DECOMPOSITION OF POLYOLEFINS

Abstract

The present invention relates to a process for the catalytic decomposition of a polyolefin. More particularly, the present invention relates hydrocarbon-aided catalytic decomposition of a polyolefin using an aluminosilicate.

Claims

1. A process for the catalytic decomposition of a polyolefin, the process comprising a step of contacting a polyolefin with: (a) an aluminosilicate, and (b) a hydrocarbon at a temperature of at least 200 C. and under an inert atmosphere, wherein the hydrocarbon comprises 2-20 carbon atoms and the aluminosilicate comprises a plurality of Brnsted acid sites.

2. The process of claim 1, wherein the polyolefin comprises greater than 80 wt % of polyethylene, polypropylene or a combination thereof.

3. The process of claim 1, wherein the polyolefin is polyethylene, polypropylene or a combination thereof.

4. The process of claim 1, 2 or 3, wherein the polyolefin is selected from the group consisting of high density polyethylene (HDPE), low density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high density polypropylene (HDPP), low density polypropylene (LDPP), linear low-density polypropylene (LLDPP) and a combination of two or more thereof.

5. The process of any one of the preceding claims, wherein the polyolefin is selected from the group consisting of high density polyethylene (HDPE), low density polyethylene (LDPE), high density polypropylene (HDPP) and a combination of two or more thereof.

6. The process of any one of the preceding claims, wherein the aluminosilicate is crystalline (e.g. a zeolite) or amorphous.

7. The process of any one of the preceding claims, wherein the aluminosilicate is selected from the group consisting of Y zeolite, ultrastable Y zeolite and amorphous SiO.sub.2Al.sub.2O.sub.3, each of which having a plurality of BAS.

8. The process of any one of the preceding claims, wherein the aluminosilicate comprises one or more transition metal promoter.

9. The process of claim 8, wherein the one or more transition metal promoters are selected from the group consisting of W, Re, Pt, Sn, Ir and Co.

10. The process of any one of the preceding claims, wherein the hydrocarbon is an aromatic compound comprising 5-20 carbon atoms.

11. The process of any one of the preceding claims, wherein the hydrocarbon has a molecular weight of less than 250 g mol.sup.1.

12. The process of any one of the preceding claims, wherein the hydrocarbon has a molecular weight of less than 200 g mol.sup.1.

13. The process of any one of the preceding claims, wherein the hydrocarbon has a molecular weight of less than 175 g mol.sup.1.

14. The process of any one of the preceding claims, wherein the hydrocarbon has a molecular weight of less than 150 g mol.sup.1.

15. The process of any one of the preceding claims, wherein the hydrocarbon is benzene, optionally substituted with one or more substituents independently selected from (1-5C)alkyl, (2-5C)alkenyl and (2-5C)alkynyl.

16. The process of any one of claims 1 to 9, wherein the hydrocarbon is selected from the group consisting of ethene, propene, butene, ethane, propane, butane, pentane, hexane, heptane, nonane, decane, benzene, toluene, xylene, cumene, mesitylene, 1,2,4,5-tetramethyl benzene and naphthalene

17. The process of claim 16, wherein the hydrocarbon is selected from the group consisting of benzene, toluene, xylene, cumene, mesitylene, 1,2,4,5-tetramethyl benzene and naphthalene.

18. The process of claim 16, wherein the hydrocarbon is toluene or decane.

19. The process of any one of the preceding claims, wherein the step of contacting the polyolefin with the aluminosilicate and the hydrocarbon is conducted at a temperature of 300-450 C.

20. The process of any one of the preceding claims, wherein the step of contacting the polyolefin with the aluminosilicate and the hydrocarbon is conducted at a temperature of 300-400 C.

21. The process of any one of the preceding claims, wherein the step of contacting the polyolefin with the aluminosilicate and the hydrocarbon is conducted at a temperature of 300-350 C.

22. The process of any one of the preceding claims, wherein the step of contacting the polyolefin with the aluminosilicate and the hydrocarbon is conducted under an atmosphere of nitrogen and hydrogen.

23. The process of any one of the preceding claims, wherein the step of contacting the polyolefin with the aluminosilicate and the hydrocarbon is conducted under an atmosphere of hydrogen.

24. The process of any one of the preceding claims, wherein the weight ratio of aluminosilicate to hydrocarbon is 1: (0.1-10).

25. The process of any one of the preceding claims, wherein the weight ratio of aluminosilicate to hydrocarbon is 1: (0.5-5).

Description

EXAMPLES

[0068] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures:

[0069] FIG. 1. The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 4h over 0.2 g aluminosilicate catalyst (with and without varying amounts of toluene) compared to pyrolysis with no aluminosilicate catalyst.

[0070] FIG. 2. The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 4 h and after 6h over 0.2 g aluminosilicate catalyst.

[0071] FIG. 3. The final product distribution from 2 g HDPE at 330 C., 30 bar N.sub.2 after 4h over 0.2 g HY (30) catalyst.

[0072] FIG. 4. Gas chromatography (GC) pattern of liquid products in CHCl.sub.3. Reaction conditions: 0.2 g toluene, at 330 C., 20 bar N.sub.2 after 4h over 0.2 g HY (30) catalyst.

[0073] FIG. 5. The final product distribution from 2 g HDPE at 300 C., 20 bar N.sub.2 after 4h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with and without an acid wash) catalyst.

[0074] FIG. 6. GC pattern of liquid products in CHCl.sub.3. Reaction conditions: 0.2 g toluene, 2 g HDPE at 300 C., 20 bar N.sub.2 after 4h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 catalyst.

[0075] FIG. 7. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for SiO.sub.2Al.sub.2O.sub.3 catalyst (solid residue). Ramp 10 C. min.sup.1 from room temperature to 650 C. in N.sub.2 flow and then isothermal in air flow.

[0076] FIG. 8. Gel permeation chromatography (GPC) results for the SiO.sub.2Al.sub.2O.sub.3 catalyst (solid residue). 2 g HDPE at 300 C., 20 bar N.sub.2 after 4h.

[0077] FIG. 9. The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 4h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with acid wash) with and without toluene.

[0078] FIG. 10. The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 2h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with acid wash) with and without toluene.

[0079] FIG. 11. The final product distribution from 0.2 g WO@SiO.sub.2Al.sub.2O.sub.3, 0.1 g PtSn@SiO.sub.2Al.sub.2O.sub.3, 2 g HDPE, 1 g (1.37 mL) n-decane for the 1st cycle only (polymer: catalyst ratio of 6.67:1). 2 g HDPE was added for each subsequent cycle at 390 C., 4 h, 30 bar H.sub.2, batch reactor. % mass balance=985 for all entries.

[0080] FIG. 12. The gas chromatography-mass spectrometry (GC-MS) analysis of the final product from 0.2 g WO@SiO.sub.2Al.sub.2O.sub.3, 0.1 g PtSn@SiO.sub.2Al.sub.2O.sub.3, 2 g HDPE, 1 g (1.37 mL) n-decane for the 1st cycle only (polymer: catalyst ratio of 6.67:1). 2 g HDPE was added for each subsequent cycle at 390 C., 4 h, 30 bar H.sub.2, batch reactor. % mass balance=985 for all entries.

[0081] FIG. 13. DSC and TGA analysis for the WO@SiO.sub.2Al.sub.2O.sub.3 and PtSn@SiO.sub.2Al.sub.2O.sub.3 catalyst mixture after polyolefin decomposition.

[0082] FIG. 14. n-decane promoted decomposition of HDPE via molecular averaging through dehydrogenation, exhaustive cross-metathesis and hydrogenation.

MATERIALS AND METHODS

[0083] HDPE (Mw, 88707 g/mol, Mn, 10794 g/mol) was received from SCG Ltd. The polyolefin was used without further treatment. Aluminosilicate catalysts SiO.sub.2Al.sub.2O.sub.3 Grade 135, HY (30) zeolite and USY zeolite were purchased from Sigma-Aldrich. Chloroform (puriss. p.a., reag. ISO, reag. Ph. Eur., 99.0-99.4% GC), toluene (anhydrous, 99.8%) and ammonium nitrate (ACS reagent, >98%) were also purchased from Sigma-Aldrich.

Catalyst Pre-Treatment and Cation Ion Exchange

[0084] All aluminosilicate catalysts except proton-exchanged SiO.sub.2Al.sub.2O.sub.3 were pre-treated at 400 C. (ramp 5 C. min.sup.1) in air flow (30 mL min.sup.1) for 3h prior to use. Proton exchanged SiO.sub.2Al.sub.2O.sub.3, denoted SiO.sub.2Al.sub.2O.sub.3 (H+), was synthesised as follows: ammonium nitrate was weighed and mixed with DI water to form 15 wt % ammonium nitrate solution. 3 g of SiO.sub.2Al.sub.2O.sub.3 was then put into the ammonium nitrate solution and heated to 80 C. for 4 h under stirring. After the hot suspension was cooled to room temperature, it was centrifuged and the solid was further washed with DI water three times. The washed solid was dried at 105 C. overnight before it was calcined in air flow at 600 C. for 4h prior to use.

Catalytic Test

[0085] The catalytic test was carried out in a 50 mL autoclave, wherein 2 g of polyolefin was mixed with the aluminosilicate catalyst and toluene. Typically, 0.2 g of aluminosilicate catalyst and 0.2 g of toluene were introduced under 20 bar nitrogen after the air inside the autoclave was removed. The autoclave was heated to the target temperature in 1.5h. Meanwhile, the reactor was kept stirring with a glassy coated stirrer. After the heating program was finished, the temperature of the autoclave was allowed to cool to room temperature.

[0086] The gaseous product was analysed by GC while the liquid phase product was analysed by GC-MS (Agilent GC-MS 6890). The liquid-solid mixture was separated by centrifugation before the collected liquid product was injected into the GC-MS for analysis. Generally, chloroform was used to help with collection of the liquid-solid mixture from the autoclave. The solid from the centrifugation was dried in vacuo at 80 C. overnight before it was weighed at room temperature.

[0087] The final product was typically divided into three phases (gas, liquid, and solid). The mass of the autoclave including the stirrer was initially weighed using a balance with a measuring range and accuracy of 5 kg0.05 g. The gas mass was verified by the pressure difference of the autoclave before and after the reaction and then calculated according to the Ideal Gas Law. The liquid-solid mixture mass was measured by the weight difference between the autoclave after discharging the gas and the empty autoclave (stirrer included). The solid mass was obtained by removing the weight of the aluminosilicate catalyst added and the weight of the liquid was verified by deducting the weight of the solid residue and aluminosilicate catalyst added from the liquid-solid mixture. The fraction of the desired compound (compound I) in the product and mass balance was performed as follows (initial toluene added was deducted from final calculation):

[00001]$\begin{array}{cc}\mathrm{The}\mathrm{fraction}\mathrm{of}\mathrm{compound}I=\frac{\mathrm{The}\mathrm{mass}\mathrm{of}\mathrm{compound}I}{\mathrm{Total}\mathrm{mass}\mathrm{collected}-\mathrm{mass}\mathrm{of}\mathrm{catalyst}}100\%& \left(1\right)\end{array}$$\begin{array}{cc}\mathrm{Mass}\mathrm{Balance}=\frac{\mathrm{Total}\mathrm{mass}\mathrm{collected}-\mathrm{mass}\mathrm{of}\mathrm{catalyst}}{\mathrm{Total}\mathrm{mass}\mathrm{input}-\mathrm{mass}\mathrm{of}\mathrm{catalyst}}100\%& \left(2\right)\end{array}$

Results and Discussion

TABLE-US-00001 TABLE 1 Product distribution in mass and mass balance in 2 g HDPE at 330 C., 20 bar N.sub.2, 4 h. Gasoline (C5-C12); Diesel (C9-C22). Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance 6.72% 42.52% 72.64% 3.72% 0.53% 84.4% W/USY 0.2 g 8.86% 67.11% 52.06% 3.89% 7.10% 89.1% Re/USY 0.2 g 10.01% 57.43% 53.10% 3.49% 12.88% 93.5% Re/USY 0.4 g 10.00% 58.44% 58.57% 5.71% 8.23% 86.0% W/USY 0.4 g 13.56% 65.62% 53.32% 2.70% 3.98% 94.2% W/USY (6 hours) 0.2 g 11.90% 63.34% 53.40% 4.53% 5.66% 92.6% W/USY 12.37% 56.02% 41.13% 0.85% 17.36% 96.8%

[0088] The main objective was to optimize gasoline production (C5-C12) from waste plastics without excessive contamination with heavy hydrocarbon products over the aluminosilicate catalysts. As seen from the catalyst screening in Table 1 and the product distribution in FIG. 1, pyrolysis without the presence of an aluminosilicate catalyst can be observed to give nearly complete decomposition of HDPE (0.53% residue left) when heated to 330 C. The reaction yielded 42.52% gasoline products (sum of C5-C7 and C8-C12) and showed contamination with gaseous hydrocarbons (6.72%) (C1-C4) as well as heavy hydrocarbons (50.23%). Using the W/USY catalyst without promotion with a hydrocarbon (toluene) promoter increased the gaseous hydrocarbon (12.37%) and gasoline (56.02%) fractions at the expense of heavy hydrocarbons. Unconverted plastic residues (i.e., plastic which has not decomposed) remained relatively high (17.36%), however, indicating that some of the plastic was trapped in the porous structure of the aluminosilicate catalyst. Interestingly, adding 0.2 g of toluene into the reaction, enhanced the conversion of unconverted plastic (reduced to 7.1%) and increased gasoline production (67.11%). Without wishing to be bound by theory, the inventors believe that the presence of a hydrocarbon promoter improves the rate of CC bond cleavage in the polyolefin, thereby producing more valuable hydrocarbon fractions such as gasoline. Increasing the toluene content from 0.2 g to 0.4 g increased the gaseous hydrocarbon fraction (13.56%) at the expense of heavy hydrocarbons to account for a total gas and gasoline content of 79%. Using Re/USY showed a similar trend but with a slightly lower gasoline fraction. Similar observations were also obtained when increasing the reaction time (Table 2 and FIG. 2), indicating that longer reaction times results in a higher degree of CC bond cleavage.

TABLE-US-00002 TABLE 2 Product distribution in mass and mass balance: 2 g HDPE at 330 C., 20 bar N.sub.2 for different reaction times. Gasoline (C5-C12); Diesel (C9-C22) Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance W/USY (4 hours) 0.2 g 8.86% 67.11% 52.06% 3.89% 7.10% 89.1% W/USY (6 hours) 0.2 g 11.90% 63.34% 53.40% 4.53% 5.66% 92.6%

TABLE-US-00003 TABLE 3 Product distribution in mass and mass balance: 2 g HDPE at 330 C., 30 bar N.sub.2 over HY (30) catalyst. Gasoline (C5-C12); Diesel (C9-C22) Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance HY (30) 0 12.10% 54.69% 35.42% 0.33% 22.22% 92.5% HY (30) 0.2 g 10.52% 61.82% 44.51% 0.81% 12.21% 90.3%

[0089] Table 3 and FIG. 3 highlight the effect of the hydrocarbon promoter when added to a zeolite catalyst without W or Re. The data indicates that the presence of the hydrocarbon promoter enhances CC bond cleavage in HDPE giving higher overall decomposition and gasoline production. Comparatively, the incorporation of W into the USY zeolite (W/USY) gave slightly higher gasoline yield (67.11%) with 0.2 g toluene albeit with increased liquid product (46% in mass), which is thought to correspond to substituted aromatic compounds (see FIG. 4). The formation of substituted aromatic products, such as multi methylbenzene, suggests that toluene can scavenge CH.sub.2 moieties from the polyolefin. It is thought that this occurs via toluene alkylation of the polyolefin over the BAS of the aluminosilicate at elevated temperatures. It is also thought that the removal of an electron from the aromatic anchored polyolefin over the BAS could favourably lead to the formation of a radical cation, a species capable of undergoing -scission of CC bonds to induce fragmentation of the polymer. It is widely reported that -scission of CC bonds is an essential step in the side-chain oxidation of alkyl aromatics and related compounds (Lai, et al. 2018., Ratkiewicz, 2011., Zhang et al. 2017).

TABLE-US-00004 TABLE 4 The final product distribution from 2 g HDPE over at 300 C., 20 bar N.sub.2 after 4 h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with and without an acid wash) catalyst Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance SiAl (H+) 0.2 g 10.55% 60.91% 55.27% 0.82% 6.25% 94.9% SiAl (H+) 0 g 6.58% 42.77% 33.77% 0.50% 36.96% 93.9% SiAl 0.2 g 6.94% 43.33% 32.37% 0.29% 37.60% 93.4%

[0090] Table 4 and FIG. 5 demonstrate the effects of a hydrocarbon promoter when added to a non-zeolite catalyst (SiO.sub.2/Al.sub.2O.sub.3 with and without an acid wash) at a lower temperature of 300 C. Interestingly, the hydrocarbon promoter had a similar effect on CC bond cleavage in HDPE, giving higher overall decomposition and gasoline production (60.91%) over the acid washed aluminosilicate catalyst. FIG. 6 indicates that the liquid product comprises less substituted aromatic compounds when a non-zeolite acidic catalyst is used (38% in mass). Interestingly, the hydrocarbon promoter did not have as much of an effect on the SiO.sub.2Al.sub.203 catalyst without an acid wash indicating the need for BAS. This is further supported by FIG. 7 which highlights the importance of both the hydrocarbon promoter and BAS. Nearly no pink peak is present at around 450 C. (indicative of the starting waste plastic) for pre-treated (i.e., acid washed) SiO.sub.2/Al.sub.2O.sub.3 with toluene, implying that nearly all the waste plastic has been decomposed into smaller fractions. A large pink peak is observed at around 450 C. for the systems i) without toluene (10%/min) and ii) without reactivation of BAS (i.e., no acid wash) (6%/min). Similar conclusions can be drawn from analysing the GPC results (FIG. 8 and Table 5). Lower molecular weight and lower polydispersity index (Mw/Mn) are observed with hydrocarbon promoted SiO.sub.2/Al.sub.2O.sub.3 (with acid wash). Conversely, without the promotion with toluene and in without BAS, higher molecular weights are observed along with broader solid product distribution (indicated by a higher polydispersity index), highlighting the importance of both hydrocarbon promotion and BAS in the efficient and selective decomposition of waste plastics.

TABLE-US-00005 TABLE 5 GPC results for the SiO.sub.2Al.sub.2O.sub.3 catalyst (solid residue). 2 g HDPE at 300 C., 20 bar N.sub.2 after 4 h. Catalyst Toluene Mw(g/mol) Mn(g/mol) Mw/Mn SiAl (H+) 0.2 g 300 200 1.44 SiAl (H+) 0 g 500 500 3.67 SiAl 0.2 g 400 400 4.98

[0091] Table 6 and FIG. 9 show the effect of increasing the temperature to 330 C. It is noted that the difference in gasoline yield when comparing reactions with and without hydrocarbon promotion is reduced due to the predominant thermal cracking effect. It is noted, however, that the higher diesel fraction and lower solid fraction proves that the hydrocarbon promoter enhances polyolefin decomposition. Reducing the reaction time under the same conditions increases the difference in gasoline yield indicating that lower temperatures and shorter reaction times promote the hydrocarbon promoted polyolefin decomposition reaction to form gasoline products (Table 7 and FIG. 10).

TABLE-US-00006 TABLE 6 The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 4 h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with acid wash). Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance SiAl (H+) 0.2 g 12.04% 61.17% 41.61% 0.10% 13.87% 92.0% SiAl (H+) 0 g 11.81% 60.03% 37.59% 0.08% 15.84% 89.7%

TABLE-US-00007 TABLE 7 The final product distribution from 2 g HDPE at 330 C., 20 bar N.sub.2 after 2 h over 0.2 g SiO.sub.2Al.sub.2O.sub.3 (with acid wash). Catalyst Toluene C1-C4 Gasoline Diesel C23+ Solid Mass balance SiAl (H+) 0.2 g 11.28% 66.70% 41.14% 0.12% 9.57% 92.7% SiAl (H+) 0 g 13.49% 60.74% 44.38% 0.09% 9.76% 93.2%

[0092] FIG. 11 highlights the effect of promotion with a different hydrocarbon promoter (decane). The effect of the hydrocarbon promoter was explored using a WO.sub.@SiO.sub.2Al.sub.2O.sub.3 (cross metathesis catalyst) and PtSn@SiO.sub.2Al.sub.2O.sub.3(hydrogenation-dehydrogenation catalyst) catalyst mixture. From this investigation it was observed that promotion with decane resulted in gasoline as the major product, showing very high selectivity for this fraction. This indicates that decane is a viable alternative to toluene as a hydrocarbon promoter for the selective decomposition of a polyolefin. Furthermore, the recyclability of the system was investigated by adding fresh HDPE in each cycle without adding any more aluminosilicate catalyst or hydrocarbon promoter. With each addition of fresh HDPE (indicated by cycles 2-4 in FIG. 11), the selective decomposition of the polyolefin to gasoline as well as the overall decomposition of the polyolefin remained high. This further confirms that the addition of a hydrocarbon promoter to an aluminosilicate catalyst facilitates efficient and selective polyolefin decomposition.

[0093] Under a H.sub.2 atmosphere, it is clear from FIGS. 11 and 12 that the product distribution shifts toward the smaller hydrocarbon range with a greater degree of branching alkanes (no significant olefinic products are observed) along with the sharp reduction of n-decane. This demonstrates the effectiveness of polyolefin decomposition under a H.sub.2 atmosphere in addition to the N.sub.2 atmosphere also investigated. FIG. 13 also shows that increasing the H.sub.2 pressure suppresses carbon deposition onto the aluminosilicate catalyst.

[0094] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.

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