Method for Treating Plastic Pyrolysis Oil Including an H2s Recycling Step

The present invention relates to a process for the treatment of a plastics pyrolysis oil in order to obtain a hydrocarbon effluent which can be upgraded in a unit for the storage of petrol, jet or gas-oil fuels or as feedstock of a steam cracking unit. More particularly, the present invention relates to a process for the treatment of a feedstock resulting from the pyrolysis of plastic waste making it possible to recycle a gas phase containing HS resulting from the process in order to keep the catalysts in sulfide form in the catalytic stages of the process and thus to reduce the consumption of sulfiding agent to be added.

Plastics resulting from collection and sorting channels can undergo a stage of pyrolysis in order to obtain, inter alia, pyrolysis oils. These plastics pyrolysis oils are generally incinerated in order to generate electricity and/or used as fuel in industrial or urban heating boilers.

Another route for upgrading plastics pyrolysis oils is the use of these plastics pyrolysis oils as feedstock of a steam cracking unit in order to (re)create olefins, the latter being constituent monomers of certain polymers. However, plastic waste is generally a mixture of several polymers, for example mixtures of polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride or polystyrene. Furthermore, depending on the applications, the plastics may contain, in addition to polymers, other compounds, such as plasticizers, pigments, dyes or also residues of polymerization catalysts. Plastic waste may additionally contain, in a minor amount, biomass originating, for example, from household waste. The treatment of waste, on the one hand, in particular the storage, mechanical treatments, sorting or pyrolysis, and also, on the other hand, the storage and transportation of pyrolysis oil, can also cause corrosion. The result of this is that the oils resulting from the pyrolysis of plastic waste comprise a lot of impurities, in particular diolefins, metals, in particular iron, silicon, or also halogen compounds, in particular chlorine-based compounds, heteroelements, such as sulfur, oxygen and nitrogen, and insoluble materials, at contents which are often high and incompatible with steam cracking units or units located downstream of steam cracking units, in particular polymerization processes and selective hydrogenation processes. These impurities can give rise to operability problems and in particular problems of corrosion, coking or catalytic deactivation, or also incompatibility problems in the applications of the target polymers. The presence of diolefins can also result in problems of instability of the pyrolysis oil, characterized by the formation of gums. The gums and the insoluble materials possibly present in the pyrolysis oil can give rise to problems of clogging in the processes.

Furthermore, during the steam cracking stage, the yields of light olefins sought for the petrochemical industry, in particular ethylene and propylene, are strongly dependent on the quality of the feedstocks sent for steam cracking. The BMCI (Bureau of Mines Correlation Index) is often used to characterize hydrocarbon cuts. This index, developed for hydrocarbon products resulting from crude oils, is calculated from the measurement of the density and the average boiling point: it is equal to 0 for a linear paraffin and to 100 for benzene. Its value thus increases in proportion as the product analysed has a condensed aromatic structure, naphthenes having a BMCI intermediate between paraffins and aromatics. Overall, the yields of light olefins increase when the paraffin content increases and thus when the BMCI decreases. Conversely, the yields of undesired heavy compounds and/or of coke increase when the BMCI increases.

The document WO 2018/055555 provides an overall process for the recycling of plastic waste, which is very general and relatively complex, ranging from the very stage of pyrolysis of the plastic waste up to the steam cracking stage. The process of the application WO 2018/055555 comprises, inter alia, a stage of hydrotreating the liquid phase resulting directly from the pyrolysis, preferably under quite stringent conditions, in particular in terms of temperature, for example at a temperature of between 260 and 300° C., a stage of separation of the hydrotreating effluent and then a stage of hydrodealkylation of the separated heavy effluent at a preferably high temperature, for example of between 260 and 400° C.

The unpublished patent application FR 21/00.026 describes a process for the treatment of a plastics pyrolysis oil targeted at reducing and/or at removing the impurities contained in the pyrolysis oil in order to obtain an effluent compatible for a steam cracker. The process comprises the following stages:

One route for removing the impurities contained in the ex-plastics pyrolysis oils is thus to carry out a hydrotreating in the presence of catalysts which are active in sulfide form. In the context of feedstocks containing a plastics pyrolysis oil, the feedstocks available are generally fairly poor in sulfur. In point of fact, a minimum pHSp is necessary in the hydrotreating reactor in order to keep the catalysts in sulfide form and thus not to reduce them. In order to maintain a sufficient pHSp in the reactor and in view of the fact that the feedstocks do not contain sufficient sulfur, a sulfiding agent is generally, indeed even necessarily, continuously added, typically DMDS (dimethyl disulfide), to the feedstock. The sulfiding agent decomposes very rapidly to give HS by the action of the temperature and of the hydrogen at the reactor inlet and thus provides the amount of HS necessary to ensure a minimum and sufficient pHSp.

After the hydrotreating, at least a portion of the HS contained in the effluent forms ammonium sulfide salts ((NH)S) with the NHgenerated by the hydrogenation of nitrogen compounds during the hydrotreating. Unlike conventional feedstocks of fossil type, ex-plastics pyrolysis oils generally contain greater contents of nitrogen than contents of sulfur. These salts are generally removed by scrubbing with water, followed by a (single) stage of steam stripping of the aqueous effluent, making it possible to obtain a purified aqueous effluent and a gas phase containing HS and NH, which are generally discharged together at the top of the stripping column. The gas phase containing HS and NHis subsequently generally incinerated to form SO(sulfur oxides) and Nor NO(nitrogen oxides).

The gas phase containing HS and NHmight be recovered and returned to the inlet of the hydrotreating unit in order to maintain the pHSp in the reactor without adding a sulfiding agent. However, the NHcontained in this gas phase prevents this from being done as there would be a concentration of NHin the recycling loop which would be prejudicial to the operation of the unit. Furthermore, the presence of NHlowers the pHp. The gas phase containing HS and NHthus cannot be reused directly as source of HS for keeping the catalysts in sulfide form.

The present invention provides a process for the treatment of a feedstock comprising a plastics pyrolysis oil which makes possible the recycling of a phase containing only HS in order to use it as source of HS at the inlet of catalytic units of the process by carrying out a separation, generally by stripping, in two stages, making it possible to separate the HS and the NH. This is because the use of two stripping columns operating under different operating conditions makes it possible to separate the HS from the NHand thus to recover:

The two-stage stripping making it possible to separate the HS from the NHthus exhibits the following advantages:

This is because the NHhas been captured in the form of ammonium sulfide in the aqueous effluent by the excess HS which has been recycled. The gaseous effluent, thus freed from the NH, can thus be sent to a steam cracker so as to increase the overall yield of olefins.

More specifically, the invention relates to a process for the treatment of a feedstock comprising a plastics pyrolysis oil, comprising:

The present invention thus relates to a process making it possible to purify an oil resulting from the pyrolysis of plastic waste of at least a part of its impurities, which makes it possible to hydrogenate it and thus to be able to upgrade it in particular by incorporating it directly in the fuel storage unit or else by rendering it compatible with a treatment in a steam cracking unit while being able to recycle the HS resulting from the process continuously in order to minimize the consumption of sulfiding agent. The injection of a sulfiding agent remains in particular necessary at the start of the catalytic cycle, the time that the HS is formed in order to be separated in stage d) and recycled upstream of stage a) and/or of stage b) and/or of stage g), and/or also upstream of the selective hydrogenation stage a0). Additional injections throughout the catalytic cycle may be necessary in order to compensate for the natural loss. However, the fact of being able to recycle a gas phase containing the HS without the NHby the present invention makes it possible to considerably reduce the consumption of the sulfiding agent.

Another advantage is the removal of the NHin the gaseous effluent comprising hydrogen and/or light hydrocarbons from the top of the separation/scrubbing section (stage c)) by reaction with the recycled excess HS in the form of ammonium sulfide in the aqueous effluent. In other words, the NHleaves in the form of salt in the aqueous effluent.

Another advantage of the invention is that of preventing risks of plugging and/or of corrosion of the treatment unit in which the process of the invention is carried out, the risks being exacerbated by the presence, often in large amounts, of diolefins, metals and halogen compounds in the plastics pyrolysis oil.

The process of the invention thus makes it possible to obtain a hydrocarbon effluent, resulting from a plastics pyrolysis oil, which is freed, at least partly, of the impurities of the starting plastics pyrolysis oil, thus limiting the problems of operability, such as the corrosion, coking or catalytic deactivation problems, which may be brought about by these impurities, in particular in steam cracking units and/or in units located downstream of the steam cracking units, in particular the polymerization and hydrogenation units. The removal of at least a part of the impurities of the oils resulting from the pyrolysis of plastic waste will also make it possible to increase the range of applications of the target polymers, the incompatibilities of usages being reduced.

According to an alternative form, said gas phase containing the HS resulting from stage d) is at least partly recycled upstream of stage a) and/or stage b) and/or stage g).

According to an alternative form, the process comprises the hydrogenation stage a).

According to an alternative form, the process comprises the fractionation stage f).

According to an alternative form, the process comprises the hydrocracking stage g).

According to an alternative form, stage d) of separation of the HS contained in the first aqueous effluent is carried out by stripping said effluent with a stream containing steam at a pressure of between 0.5 and 1 MPa and a temperature of between 80 and 150° C.

According to an alternative form, stage e) of separation of the NHcontained in the second aqueous effluent is carried out by stripping said effluent with a stream containing steam at a pressure of between 0.1 and 0.5 MPa and a temperature of between 80 and 150° C.

According to an alternative form, the separation stage c) comprises the following stages:

According to an alternative form, the process comprises at least one stage a0) of pretreatment of the feedstock comprising a plastics pyrolysis oil, optionally as a mixture with the hydrocarbon effluent resulting from stage c), said pretreatment stage being carried out upstream of stage a) and/or upstream of stage b), and comprises a filtration stage and/or a centrifugation stage and/or an electrostatic separation stage and/or a stage of scrubbing by means of an aqueous solution and/or an adsorption stage and/or a selective hydrogenation stage.

According to an alternative form, the hydrocarbon effluent resulting from the separation stage c), or at least one of the two liquid hydrocarbon cuts resulting from stage f), is sent, completely or partly, to a steam cracking stage h) carried out in at least one pyrolysis furnace at a temperature of between 700 and 900° C. and at a pressure of between 0.05 and 0.3 MPa relative.

According to an alternative form, said gas phase containing NHresulting from stage e) is at least partly recycled upstream of stage a) and/or stage b) and/or stage g).

According to an alternative form, a stream containing a nitrogen compound and/or a sulfur compound is injected upstream of stage a) and/or upstream of stage b).

According to an alternative form, said hydrogenation catalyst comprises a support chosen from alumina, silica, silicas-aluminas, magnesia, clays and their mixtures and a hydro-dehydrogenating function comprising either at least one element from group VIII and at least one element from group VIB, or at least one element from group VIII.

According to an alternative form, said hydrotreating catalyst comprises a support chosen from the group consisting of alumina, silica, silicas-aluminas, magnesia, clays and their mixtures and a hydro-dehydrogenating function comprising at least one element from group VIII and/or at least one element from group VIB.

According to an alternative form, the process additionally comprises a second hydrocracking stage g′) carried out in a hydrocracking reaction section, employing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrocracking catalyst, said hydrocracking reaction section being fed with at least a part of the first hydrocracked effluent resulting from the first hydrocracking stage g) and a gas stream comprising hydrogen, said hydrocracking reaction section being employed at a temperature between 250 and 450° C., a hydrogen partial pressure between 1.5 and 20.0 MPa abs. and an hourly space velocity between 0.1 and 10.0 h, in order to obtain a second hydrocracked effluent.

According to an alternative form, said hydrocracking catalyst comprises a support chosen from halogenated aluminas, combinations of boron and aluminium oxides, amorphous silica-aluminas and zeolites and a hydro-dehydrogenating function comprising at least one metal from group VIB chosen from chromium, molybdenum and tungsten, alone or as a mixture, and/or at least one metal from group VIII chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum.

The invention also relates to the product liable to be obtained, and preferably obtained, by the process according to the invention.

According to this alternative form, the product comprises, with respect to the total weight of the product:

According to the present invention, the pressures are absolute pressures, also denoted abs., and are given in MPa absolute (or MPa abs.), unless otherwise indicated.

According to the present invention, the expressions “of between . . . and . . . ” and “between . . . and . . . ” are equivalent and mean that the limiting values of the interval are included in the described range of values. If such were not the case and if the limiting values were not included in the described range, such a piece of information will be revealed by the present invention.

Within the meaning of the present invention, the various parameter ranges for a given stage, such as the pressure ranges and the temperature ranges, can be used alone or in combination. For example, within the meaning of the present invention, a range of preferred pressure values can be combined with a range of more preferred temperature values.

Subsequently, particular and/or preferred embodiments of the invention may be described. They can be employed separately or combined together, without limitation of combination when this is technically feasible.

Subsequently, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, published by CRC Press, editor-in-chief D. R. Lide, 81edition, 2000-2001). For example, group VIII (or VIIIB) according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

The content of metals is measured by X-ray fluorescence.

According to the invention, a “plastics pyrolysis oil” is an oil, advantageously in liquid form at ambient temperature, resulting from the pyrolysis of plastics, preferably of plastic waste originating in particular from collection and sorting channels. It can also result from the pyrolysis of worn tyres.

It comprises in particular a mixture of hydrocarbon compounds, especially paraffins, mono- and/or diolefins, naphthenes and aromatics. At least 80% by weight of these hydrocarbon compounds preferably have a boiling point of less than 700° C. and preferably of less than 550° C. In particular, depending on the origin of the pyrolysis oil, the latter can comprise up to 70% by weight of paraffins, up to 90% by weight of olefins and up to 90% by weight of aromatics, it being understood that the sum of the paraffins, of the olefins and of the aromatics is 100% by weight of the hydrocarbon compounds.

The density of the pyrolysis oil, measured at 15° C. according to the ASTM D4052 method, is generally of between 0.75 and 0.99 g/cm, preferably of between 0.75 and 0.95 g/cm.

The plastics pyrolysis oil can additionally comprise, and usually does comprise, impurities such as metals, in particular iron, silicon or halogen compounds, in particular chlorine compounds. These impurities can be present in the plastics pyrolysis oil at high contents, for example up to 350 ppm by weight or also 700 ppm by weight, indeed even 1000 ppm by weight, of halogen elements (in particular chlorine) contributed by halogen compounds, and up to 100 ppm by weight, indeed even 200 ppm by weight, of metal or semi-metal elements. Alkali metals, alkaline earth metals, transition metals, post-transition metals and metalloids can be put into the same category as contaminants of metal nature, referred to as metals or metal or semi-metal elements. In particular, the metals or metal or semi-metal elements possibly contained in the oils resulting from the pyrolysis of plastic waste comprise silicon, iron or both these elements. The plastics pyrolysis oil can also comprise other impurities, such as heteroelements contributed in particular by sulfur compounds, oxygen compounds and/or nitrogen compounds, at contents generally of less than 27 000 ppm by weight of heteroelements and preferably of less than 15 500 ppm by weight of heteroelements. The sulfur compounds are generally present in a content of less than 2000 ppm by weight and preferably of less than 500 ppm by weight. The oxygen compounds are generally present in a content of less than 15 000 ppm by weight and preferably of less than 10 000 ppm by weight. The nitrogen compounds are generally present in a content of less than 10 000 ppm by weight and preferably of less than 5000 ppm by weight. The plastics pyrolysis oil can also comprise other impurities, such as heavy metals, for example mercury, arsenic, zinc and lead, for example up to 100 ppb by weight or also 200 ppb by weight of mercury.

The feedstock of the process according to the invention comprises at least one plastics pyrolysis oil. Said feedstock can consist solely of plastics pyrolysis oil(s). Preferably, said feedstock comprises at least 50% by weight, preferably between 70% and 100% by weight, of plastics pyrolysis oil, with respect to the total weight of the feedstock, that is to say preferably between 50% and 100% by weight and in a preferred way between 70% and 100% by weight of plastics pyrolysis oil.

The feedstock of the process according to the invention can comprise, in addition to the plastics pyrolysis oil(s), a conventional petroleum feedstock or a feedstock resulting from the conversion of biomass which is then co-treated with the plastics pyrolysis oil of the feedstock.

The conventional petroleum feedstock can advantageously be a cut or a mixture of cuts of naphtha, gas oil or vacuum gas oil type.

The feedstock resulting from the conversion of biomass can advantageously be chosen from vegetable oils, oils from algae or algal oils, fish oils, waste food oils, and fats of vegetable or animal origin, or mixtures of such feedstocks. Said vegetable oils can advantageously be crude or refined, completely or partly, and result from plants chosen from rape, sunflower, soybean, palm, olive, coconut, copra, castor oil plant, cotton plant, peanut oil, linseed oil and sea kale oil, and all the oils resulting, for example, from sunflower or rape by genetic modification or hybridization, this list not being limiting. Said animal fats are advantageously chosen from blubber and fats composed of residues from the food industry or resulting from the catering industries. Frying oils, various animal oils, such as fish oils, tallow or lard, can also be used. The feedstock resulting from the conversion of biomass can also advantageously be chosen from methyl esters of fatty acids of vegetable and/or animal origin or also methyl esters of fatty acids of waste food vegetable oils.

The feedstock resulting from the conversion of biomass can also be chosen from feedstocks originating from processes for thermal or catalytic conversions of biomass, such as oils which are produced from biomass, in particular from lignocellulosic biomass, with various liquefaction methods, such as hydrothermal liquefaction or pyrolysis. The term “biomass” refers to a material derived from recently living organisms, which comprises plants, animals and their by-products. The term “lignocellulosic biomass” denotes biomass derived from plants or from their by-products. The lignocellulosic biomass is composed of carbohydrate polymers (cellulose, hemicellulose) and of an aromatic polymer (lignin).

The feedstock resulting from the conversion of biomass can also advantageously be chosen from feedstocks resulting from the papermaking industry.