EP1205531A1 - Process for hydrotreatment of hydrocarbon mixtures rich in olefines and aromatics - Google Patents

Abstract

Hydro treatment of an olefin- and mono aromatics-rich hydrocarbon feed comprises: (1) adding an ammonia precursor to the feed; and (2) contacting it with hydrogen in the presence of a transition metal catalyst on a refractory oxide support. Hydro treatment of an olefin- and mono aromatics-rich 1-4C hydrocarbon feed comprises: (1) adding an ammonia precursor to the feed; and (2) contacting it with hydrogen in the presence of a transition metal catalyst on a refractory oxide support.

Description

The present invention relates to a process for hydrotreating a mixture of hydrocarbon compounds comprising from four to eight carbon atoms, rich in olefins and monoaromatic compounds. It concerns more particularly the hydrotreatment of the sections resulting from the distillation of crude oils, steam cracking, catalytic reforming, cracking catalytic, coking or any process producing such cuts and cuts from the processing of coal such as coal essences.

It is well known to hydrotreat all cuts from distillation crude oils in the presence of hydrogen and a catalyst consisting of transition metals supported on refractory oxides. He is a lot less obvious to hydrotreat hydrocarbon mixtures under these conditions containing large amounts of olefins from C4 to C8 and containing high proportions of monoaromatic compounds such as benzene, toluene and xylene. During hydrotreatment, there is total hydrogenation or partial olefins and diolefins and oligomerization of compounds monoaromatics forming C12 and higher compounds. Now when the charge hydrogenated and desulfurized subsequently undergoes the conventional treatment of extractive solvent distillation to extract monoaromatic compounds contained, certain oligomers present, formed during hydrotreatment do not can be removed from the solvent because their boiling point is too close to that of the solvent. As a result, these oligomers accumulate in the extraction solvent and it becomes periodically necessary to stop the distillation to change the solvent in order to purify it. The cost of this operation is not negligible in that it includes the cost of cleaning the solvent, the possible purchase cost of the new clean solvent, the operating cost linked to the interruption of the unit to change the solvent and the cost corresponding to the loss of monoaromatic compounds which cannot be sold.

These problems of selective hydrogenation of olefinic compounds into presence of large amounts of aromatics have been resolved in the French patent 2,376,100. This patent proposes to pretreat the catalyst supported consisting of at least one noble metal on alumina, such as ruthenium, rhodium, platinum and / or palladium by a stream of ammonia gaseous and possibly continuing the injection treatment of this gaseous ammonia in the reactor during the hydrogenation itself. Such treatment has the major drawback of having to pretreat the catalyst in situ in a controlled atmosphere of ammonia alone or mixed with a other inert gas such as nitrogen, therefore under pressure. Such a situation is little appreciated in an industrial environment because it imposes security constraints. In moreover, by this route, it is difficult to control the amount of ammonia put in contact with the catalyst: too much ammonia leads to deactivation of the catalyst, including for the expected reactions.

The present application therefore relates to a process which neither requires nor pretreatment of the catalyst, or introduction of nitrogenous gaseous compounds into hydrogenation gas. It aims at a simple process which can be easily implemented whatever the hydrotreatment unit, with a little catalyst expensive compared to catalysts containing noble metals such as platinum and palladium, which can adapt to fillers whose composition can vary in concentration of olefins and monoaromatic compounds and which allows good desulfurization of the feed.

By olefins is meant here the monoolefinic and diolefinic compounds generally present in the charges sent for hydrotreatment.

The present invention therefore relates to a hydrotreatment process a mixture of hydrocarbon compounds from C4 to C8, rich in olefins and monoaromatic compounds, by hydrogenation in the presence of a catalyst solid, characterized in that an ammonia precursor is introduced into the charge of hydrocarbon compounds and that the catalyst comprises at least a transition metal supported on at least one refractory oxide.

Transition metal means any transition metal except so-called noble metals, in particular platinum and palladium.

One of the advantages of the process is linked to the introduction of a precursor of ammonia in the charge which makes it possible to release, during the reaction, from gaseous ammonia which is present during the selective hydrogenation reaction olefins and which can be recovered and recycled with unused hydrogen. Among the other advantages linked to the invention, this method makes it possible to control precisely the amount of ammonia released during the reaction hydrotreating. In addition, it helps to limit unwanted reactions oligomerization while maintaining excellent catalyst activity for the desired reactions for selective hydrogenation of olefins and charge desulfurization.

Without being bound by a theory, the Applicant has found that from a On the other hand, the oligomerization of aromatic compounds results from the presence of acid sites on the catalyst, these sites being of variable acid forces. On the other hand, the efficiency of the hydrotreatment reaction depends on the electrodeficiency of the catalytic support which itself is correlated with its acidity.

It is therefore a matter of selectively blocking the sites responsible for oligomerization reactions of aromatic compounds, sites whose strength acid is such that they remain saturated with ammonia under the conditions selected of temperature and pressure for the hydrotreatment reaction in the context of the present invention. However, under these conditions, there is still enough electrodeficient sites to maintain good process activity hydrotreating.

More specifically, in the context of the present invention, injected not more than 1000 ppm by weight of molar equivalent nitrogen of precursor of ammonia in the feed. For optimal process efficiency according to the invention, 5 to 1000 ppm by weight of nitrogen molar equivalent will be injected nitrogen precursor, and preferably from 10 to 200 ppm.

For the implementation of the process, the ammonia precursors are chosen from nitrogen compounds capable of releasing ammonia gas under hydrotreatment conditions.

In a preferred embodiment of the invention, the ammonia precursor is chosen from linear and branched amines, polyamines, imines, and urea and its derivatives. The amines and polyamines are chosen from the group consisting of mono, di and trialkylamines comprising from 1 to 10 carbon atoms by alkyl group, the alkyl groups being linear or cyclic, and polyalkylamines comprising from 1 to 5 atoms nitrogen, each alkyl group comprising from 1 to 6 carbon atoms in linear or branched form. Preferred amines and polyamines are selected from methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, cyclohexylamine, cycloheptylamine, dimethylamine, diethylamine dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, methylenediamine, ethylenediamine, propylenediamine, butylenediamine, dimethylenetriamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tripropylenetetramine, tetraethylenepentamine and tetrapropylenepentamine, cyclohexylamine, triethylamine and ethylenediamine being preferred.

The catalyst necessary for the process according to the invention consists of at least minus one metal chosen from the group consisting of nickel, cobalt, molybdenum, vanadium and tungsten; nickel alone and combinations nickel / molybdenum, cobalt / molybdenum and nickel / tungsten are preferred. This or these metals are supported on at least one refractory oxide chosen from alumina, silica, silicoalumines, aluminophosphates, zirconia, magnesia and the oxides of titanium, rutile and anatase, these oxides occurring in amorphous or crystalline form.

For optimal efficiency of the hydrotreatment reaction, the operation is carried out at a temperature between 50 and 400 ° C., under a pressure between 10 ⁶ Pa and 10 ⁷ Pa, preferably between 3 × 10 ⁶ Pa and ⁶ × 10 ⁶ Pa, and a hvv varying from 0.5 to 10h ^-1 .

In a preferred mode of the hydrotreatment process, ammonia gaseous excess formed can be recycled into the recycle gas rich in hydrogen. This has the advantage of limiting the amount of precursor of ammonia injected into the load.

The examples below are given to illustrate the invention without wishing to limit its scope.

EXAMPLE I

This example describes the conditions under which the invention is achieved by presenting the gain brought by the introduction of precursor of ammonia in an industrial load to be hydrotreated and this for different ammonia precursors and for different concentrations thereof.

• 57% en poids de benzène
• 12% en poids d'oléfines
• 12 ppm en poids de soufre total

The feed to be hydrotreated is a mixture at 21% by weight of a C6 reforming cut and 79% by weight of a C6 cut of pyrolysis gasoline. It contains :

• 57% by weight of benzene
• 12% by weight of olefins
• 12 ppm by weight of total sulfur

The benzene content was measured using the UOP 744-86 method referenced in the "Laboratory test methods for petroleum and its products", published by UOP Process Division, (UOP Inc. 20 UOP Plaza-Algonquin Mt Prospect Roads-Des Plains-Illinois 60016).
The olefin content is determined by measuring the number of bromine in application of standard ASTM D1159, and the sulfur content by method ASTM D2622.

Three ammonia precursors were used on a hydrotreatment pilot unit for 100 ml of catalyst, at a temperature of 200 ° C., a pressure of 26.5 × 10 ⁵ Pa, operating with an H2 / hydrocarbon ratio of 230NI / l, wh of the charge being 1.6h ^-1 .

These precursors are triethyleneamine or TEA, cyclohexylamine or CHA and ethylenediamine or EDA.

The efficiency for each of the tests carried out is assessed in relation to the decrease in the number of C12 compounds formed, the decrease in the number of bromine and the decrease in the sulfur content. The results are given in Table I below. Nature of the precursor N equivalent (ppm wt) C ₁₂ content (ppm wt) Bromine index (mgBr ₂ / 100g) Sulfur (ppm wt) Nitrogen (ppm wt) No 0 215 8 <0.5 <0.5 TEA 25 11 76 0.5 <0.5 100 12 657 <0.5 <0.5 200 13 758 1 <0.5 CHA 10 5 14 <0.5 <0.5 EDA 25 1 63 <0.5 <0.5 30 1 99 0.5 <0.5

The results obtained indicate that the injection of EDA, TEA or CHA as ammonia precursors in the feed entering a hydrotreatment unit makes it possible to significantly reduce the formation of C ₁₂ compounds. It can easily be seen that it is possible to optimize the amount of amine to be added to the feed in order to simultaneously satisfy the specifications in terms of bromine index, linked to the concentration of olefins, and to the sulfur concentration. Note that the amines are completely decomposed during the reaction since the nitrogen content is less than 0.5 ppm by weight.

EXAMPLE II

The present example aims to emphasize the effectiveness of the process whatever either the relative concentrations of the load in olefins and in compounds monoaromatic.

In this sense, two industrial charges, the composition of which is given below, were tested according to the procedure described in Example I but at different reaction temperatures. Their composition is given in Table II below. Charge Nature T ° C Bromine number (gBr ₂ / 100g) Benzene (% wt) Sulfur (ppm wt) 1 C6 cut pyrolysis gasoline 240 30 85 60 2 21% (1) + 79% (2) 200 7 57 12

In the example, cyclohexylamine or CHA is used as ammonia precursor.

The results obtained with and without an ammonia precursor for each of these charges are given in Table III below. Charge CHA (Molar equivalent N in ppm wt) C _{12 production} (ppm wt) Bromine index (mgBr ₂ / 100g) Sulfur (ppm wt) Nitrogen (ppm wt) 1 0 489 78 <0.5 <0.5 40 8 83 <0.5 <0.5 2 0 276 11.5 <0.5 <0.5 10 4.5 14 <0.5 <0.5

It can be seen from this table that the addition of the nitrogen precursor allows whatever the nature of the charge of reducing the formation of compounds into C12 by oligomerization, while maintaining the required characteristics of the expected end product, including nitrogen, the precursor decomposing totally.

Claims (11)

Process for the hydrotreatment of a mixture of hydrocarbon compounds from C4 to C8, rich in olefins and in monoaromatic compounds, by hydrogenation in the presence of a solid catalyst characterized in that an ammonia precursor is introduced into the charge of compounds hydrocarbon and that the catalyst comprises at least one transition metal supported on at least one refractory oxide. Process according to claim 1, characterized in that one injects with plus 1000 ppm molar equivalent nitrogen precursor ammonia in hydrocarbon compounds. Process according to Claims 1 and 2, characterized in that 5 to 1000 ppm molar nitrogen equivalent of nitrogen precursor is injected, and preferably 10 to 200 ppm. Process according to Claims 1 to 3, characterized in that the ammonia precursor is chosen from nitrogen compounds capable of releasing gaseous ammonia under the conditions of the hydrotreatment. Process according to Claims 1 to 4, characterized in that the ammonia precursor is chosen from linear and branched amines, polyamines, imines, and urea and its derivatives. Process according to Claim 5, characterized in that the amines and polyamines are chosen from the group consisting of mono, di and trialkylamines comprising from 1 to 10 carbon atoms per alkyl group, the alkyl groups being linear or cyclic, and the polyalkylamines comprising from 1 to 5 nitrogen atoms, each alkyl group comprising from 1 to 6 carbon atoms in linear or branched form. Process according to Claims 5 and 6, characterized in that the alkylamines and the polyalkylamines are chosen from methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, cyclohexylamine, cycloheptylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, methylenediamine, ethylenediamine, propylenediamine, butylenediamine, dimethylenetriamine, diethylenetriamine, dipropylenetriethylenetrietrietinetriamine triethane tetraethylenepentamine and tetrapropylenepentamine, cyclohexylamine, triethylamine, and ethylenediamine being preferred. Process according to Claims 1 to 7, characterized in that the hydrotreatment reaction is carried out at a temperature between 50 and 400 ° C, a pressure between 10 ⁶ Pa and 10 ⁷ Pa, preferably between 3x10 ⁶ Pa and 6x10 ⁶ Pa, and a vvh varying from 0.5 and 10h ^-1 . Process according to Claims 1 to 8, characterized in that the refractory oxide forming a support in the catalyst is chosen from alumina, silica, zirconia, silicoalumines, aluminophosphates, zirconia, magnesia and titanium oxides, rutile and anatase, in amorphous or crystalline form. Process according to Claims 1 to 9, characterized in that in the catalyst, the transition metals are chosen from nickel, cobalt, molybdenum, vanadium and tungsten taken alone or as a mixture, nickel alone and the nickel / molybdenum, cobalt / molybdenum and nickel / tungsten being preferred. Process according to any one of Claims 1 to 9, characterized in that the excess ammonia gas formed is recycled into the recycle gas rich in hydrogen.