Hydrogen-assisted adsorption of sulphur compounds from olefin mixtures

Abstract

The invention relates to a process for purifying hydrocarbon mixtures, in which a contaminated hydrocarbon mixture comprising olefins having three to eight carbon atoms is at least partly freed of sulphur-containing contaminants by contacting it with a solid sorbent, the hydrocarbon mixture being exclusively in the liquid state during the contact with the sorbent. The problem that it addressed was that of virtually completely removing sulphur compounds present in the mixture without forming new sulphur compounds again at the same time. At the same time, 1-butene present therein was not to be lost in the purification of the mixture. Finally, the sorbent used was to have a high sorption capacity, be very substantially free of carcinogenic constituents and be readily available. This problem is solved by using a sorbent based on copper oxide, zinc oxide and aluminium oxide in a particular composition, and by conducting the purification in the presence of a small amount of hydrogen.

Claims

1. A process for purifying hydrocarbon mixtures, in which a contaminated hydrocarbon mixture comprising olefins is at least partly freed of sulphur-containing contaminants by contacting the contaminated hydrocarbon mixture with a solid sorbent in the presence of hydrogen, wherein the contaminated hydrocarbon mixture, immediately prior to the contacting with the solid sorbent, contains hydrogen in a concentration, based on the total mass of the contaminated hydrocarbon mixture, between 1 ppm by weight and 10 000 ppm by weight, wherein the contaminated hydrocarbon mixture is exclusively in the liquid state during the contacting with the solid sorbent wherein the contaminated hydrocarbon mixture comprises 1-butene and the contacting with the solid sorbent converts less than 5% by weight of the 1-butene in the contaminated hydrocarbon mixture, wherein the solid sorbent has the following composition that adds up to 100% by weight: copper oxide: 10% by weight to 60% by weight calculated as CuO; zinc oxide: 10% by weight to 60% by weight calculated as ZnO; aluminium oxide: 10% by weight to 30% by weight calculated as Al.sub.2O.sub.3; and other substances: 0% by weight to 5% by weight, wherein the solid sorbent has a copper oxide surface area of at least 50 m.sup.2/g, and wherein the contaminated hydrocarbon mixture fulfills one of the following specifications A, B, C and D, each of which adds up to 100% by weight, the stated proportions by weight each being based on the total weight of the contaminated hydrocarbon mixture: Specification A: isobutane 15% to 45% by weight; n-butane 5% to 18% by weight; 1-butene 5% to 20% by weight; isobutene 12% to 25% by weight; 2-butenes 9% to 40% by weight; 1,3-butadiene 0% to 3% by weight; water 0% to 1% by weight; sulphur-containing impurities less than 0.5% by weight; and hydrogen less than 1 ppm by weight; Specification B: isobutane 0.5% to 15% by weight; n-butane 0.5% to 20% by weight; 1-butene 9% to 25% by weight; isobutene 10% to 35% by weight; 2-butenes 3% to 15% by weight; 1,3-butadiene 25% to 70% by weight; water 0% to 1% by weight; sulphur-containing impurities less than 0.5% by weight; and hydrogen less than 1 ppm by weight; Specification C: isobutane 0.5% to 18% by weight; n-butane 0.5% to 25% by weight; 1-butene 9% to 40% by weight; isobutene 10% to 55% by weight; 2-butenes 3% to 25% by weight; 1,3-butadiene 0% to 5% by weight; water 0% to 1% by weight; sulphur-containing impurities less than 0.5% by weight; and hydrogen less than 1 ppm by weight; and Specification D: isobutane 0% to 20% by weight; n-butane 10% to 35% by weight; 1-butene 0.2% to 45% by weight; 2-butenes 35% to 85% by weight; water 0% to 1% by weight; sulphur-containing impurities less than 0.5% by weight; and hydrogen less than 1 ppm by weight.

2. The process according to claim 1, wherein the hydrogen is fully dissolved in the contaminated hydrocarbon mixture in the liquid state.

3. The process according to claim 1, wherein the concentration of hydrogen is established by adding hydrogen to the contaminated hydrocarbon mixture immediately prior to the contacting with the solid sorbent, wherein the contaminated hydrocarbon mixture prior to addition of the hydrogen contains less than 1 ppm by weight of hydrogen.

4. The process according to claim 1, wherein the solid sorbent has the following composition that adds up to 100% by weight: copper oxide: 30% by weight to 45% by weight calculated as CuO; zinc oxide: 30% by weight to 50% by weight calculated as ZnO; aluminum oxide: 10% by weight to 15% by weight calculated as Al.sub.2O.sub.3; further metal oxides: 0% by weight to 2% by weight; graphite: 0% by weight to 3% by weight; and other substances: 0% by weight to 1% by weight.

5. The process according to claim 1, wherein the contacting with the solid sorbent is conducted under the following conditions: a temperature range between 10? C. and 150? C.; a pressure range between 0.5 and 3.5 MPa; and a weight hourly space velocity range between 0.5 h.sup.?1 and 20 h.sup.?1.

6. The process according to claim 1, wherein the contaminated hydrocarbon mixture contains, as sulphur-containing contaminant, at least one compound from one of the following substance classes: a) thiols having the general formula RSH where R is an alkyl, aryl, cycloalkyl or alkenyl radical; b) disulphides having the general formula RSSR where R and R are identical or different alkyl, aryl, cycloalkyl or alkenyl radicals; c) sulphides having the general formula RSR where R and R are identical or different alkyl, aryl, cycloalkyl or alkenyl radicals; and d) substituted or unsubstituted sulphur-containing heterocycles.

7. The process according to claim 6, wherein the contaminated hydrocarbon mixture contains less than 0.2% by weight of the sulphur-containing contaminants, calculated as sulphur based on the total weight of the contaminated hydrocarbon mixture.

8. The process according to claim 7, wherein the contaminated hydrocarbon mixture is freed by the contacting with the solid sorbent of at least 90% by weight of the sulphur-containing contaminants present in the contaminated hydrocarbon mixture.

9. The process according to claim 7, wherein the contaminated hydrocarbon mixture is obtained from a pre-purification stage which pre-purifies a more highly contaminated raw material mixture to obtain the contaminated hydrocarbon mixture.

10. The process according to claim 9, wherein the solid sorbent is used irreversibly.

11. The process according to claim 1, wherein a hydrocarbon mixture which has been at least partly freed of contaminants by the process according to claim 1 is subjected to at least one of the workup steps enumerated below: a) extraction of 1,3-butadiene present in the hydrocarbon mixture; b) selective hydrogenation of diolefins and/or acetylenes present in the hydrocarbon mixture to olefins; c) oligomerization of olefins present in the hydrocarbon mixture to corresponding oligomers; d) distillative removal of 1-butene and/or isobutane present in the hydrocarbon mixture; e) removal of isobutene present in the hydrocarbon mixture by conversion of the isobutene with water to tert-butanol and/or with methanol to methyl tert-butyl ether; f) dehydrogenation of butanes present in the hydrocarbon mixture to butenes; g) oxidative dehydrogenation of butenes present in the hydrocarbon mixture to butadiene; h) alkylation of n-butene present in the hydrocarbon mixture with isobutane present therein; and i) oxidation of hydrocarbons having four carbon atoms present in the hydrocarbon mixture for preparation of maleic anhydride.

Description

EXAMPLES

First Experiment

Removal of Ethanethiol According to the Invention

(1) The sorbent used is a solid purchased from Clariant AG, which is usable as methanol catalyst. The sorbent contains about 42% by weight of CuO, about 44% by weight of ZnO, about 12.5% by weight of Al.sub.2O.sub.3 and about 2% by weight of graphite, and is in the form of tablets (5?3 mm). The specific copper oxide surface area, measured by means of nitrogen sorption, is 100 m.sup.2 per g of copper oxide content.

(2) 27 g of sorbent are introduced into a reaction tube having diameter 1 cm. The bulk density is about 1.2 kg/dm.sup.3. A sampling valve is mounted in the feed and in the outlet of the tube. The sorbent is brought to a temperature of 80? C. by heating the tube wall, and a liquid mixture containing about 37% by weight of 1-butene, about 24% by weight of trans-2-butene, about 14% by weight of cis-2-butene and about 24% by weight of n-butane and 252 ppm by weight of homogeneously dissolved H.sub.2 is allowed to flow through them at a pressure of 21 bar. As contaminant, the material contains an average of 21.8 mg/kg of sulphur, predominantly in the form of ethanethiol. The load on the sorbent is 357 g/h, and so the sulphur input is about 7.8 mg/h. As shown by the analyses, the sulphur is removed virtually quantitatively from the mixture. From an operating time of 281 hours onward, the sulphur content at the outlet rises rapidly. This sharp breakthrough corresponds to an arrested amount of sulphur of about 2.1 g or a sulphur sorption by the sorbent of about 7.8% by weight. The output values of the individual C4 components remained virtually unchanged compared to the corresponding feed values over the entire experimental period. After the end of this experiment, the bed comprising the sorbent is purged with nitrogen. The sorbent can be removed intact and with sufficient stability. The results of the experiment are recorded in Table 1.

(3) TABLE-US-00002 TABLE 1 Results from experiment 1 Mean decrease in S Mean S content [% by wt.] Mean 1-butene Mean S content [% by wt.] in output conversion [% by wt.] in output compared to feed [%] in feed up to 281 h up to 281 h up to 281 h 0.00218 0.00006 97 2.3

Second Experiment

Removal of Methanethiol According to the Invention

(4) The sorbent used and the experimental setup correspond to the first experiment. Analogously to experiment 1, an average of 20.6 mg/kg of sulphur is supplied as impurity, predominantly in the form of methanethiol. The content of homogeneously dissolved H.sub.2 is 170 ppm by weight. The load on the sorbent, charged in an amount of 28 g, is 350 g/h, i.e. the sulphur input is about 7.2 mg/h. The contact temperature was set to 80? C. As shown by the analyses in the sorbent, the sulphur is removed virtually quantitatively from the mixture. From an operating time of about 295 hours onward, the sulphur content at the outlet rises. This sharp breakthrough corresponds to an arrested amount of sulphur of about 2.1 g or a sulphur sorption by the sorbent of about 7.6% by weight. The output values of the individual C4 components remained virtually unchanged compared to the corresponding feed values over the entire experimental period. After the end of this experiment, the beds are purged with nitrogen. The sorbent can be removed intact and with sufficient stability. The experimental results are shown in Table 2.

(5) TABLE-US-00003 TABLE 2 Results from experiment 2 Mean decrease in S Mean S content [% by wt.] Mean 1-butene Mean S content [% by wt.] in output conversion [% by wt.] in output compared to feed [%] in feed up to 295 h up to 295 h up to 295 h 0.00206 0.00007 97 1.9

Third Experiment

Removal of Diethyl Disulphide According to the Invention

(6) The sorbent used and the experimental setup correspond to the first and second experiments. Analogously to experiment 1, about 1 mg/kg of sulphur is supplied as impurity, in the form of diethyl disulphide. The supplied concentration of homogeneously dissolved H.sub.2 is 170 ppm by weight. The load on the bed, containing 27 g of the sorbent, is 350 g/h, and so the sulphur input is about 0.35 mg/h. The operating temperature is 80? C. As shown by the analyses, the sulphur is removed quantitatively from the mixture. Up to an operating time of 2865 hours, no sulphur components at all could be detected in the output. Up to that point, about 0.91 g of sulphur had been arrested. This corresponds to a sulphur sorption by the sorbent of about 3.3% by weight by this time. The output values of the individual C4 components remained virtually unchanged compared to the corresponding feed values over the entire experimental period. The experimental results are shown in Table 3.

(7) TABLE-US-00004 TABLE 3 Results from experiment 3 Mean decrease in S Mean S content [% by wt.] Mean 1-butene Mean S content [% by wt.] in output conversion [% by wt.] in output compared to feed [%] in feed up to 2865 h up to 2865 h up to 2865 h 0.000082 0.000000 100 1.6

Fourth Experiment

Removal of Ethanethiol (Noninventive)

(8) The sorbent used and the experimental setup correspond to the first experiment. However, the experiment is conducted without metered addition of hydrogen.

(9) As a contaminant, the material contains an average of 5.4 mg/kg of sulphur, predominantly in the form of ethanethiol. The load on the bed, containing 120 g of the adsorbent, is 600 g/h, and so the sulphur input is about 3.2 mg/h.

(10) As shown by the analyses, the sulphur is at first removed virtually quantitatively from the mixture. From an operating time of 480 hours onward, the sulphur content at the outlet rises rapidly. This sharp breakthrough corresponds to an arrested amount of sulphur of about 1.7 g or a sulphur sorption by the sorbent of about 1.4% by weight.

(11) The discharge values of the individual C.sub.4 components remained unchanged compared to the corresponding feed values over the entire experimental period.

(12) After the end of this experiment, the bed is purged with nitrogen. The sorbent can be removed intact and with sufficient stability.

(13) The results of the experiment are recorded in Table 4.

(14) TABLE-US-00005 TABLE 4 Results from experiment 4 Mean decrease in S Mean S content [% by wt.] Mean 1-butene Mean S content [% by wt.] in output conversion [% by wt.] in output compared to feed [%] in feed up to 480 h up to 480 h up to 480 h 0.00054 0.00003 94 0.3

Conclusions from the Experiments

(15) The experiments demonstrate that the process conducted in accordance with the invention, by virtue of the combination of a suitable sorbent with metered addition of hydrogen, has the following properties: sulphur from various sulphur compounds is virtually fully bound; the sorbent does not require any activation in the hydrogen stream; the sorbent does not require any periodic purifying and desorption streams, since it is an irreversible sorbent; the sorbent can be accommodated in a simple vessel through which the mixture simply flows, preferably at slightly elevated temperature, as is typically often necessary in any case for the feeding of downstream reactors; in spite of metered addition of hydrogen, the process causes virtually no side reactions of the olefins, such as oligomerization, isomerization and hydrogenation, and hence no significant losses of the constituents of value of the mixture to be purified either; the metered addition of hydrogen increases the capacity and hence the service life of the sorbent compared to the prior art known to date; the process does not release any substances whatsoever in concentrations that have any influence at all on the downstream processing stages; in view of the long lifetime at typical sulphur concentrations below 5 ppm by weight, accounted for by the capacity of the sorbent of at least 3% by weight of sulphur, the process is very inexpensive to operate, even though the sorbent cannot be regenerated directly, and can instead only be sent to a raw material utilization after the capacity has been exhausted; this seems attractive because of the high copper content; the sorbent can be handled and disposed of without any problem, since it is neither classified as carcinogenic nor exhibits pyrophoric properties.