EP3121250A1 - Method for removing mercury from a feedstock downstream from a fractionating unit - Google Patents

Abstract

A process for removing mercury contained in a heavy hydrocarbon feedstock downstream of a main fractionating unit, wherein
a) the non-elemental mercury contained in the compounds of said feedstock is converted into elemental mercury;
b) fractionating said hydrocarbon feedstock in a fractionation unit to produce an overhead effluent comprising elemental mercury;
c) contacting the overhead effluent obtained in step b) with a mercury collection mass included in a mercury capture unit to obtain an effluent at least partially demercurized.

Description

Technical area

The present invention relates to a process for removing heavy metals, and more particularly mercury, present in a liquid or gaseous feed.

State of the art

Mercury is a metal contaminant found in gaseous or liquid hydrocarbons produced in many parts of the world, such as the Gulf of Niger, South America or North Africa.

• pour des raisons de sécurité des opérateurs : le mercure élémentaire est volatil et présente de graves risques de neurotoxicité par inhalation alors que ses formes organiques présentent des risques similaires par contact cutané ;
• pour des raisons de prévention de la désactivation des catalyseurs hétérogènes servant à valoriser ces coupes hydrocarbures liquides : le mercure s'amalgame très facilement avec les métaux nobles tels que le platine ou le palladium utilisés pour des opérations catalytiques diverses, et notamment l'hydrogénation sélective des oléfines produites par vapocraquage ou craquage catalytique des hydrocarbures liquides.

The elimination of mercury from hydrocarbon cuts is desired at the industrial level for several reasons:

• for reasons of operator safety: elemental mercury is volatile and presents a serious risk of inhalation neurotoxicity while its organic forms pose similar risks through skin contact;
• for reasons of prevention of the deactivation of heterogeneous catalysts used to valorize these liquid hydrocarbon cuts: mercury amalgamates very easily with noble metals such as platinum or palladium used for various catalytic operations, and especially selective hydrogenation olefins produced by steam cracking or catalytic cracking of liquid hydrocarbons.

Industrially, the removal of heavy metals, in particular mercury, from liquid or gaseous hydrocarbon cuts is carried out by circulating them through beds of capture mass. The term "capture mass" in the present invention is understood to mean any type of solid in solid or supported form containing within it or on its surface an active element capable of irreversibly reacting with an impurity such as the mercury contained in the charge to be purified. The removal of mercury from liquid or gaseous hydrocarbon cuts is generally carried out by circulating said charge to be treated through capture mass beds containing an active phase that can react with mercury. It is particularly known to those skilled in the art that mercury uptake can be conducted easily by reacting the latter with an active phase based on sulfur or a sulfur compound, and in particular metal sulfides, the mercury then forming with sulfur the chemical species HgS called cinnabar or metacinabrium. These different chemical reactions are generally carried out in a process by means of a contacting the feed to be treated with a capture mass or mass wherein including active phase particles may be bonded together by means of binders, is supported in which the active phase is dispersed within or on the surface of a porous solid support.

However, it is not possible to perform such a purification operation directly on crude oil cuts or gas condensates for several reasons. The first is that the porosity of these capture masses would be very quickly blocked by the heavy compounds present in said charge, which would be deposited on the surface of the masses. In addition, these crude oil cuts or gas condensates contain mercury in various forms. Indeed, unlike the gaseous phases, they contain not only elemental mercury but also mercury in complexed or ionic form, or organic. However, these complexed or ionic and organic mercury compounds are said to be refractory because they are stable under normal operating conditions and non-reactive with the heavy metal capture masses. It therefore appears necessary to convert the refractory mercury compounds into elemental mercury.

Many ways have been developed to convert the refractory forms of mercury into elemental mercury (also called mercury in atomic form Hg ⁰ ). For example, the patent US 4,911,825 discloses a process for converting refractory mercury species from elemental mercury feed in the presence of a catalyst and under high pressure to hydrogen and at high temperature.

The patent US5,384,040 discloses a process for removing mercury from a hydrocarbon feedstock comprising a step of converting the mercury contained in the feedstock compounds into elemental mercury, the conversion step being carried out at 120 to 400 ° C and at a pressure of 0.1 at 6.0 MPa. Preferably, the transformation step is carried out in the presence of a catalyst comprising at least one metal M selected from the group consisting of iron, nickel, cobalt, molybdenum, tungsten and palladium.

Alternatively, the transformation step can be carried out in the absence of catalyst. In the latter case, the temperature must be at least 180 ° C. Indeed, in the article of Masatoshi Yamada et al. entitled "Mercury removal from natural gas condensate "in the journal Studies in Surface Science and Catalysis, volume 92, pages 433-436, 1995 it is shown that the diethylmercury conversion starts at 180 ° C and reaches 100% conversion at 240 ° C. In parallel, it is shown that it is possible to reduce the transformation temperature in the presence of a catalyst. In fact, the conversion of refractory mercury species starts at 130 ° C and reaches more than 90% from 200 ° C. However, the problem of the use of a catalyst, besides its cost, is that it tends to favor the cracking of molecules and therefore the formation of coke. Moreover, in the case of very fouling charges such as crude oil, there is a very rapid deactivation of the porous catalyst by deposition of heavy compounds, such as asphaltenes, within the porosity of said catalyst. Such a process is therefore rather suitable for the treatment of hydrocarbons from a first fractionation.

The Applicant has surprisingly discovered that it is possible to efficiently remove heavy metals, and more particularly mercury, contained in a gaseous or liquid charge, and more particularly a crude oil charge, by performing upstream of the main fractionation unit, a step of heating said charge to a target temperature and for a residence time sufficient to allow the conversion of the heavy metals, present in different forms, into metals in atomic (or elemental) form, and this without doing use of any catalytic treatment or under hydrogen, and immediately downstream of the main fractionation unit, a step of capture of heavy metals, and more particularly of mercury. Indeed, although the crude oil feedstocks comprise a very large diversity of molecules, the heating of said feedstock for a sufficient residence time upstream of the main fractionation unit makes it possible to convert the majority of the refractory compounds into compounds. metal that can be captured by a single capture mass located immediately downstream of the main fractionation unit.

Objects of the invention

1. a) on transforme le mercure non élémentaire contenu dans les composés de ladite charge en mercure élémentaire, ladite étape étant réalisée dans une unité de conversion à une température cible pendant un temps de séjour fixé et adapté à ladite température cible de manière à ce qu'au moins 90% en poids du mercure non élémentaire contenu dans les composés de ladite charge soient convertis en mercure élémentaire, ladite étape de transformation étant réalisée en l'absence d'hydrogène et en l'absence de catalyseur, étant entendu que :
   • lorsque la température cible de ladite charge est comprise entre 150°C et 175°C, le temps de séjour de ladite charge dans l'unité de conversion est compris entre 150 et 2700 minutes ; et/ou
   • lorsque la température cible de ladite charge est supérieure à 175°C et inférieure ou égale à 250°C, le temps de séjour de ladite charge dans l'unité de conversion est compris entre 100 et 900 minutes ; et/ou
   • lorsque la température cible de ladite charge est supérieure à 250°C et inférieure ou égale à 400°C, le temps de séjour de ladite charge dans l'unité de conversion est compris entre 5 et 70 minutes ; et/ou
   • lorsque la température cible de ladite charge est supérieure à 400°C, le temps de séjour de ladite charge dans l'unité de conversion est compris entre 1 et 10 minutes ;
2. b) on effectue un fractionnement de ladite charge hydrocarbonée dans une unité de fractionnement pour produire un effluent de tête comprenant du mercure élémentaire;
3. c) on met en contact l'effluent de tête obtenu à l'étape b) avec une masse de captation au mercure comprise dans une unité de captation au mercure pour obtenir un effluent au moins partiellement démercurisé.

The present invention relates to a process for removing mercury contained in a heavy hydrocarbon feedstock downstream of a main fractionating unit, in which process:

1. a) the non-elemental mercury contained in the compounds of said feedstock is converted into elemental mercury, said step being carried out in a conversion unit at a rate of target temperature during a residence time set and adapted to said target temperature so that at least 90% by weight of the non-elemental mercury contained in the compounds of said feed are converted into elemental mercury, said processing step being carried out in the absence of hydrogen and in the absence of catalyst, it being understood that:
   • when the target temperature of said charge is between 150 ° C and 175 ° C, the residence time of said charge in the conversion unit is between 150 and 2700 minutes; and or
   • when the target temperature of said charge is greater than 175 ° C and less than or equal to 250 ° C, the residence time of said charge in the conversion unit is between 100 and 900 minutes; and or
   • when the target temperature of said charge is greater than 250 ° C and less than or equal to 400 ° C, the residence time of said charge in the conversion unit is between 5 and 70 minutes; and or
   • when the target temperature of said charge is greater than 400 ° C, the residence time of said charge in the conversion unit is between 1 and 10 minutes;
2. b) fractionating said hydrocarbon feedstock in a fractionation unit to produce an overhead effluent comprising elemental mercury;
3. c) contacting the overhead effluent obtained in step b) with a mercury collection mass included in a mercury capture unit to obtain an effluent at least partially demercurized.

Advantageously, the reduction in the total content by weight of mercury of said charge taken before step a) and after step c) is at least 90%.

According to the invention, steps a) and b) are performed simultaneously.

In an embodiment according to the invention, the overhead effluent resulting from the fractionation of said feedstock in the main fractionation unit is cooled by means of a heat exchanger so as to produce a liquid effluent. Advantageously, the liquid effluent is sent to a separation unit to provide a liquid organic phase, part of which is recycled to the main fractionating unit as reflux, and the other part is sent via the pipe to the said unit. mercury capture.

In another embodiment according to the invention, the overhead effluent resulting from the fractionation of said feedstock in the main fractionation unit is heated by means of a heat exchanger so as to produce a gaseous effluent. Advantageously, the gaseous effluent is compressed by means of a compressor before being sent to the mercury capture unit.

Preferably, before step a) of transforming the non-elemental mercury contained in the compounds of said elemental mercury charge, said charge is desalted in a desalting unit.

In one embodiment of the invention, during step c), said charge is brought into contact with a mass mercury or supported mercury collection mass comprising a phase comprising at least one metal sulphide based on a metal M selected from the group consisting of copper, chromium, manganese, iron, cobalt and nickel.

In another embodiment according to the invention, during step c), said charge is brought into contact with a mass or supported capture mass comprising a phase containing at least sulfur in elemental form.

Preferably, said hydrocarbon feedstock comprises between 1 and 10 mg of mercury per kg of filler, preferably 1 to 1200 μg / kg, more preferably 10 to 500 μg / kg.

Advantageously, the heavy hydrocarbon feedstock is a crude oil feedstock.

Description of figures

• The figure 1 schematically illustrates a conventional method of fractionation of a heavy hydrocarbon feedstock, and more particularly a crude oil feedstock. Equipment (pumps, valves, heat exchangers, etc.) dedicated are not deliberately represented for the sake of clarity.
• The figure 2 schematically illustrates an embodiment of the method according to the invention wherein the single capture unit is located downstream of the main fractionation unit.
• The figure 3 represents an embodiment according to the invention for which the mercury capture step is carried out in the liquid phase.
• The figure 4 represents an embodiment according to the invention for which the mercury capture step is carried out in the gas phase.

Detailed description of the invention

In order to better understand the invention, the following description given by way of example of application relates to a process for the removal of heavy metals, and more particularly mercury, from a crude hydrocarbon feedstock of crude oil. Of course, the process according to the invention can be used for the removal of other heavy metals, such as arsenic, lead, vanadium and cadmium, contained in a heavy hydrocarbon feedstock.

For the purposes of the present invention, the term "heavy hydrocarbon feedstock" means a feedstock having a density at 15 ° C. of greater than about 750 kg / m ³ , composed essentially of hydrocarbons, but also containing other chemical compounds which, in addition to carbon and hydrogen atoms, they have heteroatoms, such as oxygen, nitrogen, sulfur and heavy metals such as mercury, arsenic, lead, vanadium or cadmium. Preferably, said hydrocarbon feedstock comprises between 1 and 10 mg of mercury per kg of filler, preferably 1 to 1200 μg / kg, more preferably 10 to 500 μg / kg.

By non-elemental mercury is meant any form of mercury other than in elemental (or atomic) form, i.e. in molecular form, and / or in ionic form, and / or in complexed forms.

The description of the figure 1 relates to a conventional heavy metal removal process contained in a crude oil feedstock; the description of Figures 2 to 4 relate to a heavy metal removal process according to the invention. The Figures 2 to 4 take up some elements of the figure 1 ; references Figures 2 to 4 identical to those of the figure 1 designate the same elements.

Process according to the prior art (FIG. 1)

The figure 1 illustrates schematically the first treatments undergone by a heavy hydrocarbon feedstock, and more particularly crude oil, for its initial fractionation, generally carried out by atmospheric distillation. Typically, a heavy hydrocarbon feedstock, and more particularly a crude oil feedstock, is fed via line 100 to a desalting unit 1000, generally consisting of a water wash. The main function of this step is to remove most of the soluble inorganic species contained in said feed. The desalted feedstock is then sent via line 101 to a preheating unit 2000. The purpose of this stage of heating the desalted feedstock is to bring said feedstock to a temperature close to the bottom temperature of the feed unit. fractionation 3000 located downstream of the preheating unit 2000. The preheating temperature is generally between 200 and 400 ° C, and depends on the number of distillation columns used in the main fractionating unit 3000. The preheated charge is then sent via the line 104 to the main fractionator 3000.

The main fractionation unit 3000 may comprise one or more distillation columns (on the figure 1 only one distillation column is shown). The main fractionation unit 3000 makes it possible to produce different cuts of hydrocarbons according to their molecular weight and more particularly according to their difference in volatility. For example, the fractionation of the feedstock by atmospheric distillation associated with the distillation columns of the main fractionation unit allows separation of the feedstock in different cuts, from the lightest to the heaviest, and more particularly into combustible gases (C1 , C2), propane (C3), butane (C4), light gasoline (C5 to C6), heavy gasoline (C7 to C10), kerosene (C10 to C13), gas oil (C13 to C20 / 25) or atmospheric residue (C20 / C25 +).

• les gaz combustibles (« fuel gas » selon la terminologie anglo-saxonne) évacués par la conduite 401 comprenant majoritairement des espèces hydrocarbonées à un ou deux atomes de carbone (C1/C2) ainsi que des effluents des purifications, tels que l'H₂ ou l'H₂S. Par soucis de clarté, un unique flux de gaz combustibles a été représenté sur la figure 1, mais ce nombre peut varier dans un site industriel selon le choix de l'opérateur ;
• du gaz de pétrole liquéfié (GPL) évacué par la conduite 402 comprenant majoritairement des espèces hydrocarbures à trois ou quatre atomes de carbone (C3/C4) ;
• les coupes naphtas évacuées par la conduite 403 comprenant majoritairement des composés hydrocarbures à 5 atomes de carbone ou plus (C5+), la limite haute en nombre d'atomes de carbone dépendant du choix du point de coupe réalisé en tête de l'unité de fractionnement principal 3000. Par ailleurs, selon le schéma de fractionnement choisi par l'opérateur, il peut y avoir plusieurs coupes naphta (non représentées sur la figure), par exemple une coupe naphta lourde et une coupe naphta légère.

At the outlet of the main fractionation unit 3000, the main effluent of the main fractionation unit generally contains hydrocarbon compounds, 90% of which of these compounds have a boiling point below 200 ° C. at atmospheric pressure. (1,01325.10 ⁵ Pa). The overhead effluent is sent via line 400 to a secondary fractionation unit 4000 comprising one or more fractionation columns, making it possible to produce different hydrocarbon cuts. Generally, at the outlet of the secondary fractionation unit 4000, it is possible to distinguish several hydrocarbon cuts such as:

• fuel gases (" fuel gas " according to the English terminology) discharged through line 401 mainly comprising hydrocarbon species with one or two carbon atoms (C1 / C2) and effluents purifications, such as H ₂ or H ₂ S. For the sake of clarity, a single flow of combustible gases has been represented on the figure 1 , but this number can vary in an industrial site according to the choice of the operator;
• liquefied petroleum gas (LPG) discharged through line 402 comprising predominantly hydrocarbon species with three or four carbon atoms (C3 / C4);
• the naphtha cuts evacuated via line 403 mainly comprising hydrocarbon compounds with 5 or more carbon atoms (C5 +), the upper limit in number of carbon atoms depending on the choice of the cutting point made at the top of the fractionation unit main 3000. Moreover, according to the splitting scheme chosen by the operator, there may be several naphtha cuts (not shown in the figure), for example a heavy naphtha cut and a light naphtha cut.

The hydrocarbon cuts discharged via the lines 401, 402 and 403 are generally treated for each by a unit for capturing heavy metals in elemental form, and more particularly for capturing mercury in elemental form. As represented on the figure 1 the capture units 5001, 5002, 5003 are generally placed downstream of the main fractionating unit 3000, in the direction of flow of the charge, and this for each of the hydrocarbon cuts circulating in the lines 401, 402 and 403 . 5001 capture units, 5002 and 5003 each comprise a mercury collecting mass in the form of a fixed bed. The mercury uptake masses can be all those known by those skilled in the art for the capture of elemental mercury. The demercurized hydrocarbon cuts are removed respectively by lines 411, 412 and 413.

Thus, because of the presence of a multiplicity of hydrocarbon cuts in such a process, the number of capture units comprising the capture masses becomes important (for each hydrocarbon compound cut from the treatment unit 4000 is associated with a specific capture unit), especially as the number of capture units is generally doubled in order to regenerate the capture masses without interrupting the operation of the unit.

Furthermore, in such a process scheme, different types of capture mass are used to treat on the one hand the gas flows, for example discharged through the pipe 401, and on the other hand the liquid flows, for example discharged by the pipe 403, but also the streams that may contain hydrogen, such as certain combustible gases, requiring specifically adapted capture masses.

Surprisingly, the applicant has discovered that it is possible to eliminate heavy metals and more particularly the non-elemental mercury contained in the compounds of a hydrocarbon feedstock, and more particularly a crude oil feedstock, by carrying out a step of transforming the non-elemental mercury contained in the compounds of said feed into elemental mercury, and a step of capturing elemental mercury; said step of transforming the non-elemental mercury contained in the compounds of said feed being carried out by a heat treatment of said feedstock at a target temperature for a residence time sufficient to allow the conversion of the non-elemental mercury contained in the compounds of said feedstock. elemental mercury, without the use of catalytic treatment or hydrogen. The method according to the invention thus comprises a single unit for capturing elemental mercury and therefore comprises a single capture mass.

Indeed, although the crude oil feedstocks comprise a very large diversity of hydrocarbon molecules, heating said feedstock for a sufficient residence time makes it possible to convert the non-elemental mercury contained in the feedstock components into elemental mercury, the latter can then be captured by a single mass of capture.

1. a) une étape de transformation du mercure non élémentaire contenu dans les composés de la charge hydrocarbonée lourde, et plus particulièrement dans une charge de pétrole brut, en mercure élémentaire ;
2. b) une étape de fractionnement de ladite charge hydrocarbonée par une unité de fractionnement principal ;
3. c) une étape de captation du mercure sous forme élémentaire récupéré en tête de ladite unité de fractionnement principal au moyen d'une unité de captation au mercure comprenant une masse de captation.

More particularly, the method according to the invention comprises:

1. a) a stage of transformation of non-elemental mercury contained in the compounds of the heavy hydrocarbon feedstock, and more particularly in a crude oil feedstock, into elemental mercury;
2. b) a step of fractionating said hydrocarbon feedstock by a main fractionating unit;
3. c) a mercury recovery step in elemental form recovered at the head of said main fractionation unit by means of a mercury capture unit comprising a capture mass.

According to the invention, steps a) and b) can be performed separately or simultaneously.

Thus, it is possible to remove the mercury included in the main effluent of the main fractionation unit by the use of a suitable mercury capture unit, and thus to eliminate the capture units positioned generally on the main fractionation units. different streams of light compounds located in the main fractionator unit in a conventional refinery scheme.

Process according to the invention (Figures 2 to 4)

Referring to the figure 2 , schematically illustrating the process according to the invention, a heavy hydrocarbon feed is sent via line 100 to a desalting unit 1000. The desalted feed is then sent via line 101 to a non-elemental mercury conversion unit 200 in the compounds of the heavy hydrocarbon feedstock elemental mercury.

• selon un mode de réalisation à l'unité de chauffage 2000, telle qu'un ballon, et éventuellement à une conduite ou un ensemble de conduites destinée(s) au transport de ladite charge jusqu'à l'unité de fractionnement principal 3000. Dans ce mode de réalisation, les étapes a) et b) du procédé selon l'invention sont réalisées séparément, c'est-à-dire que la transformation du mercure en mercure élémentaire est réalisée en amont de l'unité de fractionnement principal 3000 ; ou
• selon un autre mode de réalisation à l'unité de chauffage 2000, telle qu'un ballon, et éventuellement à une conduite ou un ensemble de conduites destinée(s) au transport de ladite charge jusqu'à l'unité de fractionnement principal 3000, et à l'unité de fractionnement principal 3000. Dans ce mode de réalisation, les étapes a) et b) du procédé selon l'invention sont réalisées simultanément, c'est-à-dire que la transformation du mercure en mercure élémentaire est réalisée aussi bien pendant le transport de ladite charge vers l'unité de fractionnement principal 3000 que lors de l'étape de fractionnement de ladite charge dans l'unité de fractionnement principal 3000.

In the context of the present invention, the conversion unit 200 corresponds to:

• according to an embodiment at the heating unit 2000, such as a balloon, and optionally to a pipe or a set of pipes for transporting said load to the main fractionator 3000. this embodiment, steps a) and b) of the process according to the invention are carried out separately, that is to say that the conversion of mercury elemental mercury is carried out upstream of the main fractionation unit 3000; or
• according to another embodiment of the heating unit 2000, such as a balloon, and optionally to a pipe or a set of pipes for transporting said charge to the main fractionation unit 3000, and in the main fractionating unit 3000. In this embodiment, steps a) and b) of the process according to the invention are carried out simultaneously, that is to say that the conversion of mercury to mercury elementary is performed both during the transport of said load to the main fractionator unit 3000 as in the step of fractionation of said charge in the main fractionator unit 3000.

According to the invention, the term "main fractionating unit 3000" is understood to mean a unit for fractionating the feedstock by atmospheric distillation (as described previously in the process part according to the prior art). The main fractionator 3000 may comprise one or more distillation columns. The main fractionation unit 3000 makes it possible to produce different cuts of hydrocarbons according to their molecular weight and more particularly according to their difference in volatility.

When the conversion unit 200 comprises a balloon, said balloon advantageously comprises a double wall covering the balloon in which a coolant circulates in order to maintain the temperature of said charge at the target temperature up to the main fractionation unit 3000, or advantageously comprises a heating resistor directly inserted inside said balloon.

When the conversion unit 200 comprises a pipe or a set of pipes, the pipe or set of pipes advantageously comprise a jacket in which a coolant circulates in order to maintain the temperature of said charge at the target temperature up to the main fractionator 3000.

a) Transformation step of non-elemental mercury contained in the compounds of the heavy hydrocarbon feedstock into elemental mercury

Stage a) of transforming the non-elemental mercury contained in the compounds of the heavy hydrocarbon feedstock into elemental mercury is essential according to the invention since it makes it possible to maximize the conversion of non-elemental mercury into elemental mercury. Indeed, whatever the nature and / or the origin of the heavy hydrocarbon feedstock, the latter may comprise mercury in different forms. For example, mercury can be found in the form of elemental or atomic mercury (also called Hg °), and / or in organic molecular form, and / or in ionic form, for example in Hg ²⁺ form and its complexes.

According to the invention, the transformation of the non-elemental mercury contained in the compounds of the feedstock into elemental mercury is carried out via a conversion unit 200.

Thus, according to the invention, the process for converting the non-elemental mercury contained in the compounds of said elemental mercury charge comprises the passage of said charge, at a temperature determined by those skilled in the art, in a conversion unit 200 during a residence time set so that at least 90% by weight, preferably at least 95% by weight, and even more preferably at least 99% by weight of the non-elemental mercury contained in the compounds of said filler are converted in elemental mercury, and this in the absence of catalyst.

dans laquelle :

• C_s correspond à la concentration du mercure (hors mercure élémentaire) contenu dans les composés de ladite charge en sortie de l'unité de conversion 200 (en mol.L^-1) ;
• C_o correspond à la concentration du mercure (hors mercure élémentaire) contenu dans les composés de ladite charge en entrée de l'unité de conversion 200 (en mol.L^-1) ;
• t correspond au temps de séjour (en seconde) ;
• k₀ correspond à la constante de vitesse de transformation du mercure non élémentaire en mercure élémentaire (en seconde^-1);
• E_a correspond à l'énergie d'activation de la réaction de transformation du mercure non élémentaire en mercure élémentaire (en J.mol^-1) ;
• R correspond à la constante des gaz parfait (R = 8,314 J.K^-1.mol^-1) ;
• T correspond à la température de la charge (en K).

Thus, depending on the temperature of the feedstock, the residence time required to effect the conversion of the non-elemental mercury contained in the compounds of said elemental mercury feedstock corresponds to equation (1) below: $$\ln \left(\frac{-\ln \frac{{\mathrm{VS}}_S}{{\mathrm{VS}}_0}}{t}\right)=\ln \left(k_0\right)-\frac{E_{\mathrm{at}}}{\mathit{RT}}$$

in which :

• C _s is the concentration of mercury (excluding elemental mercury) contained in the compounds of said charge at the outlet of the conversion unit 200 (in mol.L ^-1 );
• C _o is the concentration of mercury (excluding elemental mercury) contained in the compounds of said input charge of the conversion unit 200 (in mol.L ^-1 );
• t is the residence time (in seconds);
• k ₀ is the transformation rate constant of non-elemental mercury to elemental mercury (in second ^-1 );
• E _a corresponds to the activation energy of the transformation reaction of non-elemental mercury into elemental mercury (in J. mol ^-1 );
• R is the perfect gas constant (R = 8.314 JK ^-1 .mol ^-1 );
• T corresponds to the temperature of the load (in K).

In the embodiment for which steps a) and b) are carried out separately, ie that the conversion of mercury into elemental mercury is carried out upstream of the main fractionation unit 3000, the concentration C _s corresponds to the concentration of mercury. (excluding elemental mercury) measured in line 102 at the inlet of the fractionation unit main 3000, and the concentration C _o is the concentration of mercury (excluding elemental mercury) measured in line 101.

In the embodiment for which steps a) and b) are carried out simultaneously, ie that the conversion of mercury to elemental mercury is carried out both during the transport of said feedstock to the main fractionating unit 3000 as well as during the step of separating said charge in the main fractionation unit 3000, the concentration C _s corresponds to the mercury concentration (excluding elemental mercury) measured in line 400, and the concentration C _o corresponds to the concentration of mercury (excluding mercury elementary) measured in line 101.

Moreover, according to the invention, the total volume V of the conversion unit 200 is defined such that the ratio V / Q, with Q corresponding to the volume flow of the charge to be treated, is equal to the residence time " t "associated with the temperature of the target" T "charge.

Thus, in the embodiment for which steps a) and b) are carried out separately, ie when the conversion of mercury into elemental mercury is carried out upstream of the main fractionating unit 3000, the volume V of the unit of conversion 200 corresponds to the volume of the heating unit 2000, such as a balloon, and possibly the pipe or the pipe assembly for transporting the load to the main fractionation unit 3000.

In the embodiment for which steps a) and b) are carried out simultaneously, that is to say when the conversion of mercury into elemental mercury is carried out both during the transport of said charge to the main fractionation unit 3000 that during the step of separating said charge in the main fractionating unit 3000, the volume V of the conversion unit 200 corresponds to the volume of the heating unit 2000, such as a balloon, and possibly the volume of the pipe or pipe assembly for transporting the load to the main fractionator 3000 and the volume of the main fractionator 3000 in which the unit non-elemental mercury contained in the compounds of the heavy hydrocarbon feedstock elemental mercury is also carried out.

Referring to the figure 2 the volume V of the conversion unit 200 corresponds to the cumulative volume of the heating unit 2000, the pipe 102 and the volume of the main fractionating unit 3000.

• lorsque la température cible de ladite charge est comprise entre 150 et 175°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 150 et 2700 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 175°C et inférieure ou égale à 250°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 100 et 900 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 250°C et inférieure ou égale à 400°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 5 et 70 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 400°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 1 et 10 minutes.

Advantageously, during the transformation step, and according to any one of the embodiments according to the invention (ie the steps a) and b) being carried out separately or not):

• when the target temperature of said charge is between 150 and 175 ° C, the residence time of said charge in the conversion unit 200 is between 150 and 2700 minutes; and or
• when the target temperature of said charge is greater than 175 ° C and less than or equal to 250 ° C, the residence time of said charge in the conversion unit 200 is between 100 and 900 minutes; and or
• when the target temperature of said charge is greater than 250 ° C and less than or equal to 400 ° C, the residence time of said charge in the conversion unit 200 is between 5 and 70 minutes; and or
• when the target temperature of said charge is greater than 400 ° C, the residence time of said charge in the conversion unit 200 is between 1 and 10 minutes.

• lorsque la température cible de ladite charge est comprise entre 150 et 175°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 150 et 2700 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 175°C et inférieure ou égale à 200°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 100 et 900 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 200°C et inférieure ou égale à 225°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 30 et 300 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 225°C et inférieure ou égale à 250°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 15 et 150 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 250°C et inférieure ou égale à 300°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 5 et 70 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 300°C et inférieure ou égale à 400°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 1 et 40 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 400°C et inférieure ou égale à 500°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 1 et 10 minutes ; et/ou
• lorsque la température cible de ladite charge est supérieure à 500°C, le temps de séjour de ladite charge dans l'unité de conversion 200 est compris entre 1 et 5 minutes.

Even more preferably:

• when the target temperature of said charge is between 150 and 175 ° C, the residence time of said charge in the conversion unit 200 is between 150 and 2700 minutes; and or
• when the target temperature of said charge is greater than 175 ° C and less than or equal to 200 ° C, the residence time of said charge in the conversion unit 200 is between 100 and 900 minutes; and or
• when the target temperature of said charge is greater than 200 ° C and less than or equal to 225 ° C, the residence time of said charge in the conversion unit 200 is between 30 and 300 minutes; and or
• when the target temperature of said charge is greater than 225 ° C and less than or equal to 250 ° C, the residence time of said charge in the conversion unit 200 is between 15 and 150 minutes; and or
• when the target temperature of said charge is greater than 250 ° C and less than or equal to 300 ° C, the residence time of said charge in the conversion unit 200 is between 5 and 70 minutes; and or
• when the target temperature of said charge is greater than 300 ° C and less than or equal to 400 ° C, the residence time of said charge in the conversion unit 200 is between 1 and 40 minutes; and or
• when the target temperature of said charge is greater than 400 ° C and less than or equal to 500 ° C, the residence time of said charge in the conversion unit 200 is between 1 and 10 minutes; and or
• when the target temperature of said charge is greater than 500 ° C, the residence time of said charge in the conversion unit 200 is between 1 and 5 minutes.

According to the invention, the non-elemental mercury conversion step contained in the compounds of the elemental mercury charge is carried out at a pressure of between 0.1 and 12 MPa, preferably between 0.1 and 6 MPa.

Thus, it is possible to convert the non-elemental mercury contained in the compounds of the heavy hydrocarbon feedstock, and more particularly crude oil, into elemental mercury, and this from 150 ° C., by adjusting the residence time of the feedstock. in the conversion unit 200. Furthermore, the absence of catalyst simplifies the implementation of the method and avoids clogging of the heavy metal capture masses in the subsequent step or steps by depositing gums whose precursors are products (for example by cracking hydrocarbon molecules) by contact with a mercury uptake mass.

b) Fractionation step

According to the invention, a step of fractionation of the feedstock is carried out in a main fractionating unit 3000. The main fractionating unit 3000 may comprise one or more distillation columns (on the figure 2 only one distillation column is shown). The main fractionation unit 3000 makes it possible to produce different cuts of hydrocarbons according to their molecular weight and more particularly according to their difference in volatility. For example, the fractionation of the feedstock by atmospheric distillation associated with the distillation columns of the main fractionation unit allows separation of the feedstock in different cuts, from the lightest to the heaviest, and more particularly into combustible gases (C1 , C2), propane (C3), butane (C4), light gasoline (C5 to C6), heavy gasoline (C7 to C10), kerosene (C10 to C13), gas oil (C13 to C20 / 25), or atmospheric residue (C20 / C25 +).

Mercury in elemental form and the most volatile hydrocarbon compounds are recovered via line 400 in the overhead effluent of the main fractionator.

The main effluent 400 of the main fractionation unit generally contains hydrocarbon compounds 90% of whose said compounds have a boiling point of less than 200 ° C. at atmospheric pressure (1.01325 × 10 ⁵ Pa).

Furthermore, the overhead effluent 400 comprises at least 90% by weight of elemental mercury relative to the total weight of the mercury present in the initial charge, preferably at least 95% by weight and even more preferably at least 99% by weight.

c) Stage of capture of elemental mercury

The overhead effluent 400 of the main fractionation unit 3000, comprising the mercury in elemental form, is then sent to a mercury collection unit 5000 comprising a capture mass capable of reacting with the elemental mercury to trap it in the reactor. bed to produce an effluent at least partially demercurized 420. The mercury capture unit 5000 may further comprise means for adjusting the pressure and the temperature (not shown in FIG. figure 2 ) to adapt to the selected mercury removal method.

More specifically, the capture mass used in the capture unit 5000 is chosen from those known to those skilled in the art. The capture mass is preferably in the form of a bed composed of elementary particles which may be of any form known to those skilled in the art. The latter may for example be in the form of beads, mono- or multilobed cylinders, preferably with a number of lobes between 2 and 5 or in the form of rings.

The capture mass comprises a compound, commonly called the active phase, which reacts with the heavy metal so as to capture the heavy metal on the capture mass.

For mercury, the active phase of the capture mass may include metals that, in their sulphide form, react with mercury. The metal sulphide or sulphides contained in the capture mass according to the invention are based on a metal chosen from the group consisting of copper (Cu), chromium (Cr), manganese (Mn), iron (Fe ), cobalt (Co) and nickel (Ni). Preferably, the metal (s) of the metal sulphide (s) are chosen from the group consisting of copper (Cu), manganese (Mn), iron (Fe) and nickel (Ni). Very preferably, if a single metal sulphide is present, the choice is on copper sulphide.

Alternatively, the active phase used may also be elemental sulfur as described in the patent document FR 2,529,802 .

Preferably, the capture mass may consist of an active phase, as described above, distributed on a porous support.

The porous support may be chosen preferably from aluminas, phosphorus aluminas, silica-aluminas, silicas, clays, activated carbons, zeolites, titanium oxides, zirconium oxides, silicon carbide and the like. mixtures thereof.

A capture mass containing a support and copper sulphide is for example described in the document US 4094777 .

The capture mass may be obtained by any preparation route known to those skilled in the art such as, for example, impregnation, co-kneading or co-granulation.

The contacting of the effluent to be treated with the capture mass may be carried out at a temperature of between -50 ° C. and 1550 ° C., preferably between 0 ° C. and 1120 ° C., and more preferably between 20 ° C. and 100 ° C. In addition, it can be carried out at an absolute pressure of between 0.01 MPa (0.1 bar) and 20 MPa (200 bar), preferably between 0.1 MPa (1 bar) and 15 MPa (150 bar), and more preferably between 0.1 MPa (1 bar) and 12 MPa (120 bar).

In addition, this step of contacting the effluent to be treated with the capture mass can be carried out with a VVH (Hourly Volumic Speed of the gaseous or liquid effluent) of between 0.1 h ^-1 and 50000 hr ^{. 1} . The unit of the hourly volume velocity being expressed in liter of the gaseous or liquid effluent per hour per liter of catalyst (Uh / L), ie h-1). For an effluent to be treated gas, the VVH may be preferably between 50 h ^-1 and 500 h ^-1 .

The contact with the capture mass advantageously makes it possible to capture the heavy metals, in particular mercury, contained in the effluent to be treated, and to obtain an effluent having a content of heavy metals, in particular mercury, reduced in relation to the content of the initial effluent, or even completely eliminate heavy metals from the effluent.

Advantageously, the reduction in the total content by weight of mercury between the gaseous or liquid effluent before treatment and the effluent obtained after treatment with the capture mass can represent at least 90%, preferably at least 95%, and more preferably at minus 99%.

The figure 3 represents a detailed diagram of the c) mercury uptake step according to the invention when the latter is carried out in the liquid phase. This configuration is particularly suitable for recovering elemental mercury in the condensed phase. The overhead effluent recovered via the line 400 from the main fractionator unit 3000 is cooled via a heat exchanger 6000 so as to condense it. The condensed overhead effluent recovered via line 430 is fed to a separation unit 7000. Separation unit 7000 may be a balloon. The separation unit 7000 may optionally comprise a separation of the condensed aqueous phases discharged via the pipe 500. Part of the condensed organic phase 431 is raised in pressure, for example with the aid of a pump 8000, to be recycled via line 432 to main fractionator 3000 as reflux. The remaining portion recovered via the pipe 433 is optionally raised in pressure, for example using a pump 8001, to be sent via the pipe 434 to a capture unit 5000 comprising a metal capture mass. heavy, and more particularly a mass of mercury capture. This results in an at least partially demercurized liquid stream recovered via line 420.

The figure 4 represents a detailed diagram of step c) of mercury capture according to the invention when the latter is carried out in the gas phase.

The overhead effluent recovered via the line 400 from the main fractionator unit 3000 is optionally heated via the heat exchanger 6001 so as to create an overheated gaseous effluent 435. This optional step may be useful to avoid Capillary condensation phenomena that may appear in the heavy metal collection masses. Optionally, the superheated effluent can be raised in pressure, for example, using a compressor 9000. The purpose of this re-pressurization step is, in case it is necessary, to compensate for the pressure loss induced. by the capture unit 5000. The optionally superheated and / or optionally compressed overhead effluent is sent via the pipe 436 to the capture unit 5000 comprising a heavy metal capture mass, and more particularly a capture mass of mercury. This results in an at least partially demercurized gaseous hydrocarbon phase recovered via line 420.

d) Complementary treatment step

At the outlet of the mercury capture unit 5000, the at least partially demercurized effluent is sent via the pipe 420 to a treatment unit 4000 as described above (see the method paragraph according to the prior art). As a result, at the outlet of the treatment zone 4000 a plurality of effluents 411, 412 and 413 do not comprise mercury, and therefore do not need to be treated on mercury capture units.

So, unlike the state of the art illustrated in figure 1 the method according to the invention requires only one and only mercury capture unit, said capture unit possibly being doubled in parallel or in series to ensure maintenance without impacting the operation of the fractionation unit. Furthermore, the process according to the invention makes it possible to recover the mercury contained in the feedstock compounds, and more particularly in the crude oil feedstock, immediately at the outlet of the main fractionation unit in a refining scheme. For the purposes of the invention, the term "refining" is understood to mean all the operations that make it possible to convert crude oil into petroleum products of current use. Crude oils are in the form more or less viscous liquids essentially consisting of hydrocarbons of varying volatility and chemical nature.

Example

The example is based on Figures 2 and 3 .

In this example, it is considered that the conversion unit 200 is composed of the heating unit 2000, the pipe 102 and the main fractionating unit 3000.

A crude oil charge 100 is sent to a desalting unit 1000 consisting of a water wash. The desalted feed 101 is heated via the heat exchanger 2000 to a target temperature of 380 ° C is then directed via the line 102 to the main fractionator 3000 consisting of a distillation column to produce different feeds. hydrocarbons according to their molecular weight. The contact time (residence time) of the charge in the conversion unit 200 is 10 minutes.

At the outlet of the main fractionation unit 3000, the overhead effluent 400 is composed of a hydrocarbon fraction of which 90% of the compounds have a boiling point of less than 200 ° C. The overhead effluent 400 is, after cooling to 46 ° C. via a heat exchanger 6000, is treated by a capture unit 5000 comprising a CuS mercury collection mass deposited on an alumina, capable of capturing the mercury. in elementary form. This results in the production of an effluent 420 at least partially demercurized which is sent to a treatment unit 4000 in the form of a secondary fractionation unit. Three effluents 411, 412 and 413 are extracted at the outlet of the treatment zone 4000.

The different feeds and effluents 100, 101, 102, 400 and 420 were analyzed for their mercury content. The analysis of total mercury in the liquid and gaseous fractions is carried out respectively using a PE-1000® device specific for mercury analyzes and an SP-3D® device from Nippon Instruments Corporation (NIC). The total mercury content in lines 101, 102, 102, 400 and 420 is determined in μg / L.

• filtration pour éliminer le mercure particulaire ;
• purge du filtrat pour éliminer le mercure élémentaire volatil ;
• extraction à la cystéine du filtrat purgé : séparation du mercure ionique extractible et organique non extractible (analyse de la solution aqueuse à l'aide du DMA-80 (Milestone Inc)).

For the chemical speciation of mercury, the method as described in the scientific publication of Charles-Philippe Lienemann et al. published in Fuel Processing Technology, 131, 2015, pages 254-261 , entitled: " Mercury speciation in liquid petroleum products: Comparison between plasma concentration and mass spectrometric detection (SEC-ICP-HR MS) " and comprising the following steps:

• filtration to remove particulate mercury;
• purging the filtrate to remove volatile elemental mercury;
• cysteine extraction of the purged filtrate: separation of extractable and non extractable ionic mercury (analysis of the aqueous solution using DMA-80 (Milestone Inc)).

The results obtained are reported in Table 1 below. Table 1 - Mercury Concentrations and Compositions piping [Hg] total (μg / L) % weight Hg particulate % weight Hg ° (elemental) % Hg ionic weight % organic Hg weight 100 182 63 0 5 32 101 124 82 7 2 9 102 127 79 12 1 8 400 117 0 100 0 0 420 2 0 0 40 60

The implementation of the process according to the invention makes it possible on the one hand to effectively convert the non-elemental mercury contained in the compounds of the crude oil feedstock into elemental mercury. On the one hand, it is noted that most of the conversion of non-elemental mercury into elemental mercury is carried out in the main fractionation unit 3000. In line 102, ie at the inlet of the main fractionation unit 3000 include 12% by weight of mercury in elemental form, and in the conduit 400, ie the output of the overhead stream from the main fractionation unit 3000, there are 100% by weight of mercury in elemental form. On the other hand, the process according to the invention makes it possible to efficiently capture the elemental mercury at the outlet of the main fractionation unit 3000 via the mercury capture unit 5000 situated between the lines 400 and 420, which allows not to pollute all units downstream of the main fractionation unit of the crude oil load in a refinery scheme.

Claims (12)

A process for removing mercury contained in a heavy hydrocarbon feedstock downstream of a main fractionator (3000), wherein a) the non-elemental mercury contained in the compounds of said feedstock is converted into elemental mercury, said step being carried out in a conversion unit (200) at a target temperature for a residence time fixed and adapted to said target temperature so as to at least 90% by weight of the non-elemental mercury contained in the compounds of said feedstock are converted into elemental mercury, said transformation step being carried out in the absence of hydrogen and in the absence of a catalyst, it being understood that : when the target temperature of said charge is between 150 ° C and 175 ° C, the residence time of said charge in the conversion unit (200) is between 150 and 2700 minutes; and or when the target temperature of said charge is greater than 175 ° C and less than or equal to 250 ° C, the residence time of said charge in the conversion unit (200) is between 100 and 900 minutes; and or when the target temperature of said charge is greater than 250 ° C. and less than or equal to 400 ° C., the residence time of said charge in the conversion unit (200) is between 5 and 70 minutes; and or when the target temperature of said charge is greater than 400 ° C., the residence time of said charge in the conversion unit (200) is between 1 and 10 minutes; b) fractionating said hydrocarbon feedstock in a fractionation unit (3000) to produce an overhead effluent (400) comprising elemental mercury; c) contacting the overhead effluent (400) obtained in step b) with a mercury collection mass included in a mercury collection unit (5000) to obtain an effluent that is at least partially demercurized (420) . Process according to claim 1, characterized in that the reduction in the total content by weight of mercury of said charge taken before step a) and after step c) is at least 90%. Process according to claims 1 or 2, characterized in that steps a) and b) are carried out simultaneously. Process according to any one of Claims 1 to 3, characterized in that the overhead effluent (400) resulting from the fractionation of said feedstock in the main fractionation unit (3000) is cooled by means of a heat exchanger ( 6000) to produce a liquid effluent (430). Process according to claim 4, characterized in that the liquid effluent (430) is sent to a separation unit (7000) to provide a liquid organic phase, a portion of which is recycled to the main fractionator (3000) as a reflux, and the other part is sent via the pipe (434) to said mercury capture unit (5000). Process according to any one of Claims 1 to 3, characterized in that the overhead effluent (400) resulting from the fractionation of said feedstock in the main fractionation unit (3000) is heated by means of a heat exchanger (6001) to produce a gaseous effluent (435). Process according to Claim 6, characterized in that the gaseous effluent (435) is compressed by means of a compressor (9000) before being sent to the mercury capture unit (5000). Process according to any one of Claims 1 to 7, characterized in that before stage a) of transformation of the non-elemental mercury contained in the compounds of said elemental mercury charge, said charge is desalted in a desalting unit ( 1000). Process according to any one of Claims 1 to 8, characterized in that, during stage c), said charge is brought into contact with a mass mercury or supported mercury collection mass comprising a phase comprising at least one metal sulphide with base of a metal M selected from the group consisting of copper, chromium, manganese, iron, cobalt and nickel. Process according to any one of claims 1 to 8, characterized in that during step c), said charge is brought into contact with a mass or supported mass capture comprising a phase containing at least sulfur in elemental form. Process according to any one of Claims 1 to 10, characterized in that the said hydrocarbon feedstock comprises between 1 and 10 mg of mercury per kg of filler. Process according to any one of claims 1 to 11, characterized in that the heavy hydrocarbon feedstock is a crude oil feedstock.

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