WO2023031895A1

WO2023031895A1 - System and process for desulphurisation of pyrolysis feedstocks

Info

Publication number: WO2023031895A1
Application number: PCT/IB2022/058370
Authority: WO
Inventors: Johann Ferdinand GÖRGENS; Adam Johannes STANDER; Johannes Hendrik KNOETZE; Louis Jacobus DU PREEZ; Somayeh FARZAD
Original assignee: Stellenbosch University
Priority date: 2021-09-06
Filing date: 2022-09-06
Publication date: 2023-03-09
Also published as: ZA202209922B

Abstract

The invention provides a desulphurisation system for at least partially removing a sulphur compound such as H₂S from a sulphur-containing organic feedstock such as scrap tyres. The desulphurisation system comprises an inert heating reactor or chamber, an inert gas delivery system and a vapour transfer component. The heating reactor is configured to heat the sulphur-containing feedstock to a desulphurisation temperature of 300 ºC or lower under an inert atmosphere, which liberates a volatile component containing the sulphur compound. The vapour transfer component transfers the volatile component downstream while leaving behind a desulphurised feedstock residue. The gas delivery system is connected to the heating reactor and provides the inert atmosphere in the heating reactor. The invention extends to a pyrolysis reaction system which includes the described desulphurisation system and a pyrolysis reactor configured to perform a pyrolysis reaction of the residue, typically at a temperature higher than the desulphurisation temperature.

Description

SYSTEM AND PROCESS FOR DESULPHURISATION OF PYROLYSIS FEEDSTOCKS

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from South African provisional patent application number 2021/06492 filed on 6 September 2021 , which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to the desulphurisation of feedstocks for subsequent pyrolysis. The invention relates particularly, although not exclusively, to the desulphurisation of feedstocks comprising waste tyres and sulphur-containing plastics materials.

BACKGROUND TO THE INVENTION

Pyrolysis is a process of chemically decomposing organic substances at elevated temperatures in the partial or complete absence of oxygen. The process typically occurs at temperatures above 430 °C and may be carried out under pressure. In general, pyrolysis of organic substances produces volatile products and leaves a solid residue enriched in carbon char.

Pyrolysis can be used to break down post-consumer polymeric wastes. For example, it can be used to break down the rubber in scrap or waste tyres with recovery of chars, oils, and gases. The rubber in tyres usually contains sulphur from the vulcanization process, which can be an undesirable contaminant in pyrolysis products. Conventional pyrolysis for processing waste tyres produces char products with sulphur contents that are too high for many industrial applications, resulting in products with little or no commercial value.

A need accordingly exists for processes and systems that can remove sulphur compounds from pyrolysis feedstocks. Existing processes for carrying out desulphurisation have disadvantages, however. For example, a known desulphurisation process which treats feedstocks with microwave radiation is highly energy intensive. Conventional pyrolysis processes also suffer a drawback insofar as they typically produce just a single fraction of pyrolysis oils, which is a crude mixture of a wide range of products and has low commercial value.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention there is provided a desulphurisation system for at least partially removing at least one sulphur compound from a sulphur-containing organic feedstock, the desulphurisation system comprising: an inert heating reactor or chamber configured to heat the sulphur-containing organic feedstock to a desulphurisation temperature under an inert atmosphere, thereby to liberate a sulphur-containing volatile component from the sulphur-containing organic feedstock, said volatile component comprising said sulphur compound; an inert gas delivery system connected to the inert heating reactor and configured to provide said inert atmosphere in the inert heating reactor; and a vapour transfer component configured to liberate the sulphur-containing volatile component from the inert heating reactor and to transfer it downstream thereof as a process fluid, while leaving behind a desulphurised feedstock residue or remnant; wherein the desulphurisation temperature is < 300 ^eC.

The desulphurisation temperature may be in a range from about 150°C to about 240°C.

The vapour transfer component may comprise a vacuum drawing component arranged downstream of the inert heating reactor and in communication with it, the vacuum drawing component being configured to draw at least a partial vacuum inside the inert heating reactor. Instead, or in addition, the vapour transfer component may comprise an apparatus for flushing the inert heating reactor with inert gas. The inert gas may comprise nitrogen gas although it will be appreciated that other inert gases may be suitable for use.

The vacuum drawing component may be configured to reduce the pressure in the inert heating reactor to an operating pressure below atmospheric pressure. In certain embodiments it may be configured to reduce the pressure by between 0 and 50 kPa, although in some embodiments the pressure may be reduced by as much as 100 kPa vacuum draw. The vacuum drawing component may accordingly be configured to reduce the pressure in the inert heating reactor to an operating pressure of < 10 kPa (gauge), and in some embodiments to an operating pressure of about 2 kPa (gauge). The inert heating reactor may comprise a vacuum heating system configured to heat the sulphur- containing organic feedstock and draw a vacuum in the reactor. The vacuum heating system may comprise a vacuum oven.

The desulphurisation system may include a feed component arranged to feed the sulphur- containing organic feedstock to the inert heating reactor.

The sulphur-containing organic feedstock may comprise a polymeric substance. Without limitation thereto, the polymeric substance may be selected from the group consisting of natural rubbers, synthetic rubbers, and plastics materials. The polymeric substance may comprise a postconsumer polymeric waste product. The polymeric substance may comprise processed scrap tyres or waste tyres. The sulphur-containing organic feedstock may comprise a feedstock for a pyrolysis process.

The liberated volatile component may comprise H₂S.

The invention extends to a pyrolysis reaction system which includes the desulphurisation system described above. The pyrolysis reaction system may further comprise a pyrolysis reactor or chamber configured to perform a pyrolysis reaction of the desulphurised feedstock residue. It may be configured to perform the pyrolysis reaction at a temperature higher than the desulphurisation temperature, i.e., higher than the temperature to which the inert heating reactor of the desulphurisation system is configured to heat the sulphur-containing organic feedstock. The pyrolysis reaction system may therefore be configured so that, in use, it performs the pyrolysis reaction at a temperature higher than the temperature range used for desulphurising the feedstock.

The pyrolysis reactor may be configured to perform the pyrolysis reaction at a temperature above 300 ^eC. It may be configured to perform the pyrolysis reaction at a temperature in a range between 300 ^eC and 900 ^eC. In certain embodiments, the pyrolysis reactor may be configured to perform the pyrolysis reaction at a temperature in a range between 300 ^eC and 800 ^eC. For selected applications involving the processing of scrap tyre feedstock, the pyrolysis reactor may be configured to perform the pyrolysis reaction at a temperature in a range from 450 °C to 700 °C.

The inert heating reactor of the desulphurisation system and the pyrolysis reactor of the pyrolysis reaction system may be provided by the same component, that is, they may comprise a common heating reactor configured to perform both the inert heating process and the pyrolysis reaction as separate and consecutive operations in the lower and higher relative temperature ranges, respectively. For purposes of this specification, the term “inert heating process” refers to the process of heating the sulphur-containing organic feedstock to the desulphurisation temperature under the inert atmosphere.

Alternatively, the pyrolysis reactor may be provided as a further heating reactor separate from the inert heating reactor. In such embodiments the pyrolysis reactor may be arranged downstream of the inert heating reactor, and the pyrolysis reaction system may include a feedstock transfer system configured to transfer the desulphurised feedstock residue from the inert heating reactor to the pyrolysis reactor to undergo the subsequent, higher temperature pyrolysis.

The pyrolysis reactor may comprise a vacuum heating system configured to heat the desulphurised feedstock and draw a partial vacuum in the reactor. The vacuum heating system may comprise a vacuum oven. The vacuum heating system may include a vacuum drawing component configured to reduce the pressure in the pyrolysis reactor to an operating pressure below atmospheric pressure. In certain embodiments it may be configured to reduce the pressure in the pyrolysis reactor by between 0 and 50 kPa, although in some embodiments it may be configured to reduce the pressure by as much as 100 kPa vacuum draw. The vacuum drawing component may accordingly be configured to reduce the pressure in the pyrolysis reactor to an operating pressure of < 10 kPa (gauge), and in some embodiments to an operating pressure of about 2 kPa (gauge).

The pyrolysis reaction system may be configured to liberate or evolve a sulphur-depleted volatile component from the desulphurised feedstock residue.

Optionally, the pyrolysis reaction system may comprise at least one fractional condensation system arranged downstream of the pyrolysis reactor. The fractional condensation system may comprise one or more condensation subsystems. The number of condensation subsystems is variable according to requirements and may range from one up to 10 or more subsystems in certain embodiments. Each condensation subsystem may be configured to operate through a different temperature or residence time range, or both. Having a plurality of different condensation subsystems accommodates the use of different pyrolysis feedstocks and temperatures for the pyrolysis reaction.

The fractional condensation system may be configured to condense the sulphur-depleted volatile component evolved from the pyrolysis reaction, thereby to yield a plurality of discrete condensed fractions thereof. With strict control of condenser exit temperature and residence times, multiple fractions can be separated. The fractional condensation system may be equipped with valve means to permit the flow of process fluid to be selectively diverted between the various condensation subsystems.

The pyrolysis reaction system may include an inert gas delivery system connected to the pyrolysis reactor and configured to provide an inert atmosphere therein. This gas delivery system may be the same as that used for the desulphurisation step, i.e., the inert gas delivery system connected to the pyrolysis reactor may be the same component as the inert gas delivery system connected to the inert heating reactor. (This may be the case, for example, where a common heating reactor is used to perform the desulphurisation step and the subsequent, higher-temperature pyrolysis.)

The inert gas delivery system may further comprise an apparatus for flushing the pyrolysis reactor (or common heating reactor) with inert gas to assist in transferring volatiles out of the reactor.

In accordance with a further aspect of the invention there is provided a desulphurisation process for at least partially removing at least one sulphur compound from a sulphur-containing organic feedstock, the process comprising the steps of:

(i) providing a desulphurisation system which comprises an inert heating reactor or chamber; an inert gas delivery system connected to the inert heating reactor and configured to provide an inert atmosphere in the inert heating reactor; and a vapour transfer component configured to remove volatiles from the inert heating reactor and transfer them downstream thereof as a process fluid;

(ii) feeding the sulphur-containing organic feedstock into the inert heating reactor;

(iii) heating the sulphur-containing organic feedstock in the inert heating reactor to a desulphurisation temperature < 300 ^eC under the inert atmosphere, thereby to liberate a sulphur-containing volatile component from the sulphur-containing organic feedstock, while leaving behind a desulphurised feedstock residue or remnant; said sulphur- containing volatile component comprising said sulphur compound; and

(iv) utilising the vapour transfer component to transfer the sulphur-containing volatile component downstream of the inert heating reactor. The vapour transfer component may comprise a vacuum drawing component arranged downstream of the inert heating reactor and in communication with it, the vacuum drawing component being configured to draw at least a partial vacuum inside the inert heating reactor. In such a case, the disclosed desulphurisation process may include a step of drawing a partial vacuum in the inert heating reactor. Instead, or in addition, the desulphurisation process may include flushing the inert heating reactor with an inert gas, thereby to displace the sulphur containing volatile component and to transfer it downstream.

The step of drawing a partial vacuum may comprise reducing the pressure in the inert heating reactor to an operating pressure at or below atmospheric pressure. The pressure may be reduced by between 0 and 50 kPa, although in some cases the pressure may be reduced by as much as 100 kPa vacuum draw. The step of drawing a partial vacuum may accordingly comprise reducing the pressure in the inert heating reactor to an operating pressure of < 10 kPa (gauge), and in some cases to an operating pressure of about 2 kPa (gauge).

Details of the desulphurisation system, inert heating reactor, inert gas delivery system, vacuum drawing component, sulphur-containing organic feedstock and other salient components used in the method may be as described above. Corresponding embodiments may accordingly also be applicable for this aspect of the invention.

The invention extends to a pyrolysis method which comprises: utilising the desulphurisation process described above to remove at least one sulphur compound at least partially from a sulphur-containing organic feedstock, thereby to yield a desulphurised feedstock residue; and utilising a pyrolysis reactor to perform a pyrolysis reaction of the desulphurised feedstock residue.

The pyrolysis method may comprise performing the pyrolysis reaction at a temperature higher than the temperature range of the heating step of the desulphurisation process.

The pyrolysis method may comprise performing the pyrolysis reaction at a temperature between 300 ^eC and 900 ^eC. The pyrolysis method may comprise performing the pyrolysis reaction at a temperature in a range from 300 ^eC to 800 ^eC.

For selected applications involving the processing of scrap tyre feedstock, the pyrolysis method may comprise performing the pyrolysis reaction at a temperature in a range from 450 °C to 700 °C. The inert heating reactor and the pyrolysis reactor may be provided by the same component, that is, they may comprise a common heating reactor configured to perform the desulphurisation process and the pyrolysis reaction as separate and consecutive operations in the lower and higher relative temperature ranges, respectively.

The pyrolysis method may include liberating or evolving a sulphur-depleted volatile component from the desulphurised feedstock residue by either or both of the following processes: (i) applying a partial vacuum, or (ii) flushing the pyrolysis reactor with the inert gas.

The pyrolysis reaction may be performed at an operating pressure in the pyrolysis reactor that is below atmospheric pressure and, in some cases, at an operating pressure of about 2 kPa (gauge).

The pyrolysis method may comprise at least one fractional condensation step wherein the sulphur-depleted volatile component from the pyrolysis reaction is fractionally condensed to yield a plurality of discrete condensed fractions thereof.

Details of the salient components used in the pyrolysis method may be as described elsewhere in this disclosure. Corresponding embodiments may accordingly also be applicable for this aspect of the invention.

The invention may extend to products manufactured using the disclosed pyrolysis method. These products may, without limitation, include fuels, chemicals, chars and other solid products, oils, and gases. The fuels may be selected from the group consisting of marine bunker oil, diesel, and naphtha. The chemicals may, for example, include dl-limonene.

Embodiments and modes of performing the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a process flow diagram of an embodiment of the disclosed pyrolysis reaction system which includes a desulphurisation system, heating reactor and fractional condensation systems; Figure 2 is a block diagram illustrating the desulphurisation process described herein;

Figure 3 is a schematic flow diagram illustrating an exemplary mode of desulphurisation using the disclosed desulphurisation process (Process 1 ); and

Figure 4 is a schematic flow diagram illustrating a subsequent process (Process 2) which involves pyrolysis and fractional condensation of the desulphurised residue of Process 1 .

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Embodiments of the invention are explained in greater detail in the following description. A desulphurisation system and process are provided for removing sulphur compounds from sulphur-containing organic feedstocks intended for subsequent pyrolysis.

A pyrolysis reaction system and method are also described. The pyrolysis reaction system includes the abovementioned desulphurisation system as well as equipment for carrying out pyrolysis of the desulphurised feedstock and for fractionally condensing the evolved volatiles and oils.

Without limiting the generality thereof, the raw feedstock may include post-consumer polymeric waste products such as processed scrap tyres and plastics. In part, therefore, the present disclosure describes a process for separating sulphur products out of raw, sulphur-containing tyre-derived feedstocks and for fractionating volatiles evolved from pyrolysis oil produced from such feedstocks. There are two main pyrolytic products from passenger car tyres, liquid oils and solid chars. The disclosed process may yield low-sulphur solid products, such as low-sulphur char and low-sulphur oil and gaseous products or volatiles in selectable and variable fractions.

It will be appreciated, however, that a wide range of other sulphur-containing organic feedstocks may be suitable for processing using the method.

Pyrolysis Reaction System

Referring to Figure 1 , the invention provides a pyrolysis reaction system (101 ) which includes a desulphurisation system (103) and a pyrolysis apparatus (105). The pyrolysis reaction system (101 ) may comprise a two-zone heating reactor (107).

The pyrolysis reaction system (101 ) may further include a fractional condensation system (109). In the illustrated embodiment, this system (109) comprises first and second condensation subsystems (110, 11 1 ). However, it will be appreciated that additional condensation subsystems may also be provided as required.

The desulphurisation system (103) and the pyrolysis apparatus (105) may make use of the same heating reactor (107). Thus, the heating reactor (107) may be configured to perform (i) an inert heating process for the desulphurisation process, carried out at a temperature lower than that typically employed for pyrolysis (Process 1 ), and (ii) a higher-temperature process comprising a pyrolysis reaction (Process 2). In the former context, the heating reactor (107) may be referred to as an inert heating reactor (107.1 ). In the latter context, it may be referred to as a pyrolysis reactor (107.2).

In the illustrated embodiment, the heating reactor (107) serves as a common reactor that carries out both abovementioned processes (i) and (ii). However, it will be appreciated that in other embodiments of the system (not shown), separate reactors may be used to perform these two different processes.

The heating reactor (107) may comprise a vacuum heating system configured to heat the feedstock and at the same time maintain a partial vacuum in the reactor. The vacuum heating system may comprise at least one vacuum oven.

The inert heating reactor (107.1 ) may be configured to heat the sulphur-containing organic feedstock to a desulphurisation temperature no higher than about 300 ^eC. In certain embodiments, it may be configured to heat the feedstock to a desulphurisation temperature in a range from about 150 ^eC to about 240 ^eC. Significant cleavage of hydrocarbons may occur at temperatures above 200 °C to 250°C, however, and condensable vapours can be formed at temperatures above 250°C, which would negatively affect the quality and yield of oil during the subsequent pyrolysis and fractionation (Process 2). These considerations must be taken into account when selecting an appropriate desulphurisation temperature.

For Process 2, the pyrolysis reactor (107.2) may be configured to perform the pyrolysis reaction at a temperature above 300 ^eC. For example, it may be configured to perform the pyrolysis reaction at a temperature in a range between about 300°C and about 900°C. Thermal degradation of scrap tyres at atmospheric pressure begins at around 250 °C and pyrolysis of tyres is typically carried out in a temperature range from about 450 °C to about 700 °C. Therefore, when used for the processing of scrap tyre feedstocks, the pyrolysis reactor (107.2) may be configured to perform the pyrolysis reaction in that temperature range.

Low temperature pyrolysis of biomass, plastics and rubber can be achieved at a temperature of 310 °C. Pyrolysis is possible at lower temperatures when employing Fluid Catalytic Cracking (FCC) catalysts. However, for non-catalytic pyrolysis it is typically not practical to conduct pyrolysis at temperatures lower than about 300 °C to produce high quality fuel products.

The inert heating reactor (107.1 ) may be configured to heat the sulphur-containing organic feedstock under the inert atmosphere and partial vacuum. In use, the inert heating reactor (107.1 ) may liberate a sulphur-containing volatile component from the sulphur-containing organic feedstock, while leaving a desulphurised feedstock residue in the reactor. In use, the liberated volatile component may comprise sulphur compounds such as, but not limited to, H₂S.

The desulphurisation system (103) may also include a vapour transfer component configured to transfer the sulphur-containing volatile component as a process fluid to a location downstream of the inert heating reactor. The vapour transfer component may include an oil sealed vacuum pump (1 13) or other suitable vacuum system. In use, the vacuum pump (1 13) may be used to apply a suction to the interior of the inert heating reactor (107.1 ) so that a partial vacuum is established in it. This may assist in liberating the sulphur-containing volatile component from the feedstock as well as transferring it out of the reactor.

Pyrolysis is typically performed under an inert gas atmosphere to provide anaerobic or substantially oxygen-free reaction conditions. Accordingly, in addition to the vacuum pump (1 13), the desulphurisation system (103) and the pyrolysis apparatus (105) may be serviced by an inert gas delivery and flushing system (1 15) connected to the heating reactor (107) to provide an inert atmosphere therein. This system may be used to displace the evolved gases in the heating reactor (107) and substitute them with an inert or oxygen-depleted gas such as nitrogen gas. The gas delivery and flushing system (115) may include a nitrogen gas cylinder (117) and conduit system (1 19) connected to the heating reactor (107). The conduit system (119) may include valve means (121 ) and a nitrogen gas control unit or module (123). The control unit may be used to control the valve means (121 ) and hence the flow of nitrogen gas.

The pyrolysis reaction system (101 ) may include a char pot (124) for receiving char produced during pyrolysis in the heating reactor (107). Conduiting (125) may be used to connect the heating reactor (107) to the first condensation subsystem (110) via the char pot (124). The conduiting may be provided with a trace heating system (127) comprising trace heater couples. This may include one or more electrical heating elements running in physical contact along pipes carrying the process fluid, for transferring heat into the fluid.

The first condensation subsystem (110) may comprise a series of fractionating condensers (131 , 133, 135) arranged downstream of the pyrolysis reactor (107.2). These condensers may be configured to condense and fractionate the sulphur-depleted volatile component liberated or evolved by pyrolysis of the desulphurised feedstock residue. By way of example only, the condenser (131 ) may comprise an electrically heated condenser; the three condensers (133) may each comprise a water-cooled condenser; and the condenser (135) may comprise a countercurrent water cooled condenser.

The second condensation subsystem (1 11 ) is shown in the block delineated with broken lines in Figure 1. This subsystem (11 1 ) may include a series of fractionating condensers (137, 139, 141 , 143) arranged downstream of the pyrolysis reactor (107.2).

These condensers may also be configured to condense and fractionate a sulphur-depleted volatile component that results from a pyrolysis reaction, but may be used when the feedstock is different than that for which the first condensation subsystem (110) is used. The first two condensers (137.1 , 137.2) of the second condensation subsystem (1 11 ) may each comprise a sand bath high temperature condenser. The condenser (139) may comprise an electrically heated condenser. The condenser (141 ) may comprise a water-cooled condenser. The final condenser (143) may comprise a counter-current water cooled condenser.

A branched valve arrangement (145) may be provided and may be controllable to selectively draw the volatiles through either the first or the second condensation subsystems (110, 11 1 ). The reason for having different condensation subsystems is to be able to vary the fractions obtained from the oils produced. This could vary depending on feedstock, pyrolysis conditions and condensation conditions. Different fractions will have different properties as either fuels in themselves or feedstocks for chemicals extraction.

The desulphurisation system (103) and, by extension, the pyrolysis apparatus (105), may include a feed component (147) arranged to feed the sulphur-containing organic feedstock to the heating reactor (107). In the illustrated embodiment (101 ), the feed component (147) includes a feeding piston (149) and feeding hopper (151 ). The pyrolysis reaction system (101 ) may be controllable by means of a main control unit or module (153).

As noted previously, the inert heating reactor (107.1 ) and the pyrolysis reactor (107.2) may be provided by a single, two zone heating reactor (107) that is common to the inert heating and the pyrolytic processes. This heating reactor (107) may thus be configured to perform both the initial desulphurisation process as well as the subsequent high-temperature pyrolysis reaction. These two operations can be performed as separate and consecutive operations in the lower and higher temperature ranges, respectively.

However, in alternative embodiments (not shown), the pyrolysis reactor may be provided as a separate reactor that is arranged downstream of the inert heating reactor. In such embodiments the pyrolysis reaction system may include a feedstock transfer system (not shown) configured to transfer the desulphurised feedstock residue from the inert heating reactor of the desulphurisation system into the pyrolysis reactor for the subsequent, higher temperature pyrolysis.

The latter type of embodiment may permit the disclosed desulphurisation system to be retrofitted to existing pyrolysis installations, thereby serving as a pre-treatment apparatus to feed desulphurised feedstock to the existing installation.

In use, the pyrolysis reaction may be performed on the desulphurised feedstock residue yielded by the inert heating process.

Gas collection towers (155) may be included to collect remaining gas after the various fractions have been removed. One or more extraction fans (157) may be provided to remove excess processed gas product from the gas collection towers (155), or from other parts of the pyrolysis reaction system (101 ), and vent them to the atmosphere. The extraction fans may also inhibit escape of vapours from the pyrolysis reaction system in case of leaks.

Desulphurisation Process

Referring now to Figure 2, the desulphurisation system (103) may be used to carry out a desulphurisation process (200) for removing sulphur compounds from sulphur-containing organic feedstocks. The desulphurisation process (200) may involve feeding (210) the sulphur-containing organic feedstock into the inert heating reactor (107.1 ), then heating (220) the feedstock to a desulphurisation temperature < 300 ^eC under inert atmosphere. The desulphurisation temperature may be in a range from about 150°C to about 240°C, for example.

The desulphurisation process may include a step of drawing a partial vacuum or suction (230) in the inert heating reactor. In one exemplary mode of performing the desulphurisation process, the pressure inside the reactor can be reduced by between 0 and 50 kPa, resulting in an operating pressure in a range from about 50 kPa up to atmospheric pressure. However, it will be appreciated that a range of other operating pressures may also be effective. For example, in some cases the pressure in the inert heating reactor may be reduced by as much as 100 kPa vacuum draw, resulting in an operating pressure of < 10 kPa (gauge) and in some cases about 2 kPa (gauge).

In addition to the vacuum drawing step, or instead of it, the desulphurisation process may optionally include flushing (240) the heating reactor (107) with an inert gas such as nitrogen. This may assist in displacing evolved sulphur-containing volatiles from the heating reactor.

The heating and the application of the partial vacuum may cause a sulphur-containing volatile component to be evolved or liberated (250) from the feedstock. The evolved volatile component may be transferred (260) downstream of the inert heating reactor (107.1 ) for further processing to separate and recover or sequestrate sulphur contaminants such as H₂S.

A sulphur-depleted residue may be left behind (270) after completion of the desulphurisation process (200). This residue may comprise solid substances and oils. It may be used as a sulphur- depleted feedstock for the subsequent, high-temperature pyrolysis and fractional condensation that are described in more detail below.

The described desulphurisation process (200) may be employed as a first step in a larger pyrolysis method discussed below. The desulphurisation process may thus be used to pre-treat sulphur-containing tyres, plastics and other such feedstocks before they are processed by conventional, higher-temperature pyrolysis.

Pyrolysis Method

The pyrolysis reaction system (101 ) of Figure 1 may be used to carry out a pyrolysis method to liberate and fractionate a sulphur-depleted volatile component from the desulphurised feedstock residue produced during the desulphurisation process (200). Figures 3 and 4 illustrate an exemplary mode of carrying out the pyrolysis method. The pyrolysis method may involve first and second subsidiary processes (301 , 401 ), referred to in this explanation as Processes 1 and 2 respectively. Process 1 is equivalent to the desulphurisation process (200) described above. Process 2 involves pyrolysis of the desulphurised residues from Process 1 at higher temperatures, followed by fractional condensation of the resultant, sulphur- depleted volatiles.

Process 1 : Desulphurisation by heating under vacuum draw

Process 1 yields desulphurised solid and liquid residues of the feedstock. The process may involve the following two main steps:

1 (a) Heating the raw sulphur-containing organic feedstock to a desulphurisation temperature under an inert or oxygen-depleted atmosphere in the heating reactor or vacuum oven (107).

1 (b) Drawing a partial vacuum in the heating reactor or vacuum oven (107) to remove sulphur compounds from the raw feedstock, primarily as a gaseous vapour or a volatile component which contains H₂S.

Steps 1 (a) and 1 (b) can be performed together as part of a single, concurrent, and contemporaneous operation. However, they may also be performed as two discrete consecutive operations.

As explained previously, the desulphurisation process can be conducted at or near atmospheric pressure. However, there may be advantages to conducting it under partial vacuum according to step 1 (b) above. For example, this can facilitate performing Process 1 and Process 2 in series, both under vacuum to permit a simpler design of the overall system. The reduced pressure within the reactor may inhibit liberated sulphur radicals from rebonding with the rubber or other polymeric feedstock by reducing the volatile residence time within the heated reactor system.

Referring to Figure 3, a sulphur-containing rubber or plastics feedstock may be fed (303) into the heating reactor or vacuum oven (107) which performs steps 1 (a) and 1 (b) above. The H₂S- containing gaseous vapour mentioned in step 1 (b) is liberated (307) from the feedstock under a partial vacuum generated downstream of the vacuum oven (107). Desulphurised rubber or plastics are produced (309) as a residue in solid form together with a small fraction of non- condensable gas comprising H₂S. The residue may be suitable for subsequent conversion in Process 2 (below), which relies upon the higher temperature pyrolysis.

Process 2: Pyrolvsis at higher temperature followed bv fractional condensation

The following three steps may be performed in this second process:

2(a) Pyrolysis of a feedstock comprising the desulphurised feedstock residues from Process 1 above, but in this case carried out at higher temperatures than the temperature of Process 1 , and also with limited presence of oxygen The temperature of this pyrolysis reaction typically exceeds 300 °C. Advantageously, the pyrolysis may be carried out at a temperature in a range between about 300°C and about 900°C. For selected applications involving the processing of scrap tyre feedstock, the pyrolysis may be carried out at a temperature in a range from 450 °C to 700 °C. This pyrolysis may be conducted in the heating reactor (107). A volatile residence time of 1 minute to 3 hours may be used.

2(b) Extraction of hot volatile products from the pyrolysis reactor, consisting of both condensable oils and permanent gases. The extraction can be carried out by applying a vacuum downstream of the reactor, or by flushing the reactor with inert gas (such as nitrogen gas), or, or by both means. A combination of flushing the reactor with N₂ and applying about 0 to 10 kPa (gauge) of vacuum was used for the experimental extraction.

2(c) Stepwise fractional condensation of the volatile products of the pyrolysis reaction.

Steps 2(a), 2(b) and 2(c) can be performed together as part of a single, concurrent, and contemporaneous operation. However, they may also be performed as discrete consecutive operations.

Referring to Figure 4, the desulphurised rubber or plastics feedstock may be fed (403) into the heating reactor or vacuum oven (107) for pyrolysis. As indicated, Processes 1 and 2 may employ the same heating reactor or vacuum oven (107). For example, the vacuum oven referred to in the description for Process 1 may also be employed for Process 2 provided it is operated at the higher temperature range required for Process 2. Alternatively, they may comprise separate heating reactors or vacuum ovens. Embodiments of the system which include two separate heating reactors may be preferred where efficiency is a key consideration, since this configuration may permit Process 1 and Process 2 to be operated continuously instead of as a batch process. The vacuum oven (107) may be flushed (407) with nitrogen gas while a partial vacuum is drawn downstream of the oven, causing hot volatile products to be extracted from the vacuum oven (107). This process may produce desulphurised waste rubber char which may be deposited or conveyed (409) out of the vacuum oven (107) and collected in the char pot (124).

Fractional condensation is then performed. During this step, a volatile component liberated from the pyrolysis oil of the higher temperature pyrolysis reaction is drawn from the vacuum oven (107) as a process stream (411 ) and fractionally condensed. It will be appreciated that the liberated volatile component in this case will have a lower sulphur content than that of the desulphurisation process, since it will have been evolved from the desulphurised or sulphur depleted feedstock produced by Process 1. This volatile component is therefore referred to herein as a sulphur- depleted volatile component.

The fractional condensation system which carries out this step may comprise variable numbers, types and configurations of condensation subsystems and fractionating condensers. For example, it may comprise the specific arrangement of condensers shown in Figure 4, i.e., condensers 413, 415, 417, and 41 n where n is a variable number. (A further exemplary embodiment of the fractional condensation system is the system (109) shown in Figure 1 .)

Each condenser may be operated in a distinct range of temperatures, depending upon the fractions required to be obtained from the oils produced, the type of feedstock, the pyrolysis conditions and the condensation conditions, with the condensers for the highest temperature ranges being arranged first in series. By way of example, the first condenser (413) could be configured to operate at 250 °C to 350 °C, the second (415) at 100 °C to 250 °C, and the third (417) at ambient temperature to 250 °C.

Fractions of condensable oils may be obtained from the condensers. For example, an oil fraction close to marine bunker oil (MBO) may be obtained from the first condenser (413). A fuel fraction similar to diesel fuel may be obtained from the second condenser (415). A fuel fraction comparable to gasoline may be obtained from the third condenser (417). Additional fuel fractions may be obtained from the variable number (n) of the further condensers (41 n).

More temperature-controlled condensers could be added to the condensation system to produce additional fuel or chemical fractions. These added condensers could be operated in temperature ranges which are higher than those of the above-mentioned fractions, or intermediate between them, or lower than them. These condensers would be placed before, between or after the first mentioned condensers, respectively, depending on their specific operating temperatures. Some of the condensers may be specifically designed to maximize the concentrations of high value chemicals such as, but not limited to, limonene in particular oil fractions.

Downstream condensers operating at or below room temperature can be provided to carry out a last series of condensation steps to obtain gaseous pyrolysis products. These condensers may be configured to condense fractions which would typically otherwise be gaseous at standard temperature and pressure. This series of condensations may also result in the production of water fractions.

The number of condensers can be reduced if fewer fractions are required.

Process 1 typically does not produce condensable vapours in quantities which would justify fractional condensation. The operating temperature range of Process 1 is typically too low to break carbon-carbon bonds within the waste tyre rubber polymer. Thus, the fractional condensation system described above will typically only be employed for fractionation while carrying out Process 2 using feedstock treated and generated during Process 1 . However, the sulphur-contaminated gases evolved during Process 1 can optionally be made to pass through the fractional condensation system in certain embodiments. In such cases the condensation system can be set to a low temperature to remove any condensable vapours which may accompany the sulphur gases evolved during Process 1 . Condensable volatiles may only be expected to form when desulphurisation temperatures in excess of 200 ^eC are used, however.

Pyrolysis gas may exit (419) the fractional condensation system.

The char, oil and gaseous products obtained from the desulphurised solids may be expected to have a substantially lower sulphur content than pyrolysis products obtained from feedstocks not processed with the disclosed desulphurisation process (200).

Experimental Process Conditions and Operational Parameters

Experimental desulphurisation was conducted using a pyrolysis pilot plant which included a desulphurisation system (103) as disclosed herein.

The feedstock used for the experimental process was waste tyre rubber granules which were free from fibres and steel. The granules were manufactured from truck tyres and sourced from Trident Fuels, Germiston, South Africa. The conditions for the experimental desulphurisation process are summarised in Table 1 below. The inert heating reactor (107.1 ), char pot (124) and trace heater (127.1 ) were set to specific temperatures. Although no liquid products were expected to be formed at the lower operating temperatures, the fractional condensation system of the pilot plant (comprising glass water cooled condensers arranged in series) was cooled to 5 °C. After all the allotted feedstock was fed to the pilot plant, the system was allowed to operate at the set process conditions for an additional two hours to allow entrained feedstock to be migrated out of the reactor.

Table 1 : Experimental Process Conditions for Desulphurisation

* For those embodiments of the system which include a vacuum drawing component, the desulphurisation of the raw sulphur-containing organic feedstock may be carried out at a pressure below ambient atmospheric pressure.

The following Table 2 summarises the process conditions used for the experimental pyrolysis and fractional condensation using Process 2:

Table 2: Experimental Process Conditions for Pyrolysis and Fractional Condensation

It will be appreciated that variations may be made to any of the process conditions and operating parameters, including but not limited to temperature, pressure, gas flow rates, and types of activating or inert gases.

Appropriate temperature selections are required for the fractional condensation process since pyrolysis oil derived from waste tyre rubber has a different chemical composition than that obtained from other types of pyrolysis, e.g., pyrolysis of biomass, and the chemical and fuel properties of the fractions obtained are different. These differences require modifications to the preferred temperatures in the fractionation condensers. The operating temperatures tabulated above were found to be advantageous, although it will be appreciated that a range of other temperatures may also fall within the scope of the invention.

Fuel Characteristics of Obtained Fractions

Fractions of the tyre derived fuel (TDF) obtained from the pyrolysis and fractional condensation process were analysed to determine their characteristics and properties. The results are tabulated in the following Table 3:

Table 3: Characteristics of Fuel Fractions from Fractional Condensation

* Marine Bunker Oil

Elemental Analysis of Feedstock and Char

The following Table 4 compares the carbon, hydrogen, nitrogen, and sulphur (CHNS) content of a raw sulphur-containing organic feedstock with the CHNS content of a desulphurised feedstock produced with the disclosed desulphurisation system and method:

Table 4: CHNS Elemental Analysis of Raw Feedstock, Desulphurised Feedstock, and Char

The experimental results indicated that the disclosed desulphurisation process may significantly decrease the sulphur content of rubber and plastics feedstocks, resulting in low sulphur solid products that are suitable for subsequent conversion through pyrolysis. The char, oil and gaseous products obtained from the desulphurised solids also each had a substantially lower sulphur content compared to pyrolysis products obtained from solid feedstocks not processed through desulphurisation.

The disclosed desulphurisation system and process may have advantages over other technologies for desulphurisation of pyrolysis feedstocks. For example, the present method may be relatively simple to implement compared to desulphurisation techniques based on microwave treatment, wet methods, or the use of additives.

Also, the lower temperature desulphurisation of the present method may permit operational energy savings and fewer downstream purification processes, which may in turn even further reduce the energy demands. This is evident in comparison to methods of microwave desulphurisation, for example, and other literature describes desulphurisation temperatures which are significantly higher (325 °C to 1000 °C) than the temperatures used for the present method (150 °C to 240°C, for example). Such prior art disclosures therefore teach away from the presently disclosed desulphurisation method, instead of towards it.

The disclosed technology may provide several other benefits not offered by conventional processes for pyrolysis and product condensation. These may include:

• Lower sulphur content in the produced char and pyrolysis oils; this stands in contrast to conventional pyrolysis processes for waste tyres which produce char products having sulphur contents that are too high for industrial application and have little or no commercial value. The presently disclosed technology may accordingly produce both char and oil products that have higher economic value, particularly in the case of MBO, than those produced by standard pyrolysis processes.

• Oil products with greater commercial values may be obtained by splitting the pyrolysis volatiles and oils into fractions through the stepwise condensation of the hot pyrolysis vapours. The oil fractions may have specifications closer to commercial fuels, giving better economic values.

• The produced fractions have fewer requirements for further refining before they are suitable for use as commercial fuels and sources of valuable chemicals. These include fewer chemical, and energy demands for their further processing, which has financial benefits.

• Reduced potential for secondary cracking reactions during product refining since the need for refining is reduced.

• The pyrolysis oil fractions can be manipulated with respect to their different fuel and chemical characteristic properties. Some fractions can also be isolated that are suitable for chemicals extraction, and such chemicals may have higher value than the fuel-only products obtained from conventional pyrolysis. Conventional pyrolysis processes may produce just a single fraction of pyrolysis oils comprising a crude mixture of a wide range of products with low commercial value.

• The technology may provide enhanced commercial viability of pyrolysis processing of sulphur-containing organic feedstocks, resulting from the abovementioned cost savings and other financial benefits which the disclosed system and process may provide.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that may issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention.

Finally, throughout the specification, unless the context requires otherwise:

• “comprise” or variations such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers;

• “desulphurisation” or variations such as “desulphurised” will be understood to encompass partial desulphurisation, i.e., the term does not necessarily imply complete desulphurisation; and may also be referred to as desulfurisation, desulphuration or desulfuration;

• “inert atmosphere” will be understood to refer to an atmosphere having a limited oxygen content, i.e., an atmosphere from which oxygen is at least partially depleted or absent;

• “inert heating process” will be understood to refer to a process in which a substance is heated under an inert atmosphere; and

• “inert heating reactor” will be understood to refer to a reactor configured to heat a substance under an inert atmosphere.

Claims

23 CLAIMS:

1. A desulphurisation system for at least partially removing at least one sulphur compound from a sulphur-containing organic feedstock, the desulphurisation system comprising: an inert heating reactor configured to heat the sulphur-containing organic feedstock to a desulphurisation temperature under an inert atmosphere, thereby to liberate a sulphur-containing volatile component from the sulphur-containing organic feedstock, said volatile component comprising said sulphur compound; an inert gas delivery system connected to the inert heating reactor and configured to provide said inert atmosphere in the inert heating reactor; and a vapour transfer component configured to liberate the sulphur-containing volatile component from the inert heating reactor and to transfer it downstream thereof as a process fluid, while leaving behind a desulphurised feedstock residue; wherein the desulphurisation temperature is < 300 ^eC.

2. The desulphurisation system as claimed in claim 1 , wherein the vapour transfer component comprises a vacuum drawing component arranged downstream of the inert heating reactor and in communication with it, the vacuum drawing component being configured to draw at least a partial vacuum inside the inert heating reactor; and wherein the vapour transfer component further comprises an apparatus for flushing the inert heating reactor with inert gas.

3. The desulphurisation system as claimed in claim 1 or claim 2, wherein the sulphur- containing organic feedstock comprises processed scrap tyres or waste tyres.

4. A pyrolysis reaction system which includes the desulphurisation system as claimed in any one of claims 1 to 3.

5. The pyrolysis reaction system as claimed in claim 4, comprising a pyrolysis reactor configured to perform a pyrolysis reaction of the desulphurised feedstock residue at a temperature higher than the desulphurisation temperature.

6. The pyrolysis reaction system as claimed in claim 5, wherein the pyrolysis reactor is configured to perform the pyrolysis reaction at a temperature above 300 ^eC.

7. The pyrolysis reaction system as claimed in claim 5 or claim 6, wherein the pyrolysis reactor is arranged downstream of the inert heating reactor and the pyrolysis reaction system includes a feedstock transfer system configured to transfer the desulphurised feedstock residue from the inert heating reactor to the pyrolysis reactor. The pyrolysis reaction system as claimed in any one of claims 4 to 7, further comprising at least one fractional condensation system arranged downstream of the pyrolysis reactor and comprising a plurality of condensation subsystems, each subsystem being configured to operate in a different operational range than the other subsystems in respect of temperature, residence time, or temperature and residence time. A desulphurisation process for at least partially removing at least one sulphur compound from a sulphur-containing organic feedstock, the process comprising the steps of:

(i) providing a desulphurisation system which comprises an inert heating reactor; an inert gas delivery system connected to the inert heating reactor and configured to provide an inert atmosphere in the inert heating reactor; and a vapour transfer component configured to remove volatiles from the inert heating reactor and transfer them downstream thereof as a process fluid;

(iii) heating the sulphur-containing organic feedstock in the inert heating reactor to a desulphurisation temperature < 300 ^eC under the inert atmosphere, thereby to liberate a sulphur-containing volatile component from the sulphur-containing organic feedstock, while leaving behind a desulphurised feedstock residue; said sulphur- containing volatile component comprising said sulphur compound; and

(iv) utilising the vapour transfer component to transfer the sulphur-containing volatile component downstream of the inert heating reactor. The desulphurisation process as claimed in claim 9, which includes a step of drawing a partial vacuum in the inert heating reactor and flushing the inert heating reactor with an inert gas. The desulphurisation process as claimed in claim 9 or claim 10, which includes reducing the pressure in the inert heating reactor to an operating pressure of < 10 kPa (gauge). The desulphurisation process as claimed in any one of claims 9 to 1 1 , which comprises heating the sulphur-containing organic feedstock to a desulphurisation temperature in a range from about 150°C to about 240°C. The desulphurisation process as claimed in any one of claims 9 to 12, wherein the sulphur- containing organic feedstock comprises processed scrap tyres or waste tyres. A pyrolysis method comprising: utilising the desulphurisation process as claimed in any one of claims 9 to 13 to remove at least one sulphur compound at least partially from a sulphur-containing organic feedstock, thereby to yield a desulphurised feedstock residue; and utilising a pyrolysis reactor to perform a pyrolysis reaction of the desulphurised feedstock residue. The pyrolysis method as claimed in claim 14, wherein the pyrolysis reactor is configured to perform the pyrolysis reaction at a temperature higher than the temperature range of the heating step (iii) of the desulphurisation process.