WO2025072985A1

WO2025072985A1 - Method and apparatus for producing usable hydrocarbons from a heterogeneous solid waste stream

Info

Publication number: WO2025072985A1
Application number: PCT/ZA2024/050052
Authority: WO
Inventors: Mark Hobbs
Original assignee: Rooikat Recycling (Pty) Ltd
Priority date: 2023-09-27
Filing date: 2024-09-23
Publication date: 2025-04-03

Abstract

The invention provides a method for transforming a waste stream into hydrocarbon fractions using separate vessels. It involves (a) separating an unsorted solid waste stream in a first vessel into a fluid fraction and a waste fraction by dissolving polymeric hydrocarbons in a solvent; (b) de-viscifying the fluid fraction in a second vessel by shortening polymeric chain lengths through thermal decomposition; and (c) distilling the fluidised stream in a third vessel to obtain multiple distillate fractions and a residue. This method allows for the recovery of gases, naphtha, kerosene, diesel, and wax, with optimized temperature and pressure conditions for each vessel.

Description

METHOD AND APPARATUS FOR PRODUCING USABLE

HYDROCARBONS FROM A HETEROGENEOUS SOLID WASTE STREAM

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to a method and apparatus for sustainable waste management by transforming a solid, primarily plastic, waste stream, typical of a household waste stream, into useful hydrocarbon products.

BACKGROUND OF THE INVENTION

[0002] The conversion of waste, mainly plastic waste, into oil (used for fuels and chemicals) is a topic that has been explored extensively, driven by the imperative of rapidly increasing and increasingly affluent urban populations, the profusion of plastic waste that is chocking natural ecosystems and large, polluting and land consuming landfills. Considerable effort has gone into laboratory and pilot-scale experimentation; however, transitioning this into a viable commercial process has presented significant challenges.

[0003] Existing technologies demand a sorted waste feedstock, i.e. a clean feedstock. These technologies were conceived at the laboratory level using uncontaminated plastic materials. As a result, they cannot effectively eliminate substantial levels of contaminants.

[0004] Tackling the issue of oxygen infiltration during the pyrolysis process is a complex task. The entry of oxygen leads to oxidation within the pyrolysis process, negatively affecting the quality of the end products and even posing a safety hazard regarding fire risk. Managing air presence in the context of a solid substance undergoing rotary manipulation has proven to be a daunting challenge. Various approaches have been attempted but with limited success.

[0005] Many technologies utilise a solitary vessel or reactor for the sequential steps of liquefaction, pyrolysis, and distillation (furnace section). Consequently, it becomes intricate to regulate each step and process independently, thus compromising the ability to optimise the overall procedure.

[0006] Existing technologies have evolved from laboratory-scale experimentation and do not seamlessly transition to large-scale implementation. The applicant recognised that it is only during scaling up a project that specific issues, unapparent in laboratory settings, come to the forefront. Subsequently, the applicant undertook the task of rectifying the challenges that were encountered. This process made it evident that the existing technology needed to be comprehensively understood and proved less efficient in practical application.

[0007] The present invention at least partially addresses the problem.

SUMMARY OF INVENTION

[0008] "Unsorted" concerning a waste stream refers to a waste stream that has undergone little or no separation into streams of similar waste types. [0009] "Polymeric hydrocarbons" refers to compounds composed exclusively of hydrogen and carbon atoms, without other elements.

[0010] “Pyrolysis”, used interchangeably with “de-viscification” and “cracking” in this context, is the thermal breakdown of hydrocarbons into smaller molecules to reduce viscosity by shortening chain lengths, transforming heavier hydrocarbons into lighter, more usable forms.

[0011] The invention provides a method of transforming a waste stream into a plurality of hydrocarbon fractions comprising:

(a) separating a solid unsorted waste stream in a first vessel into a fluid fraction by dissolving a polymeric hydrocarbon portion of the waste stream in a solvent and a waste fraction,

(b) de-viscifying the fluid fraction by shortening the chain lengths of the polymeric hydrocarbon portion in a second vessel to produce a fluidised stream;

(c) distilling the fluidised stream in a third vessel to separate the fluidised stream into a plurality of distillate fractions and a residue.

[0012] The waste stream may be an unsorted waste stream.

[0013] The solid unsorted waste stream may be primarily a plastic waste stream, such as a waste stream generated by a typical household.

[0014] The waste fraction may contain one or more: glass, metal, polyethene Terephthalate (PET) and polytetrafluoroethylene (PTFE). [0015] The waste fraction may be removed from the first vessel for further processing or disposal.

[0016] The polymeric hydrocarbon part may contain one or more of the following: polyethene (PE) and polypropylene (PP), polyisobutylene (PIB), polystyrene (PS) and polybutylene (PB).

[0017] The polymeric hydrocarbon part of the waste stream may be liquified by dissolution with a solvent.

[0018] The solvent may be chosen to dissolve the polymeric hydrocarbons selectively and partially.

[0019] The solvent may be a nonpolar solvent such as wax or naphtha.

[0020] The temperature in the first vessel may be within a range of 120°C to 260°C.

[0021] Preferably, the pressure in the first vessel may be atmospheric.

[0022] The first vessel may be a rotary drum.

[0023] The second vessel may be a jacketed coil visbreaker, which includes a heating device, such as a furnace, and a coil within the heating device through which the fluid fraction passes.

[0024] The fluid fraction may be de-viscified by a non-catalytic thermal decomposition process such as a liquid pyrolysis process, specifically viscosity breaking (“visbreaking”). [0025] The gauge pressure in the second vessel may be set within a range of 500 kPa (g) to 1000 kPa (g).

[0026] The temperature in the second vessel may be within a range of 200°C to 450°C. [0027] Preferably, the temperature in the second vessel is within a range of

400°C to 500°C. More preferably, the temperature in the second vessel is within a range of 420°C to 450°C.

[0028] Preferably, between an outlet end of the second vessel and the third vessel, the fluidised stream is cooled with a coolant to within a range of 340°C to 360°C.

[0029] The third vessel may be a distillation column.

[0030] The temperature in the distillation column may be controlled to maintain a temperature gradient of between 300°C to 380°C at a lower end of the column and 120°C to 200°C at a top end of the column. [0031] The plurality of distillate fractions may include at least a first, a second and a third fraction.

[0032] The first distillate fraction may be a gas offtake, including hydrocarbons with carbon chain lengths between C1 and C4 i.e. methane, ethane, propane, and butane. [0033] The gas offtake may be burned to heat the fluid fraction within the second vessel.

[0034] The second distillate fraction may be liquid, including hydrocarbons with carbon chain lengths between C5 and C12, i.e., naphtha.

[0035] The third distillate fraction may be liquid, including hydrocarbons with carbon chain lengths between C12 and C20, i.e., kerosene, diesel, or light and heavy gas oil.

[0036] The residue may be a wax fraction with carbon chain lengths above C20.

[0037] The third distillate fraction, more particularly the gas oil of this fraction, may be used as the coolant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention is further described by way of examples with reference to the accompanying drawing, in which:

Figure 1 is a high-level flow diagram illustrating the process steps in a method of transforming a solid unsorted waste stream into a plurality of hydrocarbon fractions, in accordance with the invention,

Figure 2 is a detailed flow diagram illustrating the specific sub-processes involved in the method shown in Figure 1 , and

Figure 3 schematically illustrates a first vessel and a second vessel in which a first and second step, respectively, of the method take place, and Figure 4 schematically illustrates the complete process in transforming a waste stream into a plurality of hydrocarbon fractions in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Figures 1 and 2 illustrate a method 10 of transforming a solid unsorted waste stream (Mixed Solid Domestic Waste or “MSDW’) into a plurality of hydrocarbon fractions that can be used as fuel or feedstock for other chemical products.

[0040] The method differs from prior art processes, including three primary process steps, each taking place within its vessel.

[0041] In a first step 12, a solid hydrocarbon liquefaction step takes place in a first vessel 14, a rotary drum (see Figure 3), and a solid unsorted waste stream 16 is fed to the first vessel. The waste stream is separated within the vessel into a fluid fraction 18 and a waste fraction 20. The fluid fraction is a partially dissolved polymeric hydrocarbon fraction resulting from contact of the waste stream with a non-polar solvent 22.

[0042] Depending upon its contents, constituent parts of the waste fraction can be recycled, sold to traditional recyclers, or disposed of.

[0043] In a second step, 24, a liquid hydrocarbon cracking step, which takes place in a second vessel 26, the fluid fraction 18 is heated in an oxygen-free environment to thermally crack or decompose the hydrocarbons in the fluid fraction into shorter chain hydrocarbons. In this process the fluid fraction becomes less viscous i.e., the fluid fraction undergoes de-viscification or viscosity breaking to provide a fluidised stream 28 as output from this step.

[0044] In a third step 30, a distillation step, the fluidised stream is input to the third vessel 32, a distillation column. The fluidised stream is separated within the column into a first distillate fraction 34, a second distillate fraction 36, and a third distillate fraction 38. After all the volatiles have been distilled off, what remains from this step is a wax fraction 40.

[0045] Each of these principal steps will be described below in greater detail.

Solid Hydrocarbon Liquefaction

[0046] The liquefaction step 12 serves two objectives: the primary objective is to produce a fluid fraction 18, which becomes the input to the downstream steps, and the secondary objective is to remove contaminants (waste) from the fluid fraction.

[0047] Step 12, comprising these two sub-steps, a heating or gasification step 42 and a dissolution step 44, takes place in the first vessel 14, a rotary drum, illustrated in Figure 3. Both sub-steps occur simultaneously within the first vessel, contrary to the sequential depiction in Figure 2, which is for illustrative purposes only.

[0048] Solid waste stream 16 and liquid solvent 22 are loaded into the rotary drum 14. The solid and liquid blend is mixed by rotation and heated to between 120°C and 260°C at atmospheric pressure. The solid polymeric hydrocarbon part of this waste stream partially dissolves in the solvent and exits the drum as a gelatinous fluid, i.e., the fluid fraction 18. This fluid fraction lacks inert components, such as glass and metals, and haloalkanes or alkyl halides, such as PET, PTFE, and PVC.

[0049] The rotary drum 14 is heated through its proximity to the second vessel 26, a furnace that is heated directly, as will be explained in more detail below.

[0050] The solvent is a nonpolar solvent, such as wax, which can be sourced from the distillation step of method 10, as will be more fully described below.

[0051] The solvent is selected to be insoluble to the following contaminants: glass, metals, PET, and PTFE. The non-dissolved material remains solid and is removed as the waste fraction 18.

[0052] PVC, a contaminant, is not removed as a solid. It is removed by heating it above its dissociation temperature (approximately 110 °C) during the heating step 42. At this temperature, the PVC dissociates with HCI (hydrochloric acid) as a dissociation product. The gaseous dissociation products are vented from rotary vessel 14 as part of a gas fraction 46 (or flue gas).

[0053] Due to its highly corrosive properties, the gas fraction 46, which may contain HCI, is treated in a scrubber 48 with a basic aqueous solution to remove HCI. The gas fraction also contains free water, which may be present in the waste stream and boiled off at the high temperatures experienced in the rotary drum.

[0054] The fluid fraction 18 leaves the rotary drum, through a filtered outlet 50, as a hydrocarbon-rich feedstock for the downstream steps, with little contaminants.

Liquid Hydrocarbon Cracking

[0055] The fluid fraction 18, leaving the preceding liquefaction step 12, enters the liquid hydrocarbon cracking (or pyrolysis) step 24. Pyrolysis is the application of heat to a process stream in the absence of oxygen to crack large molecules into smaller molecules without using a catalyst.

[0056] In this process step, pyrolysis is conducted in the liquid/gas phase utilising an established thermal decomposition (cracking) process known as viscosity breaking or visbreaking, in which the viscosity of a long chain hydrocarbon feedstock is reduced by the breaking down of these long-length molecules into lighter, less viscous (and therefore more manageable) chain hydrocarbons, for example, LPG, gasoline and diesel. Visbreaking was chosen ahead of a delayed coking process because the objective is to minimise the formation of solid products, e.g., carbon black or coke, thereby maximising liquid fuel production.

[0057] In step 24, the second vessel 26 is a visbreaker, which includes a furnace 52 and a tubular coil 54 within the furnace. This is illustrated in Figure 4. The tubular coil enters the furnace at inlet 56 and exits at outlet 58. [0058] The fluid fraction 18 is pumped via a flash drum 60 to and through coil 54. In the flash drum, a liquid mixture is separated into a vapour phase 61 , which leaves the drum at an upper end 62, and a liquid phase exits the drum at a lower end 64.

[0059] The second vessel, 26, is heated by a series of burners which burn oil and synthesis gas (syngas), a partial source of which may come from a distillate fraction (34, 36 or 38) of the upstream distillation step 30. This heats the fluid fraction in the coil to a temperature of between 420-450°C. This temperature range is lower than in other more extreme cracking processes.

[0060] The pressure within the coil is elevated and maintained at 5 kPa (g) to ensure that the fluid fraction contains a liquid phase (and some vapour) during the coil's thermal decomposition (cracking). Keeping the fluid fraction in a tube containing a liquid phase while undergoing thermal cracking allows for more efficient temperature control, uniform temperature distribution, higher fluid temperatures, lower residence time, less expensive metallurgy (now restricted to the coil), and reduced oxygen exposure.

[0061] This process changes from a traditional solid phase to a liquid/gas phase cracking, allowing better control of temperature and reaction time, resulting in better product quality and yield control.

[0062] Oxygen must be substantially removed from this step not to combust the hydrocarbons, a dangerous and wasteful occurrence. [0063] As the product of this thermal decomposition, i.e., the fluidised stream 28, exits the coil at outlet 58, the coil (and its contents) is cooled from a temperature range of 420°C to 450°C down to 360 °C by injection of gas oil 60. This temperature quenching intervention stops the cracking reaction, ensuring that the desired product distribution is obtained and, if allowed to continue uncontrolled, may result in the formation of unwanted byproducts.

[0064] The fluidised stream 28 is depressurised at control valve 62 from 5 bar (500kPa) to 5kPa before it enters distillation column 26 as a mixture of liquid and vapour.

Hydrocarbon Distillation

[0065] In the third step 30, the hot (+/-360°C) fluidised stream 24 is introduced into the packed distillation column 32 to undergo fractional distillation, with distillate fractions (34, 36, 38) collected at offtake outlets (not illustrated) horizontally spaced down the length of the column.

[0066] A flow of steam or water, identified as stream 64, is introduced at the lower end 66 of the column to strip the lighter hydrocarbons dissolved in the heavier hydrocarbons (by reducing the localised partial pressure) to increase the recovery of distillates.

[0067] The flow rate of the fluidised stream A and stream B are controlled to maintain a temperature gradient within the column between 380°C at the lower end 66 of the column and 120°C at the top end 68 of the column. [0068] The more volatile components of the fluidised stream 28 begin to vaporise first, rising through the column in the process, to be collected at the top end 68 as the first distillate fraction 34.

[0069] The first distillate fraction 34 is cooled with cooling water or air. Cooling this fraction at heat exchanger 70 causes the fraction to transition into a liquid and a vapour phase. This mixed phase then undergoes separation in a separator 72 to separate the gas 34 from the resulting two distinct immiscible liquid streams, i.e., a water component containing light organic compounds and a hydrocarbon (naphtha) component 36. Water is removed. Some naphtha is removed, and some is returned to the column.

[0070] After leaving the separator 72, the gas 34 stream is directed to a scrubber (not illustrated) to contact basic water to remove the acidic components effectively. This treated gas 34 may be routed to the furnace, fuel for heating vessel 26 (visbreaker).

[0071] The less volatile components, which remain liquid, travel down column 32 until they reach the boiling point specific to each component. At this temperature, the component vaporises, and the resulting vapour rises through the column. As the vapour ascends, it condenses at designated temperature points, collecting at the respective outlets as either the second distillate fraction 36 (naphtha) or the third distillate fraction (gas oil) 38.

[0072] The naphtha and gas oil fractions (36, 38) are collected and stored (for sale as a fuel or chemical feedstock) or recycled at an upstream part of the method. Examples are using naphtha as a solvent in the solid hydrocarbon liquefaction (first) step or directing naphtha back into the column to serve as cooling material (reflux).

Benefits

[0073] The benefits of a liquid pyrolysis process are:

• increased efficiency, product yield and quality because of better reaction control, and better contaminant removal, and

• reduction/elimination of oxygen ingress could result in combustion during pyrolysis and odours in the pyrolysis products.

[0074] The benefit of separating the method into three main and distinct steps are:

• independent control for optimisation,

• the process can be scaled up by scaling up each step individually,

• each step, in isolation, is conventional, using well-understood technologies, thereby reducing technical risk when scaling up.

[0075] The benefit of the first or liquefaction step is that it allows the method to be used with “dirty” feed. As mentioned, current state-of-the-art methods require “clean” feed, i.e., contaminant-free. Clean feed competes with mechanical recycling for feedstock and significantly reduces the quantities of waste that can be processed because most waste is “dirty”. [0076] The system that employs the method, i.e., the plant, is designed so there are no significant waste streams. The following environmental measures are included in the plant design:

• the scrubber is a chemical scrubber to remove acid gas if required, e.g., HCI, SO2,

• all gas released from the process is routed to the furnace, where it is combusted, thereby oxidising odour molecules.

Claims

1 . A method of transforming a waste stream into a plurality of hydrocarbon fractions comprising:

(a) separating a solid unsorted waste stream in a first vessel into a fluid fraction by dissolving a polymeric hydrocarbon portion of the waste stream in a solvent and a waste fraction;

(b) de-viscifying the fluid fraction by shortening the chain lengths of the polymeric hydrocarbon portion in a second vessel to produce a fluidised stream; and

2. A method according to claim 1 wherein the waste stream is unsorted waste stream.

3. A method according to claim 2 wherein the solid unsorted waste stream is a plastic waste stream.

4. A method according to anyone of claims 1 to 3 wherein the waste fraction contains one or more: glass, metal, polyethene terephthalate (PET) and polytetrafluoroethylene (PTFE).

5. A method according to claim 4 wherein the waste fraction is removed from the first vessel for further processing or disposal.

6. A method according to any of claims 1 to 5 wherein the polymeric hydrocarbon part contains one or more of the following: polyethene (PE) and polypropylene (PP), polyisobutylene (PIB), polystyrene (PS) and polybutylene (PB).

7. A method according to any of claims 1 to 6 wherein the solvent is wax or naphtha.

8. A method according to any of claims 1 to 7 wherein the temperature in the first vessel is within a range of 120°C to 260°C.

9. A method according to any of claims 1 to 8 wherein the pressure in the first vessel is atmospheric.

10. A method according to any of claims 1 to 9 wherein the first vessel is a rotary drum.

11 . A method according to The second vessel is a jacketed coil visbreaker, which includes a housing and a coil through which the fluid fraction passes.

12. A method according to claim 11 wherein the fluid fraction is de-viscified by a non-catalytic thermal decomposition process.

13. A method according to any of claims 1 to 12 wherein the gauge pressure in the second vessel is within a range of 500 kPa to 1000 kPa.

14. A method according to any of claims 1 to 14 wherein the temperature in the second vessel is within a range of 200°C to 450°C.

15. A method according to claim 14 wherein the temperature in the second vessel is within a range of 420°C to 450°C.

16. A method according to claim 14 or 15 wherein between the second vessel and the third vessel the fluidised stream is cooled with a coolant to within a range of 340°C to 360°C.

17. A method according to claim 16 wherein the third vessel is a distillation column.

18. A method according to claim 17 wherein the temperature in the distillation column is controlled to maintain a temperature gradient of between 300°C to 380°C at a lower end of the column and 120°C to 200°C at a top end of the column.

19. A method according to claim 17 or 18 wherein the plurality of distillate fractions includes at least a first, a second and a third fraction.

20. A method according to claim 19 wherein the first distillate fraction is a gas offtake, including hydrocarbons with carbon chain lengths between C1 and C4.

21 . A method according to claim 20 wherein the gas offtake is burned to heat the fluid fraction within the second vessel.

22. A method according to any of claims 19 to 21 wherein the second distillate fraction is a liquid, including hydrocarbons with carbon chain lengths between

C5 and C12.

23. A method according to any of claims 19 to 22 wherein the third distillate fraction is a liquid, including hydrocarbons with carbon chain lengths between C12 and C20.

24. A method according to claim 23 wherein the gas oil of the third distillate is used as the coolant.

25. A method according any of claims 19 to 24 wherein the residue is a wax fraction with carbon chain lengths above C20.