APPARATUS, METHOD AND CATALYST FOR PROCESSING HYDROCARBONS FOR RECYCLING

Abstract

An apparatus for processing a mixture of solid and/or liquid hydrocarbons for recycling without using hydrogen gas, the apparatus including a heating system including a heating chamber for receiving solid and/or liquid hydrocarbons, a feed system for transferring hydrocarbons into the heating chamber, and heating means for removing water from the mixture of solid and/or liquid hydrocarbons outside the heating chamber and configured for subsequently, in the absence of air and the water, gasifying or vapourising at least some of the solid and/or liquid hydrocarbons in heating chamber into hydrocarbon gas, a reactor or conduit connected to and downstream from the heating chamber for receiving the hydrocarbon gas, the reactor or conduit including a catalyst for breaking down higher molecular weight hydrocarbons into lower molecular weight hydrocarbons, in which the catalyst includes a zirconium sulfate, and a carbide.

Claims

1. An apparatus for processing a mixture of solid and/or liquid hydrocarbons for recycling without using hydrogen gas, the apparatus comprising: a heating system including at least one heating chamber for receiving the mixture of solid and/or liquid hydrocarbons, a feed system for transferring hydrocarbons into the at least one heating chamber, and heating means for removing water from the mixture of solid and/or liquid hydrocarbons prior to entry into the at least one heating chamber and configured for subsequently, in the absence of air and the water, gasifying or vaporising at least some of the solid and/or liquid hydrocarbons in the at least one heating chamber into hydrocarbon gas, wherein at least one reactor or conduit is connected to and downstream from the at least one heating chamber for receiving the hydrocarbon gas, the at least one reactor or conduit including a catalyst for breaking down higher molecular weight hydrocarbons into lower molecular weight hydrocarbons, in which the catalyst includes a zirconium sulfate, and a carbide, wherein the weight ratio of the zirconium sulfate to the carbide is from about 2:3 to 3:2, wherein the zirconium sulfate and the carbide are coated either on a bead to provide a catalytic bead or on a substrate, for reducing chain lengths of hydrocarbons in the hydrocarbon gas and producing hydrocarbon products, and at least one of: a collection system for condensing the hydrocarbon products into liquid, and an outlet conduit for transferring the hydrocarbon products away from the at least one reactor or conduit.

2. The apparatus as claimed in claim 1, further including a shredding or grinding system for mechanically breaking down solid hydrocarbons, connected to the heating system for transferring hydrocarbons to the heating system.

3. The apparatus as claimed in claim 1, in which the heating system includes one or more Archimedes' screws for one or both of: removing contaminants from the mixture of hydrocarbons before gasification; and removing moisture from the mixture of hydrocarbons before gasification.

4. The apparatus as claimed in claim 1, in which the heating system includes one or more vented stuffing machines.

5. The apparatus as claimed in claim 1, in which the heating means includes one or both of: one or more variable geometric elements for establishing one or more melt seals where hydrocarbons enter the at least one heating chamber; and one or more lobed elements for mixing the hydrocarbons during heating in the at least one heating chamber.

6. The apparatus as claimed in claim 1, in which the at least one heating chamber includes: a first heating chamber for converting lower molecular weight hydrocarbons into hydrocarbon gas; and a second heating chamber connected to the first heating chamber for converting higher molecular weight hydrocarbons into hydrocarbon gas.

7. The apparatus as claimed in claim 6, in which the second heating chamber has a larger volume than the first heating chamber.

8. The apparatus as claimed in claim 6, in which the first heating chamber is configured to heat to a first temperature, and the second heating chamber is configured to heat to a second temperature, the second temperature being greater than the first temperature, in which the first temperature is between 320? C. and 460? C., and the second temperature is between 320? C. and 500? C.

9. The apparatus as claimed in claim 1, including one or more of the following: the collection system includes a fractional distillation system or condensing means for condensing the gaseous hydrocarbon products into liquid; means to feed hydrocarbons or plastics into the apparatus under gravity; and the feed system is a continuous feed system.

10. The apparatus as claimed in claim 1, in which the at least one reactor or conduit includes a vertical fixed bed reactor, and the vertical fixed bed reactor is configured to heat to a temperature of between 380? C. and 420? C.

11. The apparatus as claimed in claim 1, in which the at least one reactor or conduit includes a first reactor or conduit and a second reactor or conduit, and the apparatus is configured to during use convey a first hydrocarbon gas portion from the at least one heating chamber to the first reactor or conduit, and a second hydrocarbon gas portion from the at least one heating chamber to the second reactor or conduit.

12. The apparatus as claimed in claim 11, in which the catalyst includes a first catalyst and a second catalyst which is different to the first catalyst, in which the first catalyst is disposed in the first reactor or conduit and the second catalyst is disposed in the second reactor or conduit.

13. The apparatus as claimed in claim 12, in which the first catalyst includes one or more first metal carbides or first semi-metal carbides, and the second catalyst includes one or more second metal carbides or second semi-metal carbides, wherein the one or more first metal carbides or first semi-metal carbides is different to the one or more second metal carbides or second semi-metal carbides.

14. The apparatus as claimed in claim 12, in which the first catalyst includes one or more first transition metals or first transition metal salts, and the second catalyst includes one or more second transition metals or second transition metal salts, wherein the one or more first transition metals or first transition metal salts is different to the one or more second transition metals or second transition metal salts.

15. The apparatus as claimed in claim 12, in which the first catalyst has a first weight ratio of zirconium sulfate to carbide, and in which the second catalyst has a second weight ratio of zirconium sulfate to carbide, in which one or both of the first weight ratio and the second weight ratio of the respective zirconium sulfate to the respective carbide is from about 2:3 to 3:2, and in which the first weight ratio is different to the second weight ratio.

16. A catalyst for breaking down higher molecular weight hydrocarbons into lower molecular weight hydrocarbons, the catalyst comprising zirconium sulfate, and a carbide, where the ratio of zirconium sulfate to carbide is from about 2:3 to 3:2, wherein the zirconium sulfate is coated either on a bead to provide a catalytic bead or on a substrate, and the carbide is coated on at least part of the zirconium sulfate for inhibiting or suppressing or regulating catalytic activity of the zirconium sulfate.

17. The catalyst as claimed in claim 16, in which the carbide is independently selected from a group comprising: titanium carbide; tungsten carbide; niobium carbide; calcium carbide; molybdenum carbide; silicon carbide.

18. A method of preparing a catalyst comprising a zirconium sulfate and a carbide, wherein the weight ratio of the zirconium sulfate to the carbide is from about 2:3 to 3:2, for use in processing hydrocarbons for recycling, the method comprising the steps of: a) providing a zirconium sulfate on one or more substrates or on one or more beads to provide one or more catalytic beads; and b) adding a carbide to the one or more substrates or the one or more beads to provide one or more catalytic beads.

19. The method as claimed in claim 18, including one or both of: the step of heating or calcining the zirconium sulfate after step (a) and before step (b); and the step of heating or calcining the zirconium sulfate and the carbide after step (b).

20. The method as claimed in claim 18, in which the zirconium sulfate is prepared from zirconia or zirconium hydroxide by using sulfuric acid having a concentration in the range of 0.05 to 1 mol dm.sup.?3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0129] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

[0130] FIG. 1 shows a flowchart of steps for recycling hydrocarbons such as mixed plastics.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0131] Referring to FIG. 1, a process for recycling hydrocarbon waste is indicated generally at 10. The process 10 may be carried out as a continuous process using suitable apparatus, as described below. The process 10 is particularly suitable for converting mixed polymers and/or heavy hydrocarbon oils into fuels or small to medium weight hydrocarbons or monomers. The average throughput in this embodiment about 350 kg of waste hydrocarbon material per hour (approximately 100 g per second).

[0132] Hydrocarbon feedstock (not shown) is initially provided at the stage indicated generally at 12. The feedstock may include solid components, such as plastic bottles, trays or containers, and/or may include one or more liquid components, such as engine oil. In this embodiment, the feedstock contains a mixture of products made of first or second polyolefins. The solid and liquid states are used to describe the materials to be recycled when they are at ambient temperature and pressure (r.t.p.). Any solid components have been shredded for processing in this embodiment.

[0133] The feedstock is heated to a temperature of around 100? C. or so. This is not generally sufficient to melt the plastic waste in the feedstock yet, but the temperature should be sufficient to allow the plastic to flow. The temperature may be increased if necessary for particular solid feedstock combinations to flow.

[0134] The heated hydrocarbon feedstock is directed to flow through feed screws (not shown) at the stage indicated generally at 14. The feed screws rotate in a direction which allows water vapour to vent from the heated hydrocarbons, whilst the hydrocarbons flow in the opposing direction. The direction of rotation also keep contaminant material from progressing beyond the feed screws. The feed screws in this embodiment help to melt the plastic.

[0135] The melted material is then forced via the screws directly into a conventional heated twin rotation primary reactor (not shown), at the stage indicated generally at 16. The reactor includes a heating system (not shown) and a chamber (not shown) including rotatable geometric elements (not shown). The configuration of the geometric elements helps to establish melt seals at the entry to the reactor. This prevents air from entering the chamber and reacting with the melted hydrocarbon material, for example.

[0136] Rotation of the geometric elements generates friction which can heat the mixture, although other heating means are also used. The geometric elements have a very high surface area and are grouped such that their rotation transfers heat evenly and efficiently within the entire melted hydrocarbon mixture that occupies the chamber. This contributes to phase transitions in the hydrocarbon mixture, at the expense of a reduced free volume within the reactor. This has been confirmed by using thermogravimetric analysis (TGA) to obtain a temperature profile of the mixture.

[0137] The primary reactor is usually at a temperature of between 320 to 460? C. In this embodiment, the primary reactor is at a temperature of 400? C. This is sufficient to gasify lighter molecular weight hydrocarbons in the mixture, creating a hydrocarbon gas. Typically, the mixture is heated for about 30 seconds (t.sub.1) to generate an amount of hydrocarbon gas. The hydrocarbon gas is routed to vertical fixed bed reactors (not shown) via a conduit as indicated at 16a.

[0138] In the meantime, the non-gaseous hydrocarbons in the primary reactor are passed into chamber (not shown) in a secondary reactor (not shown) as indicated at 16b. Material passes from the first reactor to the secondary reactor under gravity. A heating system (not shown) is provided for the second chamber, or in some cases the heating system for the first chamber may be configured to heat the second chamber as well.

[0139] The secondary reactor has a larger free volume than the primary reactor. The secondary reactor has an L-shaped profile as seen from above. The secondary reactor is usually at a temperature of between 320 to 460? C. In this embodiment, the secondary reactor is at a temperature of 410? C., i.e. it has a slightly higher temperature profile.

[0140] In order to gasify the heavier molecular weight portions of the hydrocarbon mixture, the mixture is kept in the secondary reactor for a longer time than in the primary reactor. Typically it takes a matter of seconds (a under a minute, t.sub.2) to convert most of the remaining hydrocarbons into a hydrocarbon gas. The hydrocarbon gas is routed to the vertical fixed bed reactors (not shown) via another conduit as indicated at 18a. The residual hydrocarbons and filler material left in the second chamber are removed as indicated at 18b.

[0141] Although the flows of hydrocarbon gas 16a, 18a are shown as joining prior to reaching the fixed bed reactors, it will be appreciated that this is not essential and the flows may instead feed separately into the reactors. It will also be appreciated that the flow of hydrocarbon gas may be routed to a plurality of reactors in parallel, or passed sequentially through a series of one or more reactors.

[0142] The vertical fixed bed reactors, indicated generally at 20, contain a catalyst (not shown) as indicated generally at 22. The catalyst is provided on a plurality of catalytic beads in this embodiment. The catalytic beads substantially fill each fixed bed reactor.

[0143] In this embodiment, the catalyst contains a 1:1 weight ratio (w/w) of zirconium sulphate and calcium carbide. This catalyst has been found to be stable for the range of reaction conditions tested and selective for the desired hydrocarbon products. The ratio may be varied from 2:3 to 3:2, in some embodiments.

[0144] The catalyst can be prepared as follows. A solution of zirconia is prepared and acidified by addition of sulphuric acid (0.5M). The acidified solution is stirred and, once the reaction is complete, drained to provide zirconium sulphate in a conventional manner. It will be appreciated that zirconium sulphate may be prepared or provided by alternate means.

[0145] Catalytic beads are coated with an amount of the zirconium sulphate. The catalytic beads are subsequently calcined, for example at approximately 400? C. in a ball mill. The catalytic beads are next coated in an approximately equivalent amount of calcium carbide powder. The catalytic beads are subsequently calcined again, for example at approximately 400? C. in a ball mill. The beads are then ready for use as a catalyst in the vertical fixed bed reactors.

[0146] The vertical fixed bed reactors are usually at a temperature of between 380 to 420? C. In this embodiment, the reactors are at a temperature of 400? C. Preferably, this temperature is not exceeded for the catalyst in this embodiment. The heating system for the primary or secondary reactors may be used to control the fixed bed reactor temperatures, or a separate heating system may be provided.

[0147] As hydrocarbon gas passes through the vertical fixed bed reactors, it is decomposed by the catalyst into hydrocarbon products. The catalyst is regenerated at the relatively low temperatures used during the process. The hydrocarbon gas takes at least two seconds (t.sub.3) to pass through a fixed bed reactor system in this embodiment. The longer the residence time in presence of the catalyst, the greater the degree of hydrocarbon decomposition. The extent of hydrocarbon decomposition can be controlled by modifying the catalyst composition to include more or less carbide, as described above.

[0148] A condensation system (not shown) is then used to condense the hydrocarbon products into liquid form at room temperature (20? C.), as indicated generally at 24. The condensation system includes a fractional distillation system (not shown) in this embodiment, in order to obtain hydrocarbon fractions containing specific ranges of carbon chain lengths for petrol and diesel fuels, for example. The hydrocarbon products can be sent for further processing such as refinement, indicated at 26a. The hydrocarbon products can be sent to a power plant or generator to generate electricity, indicated at 26b. The hydrocarbon products could be put into a container or pumped into a tanker for delivery to a fuel station, for example.

[0149] The invention therefore enables relatively low temperature processing of a mixture of different plastics or hydrocarbon polymers using a thermo sulphated catalytic process.

[0150] It will be appreciated that other embodiments may include other features, such as any features or features in the above statements of invention.

[0151] The invention is mainly used to decompose thermoplastics, but it is possible to include some thermosetting plastics in the hydrocarbon feedstock. Thermosetting plastics may not gasify to a significant extent, but may form part of the bulk material of the solid matter which remains post-gasification.

[0152] It is also possible to decompose some rubber or rubberised material (such as vehicle tyres) using the invention. It is usually better to recycle rubber in combination with polyolefins and/or polystyrenes, to limit the amount of the carbon black from the rubber in the resulting residue.

[0153] It will be appreciated that other transition metal elements or transition metal salts may be used to put the invention into effect. For example, in some embodiments, another of the transition metal elements mentioned in the statements of invention may be used in combination with a carbide.

[0154] In some embodiments, any of the carbides mentioned in the statements of invention may be used instead of or in addition to calcium carbide, or another carbide may be used.

[0155] The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.