Process for the preparation of a C.SUB.20 .to C.SUB.60 .wax from the selective thermal decomposition of plastic polyolefin polymer

Abstract

The present invention relates to a process for the preparation of a C.sub.20 to C.sub.60 wax from the thermal decomposition of a particular plastic polyolefin polymer blend. The present invention provides a vacuum pyrolysis process for preparing a C.sub.20 to C.sub.60 wax from the thermal decomposition of plastic polyolefin polymer, the method comprising the steps of: i) introducing plastic polyolefin polymer into a thermal reaction zone of a vacuum pyrolysis reactor; ii) heating the plastic polyolefin polymer at sub-atmospheric pressure, wherein the temperature in the thermal reaction zone of the reactor is from 500° C. to 750° C., to induce thermal decomposition of the plastic polyolefin polymer and to form a thermal decomposition product effluent which comprises a major portion by weight of a C.sub.20 to C.sub.60 wax fraction; and iii) condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor;
wherein the plastic polyolefin polymer comprises polyethylene and polypropylene in a polyethylene to polypropylene weight ratio of from 60:40 to 90:10.

Claims

1. A vacuum pyrolysis process for preparing a C.sub.20 to C.sub.60 wax from the thermal decomposition of plastic polyolefin polymer, the method comprising the steps of: i) introducing a feed comprising plastic polyolefin polymer into a thermal reaction zone of a vacuum pyrolysis reactor; ii) heating the plastic polyolefin polymer at a pressure of less than 50 kPa, wherein the temperature in the thermal reaction zone of the reactor is from 500° C. to 750° C., to induce thermal decomposition of the plastic polyolefin polymer and to form a thermal decomposition product effluent which comprises a major portion by weight of a C.sub.20 to C.sub.60 wax fraction; and iii) condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor, wherein the plastic polyolefin polymer comprises polyethylene and polypropylene in a polyethylene to polypropylene weight ratio of from 60:40 to 90:10, and wherein the feed to the vacuum pyrolysis reactor comprises less than 1.0 wt. % of halogenated polymers.

2. A process according to claim 1, wherein the plastic polyolefin polymer is introduced into the pyrolysis reactor by means of an extruder.

3. A process according to claim 2, wherein the process includes at least one member of a group consisting of: the extruder is heated, and the plastic polyolefin polymer fed to the extruder is in flaked, pelletized, or granular form.

4. A process according to claim 1, wherein the plastic polyolefin polymer is in molten form when introduced into the thermal decomposition zone of the pyrolysis reactor.

5. A process according to claim 1, wherein the temperature in the thermal reaction zone of the vacuum pyrolysis reactor is from 500° C. to 650° C.

6. A process according to claim 1, wherein the temperature in the thermal reaction zone of the reactor is from 525 to 650° C.

7. A process according to claim 1, wherein the pressure in the thermal reaction zone of the vacuum pyrolysis reactor is less than 30 kPa absolute.

8. A process according to claim 1, wherein the plastic polyolefin polymer comprises or consists essentially of used or waste plastic.

9. A process according to claim 1, wherein an optical sorting process is utilised to obtain plastic polyolefin polymer of the desired composition and the optical sorting process is selected from near-Infrared (NIR) absorption spectroscopy, camera color sorters, and X-ray fluorescence.

10. A process according to claim 1, wherein the plastic polyolefin polymer comprises high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low density polyethylene (LLDPE) or a mixture thereof.

11. A process according to claim 1, wherein the weight ratio of polyethylene to polypropylene in the plastic polyolefin polymer is from 65:35 to 85:15.

12. A process according to claim 1, wherein the vapour component of the thermal decomposition product effluent is condensed in step iii) in a multistage condensation comprising a plurality of condensation stages connected in series.

13. A process according to claim 12, wherein the multistage condensation includes only two stages connected in series, or wherein the multistage condensation corresponds to a fractional condensation and includes at least three condensation stages connected in series.

14. A process according to claim 12, wherein the first condensation stage is operated as a direct liquid quench.

15. A process according to claim 1, wherein the majority of the C.sub.20 to C.sub.60 wax fraction is collected in a collection vessel of the first condensation stage of the series.

16. A process according to claim 1, wherein the process further comprises a step iv) of fractionating the thermal decomposition product effluent to obtain a C.sub.20 to C.sub.60 wax fraction substantially free of lighter and/or heavier thermal decomposition products.

17. A process according to claim 16, wherein a lighter boiling point fraction separated from the C.sub.20 to C.sub.60 wax fraction in step iv) is used as a source of fuel for heating the pyrolysis reactor.

18. A process according to claim 1, wherein the process includes at least one member of a group consisting of: the C.sub.20 to C.sub.60 wax fraction comprises a mixture of paraffins and olefins, and the C.sub.20 to C.sub.60 wax fraction comprises from 20 wt. % to 80 wt. % olefins.

19. A process according to claim 1, wherein the process includes at least one member of a group consisting of: the C.sub.20 to C.sub.60 wax fraction comprises at least 50 wt. % of a C.sub.25 to C.sub.55 wax sub-fraction, the C.sub.20 to C.sub.60 wax fraction comprises at least 50 wt. % of a C.sub.25 to C.sub.50 wax sub-fraction, the C.sub.20 to C.sub.60 wax fraction comprises at least 50 wt. % of a C.sub.30 to C.sub.45 wax sub-fraction, the C.sub.20 to C.sub.60 wax fraction comprises at least 50 wt. % of a C.sub.30 to C.sub.40 wax sub-fraction, and the C.sub.20 to C.sub.60 wax fraction comprises at least 50 wt. % of a C.sub.30 to C.sub.35 wax sub-fraction.

20. A process according to claim 1, wherein the pyrolysis reaction is conducted in the absence of a catalyst.

Description

(1) The present invention will now be illustrated by way of the following examples and with reference to the following figures, wherein:

(2) FIG. 1: shows a schematic diagram of a vacuum pyrolysis process for producing a C.sub.20 to C.sub.60 wax as part of the process of the present invention including a multistage condensation according to preferred embodiments;

(3) FIG. 2: shows a schematic diagram showing fractionation and downstream processing of the C.sub.20 to C.sub.60 wax to produce a lubricant base stock;

(4) FIG. 3: shows a plot illustrating the effect of pressure in the pyrolysis reactor on the thermal decomposition product distribution from pyrolysis of polypropylene in terms of boiling point of constituents;

(5) FIG. 4: shows a bar graph illustrating the effect of pressure in the pyrolysis reactor in the pyrolysis of polypropylene on the C.sub.20 to C.sub.60 fraction yield;

(6) FIG. 5: shows a plot illustrating the effect of pressure in the pyrolysis reactor on the thermal decomposition product distribution from pyrolysis of polyethylene in terms of boiling point of constituents;

(7) FIG. 6: shows a bar graph illustrating the effect of pressure in the pyrolysis reactor in the pyrolysis of polyethylene on the C.sub.20 to C.sub.60 fraction yield;

(8) FIG. 7: shows a plot illustrating the effect of pressure in the pyrolysis reactor on the thermal decomposition product distribution from pyrolysis of a polyethylene/polypropylene blend in terms of boiling point of constituents;

(9) FIG. 8: shows a bar graph illustrating the effect of pressure in the pyrolysis reactor in the pyrolysis of a polyethylene/polypropylene blend on the C.sub.20 to C.sub.60 fraction yield;

(10) FIG. 9: shows a plot illustrating the effect of temperature in the pyrolysis reactor on the thermal decomposition product distribution from pyrolysis of polypropylene in terms of boiling point of constituents;

(11) FIG. 10: shows a bar graph illustrating the effect of temperature in the pyrolysis reactor in the pyrolysis of polypropylene on the C.sub.20 to C.sub.60 fraction yield;

(12) FIG. 11: shows a plot illustrating the effect of temperature in the pyrolysis reactor on the thermal decomposition product distribution from pyrolysis of polyethylene in terms of boiling point of constituents; and

(13) FIG. 12: shows a bar graph illustrating the effect of pressure in the pyrolysis reactor in the pyrolysis of polyethylene on the C.sub.20 to C.sub.60 fraction yield.

(14) With reference to FIG. 1, a plastic polyolefin polymer having a weight ratio of polyethylene to polypropylene of from 60:40 to 90:10 is supplied to extruder (E1) from a hopper (not shown). The extruder (E1), which in this instance is heated, produces a molten stream of plastic polyolefin polymer (101) which is fed to a vacuum pyrolysis reactor (R1) and the molten feed enters the thermal decomposition zone of the reactor (R1). The reactor (R1) is operated at sub-atmospheric conditions and at a temperature to give rise to thermal decomposition of the molten plastic polyolefin polymer, thereby producing pyrolysis vapours.

(15) The configuration shown in FIG. 1 includes three condensation stages (C1, C2, C3) exemplifying a fractional condensation process according to some of the preferred embodiments. As will be appreciated, the multistage condensation may be operated with only two condensation stages, or more than three condensation stages, if desired. These pyrolysis vapours produced in the reactor, which may be in the form of an aerosol in which liquid thermal decomposition products are entrained therein, rapidly exit the pyrolysis reactor via an outlet, and the stream of pyrolysis vapours (102) is fed to a first condensation stage (C1). The first condensation stage (C1) is preferably cooled by means of a circulating liquid coolant, for example water. At least partial condensation of pyrolysis vapours occurs in the first condensation stage (C1), thereby producing an amount of liquid condensate, in addition to any liquid thermal decomposition product already present. First condensation stage (C1) includes a collection vessel to hold liquid condensate and liquid thermal decomposition product such that substantially only remaining pyrolysis vapours are fed to the second condensation stage (C2) in stream (103). The condensed product may be extracted from the collection vessel of the first condensation stage as stream (109) via an outlet. Stream (109) comprises the C.sub.20 to C.sub.60 wax fraction, together with any lighter and/or heavier fractions of the condensed thermal decomposition products. A stream (103), containing remaining pyrolysis vapours, exits the first condensation stage (C1) and is fed to a second condensation stage (C2).

(16) Second condensation stage (C2) condenses pyrolysis vapours that have not been condensed in the first condensation stage (C1). The second condensation stage (C2) is preferably cooled by means of a circulating liquid coolant, for example water, which is at a colder temperature than that of the coolant in the first condensation stage (C1). Condensation of at least a portion of the remaining pyrolysis vapours occurs in the second condensation stage (C2), which may comprise a collection vessel for holding the condensate. The condensed product may be extracted from a collection vessel of the second condensation stage as stream (110) via an outlet. Stream (110) primarily comprises lighter fractions of the condensed thermal decomposition products, for example in the naphtha and/or diesel boiling ranges. This light fraction may be conveniently used as fuel source for heating the pyrolysis reactor.

(17) Remaining pyrolysis vapours are carried in stream (104) and fed to the third and final condensation stage (C3) shown in FIG. 1. However, as the skilled person will be aware, additional condensers can also be integrated into the series of the multistage condensation, which may be of use as a means for improved separation of pyrolysis products as part of a fractional condensation. The third condensation stage (C3) is preferably cooled by means of a circulating liquid coolant, for example water or glycol, which is at a colder temperature than that of the coolant in the second condensation stage (C2), or the preceding condensation stage if more than three condensation stages are used. Condensation of residual pyrolysis vapours occurs in the third condensation stage (C3), which may comprise a collection vessel for holding the condensate. The condensed product may be extracted from a collection vessel of the third condensation stage as stream (111) via an outlet. Stream (111) comprises the lightest fractions of the condensed thermal decomposition products. This lightest fraction may also be conveniently used as fuel source for heating the pyrolysis reactor.

(18) Any non-condensable gas that is present is carried in stream (105) and may ultimately come into contact with variable speed vacuum pump (V). However, as the skilled person will appreciate, the presence of any pyrolysis vapours is preferably kept to a minimum and preferably completely removed by means of the final condensation stage. Nevertheless, the vacuum may be configured to accommodate various degrees of non-condensable gases being present in the stream which exits the final condensation stage.

(19) FIG. 2 illustrates a possible downstream processing of the wax product of the invention. In particular, the stream (109) is fed to a fractional distillation column (F) where a stream (202) comprising substantially only a C.sub.20 to C.sub.60 wax fraction is produced together with a waste stream (210), which may be either used as a fuel source for the pyrolysis reactor or heavier fractions of this stream may be recycled to the pyrolysis reaction. Stream (202), comprising substantially no heteroatoms, is fed to a hydroisomerization reactor (HI) which is operated under hydroisomerization conditions in the presence of hydrogen and a bifunctional hydroisomerization catalyst. A stream (203) comprising a lubricant base stock exits the hydroisomerization reactor (HI), is optionally fractionated (not shown) before being fed into solvent dewaxing unit (DW) where any residual wax is removed. Product lubricant base stock (204) is thus obtained having both high viscosity index and low pour point which may be blended to form a commercially usable lubricant composition.

EXAMPLES

(20) Preparation of Plastic Feedstock

(21) Pelletized samples of polyethylene (PE) and polypropylene (PP) were obtained from ADN Materials Ltd. In each of the experiments below, samples of PE, PP or a combination thereof were first pre-melted at 400° C. in a quartz tube reaction vessel under atmospheric pressure for at least 10 minutes to provide a homogeneous molten material.

(22) General Vacuum Pyrolysis Method

(23) 10 g of molten plastic sample was provided in a quartz tube reaction vessel of 24 mm outer diameter and 150 mm length. The reaction vessel was located inside a Carbolite® tubular furnace of 300 mm length and 25 mm diameter with a borosilicate glass still head fitted to the top of the quartz tube, which was in turn connected to a distillation condenser and 200 ml 2-neck round bottomed cooled collector flask. The distillation condenser was temperature controlled by means of circulating oil at a temperature of 80° C. The collector flask was cooled by acetone/dry ice bath (−78° C.) and connected to Buchi Rotavapor® membrane pump equipped with a digital vacuum controller.

(24) Pyrolysis of the molten plastic sample began after applying the vacuum to establish sub-atmospheric pressure and increasing the heating to pyrolysis temperature. Temperature and pressure conditions were thereafter maintained for one hour, after which the pyrolysis reaction was complete and no further effluent from the reaction vessel was observed. A condensate product was collected in the collector flask comprising the wax product.

Example 1

(25) The above general procedure for pyrolysis was followed for a series of four experiments using 10 g samples of the same propylene feedstock. Pyrolysis temperature was set at 550° C. and four different reaction pressures were adopted: i) 10 kPa; ii) 30 kPa; iii) 50 kPa; and iv) 70 kPa.

(26) The collected effluent from the pyrolysis reaction (excluding uncondensable gases) for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on boiling point are represented graphically in FIG. 3 whilst the results showing the product distribution based on carbon number are provided in Table A below and represented graphically in FIG. 4.

(27) TABLE-US-00002 TABLE A Pyrolysis pressure 10 kPa 30 kPa 50 kPa 70 kPa C.sub.20-C.sub.60 (%) 73 57 52 37 <C.sub.20 (%) 27 43 48 63

(28) FIG. 3 generally illustrates the trend that as pressure inside the pyrolysis reactor decreases, the boiling point of the constituents of the thermal decomposition product obtained is increased. The results in Table A (as also illustrated in FIG. 4) are consistent in that they show that the amount of higher boiling point C.sub.20-C.sub.60 fraction is greatest at lowest pressure.

(29) This is believed to relate to lowering of vapour residence time in the pyrolysis reactor as pressure decreases which minimises secondary cracking reactions so that the thermal decomposition product has higher carbon number and therefore higher boiling point.

(30) The results of Example 1 also demonstrate that pressure conditions of the pyrolysis can be adjusted in order to increase the proportion of C.sub.20-C.sub.60 wax fraction that is produced.

Example 2

(31) The series of experiments according to Example 1 was repeated except that samples of the same polyethylene feedstock were used in place of polypropylene.

(32) The collected effluent from the pyrolysis reaction (excluding uncondensable gases) for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on boiling point are represented graphically in FIG. 5 whilst the results showing the product distribution based on carbon number are provided in Table B below and represented graphically in FIG. 6.

(33) TABLE-US-00003 TABLE B Pyrolysis pressure 10 kPa 30 kPa 50 kPa 70 kPa C.sub.20-C.sub.60 (%) 74 57 47 29 <C.sub.20 (%) 26 43 53 71

(34) FIGS. 5 and 6 illustrate the same trends as observed for the polypropylene experiments according to Example 1 and these results also demonstrate that pressure conditions of the pyrolysis can be adjusted in order to increase the proportion of C.sub.20-C.sub.60 wax fraction that is produced.

Example 3

(35) The above general procedure for pyrolysis was followed for a series of three experiments using 10 g samples of the same 50:50 mixture by weight of polyethylene and polypropylene feedstock. Pyrolysis temperature was set at 550° C. and three different reaction pressures were adopted: i) 10 kPa; ii) 30 kPa; and iii) 70 kPa.

(36) The collected effluent from the pyrolysis reaction (excluding uncondensable gases) for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on boiling point are represented graphically in FIG. 7 whilst the results showing the product distribution based on carbon number are provided in Table C below and represented graphically in FIG. 8.

(37) TABLE-US-00004 TABLE C Pyrolysis pressure 10 kPa 30 kPa 70 kPa C.sub.20-C.sub.60 (%) 78 55 28 <C.sub.20 (%) 21 44 71

(38) FIGS. 7 and 8 illustrate the same trends as observed for the polypropylene experiments according to Example 1 and the polyethylene experiments of Example 2 and these results also demonstrate that pressure conditions of the pyrolysis can be adjusted in order to increase the proportion of C.sub.20-C.sub.60 wax fraction that is produced in a mixed blend of plastic feed.

Example 4

(39) The above general procedure for pyrolysis was followed for a series of four experiments using 10 g samples of the same propylene feedstock. Pyrolysis pressure was set at 30 kPa and four different pyrolysis temperatures were adopted: i) 500° C.; ii); 550° C. iii) 600° C.; and iv) 650° C.

(40) The collected effluent from the pyrolysis reaction (excluding uncondensable gases) for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on boiling point are represented graphically in FIG. 9 whilst the results showing the product distribution based on carbon number are provided in Table D below and represented graphically in FIG. 10.

(41) TABLE-US-00005 TABLE D Pyrolysis Temperature 500° C. 550° C. 600° C. 650° C. C.sub.20-C.sub.60 (%) 39 57 63 70 <C.sub.20 (%) 60 42 36 29

(42) FIG. 9 generally illustrates the trend that as temperature inside the pyrolysis reactor increases, the boiling point of the constituents of the thermal decomposition product obtained is increased. The results in Table D (as also illustrated in FIG. 10) are consistent in that they show that the amount of higher boiling point C.sub.20-C.sub.60 fraction is greatest at highest temperature. This is a consequence of an increase in the volatility of higher boiling (higher carbon number) components inside the pyrolysis reactor as the pyrolysis temperature increases coupled with the low vapour residence time in the pyrolysis reactor, which minimises secondary cracking reactions associated with these higher boiling point components.

(43) The results of Example 4 also demonstrate that temperature conditions of the pyrolysis can be adjusted in order to increase the proportion of C.sub.20-C.sub.60 wax fraction that is produced.

Example 5

(44) The series of experiments according to Example 4 was repeated except that samples of the same polyethylene feedstock were used in place of polypropylene.

(45) The collected effluent from the pyrolysis reaction (excluding uncondensable gases) for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on boiling point are represented graphically in FIG. 11 whilst the results showing the product distribution based on carbon number are provided in Table E below and represented graphically in FIG. 12.

(46) TABLE-US-00006 TABLE E Pyrolysis Temperature 500° C. 550° C. 600° C. 650° C. C.sub.20-C.sub.60 (%) 49 53 58 65 <C.sub.20 (%) 50 46 41 34

(47) FIGS. 11 and 12 illustrate the same trends as observed for the polypropylene experiments according to Example 4 and these results also demonstrate that temperature conditions of the pyrolysis can be adjusted in order to increase the proportion of C.sub.20-C.sub.60 wax fraction that is produced.

(48) Comparison of the results in Tables D and E shows that increasing temperature has a greater effect on the proportion of C.sub.20-C.sub.60 wax produced for polypropylene (Table D) than for polyethylene (Table E). In this way, by using a mixed feed comprising polypropylene and polyethylene, an increased benefit may be obtained by operating the pyrolysis at high temperature in terms of yield of the C.sub.20-C.sub.60 fraction which may be obtained, whilst simultaneously retaining the benefits associated with the properties of the wax resulting from the presence of both polypropylene and polyethylene (e.g. in terms of chain branching and viscosity).

(49) General Vacuum Pyrolysis Method for Scaled-Up Reactions

(50) Pelletized samples of polyethylene (PE) and polypropylene (PP) were obtained from ADN Materials Ltd. as for Examples 1 to 5.

(51) The feedstock material is loaded into a pyrolysis reactor vessel which is then sealed. Nitrogen (N.sub.2) gas is used to purge the reactor, before application of a vacuum. Three condensers are set to their respective temperatures. Condenser 1 is cooled using a Julabo with ethylene glycol/water to ca. −10° C. Condenser 2 is cooled using ethylene glycol and dry ice to ca. −15° C. Condenser 3 is cooled using dry ice to −78° C.

(52) The pyrolysis reactor vessel is heated to 275° C., held at this temperature for 1 hour to pre-melt the feedstock before being heated to the desired pyrolysis temperature. The pyrolysis reactor vessel is held at this temperature until the reaction is completed. The reaction was monitored by four temperature probes, three of which are in the reactor vessel and one of which is positioned for measuring the temperature of the vapours coming out of the vessel.

(53) The pyrolysis reactor vessel was heated using a heating source comprising 2 heat belts surrounding the vessel. Pyrolysis temperatures referred to hereafter relate to the set temperature of the heating source. Temperature measurements obtained from probes inside the reaction vessel gradually increase to reach the heating source temperature.

(54) In general, the reaction products comprise various hydrocarbon pyrolysis products collected in the condensers, char remaining in the reaction vessel and gases (e.g. hydrocarbons having a boiling point below room temperature), which are too volatile to be collected in the condensers. The products of each reaction in the first condenser were analysed by simulated distillation chromatography (SimDist, ASTM D6352). The products found in condensers 2 and 3 were typically found to be boiling below the minimum observable in the SimDist method, indicating they likely consist of hydrocarbon chains between 5 and 9 carbons in length (C.sub.5-C.sub.9).

Example 6

(55) The above scaled-up general procedure was followed for two experiments using a 67:33 HDPE:PP by weight feed. Reaction pressure was set at 350 mbar and two different reaction temperatures were adopted: i) 450° C. and ii) 600° C.

(56) The collected effluent from the pyrolysis reaction in the first condenser for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution in terms of the different fractions collected are shown in Table F below, whilst the results showing the product distribution based on carbon number for the first condenser are provided in Table G below.

(57) TABLE-US-00007 TABLE F 450° C. 600° C. (kg) (mass %) (kg) (mass %) Feedstock in 12.00 100.00 12.00 100.00 Condenser 1 10.52 87.67 9.20 76.67 Condensers 1.19 9.92 1.51 12.58 2 + 3 Char 0.19 1.58 0.87 7.25 Unaccounted 0.10 0.83 0.42 3.50 (gases)

(58) TABLE-US-00008 TABLE G 450° C. 600° C. (mass %) (mass %) C.sub.10-C.sub.25 67 51 C.sub.25-C.sub.31 13 18 C.sub.31-C.sub.36 8 12 C.sub.36+ 12 19 C.sub.20+ 49 67

(59) The data in Tables F and G illustrate that at higher reaction temperatures an increased proportion of C.sub.20+ waxes are produced. This is consistent with the data in Tables D and E, which show the same trend. In addition to the increased proportion of heavier waxes at higher temperature, Table F shows that a larger proportion of lighter hydrocarbons collected in the second and third condensers are also produced at 600° C. compared to 450° C. Thus, at higher reaction temperatures, not only are more heavy waxes produced, but there is also a more defined split in the distribution between heavy and light hydrocarbons. This leads to an increase in the amount of product collected in the second and third condensers. In this way, the increased separation provided by a multistage condensation is particularly effective in combination with a higher pyrolysis temperature, i.e. there is a certain synergy between the use of higher pyrolysis temperature and the provision of a multistage condensation in a process for isolating a C.sub.20-C.sub.60 wax from the pyrolysis process. It will be understood that convenient separation of lighter fractions during condensation may simplify or eliminate the downstream distillation requirements.

Example 7

(60) The above scaled-up general procedure was followed for two experiments using a pure HDPE feed. Reaction pressure was set at 350 mbar and two different reaction temperatures were adopted: i) 450° C. and ii) 600° C.

(61) The collected effluent from the pyrolysis reaction in the first condenser for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution based on carbon number for hydrocarbons collected in the first condenser are provided in Table H below.

(62) TABLE-US-00009 TABLE H 450° C. 600° C. (mass %) (mass %) C.sub.10-C.sub.25 49 37 C.sub.25-C.sub.31 19 13 C.sub.31-C.sub.36 12 10 C.sub.36+ 20 40 C.sub.20+ 61 69

(63) The data in Table H illustrate that at higher reaction temperatures an increased proportion of C.sub.20+ waxes are produced. This is consistent with the data in Tables D, E and G, which show the same trend.

(64) Furthermore, the data in Table H also show that increasing temperature has a greater effect on the proportion of C.sub.20-C.sub.60 wax produced for these polypropylene containing feeds (Tables D and G) than for pure polyethylene feeds (Tables E and H). In this way, by using a mixed feed comprising polypropylene and polyethylene, greater benefits in terms of yield of the C.sub.20-C.sub.60 fraction at higher temperature may be obtained whilst also retaining the benefits of having a mixture of polypropylene and polyethylene in the feed in terms of the properties of the resulting wax. Even at temperatures where ultimately less of the C.sub.20+ fraction is produced for PP containing feeds in comparison to PE feeds, higher temperatures will mitigate the loss whilst retaining the benefits of including some branching in the waxes. Thus, there is a certain synergy between the use of higher pyrolysis temperature and the use of a certain proportion of polypropylene in the feed for isolating a C.sub.20-C.sub.60 wax from the pyrolysis process with particularly beneficial properties.

Example 8

(65) The above scaled-up general procedure was followed for three experiments using a an 80:20 PE:PP by weight feed. Reaction pressure was set at 350 mbar and three different reaction temperatures were adopted: i) 450° C., ii) 525° C. and iii) 600° C.

(66) The collected effluent from the pyrolysis reaction in the first condenser for each experiment was analysed by SimDist GC chromatography in order to determine the composition of the product according to boiling point and carbon number. The results showing the product distribution in terms of the different fractions collected are shown in Table I below, whilst the results showing the product distribution based on carbon number for the first condenser are provided in Table K below.

(67) TABLE-US-00010 TABLE I 450° C. 525° C. 600° C. (kg) (mass %) (kg) (mass %) (kg) (mass %) Feedstock in 10.015 100.00 10.000 100.00 10.010 100.00 (8.005 + 2.010) (8.000 + 2.000) (8.005 + 2.005) Condenser 1 7.67 76.59 7.575 75.75 7.200 71.29 Condenser 2 + 3 0.46 4.59 0.695 6.95 0.815 8.07 Char 0.25 2.50 0.11 1.1 0.210 2.08 Unaccounted 1.635 16.33 1.62 16.2 2.21 18.56

(68) TABLE-US-00011 TABLE K 450° C. 525° C. 600° C. (mass %) (mass %) (mass %) C.sub.10-C.sub.25 55 55 42 C.sub.25-C.sub.31 18 17 14 C.sub.31-C.sub.36 11 11 16 C.sub.36+ 16 17 28 C.sub.20+ 63 62 69

(69) The results in Tables K and I are consistent with the results in Tables F and G, showing that at higher pyrolysis temperatures there are larger proportions of heavier waxes produced, particularly the C.sub.36+ fraction. As also seen in Table F, Table I also shows an increased amount of product collected in the second and third condensers at higher temperatures, suggesting a certain synergy in the use of a multistage condensation in combination with higher pyrolysis temperatures in obtaining efficient production and separation of the desirable wax fractions.