entirely converted and/or a step for separating the ionic species, for example by passage over ion exchange resins, "direct outcome" meaning that the depolymerization process does not include such pre-purification steps.
• the crude diester monomer feed which feeds the purification process according to the invention comes from a depolymerization process such as that described in patent application FR 3053691 and in which the process purification according to the invention replaces the decolorization step described. Purification process
• Purification of the crude diester monomer charge is advantageously carried out by adsorption of an aqueous solution of crude diester monomer.
• the process according to the invention thus comprises at least one step a) of mixing the diester monomer charge with an aqueous solvent, an adsorption step b) bringing the aqueous mixture of diester monomer obtained into contact with at least one adsorbent in order to obtain a purified diester monomer effluent.
• the process according to the invention may optionally comprise a step c) of separation of the diester monomer to obtain a separate purified diester monomer effluent and a used aqueous solvent effluent.
• the process according to the invention may also optionally comprise an additional stage c * ) of crystallization of the diester monomer, preferably located downstream of stage b) of adsorption and advantageously upstream of a possible stage c) of separation.
• step a) of mixing is supplied with the crude diester monomer charge, which preferably comprises BHET, and an aqueous solvent.
• Step a) makes it possible to obtain an aqueous mixture of diester monomer.
• the aqueous solvent advantageously comprises water, and preferably at least 50% by weight of water, preferably at least 75% by weight of water, preferably at least 90% by weight of water, even more preferably at least 97% weight of water, and preferably at least 99% by weight of water, the maximum being 100% by weight of water (that is to say that the aqueous solvent advantageously comprises 100% by weight of water or less, and in particular between 50 and 100% by weight, preferably between 75 and 100% by weight, preferably between 90 and 100% by weight, more preferably between 97 and 100% by weight, and preferably between 99 and 100% by weight of water) .
• the aqueous solvent in addition to water, can comprise other water-miscible compounds, for example of the alcohol, diol, acid type, etc.
• the aqueous solvent can also comprise ions and/or mineral salts in small quantities, typically in a quantity less than 1% by weight.
• the aqueous solvent comprises at least 99% by weight of water, and in particular up to 100% by weight of water, and may optionally comprise ions and/or mineral salts.
• the aqueous solvent which feeds step a) of mixing comprises, preferably consists of all or part of an aqueous solvent effluent, optionally purified, resulting from an effluent used aqueous solvent obtained at the outlet of an optional separation step c), and optionally supplemented by additional solvent external to the process according to the invention.
• the amount of aqueous solvent introduced is adjusted so that the crude diester monomer charge represents between 20 and 90% by weight, preferably between 30 and 80% by weight, preferably between 40 and 75% by weight and even more preferably between 40 and 60% by weight, of the total weight of the aqueous mixture of diester monomer.
• step a) of mixing is carried out at a temperature between 60 and 150° C., preferably between 70 and 120° C. and preferably between 75 and 110° C., and preferably at a pressure between 0.1 and 1.0 MPa, preferably between 0.1 and 0.8 MPa, and more preferably between 0.1 and 0.5 MPa.
• the aqueous solvent can be heated, prior to said step a) of mixing, preferably at the temperature at which step a) of mixing is carried out, in particular at a temperature between 60 and 150° C., preferably between 70 and 120°C and preferably between 75 and 110°C.
• the crude diester monomer charge feeds step a) of mixing at a temperature at which said crude diester monomer charge is at least partly, preferably entirely, in liquid or molten form.
• the raw diester monomer charge can be heated, prior to step a) of mixing, preferably to a temperature greater than or equal to 110° C., preferably greater than or equal to 120° C., and preferably less than or equal to equal to 220°C, preferably less than or equal to 200°C.
• the crude diester monomer charge which preferably comprises BHET, advantageously feeds step a) of mixing at a temperature (or inlet temperature) greater than or equal to 110° C., preferably greater than or equal to 120° C. C, and preferably less than or equal to 220°C, preferably less than or equal to 200°C.
• Step a) of mixing can implement any mixing equipment known to those skilled in the art, such as for example a static or dynamic mixer, in particular a static mixer.
• the aqueous mixture of diester monomer obtained at the end of step a) is advantageously a homogeneous mixture in which the diester monomer, in particular BHET, is soluble.
• Adsorption step a) is advantageously a homogeneous mixture in which the diester monomer, in particular BHET, is soluble.
• stage b) of adsorption is carried out by contact of the aqueous mixture of diester monomer with at least one adsorbent, in particular solid, advantageously at a temperature comprised between 60 and 150° C., preferably between 70° C. and 120° C. , preferably between 75 and 110° C., and very advantageously at a pressure between 0.1 and 1.0 MPa, in particular between 0.1 and 0.8 MPa and more particularly between 0.1 and 0.5 MPa.
• Adsorption step b) advantageously implements at least one adsorption unit (also called adsorption train), preferably between one and ten adsorption units, preferably between one and four adsorption units , each adsorption unit advantageously operating in parallel with respect to each other.
• each adsorption section comprises at least one adsorber and preferably up to four adsorbers, each adsorber being for example a reactor or a column.
• the residence time in each adsorber of the adsorption step is preferably between 20 minutes and 40 hours, preferably between 1 hour and 30 hours, preferably between 1 hour and 20 hours.
• the residence time is here defined as the ratio between the internal volume of the adsorber considered and the volume flow rate of the aqueous mixture of diester monomer resulting from step a) of mixing.
• Step b) of adsorption implements at least one adsorbent, in particular solid, and preferably up to five different adsorbents.
• step b) of adsorption implements one or two different adsorbents.
• adsorbents are said to be different when their nature and/or their composition and/or their particle size and/or their textural characteristics, such as the pore volume, is (are) different.
• different adsorbents are of different nature. It may indeed be advantageous to combine several different adsorbents, in particular of different nature, in order to optimize the elimination of residual impurities, in particular of residual dyes or residual salts, which may themselves also be of very different nature. .
• the polyester waste such as PET packaging waste or plastic bottles, from which can be obtained, by depolymerization of said waste, the crude diester monomer charge treated by the process according to the invention, can comprise a very a large number of colored and/or opaque PETs and therefore a very large number of different coloring compounds.
• the coloration of the crude diester monomer feedstock can also come from a degradation or transformation of compounds contained in the polyester waste during the various stages of a depolymerization process from which the crude diester monomer feedstock may come (for example the conditioning stages waste and/or depolymerization reaction).
• adsorption step b) uses between two and five different adsorbents
• said different adsorbents are mixed together or placed in series in an absorber or several adsorbers, advantageously in the same adsorption unit.
• said different adsorbents are in series relative to each other, advantageously in the same adsorption unit, and more preferably each of the adsorbents being in different adsorbers placed in series or in parallel, preferably in series advantageously in the same adsorption unit.
• the adsorbent(s), being in particular solid(s), is (are) chosen from activated carbons, aluminas and clays.
• the activated carbons are for example derived from petcoke, coal or any other fossil origin, or derived from biomass such as wood, coconut or any other source of biomass. Different raw materials can also be mixed to obtain activated carbons which can be used as adsorbents in said step b) of adsorption.
• the clays can be lamellar double hydroxides or natural or transformed clays such as those known to those skilled in the art under the term bleaching earths.
• at least one adsorbent is an activated carbon.
• adsorption step b) uses a single type of adsorbent
• said adsorbent is an activated carbon
• an adsorbent is an activated carbon and the other(s) is (are) another activated carbon, an alumina and/or a clay, preferably an activated carbon and/or a clay, more particularly a clay.
• each adsorbent used in step b) of adsorption has a pore volume (Vp), determined by mercury porosimetry, greater than or equal to 0.25 ml/g, preferably greater than or equal to 0.40 ml/g, preferably greater than or equal to 0.50 ml/g, and preferably less than or equal to 5 ml/g.
• Vp pore volume
• step b) of adsorption is implemented, advantageously in each adsorption unit:
• crossed fixed bed (or fixed bed) mode that is to say in at least one adsorber with a fixed bed of adsorbent(s), in particular at least one column of adsorbent(s), able to operate in ascending or descending mode, preferably ascending mode, or
• CSTR Continuous Stirred Tank Reactor
• step b) of adsorption is implemented in stirred mode in at least one stirred reactor of the CSTR type, the reactor(s) is (are) followed by a filtration system to recover said (or said) adsorbent (s) which is (are) in suspension in the treated liquid.
• step b) of adsorption is implemented in traversed fixed bed mode, advantageously in each adsorption unit.
• the adsorbents can be: - all present in each adsorber, or column, implemented, in a mixture or in successive fixed beds, or
• each adsorption section being made up of between one and four, preferably between two and four, fixed-bed adsorbent columns, advantageously in each adsorption unit.
• step b) of adsorption advantageously each adsorption unit or each of the adsorption sections, implements several fixed-bed columns, in particular at least two fixed-bed columns, preferably between two and four fixed-bed columns, of the same adsorbent(s).
• step b) of adsorption advantageously in each adsorption unit or an adsorption section, uses two columns of the same adsorbent(s)
• step b) of adsorption advantageously in each adsorption unit or the adsorption section, can operate according to an operation called "swing" after the accepted Anglo-Saxon term, in which one of the columns is in line while the other column is in reserve.
• adsorbent columns When the on-line column's adsorbent is used up, this column is isolated while the spare column is brought on-line. The spent adsorbent of the isolated column can then be regenerated in situ and/or replaced by fresh adsorbent to be put back on line once the other column has been isolated.
• Another mode of operation of adsorbent columns is to have at least two columns operating in series, advantageously in each adsorption unit: when the adsorbent of the column at the top (i.e. the first column of the series) is spent, this first column is isolated and the spent adsorbent is regenerated in-situ or replaced by fresh adsorbent, said column then being brought back online at the last position in the series of columns and so on .
• step b) of adsorption advantageously in each adsorption unit or each adsorption section, implements at least two columns of the same adsorbent, preferably in two to four columns of the same adsorbent, preferentially in two columns of the same adsorbent, operating in “lead-lag”.
• the combination of at least two columns of the same adsorbent, advantageously in each adsorption unit, makes it possible in particular to overcome clogging and/or possibly rapid saturation of the adsorbent.
• the presence of at least two columns of adsorbent facilitates the replacement and/or regeneration of the adsorbent, advantageously without stopping the adsorption unit, or even the process, thus making it possible to reduce the risks of clogging, avoid unit shutdowns due to adsorbent saturation, control costs and limit adsorbent consumption, while ensuring continuous production of purified diester monomers.
• This combination of at least two columns of adsorbent, in particular operating in “lead-lag”, advantageously in each adsorption unit also makes it possible to maximize the adsorption capacity of said adsorbent.
• step b) of adsorption very preferably comprises a first section adsorption section comprising at least two, preferably between 2 and 4, fixed bed columns of activated carbon, operating in swing or lead-lag, and a second adsorption section comprising at least two, preferably between 2 and 4 , columns of another adsorbent, preferably chosen from another activated carbon or a clay, in a fixed bed and operating in particular in swing or in lead-lag, and placed upstream or downstream of the first section of columns of activated carbon in a fixed bed.
• each adsorbent used in step b) adsorption is preferably in the form of granules, extrudates or powder.
• each adsorbent is:
• step b) of adsorption is implemented in traversed fixed bed mode
• step b) of adsorption is carried out in a stirred reactor of the CSTR type.
• the size of said at least one adsorbent is such that the smallest dimension of said at least one adsorbent (corresponding to the diameter of the circle circumscribing the pattern of polylobic granules or extrudates or to the diameter of the cylinder circumscribed to the cylindrical pattern of extrudates of the cylindrical type; this dimension also being called "diameter”) is preferably between 0.1 and 5 mm, preferentially between 0.3 and 2 mm.
• the extruded activated carbon with a diameter of 0.8 mm marketed by the company Cabot Norit or the granules comprised in the size range between 0.4 and 1.7 mm marketed by the company Chemviron may be suitable as adsorbent.
• the method according to the invention can advantageously also comprise a phase of regeneration of said adsorbent(s) from step b) of adsorption.
• a purified monomer effluent is obtained at the end of step b) of adsorption. It can feed an optional separation step c) or optionally a crystallization step c * ). c * ) Optional crystallization step
• the process according to the invention may optionally comprise a stage c * ) of crystallization of the diester monomer, preferably located downstream of stage b) of adsorption and very advantageously upstream of an optional stage c) of separation.
• step c * ) of crystallization implements at least one solid production section.
• the optional crystallization stage c * ) makes it possible to obtain an aqueous suspension of solid diester monomer.
• This optional crystallization step has a double effect: it facilitates the separation of the purified diester monomer in solid form from the used aqueous solvent effluent, but also improves the purification of the diester monomer.
• the process comprises a step c * ) of crystallization, downstream from step b) of adsorption and very advantageously upstream of an optional step c) of separation.
• the process may comprise, downstream of stage b) of adsorption, between two and four stages c * ) of crystallization, each being followed by an optional stage c) of separation as described below.
• the process may comprise at least one crystallization stage c * ) upstream of the adsorption stage b) and advantageously upstream of the mixing stage a).
• step c * ) of crystallization comprises a solid production section, supplied with the crude diester monomer charge, optionally filtered, and a crystallization solvent as described below, and a separation section solid-liquid to separate the solid formed in the solid production section, the separated solid then being sent to the mixing step a) in which it will be dissolved in the aqueous solvent.
• the optional crystallization stage c * ), and more particularly the solid production section, advantageously located downstream of the adsorption stage b), is supplied with the purified monomer effluent from stage b) d 'adsorption.
• Stage c * ) of crystallization may optionally further comprise a section for filtration of the purified monomer effluent resulting from stage b) of adsorption, located upstream of the solid production section.
• the solid production section can also be supplied with a crystallization solvent, which is identical to or different from the aqueous solvent introduced in stage a) of mixing.
• the crystallization solvent is advantageously chosen from: water; aqueous solvents comprising at least 50% by weight, preferably at least 75% by weight, preferably at least 90% by weight, more preferably still at least 97% by weight and preferably at least 99% by weight of water; mono-alcohols preferably having between 1 and 12 carbon atoms, such as methanol or ethanol; diols preferably having between 1 and 12 carbon atoms; ethers; aldehydes; esters; hydrocarbons, preferably aromatic, for example mono-aromatic compounds; and mixtures of at least two of these compounds belonging to the same chemical family or different chemical families.
• the crystallization solvent is chosen from: water; an aqueous solvent comprising at least 50% by weight of water, preferably at least 75% by weight of water, preferably at least 90% by weight of water, even more preferably at least 97% by weight of water and preferably at least less than 99% by weight of water; a mono-alcohol having between 1 and 12 carbon atoms, such as methanol or ethanol; a diol having between 1 and 12 carbon atoms, preferably ethylene glycol; a mono-aromatic compound, for example xylene; and a mixture thereof.
• the crystallization solvent is the same as the aqueous solvent introduced in step a) of mixing.
• the crystallization solvent comprises, preferably consists of, all or part of an aqueous solvent effluent, optionally purified, resulting from the used aqueous solvent effluent obtained at the outlet of a step c) optional separation, optionally supplemented by additional solvent external to the process according to the invention.
• the quantity of crystallization solvent introduced into the solid production section is adjusted so that the raw diester monomer charge which feeds the process and in particular step a) of mixing of the process represents between 1 and 75% by weight, preferably between 5 and 45% by weight, more preferably between 15 and 35% by weight, of the total weight of the mixture in said solid production section (that is to say the mixture comprising the crude diester monomer charge, the aqueous solvent introduced in step a) of mixing and the crystallization solvent).
• all or part of the crystallization solvent can be heated, preferably to the temperature at which adsorption step b) is carried out, or cooled and in particular brought to a temperature preferably comprised between 0 and 120°C, preferably between 5 and 100°C, and more preferably between 10 and 90°C.
• the solid production section of the optional crystallization step c * ) is operated at a temperature (that is to say such that the temperature of the effluent from said solid production section is) comprised between 0 and 100°C, preferably between 5 and 80°C, and more preferably between 10 and 70°C. More specifically, in the solid production section, the purified monomer effluent from step b) adsorption, optionally mixed with the crystallization solvent, is cooled from the temperature at which step b) is operated.
• adsorption that is to say from a temperature between 60 and 150°C, preferably between 70°C and 120°C, preferably between 75 and 110°C, at a temperature between 0 and 100°C , preferably between 5 and 80°C, and more preferably between 10 and 70°C.
• the cooling can be carried out according to any method known to those skilled in the art.
• discontinuous mode batch mode according to the established Anglo-Saxon term
• the cooling of the temperature can be carried out without regulation of the drop in temperature (that is to say without an imposed temperature ramp; thus only the initial and final temperatures are controlled) or according to at least a decreasing temperature ramp, in particular according to a decreasing temperature ramp between 5 and 30°C/hour and more particularly between 8 and 15°C/hour, or even according to the two modes which are linked successively, that is to say without control for a part of the cooling and according to a decreasing ramp of the temperature, for another part of the cooling.
• the cooling can be simply due to the introduction of the stream to be cooled, that is to say the purified monomer effluent from step b) of adsorption or the mixture comprising the effluent purified monomer and the crystallization solvent, in a capacity, the volume of which is advantageously adapted to the flow rate of the flow to be cooled, maintained at a temperature between 0 and 100°C, preferably between 5 and 80°C, and more preferably between 10 and 70°C.
• the solid production section is advantageously operated at a pressure of between 0.00001 and 1.00 MPa, preferably between 0.0001 and 0.50 MPa, and more preferably between 0.001 and 0.20 MPa.
• the solid production section is operated under vacuum, preferably at a pressure between 0.0001 and 0.10 MPa, preferably between 0.001 and 0.01 MPa.
• the solid production section is advantageously operated in a jacketed reactor, at a pressure between 0.01 and 1.00 MPa, preferably between 0.05 and 0.20 MPa, so as to preferably at atmospheric pressure, that is to say at 0.10 MPa.
• water as crystallization solvent is mixed with the purified monomer effluent from step b) and the solid production section is operated under conditions such that the temperature of the effluent from said solid production section is between 5 and 50°C, preferably between 10 and 40°C.
• the crystallization solvent introduced and mixed with the purified monomer effluent from step b) is ethylene glycol and the solid production section is operated under conditions such that the temperature of the effluent from said solid production section is between 5 and 50°C, preferably between 10 and 40°C.
• the purpose of the solid production section is to make solid, that is to say to crystallize or precipitate, at least in part the diester monomer, preferably BHET.
• the solid production section comprises, preferably consists of, a precipitation or crystallization phase carried out by any precipitation or crystallization technique known to those skilled in the art.
• the solid production section is a crystallization section, for example by cooling or by concentration, implemented in any equipment known to those skilled in the art, as for example defined in the review of Engineering Techniques "Industrial Crystallization - Practical Aspects", ref. J2788 V1, followed by a liquid-solid separation.
• the solid production section preferably by crystallization, comprises one or more crystallization operation(s), operating in series or in parallel, carried out in batch or continuously, preferably continuously.
• the solid production section of the optional crystallization stage c * ) makes it possible to obtain a heterogeneous effluent, and more particularly an aqueous suspension of solid diester monomer, comprising a solid phase of diester monomer and a liquid phase which may comprise any residual impurities, such as residual dyes, still present in the purified monomer effluent from step b) adsorption.
• the aqueous suspension of solid diester monomer obtained at the end of an optional step c * ) of crystallization is sent to a step c) of separation.
• the purification process may comprise, preferably comprises, a separation step c) located downstream of step b).
• the optional separation step is advantageously supplied with the purified monomer effluent from step b) of adsorption or with the aqueous suspension of solid diester monomer obtained at the end of the optional step c * ) of crystallization when the method according to the invention comprises such a step.
• Step c) of separation when it is integrated into the process according to the invention advantageously makes it possible to separate a separated purified diester monomer effluent and a used aqueous solvent effluent.
• Step c) optional separation can advantageously implement any separation technique known to those skilled in the art.
• the optional step c) of separation can for example implement a separation by distillation and/or evaporation of the aqueous solvent, to obtain, on the one hand, the separated purified diester monomer effluent and, on the other hand, the spent aqueous solvent effluent which includes the aqueous solvent.
• the optional step c) of separation can implement implements a solid-liquid separation, such as for example a separation by filtration, by decantation and/or centrifugation, to separate the solid diester monomer advantageously in the form of crystals, and preferably the crystals of BHET, from the liquid phase of the aqueous suspension of solid diester monomer obtained at the end of step c * ) of crystallization.
• the solid diester monomer thus separated constitutes the purified diester monomer effluent separated, the liquid phase constituting the spent aqueous solvent effluent.
• the temperature and the pressure in step c) optional separation are adjusted by the person skilled in the art to satisfactorily separate a separated purified diester monomer effluent and a used aqueous solvent effluent.
• the optional separation step c) implements a solid-liquid separation
• the temperature at which step c) is carried out varies between 0 and 100° C., preferably between 5 and 80° C. C, and preferably between 10 and 50° C.
• the pressure preferably varies between 0.0001 and 0.50 MPa, and more preferably between 0.001 and 0.20 MPa.
• the separated purified diester monomer effluent, recovered in solid form preferably by filtration or centrifugation can also advantageously undergo all or some of the following operations, carried out one or more times without chronological order pre-defined: rinsing with a solvent, identical or different from the solvent supplying the mixing section or possibly the solid production section; additional filtration or centrifugation; elimination of the residual solvent by any method known to those skilled in the art, for example by drying by evaporation; shaping, for example in powder or granules; and storage of the solid.
• the separated purified diester monomer effluent is recovered, preferably by filtration or centrifugation, then is sent directly (that is to say without a solid storage phase) to a step known to those skilled in the art, optionally with, prior to the polymerization reaction, rinsing with water or a diol effluent, such as ethylene glycol, preferably rinsing with water, the solid effluent of purified diester monomer, then heating the rinsed solid to be melted.
• a diol effluent such as ethylene glycol
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the process according to the invention is: colorless or almost colorless to the naked eye when it is in liquid form; white when in solid form.
• the purification process according to the invention which comprises a step b) of adsorption of an aqueous solution of diester monomer, and optionally a step c * ) of crystallization of said diester monomer, thus makes it possible to purify and decolorize in a satisfactory manner the charge crude diester monomer, even if the latter comes from a process of depolymerization of a polyester filler which comprises only a significant amount of colored and/or opaque PET.
• the impurities, such as dyes, present in the diester monomer charge remain trapped by the adsorbent, at least in part, and/or, for at least another part, dissolved in the aqueous solvent or the mixture of solvents introduced during the process and can also be found in a used aqueous solvent effluent which may be separated.
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the process according to the invention preferably comprises at least 90% by weight, preferentially at least 95% by weight, preferably at least least 98% by weight, of diester monomer (that is to say of the product targeted by the process according to the invention), preferably of BHET, on the basis of the dry weight (that is to say with respect to the dry matter contained in said purified or separated diester monomer effluent).
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the purification process according to the invention can very advantageously comprise less than 5% by weight, preferably 1% by weight and preferably less than 0, 5% by weight, of dicarboxylic acid ester type impurities with at least one diol dimer or trimer, such as ester compounds derived from diethylene glycol, on a dry weight basis (i.e. relative to the dry matter of said effluent).
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the process, can be characterized by UV-visible spectrometry in order to identify the presence of absorption bands in the visible range, in particular between 400 and 800 nm.
• the purified diester monomer effluent or the separated purified diester monomer effluent is preferably characterized by UV-visible spectrometry, in particular between 400 and 800 nm, advantageously in a liquid medium, i.e. that is to say advantageously after dilution or dissolution in a suitable solvent, preferably between 0.1 and 10% by mass, at room temperature, using a conventional benchtop UV-visible spectrometer.
• Ethanol can be used as a suitable solvent, making it possible to dilute or dissolve a sample of the purified diester monomer effluent or the separated purified diester monomer effluent.
• a conventional 1 cm or 1 inch pathlength cuvette can be used.
• the UV-visible spectrum of the diester monomer effluent or the separated purified diester monomer effluent is determined using a solution of said diester monomer effluent prepared at 5% by weight in ethanol, and a 1 inch path length cuvette.
• the purified or separated diester monomer effluent obtained by the process according to the invention advantageously exhibits a spectrum preferably showing no significant absorption band (that is to say which cannot be distinguished from the noise of background) in the visible wavelength range (400-800 nm), and in particular in the range between 550 and 650 nm.
• the process according to the invention which comprises a step of adsorption in water makes it possible to effectively eliminate the blue dyes which absorb visible light typically between 550 and 650 nm.
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the process, can also be characterized according to a colorimetric method such as described in ASTM D6290 2019.
• the chosen illuminant is D65, the measurements are carried out in reflection and specular mode excluded, standard observer 10°. The measurements are expressed in the CIE L * a * b * standard.
• the diester monomer effluent or the separated purified diester monomer effluent, obtained by the process according to the invention preferably in solid form, advantageously has a CIE reference system L * a * b * with:
• the used aqueous solvent effluent obtained at the end of optional step c) comprises all or part of the aqueous solvent introduced in step a) of mixing and of the crystallization solvent optionally introduced in step c * ) optional of crystallization. It may also include dyes and/or other residual impurities.
• the aqueous solvent effluent used less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight and preferably less than 5% by weight, of diester monomer (i.e. say of the targeted product), preferably of BHET monomer.
• the used aqueous solvent effluent can then be at least partly directly recycled to stage a) of mixing of the process and/or the optional stage c * ) of crystallization.
• the used aqueous solvent effluent can also be treated, at least in part, so as to, in particular, separate the dyes and/or impurities, for example by adsorption, and thus recover a purified aqueous solvent which is then recycled at least in part to step a) of mixing the process and/or the optional step c * ) of crystallization.
• the used aqueous solvent effluent can also undergo, in addition to the separation of dyes and/or impurities, a separation of solvents, for example by distillation or decantation, when a crystallization solvent is introduced and the crystallization solvent is different from the solvent aqueous introduced in stage a) of mixing, in order to then obtain two separate solvents, one capable of being recycled to stage a) of mixing and the second capable of being recycled to the solid production section of the stage c * ) of crystallization.
• a separation of solvents for example by distillation or decantation
• the purified diester monomer effluent or the separated purified diester monomer effluent, obtained at the end of the process according to the invention, can thus feed, directly or indirectly, a polymerization stage known to those skilled in the art with a view to producing a polyester polymer, in particular PET or a co-polyester based on PET, which is indistinguishable from virgin resin corresponding.
• Said polymerization step can also be supplied, in addition to the purified diester monomer effluent or the separated purified diester monomer effluent, with ethylene glycol, terephthalic acid or dimethylterephthalate or any other monomer, depending on the (co)polymer targeted.
• a polyester filler comprising in particular 20% by weight of opaque PET comes from the collection and sorting channels to be processed.
• 4 kg/h of flakes of said polyester filler comprising 20% weight of opaque PET which itself contains 6.2% weight of T1O2 pigment are brought to a temperature of 250° C. then injected with 11.5 kg/h of ethylene glycol (MEG) in a first stirred reactor maintained at 250°C then in a second and a third stirred reactor maintained at 220°C.
• the reactors are maintained at a pressure of 0.4 MPa.
• the residence time defined as the ratio of the liquid volume in the reactor to the sum of the liquid volume flow rates entering the reactor, is set at 20 min in the first reactor and 2.1 h in the second and in the third reactor.
• the reaction effluent consists of 67.7% by weight of diol composed overwhelmingly of ethylene glycol (MEG) (that is to say comprising 95% by weight or more of MEG), 25 8% by weight of diester monomer composed overwhelmingly of bis(2-hydroxyethyl terephthalate (BHET) (that is to say comprising 95% by weight or more of BHET), 0.32% by weight of T1O2, and 6.1 % by weight of heavy compounds containing, among other things, dimers and/or oligomers
• the diol present in the reaction effluent is separated by evaporation in a succession of two flash drums at temperatures ranging from 180°C to 120°C and pressures of 0.04 MPa to 0.004 MPa followed by a wiped film evaporator operated at 175°C and 0.0005 MPa At the end of this evaporation step, a stream rich in MEG of 10.46 kg/h and a BHET-rich liquid stream of 5.02
• the BHET-rich liquid stream corresponding to the liquid monomer effluent, consists of 79.6% by weight of BHET diester monomer, 0.6% by weight of MEG and 1.0% by weight of T1O2 and 18.8% by weight of heavy compounds containing, among other things, dimers of BHET.
• the liquid stream rich in BHET is then injected into a short-path evaporator, otherwise called short-path distillation or short-path distillation in English denomination, operated at a pressure of 20 Pa.
• a hot oil at 215°C allows evaporation BHET which is then condensed in the short path evaporator at 130°C to give a liquid stream of BHET as the short path evaporator distillate at a rate of 3.8 kg/h.
• the residence time in the short-path evaporator is 1 min.
• the liquid stream of BHET recovered at the outlet of the short-path evaporator corresponds to crude BHET, which is the feedstock for the purification processes described in Examples 1, 2 and 3 below.
• Raw BHET is compressed to 0.15 MPa and fed into a mixing section which is also fed by a water stream.
• the water feed rate is adjusted so that the raw BHET represents 50% weight of the mixture (raw BHET + water).
• Said mixing section is operated at 90° C., at a pressure of 0.15 MPa.
• the mixture obtained then feeds an adsorption section consisting of two columns each filled with an adsorbent (i.e. with a fixed bed of adsorbent).
• the adsorption section is operated at 90°C, at a pressure of 0.15 MPa.
• One column is put under flow (i.e. it is in operation), the other remaining in reserve.
• the adsorbent used to fill the two columns is an activated carbon consisting of cylindrical extrudates 0.8 mm in diameter, reference ROY 0.8 from Cabot Norit.
• the residence time is set at 40 minutes, in one column.
• the linear speed in an empty drum is 2.4 cm/min.
• the effluent composed of BHET at 50% by weight in the BHET-water mixture is collected at the column outlet over time.
• a measurement by UV-visible spectrometry is carried out on a BHET solution prepared with a sample of the effluent obtained at 40 hours of operation then dissolved in ethanol, so as to reach a BHET concentration in the final solution of 5 % weight.
• the UV-visible spectrometric measurement is performed using a Hach DR3900 benchtop UV-visible spectrometer in a one-inch pathlength cuvette.
• Crude BHET is compressed to 0.15 MPa and fed to a mixing section which is also fed by a water stream.
• the water feed rate is adjusted so that the crude BHET represents 50% weight of the mixture (crude BHET + water).
• Said mixing section is operated at 90° C., at a pressure of 0.15 MPa.
• the mixture obtained then feeds an adsorption section consisting of two columns each filled with an adsorbent, in a fixed bed.
• the adsorption section is operated at 90° C., at a pressure of 0.15 MPa.
• One column is put under flux flux (that is to say in operation), the other remaining in reserve.
• the adsorbent used for filling the two columns is an activated carbon consisting of cylindrical extrudates 0.8 mm in diameter, reference ROY 0.8 from Cabot Norit.
• the residence time is set at 40 minutes, in one column.
• the linear speed in an empty drum is 2.4 cm/min.
• Solid particles form during cooling to give a suspension of solid in a liquid mainly comprising water.
• the suspension obtained at 20° C. is then filtered to recover a solid cake and a colored liquid filtrate.
• the solid cake is rinsed with 1.5 L of water.
• the rinsed solid cake is recovered and then dried at 40° C. under vacuum overnight to give 320 g of a white solid containing 99% by weight of BHET diester (determination of the composition by liquid chromatography).
• the recovered solid is white.
• a measurement by UV-visible spectrometry is carried out on a BHET solution prepared with a sample of the white solid obtained dissolved at 5% by weight in ethanol.
• the UV-visible spectrometric measurement is performed using a Hach DR3900 benchtop UV-visible spectrometer in a one-inch pathlength cuvette.
• Colorimetric measurements are also carried out on the solid BHET obtained, according to the ASTM D6290 2019 method.
• a sample of 5 g of solid BHET product is ground in a mortar using a pestle.
• the 5 g of ground BHET are placed in an optical quality glass vessel, 34 mm in diameter.
• the measurements are carried out in reflection using a Konica Minolta CM-2300d colorimeter and the SpectraMagic NX software, under the following conditions: illuminant D65, specular excluded, standard observer 10°.
• the measurements are expressed in the CIE L * a * b * standard.
• the result was obtained by averaging the values obtained for 10 measurements carried out on the sample. The results are shown in Table 1.
• Table 1 Table 1
• the colorimetry values obtained are consistent with the target values.
• Crude BHET is compressed to 0.15 MPa and fed to a mixing section which is also fed with an ethylene glycol stream.
• the ethylene glycol feed rate is adjusted so that the crude BHET represents 50% by weight of the mixture (crude BHET + ethylene glycol).
• Said mixing section is operated at 120° C., at a pressure of 0.15 MPa.
• the mixture obtained then feeds an adsorption section consisting of two columns each filled with an adsorbent, in a fixed bed.
• the adsorption section is operated at 150°C, at a pressure of 0.15 MPa.
• One column is put under flow (i.e. in operation), the other remaining in reserve.
• the adsorbent used to fill the two columns is an activated carbon consisting of cylindrical extrudates 0.8 mm in diameter, reference ROY 0.8 from Cabot Norit.
• the residence time is set at 40 minutes, in one column.
• the linear speed in an empty drum is 2.4 cm/min.
• the effluent composed of BHET at 50% by weight in the BHET-ethylene glycol mixture is collected at the column outlet over time.
• the product obtained after 40 hours of operation has a bluish color.
• a measurement by UV-visible spectrometry is carried out on a BHET solution prepared with a sample of the effluent obtained at 40 hours of operation then dissolved in ethanol, so as to reach a BHET concentration in the final solution of 5 % weight.
• the UV-visible spectrometric measurement is performed using a Hach DR3900 benchtop UV-visible spectrometer in a one-inch pathlength cuvette.

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