WO2022084433A1

WO2022084433A1 - Hydrocarbon fluids

Info

Publication number: WO2022084433A1
Application number: PCT/EP2021/079172
Authority: WO
Inventors: Daniel Bien; Cody M. DIAZ; Hans K. Goris; Blaise H. BRIDIER; Chunzhao Li
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2020-10-23
Filing date: 2021-10-21
Publication date: 2022-04-28
Also published as: US20240010939A1; EP4232526A1

Abstract

Provided herein is a method for producing a hydrocarbon fluid from waste plastic feedstock, comprising (a) providing a first hydrocarbon feed stream, wherein at least 50 wt% off said first hydrocarbon feed stream is obtained from pyrolysis of plastic waste; (b) removing contaminants from said first hydrocarbon feed stream using a washing step with a polar solvent and/or contacting the stream with one or more adsorbents; thereby obtaining a first hydrocarbon fluid; and (c) hydrogenation of olefins and diolefins in said first hydrocarbon fluid; thereby obtaining a hydroprocessed hydrocarbon fluid containing less than 0.1 wt% olefins; a total amount of metals selected from mercury, lead, and iron below 5 wppm; less than 5 wppm of chlorine and fluorine; and less than 5 wppm of sulfur.

Description

HYDROCARBON FLUIDS

FIELD OF THE INVENTION

The present disclosure relates to methods for producing hydrocarbon fluids from waste plastic feedstocks obtained by pyrolysis of waste plastic.

BACKGROUND OF THE INVENTION

Due to growing environmental concerns over plastic waste and growing environmental concerns over fossil fuel extraction, there is an increased interest in the pyrolysis of plastic waste for the production of hydrocarbon products, which may then be used in the preparation of more sustainable hydrocarbon fuel products. An advantage of pyrolysis is that it can be used with mixed plastic waste, whereas conventional mechanical plastic recycling processes requires extensive sorting and cleaning.

However, the liquid plastic pyrolysis products (pyrolysis oils) generally are not readily suitable as a feedstock in conventional refinery processes, due to feed specifications requiring very low concentrations of chlorides and limited olefin content. Moreover, the plastic waste feedstock may also contain other contaminants such as metals. Therefore, whereas the use of pyrolysis oil in the manufacture of fuels is known, there is a need for processes which would allow for expanding the potential applications of pyrolysis oil obtained from waste plastic.

SUMMARY OF THE INVENTION

It is an object of the present application to provide methods for producing a hydrocarbon fluid from waste plastic feedstocks, allowing for obtaining hydrocarbon fluids having a low level of contaminants, regardless of the feedstock.

More particularly, provided herein is a method for producing a hydrocarbon fluid from waste plastic feedstock. In the method, a first hydrocarbon feed stream is provided, comprising material obtained from the pyrolysis of plastic waste. Contaminants are removed from the first hydrocarbon feed stream, by subjecting at least a portion of the first hydrocarbon feed stream to a washing step with a polar solvent (thereby reducing the content of polar contaminants in said first hydrocarbon feed stream); and/or contacting at least a portion of the first hydrocarbon feed stream with one or more adsorbents, wherein the adsorbents are suitable for removing one or more contaminants selected from water, metals, chlorides, nitrogen-containing compounds, oxygenates, and phosphorous-containing compounds; thereby obtaining a first hydrocarbon fluid. Then, at least a part of the first hydrocarbon fluid, optionally blended with a second hydrocarbon feed stream, is subjected to hydroprocessing to hydrogenate olefins and diolefins in the first hydrocarbon fluid. Thereby, a hydroprocessed hydrocarbon fluid can be obtained, containing:

- less than 0.1 percent by weight (wt%) olefins; a total amount of metals selected from mercury, lead, and iron below 5 wppm (weight parts per million);

- less than 5 wppm of chlorine, preferably less than 5 wppm of chlorine and fluorine; or less than 5 wppm of halogens; and

- less than 5 wppm of sulfur.

The present methods allow for utilizing pyrolysis oils obtained from waste plastic in the manufacture of high-purity specialty fluids, and may be integrated in conventional refining methods.

The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent or other dependent claims, and/or with features set out in the description above and/or hereinafter as appropriate.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description which illustrates, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The following figure are included to illustrate certain aspects of the present disclosure and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to one having ordinary skill in the art and having the benefit of this disclosure.

Fig- Overall flow scheme for contaminants removal from plastic waste feed according to particular embodiments of the methods described herein. DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with respect to particular embodiments.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Throughout this specification, reference to "one embodiment" or "an embodiment" are made. Such references indicate that a particular feature, described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, though they could. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

The following terms are provided solely to aid in the understanding of the invention.

The term “about” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/- 10% or less, preferably +/- 5% or less, more preferably +/- 1% or less, and still more preferably +/- 0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier “about” refers is itself also specifically, and preferably, disclosed.

The term “plastic” as used herein generally refers to a polymeric material, made in whole, or part, of at least one organic monomer, that may contain one or more modifications and/or may be compounded with one or more additives such as colorants, to form a useful material. Plastics may include thermoset as well as thermoplastic polymeric materials. The term “waste plastic” refers to a post-consumer plastic that is no longer needed for its intended purpose. Examples of waste plastic include emptied plastic containers, discarded plastic wrapping, and the like.

The term “hydrocarbon” refers to an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons include but are not limited to include paraffins, naphthenes, aromatics, and olefins. Provided herein are methods for producing a hydrocarbon fluid from plastic feedstock. The methods comprise providing a first hydrocarbon feed stream, which is at least partially obtained from the pyrolysis of plastic, preferably from the pyrolysis of plastic waste. In the pyrolysis process, plastic is depolymerized via pyrolysis conditions. The part of the first hydrocarbon feed stream that is obtained from the pyrolysis of plastic is referred to herein as “plastic pyrolysis oil”, or as “pyrolysis oil”. It will be understood by the skilled person that the first hydrocarbon feed stream contains hydrocarbons, but may additionally contain non-hydrocarbon components, such as oxygenates, halogenated compounds, and the like. Generally, the first hydrocarbon feed stream contains at least 90 wt% hydrocarbons, preferably at least 95 wt% hydrocarbons.

Pyrolysis oil

The pyrolysis oil contained in the first hydrocarbon feed stream is obtained via the pyrolysis of plastic, typically waste plastic. The pyrolysis of waste plastic is well known in the art, and may involve a catalytic or non-catalytic process, in a continuous or batch process. Examples of companies practicing waste plastic pyrolysis include Agilyx Corporation, Recycling Technologies Ltd, Plastic Energy Ltd., and Licella. Non-limiting examples of such processes are described in patent applications WO2013/070801, WO2014/128430, and WO2011/123145, which are hereby incorporated by reference.

In the present methods, a first hydrocarbon feed stream is provided, comprising a pyrolysis oil. As mentioned above, the preparation of a pyrolysis oil from waste plastic is well known in the art. Accordingly, the preparation of the pyrolysis oil is not necessarily part of the methods described herein. The pyrolysis oil may be provided as such, optionally blended with other components, thereby forming the first hydrocarbon feed stream.

However, in certain embodiments, the preparation of a pyrolysis oil from waste plastic may be a part of the method. In such embodiments, the method comprises a step of preparing a pyrolysis oil from a (waste) plastic feed. The preparation generally involves heating a container that has a waste plastic therein so as to effect depolymerization of the waste plastic, and obtaining a pyrolysis oil or condensed (liquid) pyrolysis product. A first hydrocarbon feed stream is then provided, comprising said pyrolysis oil. In such embodiments, the method described herein may be an integrated process comprising said preparation of the pyrolysis oil, wherein the pyrolysis oil is used without intermediate storage or transportation steps.

An advantage of pyrolysis is that the process is not restricted to specific plastic types. Accordingly, the waste plastic may comprise a mixture of different types of plastic, and may still be used for preparing the pyrolysis oil, without requiring sorting. Preferred plastic types are those including high density polyethylene, low density polyethylene, and propylene, and their copolymers. However, also other plastic types may be present, such as polyethylene terephthalate (PET), polystyrene, and poly(vinyl chloride) (PVC).

The pyrolysis oil may include one or more hydrocarbon materials selected from paraffins, olefins, naphthenes, and aromatics. The relative amount of these materials may depend on the specific pyrolysis process conditions and the waste plastic material. For example, a higher PET and/or polystyrene content of the plastic feed, will generally result in a higher aromatic content of the resulting pyrolysis oil.

The boiling range of the pyrolysis oil may depend on factors such as the pyrolysis conditions and the plastic feed. Optionally, a waste plastic pyrolysis oil may be fractionated in order to obtain a pyrolysis oil having a certain boiling range and/or blended with a hydrocarbon fluid having a certain boiling range. In particular embodiments, the first hydrocarbon feed stream comprises at least 30% of hydrocarbons having a boiling point from 100°C to 350°C. In preferred embodiments, the first hydrocarbon feed stream has a T10 distillation point of at least 100°C, and T90 distillation point of at most 350°C. Such a feed stream is particularly useful in the preparation of hydrocarbon fluids as described herein. The distillation points may be determined via gas chromatography according to ASTM D2887.

In the methods described herein, at least 1 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt% of the first hydrocarbon feed stream is pyrolysis oil. Using relatively low concentrations of pyrolysis oil (e.g. about 1 wt% or even lower) may allow for lowering the concentration of certain contaminants in the pyrolysis oil via dilution, thereby reducing the adverse effects of such contaminants on other process steps such as hydroprocessing. When using very low pyrolysis oil concentrations in the first hydrocarbon feed stream, in particular concentrations below 1 wt%, the contaminants may be diluted to such extent, that a special treatment of the feed stream may no longer be necessary. Such feed streams may be processed in a traditional refining process, and may not require the methods as described herein.

Accordingly, in the methods described herein, the first hydrocarbon feed stream will typically contain at least 50 wt% of pyrolysis oil obtained from waste plastic. In further embodiments, the first hydrocarbon feed stream contains at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or even 100 wt% of pyrolysis oil. This allows for an effective removal of the contaminants which can be present in the pyrolysis oil.

Contaminant removal

Plastic pyrolysis oil typically contains various contaminants such as metals and heteroatom compounds. The term “heteroatom compounds” as used herein refers to (organic) molecules that include atomic species other than carbon and hydrogen. Examples of heteroatom compounds include compounds containing nitrogen, phosphor, oxygen, or halogens (such as chlorine, fluorine and bromine). Such contamination can have a negative impact on refining processes and equipment. Moreover, the contaminants are also undesired in fluids such as solvents, which often need to be of high purity. The processes described herein not only allow for use of the pyrolysis oil in a refining process, but also allow for obtaining high-purity solvents.

In particular embodiments, the first hydrocarbon feed stream, prior to contaminant removal, may contain one or both of the following: (a) more than 20 wppm of chlorine; and a total amount of metals selected from mercury, lead, and iron above 20 wppm. In further embodiments, the first hydrocarbon feed stream, prior to contaminant removal, may contain one or both of the following: (a) more than 40 wppm of chlorine; and a total amount of metals selected from mercury, lead, and iron above 40 wppm.

In the present methods, contaminants may be removed at least partially by subjecting at least a portion of the first hydrocarbon feed stream to one or more washing steps with a polar solvent, said solvent preferably having a dielectric constant of at least 20, more preferably at least 40, most preferably at least 50 (measured at 25°C). This allows for reducing the content of polar contaminants in the first hydrocarbon feed stream. Examples of such contaminants include polar organic molecules such as ketones, ethers, phenols, carboxylic acids, and the like. Suitable solvents may include water, propylene carbonate, alcohols (e.g. ethanol, 1 -propanol, or isopropanol), or mixtures thereof. In preferred embodiments, the relative volume of the first hydrocarbon feed to the volume of solvent used in the one or more washing steps ranges from 1 : 1 to 1 :200.

Each washing step is a liquid-liquid extraction process wherein the first hydrocarbon feed stream is contacted with the solvent in order to extract (polar) impurities from the feed. The washing may be done using an extraction column or wash tower known in the art. Non-limiting examples of suitable commercially available liquid-liquid extraction columns include KARR® columns and SCHEIBEL® columns, available from Koch Modular.

The washing generally results in a solvent-rich phase (often a bottom stream) containing polar components extracted from the first hydrocarbon feed stream, and an organic fraction (often an overhead stream) containing the hydrocarbon portion of the first hydrocarbon feed stream. The solvent-rich phase may be recirculated to be contacted with further first hydrocarbon feed stream.

In preferred embodiments, the washing is done with an aqueous solution. Such washing is referred to herein as “water washing”. In such embodiments, the washing can enable the extraction of water-soluble impurities from the feed. The water washing may be done using an extraction column or wash tower, for example as described in patent applications EP2338864 and W093/13040, which are hereby incorporated by reference. The aqueous solution generally comprises at least 50 wt% water, preferably at least 75 wt%, more preferably at least 95 wt%. In particular embodiments, the aqueous solution has an initial pH (i.e. prior to contacting with the first hydrocarbon feed stream) ranging between 6 and 8, preferably about 6.5 and 7.5, more preferably about 7. The aqueous solution may be buffered to maintain a pH in such range.

Additionally or alternatively, the first hydrocarbon feed stream (or a portion thereof) is contacted with one or more adsorbents suitable for removing one or more contaminants selected from water, metals, chlorides, fluorides, nitrogen-containing compounds, oxygenates, and phosphorous-containing compounds. More particularly, the feed stream may pass over one or more adsorbent beds, each containing one or more adsorbents. Each bed can have different adsorbents, or multiple beds can have the same adsorbent, depending on the adsorption capacity and the detected or expected contaminant level. Depending on the specific contaminants present or expected to be present in the first hydrocarbon feed stream, one or more adsorbents may be bypassed to avoid unnecessary purification steps. In particular embodiments, information regarding the contaminant level in the feed may be obtained via in-line monitoring and analysis. The methods described herein are not limited to specific adsorbents. Various adsorbents suitable for removing one or more contaminants are known in the art and are commercially available. Examples of suitable multi-purpose adsorbents include Zeolite 13X adsorbents, activated carbon, (activated) alumina, and clays. Non-limiting examples of suitable adsorbents for removing selected contaminants are provided below.

Water: silica gel adsorbents (e.g. Sylobead® silica gels available from W.R. Grace) and molecular sieves (e.g. AZ-300, GB-620, Molsiv® ADG-401, and Molsiv® HPG-250 adsorbent available from UOP; and F-200 and 4A molecular sieves available from BASF).

Nitrogen compounds: Axsorb® 911 adsorbent available from Axens.

Mercury: AxTrap™ 273 adsorbent available from Axens, Durasorb™ HG available from BASF, and Mersorb® available from Selective Adsorption Associates Inc.

Chlorides: AxTrap™ 867 adsorbent available from Axens; UOP CLR-204, UOP CLR- 300, and UOP CLR-454 available from UOP; Puraspec™ Clear™ chloride guards available from Johnson Matthey; HTG-10 available from Haldor Topsoe; and BASF CL-850.

Fluorides: (activated) alumina, e.g. AxTrap™ 600 series adsorbents available from Axens.

Silicon: ACT 971 and ACT 981 available from Axens.

Oxygenates: Axsorb® 911 adsorbent available from Axens; UOP AZ-300, UOP GB- 620, Molsiv® ADG-401, and Molsiv® HPG-250 available from UOP.

Sulfur: Axsorb® 913 adsorbent available from Axens; UOP ADS-120, UOP ADS-130, UOP ADS-280, and UOP SG-731 available from UOP; D-1275E, D1280E, and Prosorb® N available from BASF.

Phosphorus: TK-31 and TK-455 MultiTrap™ catalyst available from Haldor Topsoe.

In particular embodiments, the first hydrocarbon feed stream may be subjected to the washing step(s) and be contacted with adsorbents as described above. Together, these measures can provide a broad-spectrum clean-up procedure able to remove or reduce to an acceptable level virtually all potentially present contaminants in pyrolysis oils. In such embodiments, the one or more washing steps will typically be performed prior to the contacting with the one or more adsorbents. An exemplary flow scheme is shown in the Figure. The flow scheme involves a wash (1) to remove polar contaminants, and a series (a battery) of adsorbents (2). In the washing step, the first hydrocarbon feed stream (4) is contacted with solvent (3) in an extraction column (5). The hydrocarbon-rich fraction may be transferred to a settler (6 - optional) to remove residual water, and is purified further via a battery of adsorbents (2) which can be composed of adsorbents with general functionality, such as non-selective adsorbents and/or adsorbents with a specific functionality used to remove a specific contaminant.

In particular embodiments, the entire first hydrocarbon feed stream may be subjected to the washing step and/or contacting with adsorbents. In other embodiments, only a fraction of the feed stream may be subjected to such purification. In particular embodiments, the feed stream may be distilled as to obtain fractions having a different boiling range. The process may then continue with one or more fractions of interest. In other embodiments, the feed stream may be divided in fractions having the same composition, wherein some fractions may be purified and others not. The fractions may be rejoined after the purification of one or more of the fractions. By setting the relative volume of the purified and non-purified fractions, a targeted level of purification can be reached.

After subjecting the first hydrocarbon feed stream (or a part thereof) to the washing step and/or contacting with adsorbents as described above, a (partially) decontaminated fluid is obtained, referred to herein as “first hydrocarbon fluid”. Generally, the contamination level is reduced to such amount, that the first hydrocarbon fluid is suitable for being hydroprocessed or hydrotreated, as described below; and that a final product with sufficient purity can be obtained. In particular embodiments, the total amount of metals selected from mercury, lead, and iron in the first hydrocarbon fluid is below 5 wppm, or even below 1 wppm. Additionally or alternatively, the total amount of mercury in the first hydrocarbon fluid may be below 5 wppb (weight parts per billion). Iron and lead were found to be common contaminants in pyrolysis oils obtained from waste plastic. Levels of mercury were typically significantly lower than lead. Suitable methods for determining the metal content are discussed further below. Additionally or alternatively, the first hydrocarbon fluid may contain less than 5 wppm of chlorine; preferably less than 5 wppm of chlorine and fluorine. In preferred embodiments, the first hydrocarbon fluid may contain less than 5 wppm of chlorine; and a total amount of metals selected from mercury, lead, and iron below 5 wppm. In those or other embodiments, the one or more adsorbents used may include at least one or more adsorbents suitable for removing chlorine, mercury, lead, and iron. In preferred embodiments, the first hydrocarbon fluid may contain less than 5 wppm of chlorine and fluorine; and a total amount of metals selected from mercury, lead, and iron below 5 wppm. In those or other embodiments, the one or more adsorbents used may include at least one or more adsorbents suitable for removing chlorine, fluorine, mercury, lead, and iron. Not all of the listed adsorbents may be needed to obtain a first hydrocarbon fluid of such purity, as the first hydrocarbon feed stream may already have a sufficiently low concentration of one or more impurities of interest. For example, the present inventors found chlorine to be a common contaminant in pyrolysis oils obtained from waste plastic, while fluorine contamination was found to be less common.

In other embodiments, the first hydrocarbon fluid may contain 5 wppm or more of chlorine and fluorine (for example 5 to 20 wppm); and/or a total amount of metals selected from mercury, lead, and iron of 5 wppm or more (for example 5 to 20 wppm). In such embodiments, the concentration of these contaminants may be reduced by blending the first hydrocarbon fluid (and/or second hydrocarbon fluid as described further) with a second hydrocarbon feed stream.

Oxygen stripping

In particular embodiments, the first hydrocarbon fluid obtained after decontamination as described above, is subjected to gas stripping, thereby reducing the oxygen content of the first hydrocarbon fluid. Gas stripping can remove oxygen (O2) which may be dissolved in the first hydrocarbon fluid, thereby reducing the probability of free radical formation leading to polymerization in downstream steps of the methods described herein. The process generally involves contacting the hydrocarbon fluid with a stripper gas (e.g. H2, N2, or a mixture thereof), thereby transferring at least a portion of the dissolved oxygen from the hydrocarbon fluid to the stripper gas, followed by separating the stripper gas from the hydrocarbon fluid. After the gas stripping, the oxygen content of the first hydrocarbon fluid preferably is below 5 wppm, more preferably below 2 wppm. The amount of dissolved oxygen may be determined via electrochemical detection, according to UOP678-04. The volume of stripper gas relative to the hydrocarbon fluid volume (both volumes as measured under gas stripping conditions) typically is more than 1, and preferably at least 3. In particular embodiments, the stripper gas may contain at least 60 % (molar %) H2. Any dissolved H2 remaining in the hydrocarbon fluid after the gas stripping step is not an issue, given the downstream hydroprocessing. Preferably, the gas stripping step is completed prior to any (pre)heating of the first hydrocarbon fluid, as to minimize potential fouling. Hydroprocessing

As described above, the pyrolysis oil may contain organic compounds comprising heteroatoms such as sulfur, nitrogen, and oxygen. Some of these heteroatom-comprising organic compounds may be removed through washing or adsorbents as described above. Heteroatom-containing compounds can also be removed from the first hydrocarbon fluid via one or more hydroprocessing steps (also referred to herein as “hydrotreatment steps”). In this way, the concentration of such compounds can be reduced to acceptable levels, which may vary depending on the intended use of the final hydrocarbon fluid.

The hydroprocessing steps can also result in the saturation of unsaturated organic compounds such as olefins, diolefins, and aromatic compounds (aromatics), which are typically present in the pyrolysis oil. The removal of olefins and diolefins from the first hydrocarbon fluid, and the optional removal of aromatics, will be described further below.

Pyrolysis oils obtained from the pyrolysis of plastics typically contain a high amount of olefins. The plastic pyrolysis oil used in the process described herein typically contains at least 5 wt% olefins. In particular embodiments, the plastic pyrolysis oil contains at least 10 wt% olefins, at least 15 wt% olefins, or at least 20 wt% olefins. In certain embodiments, the plastic pyrolysis oil may contain up to 90 wt% olefins. Typically however, the pyrolysis oil contains no more than 70 wt% olefins, or no more than 50 wt% olefins.

Unless specified otherwise, the content of olefins, paraffins (n-paraffins and isoparaffins), naphthenes, and aromatics, may be determined using gas chromatography with vacuum ultraviolet absorption spectroscopy detection according to ASTM D8071.

A portion of the olefins in the pyrolysis oil may be diolefins. In particular embodiments, the pyrolysis oil may contain at least 0.03 mol of diolefins per kg of pyrolysis oil, more particularly conjugated diolefins (i.e. conjugated dienes). In particular embodiments, the pyrolysis oil may contain at least 0.04, 0.05, or even 0.10 mol of diolefins per kg of pyrolysis oil. The (conj ugated) diolefin content may be measured via maleic anhydride addition, for example according to UOP326-17.

Olefins and diolefins are generally not desired in the final hydrocarbon products and are removed in one or more hydroprocessing steps (also referred to herein as “hydrotreatment steps”), wherein olefins and diolefins are saturated via hydrogenation.

Accordingly, in the methods described herein, olefins and diolefins in the first hydrocarbon fluid are hydrogenated, thereby obtaining a hydroprocessed hydrocarbon fluid. Such hydrogenation may be done in one or more hydrotreatment steps. The one or more hydrotreatment steps are typically done in a process which is separate from the decontamination (and optional oxygen stripping) described herein. Indeed, the removal of contaminants in the decontamination prior to hydrotreatment can improve the lifetime of the catalyst(s) used for the hydrotreatment. Accordingly, the first hydrocarbon fluid is typically transferred to a hydrogenation reactor, after contaminant removal and optional oxygen stripping.

Optionally, the first hydrocarbon fluid (or a portion thereof) may be blended with a second hydrocarbon feed stream prior to one of said one or more hydrotreatment steps. In particular embodiments, the first hydrocarbon fluid (or a portion thereof) may be blended with up to 99 wt%, up to 95 wt%, or up to 90 wt% of said second hydrocarbon feed stream. The expression “blended with x wt% of a component” as used herein means that the blend contains x wt% of that component. The second hydrocarbon feed stream may be obtained from another source than plastic waste. Indeed, the present method may be part of integrated refining process where also hydrocarbons from other sources (e.g. mineral oil) are refined. Whereas the decontamination via washing and/or adsorbents as described above is particularly relevant for pyrolysis oils, hydrotreatment may also be needed for refining hydrocarbons obtained from other sources. The blend ratios may be varied throughout the process depending on the properties and composition of the first hydrocarbon fluid and the second hydrocarbon feed stream. Advantageously, the second hydrocarbon feed stream may contain a lower amount of one or more contaminants (such as chlorine, iron, mercury, and lead) compared to the envisaged hydroprocessed hydrocarbon fluid. In this way, blending the first hydrocarbon fluid (or portion thereof) with the second hydrocarbon feed stream can compensate for higher contamination levels in the first hydrocarbon fluid. Additionally or alternatively, the second hydrocarbon feed stream can act as a heat sink, which can help in controlling the temperature of the exothermic hydrotreatment.

In particular embodiments, the first hydrocarbon fluid (or a portion thereof) is blended with up to 70 wt%, or up to 50 wt% of a second hydrocarbon feed stream. In specific embodiments, the first hydrocarbon fluid (or a portion thereof) is blended with at least 5 wt%, at least 10 wt%, at least 20 wt%, or at least 50 wt% of a second hydrocarbon feed stream.

The one or more hydrotreatment steps can be done in a hydrotreatment unit as known in the art. Hydrotreatment is generally done in the presence of a catalyst, under conditions suitable for the desired hydrogenation, as known by the skilled person. Suitable catalysts and process conditions are known in the art. Examples of suitable catalysts include catalysts based on nickel, cobalt, and or molybdenum, such as Nickel (Ni), Nickel-Molybdenum (NiMo), and Cobalt- Molybdenum (CoMo) catalysts, preferably provided on a solid support such as alumina.

In particular embodiments, the hydrogenation of the olefins and diolefins may be done in a single hydrotreatment step. Accordingly, the olefins and diolefins may be hydrogenated simultaneously. Suitable reaction conditions for such hydrogenation include a temperature between 200°C and 300°C, and a pressure ranging from 30 to 250 bar, preferably at least 35 bar. In certain embodiments, the catalyst may be a NiMo catalyst.

In other embodiments, the hydrogenation of the olefins and diolefins may be done in two or more separate steps. More particularly, the hydrogenation of olefins and diolefins may be done via cl) selective hydrogenation of diolefins in the first hydrocarbon fluid (or a fraction thereof), thereby obtaining a second hydrocarbon fluid; and c2) subjecting the second hydrocarbon fluid or a part thereof, optionally blended with of a second hydrocarbon feed stream, preferably up to 90 wt% of said second hydrocarbon feed stream, to one or more hydrotreatment steps.

Completion of the one or more hydrotreatment steps in c2) results in a hydroprocessed hydrocarbon fluid as described herein.

The selective hydrogenation of diolefins in a first separate step may be advantageous to integrate the methods described herein in existing refining processes involving one or more hydrotreatment steps using catalysts which are sensitive to fouling in the presence of diolefins. More particularly, diolefins, in particular conjugated diolefins, may be hydrogenated first, thereby obtaining a second hydrocarbon fluid. The second hydrocarbon fluid preferably contains less than 0.04 mol, less than 0.03 mol, less than 0.02 mol, or even less than 0.01 mol conjugated diolefins per kg of second hydrocarbon fluid. The selective hydrogenation of diolefins generally converts the diolefins to mono-olefins.

The second hydrocarbon fluid may then be subjected to one or more hydrotreatment steps which are part of a conventional (petroleum) refining process, to remove olefins and other compounds such as sulfur-, nitrogen-, and oxygen-containing compounds. Prior to those one or more hydrotreatment steps, the second hydrocarbon fluid may be blended with a second hydrocarbon feed stream. If blended, the second hydrocarbon fluid is typically blended with 1 to 99 wt% of a second hydrocarbon feed stream, preferably with 5 to 90 wt% of a second hydrocarbon feed stream. In specific embodiments, the second hydrocarbon fluid may be blended with 10 to 90 wt% of a second hydrocarbon feed stream. Advantageously, the second hydrocarbon feed stream may be a (intermediary) product obtained in such conventional refining process, i.e. a petroleum-derived hydrocarbon fluid. However, it is envisaged that also other products may be used as the second hydrocarbon feed stream.

Additionally or alternatively, the selective hydrogenation of diolefins may allow for utilizing olefins which are present in the second hydrocarbon fluid as reactants in processes such as alkylation reactions. Accordingly, in particular embodiments, a first portion of the second hydrocarbon fluid may be hydrogenated as described herein, whereas a second portion may be utilized in other processes. The composition of the first and second portions may be the same or different. In particular embodiments, the second portion may have a higher olefin content (in wt%) than the first portion.

Methods for the selective hydrogenation of diolefins are known in the art. US Patent 3,696,160, hereby incorporated by reference, discloses the selective hydrogenation of diolefins into their corresponding mono-olefins, using a sulfide nickel -tungsten catalyst. US Patent 6,118,034, hereby incorporated by reference, discloses the selective hydrogenation of diolefins at a temperature of 40°C to 100°C, over a nickel-containing precipitated catalyst. US Patent 6,469,223, hereby incorporated by reference, discloses the selective hydrogenation of diolefins over a nickel-containing catalyst. Other catalysts and/or process conditions than those described in US 3,696,160, US 6,118,034, and US 6,469,223 may be used as well. In particular embodiments, the selective hydrogenation of diolefins may be done at a temperature between 100°C and 300°C, and a pressure ranging from 20 to 40 bar, preferably from 25 to 35 bar. In certain embodiments, the catalyst may be a Ni or NiMo catalyst. In specific embodiments, the selective hydrogenation of diolefins may be performed at a temperature from 135°C to 220°C, and at a pressure from 21 bar to 26 bar, preferably using a NiMo catalyst, at a liquid hourly space velocity (LHSV, i.e. the ratio of liquid volume flow per hour to catalyst volume) of 3 h to 6 h⁴.

After the selective hydrogenation of diolefins, the remaining (mono)olefins are hydrogenated in one or more hydrotreatment steps. The reaction conditions of such hydrotreatment steps may depend on whether aromatics should also be hydrogenated or not. In various embodiments, the presence of aromatics in the hydroprocessed hydrocarbon fluid may be desired. In such embodiments, the hydrogenation of olefins (and diolefins) can be done under conditions wherein aromatics are not, or only partially, hydrogenated. Suitable reaction conditions to obtain this are known in the art. In general, the hydrogenation of aromatics can be minimized by lowering the reaction temperature, lowering the pressure, and/or increasing space velocity. In particular embodiments, a single stage reactor may be used, preferably with liquid product recycle. In particular embodiments, the reaction may be operated at a temperature from 90 to 250°C, at a pressure from 20 to 35 bar, and at a LHSV below 1.5 h⁴, for example about 1 h wherein the liquid includes fresh feed + recycle, if any). Suitable catalysts include (coprecipitated) Ni catalysts (e.g. BASF catalyst Ni 3298) and noble metal catalysts such as MAXSAT™ catalyst (available from ExxonMobil).

In other embodiments, the presence of aromatics in the hydroprocessed hydrocarbon fluid may not be desired. In such embodiments, the hydrogenation of olefins (and diolefins) may be done under conditions allowing for the hydrogenation of aromatics. In general, the hydrogenation of aromatics can be promoted by increasing the pressure, increasing the reaction temperature, and/or lowering space velocity. Additionally or alternatively, the hydrogenation of the aromatics may be done in an additional hydrogenation step. Suitable reaction conditions to obtain this are known in the art. In particular embodiments, the hydrogenation of aromatics is performed at a pressure above 20 bar, preferably above 25 bar, for example between 25 bar and 30 bar. The reaction temperature preferably is above 150°C, for example about 200°C. In particular embodiments, the pressure may be above 30 bar, or even above 45 bar. Suitable catalysts include nickel-containing catalysts, for example a NiMo catalyst; optionally in combination with a noble metal catalyst such as MAXSAT™ catalyst (available from ExxonMobil). The use of a noble catalyst may allow for further reducing the aromatic content, compared to the use of a NiMo catalyst alone. In embodiments wherein the aromatics are hydrogenated, the hydroprocessed hydrocarbon fluid may contain less than 1 wt% of aromatics, less than 0.5 wt% aromatics, or even less than 0.1 wt% of aromatics. For the measurement of such low concentrations, gas chromatography according to ASTM D8071 referred to above may not be suitable. The aromatic content in fluids containing less than 1 wt% of aromatics may be determined using High Performance Liquid Chromatography (HPLC) with Refractive Index Detection may be used, according to ASTM D7419. In the present methods, a number of contaminants can be removed in the washing step and/or the contacting with adsorbents as described above. Further undesired components such as olefins and diolefins (as well as sulfur, nitrogen, and oxygenates) can be removed in the one or more hydrotreatment steps. Accordingly, the present methods allow for obtaining a highly pure hydrocarbon fluid. More particularly, a hydroprocessed hydrocarbon fluid can be obtained, wherein said hydrocarbon fluid contains:

- less than 0.1 wt% olefins;

- a total amount of metals selected from mercury, lead, and iron below 5 wppm;

- less than 5 wppm of chlorine and fluorine; and

- less than 5 wppm of sulfur.

The 5 wppm of chlorine and fluorine refers to the combined chlorine and fluorine content.

The chlorine and fluorine content may be determined via Combustion Ion Chromatography (CIC) according to ASTM D7359. Preferably, the combined chlorine and fluorine content will be less than 2 wppm, or even less than 1 wppm.

In particular embodiments, the total amount of metals selected from mercury, lead, iron, and zinc is below 5 wppm. Additionally or alternatively, the total amount of metals selected from mercury, lead, and iron may be below 1 wppm. Additionally or alternatively, the total amount of mercury may be below 5 wppb (weight parts per billion). The concentration of mercury may be determined using a Nippon Instruments Corporation (NIC) Mercury Analyzer according to UOP938. The concentration of the other metals can be determined via Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), for example according to ASTM D5185. The sulfur content may be determined via Ultraviolet Fluorescence (UV-F) according to ASTM D5453.

Generally, at least 99.5 wt% of the hydroprocessed hydrocarbon fluid consists of one or more components selected from normal paraffins, isoparaffins, naphthenes, and aromatics.

In particular embodiments, the hydroprocessed hydrocarbon fluid contains:

- less than 0.05 wt% of olefins;

- less than 1 wppm of metals selected from mercury, lead, and iron;

- less than 1 wppm of chlorine and fluorine; and

- less than 1 wppm of sulfur.

In preferred embodiments, the hydroprocessed hydrocarbon fluid contains:

- less than 0.01 wt% of olefins; or even less than 0.001 wt% of olefins;

- less than 1 wppm of metals selected from mercury, lead, and iron; - less than 1 wppm of chlorine and fluorine; and

- less than 1 wppm of sulfur.

The hydroprocessed hydrocarbon fluids typically comprise isoparaffins, normal paraffins, naphthenes, and optionally aromatics. In particular embodiments, the hydroprocessed hydrocarbon fluids comprise at least 50 wt% of components selected from normal paraffins, isoparaffins, and naphthenes, preferably at least 60 wt%. In particular embodiments, isoparaffins, normal paraffins, and naphthenes each are present in the hydroprocessed hydrocarbon fluid in a concentration of at least 1 wt%, or even at least 5 wt%.

In particular embodiments, the methods described herein may further comprise a hydroisomerization step. Such step is preferably performed on the hydroprocessed hydrocarbon fluid (or fractions thereof). The hydro-isomerization step allows for converting normal paraffins (i.e. unbranched paraffins) in the fluid to isoparaffins (i.e. branched paraffins). Suitable process conditions and catalysts for hydro-isomerization are known in the art, for example in patent application publication US 2014/0303057, which describes the hydroisomerization of paraffins over a bifunctional catalyst at temperatures ranging from 200° to 500°C, and a pressure of 40 bar or more. Suitable catalyst may have a hydrogenation-dehydrogenation activity from one or more transition metals (such as Ni, Co, Pd, Pt, Ru, Rh, Co, Mo, and W), and acidic activity from an amorphous or crystalline support such as amorphous silica-alumina, silicon-aluminum- phosphate (such as SAPO-11), molecular sieves, or aluminum silicate zeolite. Suitable zeolites include ZSM-22, ZSM-12, ZSM-23, ZSM-4, ZSM-48, and ZSM-50. In particular embodiments, the fluid after hydro-isomerization has an isoparaffin to normal paraffin ratio of at least 10, preferably at least 15. Additionally or alternatively, the fluid after hydroisomerization may contain at least 50 wt% of isoparaffins.

In preferred embodiments, the hydroprocessed hydrocarbon fluid predominantly contains components boiling in the range from 100°C to 350°C. More particularly, at least 90 wt% of the hydroprocessed hydrocarbon fluid may have a boiling point from 100°C to 350°C. Additionally or alternatively, the hydroprocessed hydrocarbon fluid has a T10 distillation point of at least 100°C, and T90 distillation point of at most 350°C; or a T10 distillation point of at least 160°C, and T90 distillation point of at most 320°C. The skilled person knows that the boiling range of the hydroprocessed hydrocarbon fluids can be influenced mainly via the boiling range of the first hydrocarbon feed stream, and the severity of the one or more hydroprocessing steps.

In particular embodiments, the hydroprocessed hydrocarbon fluid may be subjected to distillation, thereby obtaining two or more fractions having different boiling ranges. The distillation technique may proceed at atmospheric pressures or reduced pressures and may utilize low-resolution distillation techniques (i.e., short-path) or high-resolution distillation techniques (i.e., distillation towers, spinning-band columns etc.). Each of the fractions may be used as such a fluid, or be used as a component in a fluid. Fractionation may be performed prior to or after the optional hydro-isomerization of the hydroprocessed hydrocarbon fluid described above. In particular embodiments, at least one of the fractions has a T10 distillation point of at least 160°C, and T90 distillation point of at most 320°C.

The fluids obtained by the present methods may be used as specialty fluids in a variety of applications. For example, the fluids may be used as solvents and base oils in lubricants, agricultural chemical applications (e.g. spray oil applications), coolant and/or heat transfer fluids, electric vehicle fluids, acrylic and silicone mastics and sealants, printing inks, paints, coatings, adhesives, drilling fluids, metalworking fluids, cleaning fluids, and consumer products.

Further disclosed herein is the use of a plastic pyrolysis oil for preparing a hydrocarbon fluid containing less than 0.1 wt% olefins; a total amount of metals selected from mercury, lead, and iron below 5 wppm; less than 5 wppm of chlorine and fluorine; and less than 5 wppm of sulfur. The hydrocarbon fluid preferably contains at least 99.5 wt% of paraffins, isoparaffins, naphthenes, aromatics, or a combination thereof.

Further disclosed are the following embodiments of the methods described herein: Embodiment 1 : A method for producing a hydrocarbon fluid from waste plastic feedstock, comprising: a) providing a first hydrocarbon feed stream, wherein at least 50 wt% off said first hydrocarbon feed stream is obtained from the pyrolysis of plastic waste; b) removing contaminants from said first hydrocarbon feed stream by: - subjecting at least a portion of said first hydrocarbon feed stream to a washing step with a polar solvent; and/or

- contacting at least a portion of said first hydrocarbon feed stream with one or more adsorbents, said adsorbents preferably being suitable for removing one or more contaminants selected from water, metals, chlorides, nitrogen-containing compounds, oxygenates, and phosphorous-containing compounds; thereby obtaining a first hydrocarbon fluid; c) hydrogenation, in one or more hydroprocessing steps, of olefins and diolefins in said first hydrocarbon fluid, optionally blended with a second hydrocarbon feed stream; thereby obtaining a hydroprocessed hydrocarbon fluid containing:

- less than 0.1 wt% olefins; a total amount of metals selected from mercury, lead, and iron below 5 wppm;

- less than 5 wppm of chlorine, preferably less than 5 wppm of chlorine and fluorine; and

- less than 5 wppm of sulfur.

Embodiment 2: The method of embodiment 1, wherein at least 80 wt% of said first hydrocarbon feed stream is obtained from the pyrolysis of plastic waste.

Embodiment 3: The method of embodiment 1 or 2, wherein said first hydrocarbon feed stream comprises at least 30% of hydrocarbons having a boiling point ranging from 100°C to 350°C. Embodiment 4: The method of any one of embodiments 1 to 3, wherein said hydrogenation of olefins and diolefins is done via cl) selective hydrogenation of diolefins in said first hydrocarbon fluid or a fraction thereof, thereby obtaining a second hydrocarbon fluid; and c2) subjecting said second hydrocarbon fluid or a part thereof, optionally blended with a second hydrocarbon feed stream, to one or more hydroprocessing steps.

Embodiment 5: The method of any one of embodiment 4, wherein said selective hydrogenation of diolefins is done in the presence of a nickel-containing catalyst.

Embodiment 6: The method of any one of embodiments 1 to 5, wherein at least one of said one or more hydroprocessing steps is performed under conditions allowing for the saturation of aromatics, and wherein the hydroprocessed hydrocarbon fluid contains less than 0.5 wt% of aromatics.

Embodiment 7: The method of any one of embodiments 1 to 6, wherein the hydroprocessed hydrocarbon fluid contains less than 0.05 wt% olefins; less than 1 wppm of selected from mercury, lead, and iron; less than 1 wppm of chlorine and fluorine; and less than 5 wppm of sulfur.

Embodiment 8: The method of embodiment 7, wherein the hydroprocessed hydrocarbon fluid contains less than 0.01 wt% olefins, preferably less than 0.001 wt% olefins.

Embodiment 9: The method of any one of embodiments 1 to 8, wherein said one or more adsorbents comprise one or more adsorbents selected from the group consisting of molecular sieves, silica gel, activated carbon, and (activated) alumina.

Embodiment 10: The method of any one of embodiments 1 to 9, wherein the removal of said contaminants is done by a combination of said washing step and said contacting of at least a portion of the first hydrocarbon feed stream with one or more adsorbents.

Embodiment 11 : The method of any one of embodiments 1 to 10, wherein the selective diolefin hydrogenation is preceded by a gas stripping step to reduce the O2 content in said purified hydrocarbon fluid.

Embodiment 12: The method of any one of embodiments 1 to 11, further comprising fractionation of said hydroprocessed hydrocarbon fluid, thereby obtaining two or more fractions having a different boiling range.

Embodiment 13: The method of any one of embodiments 1 to 12, wherein the first hydrocarbon feed stream contains one or both of the following: (a) more than 20 wppm of chlorine; and (b) a total amount of metals selected from mercury, lead, and iron above 20 wppm.

Embodiment 14: The method of any one of embodiments 1 to 13, wherein said first hydrocarbon feed stream comprises at least 10 wt% of olefins, preferably at least 20 wt% of olefins.

Embodiment 15: The method of any one of embodiments 1 to 14, wherein said first hydrocarbon feed stream comprises at least 1 wt% of diolefins.

Embodiment 16: The method of any one of embodiments 1 to 15, further comprising a hydroisomerization step.

Embodiment 17: The method of any one of embodiments 1 to 16, wherein said first hydrocarbon fluid is blended with up to 95 wt%, and preferably up to 90 wt%, of a second hydrocarbon feed stream.

Embodiment 18: The method of embodiment 17, wherein said first hydrocarbon fluid is blended with from 5 wt% to 90 wt%, of a second hydrocarbon feed stream.

Embodiment 19: The method of any one of embodiments 1 to 18, wherein said first hydrocarbon feed stream has a T10 distillation point of at least 100°C, and a T90 distillation point of at most 350°C. Embodiment 20: The method of any one of embodiments 1 to 19, wherein the first hydrocarbon fluid contains a total amount of metals selected from mercury, lead, and iron below 5 wppm. Embodiment 21 : The method of any one of embodiments 1 to 20, wherein the first hydrocarbon fluid further contains less than 5 wppm of chlorine. Embodiment 22: The method of embodiment 21, wherein the first hydrocarbon fluid contains less than 5 wppm of chlorine and fluorine.

Embodiment 23: The method of any one of embodiments 1 to 22, wherein the hydroprocessed hydrocarbon fluid has a T10 distillation point of at least 100°C, and a T90 distillation point of at most 350°C. Embodiment 24: The method of any one of embodiment 23, wherein the hydroprocessed hydrocarbon fluid has a T10 distillation point of at least 160°C, and a T90 distillation point of at most 320°C.

Claims

- 22 -

1. A method for producing a hydrocarbon fluid from waste plastic feedstock, comprising: a) providing a first hydrocarbon feed stream, wherein at least 50 wt% of said first hydrocarbon feed stream is obtained from the pyrolysis of plastic waste; b) removing contaminants from said first hydrocarbon feed stream by:

- subjecting at least a portion of said first hydrocarbon feed stream to a washing step with a polar solvent; and/or

- contacting at least a portion of said first hydrocarbon feed stream with one or more adsorbents suitable for removing one or more contaminants selected from water, metals, chlorides, nitrogen-containing compounds, oxygenates, and phosphorous-containing compounds; thereby obtaining a first hydrocarbon fluid; c) hydrogenation, in one or more hydroprocessing steps, of olefins and diolefins in said first hydrocarbon fluid, optionally blended with a second hydrocarbon feed stream; thereby obtaining a hydroprocessed hydrocarbon fluid containing:

- less than 0.1 wt% olefins;

- a total amount of metals selected from mercury, lead, and iron below 5 wppm;

- less than 5 wppm of chlorine and fluorine; and

- less than 5 wppm of sulfur.

2. The method of claim 1, wherein at least 80 wt% of said first hydrocarbon feed stream is obtained from the pyrolysis of plastic waste.

3. The method of claim 1 or 2, wherein said first hydrocarbon feed stream comprises at least 30% of hydrocarbons having a boiling point ranging from 100°C to 350°C.

4. The method of any one of claims 1 to 3, wherein said hydrogenation of olefins and diolefins is done via cl) selective hydrogenation of diolefins in said first hydrocarbon fluid or a fraction thereof, thereby obtaining a second hydrocarbon fluid; and c2) subj ecting said second hydrocarbon fluid or a part thereof, optionally blended with a second hydrocarbon feed stream, to one or more hydroprocessing steps. The method of any one of claims 1 to 4, wherein said hydroprocessed hydrocarbon fluid has a T10 distillation point of at least 100°C, and a T90 distillation point of at most 350°C. The method of any one of claims 1 to 5, wherein said first hydrocarbon fluid is blended with 5 wt% to 95 wt% of a second hydrocarbon feed stream. The method of any one of claims 1 to 6, wherein at least one of said one or more hydroprocessing steps is performed under conditions allowing for the saturation of aromatics, and wherein the hydroprocessed hydrocarbon fluid contains less than 0.5 wt% of aromatics. The method of any one of claims 1 to 7, wherein the hydroprocessed hydrocarbon fluid contains:

- less than 0.001 wt% olefins;

- less than 1 wppm of selected from mercury, lead, and iron;

- less than 1 wppm of chlorine and fluorine; and

- less than 5 wppm of sulfur. The method of any one of claims 1 to 8, wherein said one or more adsorbents comprise one or more adsorbents selected from the group consisting of molecular sieves, silica gel, activated carbon, and alumina. The method of any one of claims 1 to 9, wherein the removal of said contaminants is done by a combination of said washing step and said contacting of at least a portion of the first hydrocarbon feed stream with one or more adsorbents. The method of any one of claims 1 to 10, wherein the hydrogenation is preceded by a gas stripping step to reduce the O2 content in said purified hydrocarbon fluid. 12. The method of any one of claims 1 to 11, further comprising fractionation of said hydroprocessed hydrocarbon fluid, thereby obtaining two or more fractions having a different boiling range. 13. The method of any one of claims 1 to 12, wherein said first hydrocarbon feed stream comprises at least 10 wt% of olefins, preferably at least 20 wt% of olefins.

14. The method of any one of claims 1 to 13, wherein said first hydrocarbon feed stream comprises at least 1 wt% of diolefins.

15. The method of any one of claims 1 to 14, further comprising a hydro-isomerization step.