PRODUCTION OF HYDROCARBON FUELS FROM PLASTICS

Abstract

Disclosed herein is a kiln 100 for use in the production of hydrocarbon fuels from plastics. The kiln 100 comprises a scrubber 200 in fluid communication with a reaction chamber 130, the scrubber 200 being configured to condense hydrocarbons in the reaction chamber gas product stream 501 above a predetermined upper hydrocarbon range for returning to the reaction chamber 130 for further heating in the absence of oxygen. Also disclosed herein is a method of converting waste plastics to a commercially-useful form by way of diesel or the like. The method comprises treating a crude fuel produced from plastics in a pyrolytic process with a first extraction step comprising counterflow liquid-liquid extraction, and a second extraction step comprising counterflow extraction of solvents from the first extraction step.

Claims

1.-44. (canceled)

45. A method for deriving fuel from plastics, the method comprising subjecting a quantity of plastics to a pyrolytic process, thereby to convert at least a portion of the plastics to a crude fuel; and extracting the fuel in a directly usable form by way of: a first extraction step comprising counterflow liquid-liquid extraction using one or more extraction solvents to extract one or more impurities from the crude fuel; and a second extraction step comprising counterflow extraction of resultant contaminated extraction solvent(s) from the first extraction step.

46. The method according to claim 45, wherein the second extraction step comprises changing the polarity of the resultant contaminated extraction solvent(s), thereby causing the resultant contaminated extraction solvent(s) to reject the extracted one or more impurities; and removing the rejected one or more impurities, thereby resulting in decontaminated extraction solvent(s).

47. The method according to claim 46, comprising reversing the polarity of the decontaminated extraction solvent(s).

48. The method according to claim 46, wherein the polarity of the resultant contaminated extraction solvent(s) is changed by addition of one or more polar compounds thereto; and wherein the polarity of the decontaminated extraction solvent(s) is reversed by distilling the one or more polar compounds therefrom to produce purified extraction solvent(s) for reuse in the first extraction step.

49. The method according to claim 48, comprising collecting the one or more polar compounds distilled from the contaminated extraction solvent(s) for reuse in the method.

50. The method according to claim 45, wherein the second extraction step comprises adding a light end non-polar solvent, or a mixture of light end non-polar solvents, to the extraction solvent(s) obtained from the first extraction step to extract therefrom aromatics and compounds of similar polarity to that of the light end non-polar solvent(s); and then removing the light end non-polar solvent(s) by distillation.

51. The method according to claim 45, wherein the extraction solvent(s) comprise(s) one or more solvents selected from the group consisting of: N-methyl-2-pyrrolidone; and dipolar aprotic solvents.

52. The method according to claim 45, comprising purifying the resultant contaminated extraction solvent(s) for reuse in the first extraction step.

53. The method of claim 52, wherein purification of the resultant contaminated extraction solvent(s) is performed in a substantially continuous manner to provide for substantially continuous operation of the first and second extraction steps.

54. The method according to claim 52, wherein purification of the resultant contaminated extraction solvent(s) comprises the resultant contaminated extraction solvent(s) entering a rising film evaporator under vacuum.

55. The method according to claim 45, wherein, in the counterflow extraction of the first extraction step, the extraction solvent(s) enter(s) the top of a packed column and the crude fuel enters the bottom of the packed column.

56. The method according to claim 55, wherein the resultant contaminated extraction solvent(s) carrying the impurities exit(s) the bottom of the packed column, and purified fuel exits the top of the packed column.

57. The method according to claim 45, wherein the fuel is a diesel blend.

58. The method according to claim 45, wherein the pyrolytic process by which the plastics are converted to the crude fuel takes place at from about 300 C. to about 450 C., over a period of about 30 minutes.

59. The method according to claim 45, wherein the first and second extraction steps take place at substantially ambient pressure, at about 80 C. and over a counterflow extraction period of less than about 20 minutes.

60. The method according to claim 45, wherein the crude fuel is a hydrocarbon fuel obtained from plastics processed using a kiln comprising: a reaction chamber; a feed inlet for feeding plastics feed material into the reaction chamber; a heater for heating the reaction chamber; and a scrubber in direct fluid communication with the reaction chamber; wherein the kiln is configured such that plastics feed material in the reaction chamber is heated in an absence of oxygen thereby to decompose at least a portion of the plastics feed material into a reaction chamber gas product stream comprising hydrocarbons suitable for use as fuel, and wherein the scrubber is configured to remove hydrocarbons in the reaction chamber gas product stream above a predetermined upper hydrocarbon range for returning to the reaction chamber for further heating in the absence of oxygen.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0090] Embodiments of the presently disclosed kiln will now be described by way of example only, with reference to the accompanying drawings in which:

[0091] FIG. 1 is a schematic diagram of a system for the conversion of plastics to hydrocarbon fuels;

[0092] FIG. 2 is a schematic diagram of an embodiment of a method for deriving fuel from plastics;

[0093] FIG. 3 represents the same process as that depicted in FIG. 2, with an additional NMP solvent purification step being signified;

[0094] FIG. 4 is a schematic diagram of a further embodiment of a method for deriving fuel from plastics;

[0095] FIG. 5 represents the same process as that depicted in FIG. 4, with an additional NMP solvent purification step being signified;

[0096] FIG. 6 is a schematic representation of a back-end NMP solvent purification process as defined in certain embodiments of the presently disclosed principles;

[0097] FIG. 7 is a photograph of a crude plastic-derived diesel following pyrolysis of crude waste plastics;

[0098] FIG. 8 is a photograph of an extraction step; and

[0099] FIG. 9 is a final purified diesel product following the NMP extraction steps.

DESCRIPTION OF EMBODIMENTS

[0100] Referring to FIG. 1, there is provided a system 10 for the conversion of plastics to hydrocarbon fuels such as diesel, petrol and liquid petroleum gas (LPG). The classification of hydrocarbon fuels depends primarily on the range of chain lengths of the hydrocarbons in the fuel mix, for example diesel hydrocarbons typically range from C10 to C25, petrol hydrocarbons from C4 to C12, and liquid petroleum gas (LPG) typically comprises a mixture of propane (C.sub.3H.sub.8) and butane (C.sub.4H.sub.10).

[0101] The system 10 comprises a plastic feed material 500 being fed to a kiln 100. The plastic feed material 500 may be any plastic material formed of long-chain organic polymers, for example waste plastic materials such as plastic packaging or automotive tyres. The plastic feed material 500 may undergo pre-processing prior to introduction into the kiln 100, for example shredding or chopping to improve handling and surface area of the plastic feed material, or drying to minimise the amount of water introduced to the system. The plastic feed material 500 is fed to a feed inlet 110 of the kiln 100 by a feeder 120 in a manner so as to reduce heat and gas loss from the kiln. For example, the plastic feed material 500 may be fed to the feed inlet 110 using a double slide-gate feeder or a plug screw feeder. The feeder 120 also allows for the control of the rate of flow of the plastic feed material 500 into the kiln 100.

[0102] The kiln 100 is a cylindrical horizontal kiln comprising a reaction chamber 130 in the form of a central inner tube through which the plastic feed material 500 flows, and a heater comprising a heat source 800 for heating the reaction chamber. The reaction chamber 130 comprises a plurality of stirrers 140 mounted at right angles to a horizontal rotating shaft 150 for stirring the plastic feed material in the reaction chamber 130. In addition to improving heat transfer to the plastic feed material 500, the rotating stirrers 140 also assist in the removal of waste particulate material from the reaction chamber 130 and prevention of waxy build-up on the reaction chamber 130 inner walls.

[0103] The heat source 800 may be any suitable heat source for heating the reaction chamber 130 and its contents, such as a heat source medium which flows through an annular region between a concentric outer tube 160 and the reaction chamber 130, the heat source medium 800 transferring heat through an outer wall of the reaction chamber 130. The heat source medium 800 may be sourced from other process equipment used in or in conjunction with the system, for example the heat source medium 800 may be combustion gases from a cyclone combustor 170 used to treat waste products from the system, such as non-condensable gases and char. The outer wall of the reaction chamber 130 further comprises a plurality of vortex generators (not shown) to increase heat transfer efficiency between the heat source medium 800 and the reaction chamber 130.

[0104] In the reaction chamber 130, the plastic feed material 500 is heated in the absence of oxygen such that at least a portion of the plastic feed material 500 first melts, then decomposes into a reaction chamber gas product stream 501 comprising hydrocarbons ranging from hydrogen to heavy wax, with the majority of the gases being in the liquid fuel range. A catalyst such as activated bauxite may further be provided in the reaction chamber 130 for pushing the reaction towards hydrocarbons of desirable chain length and/or desired aromatic hydrocarbons. Waste particulate material such as char, dust and ash may also be formed in the reaction chamber 130 as the plastic feed material 500 is heated or may be introduced with the plastic feed material 500. The kiln is provided with a waste particulate outlet 180 in fluid communication with the reaction chamber 130 for removing at least a portion of the waste particulate material formed in the reaction chamber.

[0105] The kiln 100 further comprises a product outlet 190 and a scrubber 200 at the product outlet 190. The reaction chamber gas product stream 501 exits the reaction chamber 130 through the product outlet 190 and flows through the scrubber 200. It will be appreciated that the exiting reaction chamber gas product stream 501 may also contain a portion of the above described waste particulate material. The scrubber 200 is preferably a packed scrubbing column comprising plate or ring-type packing. In the scrubber 200, the reaction chamber gas product stream 501 is brought into contact with a hydrocarbon scrubbing liquid 502 for condensing heavier, higher boiling point, hydrocarbons present in the reaction chamber gas product stream 501, wherein the condensed hydrocarbons and the scrubbing liquid flow back into the reaction chamber to undergo further reaction. The remaining, lighter weight, hydrocarbons exit the scrubber as a scrubber gas product stream 503. The scrubbing liquid 502 also acts to wash the reaction chamber gas product stream 501 of waste particulate material which flows back to the reaction chamber 130 with the scrubbing liquid 502 and the condensed heavier hydrocarbons.

[0106] It will be appreciated that the scrubber 200 is in direct fluid communication with the reaction chamber 130 such that the reaction chamber gas product stream 501 exiting the reaction chamber 130 flows directly to the scrubber 200. This minimises any cooling of the reaction chamber gas product stream 501 prior to entering the scrubber 200 which may lead to the formation of solid waxy residue being deposited in conduits connecting the reaction chamber 130 and the scrubber 200. The above described relative positioning of the reaction chamber 130 and the scrubber 200 further avoids the need to reheat the product from the reaction chamber 130 in order to separate out the desired hydrocarbons.

[0107] The system 10 further comprises at least one hydrocarbon recovery device for recovering hydrocarbons within a predetermined hydrocarbon range. In the system 10 of FIG. 1, there is provided a number of hydrocarbon recovery devices, discussed in more detail below, for recovering various components of the hydrocarbon gas product stream produced in the kiln, including a fractionation column 210 configured to condense diesel range hydrocarbons, a condenser 240 configured to condense petrol range hydrocarbons, and a gas compression and cooling device configured to condense liquid petroleum gas (LPG) range hydrocarbons.

[0108] The scrubber gas product stream 503 then enters a fractionation column 210 where the scrubber gas product stream 503 is brought into contact with a hydrocarbon reflux 504 selected for causing diesel range hydrocarbons 506 to condense and flow to out bottom of the fractionation column 210 while the gasoline and lighter hydrocarbons exit the top of the fractionation column 210 as a fractionation gas product stream 505. A portion of the diesel range hydrocarbons 506 exiting the fractionation column 210 is used as the scrubbing liquid 502 for scrubbing the reaction chamber gas product stream 501.

[0109] The remaining diesel 507 may then be treated prior to storage is a diesel storage vessel. In one example, the remaining diesel 507 is treated to remove moisture, for example by vacuum drying 220, and with the treated diesel 508 collected and stored in a diesel storage vessel 230. In another example, the diesel may undergo a solvent extraction processes, as discussed in more detail below, to extract impurities such as aromatics, sulphur compounds and similar.

[0110] It will be appreciated that the operation conditions of the kiln 100 and scrubber 200 will be dependent on the type of plastic feed material 500 to be processed and the desired hydrocarbon product to be recovered. For example, the targeted recovery of the lighter weight liquid petroleum gas (LPG) range hydrocarbons may require higher operating temperatures in the kiln than for the targeted recovery of diesel range hydrocarbons. While temperature in the kiln 100 is important, careful control of the temperature at the product outlet 190 (i.e. the scrubber inlet) and the scrubber outlet can play an important role in the composition of the final products. These temperatures can be controlled, for example, by controlling the temperature in the reaction chamber 130 and/or controlling the flow rate of the scrubbing liquid 502 into the scrubber 200. Preferably, the temperature of the scrubber gas stream 503 exiting the scrubber is maintained below 350 C. such that heavy, long-chain hydrocarbons unsuitable for use as fuel, condense and flow back to the reaction chamber 130 for further treatment.

[0111] The fractionation gas product stream 505 exiting the fractionation column 210 flows through a condenser 240 configured to condense the petrol range hydrocarbons 504, 509 in the fractionation gas product stream 505. A portion of the condensed petrol range hydrocarbons exiting the condenser are used as the hydrocarbon reflux 504 for the fractionation column 210. The remaining petrol 509 is collected and stored in a petrol storage vessel 250. As described above for the diesel 507, the petrol 509 may be treated prior to storage in petrol storage vessel. For example, the petrol 509 may undergo a solvent extraction processes, as discussed in more detail below, to extract impurities such as aromatics, sulphur compounds and similar.

[0112] Any remaining gases that were not condensed in the condenser 240, i.e. due to very low molecular weight and low boiling points, exit the condenser 240 as a condenser gas product stream 510. The condenser gas product stream 510 is fed to a gas compression and cooling device 260 configured to extract liquid petroleum gas (LPG) range hydrocarbons from the condenser gas product stream 510. The extracted LPG range hydrocarbons 511 are collected and stored in a LPG storage vessel 270.

[0113] Non-condensable gases 512 that are not recovered in the gas compression and cooling device 260 may be used in other process equipment, such as to at least partially fuel the cyclone combustor 170 as described above.

[0114] Referring now to FIG. 2 of the accompanying drawings, there is provided a schematic diagram of the process represented according to the fourth aspect. This aspect defines a method for deriving fuel from plastics, the method comprising a preliminary step subjecting a quantity of plastics to a pyrolytic process (not shown), thereby to convert at least a portion of the plastics to a crude fuel, in this case, crude diesel (1). The pyrolytic process by which the plastics are converted to the crude fuel takes place at about 450 C., over a period of about 30 minutes.

[0115] It will be appreciated that the pyrolytic process may be that described with reference to the kiln 100 above, with the crude fuel being any of the described hydrocarbon fuel streams, e.g. diesel 507, petrol 509, resulting from the operation of the kiln 100.

[0116] The process comprises a first extraction step obtaining the fuel in a directly usable form by way of: a first extraction step comprising counterflow liquid-liquid extraction in a packed column (2) using one or more extraction solvents (3), preferably in the form of N-methyl-2-pyrrolidone (NMP). The NMP serves to extract one or more impurities from the crude fuel. The purified diesel (4) is obtained from an exit stream, either at the top, or bottom of the packed column (2).

[0117] The process then comprises a second extraction step comprising counterflow extraction of the resultant contaminated NMP from the first extraction step (5). The second extraction step comprises using water, alcohol, or the like, or mixtures thereof (6A) to increase the polarity of the contaminated extraction solvent, in turn causing the extraction solvent to reject the extract. The second counterflow step again takes place in a packed column (7) and gives rise to an exit stream of contaminants (8A) such as sulfur compounds, aromatics, etc., and an exit stream of water-contaminated NMP solvent (9).

[0118] Optionally, an extraction solvent purification step is performed, wherein the contaminated extraction solvents are purified to enable their re-use in a subsequent one or more of the extraction steps; this will be discussed further, below.

[0119] The first and second extractions steps take place at substantially ambient pressure, at about 80 C. and over a counterflow extraction period of less than about 20 minutes.

[0120] In a final step, the water-contaminated NMP solvent (9) is then distilled using a standard distillation column (10), which gives rise to recycled water (11A) and recycled NMP (12). The waste product obtained following recycling of the extraction solvent is adaptable for use as a boiler fuel or marine diesel oil.

[0121] It will be appreciated that the extraction of the purified diesel (4) takes place within the first extraction step, with the second extraction step and subsequent distillation steps serving to provide a means of recycling the NMP and water solvents.

[0122] The method is adapted to be scalable to a commercial scale of greater than 1000 tons fuel per day. However, during scale-up, the method is also scalable to a pilot plant scale.

[0123] The method gives rise to yields of about 70% w/w diesel and about 15% w/w gasoline per unit plastics. However, to an appreciable extent, the recovery of fuel from the waste plastics is dictated firstly by the composition of the waste plastics and by the conditions (temperature, pressure, period) under which the pyrolysis step is effected.

[0124] The purified diesel fuel is directly transferable to commercial at-the-pump sale and meets the Australian Diesel Fuel Quality Standard (Fuel Standard (Automotive Diesel) Determination 2001, as amended, made under section 21 of the Fuel Quality Standards Act 2000).

[0125] It will be appreciated that the process as depicted according to FIG. 3 is substantially the same as that of FIG. 2, with the additional extraction solvent purification step being performed.

[0126] Often, it is found that there is a heavy contaminant in the extraction solvent/s (NMP) that is not removed other than by one or more deliberate purification steps. It is found that the contaminant may be one or more heavy hydrocarbons with a boiling point higher than NMP. Thus the NMP can be purified by an additional simple distillation step as depicted in FIG. 6 and discussed below.

[0127] For completeness, and with regard to FIG. 4 of the accompanying drawings, there is provided a schematic diagram of the process represented according to the fifth aspect. In the ensuing description of the second aspect, actions or reagents equivalent with those referenced in the fourth aspect (FIGS. 2 and 3) have been given consistent designations, e.g., NMP (3), etc.

[0128] The fifth aspect defines a method for deriving fuel from plastics, the method comprising a preliminary step subjecting a quantity of plastics to a pyrolytic process (not shown), thereby to convert at least a portion of the plastics to a crude fuel, in this case, crude diesel (1). The pyrolytic process by which the plastics are converted to the crude fuel takes place at about 450 C., over a period of about 30 minutes.

[0129] The process comprises a first extraction step obtaining the fuel in a directly usable form by way of: a first extraction step comprising counterflow liquid-liquid extraction in a packed column (2) using one or more extraction solvents (3), preferably in the form of N-methyl-2-pyrrolidone (NMP). The NMP serves to extract one or more impurities from the crude fuel. The purified diesel (4) is obtained from an exit stream, either at the top, or bottom of the packed column (2).

[0130] The process then comprises a second extraction step comprising counterflow extraction of the resultant contaminated NMP from the first extraction step (5). The second extraction step comprises using hexanes, heptanes, or the like, or mixtures thereof (6B) to change the polarity of the contaminated extraction solvent, in turn causing the extraction solvent to reject the extract. The second counterflow step again takes place in a packed column (7) and gives rise to an exit stream of contaminants (8B) such as hexanes and heptanes impurities, etc.

[0131] The first and second extractions steps take place at substantially ambient pressure, at about 80 C. and over a counterflow extraction period of less than about 20 minutes.

[0132] In a final step, the contaminated NMP solvent (9) is then distilled using a standard distillation column (10), which gives rise to recycled hexanes/heptanes (11B) and recycled NMP (12). The waste product obtained following recycling of the extraction solvent is adaptable for use as a boiler fuel or marine diesel oil.

[0133] It will be appreciated that the process as depicted according to FIG. 5 is substantially the same as that of FIG. 4, with the additional extraction solvent purification step being performed.

[0134] Often, it is found that there is a heavy contaminant in the extraction solvent/s (NMP) that is not removed other than by one or more deliberate purification steps. It is found that the contaminant may be one or more heavy hydrocarbons with a boiling point higher than NMP. Thus the NMP can be purified by an additional simple distillation step as depicted in FIG. 5 and discussed below.

[0135] Referring now to FIG. 6, a separate (or in-line) means is provided for purifying the contaminated extraction solvents to purity levels that enable their re-use in subsequent iterations of the process.

[0136] In the purification step/s depicted in FIG. 6, contaminated NMP (12) with remaining contaminant enters a rising film evaporator (D) that is heated generally by steam or heat transfer oil (13). The rising film evaporator is under vacuum on the NMP side. Generally the vacuum conditions will be between about 80 and 90 kPa. Generally the temperature of the rising film evaporator will be controlled to facilitate the boiling of the NMP at the desired vacuum The NMP boils off as NMP vapour (14) leaving the heavy contaminant and in condensed in the NMP vacuum condenser (E). The heavy contaminants (17) leave the rising film evaporator for use as industrial heating fuel or further refining. The recycled and purified NMP (16) is then returned to subsequent iterations of the extraction method.

[0137] In respect of each of the aspects described above, it will be appreciated that the extraction of the purified diesel (4) takes place within the first extraction step, with the second extraction step and subsequent distillation steps serving to provide a means of recycling the NMP and water solvents.

[0138] The method is adapted to be scalable to a commercial scale of greater than 1000 tons fuel per day. However, during scale-up, the method is also scalable to a pilot plant scale.

[0139] The method gives rise to yields of about 70% w/w diesel and about 15% w/w gasoline per unit plastics. However, to an appreciable extent, the recovery of fuel from the waste plastics is dictated firstly by the composition of the waste plastics and by the conditions (temperature, pressure, period) under which the pyrolysis step is effected. The purified diesel fuel is directly transferable to commercial at-the-pump sale and meets the Australian Diesel Fuel Quality Standard (Fuel Standard (Automotive Diesel) Determination 2001, as amended, made under section 21 of the Fuel Quality Standards Act 2000).

[0140] FIG. 7 depicts a sample of crude plastic-derived diesel following pyrolysis of the crude waste plastics. Notable features are its darkness and its opacity. This crude product is unsuitable for commercial sale at-the-pump. FIG. 8 is a photograph of an extraction step in which NMP is mixed with the sample and allowed to settle out to the bottom. The impurities/contaminants dissolve out into the NMP; the relatively clear layer remaining on top is relatively pure diesel. FIG. 9 depicts a sample of the final purified diesel product following the NMP extraction steps. As noted elsewhere, the fuel is directly transferable to commercial at-the-pump sale and meets the Australian Diesel Fuel Quality Standard (Fuel Standard (Automotive Diesel) Determination 2001, as amended, made under section 21 of the Fuel Quality Standards Act 2000), as well as ASTM D975-15c and EN590 standards.

[0141] It will be appreciated that the above-described methods enable the conversion of waste plastics into a commercially useful form by way of purified diesel fuel. Moreover, the inventive method provides means for recycling any solvents used in such an extraction process.

[0142] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.