FR2990950A1 - PROCESS FOR PURIFYING A LIQUID LOAD OF HYDROCARBONS CONTAINING ACIDIC COMPOUNDS - Google Patents

Abstract

A process for purifying a hydrocarbon feedstock containing acidic compounds, comprising a step of contacting said hydrocarbon feedstock with an absorbent solution comprising, preferably at least one amine, water, and at least one C -C thioalkanol.

Description

PROCESS FOR PURIFYING A LIQUID LOAD OF HYDROCARBONS CONTAINING ACIDIC COMPOUNDS TECHNICAL FIELD The present invention relates to a process for purifying liquid hydrocarbon feeds containing acidic compounds such as mercaptans and other acidic compounds. The invention finds particular application in the oil and gas industry for the deacidification of liquid hydrocarbon cuts obtained during the fractionation of natural gases and petroleum fractions. STATE OF THE PRIOR ART During the fractionation of a natural gas or a petroleum fraction, the sulfur compounds such as H 2 S, mercaptans and COS are shared in the various effluents obtained. In most cases, despite treatments upstream of this fractionation, these sulfur compounds concentrate in the C3 or higher liquid cuts, and then reach concentrations requiring specific treatment of these liquid cuts. In addition, an economic comparison of the options shows that it is sometimes preferable to limit the level of treatment upstream of the fractionation and to add a treatment of the liquid phases downstream of the fractionation. The removal of the mercaptans contained in the liquid phases is generally carried out by bringing these phases into contact with an aqueous solution of sodium hydroxide. In these processes, the mercaptans react in a first step with the sodium hydroxide to form salts of the RS-Na + or mercaptide type, the oxidation of these salts in a second step, in the presence of a suitable catalyst, dissolved in the aqueous solution of sodium hydroxide, allows to form disulfide compounds of formula RSSR and regenerate the soda which is recycled to the first step. R-S-S-R disulfide compounds not soluble in water and sodium hydroxide are simply separated by decantation. The presence of COS, H2S and CO2 in the liquid feed of these washing processes with soda 20, on the other hand, poses important problems. In fact, these compounds react irreversibly with sodium hydroxide to form stable salts that accumulate in the aqueous sodium hydroxide solution. The presence of these stable salts modifies the physicochemical properties of the aqueous sodium hydroxide solution, in particular by increasing the viscosity, and hinders the settling phenomenon of the R-S-S-R disulfide compounds and the regenerated sodium hydroxide. Problems of plugging and crystallization are also mentioned, disrupting the operation of the process.

These stable salts must be removed by purging the aqueous sodium hydroxide solution. In total, the irreversible reaction of H2S, CO2 and COS with sodium hydroxide, and the purges of the aqueous sodium hydroxide solution, lead to significant losses of sodium hydroxide as well as dissolved catalyst. Another problem that arises is the elimination of waste constituted by these purges. In order to remove H2S, CO2 and COS, a preliminary treatment step of the liquid charge can be provided. This is usually a load washing step with an aqueous solution of sodium hydroxide or with an aqueous solution of amines. Thus, US-A-5,877,386 discloses a sweetening process for liquefied petroleum gases containing acidic compounds such as H 2 S, CO 2 and COS, in which these petroleum gases liquefied liquids are contacted with an absorbent mixture comprising an aqueous solution of triethanolamine (TEA) and at least one other amine selected from monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and diisopropanolamine (DIPA). Prior washing of the liquid filler with an aqueous solution of sodium hydroxide leads to the loss of the soda used for this prewash. To this disadvantage, are added the constraints due to the management of the effluent obtained.

The use of an aqueous solution of amine leads on the other hand to a considerable energy consumption for the regeneration of the solvent. It is generally advisable to consider integrated schemes, using for the regeneration of the aqueous solution of amine equipment already existing in the processing chain. Furthermore, the process which has been developed for the simultaneous removal of mercaptans and other acid gases contained in a gaseous effluent is known. This process was the subject of the application WO-A1-2007 / 083012 (FR-A1-2896244) which describes a process for purifying a gaseous mixture containing acid gases comprising a step of contacting said gaseous mixture with an absorbent solution comprising an alkanolamine, a C2-C4 thioalkanol, and water. The preferred alkanolamine is diethanolamine (DEA), and the preferred thioalkanol is thiodiglycol (TDG). However, this method applies exclusively to the treatment of gaseous mixtures, and the treatment of liquid charges is neither mentioned, nor envisaged, nor suggested. There is, therefore, in view of the above, a need for a simplified process for purifying a hydrocarbon liquid feed containing acidic compounds, ie mercaptans and other acidic compounds in a reduced number of stages. and / or by implementing smaller facilities, which use smaller amounts of reagents, and whose energy requirements are decreased. The object of the present invention is to provide a process for purifying a hydrocarbon liquid feed containing acidic compounds which, among other things, meets this need. The object of the present invention is still to provide a process for purifying a hydrocarbon liquid charge which does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art, and which solves the problems of the processes. of the prior art. SUMMARY OF THE INVENTION This and other objects are achieved, in accordance with the invention, by a process for purifying a hydrocarbon liquid charge containing acidic compounds, comprising a step of contacting the said hydrocarbon liquid feed with an absorbent solution comprising, preferably at least one amine, water, and at least one C2-C4 thioalkanol. The process according to the invention is fundamentally different from the processes of the prior art in that it uses a specific, and in some cases novel, absorbent solution for the treatment of specific fillers which are liquid hydrocarbon feedstocks. . Some of the absorbent solutions used in the process according to the invention have been used in a process for the simultaneous removal of mercaptans and acid gases, but, as already mentioned above, this process has made the subject of the application WO-A1-2007 / 083012 (FR-A1-2896244) is exclusively used for the treatment of gaseous mixtures, such as natural gases. Surprisingly, it has been demonstrated that the absorbent solutions preferably comprise at least one amine, water and at least one C2-C4 thioalkanol, some of which have already been used for the purification of mixtures. The gas containing acid gases could be successfully used for the purification of liquid hydrocarbon feeds, such as liquefied petroleum gas (LPG), containing acidic compounds such as mercaptans and other acidic compounds. All the absorbent solutions used in the process according to the invention, whether already known, such as the absorbing water-diethanolamine (DEA) -Thiodiglycol (TDG) solution, or not, have the advantage of presenting a strong reactivity towards all the acid compounds such as CO2, H2S and COS, but also mercaptans. Surprisingly, the already known absorbent solutions, which had this advantageous combination of properties for the treatment of gaseous mixtures, also exhibit this same combination of advantageous properties for the treatment of hydrocarbon liquid feeds. It is quite surprising that absorbent solutions which are suitable for the purification of gaseous mixtures may also be suitable for the purification of liquid feeds. There was no reason to suppose that absorbent solutions which had already been used successfully for the purification of gas mixtures could be used with the same success and with the same advantages, especially with regard to the simultaneous elimination of all acid compounds, for the purification of liquid charges.

Indeed, it will be readily understood that the conditions, such as the temperature and the pressure, prevailing during the absorption step by contacting two liquids are totally different from those prevailing during an absorption step by placing in contact with a gas and a liquid. The problems that arise during the absorption step by contacting two liquids are also totally different from those which arise during an absorption step by contacting a gas and a liquid. . Thus, during a liquid / liquid exchange between a hydrocarbon liquid charge and an absorbent solution, the hydrocarbons must not be soluble in the absorbing solution, must not be absorbed by the absorbing solution, and in the same manner the Absorbent solution components should not be soluble in hydrocarbons, should not be absorbed by hydrocarbons. Surprisingly, it has been shown that the absorbent solutions used in the process according to the invention meet these criteria.

The hydrocarbons are not entrained in the absorbent solution used and the components of the absorbent solution, in particular the thioalkanol such as TDG, are very sparingly soluble and have very little entrainment in the hydrocarbon liquid feeds treated by the process according to the invention. . This very low mutual solubility (hydrocarbon liquid charge / absorbent solution) does not affect the performance and quality of the process products.

Because of the very low absorption, solubilization, thioalkanols such as TDG in hydrocarbons, it thus avoids any pollution of the liquid charge by the solvent, including sulfur. It is in particular this advantageous property of the thioalkanols that makes the absorbent solutions used in the process according to the invention particularly suitable for the purification of hydrocarbon liquid feeds. The process for purifying a hydrocarbon liquid feedstock according to the invention meets the needs mentioned above, it does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art, and it provides a solution to the problems of the processes of the prior art. Laboratory tests have shown that the absorbent solutions which were known for the purification of a gaseous effluent have the same performance for the purification of a liquid hydrocarbon feed, namely: simultaneous removal of mercaptans and other compounds acids such as CO2, H2S and COS, controlled solubility of hydrocarbons in the absorbent solution, energy gain for regeneration. These same performances are presented by the new absorbent solutions used in the process according to the invention. The method according to the invention makes it possible to simplify the treatment scheme currently adopted for the purification of hydrocarbon liquid feeds which, as described above, generally comprises a prewashing step with an aqueous amine solution and then a washing step with soda. Indeed, by implementing the method according to the invention, it is possible to reduce the size of washing facilities with soda or even to remove them. The process according to the invention may thus possibly make it possible to carry out in a single step the treatment of a charge or liquid slurry charged with CO2, H2S, COS and mercaptans, whereas two steps are currently necessary: namely the pretreatment and the washing with soda. However, depending on the intended application and the feedstock to be treated, it will generally be advisable to combine an absorption step according to the invention and a washing step with sodium hydroxide, the latter being then used in a installation of reduced size, its operation being simplified, and the amount of waste produced during this washing step with sodium hydroxide being reduced because of the pretreatment performed in the first step according to the invention.

The process according to the invention makes it possible to reduce the capital expenditure ("CAPEX") and operating expenses ("OPEX") of gas treatment plants and in particular natural gas thanks to the energy savings due to the optimization of the absorbent solution implemented, and the reduction of the size of facilities planned downstream for the elimination of other sulfur compounds such as mercaptans or even the removal of some of these facilities (see examples). Another of the advantages of the process according to the invention is the high stability of the absorbent solution used. The hydrocarbon liquid feed may be any hydrocarbon liquid feed containing acidic compounds. The process according to the invention is more particularly applicable to the purification of liquid feeds containing less than 1% of H2S by weight. By hydrocarbon liquid feed, it is generally meant that the feedstock comprises 95% by weight or more, preferably 99% by weight or more, of one or more hydrocarbons. These hydrocarbons are mainly C 2, C 3, C 4 and C 5 saturated hydrocarbons: ethane, propane, butanes, pentanes, C 2, C 3, C 4 and C 5 unsaturated hydrocarbons such as propylene, or aromatic hydrocarbons such as benzene, toluene, and the like. or xylene.

The other components of the liquid feed are impurities such as acid compounds, and possibly other impurities such as water. Generally, the liquid feed contains as acidic compounds one or more mercaptan (s) and, besides these mercaptans, one or more other acid compounds. Preferably, the mercaptans which have the formula R-SH (where R is an alkyl radical comprising, for example, from 1 to 10 carbon atoms, in particular from 1 to 6 carbon atoms) include methyl mercaptan and ethyl mercaptan, but of Other mercaptans, and especially C3SH to C6SH molecules, may be present, generally at lower concentrations than methyl mercaptan and ethyl mercaptan. Generally, the other acidic compound (s) is (are) selected from carbon dioxide (CO2), hydrogen sulphide (H2S), carbonyl sulphide (COS), and carbon disulfide (CS2) .

The hydrogen sulphide content of the liquid feed to be treated is generally between 10 and 10,000 ppm by weight, and after the contacting step this content can be lowered to 1 ppm by weight.

The CO2 content of the liquid feedstock to be treated is generally between 10 and 10,000 ppm by weight, and after the contacting step this content can be lowered to 1 ppm by weight. The mercaptan content of the liquid feedstock to be treated is generally between 10 and 2000 ppm by weight, and after the contacting step this content can be lowered to 1 ppm by weight. The SOC content of the liquid feedstock to be treated is generally between 5 and 100 ppm by weight and after the contacting step this content can be lowered to 1 ppm by mass. A hydrocarbon liquid feedstock which can be treated by the process according to the invention contains, for example, COS in general at less than 100 ppm by mass, mercaptans, mainly C1SH and C2SH, generally up to 1000 ppm by weight. , and H2S generally less than 1% by weight. Liquid fillers which can be treated by the process according to the invention are, for example, the liquid cuts resulting from the fractionation of a natural gas, or the liquid cuts obtained in the gas treatment plants ("gas plant") of a refinery, or Liquefied Petroleum Gases or LPG.

Liquid cuts from the fractionation of a natural gas essentially contain saturated hydrocarbons, while liquid cuts obtained in refinery gas treatment plants contain saturated hydrocarbons as well as olefin-type unsaturated hydrocarbons. The charge is generally supplied at a temperature of between 30 ° C and 80 ° C, for example between 30 ° C and 50 ° C, and at a pressure above the bubble point to avoid any vaporization.

According to the invention, the filler is brought into contact with an absorbent solution comprising, preferably consisting of at least one amine, water and at least one C 2 -C 4 thioalkanol. Generally, the C2 to C4 thioalkanol has the formula: RS- (C2-C4 alkylene) -OH, where R is any group, for example an (usually C1-C6) alkyl group or an alkanol group (generally C1 to C6), or a thiol group, or an alkylthioalkanol group (generally C1 to C6). In a preferred embodiment, the C2 to C4 thioalkanol is a dimeric molecule. An example of a C2 to C4 thioalkanol which can be used according to the invention is ethylene dithioethanol of formula (HO-CH2-CH2) -S- (CH2-CH2) -S- (CH2-CH2-OH). The preferred thioalkanol is thiodiethylene glycol or thiodiglycol (TDG), which is the compound of formula S (CH 2 -CH 2 -OH) 2. In addition to TDG, other C2-C4thioalkanols can be used according to the invention, Especially methylthioethanol. It is also possible to use a mixture of several thioalkanols. It should be noted that another of the advantageous properties of thioalkanols, and in particular TDG, is that they are very sparingly soluble in the hydrocarbons that are present in the liquid feed. The thioalkanols are therefore very little involved in the treatments downstream of the deacidification step by the process according to the invention and they do not bring an increase of sulfur in these downstream treatments.

Any amine may be used in the absorbent solution whether it is a primary, secondary or tertiary amine, aliphatic, cyclic or aromatic.

However, the amine used should generally be soluble in water at the concentrations used in the absorbent solution. For the purposes of the invention, the term "primary amine" generally means a compound comprising at least one primary amine function. For the purposes of the invention, the term "secondary amine" generally means a compound comprising at least one secondary amine function. For the purposes of the invention, the term "tertiary amine" generally means a compound comprising at least one tertiary amine function and preferably comprising only tertiary amine functions. These primary, secondary or tertiary amines may be chosen from aliphatic amines, cyclic amines or the like. Examples of amines which can be used according to the invention are given in particular in US-Al-2010/0288125, the description of which we can refer. Preferably, the amine is selected from alkanolamines (aminoalcohols). These alkanolamines can be primary, secondary, or tertiary. Recall that the alkanolamines or aminoalcohols are amines comprising at least one hydroxyalkyl group (comprising for example from 1 to 10 carbon atoms) attached to the nitrogen atom. Tertiary alkanolamines may be trialkanolamines, alkyldialkanolamines or dialkylalkanolamines. The secondary alkanolamines may be dialkanolamines, or alkylalkanol amines, and the primary alkanolamines are monoalkanolamines. The alkyl groups and hydroxyalkyl groups of the alkanolamines may be linear or branched and generally comprise from 1 to 10 carbon atoms, preferably the alkyl groups comprise from 1 to 4 carbon atoms, and the hydroxyalkyl groups comprise from 2 to 4 atoms. of carbon. Examples of these alkanolamines are 2-aminoethanol (monoethanolamine, MEA), N, N-bis (2-hydroxethyl) amine (diethanolamine, DEA), N, N, -bis (2-hydroxypropyl) amine (diisopropanolamine). Diphenylamine (TEA), tributanolamine, bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA), dimethylaminoethanol (dimethyletanolamine, DMEA), 3-dimethylamino-1-propanol (N, N-dimethylpropanolamine), 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA), N, N-bis (2- hydroxypropyl) methylamine (methyldiisopropanolamine, MDIPA), 2-amino-2-methyl-1-propanol (AMP), 1-amino-2-methyl-propan-2-ol, 2-amino-1-butanol (2-AB) ). Examples of tertiary amines and in particular tertiary alkanolamines are given in US-Al-2008/0025893 to the description of which reference can be made. These include N-methyldiethanolamine (MDEA), N, N-diethylethanolamine (DEEA), N, N-dimethylethanolamine (DMEA), 2-diisopropylaminoethanol (DIEA), N, N, N, N'-Tetramethylpropanediamine (TMPDA), N, N, N ', N'-tetraethylpropanediamine (TEPDA), dimethylamino-2-dimethylaminoethoxyethane (Niax), and N, N-dimethyl-N', N'-diethylethylenediamine (DMDEEDA). Examples of tertiary alkanolamines which can be used in the process according to the invention are also given in US-Al-2010/0288125, to the description of which reference may be made. These include tris (2-hydroxyethyl) amine (triethanolamine, TEA), tris (2-hydroxypropyl) amine (triisopropanol), tributylethanolamine (TEA), bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA ), 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine DMEA), 3-dimethylamino-1-propanol, 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA), N N-bis (2-hydroxypropyl) methylamine (methyldiisopropanolamine, MDIPA). Other examples of tertiary alkanolamines which can be used in the process according to the invention are given in US-A-5,209,914 to the description of which reference may be made, these include N-methyldiethanolamine, triethanolamine N-ethyldiethanoamine, 2-dimethylaminoethanol, 2-dimethylamino-1-propanol, 3-dimethylamino-1-propanol, 1-dimethylamino-2-propanol, N-methyl-N-ethylethanolamine, 2-diethylaminoethanol, 3-dimethylamino 1-butanol, 3-dimethylamino-2-butanol, N-methyl-N-isopropylethanolamine, N-methyl-N-ethyl-3-amino-1-propanol, 4-dimethylamino-1-butanol, 4-dimethylamino-2 butanol, 3-dimethylamino-2-methyl-1-propanol, 1-dimethylamino-2-methyl-2-propanol, 2-dimethylamino-1-butanol and 2-dimethylamino-2-methyl-1-propanol. The amine may also be selected from aminoethers. Examples of such aminoethers are 2-2- (Aminoethoxy) ethanol (AEE), 2- (2-t-butylaminoethoxy) ethanol (EETB), and 3-methoxypropyldimethylamine. The amine may also be selected from saturated 3, 5, 6 or 7 membered heterocycles comprising at least one NH group contained in the ring. The ring may optionally further comprise one or two other heteroatoms in the ring selected from nitrogen and oxygen, and may be optionally substituted with one or more substituents selected from alkyl radicals having 1 to 6 atoms. carbon such as ethyl or methyl radicals, aminoalkyl radicals of 1 to 6 carbon atoms, and hydroxyalkyl radicals of 1 to 6 carbon atoms. Examples of such heterocycles are piperazine, 2-methylpiperazine, N-methylpiperazine, N-ethylpiperazine, N-aminoethylpiperazine (AEPZ), aminopropylpiperazine, N-hydroxyethylpiperazine (HEP), homopiperazine, bis ( hydroxyethyl) piperazine, piperidine, aminoethylpiperidine (AEPD), aminopropylpiperidine, furfurylamine (FA) and morpholine (MO). The amine used according to the invention may also be chosen from polyamines such as alkylene polyamines, in particular alkylene diamines, tertiary bis (diamines) and polyalkylene polyamines. Among the alkylene diamines, mention may be made of hexamethylenediamine, 1,4-diaminobutane, 1,3-diaminopropane, 2,2-dimethyl-1,3-diaminopropane, 3-methylaminopropylamine, N- ( 2-hydroxyethyl) ethylenediamine, 3- (dimethylaminopropylamine) (DMAPA), 3- (diethylamino) propylamine, and N, N'-bis (2-hydroxyethyl) ethylene diamine. Among the tertiary bis (diamines), mention may be made of N, N, N ', N'-tetramethylethylenediamine, N, N-diethyl-N', N'-dimethylethylenediamine, N, N, N ', N', tetraethylethylenediamine, N, N, N ', N'-tetramethyl-1,3-propanediamine (TMPDA), N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA), N, N-dimethyl- N, N'-diethylethylenediamine (DMDEEDA), 1-dimethylamino-2-dimethylaminoethoxyethane (bis [2- (dimethylamino) ethyl] ether, mentioned in the document US-Al-2010/0288125 to the description of which one will be able to refer. Among the polyalkylene polyamines, mention may be made of dipropylenetriamine (DTPA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylene pentamine (TEPA), hexamethylenediamine (HMDA), tris (3-aminopropyl) amine, and tris (2-aminoethyl) amine. In one embodiment, the absorbent solution comprises only amines comprising only tertiary amine groups and / or sterically hindered amine groups. Preferred amines comprising only tertiary amine groups are tris (2-hydroxyethyl) amine (triethanolamine, TEA), tris (2-hydroxypropyl) amine (triisopropanol), tributanolamine, bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA), 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine DMEA), 3-dimethylamino-1-propanol, 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA) N, N-bis (2-hydroxypropyl) methylamine (methyldiisopropanolamine, MDIPA). Preferred amines comprising only sterically hindered amine groups are 2-amino-2-methyl-1-propanol (AMP) and 1-amino-2-methylpropan-2-ol. The two preferred amines of the absorbent solution according to the invention are DEA and MDEA and other amines that can be used are MEA, TEA, and DIPA. In one embodiment, the absorbent solution comprises, preferably, water, at least one tertiary amine, at least one activator, and at least one C2-C4 thioalkanol. Preferably, the tertiary amine is selected from tertiary alkanolamines. Examples of tertiary amines and in particular tertiary alkanolamines have already been given above. Preferably, in this embodiment, the tertiary amine is selected from N-methyldiethanolamine (MDEA), triethanolamine (TEA), tributanolamine (TBA), and mixtures thereof. The activator may be chosen from any activator known to those skilled in the art, but may preferably be selected from primary amines and secondary amines, more preferably the activator may be selected from primary alkanolamines and secondary alkanolamines. Examples of primary and secondary amines and especially primary and secondary alkanolamines have already been given above. The activator may also be chosen from saturated 3, 5, 6, or 7-membered heterocycles comprising at least one NH group contained in the ring already mentioned above. Examples of activators are given in US-Al-2008/0025893, these are 3-methylaminopropylamine (MAPA), piperazine, 2-methylpiperazine, N-methylpiperazine, homopiperazine, piperidine, and morpholine.

Other examples of activators that can be used in the process according to the invention are given in document WO-A1-2004 / 071624: it is piperazine, hydroxyethylpiperazine (HEP), and bis (hydroxyethyl) piperazine, and mixtures thereof. Still other examples of activators that can be used in the process according to the invention are given in US-A-5,209,914; US-A-5,277,885; and US-A-5,348,714, these are polyamines such as dipropylenetriamine (DPTA), diethylene triamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). Other activators mentioned in these documents which can be used in the process according to the invention are aminoethylethanolamine (AEEA), hexamethylenediamine (HMDA), dimethylaminopropylamine (DMAPA) and 1,2-diaminocyclohexane (DACH) as well as methoxypropylamine (MOPA), ethoxypropylamine, aminoethylpiperazine (AEPZ), aminopropylpiperazine, aminoethylpiperidine (AEPD), aminopropylpiperidine, furfurylamine (FA) and ethylmonoethanolamine (EMEA). In a preferred embodiment, the activator is selected from monoethanolamine (MEA), butylethanolamine (BEA), diethanolamine (DEA), aminoethylethanolamine (AEEA), piperazine, hydroxyethylpiperazine (HEP), aminoethylpiperazine (AEP), and mixtures thereof. Advantageously, in this embodiment, or the absorbent solution comprises water, at least one tertiary amine, at least one activator and at least one C 2 -C 4 thioalkanol, the thioalkanol is preferably chosen from ethylene dithioethanol or ThioDiGlycol (TDG). Generally, the absorbent solution preferably comprises: from 20% to 60%, preferably from 30% to 50%, more preferably from 40% to 45% by weight, based on the total mass of the absorbent solution at least one amine; from 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45% by weight, based on the total weight of the water-absorbing solution; from 10% to 40%, preferably from 15% to 30%, more preferably from 17% to 25% by weight relative to the total weight of the absorbent solution of at least one thioalkanol. Of these absorbent solutions, the absorbent solutions which comprise MDEA or DEA as amine (only amine), TDG as thioalkanol, and water in the aforementioned proportions are preferred. A most preferred absorbent solution is the absorbent solution consisting of water, DEA, and TDG in the respective proportions of 40%, 40%, and 20% by weight.

In the embodiment where the absorbent solution comprises water, at least one tertiary amine, at least one activator and at least one C 2 -C 4 thioalkanol, the absorbent solution preferably comprises: 35% at 45% by weight relative to the total mass of the absorbent solution of at least one tertiary amine; from 4% to 12% by weight relative to the total mass of the absorbent solution of at least one activator chosen preferably from primary amines and secondary amines; the total content of tertiary amine and activator being from 38% to 50% by weight relative to the total mass of the absorbent solution, and the total concentration of tertiary amine and activator being between 3.8 and 4.2 mol / L; from 17% to 25% by weight relative to the total mass of the absorbent solution of at least one C 2 to C 4 thioalkanol; - the rest of water to reach 100% by mass. This absorbent solution comprises specific components in specific amounts.

Indeed, this absorbent solution advantageously comprises a mixture of specific amines, namely a mixture of a tertiary amine and a primary or secondary amine acting as an activator. Each of these amines, tertiary on the one hand, and primary or secondary, on the other hand, is respectively present in a specific amount, defined by a narrow range, and the mixture of these amines is also present in a specific amount also defined by a narrow beach. The other components of the mixture, namely water and C2-C4 thioalkanol are also present in specific amounts, defined by narrow ranges. In this embodiment, a preferred absorbent solution is a solution consisting of water, MDEA, HEP and / or piperazine and TDG, in the proportions of 30%, 42% and 8%, respectively. , and 20% by weight. In this embodiment, in which an activated tertiary amine is used, a simultaneous and one-stage elimination of all the acidic compounds, that is to say not only hydrogen sulphide and carbon dioxide, is obtained. but also other acidic compounds such as mercaptans and COS.

Advantageously, the contacting step is carried out at a temperature of 30 ° C to 60 ° C, at a pressure of 10 to 20 bar. Advantageously, the purification process as described above further comprises, after the step of contacting a regeneration step of the absorbent solution loaded with acidic compounds such as mercaptans and other acidic compounds. Advantageously, this regeneration step of the absorbent solution is carried out at a pressure of 0 to 20 bar, preferably of 1 to 3.5 bar, more preferably of 1 to 2 bar, and at a temperature of 100 ° C. to 140 bar. ° C. Advantageously, the method according to the invention further comprises at the end of the step of contacting the hydrocarbon liquid feedstock with the absorbent solution a step of treatment of the hydrocarbon feedstock by washing with a caustic solution such as an aqueous solution of sodium hydroxide. This caustic washing step is intended to eventually remove, if necessary, mercaptans that would not have been removed during the contacting step with the absorbent solution. Advantageously, the hydrocarbon liquid charge is a charge resulting from the fractionation of a gaseous mixture containing acid gases such as a natural gas, said gaseous mixture having been successively purified by placing it in contact with an absorbent solution in order to removing the acid gases, dehydrated, degassed to give a gaseous cut and a liquid cut which is then stabilized to give said hydrocarbon liquid feed, and the absorbent solution charged with acid gases from the purification of the gaseous mixture and the absorbing solution loaded with acid compounds from the purification of the hydrocarbon liquid feed are regenerated in a common regeneration plant. Alternatively, the hydrocarbon liquid feed may be a feedstock from the fractionation of crudes in petroleum refining applications or other liquid hydrocarbon mixtures. The invention will be better understood on reading the detailed description which follows, given by way of illustration and not limitation and which is particularly made with reference to an installation for implementing the method according to the invention. In this detailed description, particular examples of embodiments of the method according to the invention are furthermore exposed. This description is made with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an installation for implementing the method according to the invention; FIG. 2 is a schematic diagram of a first variant of a process for treating a gaseous mixture, such as a natural gas, in which a process according to the invention is integrated in order to purify the liquid cuts resulting from the degassing operation of the gaseous mixture treatment process; FIG. 3 is a schematic diagram of a second variant of a process for treating a gaseous mixture such as a natural gas, in which a process according to the invention is integrated for purifying the liquid cuts resulting from the degassing operation of the gas mixture treatment process. FIG. 4 is a graph which gives the partition coefficient of methyl mercaptan between the aqueous (amine phase) and organic (hydrocarbon phase HC) phases for tests carried out with the water-DEA-TDG absorbent solution according to the invention (4040- 20% by weight) (points -) and for the comparative water-DEA reference absorbent solution (60-40% by weight) (M points). The abscissa is the partition coefficient of methyl mercaptan between the amine phase and the hydrocarbon phase, and the ordinate is carried the partial pressure of methyl mercaptan (in mbar). DESCRIPTION OF THE SIZE The invention can be implemented in any conventional absorption and regeneration installation 15 using chemical absorbent solutions. Any liquid-liquid contact apparatus may be used to perform the contacting, absorption step. In particular, any type of column may be used as an absorption column. It may be in particular a perforated plate column, a valve column or a column with bells. Packed, loose or structured columns can also be used. It is also possible to use in-line, static solvent mixers. In what follows, the terms "absorption column" or "column" are used for simplification to denote the liquid-liquid contact apparatus, but it is understood that any liquid-liquid contact device can be used. to perform the absorption step. An installation suitable for carrying out the process according to the invention is described in FIG. 1. The hydrocarbon liquid charge, such as a liquefied petroleum gas (LPG) containing acidic compounds, namely mercaptans and other acid compounds is sent via a pipe (1) in the vicinity of the foot (2) of a liquid-liquid contact column (3) in which the absorption step is carried out. The absorption step is generally carried out at a temperature of 30 ° C to 60 ° C. The pressure in the absorption column is generally between 10 and 20 bar, and is determined so as to maintain the charge in the liquid state under the given temperature conditions. The absorption is carried out by counter-current contacting the liquid hydrocarbon feed circulating in an upward flow in the column, with the absorbent solution which is supplied via a pipe (4) in the vicinity of the top (5) of the column, and which flows in a downward flow in the column. The flow rate of the hydrocarbon liquid feed is generally from 1000 to 20000 kg / h. The hydrocarbon liquid feedstock such as treated and purified LPG is withdrawn at the top of the column (3) via a pipe (6) 30 and is sent to a washing plant with water (7). . The water-washed liquid feed may be routed to its use via a pipeline. The water washing installation (7) receives a water make-up through a booster pipe (8), while the used water used for washing is removed from the washing installation to the water (7) via a purge line (9) provided with a pump (10) and either recycled (11) into the washing installation or sent (12) into a storage tank (10). relaxation ("flash amine" balloon) (13) which is part of the absorbent solution circuit. The treated and purified hydrocarbon feed leaves the washing installation (7) via a pipe (14).

Advantageously, the purification process as described above further comprises a regeneration step of the absorbent solution loaded with acidic compounds such as mercaptans and other acidic compounds.

This regeneration step is generally carried out in an installation which comprises a "flash" and a regeneration column by "stripping" with steam. More precisely, as illustrated in FIG. 1, the regeneration step of the absorbing solution is conventionally carried out by heating and separating the mercaptans (RSH) and the other acid compounds, including H2S, absorbed from the solution. in a regeneration column (15). This regeneration step of the absorbent solution is generally carried out at a pressure of 0 to 20 bar, preferably 1 to 3.5 bar, more preferably 1 to 2 bar, and a temperature of 100 ° C to 140 ° C. ° C. Indeed, the solution of amines loaded with acidic compounds such as H 2 S, CO 2, COS and mercaptans (RSH) -this rich amine-from the bottom (2) of the absorption column is all of firstly sent via a line (16) to the intermediate pressure expansion flask (13).

The gases (17) resulting from the expansion of the rich amine can be used as "fuel-gas" fuel gases, or sent to a sulfur production unit implementing the mild Claus oxidation reaction of H2S.

The rich amine is then reheated and optionally partially vaporized in an amine / amine exchanger (18) with the hot amine from the bottom (20) of the regeneration column (line 19), then feeds the regeneration column (15). in which it is conveyed by the pipe (21). The reboiler (22) with which the regeneration column (15) is equipped generates vapor that flows upstream in the regeneration column (15), resulting in acidic constituents such as H2S, CO2, COS, and the RSH mercaptans. This desorption is favored by the low pressure and the high temperature prevailing in the regenerator. At the top (23) of the regeneration column (15), the acid gases are cooled in a condenser (24). The condensed water is separated from the acid gas in a reflux tank (25) and returned to the top of the regeneration column (15) via a pipe (26) provided with a pump (27) like this is shown in Figure 1, either directly to the lean amine solution tank.

The acid gases leave the reflux flask via a pipe (28). The regenerated amine which is also called poor amine is withdrawn at the base of the regeneration column and is then recycled to the vicinity of the top of the absorption column via a pipe (19, 29) provided with a pump (30) passing through the amine-amine exchanger (18) and another exchanger (31). A semi-regenerated mode of operation may also be considered. Thus, a fraction of the partially regenerated solvent taken from the intermediate expansion tanks or at an intermediate level of the regeneration column can be sent to an intermediate level of the absorption section. The process according to the invention can be integrated in a process for treating a gaseous mixture, such as a natural gas containing mercaptans and other acid gases. The process according to the invention is then used to purify the liquid cuts resulting from the degassing operation of the gaseous mixture treatment process. A schematic diagram of a first variant of a process for the treatment of a gaseous mixture, such as a natural gas, in which a process according to the invention is integrated for purifying the liquid cuts resulting from the operation degassing of the gaseous mixture treatment process such as a natural gas is illustrated in Figure 2.

In this integrated scheme, the gaseous mixture, such as a natural gas (201), is first treated, during a deacidification step (202), with an absorbent solution (203) and then dehydrated (204). and finally degazolined (206). Water is removed from the dewatering step (204) at (205). During this degassing step (206), the methane gas (and also ethane), which is generally sent (207) to the distribution network, and a liquid (208) are separated on the one hand. ) containing a section C2, and a section C3 and more (called C3 +). The recovered liquid is first stabilized (209) in order to separate the C2 section (210), then the C3 + section (211) is sent to an absorption process (212) carried out by the method according to the invention in order to remove acid compounds such as H2S, CO2, COS, and RSH (mercaptans) contained in the liquid. One can choose to treat all the C3 + cut, or proceed to the distillation of C3 + to have a C3-C4 cut and a C5 and +: C5 + cut, and then treat these two cuts. The treatment of the C3-C4 cut and the treatment of the C5 + cut by the process according to the invention are similar.

In this configuration, it should be noted that most of the RSH mercaptans have been removed during the deacidification of the gaseous mixture such as natural gas, but that, during the degassing and stabilization steps, the acidic compounds such as H 2 S, CO2, COS, and SHRs (mercaptans) are reconcentrated. This is the reason why a treatment of purification of the liquid resulting from degazolinage and stabilization must be realized. During this treatment of purification of the liquid treatment by a caustic washing with sodium hydroxide (213) makes it possible to eliminate the RSH which are transformed into DSO and evacuated (214), but it is necessary beforehand to eliminate the H2S, CO2 and COS by a treatment (212) carried out by the process according to the invention.

The process according to the invention makes it possible, in addition to these compounds, to eliminate, during the pretreatment with the absorbent solution, a fraction of the mercaptans, the rest of the mercaptans being removed by washing with sodium hydroxide (213).

At the end of the caustic washing step, a liquid is obtained, for example a C3 and more cut, treated, purified (215), and respecting the specifications as to the contents of acidic compounds. Because according to the invention the same absorbent solution can be used to effect the deacidification (202) of the gaseous mixture, such as natural gas, and the purification (212) of liquids from degassing and separation. the regeneration of these two absorbent solutions can be carried out in a single common regeneration plant ("common regenerator") (216) from which the acid gases are discharged (217), which makes it possible to reduce the number of Installation equipment and investments and operating costs of the facility.

A schematic diagram of a second variant of a process for treating a gaseous mixture, such as a natural gas, in which the process according to the invention is integrated in order to purify the liquid cuts resulting from the degassing operation the process for treating the gaseous mixture such as natural gas is illustrated in FIG. 3. In this variant, RSH mercaptans are removed with water (205) during the dehydration step (204) of the gaseous mixture, for example, using molecular sieves, which are regenerated with a fraction of the gas. Therefore, the regeneration gas of these sieves must be treated in turn in a facility provided for this purpose (218). The invention will now be described in relation to the following example, given by way of illustration and not limitation. Example. In this example, tests are carried out to measure the liquid-liquid-gas equilibrium for a system consisting of methyl mercaptan and / or H2S, of the water-DEA-TDG absorbent solution 40-40-20% by weight in accordance with the present invention. invention, and heptane (C7). Tests are also carried out with a system composed of methyl mercaptan and / or H2S, the water-DEA reference solution 60-40% by weight, and heptane (C7). The tests are carried out at a constant temperature, namely 25 ° C. or 50 ° C., for various partial pressures of sulfur compounds ranging from 2 to 20 mbar for methyl mercaptan and less than 100 mbar for H2S. The gas and liquid phases are brought into contact by stirring in a 600 ml reactor whose temperature is regulated by an electric heating mantle. The reactor is provided with magnetic drive mechanical stirring. The mobile is composed of two propellers to stir the two liquid phases.

The gaseous mixture is taken from the upper part of the capacity and is then analyzed by gas chromatography (GC). The liquid phases are analyzed by argentimetric determination of the sulfur compounds.

The results obtained with the water-DEA-TDG absorbent solution 40-40-20% by mass according to the invention, and the water-DEA reference solution 60-40% by mass, are presented in FIG. of partition, at 50 ° C, determined by the solubility ratio of methyl mercaptan between the aqueous and organic phases, is 4 to 7 times greater with the absorbing solution water-DEA-TDG 40-40-20% by weight in accordance with the invention, compared to the absorbent water-DEA solution 60-40% by mass reference.

Claims (25)

REVENDICATIONS1. A process for purifying a liquid hydrocarbon feedstock containing acidic compounds, comprising a step of contacting said hydrocarbon liquid feedstock with an absorbent solution comprising, preferably consisting of, at least one amine, water , and at least one C2-C4 thioalkanol. The process according to claim 1, wherein the hydrocarbon liquid feed contains one or more mercaptans, and one or more other acid compound (s). The process according to claim 2, wherein the one or more other acidic compound (s) is (are) selected from carbon dioxide (CO2), hydrogen sulfide (H2S), sulfide carbonyl (COS), and carbon disulfide (CS2). 4. Process according to any one of the preceding claims, in which the hydrocarbon liquid feedstock is chosen from liquid cuts resulting from the fractionation of a natural gas, the liquid cuts obtained in the gas treatment plants ("gas plant"). ) Of a refinery, and Liquefied Petroleum Gases or LPG. 5. A process according to any one of the preceding claims wherein the hydrogen sulphide content of the liquid feed to be treated is between 10 and 10,000 ppm by weight and after the contacting step this content can be lowered to at 1 ppm by weight. 6. Method according to any one of the preceding claims, wherein the CO2 content of the liquid feedstock to be treated is between 10 and 10,000 ppm by weight and after the contacting step this content can be lowered to 1 ppm by weight. 7. Process according to any one of the preceding claims, in which the mercaptan content of the liquid feedstock to be treated is between 10 and 2000 ppm by weight, and after the contacting step this content is lowered, generally up to at 1 ppm by weight. 8. A method according to any one of the preceding claims, wherein the COS content of the liquid feedstock to be treated is between 5 to 100 ppm by weight, and after the contacting step this content can be lowered up to at 1 ppm by weight. 9. A process according to any one of the preceding claims wherein the filler is supplied at a temperature of between 30 ° C and 80 ° C, for example between 30 ° C and 50 ° C, and at a pressure above bulle.30 The process according to any one of the preceding claims, wherein the thioalkanol is ethylene dithioethanol or ThioDiglycol (TDG). 11. Process according to any one of the preceding claims, in which at least one amine is chosen from alkanolamines. 12. The process according to claim 11, wherein the amine is diethanolamine DEA, or methyldiethanolamine MDEA. 13. A process according to any one of the preceding claims, wherein the absorbent solution preferably comprises: from 20% to 60%, preferably from 30% to 50%, more preferably from 40% to 45%; % by weight relative to the total mass of the absorbent solution of at least one amine; From 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45% by weight, based on the total weight of the water-absorbing solution; from 10% to 40%, preferably from 15% to 30%, more preferably from 17% to 25% by weight, based on the total weight of the absorbent solution of at least one thioalkanol. 14. The method of claim 13, wherein the absorbent solution is water, DEA, and TDG in the respective proportions of 40%, 40%, and 20% by weight. 15. A process according to any one of the preceding claims wherein the absorbent solution comprises, preferably, water, at least one tertiary amine, at least one activator, and at least one C2-C4 thioalkanol. . 16. The method of claim 15, wherein the absorbent solution preferably comprises: from 35% to 45% by weight relative to the total mass of the absorbent solution of at least one tertiary amine; from 4% to 12% by weight relative to the total mass of the absorbent solution of at least one activator; the total content of tertiary amine and activator being from 38% to 50% by weight relative to the total mass of the absorbent solution, and the total concentration of tertiary amine and activator being between 3.8 and 4.2 mol / L; from 17% to 25% by weight relative to the total mass of the absorbent solution of at least one C 2 -C 4 thioalkanol; - the rest of water to reach 100% by mass. 17. The method of claim 15 or 16, wherein the tertiary amine is selected from tertiary alkanolamines. 18. A process according to any one of claims 15 to 17, wherein the activator is selected from primary amines and secondary amines, preferably from primary alkanolamines and secondary alkanolamines. 19. A process according to any one of claims 15 to 18, wherein the tertiary amine is selected from N-methyldiethanolamine (MDEA), triethanolamine (TEA), tributanolamine and mixtures thereof, and the activator is selected from monoethanolamine (MEA), butylethanolamine (BEA), diethanolamine (DEA), aminoethylethanolamine (AEEA), piperazine, hydroxyethylpiperazine, aminoethylpiperazine and mixtures thereof. 20. A process according to any one of claims 15 to 19, wherein the absorbing solution is water, MDEA, HEP and / or piperazine and TDG, in the respective proportions of 30. %, 42%, 8%, and 20% by weight. 21. The method according to any one of the preceding claims, wherein the step of contacting is carried out at a temperature of 30 ° C to 60 ° C and a pressure of 10 to 20 bar. 22. A process according to any one of the preceding claims which further comprises, after the contacting step, a step of regenerating the absorbent solution loaded with acidic compounds. 23. The method of claim 22, wherein the step of regenerating the absorbent solution is carried out at a pressure of 0 to 20 bar, preferably 1 to 3.5 bar, more preferably 1 to 2 bar, and at a temperature of 100 ° C to 140 ° C. 24. A method according to any one of the preceding claims, which further comprises, at the end of the step of contacting the hydrocarbon liquid feedstock with the absorbent solution, a stage for treating the hydrocarbon feedstock. by washing with a caustic solution, such as an aqueous sodium hydroxide solution. 25. Process according to any one of the preceding claims, in which the hydrocarbon liquid charge is a charge resulting from the fractionation of a gaseous mixture containing acid gases such as a natural gas, said gaseous mixture having been successively purified by contacting with an absorbent solution to remove acid gases, dehydrated, degazolined, to give a gaseous cut and a liquid cut which is then stabilized to give said hydrocarbon liquid charge, and the absorbent solution loaded with acid gases from the purification of the gaseous mixture and the absorbent solution loaded with acid compounds resulting from the purification of the hydrocarbon liquid charge are regenerated in a common regeneration plant.