PROCESS FOR CONVERTING MIXED WASTE PLASTIC INTO LIQUID FUELS BY CATALYTIC CRACKING

Abstract

The present invention relates to a process for converting mixed waste plastic into liquid fuels by catalytic cracking. The process comprises the steps of introducing mixed waste plastic and a catalyst comprising an amorphous-type catalyst within a reactor; allowing at least a portion of the mixed waste plastic to be converted to liquid fuels within the reactor; and removing a product stream containing said liquid fuels from the reactor.

Claims

1. A process for converting mixed waste plastic into liquid fuels by catalytic cracking, the process comprising: introducing mixed waste plastic and a catalyst comprising an amorphous-type catalyst within a reactor; allowing at least a portion of the mixed waste plastic to be converted to liquid fuels within the reactor; and removing a product stream containing said liquid fuels from the reactor, wherein the mixed waste plastic contains from 5 to 50% by weight of polystyrene and from 50 to 95% by weight of polyolefin, each based on the total weight of polystyrene and polyolefin in the mixed waste plastic, and wherein the weight ratio of catalyst to mixed waste plastic in the reactor is above 1:10.

2. The process according to claim 1, wherein the mixed waste plastic contains from 5 to 40% by weight of polystyrene, based on the total weight of polystyrene and polyolefin in the mixed waste plastic.

3. The process according to claim 1, wherein the weight ratio of catalyst to mixed waste plastic in the reactor is above 1:8.

4. The process according to claim 1, wherein the weight ratio of catalyst to mixed waste plastic in the reactor is below 10:1.

5. The process according to claim 1, wherein the catalyst predominantly is an amorphous-type catalyst.

6. The process according to claim 1, wherein the catalyst consists of amorphous-type catalyst.

7. The process according to claim 1, wherein the catalyst additionally comprises a zeolite-type catalyst.

8. The process according to claim 1 wherein the amorphous-type catalyst comprises silica, alumina, kaolin, or a mixture thereof.

9. The process according to claim 1, wherein the catalyst is fresh catalyst, equilibrated catalyst, or a mixture thereof.

10. The process according to claim 1, wherein the temperature at which at least part of the mixed waste plastic is converted to liquid fuels in the reactor is above 350 C.

11. The process according to claim 1, wherein the mixed waste plastic comprises more than 50% by weight of polystyrene and polyolefin, based on the total weight of the mixed waste plastic.

12. The process according to claim 1, wherein the process is conducted continuously.

13. The process according to claim 1, wherein the waste plastic is selected from the group consisting of post consumer waste plastic, off-spec plastic and industrial scrap plastic.

14. The process according to claim 1, wherein the waste plastic is essentially free of thermosetting polymers.

15. The process according to claim 2, wherein the mixed waste plastic contains from 5 to 30% by weight of polystyrene, based on the total weight of polystyrene and polyolefin in the mixed waste plastic.

16. The process according to claim 15, wherein the mixed waste plastic contains from 10 to 30% by weight of polystyrene, based on the total weight of polystyrene and polyolefin in the mixed waste plastic.

17. The process according to claim 3, wherein the weight ratio of catalyst to mixed waste plastic in the reactor is above 1:5.

18. The process according to claim 4, wherein the weight ratio of catalyst to mixed waste plastic in the reactor is below 7:1.

19. The process according to claim 10, wherein the temperature at which at least part of the mixed waste plastic is converted to liquid fuels in the reactor is above 410 C.

20. The process according to claim 19, wherein the temperature at which at least part of the mixed waste plastic is converted to liquid fuels in the reactor is in the range of above 410 C. to 500 C.

Description

[0037] The effect of the polystyrene content in the mixed waste plastic at a high weight ratio of catalyst to mixed waste plastic in the reactor is now explained in more detail with reference to the following examples and the attached figures which show in

[0038] FIG. 1 the evolution with time of the overall cumulative conversion for different polystyrene loadings,

[0039] FIG. 2 the evolution with time of corrected HDPE cumulative conversion for different polystyrene loadings. To determine the corrected HDPE conversion, without the PS contribution, it is assumed that the pyrolysis process of the two different plastics is independent. Based on this premise, it is possible to subtract the PS conversion to the overall conversion, thus obtaining the HDPE conversion,

[0040] FIG. 3 the relative values of kinetic rate constant for different polystyrene loadings,

[0041] FIG. 4 the effect of polystyrene loading on selectivity,

[0042] FIG. 5 the effect of polystyrene loading on the quality of the gasoline fraction, and

[0043] FIG. 6 the effect of polystyrene loading on the quality of the diesel fraction.

[0044] The examples below were conducted according to the following general experimental procedure.

[0045] In each catalytic run in semibatch mode, 30 g of plastic (high density polyethylene (HDPE) and variable amounts of polystyrene (PS)) and a defined amount of the amorphous-type catalyst (SiO.sub.2) were loaded inside the reactor. The reactor was closed and heated from room temperature to 200 C. during 20 minutes, while simultaneously purging with a 150 mL/min nitrogen flow. When the internal temperature reached the melting point of the plastic, stirring was started and was slowly increased until 690 rpm. The temperature was held at 200 C. for 25-30 minutes. During this heating process, nitrogen coming out from the reactor was not collected.

[0046] After this first pretreatment step, the temperature was increased to the reaction temperature at a heating rate of 10 C./min, and the collection of gases and nitrogen in the corresponding gas sampling bag was started. When the internal temperature reached the reaction temperature, the circulation of the gaseous products was commuted to another pair of glass traps and corresponding gas sampling bag. This was considered as the zero reaction time.

[0047] During selected time periods, liquid and gaseous products were collected in a pair of glass traps and their associated gas sampling bag, respectively. At the end of the experiment the reactor was cooled to room temperature. During this cooling step, liquids and gases were also collected.

[0048] The reaction products were classified into 3 groups: i) gases, ii) liquid hydrocarbons and iii) residue (waxy compounds, ashes and coke accumulated on the catalyst). Quantification of the gases was done by gas chromatography (GC) using nitrogen as the internal standard, while quantification of liquids and residue was done by weight.

[0049] The simulated distillation (SIM-DIS) GC method allowed the determination of the different fractions in the liquid samples (according to the selected cuts); the detailed hydrocarbon analysis (DHA) GC method allowed the determination of the PIONA (paraffins, iso-paraffins, olefins, naphthenes, aromatics) components in the gasoline fraction of the last withdrawn sample (C5-C11: Boiling point<216.1 C.; what includes C5-C6 in the gas sample and C5-C11 in the liquid samples), and GCGC allowed the determination of saturates (everything that is not aromatic), mono-, di- and tri-aromatics in the diesel fraction of the last withdrawn liquid samples (C12-C21; 216.1<BP<359 C.).

[0050] To determine the corrected HDPE conversion, without the PS contribution, it was assumed that the pyrolysis process of the two different plastics is independent. Based on this premise, it is possible to subtract the PS conversion to the overall conversion, thus obtaining the HDPE conversion.

[0051] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

EXAMPLE 1

[0052] The experiment was carried out following the general procedure described above. In this example, the raw material was pure HDPE (labelled 0% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica were used. Catalyst to plastic weight ratio was equal to 20/30.

EXAMPLE 2

[0053] The experiment was carried out following the general procedure described above. In this example, the raw material is a mixture containing 95 wt. % HDPE and 5 wt. % PS (labelled 5% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica have been used. Catalyst to plastic weight ratio was equal to 20/30.

EXAMPLE 3

[0054] The experiment was carried out following the general procedure described above. In this example, the raw material was a mixture containing 90 wt. % HDPE and 10 wt. % PS (labelled 10% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica were used. Catalyst to plastic weight ratio was equal to 20/30.

EXAMPLE 4

[0055] The experiment was carried out following the general procedure described above. In this example, the raw material was a mixture containing 80 wt. % HDPE and 20 wt. % PS (labelled 20% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica were used. Catalyst to plastic weight ratio was equal to 20/30.

EXAMPLE 5

[0056] The experiment was carried out following the general procedure described above. In this example, the raw material was a mixture containing 50 wt. % HDPE and 50 wt. % PS (labelled 50% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica were used. Catalyst to plastic weight ratio was equal to 20/30.

EXAMPLE 6

[0057] The experiment was carried out following the general procedure described above. In this example, the raw material was pure PS (labelled 100% PS). Reaction temperature was set at 450 C. In this example, 20 g of silica were used. Catalyst to plastic weight ratio was equal to 20/30.

[0058] The evolution of the overall cumulative conversion for the different polystyrene loadings over time is shown in FIG. 1. As explained above in the general description of the experimental procedure, the PS conversion was then subtracted from the overall conversion thus obtaining the HDPE cumulative conversion for different polystyrene loadings shown in FIG. 2. From these values, the relative values of kinetic rate constant for different polystyrene loadings in HDPE pyrolysis were calculated. The results are shown in FIG. 3. It is evident that the kinetic rate constant for the polyolefin conversion has a maximum at about 20% by weight of polystyrene present in the mixed waste plastic.

[0059] The effect of polystyrene loading on the selectivity of the process is shown in FIG. 4. It is evident that the selectivity for gasoline increases with increasing polystyrene loading while the selectivity for gases, diesel and waxes decreases.

[0060] However, contrary to the expectation of the skilled person and contrary to what is described in the prior art, the process of the present invention provides a gasoline fraction as well as a diesel fraction which both comprise only a low amount of aromatic compounds. Only in case of 100% polystyrene as starting plastic (which is not according to the invention), the amount of aromatic compounds in the gasoline and diesel fractions increases. These findings are summarized in FIGS. 5 and 6.

[0061] FIG. 5 shows the effect of the polystyrene loading on the quality of the gasoline fraction (P: paraffins, I: iso-paraffins, O: olefins, N: naphthenes, A: aromatics, U: unidentified). FIG. 5 additionally shows the RON and MON of the gasoline fractions obtained with different polystyrene loadings. Surprisingly, both RON and MON increase if the amount of polystyrene in the mixed waste plastic is increased from 0% to 20%.

[0062] FIG. 6 shows the effect of the polystyrene loading on the quality of the diesel fraction (S: saturated, MA: monoaromatic, DA: diaromatic, TA: triaromatic, PA: polyaromatic). It is evident that the overall amount of aromatic compounds in the diesel fraction remains low even if the polystyrene content in the mixed waste plastic is increased up to 50% by weight. Only when the polystyrene content is increased to 100% (which is not according to the invention), the amount of aromatic compounds in the diesel fraction significantly increases.