Devices and methods for hydrogen generation via ammonia decomposition

Abstract

Systems and methods for hydrogen generation via ammonia decomposition that utilize a fixed bed reactor configured to receive inflows of NH.sub.3 and oxidant and to produce an outflow of high purity H.sub.2. The fixed bed reactor contains a fixed bed of a NH.sub.3 decomposition catalyst wherewith the NH.sub.3 decomposes to form N.sub.2 and H.sub.2; a plurality of ceramic hollows fibers with a high surface to volume ratio disposed in the fixed bed, the hollow fibers having an H.sub.2 selective membrane disposed thereon for extracting H.sub.2 from N.sub.2 and to form a permeate of the high purity H.sub.2 and a retentate of primarily N.sub.2; and a catalytic H.sub.2 burner also disposed in the fixed bed, the catalytic H.sub.2 burner for burning a portion of the H.sub.2 with the oxidant to provide thermal energy for the NH.sub.3 decomposition.

Claims

1. A system for generating hydrogen via ammonia decomposition, the system comprising: a fixed bed of a NH.sub.3 decomposition catalyst configured to receive inflows of NH.sub.3 and wherewith the NH.sub.3 decomposes to form a combined stream of N.sub.2 and H.sub.2; a plurality of spaced apart and longitudinally aligned ceramic hollow fibers, each of the plurality of spaced apart and longitudinally aligned ceramic hollow fibers including an H.sub.2 selective membrane disposed thereon for extracting H.sub.2 from the combined stream of N.sub.2 and H.sub.2 and to form a permeate comprising a high purity H.sub.2 and a retentate comprising primarily N.sub.2; and a catalytic H.sub.2 burner extending through the fixed bed, the catalytic H.sub.2 burner comprising a metal tube containing a H.sub.2 oxidizing catalyst therein and configured to receive and burn at least a portion of the retentate to provide thermal energy for the NH.sub.3 decomposition.

2. The system of claim 1 wherein the retentate additionally comprises an amount of H.sub.2 and wherein at least a portion of the retentate and an oxidant inflow are introduced into the catalytic H.sub.2 burner within the fixed bed reactor to provide thermal energy for the NH.sub.3 decomposition.

3. The system of claim 1, therein the H.sub.2 burner comprises a spiral tube configuration extending through the fixed bed.

4. The system of claim 3, wherein an outlet end of the H.sub.2 burner metal tube releases N.sub.2 and H.sub.2O.

5. The system of claim 1 wherein each of the plurality of spaced apart and longitudinally aligned ceramic hollow fibers comprises a porous ceramic material, and additionally comprising a NH.sub.3 cracking catalyst loaded within the porous ceramic material for cracking of residual NH.sub.3.

6. The system of claim 5 providing a conversion of ammonia to hydrogen and nitrogen in excess of 99%.

7. The system of claim 1 wherein the plurality of spaced apart and longitudinally aligned ceramic hollow fibers are in a parallel alignment.

8. The system of claim 1, wherein at least a portion of the NH.sub.3 decomposition catalyst is disposed around and in a space between adjacent pairs of the plurality of spaced apart and longitudinally aligned ceramic hollow fibers.

9. The system of claim 1 wherein a maximum NH.sub.3 decomposition reactor temperature of the fixed bed reactor is no more than 450 C.

10. The system of claim 1 wherein the inflow of NH.sub.3 comprises NH.sub.3 vapor at 10-15 bar.

11. The system of claim 1 wherein a conversion of ammonia to hydrogen and nitrogen is in excess of 99%.

12. The system of claim 1 additionally comprising a preheater whereby heat provided by at least one stream selected from the group consisting of a stream of permeated high purity H.sub.2 and a stream of catalytic H.sub.2 combustion exhaust preheats the inflow of NH.sub.3 to the fixed bed reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Objects and features of this invention will be better understood from the following description taken in conjunction with the drawings, wherein:

(2) FIG. 1 is a simplified schematic of a system for generating hydrogen via ammonia decomposition and more particularly a membrane reactor for H.sub.2 generation via thermal catalytic NH.sub.3 decomposition in accordance with one aspect of the subject development.

(3) FIG. 2 is a photomicrograph of designated portion A shown in FIG. 1, e.g., low-cost, highly active Ru-based catalyst for NH.sub.3 decomposition contained within the membrane reactor in accordance with one aspect of the subject development.

(4) FIG. 3 is a simplified schematic representation of designated portion B shown in FIG. 1, e.g., showing an H.sub.2 selective membrane on ceramic hollow fibers with high surface to volume ratio for extracting H.sub.2 from N.sub.2 (simultaneously shifting NH.sub.3 decomposition reaction) in accordance with one aspect of the subject development.

(5) FIG. 4 is a simplified schematic representation of designated portion C shown in FIG. 1, e.g., a catalytic H.sub.2 burner to provide thermal energy for NH.sub.3 decomposition in accordance with one aspect of the subject development.

(6) FIG. 5 is a simplified schematic of an H.sub.2 production test system in accordance with one aspect of the subject development and referenced in Example 1.

(7) FIG. 6 is a simplified schematic of an HYSIS simulation system referenced in Example 2.

DETAILED DESCRIPTION

(8) The subject development provides a novel compact intensive and modular NH.sub.3 decomposition (2NH.sub.3N.sub.2+3H.sub.2) device with high conversion and high energy efficiency (>70%) at relatively low temperature (<450 C.).

(9) An exemplary system or device in accordance with the subject development is expected to generate high purity H.sub.2 at high rate from close-to-complete NH.sub.3 conversion, in a small reactor volume.

(10) A system or device for generating hydrogen via ammonia decomposition, generally designated by the reference numeral 10 and in accord with one embodiment of the subject development, is shown in FIG. 1. The system 10 includes a membrane reactor 12 that includes or comprises three key components: i) a fixed bed of low-cost, highly active catalyst for NH.sub.3 decomposition, generally designated by the reference numeral 14 and more specifically shown in FIG. 2, ii) an H.sub.2 selective membrane on ceramic hollow fibers with high surface to volume ratio, generally designated by the reference numeral 16, for extracting H.sub.2 from N.sub.2 and simultaneously shifting NH.sub.3 decomposition reaction, more specifically shown in FIG. 3 and a catalytic H.sub.2 burner to provide thermal energy for NH.sub.3 decomposition, generally designated by the reference numeral 18 and more specifically shown in FIG. 4.

(11) In these figures, certain of the process streams are identified as follows:

(12) 101 FeedNH.sub.3

(13) 102 Cracked streamN.sub.2+H.sub.2 (75%)

(14) 103 ProductH.sub.2 (high purity)

(15) 104 Membrane retentateN.sub.2+H.sub.2 (25%)

(16) 105 Airfeed to the catalytic burner

(17) 106 Side productN.sub.2+H.sub.2O

(18) As shown in FIGS. 1-4, a feed stream of NH.sub.3 101 is introduced into the membrane reactor 12 such as through an inlet 22. In the reactor 12, the NH.sub.3 contacts the NH.sub.3 decomposition catalyst fixed bed 14 and undergoes decomposition/cracking to form nitrogen (N.sub.2) and hydrogen (H.sub.2) gas, see FIG. 2. The 142 selective membrane on ceramic hollow fibers with high surface to volume ratio 16 serve to separate or extract H.sub.2 from N.sub.2 from the cracked stream, stream 102, see FIG. 3, and form a stream 103 of high purity H.sub.2 such as discharged or recovered from the reactor, such as via the product outlet 24. Suitable ceramic hollow fibers includes aluminum hollow fibers but other ceramic materials such as known to those in the art can be used, if desired. As shown, catalyst can desirably be loaded on the external surface of the hollow fibers 30. As shown in FIG. 3, the ceramic hollow fibers 30 in a dense tube 31, e.g., stainless steel tube, wherethrough the H.sub.2 permeate is recovered, stream 103, and the membrane retentate is passed on, stream 104. As shown in FIG. 3, active catalyst 32 can also be loaded in the ceramic hollow fibers 30 to assist in the decomposition residual NH.sub.3.

(19) As noted above, the reactor 12 includes and/or contains a catalytic H.sub.2 burner 18 such as to provide thermal energy for NH.sub.3 decomposition. As shown in FIG. 4, the catalytic H.sub.2 burner 18 can desirably be formed of or include a metal tube 40 such as containing a H.sub.2 oxidizing catalyst 42, such as known in the art. As shown in FIG. 1 and FIG. 4, the catalytic H.sub.2 burner 18 desirably serves to burn a portion of the produced H.sub.2 (for example, such as hydrogen in the membrane retentate, stream 104 reacting with via intake oxidant, e.g., air, such as stream 105) to provide thermal energy for the NH.sub.3 decomposition.

(20) The subject development can and desirably does provide or result in the following advantages/characteristics: Pressurized NH.sub.3 vapor at 1015 bar (stream 101) will be used directly as feedstock; Low-cost, highly active catalysts (for example, ruthenium-based NH.sub.3 decomposition catalysts such as known in the art or other suitable NH.sub.3 decomposition catalysts such as known in the art) will be used in a compact fixed bed reactor for high rate NH.sub.3 decomposition (2NH.sub.3N.sub.2+3H.sub.2) at reaction temperature below 450 C.; H.sub.2 selective membrane on ceramic hollow fibers with high surface to volume ratio will be used as a reactor boundary to extract high purity H.sub.2 from the reaction product; the removal of the H.sub.2 will also shift the reaction towards higher conversion; If needed, active catalyst will also be loaded in the ceramic hollow fiber to decompose residual NH.sub.3; Lower concentration residual H.sub.2 in the retentate (stream 104) will be burned with air in a catalytic burner to provide thermal energy uniformly needed for NH.sub.3 decomposition; Permeated high purity H.sub.2 (stream 103) and exhaust from catalytic H.sub.2 combustion (stream 106) at elevated temperature will be used to preheat NH.sub.3 feed (stream 101); and High purity H.sub.2 (>99%) (stream 103) after heat exchange will be compressed for applications.

(21) Table 1, below, shows a comparison of the invention with current and emerging technologies for H.sub.2 generation from thermocatalytic NH.sub.3 decomposition and also with the ARPA-E technical targets.

(22) TABLE-US-00001 TABLE 1 Comparison between technologies and ARPA-E technical performance targets Bimodal catalytic Apollo membrane Palladium Invention ARPA- Energy reactor membrane membrane Description E target System.sup.[1] (BCMR).sup.[3] reactor.sup.[4] Reactor H.sub.2 delivered cost at target <$4.5/kg N/A N/A N/A $4.078/kg pressure Final prototype size, L H.sub.2/min 10 7.5 0.044 0.081 10 H.sub.2 generation rate, g H.sub.2/h/cm.sup.3 >0.15 0.126 0.038 0.0144 0.2 Conversion to H.sub.2 >99% >99.99% 74% 85% >99% Energy efficiency >80% N/A N/A N/A 88.45% Maximum cracking temperature, 450 480~660 400~450 500~600 450 C. H.sub.2 delivered pressure, bar 30 1 0.005 1 30 Life time (projected), yrs 10 N/A N/A N/A 10 Concentration of catalyst <100 ppb <100 ppm.sup.a NH.sub.3 (4.5%) <0.8% <100 ppb poisoning impurities N/A: not available; .sup.acalculated based on reported conversion;

(23) As identified above, Apollo Energy System Inc. (USA) designed an NH.sub.3 cracking device to generate H.sub.2 for fuel cell. Hz-containing anode off gas was used as a fuel for combustion to provide thermal energy for the cracker. Conversion to H.sub.2 was high (99.99%) due to the high reactor temperature (480660 C.). The energy efficiency was not reported, but it is likely high due to the efficient use of thermal energy from H.sub.2 combustion for reactor heating. An efficient commercial catalyst (70 wt % Ni on Al.sub.2O.sub.3) modified with Ru was used. Therefore, a high H.sub.2 generation rate was also obtained. Membrane reactors have been studied for H.sub.2 generation from NH.sub.3 decomposition..sup.[9][10] However, the technology is still at the early research stage, and both the H.sub.2 generation rate and conversion to H.sub.2 are much lower than ARPA-E's targets (Table 1).

(24) HYSYS simulation/calculations (Examples 1 and 2) show that the subject development is expected to have high H.sub.2 production rate, low H.sub.2 delivered cost at target pressure, and high energy efficiency at 400 C., as shown in Table 1. The lower reaction temperature is expected to extend the lifetimes of both membrane and catalyst. NH.sub.3 conversion is expected to be higher than 99% due to the equilibrium reaction shifting by selective H.sub.2 extraction. Overall, compared with existing technologies, the subject development can or does result in the following advantages: Rational and modular design of well-integrated catalyst, membrane and H.sub.2 burner; High performance of three key components as supported by our preliminary results; Lower operation temperature (350-450 C.) while close-to-complete NH.sub.3 decomposition; High H.sub.2 purity (>99%); and Higher energy efficiency and much smaller equipment size (meaning smaller footprint).

(25) Ammonia, as a promising CNLF and an effective H.sub.2 source, can be synthesized from air and water (N.sub.2 extracted from air and H.sub.2 from water) using renewable energy sources. To produce H.sub.2 as an intermediate, it is essential to develop effective and economic NH.sub.3 decomposition technologies. The subject development (such as represented the system schematic shown in FIG. 1) represents a new and innovative solution. Its innovativeness is reflected in the following aspects: Low-cost, highly active catalysts for fast NH.sub.3 decomposition; Low-cost highly H.sub.2 selective membrane for extracting H.sub.2 with purity >99% (simultaneously shifting NH.sub.3 decomposition reaction towards conversion >99%); Catalytic H.sub.2 burner embedded in the reactor for providing thermal energy for NH.sub.3 decomposition to achieve overall energy efficiency as high as 88%; and Membrane in a high packing-density (high surface to volume ratio) hollow fiber configuration capable of achieving a compact modular system that can be scaled up linearly by just adding additional membrane modules.

(26) The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES

Example 1

Calculation of H.SUB.2 .Production Rate in the Membrane Reactor

(27) FIG. 5 illustrates an Hz production test system 500 in accordance with one aspect of the subject development. The system 500 includes a NH.sub.3 supply source such as an NH.sub.3 cylinder 502, a membrane reactor 504 system such as described above, and a hydrogen product storage, such as a hydrogen product tank 506. The system 500 further include a preheater cross heat exchanger 510 and a cross heat exchanger 512 such as to appropriately preheat the feed (e.g., stream 101) to the membrane reactor 502 and to recover heat from the hydrogen product (stream 103) and the reactor flue gas (stream 106), respectively.

(28) The system 500 shows the NH.sub.3 feed stream (stream 101 at 25 C., 10 bar and a feed rate of 0.3434 mol/min), permeate stream (stream 103 at 400 C., 2.5 bar, the permeate composed of H.sub.2 at 0.4464 mol/min=10 L/min and N.sub.2 at 0.004509 mol/min), and retentate stream (stream 104 at 400 C., 2.5 bar, the retentate composed of that 0.0687 mol/min and N.sub.2 at 0.1673 mol/min) and the membrane reactor 504 operating at 400 C.

(29) H.sub.2 production rate: 10 L H.sub.2/min

(30) Input:

(31) Catalyst:

(32) K-promoted Ru/-Al.sub.2O.sub.3

(33) Catalytic activity at 400 C.: 4.5 mmol H.sub.2/min/g catalyst

(34) Packing density: 1 g/cm.sup.3

(35) Membrane:

(36) Composite SAPO-34 membrane on hollow fiber (1.5 mm od) housed in metal tube (2 mm od1.6 mm id)

(37) H.sub.2 permeance at 400 C.: 1.510.sup.4 mol/(m.sup.2.Math.s.Math.Pa)

(38) H.sub.2/N.sub.2 selectivity: >700

(39) Catalytic H.sub.2 burner:

(40) Pt-impregnated Ni foam

(41) Heat transfer rate: 1.5 kcal/(cm.sup.2.Math.h)

(42) Output:

(43) Catalyst volume: 116 cm.sup.3

(44) Membrane area: 0.2 m.sup.2

(45) Membrane volume: 133 cm.sup.3

(46) Catalytic H.sub.2 burner volume: 10 cm.sup.3 (estimated from energy needed for decomposing NH.sub.3 feed)

(47) Estimated top space of the membrane reactor: 10 cm.sup.3

(48) Total membrane reactor volume: 269 cm.sup.3

(49) Calculated H.sub.2 generation rate: 0.20 g H.sub.2/h/cm.sup.3

Example 2

Energy Efficiency Calculation Using HYSYS Simulation

(50) Referencing the HYSIS simulation system 600 shown in FIG. 6.

(51) HYSYS Flow Diagram:

(52) Stream and Energy Summary:

(53) H.sub.2 production: 10 L (STP)/min and at delivery pressure of 30 bar

(54) $\mathrm{Energy}\mathrm{Efficiency}\left(EE\right)=\frac{P}{P+E}=\frac{0.0271233.3}{0.0271233.3+848.7018/3600}=88.45\%$

(55) While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.