IE51391B1 - Process for the generation of hydrogen from carbon monoxide and water - Google Patents

Abstract

1. A process for producing hydrogen by means of a homogeneously catalysed conversion of carbon monoxide and water into carbon dioxide and hydrogen using a carbonyl compound of the metals Fe, Co, Cr, Mo, and/or W as the catalyst in the form of an aqueous basic solution, characterized in that carbon monoxide is reacted with water and one of said metal carbonyls at a temperature from 190 degrees C to 300 degrees C and at a carbon monoxide partial pressure between 40 and 500 bar.

Description

The invention relates to a process which converts carbon monoxide (CO) and water (HjO) into carbon dioxide (C02) and hydrogen (H^) by homogenous catalysis and which on suitable selection of the reaction parameters gives yields of 85 to 95 % in short reaction times.

The conversion of CO according to CO + H20 C02 + H2 (1, serves for th° technical production of hydrogen from CO-rich gases produced by gasifying coal or hydrocarbons. Because of Ιθ the unfavorable equilibrium at high temperatures reaction (1) has to be performed below 500° C. However, the equilibrium is established very slowly in this temperature region, so that highly active catalysts are required. For many years solid catalysts based on iron or copper have been utilized at 350 to 500° C (high temperature process, iron catalysts) and at 210 to 270° C (low temperature process, copper contacts). During the last years several authors attempted to develop homogenous catalyst systems which would avoid the nigh energy level of the high temperature process and the sensitivity to catalyst poison of the low temperature process in systems with minimal technical difficulties. (Bibliography in C. Ungermann, V. Landis, S.A. Moya, H. Cohen, H. Walker, R.G. Pearson, R.G. Rinker and P.C. Ford, J. Amer. Chem. Soc. 101, 5922 (1979)) .

The main component of the hitherto known systems usually consists of a transition metal carbonyl compound which has been tested in water containing solvents at CO-pressures of 0.25 to 300 bar and temperatures of 80 to ca. 180° C.

The interesting catalyst system derived from iron pentacarbonyl (Fe(CO)j.) and alkalines was already mentioned by W. Reppe in 1953 (W. Reppe and coworkers, Liebigs. Ann. Chem. 582, 121 (1953)) and has been investigated by R.B. King (C.C. Frazier, R.M. Hanes, A.D. King, Jr. and R.B. King in Inorganic Compounds with Unusual Properties (R.B. King, editor), Vol. II, Chapter 9, pages 94ff> Advances in Chemistry Series 173, Am. Chem. Soc., Washington, D.C. and R.B. King et al, J. Amer. Chem. Soc. 100, 2925 (1978)) and R. Pettit (R. Pettit, K. Cann, T. .Cole, C.H. Mauldin and W. Slegeir in Inorganic Copounds with Unusual Properties (R.B.

King, editor) Vol. Il, Chapter 11, pages 121 ff, Advances in Chemistry Series 173, Am. Chem. Soc. Washington, D.C. 1979), The conversion rates so far observed are, however, too small for technical application. Furthermore, the main disadvantage is caused by the fact that under these conditions even after longer reaction times the reaction (1) does not establish the thermodynamic equilibrium of more than 95 % hydrogen yield, but stops below 40 % hydrogen yield depending on the experimental parameters in an unclear manner.

These low hydrogen yields do not permit an economic application of the Fe(CO)^-base-system.

C.C. Frazier et al show on page 97 of the above mentioned reference in Table II the effect of pressure and temperature on the reactivity of the iron pentacarbonyl-catalys water gas shift reaction. The iron pentacarbonyl catalyst is used in butanol as solvent which contains the necessary amount of water.

According to this publication temperatures between 140 and 160°C are preferred. Runs 4 and 5 of Table II show temperatures of 181° C and 183° C respectively. The turnover numbers (mole - 3 51391 hydrogen/mole metal per 6 hours) are given in the last column of Table II. It is stated on page 96, lines 26 - 28 that the turnover numbers represent only the turnover in an early stage of the reaction. In a further reference (A.D. King, Jr.,R,B.

King and D.B. Yang, J. Am. Chem. Soc 102, p. 1028 et seg.(]g7g) King et al are discussing the homqgeneous catalysis of the water gas shift reaction using iron pentacarbonyl in a mainlymethanolic solution. From Fig. 4 on page 1003 follows'that the turnover number is not constant over the whole reaction time lu turnover number is proportional to the slope of the partial pressure of hydrogen versus time-curve). Therefore, the turnover numbers of Table II of Frazier et al cannot be used to estimate the expected hydrogen yields. Run 6 (161°<3 and run 9 (163° C) of Table II of the Frazier et al reference are des15 cribed in more detail'and evaluated in form of Fig. 1 and Fig. II on pages 98 and 99 respectively. From the last measured points of these Figures one can calculate that10 run 6 after 25 hours less than 40 % conversion and in run 9 after hours less than 24 % conversion are measured. On page 100, second paragraph, it is stated that the rate of hydrogen production increases as the reaction temperature is raised.

In thereafter following Figure 3, same page, it is only demonstrated that the rate of the very early stage of the reaction is raised by increasing temperature when the partial pressure of the carbon dioxide formed during the reaction is neglectable However, this does not permit to deduce that the obtainable hydrogen yields at the end of the reaction are also increased 51331 Frazier et al and King et al are using alcholic solutions of the catalysts which solutions contain water in a small amount. King et al state in their publication on page 1030, left column, last paragraph, that the use of water should be avoided because it is stated in line 5 pure water is seen to be a very poor choice of solvent. In this connection, Figure 3 in the same column, lowest curve, has to be considered from which follows that at 140°C after 70 hours less than 103S conversion is obtained. As explanation for these results the low solubility of carbon monoxide in water and the decomposition of the catalyst system which is connected therewith is given on page 1032, left column, last paragraph by King et al.

It follows from the above discussion that the state of the art until immediately before the priority date of the instant application has dissuaded the artisan from using high temperatures and water as solvent for the water gas shift reaction of carbon monoxide and water to carbon dioxide and hydrogen.

According to the present invention there is provided a process for producing hydrogen by means of a homogeneously catalyzed conversion of carbon monoxide and water into carbon dioxide and hydrogen using a carbonyl compound of the metals Fe, Co, Cr, Mo, and/or W as the catalyst in the form of an aqueous basic solution, wherein carbon monoxide is reacted with water and one of said metal carbonyls at a temperature from 190°C to 300°C and at a carbon monoxide partial pressure between 40 and 500 bar.

The process presented here is based on the surprising, not forseeable observation that at temperature above 220°C weakly basic aqueous solutions of Fe(C0)g do convert CO and HgO into COg and Hg with yields up to 95%. Reaction rates high enough for an application are achieved only above 180°C.

Completely unexpected is the temperature behaviour of the system: between 180 and 250°C and in some cases between 180° and 220°C the reaction (1) does not give complete conversion. but depending on the temperature a certain, not to be exceeded, maximal yield is found which is around 40 % at 180° C and can be raised to 95 % by increasing the temperature. This surprising behaviour shall be demonstrated by means of the pressure-temperature- and pressure-reaction time-diagrams in figures 1 and 2.

In figure 1 curve a describes the theoretical pressure-temperature-dependence of an inactive system (no conversion, hydrogen yield 0 %) calculated by addition of the ideal CO-pressure (gas law) and the respective steam pressure of the excessive agueous phase. Curve b is obtained in a similar manner for Figure 1 complete conversion (hydrogen yield 100% corresponds to a 51331 twofold amount of gas). The experimentally measured points of table 1 marked by (o) show that in a typical run (initial CO pressure 48 bar) heating the autoclave rapidly and continuously to 222 °C the reaction starts noticably above ca. 180 °C and g proceeds to high conversions on approaching the final temperature. Figure 2 shows the corresponding pressure-time-dependence whereby the continuous line between the experimental points represents the isothermal pressure development when the final temperature of 222 °C was reached. When the system was only 10 heated to 181 °C (experimental points (x) of table 2) the conversion reached a final reaction pressure of 115 bar asymptotically after 5-7 hours (figure 2) which according to figure 1 corresponds to a yield of about 40 %. pibarj Figure 2 On further heating to 198 °C the reaction started again until after 3 to 4 hours another limiting value of about 70 % yield was obtained. Raising the temperature once more to '217 °C . finally gave the pressure corresponding to a practically complete conversion. This observed temperature behaviour clearly indicates that despite of a low catalytic activity of the Fe(CO) (.-alkali-water-system higher yields than about 40 % are in principle not to be attained below 180 °C. Temperatures of only 220 °C and more lead to hydrogen yields which are interesting with regard to a technical application.

Mixtures of water, alkali and carbonyl compounds of the metals Cr, Mo, W, Co, Ni give results similar to the Fe(CO)^-system.

In the -conversion using metal carbonyl catalysts hydrido-metal carbonyl complexes, among others, are apparently involved, i.e. metal compounds having hydrogen bonded directly on the metal. Therefore, a catalytically active phase can be prepared using a metal carbonyl compound itself or precursors which give the metal carbonyl or the hydrido-metal carbonyl in a preceeding process or under the reaction conditions themselves. For instance Fe(CO)g is fqrmed directly from metallic Iron, iron (II) compounds or .polynuclear iron carbonyls (for instance Fe2(CO)g, Fe^ (CO)by reaction with CO.

Accordingly Fe(CO)g might be replaced by these substances.

Similarly polynuclear anionic iron complexes react to the hydrido-tetracarbonyl ferrat anion (HFe(CO)^ ) with CO, as for 2- 2instance Fe2(CO)θ and HFe3(CO)13 . Therefore, the application of such compounds - with or without an additional base 8 513 31 similarly leads to catalytically active mixtures. These examples shall illustrate that each compound or mixtures of those compounds are suitable to prepare the catalyst solution which either form metal carbonyls or hydrido-metal carbonyl compounds and higher analogs, having hydrogen bonded directly on the metal or establish equilibria with those species.

All compounds which form hydroxyl ions, under circumstances only under the reaction conditions, are suitable bases, preferably the alkali and earth alkali metal hydroxides, carbonates, and hydrogencarbonates, especially sodium carbonate and sodium hydrogencarbonate.

Generally the process is carried out by intimately mixing tne aqueous phase containing the catalyst component(s) and the gas phase of CO or CO-rich gases in a pressure vessel at temperatures of 190 to 300 °C,, preferably 200 to 270 °C, and at carbon monoxide partial pressures of 1 - 500 bar, preferably 20 to 100 bar. The concentration of the metal component and the base which has to be applied is dependent on the kind of components and the reaction parameters pressure and temperature. The carbon monoxide partial pressure can be varied in broad limits, but should not fall below the C0decomposition pressure of the metal carbonyls. Addition of organic solvents like ether or alcohols is sometimes advantageous.

Definition of some terms used hereafter: 1.) Composition of the product gas X CO molar fraction of hydrogen in the product gas and XCQ are defined in analogy 9 5139 1 2. ) hydrogen yield = x (X + x )_1 «2 L.U 3. ) Z^, Ζβ = number of catalytic cycles relative to metal and base, respectively, expressed by mole hydrogen per mole metal.or base Z„ = yield,. mole (CO) · mole (metal) 1 Μ H, z --1 Z = yield„ mole (CO) · mole (base) xi q Example 1 A 500 ml shaking autoclave with fittings, both made ' from stainless steel (DIN 1.4571), was charged with 1:96 g (0.01 mole) Fe (CO),.., 1.06 g (0.01 mole) water-free sodium carbonate (Na2CO3) and 100 g (5.56 mole) water, pressurized initially with 48 bar (0.8 mole) carbon monoxide under exclusion of oxygen and heated to 222 °C with shaking. During the whole experiment the internal temperature and the pressure wereg measured by an iron constantan thermocouple and a pressure gauge, respectively. Table 1 shows the experimental data of pressure, 'temperature and reaction time.

Composition of the product gas X- H2 0.493, XCO2 Xc0 0.093,ZM 67' ZB 67, yieldg^ 84 .1 %. Table 1 Reaction Time Temperature Pressure (h) (°C) (bar) 0 20 48 0.3 130 72 0.7 185 91 10 Reaction Time (h) Temperature (°C) Pressure (bar) 1.0 200 109 1.3 210 125 1.5 217 142 1.9 219 154 2.1 220 162 2.8 221 172 3.3 222 178 3.4 222 180 4.1 222 184 4.4 222 184 Example 2 The autoclave was charged in the same manner as in 15 Example 1 and heated stepwise first to 181 °C, then to 198 °C an finally to 217 °C. The experimental data are given,in table 2 494, 0.427, Xco 0.079, yield^ 86.2 i, Table 2 Reaction Time (h) Temperature (°C) Pressure (bar) 0 20 48 0.5 '176 87 0.7 183 90 0.8 178 90 Reaction (h) Time Temperature (°C) Pressure (bar) 1.0 178 92 1.5 181 . 98 5 2.0 185 104 3.0 181 107 4.0 181 111 5.0 '181 113 5.5 181 114 10 6.0 181 115 6.4 185 117 6.9 190 122 7.3 193 124 7.8 196 129 15 8.0 198 137 8.9 198 141 10.0 198 145 11.0 198 146 12.0 198 147 20 12.2 205 150 12.9 215 168 13.4 217 174 13.8 217 177 14.7 217 179 Example 3 4.9 g (0 .025 mole) Fe (CO) 5 were dissolved in 100 g 1 m : sium hydroxide by stirring the mixture 6 h at 60 °C with exclusion of oxygen (argon atmosphere). The brown-yellow solution of potassium hydridotetracarbonyl ferrat (KHFe(CO)4) and 46 bar initial pressure of carbon monoxide (0.77 mole) was heated to 260 °C in the 500 ml shaking autoclave. After .5 h (1.5 h heating time, 4 h isothermally at 260 °C final pressure 210 bar) a gas sample had the following composition: Xf[ 0.489, XCQ 0.452, XCQ 0.060, yieldH 89.1 %, ZM 27, Zb*9· ( Examples 4 to 13 The examples 4 to 13 were carried out similarly to Example 1. The parameters and results are given in Table 3.

Si 391 ω Μ α C -LJ Ο rt ♦fc fc — •P 0) u u tfo rt ε — fl) C) tf 0) fc 3 in w £h 0) fc fc tf rt Λ Ό rt W Φ r-l fc « α — •fc in fc jj in rt •fc 1ΙΛ C fc H CU I o u I c e c o A fc rt u cu Ό -fc tt 0) rfc E Ο cn ηί Ο ηί ηί ηί Ο m vo sr r* ΟΟ> τm m γ- ηί ηί ηί CM CM Ο Ο Ο Ο ηί τ— Ο Ο ηί ηί ηί ηί ιη σι Ο *r to m sr ηί in νο m νο ηα ηί ηί ηί m Ο in m ιη Ο τ— m in sr νο ηί ηί ηί ηί η) Ο r— co ο tn t— ΓΊ γ- co co σ σι η* Ο τ- τ- t- τ- γ-: τ- ηί vo co O -3* sr σ sr sr vo η η» n co vo vo r*· O -- Q O co vo vo vo vo •sr sr sr sr -3* O -co η η η n OOO Ο O sr njsrininiococoioco Λ m σιιηηίΓΜηηίηίηίηί >α — fl) ifc A rt fc fl) -P rt fl) rfc ε vo in in □ in rt tf fl) rfc tf •O tf x> VO vo vo vo m ni nJ ni r- in in *tn tn m m ni ni nj in tn in in nJ nJ m ni cn m cn Γ) O tf O O U K tf o L) ni tf tf tf tf o rt m rt rt a O o o tf 2 tf 2 2 tf tf w « in r- O in in O o O o o ni m m r- r" 0) ni tf »fc a) η >1 £ tn v-· vosr«nin^*r*r*nto r* n-inninin*inininm nj τO Omsrn»csovovniT— cn o -3* ni in co »— «— sr O cn αοσνσνοοοοσνσνοοσ» nl tn sr •fc O tn O U O rfc X rt rt tf n r- in ni Sf rt O 0 U 6 •P X ϋ P m CO 0 m sr fc tf tf X O cn O cn σν sr n O m n n- vo sr χ- O O O O O O 6 Ο Ο Ο O sr co co σν m co tn in co sr η ό sr sr sr sr sr ο ο ο ο O o r> ni cn ηί η σν cn ν- η* η* O co sr tn sr sr in *4* 501 0.455 0.044 463 0.450 0.087 480 0.467 0.053 >1 c /3 fc rt u co in in in in in in vo vo —- vcO o ooo O ο ο ο u υ ο u O υ υ υ O --- — U ni 0) G) fl) fl) fl) fl) fc 0 0 tf tf tf tf tf tu O S 5 U rt -P fl) QJ Ω: f: rt tt w in Ο ηί Ο vn in O m tn in m V- Γ- N OJ rin Ό r-- co σνο*—men rt o •fc 4J ϋ rt fl) tf rt a) e •fc sr incorntncn-rcnsTn· P< e rt tt tf invorxOOcnos-cMcn II . 51391 Examples 14-27: Continuous Apparatus The apparatus consists of a vertically arranged reaction tube of 1,3 litre content (2000 mm length, 28 mm inner diameter) which is heated by oil circulating around the tube, a further tube mounted thereon which is heated in the same manner and has a capacity of 1.7 1 (670 mm length, 56 mm inner diameter) and which serves for separating the gas from the liquid, and a reflux condenser (620 mm length, 56 mm inner diameter) which is water-cooled. An aqueous sodi um carbonate solution (o.l %, 1 % and 10 % respectively) was pumped through a metering pump into the lower end of the reaction tube at the beginning of the runs. The filling height was adjusted by means of an overflow valve mounted at the upper end of the reaction tube. The water consumed was supplemented by the pump when necessary. Carbon monoxide was introduced into the lower end of the reaction tube by means of a compressor operation at constant pressure on the high pressure side, through a pressure vessel (700 ml content) filled with iron pentacarbonyl (250 ml iron penta carbonyl) and through an oil-heated preheater. The pressure vessel and a downstream capillary leading to the pre-heater were maintained at the same temperature to permit the partial pressure of the iron pentacarbonyl to be adjusted to a specified value. The withdrawal of gas was controlled by means of a release valve on the top of the condenser and recorded by a flowmeter. The gas analysis was performed by means of a gas analyzing apparatus (Orsat) at specified time intervals. The temperature was measured in the upper third of the reaction tube.

The parameters of the process, experimental results and the data calculated from the results of examples 14 - 27 are given in Table 4 and defined as follows: (Na+) concentration of sodium ions in mol/1 in the agueous phase P total pressure in bar measured at the top of the reaction tube Fe(CO)t reaction tube temperature in C temperature of the iron pentacarbonyl in °C Partial pressure of iron pentacarbonyl in bar rFe(C0)5 output gas gas withdrawn in 1/h (related to 20°C and atmospheric pressure) input CO carbon monoxide calculated from output gas and hydrogen yield - input in 1/h (related to 20°C and atmospheric pressure) Input Fe(CO)g iron pentacarbonyl calculated from input CO (related to the actual process parameter TFe (C0)gand P) and PFe(CO)g inPut in 9/h· CO/FE(CO)g Calculated molar carbon monoxide-iron pentacarbonyl 5 ratio at the reaction tube inlet output H2 production rate of hydrogen calculated from output gas and hydrogen yield in 1/h (related to 20°C and atmospheric pressure).

Temperature, pressure, partial pressure of iron pentacarbonyl and jq throughput of carbonmonoxide varied in examples 14 - 22 whereby levels of conversion (=hydrogen yield) of up to 70 % were obtained when carbon monoxide was passed once through the liquid phase. As it can be seen from examples 20 and 22 respectively on the one hand and 17 and 21 respectively on the other hand, the temperature is the decisive process parameter which allows high levels of conversion. If the reaction tube is charged with fillers (cylindrical wire nets from V^A, 6 mm diameter, examples 23 - 27) this results in higher throughputs at the same yields. Pumping of a 10 % instead of a 1 $ agueous sodium carbonate solution has no significant influence. However the activity of a 0.1-percent solution decreases remarkably (examples 26 and 27).

CM 4-> CL 4-) □ O © LD O CM σι «cr o co oooooooooo LO «— ©CBCOOOsTCOCM CO r- r- CM r— CM CM CM CM O r> CM O co CM o co CM O r— CM TABLE 4 Process parameters and results for the continuous apparatus ) reaction tube charged with fillers (cylindric wire nets from V2A, 6mm diameter) -PO ri. 3 0·— CL'—' \ c φ σ> •P -C CLO S, C Oi— Ο *O I- »— υ ε φ >> Φ -fJC o >> cl ω x: -P rt'i. 3 CBr— o $ro xa + »<β Q Ζ E x UJ O CQOOOOOOOOO ©r--cM©©oog©o r-CMCMsr©srsrsTsrsr o o o sr sroOsrCMCOCO»-CMr— r- Lf) fx Π CM IS r* CO r— CO cooor--rs.rors.©cn ©rs©©©©©©© CM r— fS {s. ts CO Sf CM ST ST rs ο o in io CM CM CM CM CM CO O O O o sr © o © © © CM CM CM CM ©dodo IO O O O O CM CO LO MP © o o o o o CM CM CM CM CM CM CM CM CM CM © © CO Ο O © © sr co cm sr to cn σι ι— o vo co sr © rs io sr © cm ο o © O to O sr IO r- CM r- CM o © CM oooo oooo CM CM CM CM OOOO O O O O O © LO LO © © O O CM CM CM CM sT CO CM sr co CM O CM CM ο ο o g g © co co co co CMCMCMCMCMCMCMCMCMCM oooooooooo σι co ·— r— CM r— co co rs to LO IO r*. o sr co LO Γ-* © IO © O CO O st r— © © CM r- CM CM OOOO © © © © st sr oo co co co co co CM CM CM CM oooo co co co co <0 CM CM Ο O o o CM O

Claims (10)

1. A process for producing hydrogen by means of a homogeneously catalyzed conversion of carbon monoxide and water into carbon dioxide and hydrogen using a carbonyl com5 pound of the metals Fe, Co, Cr, Mo, and/or W as the catalyst in the form of an aqueous basic solution, wherein carbon monoxide is reacted with vzater and one of said metal carbonyls at a temperature from 190°C to 300 °C and at a carbon monoxide partial pressure betvzeen 40 and 500 bar. 10

2. The process according to claim 1, wherein the reaction is carried out at a temperature betvzeen 200°C and 270°C.

3. The process according to any of claims 1 and 2, wherein the reaction is carried out at from 50 to 100 bar.

4. The process according to any of claims 1 through 3, 15 wherein hydroxides of the alkali metals or alkaline earth metals are used as the aqueous base.

5. The process according to any of claims 1 through 3, wherein a weak base selected from the carbonates or hydrogen carbonates of the alkali metals or alkaline earth metals is used 20 as the aqueous base.

6. The process according to claim 5, vzherein sodium carbonate is used as the weak base.

7. The process according to any of claims 1 through 6, wherein iron pentacarbonyl is used as the carbonyl compound. 25

8. The process according to any of claims 1 through 7, wherein the weak base and the metal carbonyl compound are used in a molar ratio of from 1 to 3:1.

9. A process as claimed in claim 1 for the production of hydrogen by homogeneously catalysed conversion of carbon monoxide and vzater into carbon 30 dioxide and hydrogen using metal carbonyl compounds as catalysts, substantially as described herein with reference to the Exaznples.

10. Hydrogen whenever produced by a process according to any preceding claim.