Cleaning of liquid hydrocarbon streams by means of copper-containing sorbents

Abstract

The invention relates to a method for cleaning hydrocarbon mixtures, in which a contaminated hydrocarbon mixture comprising hydrocarbons having three to eight carbon atoms is at least partly freed of impurities by contacting with a solid sorbent, wherein the hydrocarbon mixture is exclusively in the liquid state during contact with the sorbent. The object of the invention is to specify a process for cleaning liquid C.sub.3 to C.sub.8 hydrocarbon mixtures, which is based on a readily available but non-carcinogenic sorbent and which achieves better purities compared to traditional molecular sieves. This object is achieved by using, as sorbents, solid materials of the following composition: copper oxide: 10% to 60% by weight (calculated as CuO); zinc oxide: 10% to 60% by weight (calculated as ZnO); aluminum oxide: 10% to 30% by weight (calculated as Al.sub.2O.sub.3); other substances: 0% to 5% by weight. Materials of this kind are otherwise used as catalysts in methanol synthesis.

Claims

1. Process for purifying hydrocarbon mixtures, in which a contaminated hydrocarbon mixture comprising hydrocarbons having three to eight carbon atoms is at least partly freed of contaminants by contacting it with a solid sorbent in the absence of hydrogen, the hydrocarbon mixture being exclusively in the liquid state during the contact with the sorbent, wherein the sorbent has the following composition that adds up to 100% by weight: copper oxide: 10% to 60% by weight (calculated as CuO); zinc oxide: 10% to 60% by weight (calculated as ZnO); aluminium oxide: 10% to 30% by weight (calculated as Al.sub.2O.sub.3); other substances: 0% to 5% by weight; wherein the sorbent is supplied in an oxidized state without being activated by a reduction reaction; and wherein the contact is effected under the following conditions: temperature between 30? C. and 120? C.; pressure between 0.5 and 3.5 MPa; and weight hourly space velocity between 0.5 h.sup.?1 and 7 h.sup.?1.

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

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

4. Process according to claim 1, wherein the proportion by weight of the contaminants in the contaminated hydrocarbon mixture, based on the total weight thereof, is less than 0.2% by weight.

5. Process according to claim 1, wherein the sorbent is used irreversibly.

6. Process according to claim 1, wherein the contaminated hydrocarbon mixture fulfils 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 20% to 40% by weight; n-butane 5% to 18% by weight; 1-butene 5% to 15% 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; contaminants less than 0.5% by weight; Specification B: isobutane 0.6% to 8% by weight; n-butane 0.5% to 8% 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; contaminants less than 0.5% by weight; Specification C: isobutane 0.6% to 8% by weight; n-butane 0.5% to 15% 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 1% by weight; water 0% to 1% by weight; contaminants less than 0.5% by weight; Specification D: n-butane 10% to 30% by weight; 1-butene 0.2% to 45% by weight; 2-butenes 35% to 85% by weight; water 0% to 1% by weight; contaminants less than 0.5% by weight.

7. Process according to claim 1, further comprising one or more of the following steps: a) extracting 1,3-butadiene from the hydrocarbon mixture which has been at least partly freed of contaminants; b) selectively hydrogenating diolefins, acetylenes, or diolefins and acetylenes in the hydrocarbon mixture which has been at least partly freed of contaminants to form olefins; c) oligomerizing olefins present in the hydrocarbon mixture which has been at least partly freed of contaminants to form oligomers; d) distilling the hydrocarbon mixture which has been at least partly freed of contaminants to remove 1-butene, isobutene or both 1-butene and isobutene from the hydrocarbon mixture which has been at least partly freed of contaminants; e) removing isobutene from the hydrocarbon mixture which has been at least partly freed of contaminants by converting the isobutene to tert-butanol with water or by converting the isobutene to methyl tert-butyl ether with methanol; f) dehydrogenating butanes present in the hydrocarbon mixture which has been at least partly freed of contaminants to form butenes; g) oxidatively dehydrogenating butenes present in the hydrocarbon mixture which has been at least partly freed of contaminants to form butadiene; h) alkylating n-butene present in the hydrocarbon mixture which has been at least partly freed of contaminants with isobutane present in the hydrocarbon mixture which has been at least partly freed of contaminants; i) oxidizing hydrocarbons having four carbon atoms present in the hydrocarbon mixture in the hydrocarbon mixture which has been at least partly freed of contaminants.

8. Process according to claim 3, where R and R are each independently selected from a methyl, an ethyl, a propyl, a butyl, a phenyl, a cyclohexyl or a butenyl radical.

9. Process according to claim 3, where the substituted or unsubstituted sulphur-containing heterocycles comprise thiophenes, thiolanes or both thiophenes and thiolanes.

10. Process according to claim 1, wherein the proportion by weight of the contaminants in the contaminated hydrocarbon mixture, based on the total weight thereof, is less than 100 ppm by weight.

11. Process according to claim 1, wherein the proportion by weight of the contaminants in the contaminated hydrocarbon mixture, based on the total weight thereof, is less than 10 ppm by weight.

Description

(1) The basic structure of such value addition chains incorporating the inventive removal of poisons are to be illustrated in detail hereinafter. The figures show, in schematic form:

(2) FIG. 1: C.sub.4 line with coarse and fine desulphurization at the start;

(3) FIG. 2: C.sub.4 line with sorptive purification immediately upstream of the oligomerization.

(4) FIG. 1 shows, in schematic form, a line for workup of C.sub.4 hydrocarbon mixtures.

(5) A raw material source 0 supplies a raw material mixture 1 comprising predominantly hydrocarbons having four carbon atoms (butenes and butanes). The raw material source 0 may, for example, be a mineral oil refinery. According to whether the cracker works by fluid catalysis or is operated as a steamcracker, a resulting raw material mixture 1 is referred to as FCC C4 or as crack C4.

(6) Alternative raw material sources 0 or raw material mixtures 1 also include DCC C4 (DCC: Deep catalytic cracking), pyrolysis C4, C4 from MTO (methanol-to-olefins) or MTP (methanol-to-propylene) processes or C.sub.4 from dehydrogenations of n-butane.

(7) Since raw C.sub.4 streams may have a high sulphur content depending on their source 0, the raw material mixture 1 is first coarsely prepurified in a prepurification stage 2, by removing sulphur-containing constituents 3 in relatively large amounts. The pre-purification stage 2 may, for example, be a MEROX? scrub or a thioetherification. Alternatively, it is also possible here to use a reversible sorbent which is regenerated cyclically. However, since the separation performance of a MEROX? scrub or a thioetherification is much greater, these prepurification stages are preferable over a sorptive coarse purification.

(8) A hydrocarbon mixture 4 which is then drawn off from the prepurification stage 2 is still contaminated (contamination level max. 0.2% by weight, preferably below 100 ppm by weight). The contaminated hydrocarbon mixture 4, for complete elimination of the catalyst poisons present therein, is run into a purifying bed 5. The purifying bed 5 is a bed of a solid comprising copper oxide, zinc oxide and aluminium oxide, the sorbent. The purifying bed 5 is present in a vessel known per se. The liquid, contaminated hydrocarbon mixture 4 flows through the vessel, such that the sorbent present therein chemically adsorbs the contaminants present in the hydrocarbon mixture 4 and hence arrests them in the purifying bed 5. In this way, a purified hydrocarbon mixture 6 is obtained, which has been virtually completely freed of catalyst poisons.

(9) In accordance with its material of value composition, a workup known per se is then effected on the materials of value present in the raw material mixture 1. If the raw material mixture 1 is crack C4, it has a high content of butadiene 7, which is removed by extraction in a butadiene removal 8.

(10) Residues of unextracted butadiene are selectively hydrogenated (not shown). This gives what is called raffinate I 9.

(11) The isobutene 10 present in the raffinate I is removed in an isobutene removal 11. The isobutene removal 10 generally involves an MTBE synthesis in which the isobutene is reacted with methanol to give methyl tert-butyl ether (MTBE) and a downstream MTBE cleavage in which the MTBE is cleaved back to isobutene 10.

(12) The mixture which has been freed of isobutene is referred to as raffinate II 12. The material of value present therein, 1-butene 13, is distilled off in a 1-butene removal 14. This gives what is called raffinate III 15.

(13) Raffinate III 15 contains, as material of value, essentially only the two 2-butenes, which are converted in an oligomerization 16 to C.sub.8 olefins. The oligomerizate 17 is separated by distillation and subsequently processed by hydroformylation and hydrogenation to give plasticizer alcohols (not shown).

(14) FIG. 2 shows one variant of a C.sub.4 line in which the purifying bed 5 is arranged immediately upstream of the oligomerization 17. This is an option especially when a thioetherification which works in the presence of hydrogen is used as prepurification stage 2. Some of the hydrogen is also required beyond the butadiene removal 8, in order to selectively hydrogenate butadiene that has not been removed. Since the hydrogen is discharged from the C.sub.4 line at a stage no later than the isobutene removal 11 or the 1-butene removal 14, the fine desulphurication then takes place in the purifying bed 5 in the absence of hydrogen.

(15) Alternatively, the purifying bed 5 could also be charged with raffinate I 9. In that case, it would be arranged beyond the butadiene removal 8 and upstream of the isobutene removal 11 (not shown). This is advantageous especially when the raw material mixture 1 used is crack C4 containing large amounts of 1,3-butadiene according to specification B. 1,3-Butadiene could deactivate the sorbent too quickly. The purifying bed should therefore if at all possible be charged with a butadiene-depleted hydrocarbon mixture, i.e. at least with raffinate I or with FCC C4.

EXAMPLES

First Experiment: Removal of Ethanethiol According to the Invention

(16) 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% 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.

(17) 120 g of sorbent are introduced into each of two reaction tubes having diameter 1 cm. The bulk density is about 1.2 kg/dm.sup.3. The filled tubes are connected in series, with one sampling valve mounted between the tubes (discharge 1) and one at the end (discharge 2). The purifying beds are brought to a temperature of 80? C. by heating the tube walls, and a liquid mixture containing about 33% by weight of 1-butene, about 23% by weight of trans-2-butene, about 15% by weight of cis-2-butene and about 27% by weight of n-butane is allowed to flow through them at a pressure of 24 bar. As a contaminant, the material contains an average of 5.4 mg/kg of sulphur, predominantly in the form of ethanethiol. The loading of the purifying beds is 600 g/h, and so the sulphur input is about 3.2 mg/h.

(18) As shown by the analyses, the sulphur is at first already removed virtually quantitatively from the mixture in the first purifying bed. From an operating time of 480 hours onward, the sulphur content at discharge 1 rises rapidly. This sharp breakthrough corresponds to an arrested amount of sulphur of about 1.7 g or a sulphur absorption in the purifying bed of about 1.4% by weight. The breakthrough downstream of the second purifying bed (discharge 2) takes place at about 1200 hours. At this time, the purifying beds have absorbed a total of about 3.9 g of sulphur, corresponding to a mean absorption of 1.7% by weight, based on the freshly introduced sorbent.

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

(20) After the end of this experiment, the beds are purged with nitrogen. The sorbent can be removed intact and with sufficient stability.

(21) The results of the experiment are recorded in Table 1.

(22) TABLE-US-00002 TABLE 1 Results from experiment 1 Mean S Mean decrease in content [% by S [% by wt.] Mean S content wt.] in Mean S content [% in discharge [% by wt.] discharge by wt.] in discharge 2 compared to in feed 1 up to 480 h 2 up to 1200 h feed up to 1200 h 0.00054 0.00003 0.00002 96

Second Experiment: Removal of Methanethiol According to the Invention

(23) The sorbent used and the experimental setup correspond to the first experiment.

(24) Analogously to experiment 1, 5 mg/kg of sulphur are supplied as impurity, predominantly in the form of methanethiol. The loading of the two purifying beds, each of which has been charged with 28 g, is 380 g/h, i.e. the sulphur input is 1.9 mg/h. The contact temperature was set to 100? C.

(25) As shown by the analyses, the sulphur is at first already removed virtually quantitatively from the mixture in the first purifying bed. From an operating time of about 410 hours onward, the sulphur content at discharge 1 rises. This sharp breakthrough corresponds to an arrested amount of sulphur of about 0.5 g or a sulphur absorption by the sorbent of about 1.9% by weight. The breakthrough downstream of the second purifying bed (discharge 2) takes place at about 720 hours. At this time, the purifying beds have absorbed a total of about 1.9 g of sulphur, corresponding to a mean absorption of 1.7% by weight, based on the freshly introduced sorbent.

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

(27) After the end of this experiment, the beds are purged with nitrogen. The sorbent can be removed intact and with sufficient stability.

(28) The experimental results are shown in Table 2.

(29) TABLE-US-00003 TABLE 2 Results from experiment 2 Mean S content [% by Mean S Mean wt.] in content [% by Mean decrease in S [% S content discharge wt.] in by wt.] in discharge 2 [% by 1 up to discharge 2 up to compared to feed up to wt.] in feed 410 h 720 h 720 h 0.00044 0.00004 0.00004 91

Third Experiment: Removal of Diethyl Disulphide According to the Invention

(30) The sorbent used and the experimental setup correspond to the first and second experiments.

(31) Analogously to experiment 1, 1 mg/kg of sulphur are supplied as impurity, predominantly in the form of diethyl disulphide. The loading of the purifying beds, each of which contains 28 g of the sorbent, is 360 g/h, and so the sulphur input is about 0.4 mg/h. The operating temperature is 100? C.

(32) As shown by the analyses, the sulphur is at first already removed virtually quantitatively from the mixture in the first purifying bed. From an operating time of 600 hours onward, the sulphur content at discharge 1 rises rapidly. This sharp breakthrough corresponds to an arrested amount of sulphur of about 0.3 g or a sulphur absorption by the sorbent of about 1.2% by weight. The breakthrough downstream of the second purifying bed (discharge 2) takes place at about 1080 hours. At this time, the purifying beds have absorbed a total of about 0.6 g of sulphur, corresponding to a mean absorption of 1.2% by weight, based on the freshly introduced sorbent.

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

(34) After the end of this experiment, the beds are purged with nitrogen. The sorbent can be removed intact and with sufficient stability.

(35) The experimental results are shown in Table 3.

(36) TABLE-US-00004 TABLE 3 Results from experiment 3 Mean S content [% by Mean S Mean S wt.] in content [% by Mean decrease in S [% content discharge 1 wt.] in by wt.] in discharge 2 [% by up to discharge 2 up to compared to feed up to wt.] in feed 600 h 1080 h 1080 h 0.00010 0.00001 0.00001 90

Fourth Experiment: Removal of Dimethyl Disulphide with the Aid of Zeolites (not Inventive)

(37) A sorbent is produced according to EP0354316. It is based on a type X zeolite and contains only 10% by weight of Cu. The two tubes, each charged with 50 g of the material, are connected in series, with one sampling valve mounted between the purifying beds (discharge 1) and one at the end (discharge 2). The beds are brought to a temperature of 120? C. by heating the tube walls, and a liquid mixture containing about 33% by weight of 1-butene, about 23% by weight of trans-2-butene, about 15% by weight of cis-2-butene and about 27% by weight of n-butane is allowed to flow through them at a pressure of 30 bar. As a contaminant, the material contains an average of 2.0 mg/kg of sulphur, predominantly in the form of dimethyl disulphide. The loading of the purifying beds is 375 g/h, and so the sulphur input is about 0.75 mg/h.

(38) As shown by the analyses, the sulphur is at first already removed virtually quantitatively from the mixture in the first reactor. From an operating time of 48 hours onward, however, the sulphur content at discharge 1 rises rapidly. This sharp breakthrough corresponds to an adsorbed amount of sulphur of only about 0.036 g or a sulphur absorption by the sorbent of about 0.036% by weight. The breakthrough downstream of the second purifying bed (discharge 2) takes place at about 96 hours. At this time, the purifying beds have absorbed a total of about 0.07 g of sulphur, corresponding to a mean absorption of 0.07% by weight, based on the freshly introduced sorbent.

(39) With the noninventive material, distinct desulphurization can accordingly be achieved only for a very short time, and the material used is not in any relation to the purifying performance.

(40) The results are shown in Table 4.

(41) TABLE-US-00005 TABLE 4 Results from experiment 4 Mean decrease Mean S in S [% by wt.] content Mean S content [% Mean S content [% in discharge [% by by wt.] in discharge by wt.] in discharge 2 compared to wt.] in feed 1 up to 48 h 2 up to 96 h feed up to 96 h 0.00020 0.000005 0.000005 97

CONCLUSION

(42) The experiments demonstrate that the sorbent used in accordance with the invention has the following properties: it binds the sulphur from sulphur compounds virtually completely; it does not require any activation in the hydrogen stream, nor any other additional operating materials; it does not require any periodic purifying and desorption streams, since it is an irreversible sorbent; it 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; it causes virtually no side reactions of olefins, such as oligomerization, isomerization and hydrogenation, and hence also no losses; it 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 ppmw and a capacity of at least 1% by weight of sulphur, it is very inexpensive to operate, even though it cannot be regenerated directly, and can instead only be sent to a raw material utilization after the capacity has been exhausted; it can be handled and disposed of without any problem, since it is neither classified as carcinogenic nor exhibits pyrophoric properties.

LIST OF REFERENCE NUMERALS

(43) 0 raw material source 1 raw material mixture 2 prepurification stage 3 sulphur-containing constituents 4 contaminated hydrocarbon mixture 5 purifying bed 6 purified hydrocarbon mixture 7 butadiene 8 butadiene removal 9 raffinate I 10 isobutene 11 isobutene removal (MTBE synthesis/MTBE cleavage) 12 raffinate II 13 1-butene 14 1-butene removal 15 raffinate III 16 oligomerization 17 oligomerizate