SATURATOR AND METHOD FOR REUSING WATER FROM A FISCHER-TROPSCH REACTOR

Abstract

The present invention relates to a saturator. The present invention further relates to a method for reusing a waste water stream from a Fischer-Tropsch reactor. The invention further relates to system for recycling waste water from a Fischer-Tropsch reactor preferably within a gas-to-liquids (GTL) plant.

Claims

1. A method for recycling waste water of a Fischer-Tropsch reactor comprising the steps of: a. Operating a gas saturator comprising a catalyst bed for converting oxygenates at a temperature ranging from 100-300° C. and at a pressure in the range of 1-100 barg; b. Providing during operation of the saturator, waste water comprising oxygenates from the Fischer-Tropsch reactor to the top of the catalyst bed; c. Providing hydrogen containing gas to the gas saturator such that the oxygenates from the waste water and the hydrogen contact the catalyst in the catalyst bed counter-currently such that at least part of the oxygenates are converted into hydrocarbons; d. Providing a feedstock gas to the gas saturator such that it moves through the catalyst bed counter-currently compared to the oxygenates.

2. A method according to claim 1 wherein the hydrocarbons exit the gas saturator with the gas mixture of water and natural gas.

3. A method according to claim 1 wherein a portion of waste water produced by a GTL plant is provided to at least one gas saturator.

4. A method according to claim 1 wherein at least a part of the water exits the saturator together with the gas mixture.

5. A method according to claim 1 wherein at least part of the hydrogen containing gas is obtained from the Fischer-Tropsch reactor as Fischer-Tropsch off-gas.

6. A method according to claim 1 wherein the oxygenates are contacted with a catalytic material comprising one or more metals selected from the group consisting of Ru, Rh, Pt, WOx, Pd and combinations thereof.

7. A gas saturator for providing water to a feed gas, comprising a vessel that is provided with at least: i. An inlet for a feed gas stream; ii. An inlet for a hydrogen containing gas stream; iii. An inlet for at least one (first) waste water stream from a Fischer-Tropsch reactor, comprising oxygenates; iv. An outlet for a gas mixture stream comprising feed gas, water and hydrocarbons; and v. An outlet for a second waste water stream comprising oxygenates; wherein the vessel of the saturator is provided with a catalyst for converting oxygenates into hydrocarbons.

8. A gas saturator according to claim 7 wherein the inlet for waste water is provided with a liquid distributor to distribute the waste water over the cross section of the catalytic section.

9. A gas saturator according to claim 7, wherein the saturator is provided with a means for holding the catalyst in the saturator, said means being such that heat and mass transfer and the conversion reaction can take place simultaneously when the hydrogen containing gas and natural gas contact the water at the catalyst surface.

10. A gas saturator according to claim 7 wherein the vessel has (from top to bottom) a top section, a catalytic section comprising as means for holding the catalyst a catalytic counter-current packed bed contact section, a non-catalytic counter-current packed bed or trayed contact section, and a bottom section.

11. A gas saturator according to claim 10 wherein, the inlet for hydrogen containing gas is located at the bottom section.

12. A gas saturator according to claim 10 wherein, the inlet for the feedstock gas is provided between the non-catalytic and catalytic section through a vapor distribution device and where the inlet for the first waste water stream and the outlet for the gas mixture are provided at the top section.

13. A gas saturator according to claim 7 wherein the saturator is provided with trays or packing or a combination of both.

14. A method according to claim 1 wherein at least a saturator is used.

15. A system for recycling waste water from a Fischer-Tropsch reaction, comprising: a. a Fischer-Tropsch reactor having a waste water stream comprising oxygenates; b. a synthesis gas reformer coupled to and upstream of the Fischer-Tropsch reactor; and c. a gas saturator according to claim 6 coupled to and upstream of the synthesis gas reformer, and coupled to an upstream feed gas stream source, and means for providing waste water originating from a downstream Fischer-Tropsch reactor, to provide a saturated feed gas stream, comprising feed gas, water and hydrocarbons obtained from the conversion of oxygenates from the Fischer-Tropsch reactor waste water stream, to the synthesis gas reformer

Description

FIGURES

[0075] The invention will be further illustrated by the figures depicting several non-limiting embodiments of the present invention.

[0076] FIG. 1 is a schematic representation of an embodiment of the present invention.

[0077] FIG. 2 is a schematic representation of a saturator according to the present invention with integrated heat system.

[0078] FIG. 3 is a schematic representation of a system according to the present invention.

[0079] FIG. 4 shows oxygenate conversion results obtained for two catalysts.

[0080] FIG. 1 shows a schematic representation of a saturator (1) according to the present invention. The arrows represent the different streams and their respective directions. The vessel (2) of the saturator (1) has (from top to bottom) a top section (3), a catalytic section (4) which preferably comprises a counter-current packed bed contact section, a non-catalytic section (5) preferably comprising a counter-current packed bed or trayed contact section, and a bottom section (6). The inlet (7) for hydrogen containing gas and waste water outlet (8) are at the bottom section (6), the inlet (9) for the feedstock gas is provided in catalytic section (4) where catalyst is provided or just underneath thereof, and the inlet (10) for the waste water and outlet (11) for the gas mixture are provided at the top section (3).

[0081] FIG. 2 depicts a saturator (1) according to the present invention with an integrated heating system. Carbonaceous feed gas is provided to the saturator (1) via conduit 13. Prior to entry into the saturator, the carbonaceous gas is heated by heater 18. A hydrogen containing gas is provided to the saturator (1) via conduit 14. The hydrogen containing gas is heated by heater 19 prior to entry into the saturator (1). Waste water, from the Fischer-Tropsch reactor is provided to the saturator (1) via conduit 17. The waste water is heated prior to entry into the saturator (1) by heater 20 and 22. Preferably, the heating of FT waste water by heater 20 is achieved by means of exchanging heat from effluent water leaving the saturator (1) via conduit 16, to the FT waste water. Part of the effluent water can also be recycled by means of pump 21 to the saturator (1).

[0082] FIG. 3 depicts an example of a system according to the present invention. In this figure items indicated with 1, 13, 14, 15, 16, 17 correspond to the items with the same numbers in FIGS. 1 and 2. To the saturated gas of stream 15 additional stream (26) can be added after which the saturated gas is fed to a pre-reformer (23). The pre-reformed gas is fed to an auto-thermal reformer (ATR; 24). The ATR (24) is also provided with oxygen. The obtained synthesis gas is fed to the Fischer-Tropsch (FT) reactor (25). The Fischer-Tropsch synthesis product (29), FT waste water (17) and Fischer-Tropsch off gas (28) exit the FT reactor (25).

EXAMPLES

[0083] The present invention will further be illustrated by the following non limiting examples.

Example 1

[0084] The experiments were conducted in a QCS Batch Reactor system consists of 12 independent cylindrical reactors. The unit is built in stainless steel. Every time a new experiment is performed, the reactors are covered with a disposable Teflon insert to prevent cross-contamination in different experiments. Next, the required mass of catalyst and a Teflon magnet are introduced and liquid volume added. A Teflon septum is then placed on top of each reactor and the QCS lid is closed by tightening bolts. A gas atmosphere is introduced via needles that penetrate through the Teflon septum. Once the system is ready, it is placed in the heating platform, where the reaction will proceed for the required duration. The reaction can is stopped by cooling down (typically over ice). Once room temperature is reached, the catalyst+liquid sample is transferred into a Teflon eppendorf and centrifuged at 3000 rpm for 10 min. After centrifuging an aliquot of the liquid supernatant is taken for analysis, which is typically carried by gas chromatography.

[0085] A number of catalysts based on Ru, Ir, Pt or Pd where investigated with respect to the effect of Temperature (T), pressure (P), time (t), and catalyst intake.

[0086] Four different conditions were tested:

[0087] 1.260° C., 25 bar (final pressure; 14 bar hydrogen, 11 bar steam), 10 mg catalyst;

[0088] 2.260° C., 10 bar (final pressure; 14 bar hydrogen, 11 bar steam), 10 mg catalyst;

[0089] 3.180° C., 10 bar (final pressure; 6.6 bar hydrogen, 3.4 bar steam), 10 mg catalyst;

[0090] 4.260° C., 25 bar (final pressure; 14 bar hydrogen, 11 bar steam), 5 mg catalyst.

[0091] For two catalysts, supported Ru and Pt, the oxygenate conversion is shown in FIG. 2. This figure shows the effect of metal, support and process conditions on the conversion of acetic acid and ethanol.

[0092] As can be observed, full conversion of ethanol is possible with both Ru and Pt catalysts. For Pt-based catalysts a high temperature is required, whereas Ru catalysts show high activity also at low (compared to Ru) temperatures and low (10 bar) final pressure. For acetic acid conversion the Ru catalyst shows the highest activity.

[0093] These results show also that the carrier material has an effect on the catalyst activity.

Example 2

[0094] Conversion tests were conducted for catalysts based on Ru. The experiments were conducted as described in Example 1.

[0095] For the Ru catalysts a lower conversion was found for hexanoic acid as compared to acetic acid. See the results of Ru/ZrO.sub.2 in Table 1. From this table, and also from data found for other catalysts, it is concluded that a high T and high P generally are beneficial for oxygenates conversion. Interestingly, lowering the catalyst intake by a factor two hardly changes the conversion of the acids.

TABLE-US-00001 TABLE 1 Effect of pressure, temperature (T) and catalyst mass on the conversion of oxygenates by 5% Ru/ZrO2. Conversion was obtained by comparing initial concentrations and the concentrations obtained after catalytic test. Pressure Conversion (%) T (Bar) Mcat Acetic Hexanoic (° C. ) [H.sub.2, steam] (mg) Acid Ethanol Propanal Acid Pentanol 260 25 10 88 100 100 76 100 [14, 11] 260 10 10 79 100 100 70 100 [5.6, 4.4] 180 10 10 72 100 100 59 100 [6.6, 3.4] 260 25  5 85 100 100 75 100 [14, 11]

[0096] For most catalysts a high conversion (>90%) of ethanol, propanal and pentanol was found irrespective of pressure (10, 25 bar) and temperature (180, 260° C.)

[0097] The appended claims also form part of the description by means of this reference.