METHOD FOR DRYING METHYL MERCAPTAN BY MEANS OF AZEOTROPIC DISTILLATION
20240043377 ยท 2024-02-08
Assignee
Inventors
Cpc classification
C07C319/08
CHEMISTRY; METALLURGY
International classification
Abstract
The present invention relates to a process for drying methyl mercaptan, notably by azeotropic distillation, comprising the following steps: 1) a stream (A) comprising methyl mercaptan and water is introduced into a distillation column (1); 2) said stream (A) is distilled in said column (1); 3) the distillate (B) is recovered in gaseous form, preferably at the top of the column; 4) the distillate (B) is condensed, preferably in a condenser (2), so as to obtain a condensate (C) in liquid form; 5) said condensate (C) is separated, preferably using a decanter (3), so as to obtain two separate liquid phases: an aqueous phase (D); and an organic phase (E) comprising methyl mercaptan; 6) all or part of the organic phase (E) is optionally introduced into the distillation column (1) as reflux; and 7) a stream (F) comprising the dried methyl mercaptan is recovered, preferably at the bottom of column (1).
The present invention also relates to processes for producing methyl mercaptan comprising said drying process.
Claims
1. A process for drying methyl mercaptan, comprising the following steps: 1) a stream (A) comprising methyl mercaptan and water is introduced into a distillation column (1); 2) said stream (A) is distilled in said column (1); 3) the distillate (B) is recovered in gaseous form, preferably at the top of the column; 4) the distillate (B) is condensed, preferably in a condenser (2), so as to obtain a condensate (C) in liquid form; 5) said condensate (C) is separated, preferably using a decanter (3), so as to obtain two separate liquid phases: an aqueous phase (D); and an organic phase (E) comprising methyl mercaptan; 6) all or part of the organic phase (E) is optionally introduced into the distillation column (1) as reflux; and 7) a stream (F) comprising the dried methyl mercaptan is recovered, preferably at the bottom of the column (1).
2. The drying process according to claim 1, in which the distillation of step 2) is performed at a pressure of between 0.05 and 75 bar absolute, preferably between 1 and 30 bar absolute, more preferentially between 5 and 15 bar absolute.
3. The drying process according to claim 1, in which the distillation of step 2) is performed at a temperature of between 20 C. and 200 C., preferably between 60 C. and 100 C., more preferentially between 65 C. and 95 C.
4. The drying process according to claim 1, in which the distillation of step 2) is an azeotropic distillation.
5. The drying process according to claim 1, in which stream (A) comprises at least 90%, preferably at least 95%, more preferentially at least 98%, for example at least 98.5%, or even at least 99% by weight of methyl mercaptan, relative to the total by weight of methyl mercaptan and water.
6. The drying process according to claim 1, in which the amount of water in stream (F) is between 0 and 1500 ppm, preferably between 0 and 1000 ppm, more preferentially between 40 and 800 ppm, relative to the total by weight of methyl mercaptan and water.
7. The drying process according to claim 1, in which, when step 6) is performed, the reflux ratio is between 0 and 0.99, preferably between 0 and 0.60.
8. The drying process according to claim 1, in which stream (A) is connected to a unit for producing methyl mercaptan from methanol and hydrogen sulfide.
9. The drying process according to claim 1, in which stream (A) is connected to a unit for producing methyl mercaptan from carbon oxide, hydrogen (H.sub.2), hydrogen sulfide (H.sub.2S) and/or sulfur (S).
10. A process for producing methyl mercaptan, comprising the following steps: a) reacting methanol with hydrogen sulfide to form a stream (M), preferably in gaseous form, comprising methyl mercaptan, water, and possibly unreacted H.sub.2S and sulfur byproducts; b) optionally, said stream (M) is condensed; c) at least one step of purification of said stream (M) is performed to obtain a stream enriched in methyl mercaptan; d) the stream obtained in step c) is dried via the drying process of claim 1.
11. The use of azeotropic distillation for drying methyl mercaptan.
Description
DESCRIPTION OF THE FIGURES
[0224]
[0225]
[0228] The organic phase (E) then serves as reflux for the distillation column (1).
[0229] The dried methyl mercaptan is recovered at the bottom of column (1) (stream (F)).
[0230]
[0231]
[0232] The reaction step a) is performed in a reactor (I) using methanol and H.sub.2S.
[0233] Stream (M) leaving the reactor (I) comprises MeSH, water, H.sub.2S and sulfur byproducts.
[0234] Stream (M) is condensed in a condenser (II). It is then separated in a decanter (III) into three streams: [0235] a stream (N) comprising H.sub.2S; [0236] a stream (O) comprising water; and [0237] a stream (P) comprising MeSH, water, H.sub.2S and sulfur byproducts.
[0238] Stream (P) is distilled in a distillation column (IV) to remove the H.sub.2S (stream (R) at the top of the column) and to obtain a stream (S) at the bottom of the column comprising MeSH, water and sulfur byproducts. Stream (S) is then distilled in a distillation column (V) to obtain a stream (U) at the bottom of the column comprising the sulfur byproducts and a stream (T) at the top of the column comprising the MeSH and the water. Stream (T) is then separated in a decanter (VI) into a stream (V) comprising MeSH and water and a stream (W) comprising water.
[0239]
[0240]
[0241] A stream (H) comprising CO, hydrogen and H.sub.2S is introduced in gaseous form into a reactor I-ox so as to recover at the outlet a stream (J) comprising methyl mercaptan, water and possibly CO, CO.sub.2, H.sub.2, unreacted H.sub.2S and carbonyl sulfide (COS).
[0242] Stream (J) is condensed and then separated in the condenser II-ox so as to obtain a stream (J) in liquid form enriched in methyl mercaptan and a stream (J) in gaseous form comprising CO, CO.sub.2, H.sub.2, unreacted H.sub.2S and carbonyl sulfide (COS);
[0243] Stream (J) is then recycled into the reactor I-ox. The following are then separated in a decanter III-ox, from stream (J): [0244] an organic phase (K) comprising methyl mercaptan and water; and [0245] an aqueous phase (L).
[0246] Stream (K) is then dried according to the drying process of the invention.
[0247] The examples that follow illustrate the present invention but are not in any way limiting.
EXAMPLES
Example 1: Comparative Test with Molecular Sieves
[0248] Continuous drying on molecular sieves requires at least two dryers in parallel (the second in regeneration when the first is in adsorption).
[0249] An adsorption column (dryer) is used which contains 1 kg of Siliporite RA molecular sieves ( inch in particle size); the flow rate of methyl mercaptan to be dried is 1 kg/h. The inlet and outlet compositions of this dryer are as follows:
TABLE-US-00001 TABLE 1 Inlet Outlet Dimethyl sulfide (DMS-ppm) 153 550 Water (ppm) 3871 80 Methyl mercaptan (MeSH-%) 99.38 99.89 Methanol (MeOH-ppm) 1962 176 TOTAL (%) 99.98 99.97
[0250] When molecular sieves are used, it can be observed that the amount of dimethyl sulfide (DMS) has been multiplied by 3 after drying and the amount of methanol has been reduced almost tenfold. Indeed, the methanol is adsorbed onto the molecular sieves with the consequence of considerably reducing the water drying capacity of these sieves, and thus of increasing the frequency of the adsorption/regeneration cycles.
Example 2: Drying Process According to the Invention
[0251] The drying process corresponds to that described for
[0252] A stream of MeSH to be dried comprising 99.77% by weight of MeSH (1000 kg/h) and 0.23% by weight of water (2.3 kg/h), relative to the total weight of MeSH and water, is introduced into a distillation column.
[0253] The azeotropic distillation column comprises 28 trays and meets the following criteria: [0254] the distillation pressure is 13 bar absolute; [0255] the temperature profile is between 90 C. at the bottom and 70 C. at the top of the column; [0256] the reflux ratio is 47%.
[0257] The distillate is recovered at the top of the column in gaseous form. It comprises 98.88% by weight of MeSH (467.4 kg/h) and 1.12% by weight of water (5.3 kg/h), relative to the total weight of MeSH and water (472.7 kg/h). The temperature of the distillate is about 72 C. for a pressure of about 12 bar absolute.
[0258] The distillate is then condensed in a condenser. Its composition remains identical and it is recovered in two-phase liquid form at a temperature of about 40 C. for a pressure of about 12 bar absolute. The condensate then settles in a decanter so as to obtain: [0259] an aqueous phase comprising 98.26% (2.26 kg/h) by weight of water and 1.74% by weight of MeSH (0.04 kg/h) relative to the total weight of the aqueous phase (2.3 kg/h), and [0260] an organic phase comprising 99.36% by weight of MeSH (467.5 kg/h) and 0.64% by weight of water (3 kg/h), relative to the total weight of MeSH and water (470.5 kg/h). The temperature is about 40 C. for a pressure of about 12 bar absolute for the two phases.
[0261] The dried MeSH is recovered at the bottom of the distillation column and contains less than 10 ppm by weight of water relative to the total by weight of methyl mercaptan and water.
[0262] The amounts of methanol and dimethyl sulfide are the same at the inlet of stream (A) as in the dried methyl mercaptan (about 0.04 kg/h and 0.1 kg/h, respectively).
[0263] Consequently, the process according to the invention makes it possible to effectively dry the methyl mercaptan while at the same time not increasing the amount of the DMS byproduct. Furthermore, the drying process is not affected by traces of methanol and may be performed continuously without its performance being impaired.