PET Waste

The subject of this invention is the installation for continuous treatment of polyethylene terephthalate PET waste, especially, for the return of PET waste raw material consisting of colorless and colored packages, most frequently empty beverage bottles, containers, foil.

From the application WO 98/03459 and P.331177 we know the way to obtain terephthalic acid and ethylene glycol from polyethylene terephthalate waste and the installation for the implementation of that way. The installation consists of two connected, identical, heated pressure reactors, working in turns. In the reactors, crushed polyethylene terephthalate waste is subjected to digestion in the environment of aqueous solution of alkaline metal carbonate or ammonium carbonate and simultaneously heated to 200°C. Each reactor is equipped with a mixer, lockable feed hole with hermetically sealed raw material feed system, outlet connector equipped with pressure check valve and saturation connector, connected with the bubbler placed inside the reactor. Reactors are connected with each other through a four-way pressure valve in such a way that the outlet connector of one reactor is connected with the saturation connector of the other reactor while conducting the hydrolytic degradation of the raw material in the first reactor. In turn, the outlet connector of the second reactor is connected with the saturation connector of the first reactor while the hydrolytic degradation of the raw material is conducted in the second reactor. The outlets of reactors at the bottom are connected through the common valve with carbon filter separating solid waste, and further with the cooler. The outlet of the cooler is connected with the oxygenator in which the reaction mixture is subjected to oxidation with aqueous solution of sulfuric acid. Oxygenator is connected through a intermediate filter with the neutralizer. The neutralizer outlet is led to centrifuge in which the liquid phase is separated from the solid phase. Liquid phase is led through evaporator to the distillation column. Solid phase which consists of terephthalic acid is led through the rinsing device and crystallizer to the dryer.

Also, from the Polish patent 201218, the method of and the installation for the recovery of terephthalic acid and ethylene glycol from the polyethylene terephthalate waste is known. This method consists of submission of flake waste to activity of ammonium solution in the minimum temperature of 170°C for 30 to 120 minutes. The treated solution is distilled under a reduced pressure. Ethylene glycol and diammonium terephthalate crystals are obtained which are treated with sulfuric acid. Terephthalic acid crystals are formed. The remaining ammonium sulfate solution is subjected to a known crystallization process. The installation for terephthalic acid and ethylene glycol recovery from the polyethylene terephthalate waste consists of consecutive process units connected in a series such as the polyethylene terephthalate waste preparation unit, waste digestion unit, glycol distillation unit, terephthalic acid precipitation unit, ammonium sulfate crystallization unit. The installation also includes tanks connected with those unit, namely, ammonium solution tank connected with the waste digestion unit, sulfuric acid tank connected with the terephthalic acid precipitation unit, ethylene glycol collector connected with the glycol distillation unit, terephthalic acid collector connected with the terephthalic acid precipitation unit, and ammonium sulfate collector connected with the ammonium sulfate crystallization unit.

Another method to obtain terephthalic acid from polyethylene terephthalate waste and installation for application of that method is the subject of the patent description US 2003/0225299.

The patent describes the method including the stage of digestion during which PET products are submitted in a continuous way to digestion in ethylene glycol in an alkaline equimolecular or excess environment in order to obtain terephthalate and ethylene glycol. In the second stage the solid phase and liquid phase are separated and contaminants are dissolved and removed. Ethylene glycol is separated from the terephthalate suspension. Terephthalate in the form of a solid phase is dissolved in water, and insoluble contaminants are removed. In the third stage of neutralization and crystallization, the terephthalate solution is neutralized with acid. In the next stage, the obtained suspension of terephthalic acid crystals is subjected to separation of the solid phase from the liquid phase and the resulting terephthalic acid crystals are washed. At the end, terephthalic acid crystals are dried and powdered.

The installation for the application of this method most frequently includes a reactor located horizontally with a spiral assembly ensuring a continuous digestion process and supply of digested pulp to the separator, connected through the vacuum pump and glycol tank with the glycol return circuit to the reactor inlet. The second separator circuit forms a connection through the pump with the column with active carbon and further with the neutralization chamber equipped with the acid injection assembly. The chamber is connected with the neutralization tank and further with the vacuum filter with water supply. Filter has two outlets. One through the vacuum pump to the glycol return to the tank. The other outlet, through the vacuum pump and belt conveyer, is connected with the dryer of the finished product in the form of a terephthalic acid. The dryer has a water drain to the filtering tank, which is connected with the evaporator, from which glycol is obtained and returned to the extruder and the waste product in the form of sodium sulfate.

In accordance with the invention, the installation for continuous polyethylene terephthalate PET waste treatment includes a dispenser for continuous feeding of crushed polyethylene terephthalate PET waste and forms a three-step production line containing the first step of digestion, transesterification with high-boiling alcohols and de-coloring, the second step of transesterification with low-boiling alcohols and separation of terephthalic acid esters and the third step of hydrolysis, distillation of low- boiling alcohol and production of terephthalic acid. Each step includes at least two flow reactors with heating and a mixer, connected with each other in a cascade, and the intermediate products return circuits to the previous steps. The first step containing a sequence of reactors has a supply of high- boiling alcohols with addition of phenol from the tank to the first reactor. The outlet of the last reactor is connected through a group of filters with the first of the at least two evaporation tanks connected with each other in a cascade. The last evaporation tank through the de-coloring tank, is connected with the second step of the installation which includes a sequence of reactors with the supply of low-boiling alcohols to the first of those reactors. The outlet of the last reactor of the second step of installation is connected through a sedimentation tank with the third step of the installation containing a sequence of reactors connected in a cascade. The outlet of the last reactor of that cascade is connected with the filter included in the return circuit of the aqueous sulfur acid solution to the first of those reactors. In turn, the filter is connected with the terephthalic acid washing tank and further, with the other filter, included in the water return circuit to the first reactor of this step of installation. The filter outlet is connected with dryer from which a finished product is obtained in the form of a dry terephthalic acid PTA powder.

The first step of the installation includes a return circuit of ethylene glycol as the intermediate product from the evaporation tanks through the vacuum pump and cooler to the glycol storage tank and has inlet to the first reactor of the first step. The glycol storage tank is equipped with the outlet of the excessive ethylene glycol as the second final product.

The second step of the installation includes a return circuit of high-boiling alcohols as the intermediate product from the sedimentation tank to the high-boiling alcohols storage tank from which next it is distributed to the inlet of the first evaporation tank and to the inlet of the first reactor of the first step of the installation.

The third step of the installation includes a return circuit of low-boiling alcohols as the intermediate product from the reactors through the cooler to the low-boiling alcohols storage tank and to the inlet of the first reactor of the second step of the installation. In accordance with a variant of the invention, the installation for continuous treatment of polyethylene terephthalate PET waste includes a dispenser for continuous feeding of crushed polyethylene terephthalate PET waste and forms a three-step production line including the first step of digestion, transesterification with high-boiling alcohols and de-coloring, the second step of transesterification with low-boiling alcohols and separation of the terephthalic acid esters and the third step of hydrolysis, distillation of low- boiling alcohol and production of terephthalic acid and return circuits of intermediate products to the previous steps. The first and the second step of the installation include at least one pipe reactor with heating and favourably with static mixers. The third step includes at least two flow reactors with heating and a mixer, connected with each other in a cascade. The third step including favourably two pipe reactors has a supply of high-boiling alcohols with addition of phenol from the tank to the inlet of the first pipe reactor. In turn, the outlet of the second pipe reactor is connected through the group of filters with the first reactor with at least two evaporation tanks connected with each other in a cascade. The last evaporation tank is connected through the de-coloring tank with the second step of the installation which includes favourably four pipe reactors with supply of low-boiling alcohols to the inlet of the first pipe reactor. The outlet of the last reactor of the second step of installation is connected through the sedimentation tank with the third step, including a sequence of reactors connected in a cascade. The outlet of the last reactor of that cascade is connected with the filter included in the return circuit of the aqueous sulfur acid solution to the first reactor out of those reactors. In turn, the filter is connected with the terephthalic acid washing tank and further with the other filter, included in the return circuit of water to the first reactor of that step of the installation. The filter outlet is connected with dryer, from which finished product is obtained consisting of dry terephthalic acid PTA powder. The first step includes a return circuit of ethylene glycol as the intermediate product from the evaporation tanks through the vacuum pump and cooler to the glycol storage tank and to the inlet of the first pipe reactor of the first step. The glycol storage tank is equipped with the outlet of the excess ethylene glycol as the second final product.

The second step of the installation includes a return circuit of high-boiling alcohols as the intermediate product from the sedimentation tank to the high-boiling alcohols storage tank from which next it is distributed to the inlet of the first evaporation tank and to the inlet of the first pipe reactor of the first step of the installation.

The third step includes a return circuit of low-boiling alcohols as the intermediate product from the reactors connected in a cascade through the cooler to the low-boiling alcohols storage tank and to the inlet of the first pipe reactor of the second step of the installation.

Crushed PET waste in the form of flakes mixed with the alkaline catalyst are fed in a continuous manner with the help of the dispenser to the reactor of the first step of the installation. A stream of ethylene glycol is supplied in a continuous manner to the above mentioned reactor from the storage tank. Besides, a mixture of high-boiling alcohols is conducted from the high- boiling alcohols storage tank . In reactors with mixers the process of continuous digestion of PET flakes is going on and the solution from the outlet of the last reactor is led to the group of filters where mechanical contaminants present in the digested PET waste are trapped, such as for example: paper, glass and other plastics. Filters are connected with each other through an automatic valve switching system in such a way that when one filter works, the other is cleaned from contaminants. The frequency of switching filters depends on the degree of contamination of the raw material being processed. The clarified PET solution is conducted from filters in a continuous stream to the first of the heated evaporation tanks, connected in a cascade, working under the pressure of 0,05 atm. From those tanks the ethylene glycol is distilled, the vapours of which are condensed in the cooler and accumulated in the glycol storage tank. The excess ethylene glycol is collected from the tank as the second final product. At the outlet from the cascade of the evaporation tanks the intermediate product is obtained delivered to the de-coloring tank. De-colored intermediate product is supplied to the first heated reactor of the second step of installation. To that reactor also a stream of low-boiling alcohols is led. In the reactors the transesterification process with low-boiling alcohols takes place. The stream of the double-phase mixture from the last reactor is led to the sedimentation tank where gravitational separation of both phases is carried out. High- boiling alcohols accumulated in the lower phase, are conducted to the high- boiling alcohols tank. The upper phase consisting of a mixture of the terephthalic acid ester with low-boiling alcohol and the excessive low- boiling alcohol are directed to the inlet of the reactor of the third step installation where the hydrolysis process takes place. In the reactors the excessive low-boiling alcohol is evaporated and the alcohol from the hydrolyzing terephthalic acid ester. The total stream of vapours of that alcohol is directed to the cooler and further to the low-boiling alcohol storage tank. From the last reactor the terephthalic acid suspension in a diluted sulfuric acid is supplied in a continuous manner to the filter where the diluted sulfuric acid is separated and returned to the first reactor of that step. The obtained filtration sediment of the terephthalic acid is fed to the washing tank where it is washed by a continuous stream of water. Water from washing that sediment is taken to the second filter and returned to the first reactor, and its excess is led outside. Washed filtration sediment of the terephthalic acid is conducted to a dryer from which a dry finished product is obtained in the form of a terephthalic acid powder PTA.

An essential advantage of this invention is the possibility to carry out PET waste treatment according to the principles of a continuous production in distinction to a commonly applied periodical production. The installation enables supply of PET waste at a fixed speed at the inlet, and the consecutive steps of the installation guarantee flow of the stream of the processed polymer pulp and intermediate products. The continuous process of PET treatment with the use of the installation allows to work in a multi- shift system for the whole day. In the installation reactors with a simple construction, working in the conditions of ordinary pressure, are applied. The installation according to the invention is very important for the ecological waste management enabling use of PET waste, most frequently in the form of bottles left after beverages and packagings of household products. Owing to that, the quantity of the waste thrown into the municipal dump, where the period of retention and disintegration is several dozen or even a few hundred years, is limited.

Besides, considerable economic profits are obtained from the use of high- boiling alcohol, low-boiling alcohol and ethylene glycol in a closed circuit.

The invention is explained closer in two examples of execution and on the drawing where Figure 1 presents the installation for continuous treatment of PET waste in a general schedule, and Fig.2 - the variant of the installation for the continuous treatment of PET waste in a general schedule.

Example 1 The installation for continuous treatment of polyethylene terephthalate PET waste, presented in Fig. 1, constitutes a three-step production line including flow reactors connected in a cascade. The installation with the capacity of 1000 kg of polyethylene terephthalate PET waste during 8 hours is fed continuously from the dispenser D in a stream of 125 kg/hour of the mixture of crushed PET waste with the sodium hydroxide granulate NaOH. The dispenser D is connected with the storage silos, supplemented from time to time, containing 3 ton of crushed PET waste in the form of flakes mixed with 40 kg of sodium hydroxide granulate NaOH. The mixture stream is let to the first reactor Rj from three identical reactors Ri, R ₂ , R3 connected in a cascade, constituting the first step of the installation. Each of the reactors Ri, R ₂ , R3 has the capacity of 0.25m and is equipped with a mixer and the heating jacket. A stream of ethylene glycol is led to reactor Ri, also in a continuous way, in the quantity of 110 kg/hour from the tank Zi which together with the cooler CI and vacuum pump V constitutes return circuit 1 of ethylene glycol as the intermediate product. Besides , a mixture of high- boiling alcohols is let in, in the quantity of 120 kg/ hour, taken from the tank Z3 included in the return circuit 2 of those alcohols.

In the cascade of reactors Ri, R2, R3, the process of PET flakes digestion and transesterification takes place, and the solution which leaves reactor R3 is fed to the group of filters Fj, F ₂ where all mechanical contaminants contained in the processed PET waste, such as paper, glass and other plastics, are trapped. Filters F _l5 F ₂ are connected with each other through an automatic system of valves switching in such a way that when one of the filters Fi works the other filter F ₂ is cleaned from the contaminants The frequency of switching between the filters Fi, F ₂ depends on the degree of contamination of the processed raw material. Clarified PET solution from filters Fi, F ₂ flows in a continuous stream in the quantity of 355 kg hour to the evaporation tank Pi. To that tank also a stream of high-boiling alcohols is conducted in the quantity of 165 kg/hour, taken from the tank Z3, included in the return circuit 2 of those alcohols from the sedimentation tank N. The tank Pi has the volume of 0.4 m ³ and is the first of the three identical evaporation tanks Pi, P ₂ , P3 connected in a cascade. Evaporation tanks Pi, P ₂ , P3 are equipped with heating jackets and work under the pressure of 0.05 atm. From tanks Pi, P ₂ , P3, ethylene glycol is distilled , the vapours of which in the quantity of 150 kg/hour are condensed in cooler Ci and accumulated in glycol storage tank Zi. The excess ethylene glycol is taken from tank Zi through the outlet W _y as an additional final product beside the terephthalic acid PTA. At the outlet from the cascade of evaporation tanks Pi, P ₂ , P3 an intermediate product is obtained in the quantity of 370 kg/hour which is transferred to de-coloring tank B. The obtained product is fed to reactor R4 for transesterification. To that reactor R4 also a stream of propyl alcohol is introduced in the quantity o 225 kg hour from tank Z ₂ . Reactor R4 for transesterification has the volume of 1.0m ³ and is the first of the three identical reactors connected in a cascade R4, R ₅ , Rg. Reactors R4, R5, R^ have heating jackets and mixers and in that cascade of reactors R4, R5, Re the transesterification process with low-boiling alcohols is going on. The stream of a double-phase mixture in the quantity of 595 kg hour from the last reactor R6 of the second step of the installation is conducted to the sedimentation tank N with the volume of 1.5m ³ , where a gravitational separation of both phases takes place. High-boiling alcohols accumulated in the bottom phase are conducted to high-boiling tank Z3. The upper phase consisting of a mixture of the terephthalic acid ester with low-boiling alcohol and the excess of low-boiling alcohol are directed to the first hydrolysis reactor R ₇ of the third step of the installation. To that reactor R ₇ , also in a continuous manner, a stream of diluted aqueous sulfuric acid solution is let in in the quantity of 625kg/hour, collected from filter F3 placed behind the cascade of three identical hydrolyzation reactors R , Rs, R9 with the volume of 2m ³ each. In reactors R ₇ , Rg, R9 the excess low- boiling alcohol and alcohol from the hydrolyzing terephthalic acid ester is evaporated. The total stream of vapours of that alcohol in the quantity of 225 kg/hour is directed through a low-boiling alcohols return circuit 3 through the cooler C ₂ to storage tank Z ₂ . From the last reactor R ₉ of that cascade the suspension of terephthalic acid in a diluted sulfuric acid in the quantity of 710 kg/hour is fed in a continuous manner to drum filter F3 where a diluted sulfuric acid is separated in the quantity of 538 kg/hour and returned through circuit 4 to the first reactor R ₇ of that cascade. Filtration sediment PTA collected from filter F3 in the quantity of 149 kg/hour is fed to washing tank M where it is washed with a continuous water stream in the quantity of 87 kg/hour. The water from washing of that sediment is drained to the second filter F and returned by circuit 5 to the first reactor R ₇ of that cascade, and its excess is conducted outside. Washed filtration sediment of terephthalic acid PTA is introduced to dryer S in the quantity of 149 kg/hour from which a finished product is obtained consisting of dry terephthalic acid PTA powder in the quantity of 108 kg hour.

Example 2

The variant of the installation for the continuous treatment of polyethylene terephthalate PET waste is presented in Fig.2 and constitutes a three-step production line in which pipe reactors were applied in the first and second steps. The installation has the capacity of 800 kg of polyethylene terephthalate PET waste during 8 hours and is fed with the mixture of crushed PET waste with sodium hydroxide NaOH granulate, in a continuous way from dispenser D in a stream of 100 kg hour. Dispenser D is connected with the storage silos, supplemented from time to time, containing 2 tons of crushed PET waste in the form of flakes mixed with 27kg of sodium hydroxide granulate NaOH. The mixture stream is let to the beginning of the first of the two identical pipe reactors connected in a series Rio, Rn, with the total volume of 0.60 m ³ . Both reactors Rio, Rn have internal pivotal mixers and are equipped with external heating jackets. In the beginning of reactor Rio a stream of ethylene glycol is introduced, also in a continuous manner, in the quantity of 88 kg/hour from tank Zi which together with the cooler Ci and vacuum pump V constitutes return circuit 1 of ethylene glycol as an intermediate product. Besides, a mixture of high-boiling alcohols is introduced to reactor Ri ₀ in the quantity of 96 kg/hour taken from tank Z ₃ included in the return circuit 2 of those alcohols. In the system of pipe reactors Rio, Rii the process of PET flakes digestion and transesterification takes place, and the solution which leaves reactor R is fed to the group of filters Fi, F ₂ where all mechanical contaminants, contained in the processed PET waste, such as paper, glass and other plastics, are trapped. Filters Fi, F ₂ are connected with each other through an automatic valves switching system in such a way that when one of the filters Fi works, the other filter F ₂ is cleaned from the contaminants. The frequency of switching between the filters Fi, F ₂ depends on the degree of contamination of the processed raw material. Clarified PET solution from filters Fi, F ₂ flows in a continuous stream in the quantity of 284 kg/hour to the evaporation tank Pi. To that tank also a stream of high-boiling alcohols is introduced in the quantity of 132 kg/hour taken from high-boiling alcohols tank Z3 included in the return circuit 2 of those alcohols as the intermediate product from the sedimentation tank N. Tank Pi has the volume of 0.4m and it is the first from the three identical evaporation tanks Pi, P ₂ , P3 connected in a cascade. Evaporation tanks Pi, P ₂ , P3 are equipped with heating jackets and work under the pressure of 0.05 atm. Ethylene glycol is distilled from tanks Pi, P ₂ , P ₃ , the vapours of which, in the quantity of 120 kg/ hour, are condensed in cooler Ci and accumulated in glycol storage tank Zi. The excess ethylene glycol is collected from tank Zi through outlet W _y as an additional final product apart from the terephthalic acid PTA. At the outlet from the cascade of evaporation tanks Pi, P ₂ , P3 an intermediate product is obtained in the quantity of 296 kg/hour which is transferred to the de-coloring tank B. The obtained product is introduced to the beginning of the first reactor R ₁₂ out of the four identical pipe reactors Ri ₂ , R13, R1 , R ₁₅ connected in a series with the total volume of 1.0 m Reactors R12, R13, R14, Ris for transesterification with low-boiling alcohols have internal pivotal mixers and are equipped with internal heating jackets. To the first reactor Ri ₂ also a stream of propyl alcohol is introduced in the quantity of 180 kg/hour from tank Z ₂ . The stream of a double-phase mixture in the quantity of 476 kg/hour from the last reactor R15, of the second step of the installation is introduced to the sedimentation tank N with the volume of 1.5m ³ , where a gravitational separation of both phases takes place. High-boiling alcohols accumulated in the bottom phase are conducted to high-boiling alcohols tank Z3. The upper phase consisting of a mixture of the terephthalic acid ester with low-boiling alcohol and the excessive low-boiling alcohol are directed to the first hydrolysis reactor R ₇ of the third step of the installation. To that reactor R also a stream of diluted aqueous sulfuric acid is introduced in a continuous manner in the quantity of 500 kg/hour collected from filter F3 placed behind the cascade of three identical hydrolysis reactors R ₇ , Re, R9 with the volume of 2 m each. In the reactors R ₇ , Re, R ₉ the excessive low-boiling alcohol and alcohol from the hydrolyzing terephthalic acid ester is evaporated. The total stream of that alcohol vapours in the quantity of 180 kg/hour is directed by low-boiling alcohol return circuit 3 through cooler C ₂ to storage tank Z ₂ . From the last reactor R9 of that cascade the suspension of terephthalic acid in diluted sulfuric acid in the quantity of 680 kg/hour is fed in a continuous manner to drum filter F3 where the diluted sulfuric acid is separated in the quantity of 430 kg/hour and returned by circuit 4 to the first reactor R ₇ of that cascade. The filtration sediment of terephthalic acid PTA collected from filter F3 in the quantity of 119 kg/hour is fed to washing tank M where it is washed with a continuous stream of water in the quantity of 70 kg/hour. Water from washing of that sediment is drained to the second filter F4 and returned by circuit 5 to the first reactor R ₇ of that cascade, and its excess is let outside. Washed filtration sediment of PTA is introduced in the quantity of 119 kg/hour to dryer S from which 86 kg/hour of finished product is obtained in the form of a dry terephthalic acid PTA powder.