Patent Application
20240025847
The present invention relates to a process for preparing mercaptans, in particular methyl mercaptan, from dialkyl sulfides and hydrogen sulfide (also known as the sulfhydrolysis process or reaction), in the presence of a specific catalyst based on titanium dioxide and/or zirconium dioxide, and also to the corresponding use of such a catalyst.
The present invention also relates to a process for preparing mercaptans and dialkyl sulfides, from at least one alcohol and hydrogen sulfide, involving the sulfhydrolysis process as defined above.
Mercaptans are of great interest industrially and are currently in widespread use in the chemical industries, notably as starting materials in the synthesis of more complex organic molecules. For example, methyl mercaptan (CH3SH) is used as a starting material in the synthesis of methionine, an essential amino acid for animal nutrition. Methyl mercaptan is also used in the synthesis of dialkyl disulfides, in particular in the synthesis of dimethyl disulfide (DMDS), a sulfiding additive for hydrotreating catalysts for petroleum fractions, among other applications.
Mercaptans, and in particular methyl mercaptan, are generally synthesized industrially by a known process starting from an alcohol and hydrogen sulfide at elevated temperature in the presence of a catalyst according to equation (1) below:
Main reaction
ROH+H2S—>RSH+H2O (1)
However, this reaction gives rise to the formation of byproducts, such as sulfides (which are symmetrical in the case below) according to equation (2) below:
ROH+RSH—>RSR+H2O (2)
Furthermore, when the main reaction is performed in the presence of several alcohols, dissymmetrical sulfides may also be obtained according to equations (3) and (4) below (example given with two alcohols):
ROH+R′OH+2H2S—>RSH+R′SH+2H2O (3)
ROH+R′SH—>RSR′+H2O (4)
The symmetrical or dissymmetrical sulfide byproducts are obtained in large amount industrially and are primarily sent for destruction. This represents a loss of efficiency in the mercaptan production process and an added cost associated with destroying them.
Thus, sulfides are occasionally upgraded to obtain the corresponding mercaptans, by means of the following reaction (5) (also known as sulfhydrolysis):
Sulfhydrolysis reaction
RSR′+H2S—>RSH+R′SH (5)
In the case of methyl mercaptan, the sulfhydrolysis reaction is written according to equation (6) below:
CH3SCH3+H2S—>2CH3SH (6)
The sulfhydrolysis reaction is generally catalyzed with catalysts of alumina type (Al2O3) or of NiMo (Nickel/Molybdenum) or CoMo (Cobalt/Molybdenum) type on an alumina support, as described in patent applications WO 2017/210070 and WO 2018/035316.
However, such a process needs to be improved so as to be more economical and more suited to the industrial scale.
There is thus a need for an improved process for the sulfhydrolysis of sulfides to mercaptans, in particular of dimethyl sulfide to methyl mercaptan.
There is also a need for an improved process for upgrading sulfides, in particular dimethyl sulfide, which are generated as byproducts during the production of mercaptans produced from alcohol(s) and hydrogen sulfide.
One objective of the present invention is to propose a catalyst for the sulfhydrolysis of sulfides to mercaptans which is easy to perform, economical and gives a satisfactory conversion.
Another objective of the present invention is to propose a process for the sulfhydrolysis of sulfides to mercaptans which can be readily integrated into a unit for the industrial production of mercaptans, notably produced from alcohol(s) and H2S.
One objective of the present invention is to provide a process for preparing mercaptans in which the sulfides generated as byproducts (for example during the reaction between an alcohol and H2S) are recycled or economically upgraded, easy to use and industrially viable.
The present inventors have discovered, surprisingly, that the use of a specific catalyst, based on titanium dioxide (of formula TiO2) and/or zirconia (also known as zirconium dioxide, of formula ZrO2) during sulfhydrolysis makes it possible to obtain a good conversion of sulfides, notably a conversion of at least 36%, preferably of at least 50%, or even of at least 70%. Furthermore, methane as a sulfhydrolysis byproduct is produced with very low selectivity, for example less than 2%.
The catalysts according to the invention are known as inert catalytic supports (i.e. supports with no catalytic activity). They are thus simple, economical and sparingly harmful compositions, making it possible to obtain a more efficient and more environmentally friendly sulfhydrolysis process.
In particular, the sulfhydrolysis process according to the invention may be integrated into a plant for the industrial production of mercaptans, notably produced from at least one alcohol and H2S. The sulfhydrolysis process according to the invention then makes it possible to increase the mercaptan productivity in a simple and economical manner by upgrading the sulfides generated as byproducts during the main reaction and transforming them also into mercaptans.
Furthermore, surprisingly, the present inventors have also discovered that the mercaptans derived from the sulfhydrolysis and the unreacted H2S could be reintroduced directly (notably without a separation and/or purification step) into the main reactor, and without this having any consequence on the main reaction between the alcohol(s) and the H2S.
The mercaptans produced by the two reactions (main reaction and sulfhydrolysis reaction) can then be separated and/or purified and/or recovered in a single place, for example at the outlet of the main reactor.
This integration of the sulfhydrolysis process into the main mercaptan production chain can be reinforced by the presence of a single H2S feed for both the main reaction and the sulfhydrolysis reaction (for example at the inlet of the sulfhydrolysis reactor).
Thus, according to the invention, a simple and efficient process for the upgrading of sulfides which is totally integrated into an industrial mercaptan production chain may be obtained. This device is notably easy to implement: it can be readily connected to the main unit and requires only minimal modifications thereof.
Thus, the present invention relates to a sulfhydrolysis process, in which a sulfide, preferably a dialkyl sulfide, is reacted with hydrogen sulfide (H2S) in the presence of ZrO2 and/or TiO2 as catalyst(s), to obtain at least one mercaptan, preferably one mercaptan.
The present invention also relates to a mercaptan preparation process comprising the steps of:
The term “catalyst” notably means a substance or a composition of chemical substances which accelerate a chemical reaction and which are unchanged at the end of this reaction.
According to the present invention, the catalyst used in the sulfhydrolysis reaction comprises titanium dioxide (TiO2) and/or zirconia (ZrO2), preferably titanium dioxide. Such catalysts may also be referred to as catalysts based on titanium dioxide and/or zirconia.
Titanium dioxide and/or zirconia are used as catalyst(s) in the sulfhydrolysis reaction. It is understood that TiO2 and/or ZrO2 are the active components of the catalyst (i.e. the compounds with catalytic activity). In particular, the catalysts according to the invention do not comprise any other compounds which have catalytic activity on the sulfhydrolysis reaction.
Preferably, the catalysts according to the invention consists essentially of, or even consist of, titanium dioxide and/or zirconia, and optionally stabilizers and/or binders. The stabilizers and binders are those conventionally used in the field of catalysts.
The term “promoter” (also known as a “dopant”) is a chemical substance or a composition of chemical substances which can modify and notably improve the catalytic activity of a catalyst. For example, the term “promoter” means a chemical substance or a composition of chemical substances for improving the conversion and/or selectivity of the catalyzed reaction relative to the catalyst alone. Preferably, the catalysts according to the invention do not comprise any promoter.
The usual definitions of conversion, of selectivity and of yield are as follows:
In particular, the sulfhydrolysis catalysts according to the invention make it possible to obtain a sulfide conversion of between 30% and 90%, preferably between 50% and 80% and even more preferentially between 50% and 75%.
The selectivity of the sulfhydrolysis reaction for mercaptans is notably greater than or equal to 98%.
The term “sulfide” means any organic compound comprising a —C—S—C— function.
Preferably, the term “sulfide” means a dialkyl sulfide.
The term “dialkyl sulfide” notably means a compound of general formula (I) below:
R—S—R′ (I)
in which R and R′, which may be identical or different, are, independently of each other, a saturated, linear, branched or cyclic, optionally substituted hydrocarbon-based radical.
Preferably, R and R′, which may be identical or different, are, independently of each other, a linear or branched alkyl radical; more preferentially, a linear or branched, preferably linear, alkyl radical containing between 1 and 18 carbon atoms, preferably between 1 and 12 carbon atoms.
R and R′, which may be identical or different, may be chosen, independently of each other, from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl, and also isomers thereof. Preferably, R and R′, which may be identical or different, may be chosen, independently of each other, from the group consisting of methyl, ethyl, octyl and dodecyl.
Preferably, R and R′ are identical (which corresponds to a symmetrical dialkyl sulfide).
Symmetrical dialkyl sulfides in particular have the general formula (II) below:
R—S—R (II)
in which R is as defined above.
In particular, the dialkyl sulfides according to the invention are chosen from the group consisting of dimethyl sulfide, diethyl sulfide, dioctyl sulfide, didodecyl sulfide and methyl ethyl sulfide. The dialkyl sulfides according to the invention may be chosen from the group consisting of dimethyl sulfide, diethyl sulfide, dioctyl sulfide and didodecyl sulfide. Most particularly preferably, the dialkyl sulfide is dimethyl sulfide.
The mercaptans according to the invention are those corresponding to the sulfhydrolysis of the sulfides as defined above. Preferably, the term “mercaptans” means alkyl mercaptans.
In particular, the term “alkyl mercaptan” means a compound of general formula (III) and/or (IV) below:
R—SH (III) and/or
R′SH (IV),
in which R and R′ are as defined above.
Particularly preferably, the mercaptan obtained according to the invention is methyl mercaptan.
The present invention thus relates to a process for preparing at least one mercaptan by sulfhydrolysis. In particular, the present invention relates to a process for preparing at least one mercaptan, in which a dialkyl sulfide is reacted with hydrogen sulfide (H2S) in the presence of ZrO2 and/or TiO2 as catalyst(s).
Preferably, said catalyst does not comprise any alkali metal oxide notably such as lithium, sodium, potassium, rubidium and cesium oxides.
Preferably, said catalyst does not comprise any promoter.
In particular, said catalyst does not comprise any alumina (Al2O3).
In particular, said catalyst does not comprise any phosphorus.
Preferably, said catalyst is TiO2. Particularly preferably, the catalyst comprises only TiO2 as active component, and in particular in its anatase crystalline form.
When the catalyst comprises TiO2 and/or ZrO2, it may then comprise between 30% and 50%, preferably between 35% and 45%, for example about 40% by weight of TiO2 relative to the total weight of the catalyst and/or between 50% and 70%, preferably between 55% and 65%, for example about 60% by weight of ZrO2 relative to the total weight of the catalyst.
The catalysts according to the invention may have a specific area of greater than 40 m2·g−1. Preferably, the specific area is at least 50 m2·g−1 for a catalyst based on ZrO2. Preferably, the specific area is at least 80 m2·g−1 for a catalyst based on TiO2.
The form of the catalysts may be of any type, for example spherical, cylindrical, ring-shaped or star-shaped, in the form of granulates or in any other three-dimensional form, or alternatively in the form of a powder which may be pressed, extruded or granulated.
The sulfhydrolysis reagents may be in gaseous, liquid or solid form, preferably gaseous or liquid form.
The sulfhydrolysis reaction temperature may be comprised between 100° C. and 500° C., preferably between 200° C. and 400° C., more preferably between 200° C. and 380° C. and more preferentially between 250° C. and 380° C.
The sulfhydrolysis reaction may be performed at a pressure of between 50 mbar and 100 bar, preferably between atmospheric pressure (about 1 bar) and 50 bar, and advantageously between 5 and 20 bar.
The H2S/sulfide mole ratio may be comprised between 0.1/1 and 50/1, preferably between 2/1 and 20/1. Preferably said ratio is between 2/1 and 15/1, more preferably between 2/1 and 10/1, for example 4/1.
Advantageously, the reagents (sulfide and H2S) may respect a particular contact time with the catalyst in the reactor where the sulfhydrolysis takes place. This parameter is expressed with the hourly space velocity equation:
(HSV)=(total flow rate of sulfide+H2S entering)/(volume of catalyst in the reactor).
The HSV may be comprised between 100 and 1200 h−1.
The sulfhydrolysis reaction may take place in any type of reactor, for example fixed-bed tube reactors, multitubular reactors, with microchannels, with a catalytic wall or with a fluidized bed, preferably a fixed-bed tube reactor.
In particular, the sulfhydrolysis process according to the invention is performed in a reactor comprising only one catalytic zone (said zone is notably continuous).
The amount of each reagent supplied to the reactor may vary as a function of the reaction conditions (for example the temperature, the hourly space velocity, etc.) and is determined according to the general knowledge. The hydrogen sulfide may be present in excess.
The present invention relates to a process for preparing mercaptan(s) and dialkyl sulfide(s) from at least one alcohol and H2S, in which said dialkyl sulfide(s) produced then react with H2S according to the sulfhydrolysis process as defined above, to obtain said mercaptan(s).
Thus, the present invention relates to a process for preparing mercaptan(s), comprising the steps of:
The reaction between an alcohol and H2S to form a mercaptan (and a sulfide as byproduct) is a known reaction, described, for example, in patents U.S. Pat. Nos. 2,820,062 A, 7,645,906 B2 and 2,820,831 A. For example, the reaction may be performed at a temperature of between 200° C. and 450° C. and/or at a pressure ranging from a reduced pressure to 100 bar. Generally, a catalyst is present, such as alumina promoted by alkali metals and/or alkaline-earth metals. The H2S may be present in excess.
Among the reagents, at least one alcohol, preferably one or two alcohols, may be used. Preferentially, only one alcohol is used. The alcohol(s) may be chosen from (C1-C18) or even (C1-C12) alcohols, and mixtures thereof. In particular, the alcohols may be chosen from the group consisting of methanol, ethanol, octanol, dodecanol and mixtures thereof. Preferably, the alcohol used is methanol.
Hereinbelow, it is understood that when two streams are introduced into a reactor, they may each be introduced separately into the reactor or may be combined before being introduced into the reactor.
In particular, the process according to the invention comprises the following steps:
A) introducing a stream comprising H2S and a stream comprising at least one alcohol into a first reactor;
B) reacting the two streams to obtain an outlet stream comprising at least one mercaptan, at least one dialkyl sulfide and optionally H2S;
C) separating the outlet stream obtained from step B) into:
D) introducing said stream comprising the dialkyl sulfide(s) into a second reactor with a stream of H2S;
E) reacting the two streams according to the sulfhydrolysis process as defined above to obtain an outlet stream comprising said mercaptan(s) and optionally H2S;
F) optionally recycling the stream of H2S obtained from step C) into step A).
The mercaptan(s) may be recovered on conclusion of step C) and/or after separation of the outlet stream from step E), preferably on conclusion of step C).
The outlet stream obtained from step B) may comprise at least one mercaptan, at least one dialkyl sulfide, optionally water, unconverted alcohol(s) and H2S. The outlet stream obtained from step E) may comprise said mercaptan(s), H2S and optionally methane and the unconverted dialkyl sulfide(s).
The outlet stream from the second reactor of step E) may be recycled, preferably entirely, into the first reactor of step A). Thus, the outlet stream from the sulfhydrolysis process comprising the mercaptan(s) and optionally the H2S may be introduced directly into the main reactor (or first reactor), notably without a prior separation and/or purification step. In particular, the outlet stream from the second reactor of step E) may correspond entirely or partially, preferably entirely, to the stream comprising H2S from step A), optionally with recycled H2S obtained from step C). In this case, the outlet stream obtained from step E) comprises H2S.
Surprisingly, the introduction of mercaptans into the main reactor has no influence on the main reaction between at least one alcohol and H2S. Furthermore, the H2S which may be obtained from step E) is thus totally recycled into step A). Such recycling notably has the advantage of having only one H2S inlet for the entire mercaptan production process, for example at the inlet of the sulfhydrolysis reactor.
Thus, the sulfhydrolysis process according to the invention integrated into an industrial mercaptan production facility makes it possible to totally reprocess the sulfide byproducts as products of interest and advantageously to recycle the H2S. The mercaptans produced will be the result of the main reaction and of the sulfhydrolysis reaction, which increases the productivity.
The separation step C) may be performed by distillation, for example under reduced pressure, according to conventional methods. For example, the distillation may take place at a pressure of between 0.1 bar and 10 bar, notably between 1 and 10 bar. Step C) may notably make it possible to separate the outlet stream obtained from step B) into:
a stream comprising the mercaptan(s),
a stream comprising the dialkyl sulfide(s),
optionally a stream comprising H2S,
optionally a stream comprising methane,
optionally water,
optionally unconverted alcohol.
According to a particular embodiment, said preparation process comprises the following steps:
a) introducing a stream comprising a mercaptan and H2S and a stream comprising at least one alcohol, preferably one alcohol, into a first reactor;
d) introducing the stream comprising the dialkyl sulfide into a second reactor with a stream of H2S;
e) reacting the two streams according to the sulfhydrolysis process as defined above to obtain an outlet stream comprising the mercaptan and H2S;
f) introducing the outlet stream obtained from step e), preferably directly, into the reactor of step a);
g) optionally recovering the stream comprising the mercaptan obtained from step c); and
h) optionally recycling the stream of H2S obtained from step c) into step a).
The outlet stream from step f) may correspond entirely or partially, preferably entirely, to the inlet stream of mercaptan and H2S of step a).
According to another particular embodiment, said preparation process comprises the following steps:
a′) introducing a stream comprising H2S and a stream comprising at least one alcohol, preferably one alcohol, into a first reactor;
b′) reacting the two streams to obtain an outlet stream comprising a mercaptan, a dialkyl sulfide and optionally H2S;
c′) separating the outlet stream obtained from step b′) into:
d′) optionally recovering the stream comprising the mercaptan obtained from step c′);
e′) optionally recycling the stream of H2S obtained from step c′) into step a′);
f′) introducing the stream comprising the dialkyl sulfide into a second reactor with a stream of H2S;
g′) reacting the two streams according to the sulfhydrolysis process as defined above to obtain an outlet stream comprising the mercaptan and H2S;
h′) separating the outlet stream obtained from step g′) into:
i′) combining the stream comprising the mercaptan obtained from step h′) with the outlet stream from step b′) before and/or during step c′);
j′) optionally recycling the stream of H2S obtained from step h′) into step f′).
This embodiment notably offers independence of the H2S feed of the main reactor relative to the sulfhydrolysis reactor.
The present invention also relates to the use of ZrO2 and/or TiO2 as catalyst(s), in the reaction reacting a sulfide with hydrogen sulfide to obtain a mercaptan. In particular, said catalyst and said reaction are as defined for the sulfhydrolysis process as described above. The sulfides and mercaptans are also as defined above.
The secondary reactor (1) (where the sulfhydrolysis takes place) comprises an H2S inlet and a dimethyl sulfide (DMS) inlet. At the outlet, stream A comprises H2S and methyl mercaptan.
Stream A enters directly into the main reactor (2) also comprising a methanol inlet. The outlet stream B from the reactor (2) comprises methyl mercaptan, dimethyl sulfide and H2S.
Stream B is then separated by distillation (3) into three different streams:
a stream comprising methyl mercaptan (MeSH);
a stream comprising dimethyl sulfide (DMS); and
a stream comprising H2S, which is subsequently recycled into the reactor (2) (not shown).
The DMS stream is then recycled into the reactor (1).
The secondary reactor (1A) (where the sulfhydrolysis takes place) comprises an H2S inlet and a dimethyl sulfide (DMS) inlet. At the outlet, stream A comprises H2S and methyl mercaptan.
Stream A undergoes a step of separation by distillation at (1B), which gives rise to a stream of H2S recycled into the reactor (1A) and a stream B which comprises methyl mercaptan which is combined at (3) with the outlet stream C from the reactor (2), where the main reaction takes place between methanol and H2S.
A step of separation by distillation (3) gives two different streams:
The DMS stream is then recycled into the reactor (1A).
Before the test, the catalysts were activated in situ by means of a procedure comprising a first step of drying with nitrogen at 250° C., followed by sulfidation with H2S at 350° C. for 1 hour.
The performance of the catalysts was evaluated for the reaction for producing MeSH from DMS in a fixed-bed reactor comprising only one catalytic zone with a catalyst volume of 30 mL, a temperature ranging from 300° C. to 350° C., under a pressure of 9 bar absolute, with a feed gas composition DMS/H2S=¼ (v/v) and an hourly space velocity of 800 h−1. The reagents are preheated to a temperature >100° C. and are flashed during their introduction into the bottom of the reactor.
The products were analyzed online by gas chromatography.
The results for the DMS conversion and the selectivity toward MeSH and CH4 obtained for three different catalysts are described in Table 1 below:
It is noted that the catalysts according to the invention make it possible to significantly increase the conversion of the dimethyl sulfide, while at the same time maintaining very good selectivity. Notably, with the catalysts according to the invention, the conversion may be greater than 70%, relative to a maximum of 35% for alumina, which is the conventional catalyst used in sulfhydrolysis.
It is also noted that only a negligible amount of methane is formed.
The influence of the sulfhydrolysis reaction on the main mercaptan synthesis reaction was evaluated.
To do this, the content of sulfides coproduced by the main mercaptan synthesis reaction was monitored as a function of the variation in the content of mercaptans entering the reactor 1 (where the mercaptans are produced from alcohol and H2S).
The conditions of the main reaction are as follows:
Pressure=3.5 bar
H2S/ethanol ratio (molar)=2.4
GHSV=580 h−1
The results for the selectivity toward sulfides obtained for three contents of mercaptans entering at three different temperatures with an alumina-based catalyst are described in
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1911005 | Oct 2019 | FR | national |
This application is the U.S. national phase of International Application No. PCT/FR2020/051682, filed 28 Sep. 2020, which claims priority to French Application No. FR 1911005, filed 4 Oct. 2019, the disclosure of each of these applications being incorporated herein by reference in its entirety for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2020/051682 | 9/28/2020 | WO |
