Synthesis of methylmercaptan from methanol and hydrogen sulfide at elevated pressure on an industrial catalyst

Article abstract of DOI:10.1134/S0965544106010063

The catalytic reaction of methanol with hydrogen sulfide at a total pressure of 0.1-1.8 MPa was investigated. The main product at different values of total pressure in the system was methylmercaptan, and the by-products were dimethyl sulfide, dimethyl ether, carbon oxides. An increase in the contact time increased the yields of methylmercaptan and dimethyl sulfide, whereas the yields of dimethyl ether and gases changed slightly. The selectivity for methylmercaptan was approximately constant up to a ～95% conversion of methanol. The elevation in temperature increased the reaction rate but barely affected the product formation selectivity. The rate of methanol conversion increases linearly with the hydrogen sulfide concentration and depends on the methanol concentration raised to a power of 0.4-0.5; water retards the process. The selectivity for methylmercaptan decreases, and that for dimethyl sulfide and dimethyl ether increases at an H₂S to methanol molar ratio below 1.4 : 1, regardless of the value of total pressure. The reaction rate increases with the total pressure raised to a power 0.4-0.5; however, the selectivities for methylmercaptan and by-products remain unchanged. MAIK "Nauka/Interperiodica".

Full text of DOI:10.1134/S0965544106010063

ISSN 0965-5441, Petroleum Chemistry, 2006, Vol. 46, No. 1, pp. 28–33. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Original Russian Text © A.V. Mashkina, 2006, published in Neftekhimiya, 2006, Vol. 46, No. 1, pp. 31–36.
Synthesis of Methylmercaptan from Methanol
and Hydrogen Sulfide at Elevated Pressure
on an Industrial Catalyst
A. V. Mashkina*
Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 5, Novosibirsk, 630090 Russia
*e-mail: amash@catalysis.nsk.su
Received September 5, 2004
Abstract—The catalytic reaction of methanol with hydrogen sulfide at a total pressure of 0.1–1.8 MPa was
investigated. The main product at different values of total pressure in the system was methylmercaptan, and
the by-products were dimethyl sulfide, dimethyl ether, carbon oxides. An increase in the contact time
increased the yields of methylmercaptan and dimethyl sulfide, whereas the yields of dimethyl ether and gases
changed slightly. The selectivity for methylmercaptan was approximately constant up to a ~95% conversion
of methanol. The elevation in temperature increased the reaction rate but barely affected the product forma-
tion selectivity. The rate of methanol conversion increases linearly with the hydrogen sulfide concentration
and depends on the methanol concentration raised to a power of 0.4–0.5; water retards the process. The selec-
tivity for methylmercaptan decreases, and that for dimethyl sulfide and dimethyl ether increases at an H2S to
methanol molar ratio below 1.4 : 1, regardless of the value of total pressure. The reaction rate increases with
the total pressure raised to a power 0.4–0.5; however, the selectivities for methylmercaptan and by-products
remain unchanged.
DOI: 10.1134/S0965544106010063
Methylmercaptan (methanethiol, MeSH) is an H2S, on the product formation rates, and on the selec-
tivity of the process is lacking.
industrially important chemical used for the production
of valuable thio compounds, in particular, methionine
(a drug and feed additive). At present, MeSH is synthe-
sized from methanol and hydrogen sulfide, primarily,
over potassium- and tungsten-modified alumina as a
catalyst. The catalyst mainly favors the formation of
MeSH, but by-processes yielding dimethyl ether
(DME), dimethyl sulfide (DMS), and carbon oxides
also proceed. The reaction conditions temperature, con-
centration of the reactants, and their feed space velocity
influence the performance of the MeSH synthesis pro-
cess [1–5]. The process is carried out in the temperature
range of 320–420°ë at either atmospheric or elevated
pressure. Reported in the literature [1, 2, 4, 5] are only
the results of methanol reaction with hydrogen sulfide
at atmospheric pressure. Surveying the industrial-scale
production of mercaptans, Forquy and Arretz [3] noted
that the process of methylmercaptan synthesis from
methanol and ç2S is carried out at P = 0.7–1.2 MPa for
engineering reasons. They reported a plot of the tem-
perature dependence of methanol conversion at P = 0.1
and 0.3 MPa and two values of space velocity of meth-
anol. Analyzing these limited data, one may conclude
that the methanol conversion at P = 0.3 MPa is some-
what higher than that at P = 0.1 MPa. Information con-
cerning the influence of pressure on the direction of cat-
alytic transformation of methanol in the presence of
In this work, we experimentally investigated the
behavior of the methanol reaction with hydrogen sul-
fide at an elevated pressure in the presence of the indus-
trial catalyst IKT-31-1.
1
EXPERIMENTAL
Hydrogen sulfide (99.5% purity) was obtained by
the reaction of hydrogen with sulfur on an AlNiMo cat-
alyst; organic substances used in the work were com-
mercial chemicals of chemically pure and reagent
grades. The experiments were carried out in a flow
reactor with a fixed IKT-31-1 catalyst bed. A mixture of
H2S and helium was sent through a pressure regulator
to a temperature-controlled saturator filled with metha-
nol. Then, the saturated gas arrived to a catalytic reactor
heated with a low thermal-inertia furnace and further to
a chromatograph. The temperature of the system was
T = 170°C. The initial mixture and the products were
periodically sampled in 15-min intervals with a six-way
cock. Their analysis was carried out on a “Tsvet-500”
chromatograph with a katharometer (a column of
1
The author is indebted to L.G. Sakhaltueva for taking part in the
experiment.
28

SYNTHESIS OF METHYLMERCAPTAN
29
Table 1. Influence of the contact time on the methanol conversion and product yields at different total pressures. T = 360°C,
[MeOH]0 = 4.5–4.7 vol %, M = 1.7–1.8
Yield, mol %
P, MPa
τ, s
X, %
MeSH
DMS
DME
CH4
CO2
CO
0.10
1.2
2.9
9.0
0.6
1.1
1.4
0.4
0.8
1.3
0.2
0.3
1.2
0.3
0.5
0.8
0.3
0.6
0.9
0.2
0.3
0.6
50
75
91
47
76
89
45
70
78
40
59
81
51
68
94
57
76
90
53
68
91
46
69
84
44
72
85
43
66
74
38
56
77
45
61
85
52
70
82
48
63
83
0.7
1.5
2.2
0.6
1.2
1.8
0.2
0.7
1.1
0.2
0.7
1.2
0.4
1.0
1.9
0.7
1.4
1.9
0.4
0.7
1.4
2.0
1.8
0.9
0.8
0.5
0.2
0.7
0.6
0.5
0.7
0.6
0.2
2.2
2.4
2.6
2.1
2.0
1.9
1.9
1.8
1.6
0.01
0.10
0.50
0.01
0.02
0.02
0.01
0.01
0.01
0.02
0.10
0.20
0.02
0.02
0.10
0.02
0.01
0.10
0.01
0.02
0.02
0.2
0.4
0.6
0.1
0.2
0.3
0.1
0.2
0.2
0.2
0.4
0.3
0.3
0.3
0.3
0.2
0.4
0.5
0.3
0.2
0.3
0.02
0.10
0.30
0.02
0.01
0.02
0.02
0.01
0.01
0.30
0.50
0.90
0.10
0.40
0.30
0.02
0.03
0.02
0.01
0.02
0.50
0.18
0.62
1.00
1.22
1.53
1.80
2 m × 3 mm in size packed with Porapak Q+R(1 : 1)
phase). The analysis error was 5 rel. %.
RESULTS AND DISCUSSION
The experiments were conducted at T = 325–380°ë
and a total pressure of 0.10–1.80 MPa; the starting
methanol and hydrogen sulfide concentration in the ini-
tial gas mixture varied within 1.3–14.7 and 2.0–
25.0 vol %, respectively; and the H2S : methanol molar
ratio (M) was 0.5–14.7.
From the analysis results, we calculated the metha-
nol conversion (X,%), product yields as the number of
moles of the product formed from one mole of metha-
nol (Y, mol %), and selectivity (S, %) defined as the
ratio of the product yield in percent of the theoretical
yield to the methanol conversion. The methanol conver-
sion rate (w, mmol/h(g cat)) was determined at a defi-
nite degree of conversion of methanol. The estimated
contact time is equal to the ratio of the catalyst volume
(cm3) to the rate of gas flow (cm3/s) at atmospheric
pressure and room temperature.
The products under the given conditions were meth-
ylmercaptan, water, dimethyl sulfide, dimethyl ether,
methane, and carbon oxides. In all experiments, the
yield of water was equal to the degree of methanol con-
version within the limits of experimental accuracy, and
the conversion of ç2S was equal to that of methanol
minus the doubled yield of dimethyl ether.
PETROLEUM CHEMISTRY Vol. 46 No. 1 2006

30
X, %
MASHKINA
kinetically controlled. At constant temperature, total
pressure, and reactant concentration, the methanol con-
version grew, approaching 100% with an increase in the
contact time. The yield of MeSH increased to a certain
value with the contact time and then changed little; the
yield of dimethyl sulfide increased somewhat in this
case and that of dimethyl ether did not change or it
decreased. Methane and carbon oxides were formed
with low yields (0.01–0.6 mol %), and their yields
slightly changed with an increase in the contact time
(Table 1, Fig. 1). With varying methanol conversion up
to X ≤ 95%, the MeSH selectivity remained practically
unchanged, the selectivity for DMS somewhat
increased, and that for DME decreased (Fig. 2). The
same trends were observed at different values of total
pressure including atmospheric. It is likely that, as in
the case of atmospheric pressure [6,7], the products are
formed as a result of parallel–consecutive processes:
methanol dehydration leads to DME formation, and the
reaction of ç2S with methanol or DME yields MeSH,
which converts further to DMS.
1
2
100
Y, mol%
60
3
2
1
20
4
4
τ, s
1
2
3
Fig. 1. Influence of the contact time on (1) methanol conver-
sion and the yields of (2) MeSH, (3) DMS, and (4) DME at
T = 360°ë, P = 1.0 MPa, [åÂéç] = 4.7 vol %, M = 1.7,
0
and d
= 0.25–0.5 mm.
cat. grain
On the catalyst with an average grain size of
0.25−0.5 mm, the reaction rate did not change with a
decrease in the catalyst grain size, i.e., the process was
CH3OH
(CH3)2S + H2O
H2S
CH3SH
(SH3)2S + H2S
CH3OH
H2S
(CH3)2O
–H2O
Partial degradation of DME and methanol leads to the performance of the process. As it is seen, an increase of
release of carbon oxides and methane; methane can
also result from MeSH and DMS degradation.
the initial reactant concentrations leads to a growth in
the rate of methanol conversion. We also observed an
increase in the reaction rate with an increase in the cur-
To elucidate the influence of the reaction conditions
on the performance characteristics of the process, we
determined the contact time corresponding to 60%
methanol conversion from the kinetic curves at T =
360°ë and calculated the methanol conversion rate and
product formation selectivity. Tables 2 and 3 list the
data on the influence of the initial methanol ([MeOH]0)
and hydrogen sulfide ([H2S]0) concentrations on the
rent concentration of methanol (CMe) or ç2S (CH S ).
2
For example, the reaction rate increased proportionally
to CMe raised to a power of 0.4–0.5 on the catalyst with
a grain size of dgrain = 0.25–0.5 mm at P = 1.0 MPa and
[H2S] of ~7.6 or ~20 vol %; the same results were also
obtained at P = 0.1 MPa (Fig. 3).
S, %
lgw
1
2
100
1
1.2
3
0.8
0.4
60
20
S, %
4
3
10
5
2
0
0.2
0.4
0.6
0.8
1.2
logCåÂ
30
50
70
90
X, %
Fig. 3. Log–log plot of the rate of methanol conversion
(w, mmol/h(g(Cat)) at T = 360°C versus the current metha-
Fig. 2. Selectivity for (1) MeSH, (2) DMS, and (3) DME at
different degrees of methanol conversion: T = 360°ë, P =
nol concentration (C ). Pressure is 1.0 (1–3) and 0.1 MPa
Me
1.0 MPa, [åÂéç] = 4.7 vol %, M = 1.7, and d
=
(4); [H S] = 20.1 (1) and 7.5–7.8 vol % (2–4); d
=
0
cat. grain
2
0
cat. grain
0.25–0.5 mm.
0.25–0.5 (1, 2, 4) and 4–6 mm (3).
PETROLEUM CHEMISTRY Vol. 46 No. 1 2006

SYNTHESIS OF METHYLMERCAPTAN
31
Table 2. Influence of the initial methanol concentration on Table 3. Influence of the starting H2S concentration on the
the reaction rate and the product selectivity. T = 360°C
reaction rate and the product selectivity. T = 360°C,
[MeOH]0 = 4.5–4.7 vol %
Selectivity, %
[MeOH]0,
vol %
w,
M
Selectivity, %
mmol/h(g Cat)
[H2S]0,
vol %
w,
MeSH DMS DME
M
mmol/h(g Cat)
MeSH DMS DME
dgrain = 0.25–0.5 mm, P = 1.0 MPa, [H2S]0 = 20.4 vol %
dgrain = 0.25–0.5 mm, P = 1.0 MPa
1.3
3.0
4.5
7.7
14.7
7.2
4.2
2.8
9.0
15.7
17.5
23.2
98
98
98
97
2.3
1.3
1.6
1.7
0
0
0
0
2.4
6.9
0.7
1.4
1.7
4.1
3.2
8.6
89
95
95
98
8.7
2.7
2.7
1.6
2.3
2.0
2.0
0
9.1
12.4
22.0
dgrain = 0.25–0.5 mm, P = 1.0 MPa, [H2S]0 = 7.6 vol %
25.0
1.8
4.6
7.0
9.9
4.2
1.7
1.1
0.7
8.9
12.4
15.0
17.0
95
95
88
82
2.0
2.7
2.3
3.0
3.0
2.0
dgrain = 4–6 mm, P = 1.0 MPa
2.5
7.8
0.5
1.7
4.5
2.7
5.7
93
95
98
5.2
4.0
1.3
0
0
0
8.7
13.0
20.7
12.0
dgrain = 4–6 mm, P = 1.0 MPa, [H2S]0 = 7.8 vol %
dgrain = 0.25–0.5 mm, P = 0.1 MPa
1.9
4.7
7.2
4.2
1.7
1.1
3.5
5.6
6.8
96
95
91
2.5
4.0
7.0
0
0
0
4.3
5.6
1.0
0.9
1.7
2.1
4.1
1.6
1.8
3.0
4.0
8.1
72
72
92
94
95
8.1
5.7
3.0
2.0
2.4
18.0
21.0
5.0
9.6
dgrain = 0.25–0.5 mm, P = 0.1 MPa, [H2S]0 = 7.5 vol %
12.3
24.3
4.0
5.0
7.1
1.5
1.1
0.6
0.5
2.0
2.4
3.0
3.2
84
80
72
64
2.5
4.0
5.0
6.0
12
15
23
28
2.1
dgrain = 4–6 mm, P = 0.1 MPa
12.5
14.7
2.0
6.5
8.6
0.6
1.3
1.7
0.7
1.6
2.2
86
94
97
6.7
2.2
1.3
6.7
2.8
1.0
From the data presented in Table 2, it follows that, at
[H2S]0 = 7.6 vol % in the reaction mixture, the selectiv-
ity for MeSH decreased from 95 to 82% with the
increase in methanol content; the selectivity for DMS
increased insignificantly and that for DME slightly
grew; at larger [H2S]0 (20.4 vol %), a change in the
methanol concentration did not affect the MeSH and
DMS selectivity and DME was not produced. At P =
0.1 or 1.0 MPa and constant [MeOH]0, an increase in
the current H2S concentration in the reaction mixture
increases almost proportionally to the reaction rate
(Fig. 4). An increase of the H2S content enhances the
selectivity for MeSH and decreases that for DMS and
DME (Table 3). A variation of methanol and H2S con-
centrations had practically no effect on the selectivity
for gases, which remained at the level of 0.02–0.5%.
The addition of water to methanol retarded the process;
the rate of methanol conversion decreased linearly with
an increase in the water content (Fig. 5a), with the
selectivity for all products being constant.
Table 4. The reaction of methanol with H2S at different
pressures. T = 360°C, [MeOH]0 = 4.5–4.7 vol %, M = 1.7–1.8
Selectivity, %
w, mmol/h(g Cat)
P, MPa
at X = 60%
MeSH
DMS
DME
0.10
0.18
0.33
0.40
0.51
0.62
1.00
1.22
1.53
1.81
3.0
5.3
94
94
95
95
95
95
95
88
90
90
2.0
2.3
2.4
2.0
1.3
1.7
2.7
2.7
3.3
2.1
4.0
3.0
3.0
3.0
3.0
2.7
2.0
8.0
6.5
6.6
6.8
7.5
8.6
9.4
12.4
14.0
16.8
18.1
The reaction of methanol with H2S was investigated
at constant initial concentrations of the reactants but at
different total pressures. It was found that an increase in
the total pressure resulted in an increase of methanol
PETROLEUM CHEMISTRY Vol. 46 No. 1 2006

32
MASHKINA
logw
logw
logw
1
2
(a)
(b)
1.4
1.2
2
1.2
1.0
0.6
0.8
0.4
3
1
3
0.1 0.3 0.5 logCH O
0.2 0.6 1.0 logP+1
0.8
0.4
0
2
4
Fig. 5. Log–log plots of the rate of methanol conversion (w,
mmol/h(g Cat)) at T = 360°ë, [åÂéç] = 4.5–4.7 vol %,
M = 1.7–1.8 versus (a) the current water concentration
0
(CH O ) and (b) the total pressure; d
= 0.25–0.5
cat. grain
2
(1, 2) and 4–6 mm (3).
logw
1.4
1.0
0.6
0.2
0.6
1
logCH S
2
Fig. 4. Log–log plot of the rate of methanol conversion (w,
mmol/h(g Cat)) at T = 360°ë versus the current hydrogen
sulfide concentration (CH S ). Pressure is 1.0 (1, 2) and
2
0.1 MPa (3, 4); d
= 0.25–0.5 (1, 3) and 4–6 mm (2, 4).
cat. grain
conversion rate following the power law with an index
of 0.4–0.5 (Fig. 5b), wherein the selectivity for MeSH
somewhat decreased, that for DMS remained approxi-
mately constant, and the DME selectivity somewhat
increased (Table 4). The gas formation rate was practically
unaffected by variation in the pressure of the system.
1/T × 104
15.4
15.8
16.2
16.6
Fig. 6. Dependence of the logarithmic rate of methanol con-
version (w, mmol/h(g Cat)) on the inverse temperature. P =
1.0 MPa, [MeOH] = 4.6–4.9 vol %, M = 1.6, d
=
0
cat. grain
0.25–0.5 mm.
When the catalyst used had coarse (dgrain = 4–6 mm)
grains, the trends in the methanol conversion rate with
varying reactant concentrations and total pressure in the
system were close to those found for the crushed cata-
lyst (dgrain = 0.25–0.5 mm) (Tables 1, 2, Figs. 3–5),
although the process on the coarse-grained catalyst pro-
ceeds in the inner-diffusion region, as shown experimen-
different depths of methanol conversion was deter-
mined as the ratio of observed rates of methanol con-
version on the large and small grain catalysts with the
assumption that the entire inner surface of small-grain
catalyst is available for the initials. The results are given
in Table 5. It is seen that at different depths of methanol
tally. The degree of usage of the catalyst surface (η) at conversion, similar trends are observed but the degree
Table 5. Degree of utilization of surface area (η) of an intact catalyst grain at different methanol conversions, T = 360°C,
[MeOH]0 = 4.6–4.7 vol %, M = 1.7–1.8
P = 0.1 MPa
w, mmol/h(g Cat)
dgrain = 0.25–0.5 mm dgrain = 4–6 mm
P = 1.0 MPa
w, mmol/h(g Cat)
dgrain = 0.25–0.5 mm dgrain = 4–6 mm
X, %
η
η
40
50
60
70
80
90
4.2
4.1
3.0
2.5
1.6
0.8
1.9
1.8
1.6
1.3
1.0
0.6
0.45
0.44
0.53
0.52
0.62
0.75
20.0
19.2
13.4
9.7
7.6
6.3
5.7
4.7
3.5
2.5
0.38
0.33
0.42
0.48
0.51
0.66
6.8
3.8
PETROLEUM CHEMISTRY Vol. 46 No. 1 2006

SYNTHESIS OF METHYLMERCAPTAN
33
Table 6. Influence of temperature on the rate of methanol
conversion and the product selectivity. P = 1.0 MPa;
[MeOH]0 = 4.6–4.9 vol %, M = 1.6, dgrain = 0.25–0.5 mm
between methanol and ç2S increases almost linearly
with the ç2S concentration and, to a smaller extent,
with the methanol concentration. Elevation of the total
pressure of the system and the reaction temperature
leads to a growth in the reaction rate but barely affects
the product selectivity. At a low ç2S : methanol ratio,
the selectivity for MeSH decreases and that for DMS
and DME increases. It is advisable to conduct the syn-
thesis of methanethiol from methanol and ç2S at an
ç2S : methanol molar ratio of at least 1.4 : 1 and at an
elevated pressure.
Selectivity, %
w, mmol/h(g Cat)
T, °C
at X = 60%
MeSH
DMS
DME
325
340
360
375
380
4.3
4.8
95
95
95
97
97
2.0
1.3
2.7
1.3
2.7
2.3
2.7
2.0
1.7
0.3
12.4
16.3
17.0
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Des. Dev. 1, 271 (1962).
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reactant concentrations were maintained constant, eleva-
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ing practically unchanged (Table 6). The value of the
apparent activation energy determined from the plot of the
logarithmic reaction rate against the inverse temperature at
XMe = 60% (Fig. 6) was 80 10 kJ/mol.
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PETROLEUM CHEMISTRY Vol. 46 No. 1 2006