Title of Invention

METHOD FOR PRODUCING METHYL MERCAPTAN FROM DIALKYL SULPHIDES AND DIALKYL POLYSULPHIDES

Abstract The invention relates to a method for the continuous production of methyl mercaptan by reacting an educt mixture containing dialkyl sulfides and dialkyl polysulfides, with hydrogen sulfide in order to form methyl mercaptan.
Full Text Method for producing methyl mercaptan from dialkyl
sulphides and dialkyl polysulphides
The invention relates to a process for preparing alkyl
mercaptan by reacting a reactant mixture comprising dialkyl
sulphides and/or dialkyl polysulphides and optionally
dialkyl ethers with hydrogen sulphide over heterogeneous
catalysts.
Methyl mercaptan is an industrially important intermediate
for the synthesis of methionine and for the preparation of
dimethyl sulphoxide and dimethyl sulphone. Methyl mercaptan
is prepared predominantly from methanol and hydrogen
sulphide by reaction over a catalyst consisting of an
aluminium oxide support and transition metal oxides and
basic promoters.
In the reaction of methanol with hydrogen sulphide, at the
typical reaction temperatures and using an economically
viable hydrogen sulphide excess, the reaction equilibrium
is such that dimethyl sulphide is always formed as well as
methyl mercaptan. In addition to thioether formation, the
reaction to give polysulphides (e.g. dimethyl disulphide)
is also observed. These compounds are removed in the course
of workup of the product gas stream. When no further
economically viable utilization of these components is
possible, the by-products are typically disposed of, for
example by incineration or reaction with alkalis. This
procedure lowers the overall selectivity of the preparation
process for methyl mercaptan and hence the economic
viability of the process. In this context, one alternative
is the recycling of the sulphides or polysulphides into the
process. When the sulphide level, according to US 2 81614 6,
is kept sufficiently high by a recycling, the new formation
of mercaptans from alcohols or ethers is suppressed. The
process has the serious disadvantage that large amounts of
sulphides have to be separated, condensed and, on recycling

into the circuit, evaporated again. For this purpose, large
amounts of heat and cooling energies are required.
Typical catalysts which are used in industrial processes
for producing methyl mercaptan from methanol and hydrogen
sulphide exhibit high selectivities for the formation of
methyl mercaptan and lead to a comparatively low evolution
of dimethyl sulphide and dimethyl disulphide. A problem in
this connection is that these compounds accumulate in the
circuit when they are recycled into the process, since the
catalysts used in the prior art can only poorly establish
the equilibrium between methyl mercaptan and dimethyl
sulphide. This means that, in each case, at most a quarter
of the undesired newly formed sulphide is converted in the
case of recycling into the circuit.
As shown by DE-C 1193038, it is also possible to separate
the sulphide and to convert it in a separate reaction step
over a different catalyst to methyl mercaptan. However, it
is necessary to select a high excess of hydrogen sulphide
in order to achieve technically relevant conversions of
dimethyl sulphide. DE-C 1193038 describes a process in
which the sulphide formed, in an upstream reactor, together
with the total amount of hydrogen sulphide required, is
passed over a catalyst which efficiently establishes the
reaction equilibrium between sulphide and mercaptan
(precatalyst, e.g. MoO3/Al2O3). The reaction products
obtained are subsequently, after addition of methanol or
dimethyl ether, conducted over a main catalyst
(K2WO4/Al2O3)over which the alcohol or the ether reacts with
as yet unconverted hydrogen sulphide to give methyl
mercaptan.
As described in the abovementioned patent application, the
separation of reaction product and hydrogen sulphide in the
case of use of large hydrogen sulphide excesses is,
however, found to be difficult.

JP 58159456 relates to a methyl mercaptan process in which
the hydrogen sulphide conducted in the circuit is mixed
with fresh hydrogen sulphide, and the overall H2S stream is
subsequently divided between a methyl mercaptan reactor and
a DMS cleavage reactor. Upstream of the methyl mercaptan
reactor, one H2S substream is mixed with methanol, while
the second substream passes into the cleavage reactor with
the DMS. The product streams of the two reactors are
subsequently fed together to a product workup.
US 2831031 discloses catalysts based on pyrophosphoric acid
on titanium dioxide, over which dimethyl sulphide is
converted to methyl mercaptan with a maximum selectivity of
97% at a conversion of 42%. US 4005149 and JP 5246203
describe aluminium oxides doped with cobalt molybdate or
tungsten sulphide, with which dimethyl sulphide conversions
of, respectively, 41 and 88% and, respectively,
selectivities of 92 and 93% for methyl mercaptan can be
achieved. Further catalysts claimed in US 4313006 are
zeolites (X, Y, L) doped with sodium or potassium ions,
with which maximum methyl mercaptan selectivities of 65%
are achieved with a dimethyl sulphide conversion of 70%.
JP 58159456 relates to aluminium oxides modified with
phosphorus oxides and tungsten oxides, with which a maximum
DMS cleavage conversion of 4 0% can be achieved. The
H2S/DMS ratio in the reactant gas is 2 to 28 in the
abovementioned applications. Preference is given to
pursuing a high H2S/DMS ratio in order to achieve
sufficiently high DMS cleavage conversions. US 4005149
describes a process for catalytically cleaving organic
sulphides with hydrogen sulphide in the presence of
sulphactive catalysts. As a result of the addition of
carbon disulphide to the reaction mixture, the overall
conversion of sulphides to mercaptans can be increased. A
disadvantage of this process is the use of toxic carbon
disulphide in the process, which has to be separated again
from the reaction products in a costly manner. Generally,

in the cleavage of dialkyl sulphides to mercaptans with
hydrogen sulphide, high selectivities for mercaptan and the
maximum suppression of by-products are pursued. In
contrast, the decomposition of (poly)sulphides to
mercaptans, for example over aluminium oxides, without the
addition of hydrogen sulphide, is characterized by
comparatively low selectivities for methyl mercaptan and a
broad spectrum of by-products. Mashkina et al. describe,
for example, in React. Kinet. Catal. Lett., Vol. 70, No. 1,
183-189, 2000, the decomposition of dimethyl disulphide to
methyl mercaptan without H2S addition over acidic catalysts
with maximum methyl mercaptan selectivities of 87%.
According to Koshelev et al. [React. Kinet. Catal., Vol.
27, No. 2, 387-391 (1985)] for the cleavage of dimethyl
sulphide with hydrogen sulphide over γ-aluminium oxide, a
maximum activity is achieved when the catalysts have a
large number of aprotic Lewis acid sites and basic sites of
moderate strength. The catalysts based on 3.5% Na2O/Al2O3
described by Koshelev et al. exhibit, at a DMS conversion
of 9.5%, however, only maximum methyl mercaptan
selectivities of 82%, while methyl mercaptan selectivities
of 97% with a conversion of 3 8% are achieved over pure
γ-Al2O3.
It is an object of the invention to provide an economically
viable process, an apparatus and specific catalysts for
preparing methyl mercaptan from dialkyl sulphides and/or
dialkyl polysulphides and hydrogen sulphide.
The invention provides a process for continuously preparing
alkyl mercaptans by reacting a reactant gas comprising
dialkyl sulphides and/or dialkyl polysulphides with an at
least molar excess of hydrogen sulphide at elevated
temperature in the gas phase and
a) in the presence of a catalyst based on or consisting
of Al2O3, SiO2, TiO2, aluminosilicates, zeolites,

bentonites or aluminas, which contain at least 1% by-
weight of alkali metal oxide,
b) in a reactor which comprises at least n = 2 separate
catalyst zones, wherein
c) the predominant portion or the total amount of the
dialkyl sulphides and/or dialkyl polysulphides
mentioned is introduced into the reactor into the
first catalyst zone together with at least a portion
of the total amount of the hydrogen sulphide used, and
d) the remaining amount of the hydrogen sulphide and of
the dialkyl sulphides and/or dialkyl polysulphides is
metered in between the catalyst zones.
Alkyl means C1 to C5-alkyl, especially methyl. The poly-
sulphides have generally 2 to 6 sulphur atoms.
The process is preferably performed continuously.
Preferred examples of dialkyl sulphides and dialkyl
polysulphides which are reacted in accordance with the
invention with hydrogen sulphide to give alkyl mercaptan
are dimethyl sulphide, dimethyl disulphide, dimethyl
trisulphide, dimethyl tetrasulphide and dithiapentanes.
These (poly)sulphides may be metered into the process alone
or in a mixture with dimethyl sulphide. It is also possible
to meter alkyl ether compounds, for example dimethyl ether,
to the reactant gas, said alkyl ether compounds being
reacted with hydrogen sulphide to give methyl mercaptan.
Equation (1) illustrates, using the example of the cleavage
of dimethyl sulphide, that the reaction can be performed
without formation of by-products. The aim of the invention
is to perform the conversion to methyl mercaptan with a
selectivity for the reaction product of greater than 98%.
The formation of further by-products, for example carbon
disulphide, should as far as possible be suppressed.


Caused by the low exothermicity of the cleavage reaction,
the preheated reactant gas mixture which comprises hydrogen
sulphide and dialkyl (poly)sulphides can be converted to
methyl mercaptan in an adiabatic reactor. The reactant gas
mixture may also comprise dialkyl ethers or diaryl ethers,
especially dimethyl ether.
The molar ratios of hydrogen sulphide and the total amount
of dialkyl sulphide and dialkyl polysulphide range from 3:1
to 25:1, preferably 5:1 to 25:1, especially 10:1 to 25:1.
The reaction is preferably performed in a reactor in which
at least 2, especially 2 to 25, catalyst zones are
connected in series. The catalyst zones may be configured,
for example, as fixed beds or tube bundles filled with
catalyst. Optionally, it is also possible for a plurality
of individual apparatuses of this type to be connected in
series. The reactant mixture comprising gaseous or liquid
dialkyl sulphides and/or dialkyl polysulphides, hydrogen
sulphide and optionally further components is metered into
the reactor in such a manner that preferably the total
amount of dialkyl (poly)sulphides, upstream of the first
catalyst zone, is added with a portion which corresponds to
at least the nth part of the total amount of hydrogen
sulphide, while the remaining amount of hydrogen sulphide
is metered in between the catalyst zones. Optionally, it is
also possible to add the total amount of hydrogen sulphide
upstream of the first catalyst zone.
The product gas mixture can be separated by various known
processes. A particularly advantageous separation is
described in EP 0850923 B1, (US 5866721). Unconverted
dialkyl sulphide or dialkyl polysulphide is recycled into
the reactor.

Figure 1 shows the preferred embodiment of the reaction
apparatus for cleaving dialkyl (poly)sulphides to
mercaptans according to Claim 1. The gas comprising these
compounds is referred to as reactant gas or reactant
mixture and stems preferably from processes for preparing
methyl mercaptan from hydrogen sulphide and methanol. In
the reactor 1, n (n = 2-25) catalyst zones which consist of
a distributor chamber and a catalyst bed are accommodated.
Preference is given to using 3-10 catalyst zones. The
reactant mixture 2 comprising the alkyl (poly)sulphides
mentioned enters the first catalyst bed 8 through the
distributor chamber 7. This first catalyst bed is
optionally, in flow direction of the reactant gas, covered
first with a bed of inert materials. For example, aluminium
oxide spheres or ceramic Raschig rings may be used as inert
materials. Downstream of the inert bed is disposed the
catalyst bed. After leaving the first stage, the gas
mixture is enriched in the distributor chamber 9 with
hydrogen sulphide 10 or optionally the reactant mixture 2.
The gas mixture subsequently flows out of the distributor
chamber 9 into the second catalyst bed 11, and devices in
the distributor chamber 9 ensure turbulent flow and
complete mixing of the reactants which is distributed
uniformly over the entire area of the second catalyst bed.
The supply of hydrogen sulphide or optionally the reactant
gas mixture is effected analogously at n - 1, preferably
(where n > 2) at n - 2, injection points between the
downstream catalyst beds of the apparatus. Optionally, it
is possible to dispense with a supply of hydrogen sulphide
or reactant gas mixture upstream of the last catalyst bed
at injection point 12 in order to obtain full conversion in
the reaction. The last catalyst zone may optionally also be
configured longer than the other zones in order to enable
full conversion.
The process is also characterized in that the reactant gas
contains optionally at least 0.1% by volume, preferably 0.1

to 10% by volume, especially 1 to 10% by volume, of
hydrogen based on the total amount. These measures suppress
the formation of oligomers and polymers. In addition,
further secondary components, for example nitrogen, water,
carbon monoxide, carbon dioxide, carbonyl sulphide or
dialkyl ether, may be present in the reactant gas.
The dialkyl (poly)sulphides are converted to mercaptans
preferably over catalysts comprising alkali metal oxides at
a temperature of 100 to 600°C, preferably 150 to 450°C,
especially 300 to 430°C, and a pressure of 1.5 to 50 bar,
preferably 8 to 40 bar. The catalyst supports used may be
silicates, titanium oxides, zeolites, aluminas, aluminium
oxides and preferably 7-aluminium oxides. The supports have
preferably been modified with alkali metal oxides such that
the Lewis acidity, compared to the unmodified catalyst
support, is reduced in a controlled manner while
simultaneously increasing the Lewis basicity. Preference is
given to using 7-aluminium oxides containing 1-50% by
weight, preferably 2 to 20% by weight, of alkali metal
oxide as catalysts. Preference is given to using
7-aluminium oxides containing caesium oxide or rubidium
oxide in the process according to the invention as
catalysts. The catalysts are prepared, for example, by
means of the impregnation of the catalyst support with
suitable alkali metal salts, which are converted to the
corresponding oxides by thermal decomposition. Preference
is given to using alkali metal nitrates, carbonates or the
alkali metal salts of carboxylic acids. The catalysts are
subsequently dried and optionally calcined at temperatures
of 50 to 600°C.
In a particular embodiment, the catalyst comprises oxidic
compounds of one or more transition metals of atomic
numbers 21 to 80, especially of V, Mn, Fe, Co, Ni, Cu, Zn,
Zr, Nb, Mo or W.

These metals may also be present in the form of phosphates
or pyrophosphates.
Before they are used for the first time, the catalysts are
advantageously sulphidated in a hydrogen sulphide stream at
a temperature of at least 100°C for at least 1 h.
Fig. 1 shows one embodiment of the reactor according to
Claim 1.
Figure 2 shows the test results of the cleavage of dimethyl
sulphide to methyl mercaptan in the presence of hydrogen
sulphide over catalysts based on Rb20-γ-Al2O3, under the
conditions of p = 9 bar and H2S/DMS = 14/1.
Figure 3 shows the test results for the cleavage of
dimethyl sulphide to methyl mercaptan in the presence of
hydrogen sulphide in a reactor with two catalyst zones and
H2S feeding upstream of the two catalyst zones in the
presence of different catalysts.
Example 1 shows, by way of example, the synthesis of the
catalysts, while Example 2 describes the catalytic cleavage
of dimethyl sulphide to methyl mercaptan.
Example 1:
Preparation of M2O-Al2O3 (M = Li, Na, K, Rb, Cs)
49.66 g of LiNO3 were dissolved in 300 ml of distilled
water. The solution was heated to approx. 60°C, such that
the salt had dissolved completely. 50 g of y-aluminium
oxide were added to the solution with stirring. The
solution was subsequently stirred for approx. 60 min. The
catalyst was stirred at a temperature of at least 60°C,
optionally under reduced pressure, until the complete
amount of liquid had been absorbed into the support. The
catalyst was dried under air at approx. 12 0°C overnight,
and then calcined at 500°C in an air stream for 3 h.

Example 2
The DMS cleavage was studied in a temperature range of
100-500°C and a pressure of 1.5 - 25 bar. The ratio of
hydrogen sulphide to dimethyl sulphide (DMS) in the
reactant gas was varied in the range of 1:1 - 25:1.
Before the start of the reaction, the fresh catalysts were
first sulphidated in the reactor at 350°C for 2.5 h in a
hydrogen sulphide stream. Figure 2 shows, for Rb2O-Al2O3
(spheralite) a comparison of the dimethyl sulphide cleavage
conversions to methyl mercaptan as a function of the
temperature with classical "overhead feeding" (fixed bed
reactor with one catalyst zone) and in "two-zone
operation", i.e. the H2S stream, similarly to a staged
reactor with H2S intermediate feeding, was fed in upstream
of the two catalyst zones. In both cases, the total H2S to
DMS ratio was 14:1. The space velocities and gas loadings
were identical in both cases. Figure 2 illustrates that, in
the inventive apparatus, over the catalysts which have been
modified with alkali metal oxides and are claimed in this
application, significantly higher DMS cleavage conversions
can be achieved than in conventional "one-zone operation",
for example in a conventional fixed bed reactor.
Figure 3 shows the positive influence of the increasing
Lewis basicity of the catalysts in the inventive apparatus
in "two-zone operation". With Cs2O-Al2O3 catalysts, both in
"one-zone" and "two-zone operation", significantly higher
cleavage conversions were achieved than with catalysts
based on Li2O-Al2O3. The overall selectivity for methyl
mercaptan in all cases is 100%, i.e. no by-products were
detected. Among other catalysts, Cs2O-Al2O3 catalysts with
different Cs2O loadings were synthesized (5 - 10% by
weight). As is evident to those skilled in the art,
modification with regard to 7-Al2O3 source, performance of
the impregnation, dispersion of the alkali metal oxides,
porosity and BET surface area of the catalyst and

performance of the catalyst conditioning or sulphidation
can achieve even higher DMS cleavage conversions.
The economic viability of the overall process depends
crucially on the product selectivity for methyl mercaptan
based on the carbon source used (e.g. methanol). It is
evident from the above that sulphides, for example dimethyl
sulphide, can be converted to methyl mercaptan with high
yields, which increases the overall selectivity of the
preparation of methyl mercaptan. A particular advantage of
the invention is that dialkyl (poly)sulphides, which would
otherwise have to be incinerated as by-products or disposed
of in a costly manner, can be utilized in a technically
simple and inexpensive transformation as a raw material for
methyl mercaptan. Moreover, in the process according to the
invention, no toxic carbon disulphide or other by-products
are formed.
The methyl mercaptan formed is removed from the product gas
mixture together with the methyl mercaptan from the first
process step (for example reaction of methanol with
hydrogen sulphide), as explained in DE 1768826 (GB
1268842), in several distillation and scrubbing columns at
temperatures between 10 and 14 0°C.

We-Claim;
1. Process for continuously preparing alkyl mercaptans by
reacting reactant gas comprising dialkyl sulphides
and/or dialkyl polysulphides with an at least molar
excess of hydrogen sulphide at elevated temperature in
the gas phase and
a) in the presence of a catalyst based on or
consisting of Al2O3, SiO2, TiO2, aluminosilicates,
zeolites, bentonites or aluminas, which contain
at least 1% by weight of alkali metal oxide,
b) in a reactor which comprises at least n = 2
separate catalyst zones, wherein
c) the predominant portion or the total amount of
the dialkyl sulphides and/or dialkyl
polysulphides mentioned is introduced into the
reactor upstream of the first catalyst zone
together with at least a portion of the total
amount of the hydrogen sulphide used, and
d) the remaining amount of the hydrogen sulphide and
of the dialkyl sulphides and/or dialkyl
polysulphides is metered in between the catalyst
zones,
e) and the reactant gas mixture may also comprise
dialkyl ethers which react with hydrogen sulphide
to give alkyl mercaptans and hence increase the
overall selectivity of the process.

2. Process according to Claim 1, in which the reactant
gas additionally comprises dialkyl ethers.
3. Process according to Claim 1 or 2, in which the total
amount of the dialkyl sulphides and/or dialkyl
polysulphides is introduced into the reactor into the

first catalyst zone together with at least the nth
part of the hydrogen sulphide used.
4. Process according to Claim 1, 2 or 3, in which
catalysts consisting of γ-Al2O3 which contains at least
1% by weight of an alkali metal oxide are used.
5. Process according to Claims 1 to 4, in which catalysts
which contain at least 1% by weight of an alkali metal
oxide selected from the group of Cs or Rb are used.
6. Process according to Claims 1 to 5, in which the
catalysts are modified with compounds of transition
metals.
7. Process according to Claim 1, characterized in that
the catalyst zones of the reactor are configured as
fixed beds, tube bundles or fluidized beds.
8. Process according to Claims 1 to 7, in which a
plurality of the reactors are connected in series.
9. Process according to Claims 1 to 8, in which the molar
ratio of hydrogen sulphide to the total amount of
dialkyl sulphide and dialkyl polysulphide is in the
range of 3:1 to 25:1.
10. Process according to Claims 1 to 9, in which reactant
gas which comprises dialkyl sulphides and/or dialkyl
polysulphides and is obtained as a by-product in the
preparation of alkyl mercaptan is used.
11. Process according to Claims 1 to 10, characterized in
that the reactant gas contains at least 0.1% hydrogen.
12. Process according to Claims 1 to 11, characterized in
that the catalysts, before being used for the first
time, are sulphidated at a temperature of at least
100°C in a hydrogen sulphide stream for at least 1 h.

13. Process according to Claims 1 to 11, characterized in
that the reaction is effected at a temperature of 100
to 600°C, preferably 300 to 430°C, and a pressure of
1.5 to 50 bar, preferably 8 to 40 bar.

The invention relates to a method for the continuous production of methyl
mercaptan by reacting an educt mixture containing dialkyl sulfides and dialkyl
polysulfides, with hydrogen sulfide in order to form methyl mercaptan.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=S/T7Gi3L5O9KKpwrzTT4Xg==&loc=wDBSZCsAt7zoiVrqcFJsRw==


Patent Number 268489
Indian Patent Application Number 3201/KOLNP/2009
PG Journal Number 36/2015
Publication Date 04-Sep-2015
Grant Date 31-Aug-2015
Date of Filing 09-Sep-2009
Name of Patentee EVONIK DEGUSSA GMBH
Applicant Address RELLINGHAUSER STRASSE 1-11, 45128 ESSEN, GERMANY
Inventors:
# Inventor's Name Inventor's Address
1 REDLINGSHÖFER, HUBERT STEIGERWALDSTR. 9, 91481 MÜNCHSTEINACH, GERMANY
2 BARTH, JAN-OLAF ZIEGELHÜTTENWEG 23, 60598 FRANKFURT, GERMANY
3 WECKBECKER, CHRISTOPH AUGUST-IMHOF-STR., 63584 GRÜNDAU-LIEBLOS GERMANY
4 HUTHMACHER, KLAUS LÄRCHENWEG 18, 63571 GELNHAUSEN, GERMANY
PCT International Classification Number C07C319/06; C07C319/08; C07C321/04
PCT International Application Number PCT/EP2008/050464
PCT International Filing date 2008-01-16
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10 2007 007 458.3 2007-02-15 Germany