Plant and process for the purification of oil made by pyrolysis or thermochemical conversion

Abstract

A plant and a purification process for the removal of metals, halogens and heteroatoms from oil made by pyrolysis or thermochemical conversion, for example of waste plastics, comprises at least the first two of the following steps: treating (4) the pyrolysis oil with an inorganic or organic acid or a combination thereof; washing (5) with a solvent, followed by separation of the pyrolysis oil from a contaminant laden solvent fraction; adding acid followed by a two-step bleaching earth process comprising a wet vacuum bleaching (16) step followed by a dry vacuum bleaching step (20); removing (24) the bleaching earths from the pyrolysis oil; and contacting the oil with an ion exchange material (27, 28). All these steps may be used in succession.

Description

[0001] Plant and Process for the Purification of Oil made by Pyrolysis or Thermochemical Conversion

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a process for the purification of oil produced from pyrolysis or thermochemical conversion before feeding into a hydrotreating reactor, fluid catalytic cracking (FCC) reactor or a steam cracking reactor, and to a plant for performing this process. This invention removes contaminants that cause operational issues in these reactors when processing oils derived from thermochemical conversion.

[0004] BACKGROUND OF THE INVENTION

[0005] Plastic production is set to quadruple by the year 2050 and in 2023 it is estimated that only 9% of all plastic waste generated globally is recycled. The remainder of this waste is incinerated, buried in landfills or ends up in nature. Traditionally, the only way to recycle plastic waste was using mechanical recycling which is a process involving sorting, grinding, separating, washing, melting, and then cooling it back to granulated recycled plastic. Currently, mechanical recycling is only economically feasible with certain types of plastics, and only if they are made up of single polymers. However, mechanical recycling requires sorting of plastic waste into the same resin type, manufacturing method, colour and requires the plastic to be clean. This results in the waste plastic having to be separated into thousands of different streams resulting in the recycling process being uneconomic in some instances for certain types of plastics.

[0006] Thermochemical conversion is a method to produce sustainable materials from wastes. Thermochemical conversion involves the heating of carbonous materials such as plastics, tyres, biomass etc. in the absence of oxygen or in limited amounts oxygen to produce hydrocarbon oils, waxes, and gases. Plastic pyrolysis is a thermochemical conversion process that involves the conversion of plastic in the absence of oxygen to produce hydrocarbon oils, waxes, and gases. Polyolefin (PO) and Polystyrene (PS) plastic wastes are typically the main plastic types that are used as feedstocks for thermochemical conversion, these plastic types being well suited as they contain only carbon and hydrogen atoms. In theory if PO plastic is separated from other plastic types and is used as a feedstock for pyrolysis the products should only contain carbon and hydrogen. This however is not the case as plastic manufacturers integrate high concentrations of additives to improve handling, flame retardancy and other properties depending on application, which contain components that reduce the quality of the oils, like halogens, silicon, phosphorus, nitrogen, sulphur, oxygen and metal compounds.

[0007] Generally, advanced or chemical recycling refers to the use of the hydrocarbon products of thermochemical conversion as a feedstock for petrochemical processes, including steam cracking and fluidised catalytic cracking, to make new plastics, replacing or offsetting feedstocks derived from fossil fuels; this results in a substantial reduction of carbon dioxide emitted during plastic manufacturing, and to less plastic being landfilled and incinerated. There is a growing demand from major consumer brands for sustainably produced materials including plastics to be used in their products, and plastic derived from chemical recycling is an ideal source for food grade recycled plastic. There have been many attempts at commercial scale advanced recycling but they have all been plagued by several technical hurdles.

[0008] One of the primary problems encountered within the existing art is that the hydrocarbon products of typical thermochemical conversion processes are of low quality and feature high concentrations of contaminants, mainly halogens, silicon, phosphorus, olefins, diolefins, nitrogen, oxygen, sulphur and metal containing compounds. The main method employed by the petrochemical industry to produce monomers such as ethylene, propylene and butadiene for producing plastics is steam cracking which cracks hydrocarbon feedstocks into such monomers. However, steam cracker units are susceptible to corrosion from contaminants even in very low concentrations, and these cracker units are also very susceptible to coking. This results in the feedstocks for cracking units having very stringent specifications for feedstock contaminant concentrations. The main method employed to reduce contamination concentrations in steam cracker feedstock in the petrochemical industry is hydrotreating, which involves reacting the feedstock with hydrogen under high temperature and pressure conditions in the presence of catalysts. The catalysts used in hydrotreating are susceptible to poisoning and premature deactivation, and other problems such as phosphorus deposition on catalysts particles causing large pressure drops across the bed and corrosion, and plugging issue caused by the high halogen concentrations present in the feed. In order to prevent these issues arising in the hydrotreating process, the products of thermochemical conversion are blended in with high volumes of fossil fuel feedstock to dilute the contaminants below the required threshold. Petrochemical companies are attempting to increase the volume of oils from thermochemical conversion being incorporated into their products, however, because of the high level of contamination in the oils from thermochemical conversion, only small volumes can be blended in this way. The blending approach has been described as unsustainable by petrochemical plant operators, “dilution is not the solution”.

[0009] Another potential end user for the products of advanced recycling is fluidised catalytic crackers (FCC). FCCs can process a wider boiling point range of feedstocks and typically process naphtha or vacuum gas oil feedstocks. The allowable concentration threshold of metals, halogens and other heteroatomic contaminants is still multiple orders of magnitude below what is typically present in the products of advanced recycling. Again, there are substantial risks of premature catalyst deactivation, and equipment corrosion risks for the plant operators. A blending approach is employed as with hydrotreating units but again this is challenging for the operators and still results in increased risk of financial losses and equipment damage.

[0010] Accordingly, there is a need within the art for a method to remove contamination from the product oils of thermochemical conversion, so larger volumes of this oil can be integrated into petrochemical value chains, enabling increased circularity and higher levels of recycled content in petrochemical products.

[0011] SUMMARY OF THE INVENTION

[0012] According to the present invention there is provided a purification process for the removal of metals, halogens and heteroatoms from oil made by pyrolysis or thermochemical conversion, the process comprising at least the first two of the following steps:

[0013] (1 ) Treating the pyrolysis oil with an inorganic or organic acid or a combination thereof,

[0014] (2) Washing with a solvent, followed by separation of the pyrolysis oil from a contaminant laden solvent fraction, (3) Contacting with solid particles of adsorbent material, and then separating the solid particles from the pyrolysis oil; and / or

[0015] (4) Contacting the oil with an ion exchange material.

[0016] By way of example the adsorbent material may comprise activated carbon, zeolites, or bleaching earths comprising montmorillonite or bentonite or sepiolite or attapulgite.

[0017] By way of example, as one step heated oil is mixed with an acid or a combination of acids in a stirred vessel. The acid(s) ionises the contaminants present increasing their solubility. 0.01 % to 2% w / w of an acid, such as citric acid, malic acid, phosphoric acid, phosphorous acid, nitric acid or sulphuric acid, or combinations thereof may be added to the oil.

[0018] In a following step, the oil and acid mixture is combined with a solvent such as water or any other suitable polar solvent such as but not limited to ethanol or isopropyl alcohol, the solvent being substantially immiscible with the oil, and mixed in a stirred vessel in order for the contaminant compounds to migrate from the oil into the solvent. The majority of the metals, salts and halogens transfer into the solvent, the acid greatly increasing the efficacy of the contamination transfer to the solvent. The individual steps, process conditions and the concentrations of the acid(s), and the volume of solvent (such as water) added will be chosen depending on the contamination profile and the targeted contaminant concentrations of the thermochemical conversion products being treated.

[0019] The oil and solvent are then separated, for example by allowing the mixture to settle into two layers and then separating by decantation, or alternatively this can be accomplished by centrifugation or by any other method known to those skilled in the art.

[0020] A second washing step, for example with water, may then be performed to ensure all the acid and the majority of the remaining contaminants are removed. The acid and water washing steps remove halogen, phosphorus, metal, sulphur and nitrogen-containing contaminants.

[0021] In another step, to remove the contaminant compounds present, the oil undergoes a two- step bleaching process using bleaching earths, comprising wet and dry bleaching process steps. Prior to the bleaching process acid is preferably added to the oil in a stirred vessel, to increase the adsorption of the contaminants; this may be performed in a stirred vessel to which bleaching earths are then added, for example at 0.2 - 1 % by weight, and steam may be sparged through the bleaching earth and oil mixture in the wet bleaching vessel to further enhance the removal efficiency. The mixture may then be transferred to a dry bleaching vessel, which is a stirred vessel under vacuum, to substantially remove the water present in the mixture. The residence time in the two bleaching earth vessels may be 10 - 30 minutes. The bleaching earths would then be separated from the oil, for example using a filter. The bleaching earths may be reused several times.

[0022] Another potential step involves passing the oil product over a bed of ion exchange resin to further reduce the concentration of metals, halogens and heteroatoms. Preferably, the ion exchange resin used is a styrene, crosslinked polystyrene, crosslinked polyacrylic, and crosslinked polymethacrylic are commercially accessible in various forms, including gel, macroporous, or isoporous structures such as Amberlyst 35 or Amberlyst 15.

[0023] In a preferred process, at least three of these steps are utilised, to remove as much as possible of the contaminants. Thus, the oil is subjected to acid treatment followed by a solvent rinse; then to a further acid treatment and either a two-stage bleaching earth treatment, and separation from the adsorbent; and / or then being contacted with ion exchange resin. Using an acid addition in the first step, followed by a solvent addition and a separation step, this then being followed by yet another acid addition, prior to the adsorption step, is advantageous because the metals in the oil mixture are initially present in organo-metal complexes, and the metals are liberated when contacted with acid; this step serves to increase the solubility of the metals, which makes their removal much more effective when using solvent extractions and adsorption methods.

[0024] The present invention provides a cost-effective purification process to remove metals, halogens and heteroatoms from oils produced by thermochemical conversion. This invention enables integration of oils produced from thermochemical conversion into steam cracking reactors, hydrotreating reactors or fluid catalytic reactors by cost effectively reducing the amount of problematic metal, halogen, phosphorus, silicon, nitrogen and sulphur, greatly reducing the need for energy intensive and expensive hydrotreating. However, this invention cannot remove olefin and diolefin therefore some degree of hydrotreatment may still be required. Consequently, the user may employ this invention to reduce the troublesome contaminations that cause several operational issues in hydrotreaters and also to reduce the operating cost of the hydrotreater.

[0025] In another aspect, the invention provides a plant for performing the above-described process.

[0026] This invention solves the aforementioned problems by cost effectively reducing the amount of problematic metal, halogen, phosphorus, silicon, nitrogen and sulphur contaminates that damage the expensive catalysts in the hydrotreater and cause several other operational issues.

[0027] Whether this invention is used to purify feedstocks to be fed to steam cracking reactors, FCC reactors or hydrotreating reactors the process is the same although it may be configured differently to suit the relevant end user.

[0028] The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:

[0029] Figure 1 shows a flow diagram of an oil purification plant and process of the invention;

[0030] Figure 2 shows a flow diagram of the integration of the purification plant of figure 1 into a standard petrochemical facility comprising a hydrotreater and steam cracker, wherein the output from the purification plant is blended with fossil-fuel derived feedstock.; and

[0031] Figure 3 shows a flow diagram of the integration of the purification plant of figure 1 into a petrochemical facility comprising a fluidised catalytic cracker and a distillation column, wherein the output from the purification plant is blended with fossil-fuel derived feedstock.

[0032] DETAILED DESCRIPTION

[0033] This invention provides an inexpensive and less energy intensive method of removing metals, halogens and heteroatom ic contaminants from product oils derived from the thermochemical conversion of carbonous materials, such as plastic, biomass and tyres. This invention greatly simplifies the integration of thermochemical conversion products into petrochemical processes such as hydrotreating, steam cracking and fluidised catalytic cracking units, through the mitigation of catalyst poisoning, corrosion and onerous blending processes that have prevented widespread adaptation of these products into petrochemical value chains to date.

[0034] This invention substantially removes the following metals: calcium, sodium, magnesium, zinc, iron and manganese. This invention substantially removes the following halogens: chlorine, bromine and fluorine. This invention substantially removes the following heteroatomic contaminants: phosphorus, silicon, nitrogen and sulphur.

[0035] Referring now to Figure 1 , a plant to perform the purification process comprises, a stirred vessel 4 for the oil and acid(s), a stirred vessel 5 for the water washing of the oil and acid mixture, a pair of centrifuges 7 and 10 for separation of the aqueous and organic layers, a wet vacuum bleaching vessel 16, a dry vacuum bleaching vessel 20, a filter 24 for the separation of bleaching earths and pyrolysis oil, and a pair of ion exchange resin beds 27 and 28 capable of operating in swing mode. (This purification plant is referred to as plant 31 in figure 2 and as plant 36 in figure 3.)

[0036] The influent product oil 1 , produced for example by pyrolysis of waste plastics, is first heated to a temperature between 50°C and 110°C using a heat exchanger 2, and an acid or a combination of different acids are then injected at inlet 3 into the oil. Acids that may be used include phosphoric acid, phosphorous acid, citric acid, sulphuric acid, nitric acid or malic acid. The amounts of the acids added are 0.02% to 0.2% by weight, for each acid. The combination of an organic and inorganic acid works synergistically, and reduces the overall quantity of acid required, so providing a broader range of contaminant molecule ionisation which is useful when treating oils with a broad and diverse range of contaminant molecules present. The oil and acid(s) are then mixed in the stirred vessel 4.

[0037] The temperature of the mixture is maintained between 50°C and 110°C, and 2% to 15% by weight of deionised water 6 is added to the mixture and the mixture is continuously agitated for 30 minutes in the stirred vessel 5. The majority of the contaminants present in the mixture will migrate to the aqueous phase. The separation of the oil and aqueous phase is carried out using the centrifuge 7. Deionised water is then added and mixed again 9 with the product layer, before being separated again using the centrifuge 10.

[0038] The temperature of the product oil stream is adjusted and maintained between 100°C and 110°C using a heat exchanger 13 before an acid, such as phosphoric acid, phosphorus acid or citric acid is injected at inlet 14 into the oil and is mixed thoroughly in a stirred vessel 15; this serves to increase the adsorption efficacy in the subsequent bleaching process. The product and acid mixture are then transferred to another stirred vessel which is the wet vacuum bleaching vessel 16, and here 0.3% - 0.7% by weight of bleaching earths 18 are added to the oil and acid mixture.

[0039] Adsorbents such as zeolites, activated carbon, or bleaching earths comprising montmorillonite, bentonite, sepiolite or attapulgite can be used and are added to the vessel 16 and continuously agitated under vacuum 19, the temperature is maintained between 60°C and 100°C, and steam is continuously sparged 17 through the mixture of product oil and bleaching earths to further enhance the adsorption process. The residence time in the wet vacuum bleaching vessel 16 is 10 - 30 minutes.

[0040] The mixture is then transferred to a dry vacuum bleaching vessel 20 which is another stirred vessel under vacuum, additional bleaching earths are added via line 21 , any water present is substantially removed via the vacuum line 22. The residence time in the dry vacuum bleaching vessel 20 is 10 - 30 minutes.

[0041] The next step features the transfer of the product oil and bleaching earths mixture to a filter 24 to separate the spent bleaching earths 23 from the product oil. The bleaching earth may be recycled several times depending on the degree of deactivation of the bleaching earths.

[0042] The final step consists of sending the product oil to a set of ion exchange resin beds 27 and 28. When one of the ion exchange beds 27, 28 is operating the other will be in regeneration mode, which consists of washing the resin with an inorganic acid such as hydrochloric acid and an alcohol like isopropyl alcohol via lines 25 and 26. The ion exchange resins used for this process are macroporous acidic or strongly acidic cation exchange resins. The product is then sent for storage through an outlet duct 29. Referring now to Figure 2, oil produced by pyrolysis of plastics and stored in a vessel 30 is sent to the purification plant 31 wherein the metal, halogen, and other heteroatom ic contaminants are substantially removed to enable a greatly simplified feeding process into the hydrotreater 32. Once the hydrotreatment is completed successfully the resulting oil is then blended into a steam cracker feedstock line prior to entering a steam cracker 33. The blending process is greatly simplified as the purification plant 31 has reduced the concentration of contaminants in line with the fossil-fuel derived feedstocks and the hydrotreatment has reduced the olefinicity to within the allowable thresholds. Referring now to Figure 3, oil produced by pyrolysis of plastics and stored in a vessel 35 is sent to the purification plant 36 where the metal, halogen, and other heteroatomic contaminants are substantially removed prior to blending into a fluidised catalytic cracker 37 feedstock line. Again, the process of blending the oil produced by pyrolysis with the fossil-fuel derived feedstock is greatly simplified, and additionally the risk of catalyst poisoning of the reactor catalysts is significantly reduced, as the concentration of contaminants in the FCC feed is below the thresholds required by the plant operators.

Claims

CLAIMS1 . A purification process for the removal of metals, halogens and heteroatoms from oil made by pyrolysis or thermochemical conversion, the process comprising at least the first two of the steps:(1 ) Treating the pyrolysis oil with an inorganic or organic acid or a combination thereof;(2) Washing with a solvent, followed by separation of the pyrolysis oil from a contaminant laden solvent fraction,(3) Contacting the pyrolysis oil with solid particles of an adsorbent material, and then separating the solid particles from the pyrolysis oil; and / or(4) Contacting the oil with an ion exchange material.

2. A purification process as claimed in claim 1 for the removal of metals, halogens and heteroatoms from oil made by pyrolysis or thermochemical conversion, the process comprising performing the steps (1 ) and (2), and then further treating the oil with acid before performing a further purification step.

3. The process as claimed in claim 1 or claim 2, wherein in step (1 ) the organic acid is citric acid and the inorganic acid is phosphoric or phosphorous acid.

4. The process as claimed in claim 1 or claim 2, in which in step (1 ) citric acid, phosphoric acid or phosphorous acid or combinations thereof are added to the oil in an amount of 0.02% to 0.2% w / w each, the mixture is continuously stirred and the temperature is maintained between 50°C and 110°C.

5. The process as claimed in any one of the preceding claims wherein in step (2) 2% to 15% by weight of water is added to the pyrolysis oil mixture, the mixture is then maintained between 50°C to 110°C and the solution is continuously stirred.

6. The process as claimed in any one of the preceding claims, wherein in step (2) the pyrolysis oil, acid and contaminant laden water fraction are separated using centrifugation or decantation.

7. The process as claimed in any one of the preceding claims, wherein in step (3) the adsorbent material is added in an amount of 0.4 wt% to 0.7 wt%.

8. The process as claimed in claim 7 wherein the adsorbent material comprises bleaching earths, zeolites, or activated carbon.

9. The process as claimed in claim 8, wherein the bleaching earths comprise montmorillonite, bentonite, sepiolite or attapulgite based bleaching earths.

10. The process as claimed in any one of claims 7 to 9, wherein the adsorbent material is separated from the pyrolysis oil using a filter or a hydrocyclone.

11. The process as claimed in any one of claims 7 to 10, wherein in the adsorbent material separated from the pyrolysis oil is reused as an adsorbent material to treat pyrolysis oil.

12. The process as claimed in any one of the preceding claims, wherein in step (4) the resin comprises one or more of the following types of commercially available microporous resins: acidic cation exchange resin or strongly acidic cation exchange resin.

13. The process claimed in claim 12, wherein one of the following resin types is employed: a matrix of styrene, cross linked polystyrene, cross linked polyacrylic, cross linked polymethacrylic resin.

14. The process as claimed in any one of the preceding claims wherein pyrolysis oils and waxes are derived from the pyrolysis of carbonous material, such as plastics, biomass, and fossil fuel derived feedstocks.

15. The process as claimed in any one of the preceding claims, wherein the contaminants include phosphorus, chlorine, bromine, fluorine, calcium, sodium, magnesium, zinc, iron and manganese.

16. A plant for performing the process of any one of the preceding claims.

17. A process wherein pyrolysis oil that has undergone the purification process as claimed in any one of claims 1 to 15, is fed:- into a hydrotreater to be reacted with hydrogen, and the resulting oil is then blended into a steam cracker feedstock line prior to entering steam cracker; or - into a steam cracker feedstock line prior to entering a steam cracker; or- into a fluidised catalytic cracker feedstock line prior to entering a fluidised catalytic cracker.

Images