CROSS-REFERENCE TO RELATED APPLICATION

This application is a Section 371 National Stage Application of International Application No. PCT/GB2019/050176, filed Jan. 23, 2019, and published as WO 2019/155183 A1 on Aug. 15, 2019, in English, which claims priority to GB patent application Serial No. 1802236.8, filed Feb. 12, 2018, the contents of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the purification of hydrocarbons contaminated with other solid and liquid materials.

BACKGROUND ART

Hydrocarbons are an essential part of the world economy, and will continue to be so for some time. They are required for a wide range of purposes, including use as fuel, for lubrication, and as a feedstock for chemical production processes.

Increasing environmental regulation aimed at reducing emissions does however require that many of those fuels are at a higher level of purity than has hitherto been the case. For example, so-called “bunker fuels” made up of the heavy oils left as a residue after fractional distillation of lighter fuels have routinely been used for powering shipping vessels but are typically very high in sulphur and other contaminants. Such fuels are now banned from use in ‘Emission Control Areas’, i.e. defined sea areas around specific jurisdictions such as the EU, USA, Canada and China, unless processed to reduce sulphur and other particulates from 3.5% m/m to 0.10% or less.

Other environmental concerns are based on the finite nature of hydrocarbon reserves, and seek to recover and re-use hydrocarbons where possible. Large volumes of contaminated hydrocarbons are disposed of after having been used as lubricants, tyres, plastics and the like. Many industrial and consumer products contain hydrocarbons that are chemically or physically bonded with other compounds within the product. When a product containing hydrocarbons has reached the end of its useful life, either by contamination, wear, damage or other reason, there is considerable commercial and environmental value in recovering the hydrocarbon content and processing it into new commercial products.

In some countries, end-of-life materials (EOL) are often classified as ‘waste’ which conveys a legal status on the material, requiring specific handling and treatment. The commercial costs and technical complications of such handling and treatment often result in ‘waste’ products being inappropriately dumped or incinerated, causing intensive water, ground and air pollution.

In many countries, legislation has banned low level recovery treatments such as incineration for rubbers, plastics and oils. Acid washing and clay filtration processes were historically employed on some oils to recover them for re-use as base oils or as secondary liquid fuels. Those processes caused significant and dangerous emissions to atmosphere or hazardous effluent emissions requiring additional specialised processing.

Where approved systems do not exist for recovering solid hydrocarbons, landfill is often a solution of last resort which itself can create long term hazardous deposits where an extended half-life of hundreds of years is common for rubbers and plastics. Legislation has banned the use of landfill for many products that cannot biodegrade, resulting in alternative process treatments being sought.

One such process is thermolysis, (herein referred to as pyrolysis) which thermally degrades materials at typical temperatures of 350-800 degrees Celsius or higher, in the absence of oxygen to prevent combustion. Pyrolysis is often a slow, simple, low cost technology which technically has advanced very little in the decades since its inception. As a low capital cost process, it has become a favoured treatment for processing rubber (in the form of end of life tyres) and waste plastics, because as the material is thermally degraded, gases are generated which when condensed have a superficial similarity to diesel fuel. A char material similar to carbon black also emanates from the rubber pyrolysis process.

By nature of the technology employed in the design of many simple pyrolysis plants, they are only suitable for batch processing rather than continuous processing. This is wasteful in terms of energy as at the end of a batch, the entire process must be cooled to a temperature that will allow safe unloading of the remaining residue. A high-energy input will be required to elevate the entire process to operating temperature once again.

Where plastic materials are intended for pyrolysis, pre-sorting is traditionally required to ensure that Polyvinylchloride (PVC) material is not processed as this allows chlorinated compounds to be formed which are extremely hazardous to human health and corrosive to materials of construction of the process equipment.

In batch pyrolysis, gases are generated slowly and remain within the pyrolysis chamber (described as dwell time) until sufficient pressure has built up to cause the gases to exit the pyrolysis chamber via pipework usually leading to a condensation process. Dwell times allow multiple gases to mix and for complex gas reactions occur, potentially allowing carcinogenic and other hazardous compounds to be formed. When the gases exit the process and are condensed, the hazardous compounds remain in the hydrocarbon condensate which if then used as a raw fuel, will allow the compounds to be released into the atmosphere creating hazardous airborne emissions.

During the manufacture of rubber products, sulphur is usually added to aid vulcanisation and provide required mechanical properties. The hydrocarbon condensate from rubber pyrolysis will therefore contain virtually the same level of sulphur as originally added. Depending upon the temperature achieved and dwell time during the pyrolysis process, additional sulphur species can be formed which will appear in the hydrocarbon condensate, which if then used as a raw fuel, will allow a high level of sulphur oxides to be generated and released into the atmosphere.

Where complex sulphur and other contaminant species have been allowed to form, it is difficult and energy intensive to re-process the liquid hydrocarbon condensate to remove those contaminants and in laboratory tests, it has been found that the time, energy cost and yield loss significantly negates any commercial value that might have applied to the hydrocarbon condensate as a fuel.

Some naturally arising products (natural gas, crude oil, biomass) can also contain sulphur, organic acids and other contaminants that prevent commercial use of the pyrolysed products without extensive further processing. Where liquids are derived from biomass pyrolysis, they are highly oxygenated which will cause instability and rapid deterioration of the liquid unless it is further processed by hydrotreating with catalysts to remove the excess oxygen. Hydrotreating is extremely energy intensive and results in substantial CO2emissions.

SUMMARY OF THE INVENTION

A number of needs therefore exist in this area. ‘End of life’ (EOL) liquid hydrocarbons, and waste materials containing hydrocarbons, need to be disposed of by routes that do not involve disposal into the natural environment. Such a route needs to be economically viable and environmentally positive, thereby reducing ground, water and air emissions that are likely to cause harm to humans, animals and the natural environment.

EOL waste hydrocarbons need to be recovered and processed to yield new forms of usable energy, ideally by a process that has a low energy requirement, low operating cost, prevents hazardous compounds from being created within the process and significantly reduces carbon footprint compared to current practices.

Contaminants need to be removed from naturally arising liquid and gaseous hydrocarbons by an economically viable and environmentally acceptable process that has a low energy requirement, low operating cost and reduces carbon footprint compared to known current practices. In particular, a process is needed by which oxygen and acidic compounds can be removed from biomass pyrolysis distillate.

The present invention therefore seeks to provide a process for purification of hydrocarbons. It can be applied to a wide range of contexts, for example to process or re-process bunker fuels to yield low-sulphur fuels, cleaning of waste engine oils (etc) to yield a usable hydrocarbon product, recovery of hydrocarbons from used tyres, plastics etc, as well as the treatment of crude oils, shale and other solids or near solids containing oils, and the tailings remaining after fractionation, separation and like processes.

Thus, the process is useful for both extraction of hydrocarbons from solid and liquid materials, and the removal or reduction of contaminants such as Sulphur, halogens, Nitrogen, metals, chars, ash and the like.

In its first aspect, the present invention therefore provides a method of treating hydrocarbons comprising the steps of heating the hydrocarbon thereby to release a gas phase, contacting the gas with of an aqueous persulphate electrolyte, condensing the gas to a liquid or a liquid/gas mixture, and removing its aqueous component.

The persulphate electrolyte is thus able to react with contaminants in the hydrocarbon (such as sulphur-containing impurities in the hydrocarbon which are oxidised to sulphates) and draw them into solution in an aqueous phase together with the remaining persulphate. Separation of an aqueous phase from a hydrocarbon phase is relatively straightforward, and will then take with it the contaminants leaving behind a cleaner hydrocarbon. Thus, the separation step removes the aqueous component and recovers the hydrocarbon condensate as a low sulphur fluid.

Contact between the gas and the aqueous persulphate electrolyte can be by spraying the electrolyte into the gas or a stream of the gas, or by bubbling the gas through the electrolyte in solution, or by other means.

Separation can be by way of a mechanical means such as are known in the art. Following separation, the hydrocarbon liquid is admixed with a polar aprotic solvent so that non sulphated polar contaminants in the hydrocarbon phase are attracted to and dissolved into the solvent and then passed to a solvent recovery process such as a vacuum distillation step.

The aqueous persulphate electrolyte can be held in a reservoir prior to being contacted with the gas phase hydrocarbon. In this case, we prefer that the reservoir is maintained at a temperature of less than about 50, ideally less than 30 degrees Celsius.

The hydrocarbon is preferably supplied in a continuous stream, to which the method is then applied.

In its second aspect, the present invention provides a method of treating liquid hydrocarbons, comprising reacting the hydrocarbon with a persulphate thereby to oxidise sulphur-containing species in the hydrocarbon and subjecting the reaction product to an electrical field generated by at least two opposing electrode plates between which the reaction product flows.

The electrode plates are ideally substantially parallel, spaced apart by a distance between each electrode surface of between 1 and 5 millimetres, and carry an electrical current density between 2 and 3 amps per square centimetre of electrode surface area. A DC voltage in the range of 80-100 volts is usually sufficient for this purpose.

This electrolytic step regenerates the persulphate electrolyte within the reaction product. The aqueous phase containing it can be separated and, ideally, passed through an ion exchange device to remove sulphates therein, thus yielding substantially uncontaminated persulphate electrolyte that can be recirculated within the process.

The above methods may be applied in an environment at lower than atmospheric pressure. This assists by reducing the effective boiling temperature of the hydrocarbons being processed, allowing heavier fractions to be processed whilst remaining at manageable temperatures. A pressure of 1500 Pa or lower is preferred.

A wide range of hydrocarbons can be treated in this way. Used hydrocarbons such as engine oils and sulphur-contaminated marine fuels are prime examples, but there are a wide range of others such as hydrocarbons derived from the pyrolysis of a material having a hydrocarbon content. One such example is a mix of used rubber (such as end-of-life tyres) and used oils (such as engine oils), which can be pyrolysed together to yield a hydrocarbon liquid which can be treated as above, and a residue that provides a useful solid fuel.

