RU2600637C2 - Method of processing wastes containing thermosetting polymers - Google Patents

Abstract

FIELD: recycling.

SUBSTANCE: invention relates to a method of processing wastes containing thermosetting polymers in the form of cured or uncured phenol or epoxy resins, and can be used in machine building, instrument making, aircraft and space industry and other departments. Method involves thermal decomposition of wastes in a solvent with extraction of phenol products. At that processing is carried out in coal-tar pitch or material containing coal-tar pitch, at a weight ratio of polymer: peck or material containing peck, -1: (3-10) at a temperature of 320-420 °C at atmospheric pressure. Solvolysis in a solvent medium can be used for spent polymer products, both without filler, and with filler. Use of coal-tar pitch as solvent allows to carry out solvolysis of thermosetting polymers at atmospheric pressure and to receive phenol compounds with high output as a result of decomposition.

EFFECT: technical result consists in improvement of efficiency of process of processing wastes.

1 cl, 4 dwg, 8 ex

Description

The invention relates to the field of processing waste products containing thermosetting polymers, in particular polymers based on phenolic and epoxy resins. Products may consist entirely of polymeric material or be a composite material in which the polymer serves as a matrix for a solid filler, for example carbon or other fibers. Composite polymeric materials with high strength and low specific gravity are easily processed and are widely used in mechanical engineering, instrument making, aviation and space industries. The ever-increasing volume of products based on thermosetting polymers requires the development of methods for their disposal, preferably with a return for reuse, especially of such expensive fillers as carbon fibers.

The preparation of individual phenolic compounds from thermosetting polymers is possible after their destruction, for which pyrolysis (thermal destruction of organic compounds at elevated temperatures, usually above 550 ° C) and thermal solvolysis (heat treatment in solvents) can be used.

Pyrolysis leads to the formation of gaseous products, condensable organic compounds and a carbonized solid residue. The use of pyrolysis to obtain chemical raw materials from wastes containing thermosetting polymers is inefficient, since the radicals formed during thermal decomposition react with each other to form condensed compounds, ultimately leading to the formation of a carbonized solid residue. Therefore, it is difficult to obtain liquid pyrolysis products in good yield, especially from crosslinked phenolic resins.

The yield of the pyrolysis solid residue of phenolic novolac resin cured with urotropine at 33 ° C is 33%, at 700 ° C - 47% [S. Theodoropoulou, D. Papadimitriou, L. Zoumpoulakis, J. Simitzis // Structural and optical characterization of pyrolyticcarbon derived from novolacresin. BioanalChem (2004) 379: 788-791]. The yield of phenolic products during the pyrolysis of thermoset crosslinked polymers is low and for phenolic resins does not exceed 33% of the feedstock [US 6,465,702 B1].

Known methods for processing waste containing thermosetting polymers using thermal solvolysis in a solvent environment. As the solvent used tetralin [D. Braun und R. Steffan Chemische Untersuchungenzum Abbauvernetzter Phenol-Formaldehyd-Harze // Die Angewandte Makromolekulare Chemie 92 (1980) 169-189 (Nr. 1523)] and other hydroaromatic compounds that act as hydrogen donors in the presence of amines [US 6465702] . In US patent 61628694, the epoxy polymer is subjected to degradation to obtain liquid products in a hydroaromatic solvent in the presence of a catalyst, active carbon or carbon black, in the temperature range 300-400 ° C.

Effective reaction medium for the decomposition of thermosetting polymers are subcritical and supercritical fluids such as water, glycols and alcohols [G. Motonobu. Chemical recycling of plastics using sub-and supercritical fluids // Journal of Supercritical Fluids 47 (2009) 500-507; Jiang, G.Z .; Pickering, S.J .; Lester, E .; Blood, P .; Warrior, N. Characterization of carbon fibers recycled from carbon fiber / epoxy resin composites using supercritical n-propanol // Compos. Sci. Technol. 2009, 69, 192-198]. Thermosetting polymers, in particular, based on phenolic and epoxy resins, are subjected to thermal solvolysis in supercritical or subcritical water containing oxygen or hydrogen peroxide to obtain phenolic compounds in the temperature range 180-1000 ° C and a pressure of 2-100 MPa [JPH 10287766] . The use of water or organic solvents in a supercritical or subcritical state as a solvent requires the use of special equipment operating under pressure and made of expensive materials. The critical temperature and pressure for water are 647 K and 22.1 MPa, respectively, for methanol - 513 K and 8.1 MPa. Carrying out the process under pressure complicates the process and reduces its productivity.

The closest in technical essence is a method of processing thermosetting materials [US 6465702] - a prototype in which a material whose polymer component is a cross-linked phenolic or epoxy resin is subjected to processing in a hydroaromatic solvent at a temperature of 200-350 ° C in the presence of an amine, for epoxy resin processing option at 300-350 ° C in the absence of amine. As hydroaromatic solvents, tetralin and dihydroanthracene are used. The proposed method can also be applied to composites based on thermosetting polymers with fillers such as carbon fibers. The destruction is carried out for 2-5 hours in solvents at a temperature above 300 ° C under pressure, the process without pressure at a temperature below the boiling point of the solvent increases the polymer destruction time by several times. Phenolic degradation products of thermosetting polymers remain in the solvent; obtaining them in pure form requires additional technological operations, for example rectification, which is complicated by the proximity of the boiling points of the phenols formed (phenol, alkyl phenols) and the solvent components tetralin and naphthalene.

The objective of the invention is to simplify the processing of wastes containing thermosetting polymers using thermal solvolysis and obtaining phenolic compounds suitable for reuse.

The problem is solved in that in the method of processing waste containing thermosetting polymers, heat treatment is carried out at a temperature of 320-420 ° C at atmospheric pressure in a solvent with the release of phenolic products. As a solvent, coal tar pitch or a material containing coal tar pitch can be used, with a mass ratio of thermosetting polymer: pitch or a material containing pitch, 1: (3-10).

Coal tar pitch is the residue of distillation of coal tar after reaching a temperature in the vapor phase of 360 ° C. The authors found that the thermal treatment of thermosetting phenolic and epoxy resins in coal tar pitch in the temperature range of 320-420 ° C allows the thermosetting polymer to be destroyed and phenolic compounds, mainly phenol and methyl substituted phenols from phenolic resins and a mixture of phenol and p- isopropylphenol from epoxies. The preparation of thermoset polymers during thermal solvolysis using coal tar pitch as a solvent with a high yield of liquid products indicates the reaction of free radicals formed during the thermal decomposition of polymers with pitch molecules, which prevent condensation reactions with the formation of an insoluble polymer degradation residue. Coal tar pitch is a cheap large tonnage industrial product. The absence of compounds with a low boiling point in the coal tar pitch allows the process to be carried out at atmospheric pressure and it is easy to separate the formed monatomic phenols, which are released from the solvent in the form of vapors and condense as distillate products. A small amount of multinuclear aromatic hydrocarbons, pitch components, such as anthracene, phenanthrene, etc., which have a boiling point significantly higher than mononuclear phenols, evaporated during the process, can be separated from phenols by distillation or using fractional condensation of distillate products during the thermal process solvolysis. The obtained phenolic products consist of phenol and its methyl and alkyl homologs and can be used for the re-synthesis of phenolic resins, thereby solving the problem of recycling the original chemical feedstock.

The proposed method can be used for spent polymer products from thermosetting polymers based on phenolic and epoxy resins, both without filler and with filler. In the latter case, the cementing function of the polymer matrix is destroyed and the filler in the form of carbon or other fibers can be easily isolated in pure form and again used in production. The filler in the form of carbon or other fibers is a chemically inert material with respect to coal tar pitch and products formed in the process of thermal solvolysis of thermosetting polymers, and does not affect the yield of phenolic compounds. For complete cleaning of fibers from adhering coal tar pitch, treatment with various solvents can be used. Fractions of a coal tar processing having a high solubility with respect to coal tar pitch can be used, such as an absorption fraction (boiling range 230-270 ° C.) and anthracene fraction (boiling range 270-360 ° C.).

For thermal solvolysis, industrial coal tar pitch is used as a solvent. The pitch is the remainder of the distillation of coal tar, so coal tar containing tar can also be used as a solvent for thermal solvolysis. But in this case, the obtained distillate products will contain, in addition to phenolic products, a certain amount of low-boiling coal tar compounds. To prevent this phenomenon, it becomes necessary to use increased pressure during thermal solvolysis, which imposes certain difficulties on the process. From this point of view, a mixture of coal tar pitch and oil pitch i.e. petroleum tar pitch obtained by the joint distillation of catalytic gas oil and coal tar mixed in a ratio of 40:60 [Perez M., Granda M., Garcia R. et. al. Preparation of binder pitches by blending coal-tar and petroleum pitches // Light Metals. 2001. P. 573].

For thermal solvolysis, the authors used industrial medium-temperature coal tar pitch with the following characteristics according to GOST 10200: softening temperature 69 ° C according to the “Ring and Rod” method, the yield of volatile substances 60%. As a mixture containing coal tar pitch, oil-tar pitch was used, which contains 60% coal tar pitch and has a softening temperature T _p = 55 ° C.

Thermal solvolysis is carried out under isothermal conditions in a metal reactor at atmospheric pressure with vigorous stirring with a propeller stirrer. The starting materials are loaded into the reactor in a predetermined ratio, mixing is switched on after the pitch is melted and the temperature in the reactor reaches 180-200 ° C. After heating the reactor to the required temperature in the range of 320-420 ° C, the process is carried out in isothermal conditions for 1-1.5 hours. Distilled products separated from the reactor and condensed, as well as the residue in the reactor, are weighed, the amount of gaseous products is determined by the difference between the loading mass and the sum of the masses of liquid products released from the reactor and the residue in the reactor. Distillate products are a mixture of organic products, mainly phenolic in nature, formed during the decomposition of the polymer, and aromatic hydrocarbons evaporated from the pitch. The qualitative composition of distillate products is determined by gas-liquid chromatography - mass spectroscopy, the content of individual phenols - using gas-liquid chromatography.

On page 12 are photographs of composite samples before and after thermal solvolysis in coal tar pitch and processing in the absorption fraction.

In FIG. 1 shows a sample of an initial composite based on fiberglass with an epoxy binder.

In FIG. 2 shows the pure fibers of the composite after processing.

In FIG. Figure 3 shows a photograph of an initial carbon fiber composite with an epoxy binder.

In FIG. 4 shows the pure carbon fibers of the composite after processing.

Although the present invention has been described using the most preferred examples, they cannot be interpreted as the only true ones. It is understood that the appended claims may include all variations and modifications reflecting its nature.

The invention is illustrated by the following examples.

Example 1

A mixture containing 50.2 g of coal tar pitch and 10.2 g of uncured novolac resin was charged into the reactor. Thermal solvolysis is carried out at a temperature of 380 ° C for 45 minutes, then the temperature is raised to 400 ° C and incubated for another 45 minutes. Obtained 51.8 g of residue in the reactor, 7.5 g of distillate liquid products and 1.1 g of gaseous products. The total phenol content in liquid products is 87%, or 6.5 g, including 49.0% phenol, 8.6% 2-methylphenol, 33.6% 4-methylphenol, 5.4% dimethylphenols and 0.3% trimethylphenols. The yield of phenolic products based on the initial phenolic resin is 64%.

Example 2. A mixture of 45.1 g of coal tar pitch and 15.1 g of uncured novolac resin was loaded into the reactor. Thermal solvolysis is carried out at a temperature of 400 ° C for 60 minutes. Received 47.2 g of residue in the reactor, 11.5 g of distillate liquid products and 1.5 g of gaseous products. The total phenol content in liquid products is 85%, or 9.8 g, including 51.7% phenol, 28.2% methyl phenols, 4.3% dimethyl phenols and 0.9% trimethyl phenols. The yield of phenolic products based on the initial phenolic resin is 65%.

Example 3. A mixture of 44.9 g of coal tar pitch and 15 g of cured novolac resin, which is obtained by heating the initial uncured novolac resin with 10% hexamethylenetetramine to a temperature of 150-160 ° C and holding for 30 minutes at this temperature, is loaded into the reactor. for 1 hour at 180 ° C. Thermal solvolysis is carried out at a temperature of 380 ° C for 60 minutes. Obtained 51.0 g of residue in the reactor, 7.0 g of distillate liquid products and 1.9 g of gaseous products. The total phenol content in liquid products is 82.2%, or 5.8 g, including 33.5% phenol, 35.6% methyl phenols, 12.0% dimethyl phenols and 1.0% trimethyl phenols. The yield of phenolic products based on the initial phenolic resin is 43%.

Example 4. A mixture of 45.1 g of coal tar pitch and 15.3 g of cured novolac resin obtained in the same manner as in Example 3 was loaded into the reactor. Thermal solvolysis was carried out at a temperature of 400 ° C. for 60 minutes. Received 49.8 g of residue in the reactor, 9.4 g of distillate liquid products and 1.2 g of gaseous products. The total phenol content in liquid products is 62%, or 5.8 g, including 26.7% phenol, 27.8% methyl phenols, 5.5% dimethyl phenols and 2.0% trimethyl phenols. The yield of phenolic products based on the initial phenolic resin is 43%.

Example 5. A mixture of 40.0 g of coal tar pitch and 8.0 g of cured epoxy obtained by curing the initial uncured epoxy with polyethylene diamine at a ratio of resin: hardener 5: 1 was loaded into the reactor. Thermal solvolysis is carried out at a temperature of 360 ° C for 15 minutes, then the temperature is increased to 400 ° C and maintained at this temperature for 60 minutes. Received 40.4 g of residue in the reactor, 6.6 g of distillate liquid products and 1.0 g of gaseous products. The total phenol content in liquid products is 78.4%, or 5.2 g, including 31.2% phenol, 36.6% p-isopropylphenol and 10.6% other phenols. The yield of phenolic products based on the starting epoxy resin is 65%.

Example 6. A mixture of 40.0 g of coal tar pitch and 8.0 g of cured epoxy obtained by curing the starting uncured epoxy with isomethyltetrahydrophthalic anhydride at a ratio of resin: hardener 5: 1 was loaded into the reactor. Thermal solvolysis is carried out at a temperature of 360 ° C for 15 minutes, then the temperature is increased to 380 ° C and maintained at this temperature for 60 minutes. 40.2 g of residue are obtained in the reactor, 6.0 g of distillate liquid products and 1.8 g of gaseous products. The total phenol content in liquid products is 65.9%, or 4.0 g, including 23.4% phenol, 32.2% p-isopropylphenol and 10.3% other phenols. The yield of phenolic products based on the starting epoxy resin is 65%.

Example 7. 29.0 g of coal tar pitch and 5.8 g of a composite consisting of fiberglass as a filler and a cured epoxy resin as a binder are loaded into the reactor. In this case, the composite is placed in a basket of metal mesh. Thermal solvolysis of the composite is carried out at a temperature of 360 ° C and maintained at this temperature for 60 minutes. Obtained 33.0 g of the residue in the reactor together with the fibers of the composite, 1.0 g of distillate liquid products and 0.8 g of gaseous products. After solvolysis, the metal basket with the composite is removed from the molten coal tar pitch and the remains of the coal tar pitch are removed from the surface of the fiberglass by treatment in a hot absorption fraction. The weight of the processed fibers is 3.8 g.

Example 8. A mixture of 45.0 g of coal tar pitch and 15.0 g of uncured novolac resin was charged into the reactor. Thermal solvolysis is carried out at a temperature of 400 ° C for 60 minutes. 46.6 g of a residue were obtained in the reactor, 11.6 g of distillate liquid products and 1.8 g of gaseous products. The total phenol content in liquid products is 97.6%, or 11.3 g, including 59.4% phenol, 10.1% o-methylphenol, 22.1% n-methylphenol and 6.0% other phenols.

The proposed method of processing waste containing thermosetting polymers allows the process to be carried out at relatively low temperatures of 320-420 ° C and at atmospheric pressure, which is the main advantage of this invention. In addition, coal tar pitch, used as a solvent for thermal solvolysis, is a low-cost, large-tonnage industrial product. The results of the experiments indicate the possibility of practical application of the proposed method for processing polymer products both without filler and with filler in the form of fiberglass, carbon, quartz and aramid fibers. The results of processing composite samples are presented in the form of photographs.

Claims (2)

1. The method of processing waste containing thermosetting polymers in the form of cured or uncured phenolic or epoxy resins by thermal destruction in a solvent with the release of phenolic products, characterized in that the processing is carried out in coal tar pitch or material containing coal tar pitch, in the mass ratio of thermosetting polymer: pitch or a material containing pitch, 1: (3-10) at a temperature of 320-420 ° C at atmospheric pressure. 2. The method according to claim 1, in which, as thermosetting polymers containing cured phenolic or epoxy resins, composite polymeric materials are used with a filler in the form of fiberglass, carbon and aramid fibers.

Images