Process for the preparation of low molecular weight aromatic compounds such as benzene, toluene, and xylenes (BTX) from plastics

Abstract

The present invention relates to a novel process for the preparation of low molecular weight aromatic compounds such as benzene, toluene, and xylenes (BTX) from plastics. Provided is a thermo-catalytic pyrolysis process for the preparation of aromatic compounds from a feed stream comprising plastic, comprising the steps of: a) subjecting a feed stream comprising a plastic to a pyrolysis treatment at a pyrolysis temperature in the range of 600-1000° C. to produce pyrolysis vapors; b) optionally cooling the pyrolysis vapors to a temperature that is below the pyrolysis temperature; e) contacting the vaporous phase with an aromatization catalyst at an aromatization temperature in the range of 450 700° C., which aromatization temperature is at least 50° C. lower than the pyrolysis temperature, in a catalytic conversion step to yield a conversion product comprising aromatic compounds; and d) optionally recovering the aromatic compounds from the conversion product.

Claims

1. A two-step thermo-catalytic pyrolysis process for the preparation of low molecular weight monocyclic aromatic compounds from a feed stream comprising plastic, comprising the steps of: a) subjecting a feed stream comprising a plastic to a pyrolysis treatment at a pyrolysis temperature (T.sub.pyr) in the range of 600-1000° C. to produce pyrolysis vapors; b) optionally actively cooling the pyrolysis vapors to a temperature that is below the pyrolysis temperature; and c) contacting the pyrolysis vapors with an aromatization catalyst at an aromatization temperature (T.sub.arom) in the range of 450-700° C., which aromatization temperature is at least 50° C. lower than the pyrolysis temperature, in a catalytic conversion step to yield a conversion product comprising low molecular weight aromatic compounds; and d) optionally recovering the low molecular weight monocyclic aromatic compounds from the conversion product.

2. Process according to claim 1 wherein T.sub.pyr is in the range of 650 to 950° C., preferably in the range of 700 to 850° C.

3. Process according to claim 1 or 2, wherein in step a) the residence time in the pyrolysis reactor is less than 2 minutes, preferably less than 1 minute, more preferably less than 30 seconds.

4. Process according to any one of claims 1-3, wherein T.sub.arom is in the range of 500 to 700° C., preferably 500 to 650° C., more preferably 500 to 600° C.

5. Process according to any one of claims 1-4, wherein T.sub.arom is at least 80° C. lower, preferably at least 100° C. lower, than T.sub.pyr.

6. Process according to any one of claims 1-5, wherein T.sub.arom is up 200° C. lower, preferably up to 175° C. lower, than T.sub.pyr.

7. Process according to any one of the preceding claims, wherein T.sub.pyr is in the range of 650-850° C. and T.sub.arom is in the range of 500-600° C.

8. Process according to any one of the preceding claims, wherein in step c) the residence tune in the aromatization reactor is less than 2 minutes, preferably less than 1 minute, more preferably less than 30 seconds.

9. Process according to any one of the preceding claims, wherein step d) comprises recovering benzene, toluene, and xylenes (BTX) from the conversion product.

10. Process according to any one of the preceding claims, wherein the pyrolysis step a) and the catalytic conversion step c) take place in two different reactors.

11. Process according to any one of the preceding claims, wherein the aromatization catalyst is selected from the group consisting of ZSM-5, ZSM-11, IST-35, ZSM-23, ferrierite, zeolite beta, zeolite Y, zeolite X, mordenite, zeolite A, IM-5, SSZ-20, SSZ-55, MCM-22, TNU-9, metal treated, exchanged or impregnated catalyst and combinations thereof.

12. Process according to any one of the preceding claims, wherein the feed stream comprises synthetic or semi-synthetic polymers or mixtures thereof, including polyolefines, aromatic polymers, fibre enforced composite materials, multi-layered plastics, mixed plastics waste polyamides, and/or recycling refuses, or a liquid stream derived from the pyrolysis of any of the preceding materials.

13. Process according to any one of the preceding claims, wherein the feed stream comprises or consists of one or more of polypropylene (PP), polyethylene (PE), Polybutylene terephthalate (PBT) and Polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polystyrene (PS) and poly amide (PA).

14. Process according to any one of the preceding claims, wherein step b) comprises cooling the pyrolysis vapors with the aid of a heat exchanger.

15. Process according to any one of the preceding claims, wherein step c) is performed in a vapour upgrading reactor comprising a heat carrier.

16. Process according to any one of the preceding claims, wherein the pyrolysis treatment of step a) is performed in the presence of a cracking catalyst to yield pyrolysis vapors and a coke-laden cracking catalyst, followed by separating the pyrolysis vapors from the coke-laden cracking catalyst.

17. Process according to claim 16, wherein the cracking catalyst is selected from the group consisting of acidic or alkaline inorganic materials, and amorphous or crystalline silica-alumina-comprising materials.

Description

LEGEND TO THE FIGURES

[0095] FIG. 1 provides a schematic diagram of a catalytic pyrolysis process according to the invention.

[0096] FIG. 2 provides a schematic diagram of a catalytic pyrolysis process according to one embodiment of the invention.

[0097] FIG. 3 displays the effect of the T.sub.pyr (500, 700 or 800° C.) for pyrolysis in the ex situ pyrolysis of the plastics high density polyethylene (HDPE), polypropylene (PP), mixture of polybutylene terephthalate/polyethylene terephthalate (PBT-PET), Acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polyethylene-polypropylene mixture (PP-PE mix), multi-layered plastic bags (MPB).

[0098] FIG. 4 displays the effect of the T.sub.pyr (600, 650, 700, 750, 800, 850 or 900° C.) for pyrolysis in the ex situ pyrolysis of the plastic polypropylene, whereby T.sub.arom is constant at 550° C.

[0099] FIG. 5 displays the effect of the difference between T.sub.pyr (600, 650, 700, 750, 800, 850 or 900° C.) and T.sub.arom (450, 500, 550, 600, 650, 700° C.) on the xylenes yield.

EXPERIMENTAL SECTION

Materials and Methods

[0100] The experiments were performed on a Tandem μ-Reactor from Frontier Lab (Rx-3050TR) equipped with a single shot sampler (PY1-1040). The temperatures of both reactors and interfaces were controlled separately, allowing different reaction conditions for the pyrolysis (first reactor) and aromatization unit (second reactor). A carrier gas inlet was connected on the top of the first reactor, providing carrier gas flow through the reactors into the GC-MS. The entire system was attached by a docking station on top of the GC-MS and connected by an injection needle through a rubber septum.

[0101] Before experiments, approximately 80 mg of a H-ZSM-5 (23) catalyst (size 212-425 μM) was put in a quartz liner inside the second reactor. Thereafter, the system was pressurized to 150 kPa with an inert carrier gas (helium) to check for leakage. After the leak check, the pressure was set back to 50 kPa using a helium flow rate of 50 mL/min and the system was heated to the desired T.sub.pyr and T.sub.arom.

[0102] In experiment A: reactor 1 (T.sub.pyr): 500° C., 700° C. or 800° C., reactor 2 (T.sub.arom); 550° C. and for both interfaces: 300° C.

[0103] In experiment B: reactor 1 (T.sub.pyr): 600, 650, 700, 750, 800, 850 or 900° C., reactor 2 (T.sub.arom): 550° C. and for both interfaces: 300° C.

[0104] In experiment C: reactor 1 (T.sub.pyr): 600, 650, 700, 750, 800, 850 or 900° C. reactor 2 (T.sub.arom): 450, 500, 550, 600, 650, 700° C. and for both interfaces: 300° C.

[0105] The residence time in each of the reactors was as follows: reactor 1 is estimated to be less than 3 seconds and reactor 2 is estimated to be 0.09 seconds.

[0106] A thin stainless steel cup was filled with a feed stream comprising different types of plastic(s) and attached to the sample injector, which hangs slightly above the first reactor. The system was closed and flushed for 3 min with helium gas. After flushing, the cup was dropped into the first reactor to start the pyrolysis reaction. The vapour products travel through the ZSM-5 (23) catalyst bed before entering the GC-MS.

[0107] The total yield of BTX (as well as the contribution of individual compounds benzene, toluene, m,p-xylene and o-xylene) obtained in experiment A is presented in FIG. 3 as the average of duplicate measurements and expressed in wt % based on the organic fraction present in the plastics. It clearly shows that, the yield of BTX significantly increases by increasing the temperature for pyrolysis from the conventional 500° C. to higher values such as 700 or 800° C.

[0108] The total yield of BTX (as well as the contribution of individual compounds benzene, toluene, and m,p,o-xylene) obtained in experiment B is presented in FIG. 4 and is expressed in wt % based on the organic fraction present in the plastics. It clearly shows that the yield of BTX, benzene and toluene significantly increases by increasing the temperature for pyrolysis from the conventional 600° C. to higher values such as 900° C. It also shows that the yield of xylenes initially increases increasing the temperature for pyrolysis from 600° C. to 700° C., but decreases increasing the temperature for pyrolysis above 800° C.

[0109] FIG. 4 shows that the yields of BTX, benzene, toluene, and xylenes significantly increase as T.sub.pyr increases, while keeping T.sub.arom constant at 550° C. Moreover, it indicates that, for xylenes, the T.sub.pyr should not be above 800° C.

[0110] The total yield of m,p,o-xylene (xylenes) obtained in experiment C is presented in FIG. 5 and is expressed in wt % based on the organic fraction present in the plastics. It clearly shows that the yield of xylenes increases by increasing the temperature difference between T.sub.pyr and T.sub.arom from zero to 150° C.

[0111] FIG. 5 depicts the xylenes yields from polypropylene catalytic pyrolysis, as a function of T1 (T.sub.pyr) minus T2 (T.sub.arom), with T1 in the range of 600 to 900° C. and T2 in the range of 450 to 700° C. The data shows that a ΔT.sub.pyrT.sub.arom, of at least 50° C. results in a significant increase in the xylene yield. A further increase in ΔT.sub.pyrT.sub.arom up to 150° C. results in even higher xylenes yields, after which a flattening of the curve is observed.