A PROCESS FOR RECOVERY OF HYDROGEN DURING HYDROPROCESSING OF A FEEDSTOCK COMPRISING OXYGENATES

Abstract

A process and process plant for partial hydroprocessing of a feedstock including oxygenates, including the steps of directing the feedstock, an amount of make-up hydrogen and a recycle gas to a catalytic hydrotreatment process under conditions converting 30-95% of oxygenates to hydrocarbons, to provide a partially hydroprocessed product stream, adding an amount of recycled wash water including at least 0.1 wt % oxygenates, to an amount of the hydroprocessed product stream, optionally in combination with a further amount of wash water, to provide a combined hydroprocessed product stream, cooling the combined hydroprocessed product stream and separating it in a vapor product fraction, a liquid aqueous fraction and a liquid product fraction, withdrawing as a waste stream a first amount of the liquid aqueous fraction either as a purge or by a purification process, directing as the amount of recycled wash water, at least a second amount of said liquid aqueous fraction.

Claims

1. A process for partial hydroprocessing of a feedstock comprising oxygenates, comprising the steps of a. directing said feedstock, an amount of make-up hydrogen and a recycle gas to a catalytic hydrotreatment process under conditions converting 30-95% of oxygenates to hydrocarbons, to provide a partially hydroprocessed product stream, b. adding an amount of recycled wash water comprising at least 0.1 wt % oxygenates, to a stream comprising at least 50 wt % of said partially hydroprocessed product stream, optionally in combination with a further amount of wash water, to provide a combined hydroprocessed product stream, c. cooling the combined hydroprocessed product stream and separating it in a vapor product fraction, a liquid aqueous fraction and a liquid product fraction, d. withdrawing as a waste stream, a first amount of said liquid aqueous fraction, e. directing as said amount of recycled wash water, a second amount of said liquid aqueous fraction.

2. The process according to claim 1, wherein the liquid aqueous fraction comprises at least 0.1 wt % 0.2 wt % or 0.5 wt % oxygenates and less than 20 wt %.

3. The process according to claim 1 wherein the liquid aqueous fraction comprises at least 50 ppm.sub.wt inorganic salts and less than 15 wt % inorganic salts.

4. The process according to claim 1, wherein the ratio of the mass of the wash water to the mass of the amount of said hydroprocessed product stream combined with wash water is more than 1:50 and less than 1:1.

5. The process according to claim 1, wherein an amount of the liquid aqueous fraction is directed to purge.

6. The process according to claim 5 wherein the amount of liquid aqueous fraction is directed to purge is more than 5%, 10% or 15% and less than 95% of said liquid aqueous fraction.

7. The process according to claim 5, wherein the amount of liquid aqueous fraction is directed to purge is more than 2%, and less than 50%.

8. The process according to claim 5, wherein the amount of liquid aqueous fraction directed to purge is separated in a concentrated salt brine or precipitate and an amount of purified water by use of evaporation, membrane separation or precipitation.

9. A process plant configured for carrying out a process according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] FIG. 1 shows a process layout with recycle of wash water without purification.

[0054] FIG. 2 shows a process layout with addition of fresh wash water.

FIG. 1

[0055] In FIG. 1 a feedstock comprising oxygenates (2) is pressurized in a feedstock pump (FP) and is, after heating with the reactor effluent (10) in a heat exchanger (HX), combined with a make up hydrogen gas (4) pressurized in make up gas compressor (MUGC) and a recycle gas (6) pressurized in recycle gas compressor (COMP). This feedstock stream (8) is directed to a hydrodeoxygenation reactor (HDO) comprising one or more catalysts configured, by control of conditions including composition, temperature, pressure and space velocity, to provide a desired hydrodeoxygenation conversion of the reactor feed stream (8). The conditions may be chosen to only support a limited extent of reaction, e.g. by limiting the temperature, the residence time or the availability of hydrogen. The reactor effluent (10) is cooled and the cooled reactor effluent (12) is directed to a hot high pressure separator (HHPS) providing a first product stream (14) and a vapor stream (16). The vapor stream (16) is combined with a stream of wash water (18), and the combined stream (20) is cooled in cooler (C) and directed as cold combined stream (22) to a three phase separator (TPS) from which condensed sour water (28) and light product (24) is separated from light gases (32), which are directed to the recycle compressor (COMP). An amount of the condensed sour water (28) is pressurized in recycle pump (RP) and directed as wash water, while another amount (30) may be withdrawn from the system. The first product stream (14) and light product (24) may be withdrawn as combined product stream (26).

[0056] In other embodiments additional water may be added to the recycled wash water and the process may include further steps, including purification of the recycled light gases (32) and hydroprocessing other than hydrodeoxygenation (HDO), such as hydrogenation of olefins, hydrodearomatization, isomerization. These process steps may be in series with the hydrodeoxygenation step or positioned either upstream or downstream the process illustrated in FIG. 1.

[0057] In further embodiments, the product stream (26) may be directed to a fractionation process to provide products for specific applications according to boiling point, such as naphtha for gasoline, naphtha for use in steam cracking, aviation fuel, automotive diesel or marine fuel. The product stream (26) or a fraction thereof may also be directed to further hydroprocessing steps, including isomerization, hydrocracking and hydrodearomatization.

[0058] In further embodiments, the hydrogen rich gas phase (32) may also be purified to increase the effective hydrogen pressure in the process.

FIG. 2

[0059] In FIG. 2 a comparative process is illustrated. Here a feedstock comprising oxygenates (2) is pressurized in a feedstock pump (FP) and is, after heating with the reactor effluent (10) in a heat exchanger (HX), combined with a make up hydrogen gas (4) pressurized in make up gas compressor (MUGC) and a recycle gas (6) pressurized in recycle gas compressor (COMP). This feedstock stream (8) is directed to a hydrodeoxygenation reactor (HDO) comprising one or more catalysts configured, by control of conditions including composition, temperature, pressure and space velocity, to provide a desired hydrodeoxygenation conversion of the reactor feed stream (8). The conditions may be chosen to only support a limited extent of reaction, e.g. by limiting the temperature, the residence time or the availability of hydrogen. The reactor effluent (10) is cooled and the cooled reactor effluent (12) is directed to a hot high pressure separator (HHPS) providing a first product stream (14) and a vapor stream (16). The vapor stream (16) is combined with a stream of fresh wash water (18), and the combined stream (20) is cooled in cooler (COOL) and directed as cold combined stream (22) to a three phase separator (TPS) from which condensed sour water (30) and light product (24) is separated from light gases (32), which are directed to the recycle compressor (COMP). In this process all of the condensed sour water (28) is withdrawn to the water treatment of the plant. The first product stream (14) and light product (24) may be withdrawn as combined product stream (26).

DESCRIPTION OF EMBODIMENTS

[0060] A first broad aspect of the present relates to a process for partial hydroprocessing of a feedstock comprising oxygenates, comprising the steps of directing said feedstock, an amount of make-up hydrogen and a recycle gas to a catalytic hydrotreatment process under conditions converting 30-95% of oxygenates to hydrocarbons, to provide a partially hydroprocessed product stream, adding an amount of recycled wash water comprising at least 0.1 wt % oxygenates, to at least an amount of said hydroprocessed product stream, such as a stream comprising at least 50 wt % of said partially hydroprocessed product stream, optionally in combination with a further amount of wash water, to provide a combined hydroprocessed product stream, cooling the combined hydroprocessed product stream and separating it in a vapor product fraction, a liquid aqueous fraction and a liquid product fraction, withdrawing as a waste stream a first amount of said liquid aqueous fraction, directing as said amount of recycled wash water, at least a second amount of said liquid aqueous fraction.

[0061] This is related to the benefit of minimizing the withdrawal of oxygenates in the wash water, since the wash water is at least partially saturated with oxygenates. The withdrawing of the first amount of said liquid aqueous fraction may either be as a purge or by a purification process.

[0062] A second aspect relates to a process according to the first aspect wherein the liquid aqueous fraction comprises at least 0.1 wt % 0.2 wt % or 0.5 wt % of oxygenates.

[0063] This has the associated benefit of providing a liquid aqueous fraction which will withdraw a minimum of oxygenates from the process.

[0064] One aspect relates to a process according to the first aspect wherein the liquid aqueous fraction comprises less than 20 wt %, 10 wt % or 5 wt % of oxygenates, such that the amount of oxygenates bound in the liquid aqueous fraction is moderate.

[0065] A third aspect relates to a process according to the first or second aspect wherein the liquid aqueous fraction comprises at least 50 ppm.sub.wt or 100 ppm.sub.wt inorganic salts and less than 15 wt % or 10 wt % inorganic salts.

[0066] This has the associated benefit of such a process being able to hydroprocess a feedstock comprising inorganic salts, and recycling wash water having a capacity for recuperation of salts.

[0067] A fourth aspect relates to a process according to the first three aspects wherein the ratio of the mass of the wash water to the mass of the amount of said hydroprocessed product stream combined with wash water is more than 1:50, 1:20 or 1:10 and less than 1:1, 1:2 or 1:5.

[0068] This has the associated benefit of balancing the process convenience of a low amount of water relative the partially hydroprocessed product stream against the increased level of removal of water soluble impurities such as salts.

[0069] A fifth aspect relates to a process according to the first four aspects wherein an amount of liquid aqueous fraction is directed to purge.

[0070] This has the associated benefit of continuously removing an amount of impurities and produced water from the process, but centralizing the purification of the purged water in a process plant water treatment system.

[0071] A sixth aspect relates to a process according to the fifth aspects wherein the fraction of liquid aqueous fraction is directed to purge is more than 5%, 10% or 15%.

[0072] This has the associated benefit of a high purge corresponding to a process in which the net production of water is higher than the amount required as wash water, which typically would be the case for thermally decomposed biological feedstocks, with 5%, 10% or even up to 50% oxygen content.

[0073] At the same time the amount directed to purge must be limited such as less than 95% or 90% to provide a remaining amount of liquid aqueous fraction for recycle.

[0074] A seventh aspect relates to a process according to the fifth or sixth aspect wherein the amount of liquid aqueous fraction is directed to purge is less than 50%, 25% or 15% with the associated benefit of a moderate purge corresponding to a process in which the net production of water is less than the amount required as wash water, which typically would be the case for thermally decomposed feedstocks with a low content of biological materials and having less than 5% oxygen content. The amount of liquid aqueous fraction is directed to purge may be more than 2%, 5% or 10% to ensure salts and other impurities are withdrawn from the process.

[0075] An eighth aspect relates to a process according to the fifth, sixth or seventh aspect wherein the amount of liquid aqueous fraction directed to purge is separated in a concentrated salt brine or precipitate and an amount of purified water by use of evaporation, membrane separation or precipitation.

[0076] This has the associated benefit of reducing the amount of water directed to waste.

[0077] A ninth aspect relates to a process plant configured for carrying out a process according to any of the aspects above.

Examples

[0078] To illustrate the benefits of the present disclosure, a process has been studied with pure make up wash water and with recycled wash water.

[0079] The process studied is a process where the liquid feedstock produced in hydrothermal liquification of forest waste is partially hydroprocessed with the objective of producing a fuel comprising hydrocarbons and oxygenates (HC+Oxyg). The liquid feedstock comprises an amount of chloride and washing to remove the chloride is required to obtain a satisfactory product. The hydroprocessed product stream has the composition shown in Table 1, stream 12, and is subsequently washed and separated in gas, sour water and product, either in Example 1 using recycled wash water according to the present disclosure and FIG. 1, or in Example 2 using pure or purified wash water according to the comparative process of FIG. 2. For practical reporting, the amount of nitrogen and chloride are reported as NH.sub.3 and HCl respectively even though the aqueous solutions would contain this in ionic form such as NH.sub.4.sup.+ and Cl.sup..

[0080] The performance of Example 1 is reported in Table 1. Here it is seen that with recycle of wash water, 896 kg/hr of sour water is still withdrawn in stream (30) as purge from the process, and that this water contains about 1 kg/hr of Cl. The heavy product stream (14) contains 1.9 kg/hr, corresponding to 166 ppm Cl and the light product stream (24) contains 3 g/hr HCl, corresponding to 2.4 ppm Cl. The purge of water (30) contains 1.1 kg/hr (1232 ppm) Cl and 145 kg/hr dissolved hydrocarbons and oxygenates. Due to the residual Cl, especially in the heavy product stream, it is necessary to direct the product to a stripper.

[0081] The corresponding performance of Example 2 is reported in Table 2. Here it is seen that with recycle of wash water, 1312 kg/hr of sour water is withdrawn in stream (30) as purge from the process, and that this water contains about 1.1 kg/hr of Cl. The heavy product stream (14) contains 1.9 kg/hr Cl, corresponding to 166 ppm Cl and the light product stream (24) contains 1 g/hr HCl, corresponding to 1.0 ppm Cl. The purge of water (30) contains 1.1 kg/hr (842 ppm) Cl and 160 kg/hr dissolved hydrocarbons and oxygenates. As for Example 1 the heavy product stream dictates a requirement to direct the product to a stripper.

[0082] Since significant amounts of CO.sub.2 are present in the hydrogen rich gas stream (32), both process layouts would typically involve purification of this stream, e.g. by amine wash.

[0083] From these data it is seen that recycle of the wash water without purification results in lower removal of compounds soluble in water; both Cl and oxygenate product. Washing with pure or purified wash water will reduce the Cl concentration in the light product from 2.4 ppm Cl to 1.0 ppm Cl, but since the heavy product requires stripping, this difference is not of significance. At the same time, washing with pure wash water will withdraw an extra 15 kg/hr product to waste as dissolved oxygenates.

TABLE-US-00001 TABLE 1 Stream 12 14 16 18 20 30 24 32 Phase Mixed Liquid Vapor Mixed Mixed Liquid Liquid Vapor Temp. [ C.] 274 240 240 47 214 50 50 50 Total [kg/hr] 16753 11927 4826 400 5226 896 1239 2691 H.sub.2O [kg/hr] 1167 328 839 331 1170 741 89 10 NH.sub.3 [kg/hr] 10.9 1.3 9.6 2.6 12.2 5.9 0.5 3.2 H.sub.2S [kg/hr] 13.5 1.5 12.0 0.1 12.1 0.2 1.4 10.4 CO.sub.2 [kg/hr] 532 29 503 1 505 3 17 483 H.sub.2 [kg/hr] 658 11 647 0 647 0 1 646 HCl [kg/hr] 3.0 1.9 1.1 0.5 1.6 1.1 0.003 0.002 HC + Oxyg [kg/hr] 14371 11556 2815 65 2880 145 1131 1538 Cl [ppm] 184 166 230 1232 306 1232 2.4 0.6

TABLE-US-00002 TABLE 2 Stream 12 14 16 18 20 30 24 6 Phase Mixed Liquid Vapor Mixed Mixed Liquid Liquid Vapor Temp. [ C.] 274 240 240 50 214 50 50 50 Total [kg/hr] 16753 11927 4826 400 5226 1312 1224 2689 H.sub.2O [kg/hr] 1167 328 839 400 1239 1142 87 10 NH.sub.3 [kg/hr] 10.9 1.3 9.6 0.0 8.6 6.2 0.3 2.0 H.sub.2S [kg/hr] 13.5 1.5 12.0 0.0 11.9 0.3 1.3 10.3 CO.sub.2 [kg/hr] 532 29 503 0 503 4 16 482 H.sub.2 [kg/hr] 658 11 647 0 647 0 1 646 HCl [kg/hr] 3.0 1.9 1.1 0.0 1.1 1.1 0.001 0.001 HC + Oxyg [kg/hr] 14371 11556 2815 0 2815 160 1117 1538 Cl [ppm] 184 166 230 0 212 842 1.0 0.2