PROCESS TO PREPARE PARAFFINS AND WAXES

Abstract

Paraffins and waxes are produced from a gaseous feed stream comprising hydrogen and carbon monoxide in a Fischer-Tropsch reactor using a fixed bed of reduced Fischer-Tropsch catalyst having cobalt as catalytically active metal. A nitrogen-containing compound is added to the gaseous feed stream in a concentration of up to 10 ppmV and the mixture if fed to the reactor to obtain paraffins having from 5 to 300 carbon atoms. The product is subjected to a hydrogenation step, to obtain a hydrogenated fraction comprising 5 to 300 carbon atoms. The hydrogenated product is separated into C5-C9, C10-C17, and C18-300 fractions. The C18-C300 fraction is separated to obtain one or more first light waxes having a congealing point in the range of 30 to 75 C. and a second heavy wax having a congealing point in the range of 75 to 120 C.

Claims

1. Process to prepare paraffins and waxes from a gaseous feed stream comprising hydrogen and carbon monoxide in a Fischer-Tropsch reactor comprising a fixes bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal, said process at least comprises the following steps: (a) adding to the gaseous feed stream a nitrogen-containing compound such that the nitrogen-containing compound is present in the gaseous feed stream in a concentration of up to 10 ppmV to obtain a mixture, wherein the nitrogen-containing compound is a compound selected from ammonia, HCN, NO, amines, nitriles, and a heterocyclic compound containing at least one nitrogen atom as ring member of a heterocyclic ring; (b) feeding the mixture of step (a) to the Fischer-Tropsch reactor to obtain a Fischer-Tropsch product comprising paraffins having from 5 to 300 carbon atoms; (c) subjecting the Fischer-Tropsch product of step (b) to a hydrogenation step, thereby obtaining hydrogenated fraction comprising 5 to 300 carbon atoms; (d) separating the hydrogenated Fischer-Tropsch product stream of step (c), thereby obtaining at least a fraction comprising 5 to 9 carbon atoms, a fraction comprising 10 to 17 carbon atoms and a fraction comprising 18 to 300 carbon atoms; (e) separating the hydrogenated fraction comprising 18 to 300 carbon atoms of step (d), thereby obtaining one or more first light waxes having a congealing point in the range of 30 to 75 C. and a second heavy wax having a congealing point in the range of 75 to 120 C.

2. A process according to claim 1, wherein a nitrogen-containing compound other than molecular nitrogen is added to the gaseous feed stream in step (a) such that the nitrogen-containing compound is present in the gaseous feed stream in a concentration in the range of 0.05 to 10 ppmV.

3. A process according to claim 1 or 2, wherein the nitrogen-containing compound is a compound selected from the group consisting of ammonia, HCN, NO, an amine and combinations or two or more thereof.

4. A process according to claim 3, wherein the nitrogen-containing compound is ammonia.

5. A process according to any one of claims 1 to 4, wherein the amount of the fraction comprising 5 to 9 carbon atoms of step (e) is in the range of from 3-16 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

6. A process according to any one of claims 1 to 5, wherein the fraction comprising 10 to 17 carbon atoms of step (d) is separated into a fraction comprising 10 to 13 carbon atoms and a fraction comprising 14 to 17 carbon atoms.

7. A process according to claim 6, wherein the amount of the fraction comprising 10 to 13 carbon atoms is in the range of from 3-12 wt. % and the amount of the fraction comprising 14 to 17 carbon atoms is in the range of from 3-11 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

8. Process according to any one of claims 1 to 7, wherein one or more wax fractions having a congealing point in the range of 30 to 75 C. of step (e) are hydrofinished to obtain one or more hydrofinished wax fractions having a congealing point in the range of 30 to 75 C.

9. Process according to any one of claims 1 to 8, wherein the amount of hydrofinished wax fraction having a congealing point of 30 C. is in the range of from 2-8 wt % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

10. Process according to any one of claims 1 to 9, wherein the amount of hydrofinished wax fraction having a congealing point of 50 C. is in the range of from 4-15 wt % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

11. Process according to any one of claims 1 to 10, the second heavy wax of step (e) is separated, thereby obtaining at least one distillate wax fraction having a congealing point in the range of between 75 to 85 C. and at least one residual wax fraction having a congealing point in the range of from 95 to 120 C.

12. Process according to any one of claims 1 to 11, wherein the amount of hydrofinished wax fraction having a congealing point of 70 C. is in the range of from 6-20 wt % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

13. Process according to claim 11, the heavy distillate wax fraction having a congealing point in the range of between 75 to 85 C. is hydrofinished to obtain a hydrofinished heavy distillate wax fraction having a congealing point in the range of between 75 and 85 C.

14. Process according to claim 11, wherein the heavy residual wax fraction having a congealing point in the range of 95 to 120 C. is hydrofinished to obtain a hydrofinished heavy residual wax fraction having a congealing point in the range of 95 to 120 C.

15. Process according to any one of claims 1 to 12, wherein the amount of hydrofinished wax fraction having a congealing point of 100 to 105 C. is in the range of from 10-75 wt % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.

16. Process according to any one of claims 1 to 15, wherein a part of the first light and second heavy waxes of step (e) is subjected to a hydrocracking/hydroisomerisation step to obtain a partly isomerised product.

Description

[0078] FIG. 1 schematically shows a process scheme of the process scheme of a preferred embodiment of the process according to the present invention.

[0079] For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line.

[0080] The process scheme is generally referred to with reference numeral 1.

[0081] Fischer-Tropsch derived paraffin fractions (Fraction 1 (C5-C9), Fraction 2 (C10-C13), Fraction 3 (C14-C17)) and Fischer-Tropsch derived paraffin wax fractions (Paraffin wax 1, Paraffin wax 2, Paraffin wax 3, Paraffin wax 4 and Paraffin wax 5) were obtained using a Fischer-Tropsch process. In general a Fischer-Tropsch effluent was prepared as follows. A cobalt-based Fischer-Tropsch catalyst was loaded in a reactor tube 2 and reduced. The initial reaction was set such that the resulting space time yield (STY) was 200 grams hydrocarbon products per litre catalyst per hour. The pressure of the syngas was 60 bar. Ammonia was fed to the syngas stream fed into the reactor 2 at an amount of 4.4 ppmv. The reaction temperature was kept at 220 C. and the STY was 201 g/l.h.

[0082] The effluent was separated in a fraction A which is in the gas phase at ambient conditions and a fraction B which is in the liquid or solid phase at ambient conditions.

[0083] For all distillations described below care was taken to avoid temperatures above 370 C. for any part of the distillation equipment in contact with hydrocarbons and to avoid contact of hydrocarbons with oxygen. All distillations described below were carried out in a continuous mode.

[0084] Fraction B was hydrogenated over a nickel catalyst as described in WO 2007/082589 (Catalyst G) in a hydrogenation reactor 3. Process conditions were: a weight hourly space velocity (WHSV) of 1.0 kg/l/h, 30 bar of pure hydrogen at reactor inlet, a hydrogen over feedstock ratio of 1000 Nl/kg and a temperature of 220 C.

[0085] The hydrogenated product C was subjected to a distillation column 4 at atmospheric pressure yielding a top stream D comprising a fraction containing molecules with 9 or less carbon atoms (Fraction 1 (C5-C9)), a side cut E containing molecules with 10 to 17 carbons atoms and a bottom stream F containing molecules with 18 to 300 carbon atoms. The effective cutpoint for the separation between streams E and F was 310 C.

[0086] Fraction E was separated in a distillation column 5 in a fraction G (Fraction 2 (C10-C13)) and a fraction H (Fraction 3 (C14-C17)).

[0087] Fraction F consists of hydrogenated normal paraffins in the C18 to C300 range.

[0088] Fraction F is subjected to a vacuum distillation column 6. Besides a top product (stream I), a side cut (stream J) and a heavier side cut (stream K) were obtained as well as a bottom product (stream L). The distillation was run at a bottom temperature of 320 C. and a pressure of 15 mbar. The effective cutpoint between stream I and stream J was 340 C. The effective cutpoint between stream J and stream K was 445 C. The effective cutpoint between stream K and bottom stream L was 495 C. Stream I is obtained as a refined wax with a congealing point of about 30 C. (Paraffin wax 1). Stream J is obtained as a refined wax with a congealing point of about 50 C. (Paraffin wax 2). Stream K is obtained as a wax with a congealing point of about 70 C. Stream L is subjected to a hydrofinishing operation in a hydrofinishing reactor 7 over a nickel catalyst as described in WO 2007/082589 (Catalyst G). Process conditions were: a weight hourly space velocity (WHSV) of 1.0 kg/l/h, 60 bar of pure hydrogen at reactor inlet, a hydrogen over feedstock ratio of 1000 Nl/kg and a temperature of 240 C. The product was separated in a fraction M which is in the gas phase at ambient conditions and a fraction N which is in the solid phase at ambient conditions.

[0089] Fraction N is obtained as a refined wax with a congealing point of about 70 C. (Paraffin wax 3).

[0090] The residue of this vacuum distillation (fraction L) is subjected to a short path distillation column 8 with an effective cut point of 525 C. The distillation was run at 0.2 mbar and 260 C. The distillate of the short path distillation (fraction O) is subjected to a hydrofinishing operation in a hydrofinishing reactor 9 over a nickel catalyst as described in WO 2007/082589 (Catalyst G). Process conditions were: a weight hourly space velocity (WHSV) of 1.0 kg/l/h, 60 bar of pure hydrogen at reactor inlet, a hydrogen over feedstock ratio of 1000 Nl/kg and a temperature of 240 C. The product was separated in a fraction S which is in the gas phase at ambient conditions and a fraction T which is in the solid phase at ambient conditions. Fraction T is obtained as a refined wax with a congealing point of about 80 C. (Paraffin wax 4).

[0091] The residue of the short path distillation (fraction P) is subjected to a hydrofinishing operation in a hydrofinishing reactor 10 over a nickel catalyst as described in WO 2007/082589 (Catalyst G). Process conditions were: a weight hourly space velocity (WHSV) of 1.0 kg/l/h, 60 bar of pure hydrogen at reactor inlet, a hydrogen over feedstock ratio of 1000 Nl/kg and a temperature of 240 C.

[0092] The product was separated in a fraction U which is in the gas phase at ambient conditions and a fraction V which is in the solid phase at ambient conditions.

[0093] Fraction V is obtained as a refined wax with a congealing point of about 100-110 C. (Paraffin wax 5). The invention is illustrated by the following non-limiting examples.

EXAMPLES

[0094] In general the following experiments were conducted as follows.

[0095] A cobalt-based Fischer-Tropsch catalyst was loaded in a reactor tube and reduced. The initial reaction was set such that the resulting space time yield (STY) was 200 grams hydrocarbon products per litre catalyst per hour. The reaction temperature thus set was 220 C. The STY was maintained at a value of 200 g/l.h. and the pressure of the syngas was 60 bar.

Experiment 1 (Invention)

[0096] Experiment 1 was conducted as described above with the exception that ammonia was added to the syngas stream fed into the reactor at an amount of 4.4 ppm. The reaction temperature was kept at 220 C. and the STY was 201 g/l.h.

Experiment 2 (Comparative Example)

[0097] In Experiment 2 no ammonia was added to the syngas stream provided to the reactor. The reaction temperature was kept at 210 C. and the STY was 206 g/l.h.

[0098] The results obtained in experiment 1 and 2 are listed in table 1. The content is expressed in weight percent based on the total content of the product stream exiting the reactor. The fractions are classified and identified by their hydrocarbon chain lengths per fraction.

TABLE-US-00001 TABLE 1 Content (wt %) Fraction Experiment 1 Experiment 2 C1-C4 8.3 7.9 Fraction 1 (C5-C9) 13 8.5 Fraction 2 (C10-C13) 10 7.1 Fraction 3 (C14-C17) 8.7 6.5 Paraffin wax 1 (SX30- 5.6 4.2 C18-C20) Paraffin wax 2 (SX50 11 8.3 (C21-C40) Paraffin wax 3 (SX70- 15 12 C28-C40) Paraffin wax 4 (SX100 28 45 (OR 105)-C41+)

Discussion

[0099] The results in Table 1 show a clear increase in the concentration of the fractions 1 to 3 and paraffin wax fractions 1 to 4 from 46.6 wt. % to 63.3 wt. %. Hence a clear increase in selectivity towards C5 to C40 hydrocarbons is observed. These observations indicate that upon addition of ammonia to the syngas stream results in a decrease in C41+ selectivity of the Fischer-Tropsch catalyst.

[0100] While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure need not be limited to the disclosed embodiments. It is intended to cover various modifications, combinations and similar arrangements included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. The present disclosure includes any and all embodiments of the following claims.

[0101] It should also be understood that a variety of changes may be made without departing from the essence of the invention. Such changes are also implicitly included in the description. They still fall within the scope of this invention. It should be understood that this disclosure is intended to yield a patent covering numerous aspects of the invention both independently and as an overall system and in both method and apparatus modes.

[0102] Any patents, publications, or other references mentioned in this application for patent are hereby incorporated by reference. In addition, as to each term used, it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood as incorporated for each term and all definitions, alternative terms, and synonyms such as contained in at least one of a standard technical dictionary recognized by artisans.