DE102007002511A1 - Continuous separation of sulfur compounds from a fluid comprises using a membrane comprising an immobilized ionic liquid - Google Patents

Abstract

Continuous separation of sulfur compounds from a fluid using a membrane comprising an immobilized ionic liquid comprises passing the fluid over one side of the membrane while passing another fluid over the other side to carry off the suulfur compounds.

Description

Summary:

method for the continuous separation of sulfur-containing compounds gaseous or liquid media by means of immobilized ionic liquids.

Background of the invention:

Sulfur compounds in industrial fluids such as in liquid fuels such. As gasoline or diesel or in gases such. As natural gas, synthesis gas or biogas are usually undesirable components, since sulfur compounds such. For example, H ₂ S, SO ₂ , mercaptans, sulfides or tetrahydrothiophene are toxic, corrosive and / or malodorous. When technical fluids are used in chemical reactions, sulfur compounds also act as strong catalyst poisons. As an example, the catalyst poisoning in fuel cells called to be operated with natural gas (methane). Even a few ppm (parts per million) of sulfur compounds already lead to a strong degradation of the performance of the fuel cell. Sulfur components in automotive fuels lead to SO ₂ emissions and acid rain. DeNOx storage catalytic converters in motor vehicles are also damaged by traces of sulfur in the engine exhaust.

For the reasons mentioned, it is often necessary to desulphurise fluids before use. The state of the art in gas desulfurization is z. As the gas scrubbing by absorption, the adsorption of solids or modern oxidation processes in the liquid phase. Such commercial methods are for. B. as STRETFORD, LOCAT, SULFEROX or UNISULF method known; also in WO 2005/053820 A1 Such a method is described. In the desulphurisation of liquid fuels, hydrodesulphurisation is state of the art. In refineries, the sulfur compounds are hydrogenated in the oil-derived hydrocarbon streams in the so-called HDS process (hydrodesulfurization) to H ₂ S and removed by gas scrubbing from the hydrocarbon stream.

Ionic liquids are by definition salts which are liquid at below 100 ° C. A description of ionic liquids is z. B. of Wasserscheid and germ ( Angewandte Chemie 2000, 112, 3926-3945 ) to find. Ionic liquids have good solubility for a range of organic, inorganic and polymeric compounds. In addition, the solubility properties can be adjusted in a wide range by selecting the respective cation and anion components of the ionic liquid.

Ionic liquids have no or a measurable low vapor pressure and are therefore not volatile. You can therefore z. B. permanently fixed on porous supports, which z. B. in the field of homogeneous catalysis can be used when the catalyst is soluble in the ionic liquid ( Riisager et al., J. of Cat. 2003, 219, 452-455 ; Riisager et al. Cat. Letters 2003, 90, 149-153 ; Mehnert et al., J. of the American Chem. Soc. 1998, 120, 12289-12296 ; Mehnert et al., Chem. Comm. 2002, 24, 3010/11 ; Wolfson et al., Tetrahedron Letters 2003, 44, 1195-1198 )

The ability of ionic liquids polar compounds such. B. to absorb sulfur compounds is already known from the literature. Both from the liquid phase (eg Esser et al., Green Chem. 2004, 6, 316-322 ) as well as from the gas phase, ionic fluids can absorb sulfur compounds. However, the separation of gaseous sulfur compounds has hitherto been reported only for the reversible absorption of SO 2 (gas scrubbing) in a paper by Huang et al. ( Chem. Comm. 2006, 4027-4029 ).

US patent application 2002/0189444 ( U.S. Patent 6579343 ) discloses an absorptive process for purifying a gas with the aid of ionic liquids. It will be explained how CO ₂ , water and other gases can be separated from gas mixtures and so z. B. natural gas can be cleaned.

The international patent application WO 2006/045518 A1 discloses an absorptive process for the separation of HCl, HF or HBr from gas mixtures using ionic liquids.

task It is the object of the present invention to provide a new, simple and effective to provide a continuous process with the undesirable sulfur compounds continuously from liquid and gaseous media can be separated by ionic liquids. This object is achieved by the features of claim 1 of the present Invention solved.

Description of the invention:

The present invention discloses a continuous process for the desulfurization of a fluid stream by means of an immobilized ionic liquid. In the present invention, an ionic liquid is understood as meaning a liquid or a mixture of liquids which consists only of cations and anions and has no measurable vapor pressure. The arbitrary definition used in the literature, to designate only those molten salts with a melting point of less than 100 ° C as ionic liquids will be present in the present extended the patent. In the present patent, ionic liquids have a melting point of less than 400 ° C. In particular, the ionic liquids belong to the group of imidazolium, ammonium, imidazolinium, pyrazolium, oxazolium, oxatriazolium, thiazolium, triazolium, pyridinium, pyridazinium, pyrimidinium, guanidinium or pyrazinium salts.

A first fluid ( 1 ) which, among other compounds, contains one or more sulfur compounds ( 2 ) is continuously attached to one side of an immobilized ionic liquid ( 3 ) (see picture 1).

immobilized means that the ionic liquid as a coherent Liquid film on a fluid-permeable Carrier material is present or the porous openings a fluid-permeable carrier material fills or both properties at the same time. This immobilization The ionic liquid is used in the present invention as Understood ionic liquid membrane. It can for producing a coherent liquid film the ionic liquid directly on a fluid-permeable Substrate can be applied. In addition, if necessary, the substrate first additionally with a substance be coated, the adhesion of the liquid film improves the ionic liquid on the substrate. For use can be both flat substrates such as nets or tissue as well as round or tubular substrates come to the Passed inside or outside of the aufzurinigende fluid flow can be. If necessary, the ionic liquid can also directly in the pores of a fluid-permeable substrate be immobilized.

The sulfur compounds ( 2 ) are selectively absorbed (in the case of gases) or extracted (in the case of liquids) and transported diffusively to the second side of the immobilized ionic liquid, where a second fluid ( 4 ) is continuously passed, which receives the sulfur compounds, continuously transported away and thus builds up necessary for the mass transport through the ionic liquid concentration gradients. The reason for the selective absorption of the sulfur compounds from the fluid mixture is the different solubility of the molecules involved in the ionic liquid or the mixture of ionic liquids. The solubility of sulfur-containing substances in ionic liquids is z. B. usually much larger than the solubility of CH ₄ . Of course, the choice of ionic liquid must be such that the solubility for the sulfur compounds to be separated in the ionic liquid is as large as possible, as small as possible for the other molecules involved.

Experimental data:

According to Figure 1, experiments were carried out with the following parameters:
The ionic liquid 1-butyl-3-methylimidazolium-bis (trifluoromethansulfon) was imide in the pores of a PTFE membrane produced by Donaldson filter Components Ltd (Tetratex ^® 0.07 .mu.m PTFE membrane, product code: # 1316 nominal pore diameter: 0 , 07 μm) immobilized ( 3 ). The contact surface of the two gas streams ( 1 ) and ( 4 ) on both sides of the coated membrane is 16 square centimeters. The thickness of the membrane and thus the layer of the ionic liquid ( 4 ) is 18 μm.

A gas stream to be cleaned off ( 1 ) consisting of CH ₄ with a sulfur concentration ( 2 ) of 100 ppm tetrahydrothiophene (THT) is reacted with a standard volume flow of 1.08 liters per hour at 25 ° C and atmospheric pressure on the first side of the immobilized ionic liquid ( 3 ) passed by. On the second side, a purge gas stream ( 4 ), consisting of nitrogen, with 10.2 Normlitern per hour passed at atmospheric pressure. After setting a steady state, the sulfur concentration in the CH ₄ volumetric flow is only about 20 ppm, ie 80% of the sulfur compound has passed through the IL layer into the purge gas stream. The corresponding concentration of THT (9 ppm) is also detected in the purge gas stream. The THT concentrations were measured by the THT sensor THT 3E 50 from Sensoric Gas Sensors. At the same time, no CH _{4 is} detected in the purge gas stream (measurement limit of the CH ₄ analyzer approx. 0.1%, measuring instrument: Fisher-Rosemount NGA 2000). The separation of the THTs is thus highly selective.

For comparison, the PTFE membrane described above was also used without the immobilized ionic liquid for gas separation. It was again a gas stream ( 1 ) consisting of CH ₄ with a sulfur concentration ( 2 ) of 100 ppm tetrahydrothiophene (THT) at a flow rate of 1 liter per hour at 25 ° C and atmospheric pressure past the first side of the PTFE membrane. On the second side was again a purge gas stream ( 4 ) of nitrogen (10 standard liters per hour, atmospheric pressure) passed.

The Results show that the uncoated PTFE membrane is the second not on both sides passing gas streams can separate. All involved gas molecules can through the membrane on the other side until the concentration is equalized flow and mix with each other, making a selective Gas separation is not possible. The separation effect is so caused only by the ionic liquid, and the PTFE membrane acts only as a scaffold.

In a further experiment, a hydrogen sulphide-containing gas is (with the help of the same experimental design) ( 1 ), consisting of 2.84% H ₂ S, 27% hydrogen, balance argon, at 25 ° C and atmospheric pressure on the first side of the immobilized ionic liquid ( 3 ) passed by. On the second side, a purge gas stream ( 4 ), consisting of nitrogen, with 9.7 l / h passed at atmospheric pressure. After setting a steady state, the hydrogen sulfide concentration in the sulfur-containing gas is 2.41% (15% purification level). The corresponding amount of sulfur compound is also detected in the purge gas stream. In a further experiment, the volume flow of the hydrogen sulphide-containing gas was reduced to 0.42 standard liters per hour under otherwise constant conditions. Then the degree of cleaning increased to 34%. The analysis of the H ₂ S concentration was carried out with the device Radas 2 from Hartmann & Braun (measurement limit: 1 ppm). At the same time, no hydrogen was detected in the purging gas stream (measuring device: Fisher-Rosemount BINOS 100 2M, measurement limit: 0.1%), so that a highly selective separation of the hydrogen sulfide is present.

The experimental data show that with the present invention a very selective and continuous desulfurization of a gas mixture carried out with the aid of immobilized ionic liquids can be.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2005/053820 A1 [0003]
• - US 6579343 [0007]
• - WO 2006/045518 A1 [0008]

Cited non-patent literature

• - Angewandte Chemie 2000, 112, 3926-3945 [0004]
• Riisager et al., J. of Cat. 2003, 219, 452-455 [0005]
• Riisager et al. Cat. Letters 2003, 90, 149-153 [0005]
• Mehnert et al., J. of the American Chem. Soc. 1998, 120, 12289-12296 [0005]
• Mehnert et al., Chem. Comm. 2002, 24, 3010/11 [0005]
• Wolfson et al., Tetrahedron Letters 2003, 44, 1195-1198 [0005]
• Eßer et al., Green Chem. 2004, 6, 316-322 [0006]
• - Chem. Comm. 2006, 4027-4029 [0006]

Claims (7)

A process for the continuous separation of sulfur-containing compounds from fluids, characterized in that a membrane of an immobilized ionic liquid is provided, at its first side, a sulfur-containing first fluid passes continuously past and on the second side, a second fluid is continuously passed, which removes the sulfur compounds , The method of claim 1, wherein both the to be purified first fluid as well as the second fluid a gas flow or a liquid flow can be. The method of claim 1, wherein the first fluid to be separated is a natural gas, synthesis gas or a biotechnologically produced biogas containing organic sulfur compounds such as H ₂ S, SO ₂ , COS, tetrahydrothiophene or sulfides. The method of claim 1, wherein the to be separated first fluid is a liquid hydrocarbon mixture, the organic sulfur compounds such as. Thiophene, tetrahydrothiophene, Benzothiophene, dibenzothiophene and alkylated foms of these sulfur compounds contains sulfur compounds such as sulfides, Disulfides, thiols, sulfoxides and sulfones, and sulfur-containing polycyclic ones Contains aromatics. Method according to claim 1, characterized in that that the ionic liquid consists of compounds of the class imidazolium, ammonium, imidazolinium, pyrazolium, oxazolium, Oxatriazolium, thiazolium, triazolium, pyridinium, pyridazinium, Pyrimidinium, guanidinium or pyrazinium salts. The method of claim 1, wherein the water content in the ionic liquid less than 1 percent, preferably is less than 0.1 percent. The method of claim 1, wherein the to be separated first fluid with a temperature of 0 ° C and 400 ° C and a pressure of 1 bar to 50 bar at the membrane of ionic Liquid is passed.