CA1194012A

CA1194012A - Catalyst for converting sulfur-containing gases

Info

Publication number: CA1194012A
Application number: CA000429089A
Authority: CA
Inventors: Max Appl; Karl-Heinz Gruendler; Guenter Zirker; Peter R. Laurer; Matthias Irgang
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1982-06-08
Filing date: 1983-05-27
Publication date: 1985-09-24
Also published as: ZA834109B; DE3367171D1; DE3221582A1; ES523059A0; IN157344B; JPS58214342A; ES8406222A1; EP0096322B1; EP0096322A3; AU1546183A; EP0096322A2

Abstract

O.Z. 0050/3595 Abstract of the Disclosure: A catalyst which comprises oxides and/or sulfides of cobalt and/or nickel or molyb-denum, an alkali metal salt and a carrier composed of magnesium aluminum spinel, and whose moldings possess a star-shaped cross-section, star-shaped cross-sectional surfaces with rounded points or a clover leaf-shaped cross-section, a process for the preparation of such a catalyst and its use for converting carbon monoxide and steam in sulfur-containing gases, to carbon dioxide and hydrogen.

Description

- 1 - 2.Z. 0050/359S8 C l t f r convertin sulfur-containin ases ata ys o ~ g g In the production of synthesis g3s, gases com-prising var;ous amounts of carbon monoxide and sulfur-containing impurities are obtained. In partic~lar, the partial oxidation of heavy fuel oil and~or coal gives the sulfur-containing, CO-rich gases, ~hich for many synthe-ses have to be converted in greater or lesser amounts to hydrogen-rich gases. It is frequent~y advantageous to carry out the conversion ~;thout remov;ng H2S beforehand, and sulfur-res;stant catalysts are employed for this purpose.
Catalysts which contain molybdenum and cobalt and, ;n the sulfid;c state, 3ccelerate the conversion react;on are disclosed in German ?atent 1,085,787, German Published Applicat;ons DAS 1,667,_ o and DAS 7,054,869 and U.S.
Patent 4,153,580, and th~ addit on of an alkali metal is disclosed in 8rit;sh Patent ~48,û85.
The conventional catalysts are employed in the form of e~trudates, tablets or beads.
Although the catalysts contain;ng lanthanum com-pounds or rare earth metal compounds, as describeG in U.S.Patent 4,153,58û, and the ZnO-containing or MgO-containing catalysts described in German Published Application DAS
1,o67,386 possess good long-term stability in respect of mechanical strength and BET surface area, their activity in the convers;on is inadequate below 280C.
Alkal; metal-containing catalysts having a pure Al2n3 carrier, as described in German Published Application DAS 2,054,869, give high CO conversions even at low temperatures (220 - 280C) and low pressures, but gamma- or eta-aluminum oxide carriers have the disadvantage that they are very sensitive to steam at high pressures. The AL2O3 is converted hydrothermally to autoclave boehmite, with the result that the moldings lose their strength and the amount of rubbings increases subs~antiallY.
The present invention relates to a catalyst which can be used Eor converting carbon monoxide and steam in sulfur-containing gases to carbon dioxide and hydrogen and comprises an oxide, a sulfide or a mixture thereif of at least one metal selected from the group consisting of cobalt, nickel and molybdenum, an alkali metal salt and a carrier composed of magnesium aluminum spinel, and whose moldings possess a star-shaped cross-section, star-shaped cross-sectional surfaces with round~d points or a clover leaf-shaped cross-section.
The present invention furthermore relates to a process ~or the preparation of a catalyst of this type, wherein the carrier material is mixed with the active com-ponents, and the material is brought to a moldable consistency and is then extruded or tabletted. Either the carrier material itself or the carrier material together with some of the active components can be converted to mold~ngs, and the active components or some of the active components, respectively, can be applied onto the moldings in one or more steps, by impregnation.
The present invention furthermore relates to the use of this catalyst for converting carbon monoxide and steam 3G in sulfur-containing gases to carbon dioxide and .~ _ - 3 - 0.~. 0050/359S~
hydrogen at from 180 to 550C and under from 1 to 150 bar, in a singte-stage or multi-stage conversion reactor with intermediate cooling between the individual stages.
In the multi-stage conversion, the catalyst is advantageously employed as a ~ow-temperature conversion catalyst in the second and third conversion stagesoronly in the last convers;on stage, while a conventional con-version catalyst is used ;n the remaining conversion stages. In e;ther a single-stage or a multi-stage con-version reactor, only a part of the convent;onal catalyst in one stage or in each of severa~ stages may be replaced by the novel catalyst; in particu~ar from 10 to 50~ of the upper parts of the catalyst bed in a conversion stage may be replaced.
It is an object of the pr-sent invention to oro-vide a catalyst ~hich gives 3 high C0 conversion and a~so possesses a long service life under the cond;tions of the process. This means that the residual C0 content should be only slightly above the equilibrium value even at from 220 to 2~0C and under low pressures, that a h;gh space-time y;eld is achieved so that the desired C0 convers;on can be reached using low catalyst volumes, and that the catalyst possesses h;gh mechan;cal strength, and the act-ive components and the carrier show only sl;ght signs of aging. Finally, pressure loss and weight per l;ter should also be very low.
In accordance w;th the invention, the catalyst shapes used possess a relatively high surface area to volume ratio. Particularly suitable for this purpose are o~
- 4 - O.Z. OaS0/35953 annular, star-shaped or clover leaf-shaped catalyst cross-sections, ie. all geometric shapes which differ from a spherical or cylindrical shape in that their cross-sec-tional area is smaller than a circumscribed circle. In particular, the invention relates to all concave catalyst shapes. A ~eometric body is concave when the cross-sectional surface possesses pairs of points which can be joined by a straight line which does not lie ent;rely within the cross-sectionaL area.
These particular catalyst shapes simultaneously fulf;l the requirements in respect of high surface area to volume ratio and of lo~ pressure loss.
The pressure loss is stated as the dimensionless friction factor ~1,000 of a cata~yst charge, standardized to a Reynolds7 number of 1,000 and spherical catalyst particles of 1û mm diameter.
The most advantageous shape for the present prob-lem possesses a particularly high A/V ratio coupled ~ith a very small~ 1,000.

O.Z. 0050/35958 Shape D L 0 ~ A/~~1,000 (mm) (mm) ~cm2) (cm3) -1 _ Sphere 3 - 0 28 0 014 20 200 Sphere 6 - 1 13 0 113 10 ~C
Cylinder 1.5 4 0.23 0.007 33 ~6û
Cylinder 4 7 1.13 0.088 13 1Q0 Three-pointed star 4 7 0 94 0.035 27 90 F;ve-pointed star 4 7 1.40 0.042 34 8Q

The table shows that the best values are obtained for the star-shaped catalysts. The three-pointed star has the advantage that it is mechanically more stable and easier to produce than the five-pointed star.
We have found that when the star-shaped catalysts are employed the C0 equilibrium concentration can be approached Yery closely. Particularly at low reaction temperatures, use of the star-shaped catalysts permitted a reduct;on in the residual C0 content by 30 - 50% com-pared with the res;dual C0 content obtained using cylin-dr;cal catalysts under the same experimental conditions~
Reduction in the residual C0 conten-t has substantial advantages in particular when, as in the case of the pro-duction of synthesis gas for the ammonia synthesis, a com-pletely C0-free gas is required. In this case~ the major part of the C0 which is not transformed by the above con-vers;on process is converted to CH4 by methanization, and this CH4 enters the ammonia synthesis cycle as an inert lZ

~ 6 - O.Z. 0050/35958 gas. The reduction in the inert 935 content has the effect of saving energy and improving the y;eld, based on synthesis gas employed; th;s also means that a smaller amount of waste gas is produced.
The improved low~temperature act;v;ty obta;ned by using star-shaped catalysts has the advantage that ;t also permits energy to be saved ;n that a lowering of the reaction temperature, for example in 3 second conversion stage, allows a greater amount of heat to be recovered between the convers;on stages. ~xamples of possible geo-metric cross-sections are those shown in Figures 1, 2 and 3. The production of concave moldings of this type offers the following advantages over the conventional catalysts:
higher activity, ie. lower residual C0 concentration and lower reactor temperature, longer service life, resu~ting from higher initial activity and lower operating tempera-ture, low pressure loss, and greater volume of voids and hence better dust retention.
The sulfur-resistant catalysts which are suitable for the conversion contain elements of sub-groups 6 and 8 of the periodic table, in particular Mo/Co, Mo/Ni and Cr/
Fe, as active components, and in many cases contain alk-ali metal or alkaline earth metal compounds as promoters.
The no~el catalysts are prepared from a suitable carrier comprising, for example, magnesium aluminum spinel, zinc aluminum spinel or a magnesium oxide/aluminum hyd-roxide mixture. This pulverulent carrier material is mixed thoroughly with the active components, and is - 7 - O.ZO 005~/35958 brought to a moldable cons;stency in a kneader or a simi-lar mixing apparatus. Molding is then carried out as a rule by extruding the paste throush a su;table die, for example a star-shaped die. For conventional catalysts, the extrusion die used is in general circular. Shaping by tabletting is also possible and can give concave mold-ings. In preparing the catalyst, it is also possible to start from pre-shaped carr;ers, and the active components and promoters are then appl;ed by ;mpregnation or are sprayed on.
The activity of the catalysts was tested under superatmospheric pressure, eg. 10, 30 and 50 bar, and for a dry gas containing 10% of CO, 34Y, of C02, 55% of H2, 0.5%
of H2s and 0 5X of inert gas. The steam/dry gas ratio was 1.0, and the temperature, pressure and catalyst load were var;ed A mixture of 5~ of AlOOH and 25% of MgO ;s very finely milled, and the milled mixture is mixed in a kneader, with the addition of 6% of 65Y. strength nitric acid~ and is then compacted in the kneader for 3 hours with the addition o-f water, until the material is capable of being molded. It is then extruded through a star-shaped matrix (diameter of circumscribed circle: 4 mm, cf. Figure 1), and the carrier is dried, and calc;ned at 55~C.
The active components are applied by impregnation, 700 ml of 18% strength ammonium heptamolybdate solut;on, ._ ~ 9~
- 8 - O.Z. OOSOJ35958 700 ml of cobaLt nitra~e solution (7~ of CoO) and 700 ml of 2Q~ strength potass;um oxalate solution be;ng employed per kilogram of carrier. Each impregnation step is fol-lowed by drying and calcination at 550C
Pressure loss per m of height at a gas velocity of 1 m/sec: ~P = 60~ mm water column The procedure described in Example ~ is followed, except that a circular extrusion die of 4 mm diameter is used. The chemical composition of the catalyst corres-ponds to that of Example 1.
~ mm water column Pressure loss per m of height: ~ P= 6Z0 mEXAMPLE 3 The ca~alysts described in Examples 1 and 2 are employed for converting a steam/g3s mixture in a pressure reactor. The gas to be converted has the above composition.
The catalyst is first sulfurated with an H2S/H2 mixture for twelve hours at 350C, and the gas mixture is then fed in together with steam in a ratio of 1 : 1.
The total pressure is 30 bar and the catalyst load is zo 6,0ûO liters of dry gas per liter of catalyst per hour.
The following results are obtained:

._ 4~

- 9 - 0.~. 0050/35958 Volume-% Ot CO in the exit gas T (C) 4 mm star 4 mm extrudate Equilibrium as described as described in Example 1 in Example 2 2Sû 0 85 1 3û 0 36 275 0.65 0.95 0 53 300 û 80 û 90 0 76 The procedure described in Example 3 is followed, except that the following cond;tions are employed:

Volume-'~ of CO in the exit gas T (C) 4 mm star 4 mm extrudate Equilibrium Pressure: 10 bar, space velocity: 3,000 liters per liter of catalyst per hour 250 0.5û 1.02 0.34 275 0 55 0 ~5 0 51 300 0.75 1.05 0.73 Pressure: 10 bar, space velocity: 1,000 liters per liter of catalyst per hour 22û 0 40 0 75 0 20 250 0 ~5 0 60 0 34 280 0.62 0 80 0 51 7.5 kg or aluminum hydroxide tAlOOH), 2.5 kg of magnes;um ox;de, 1.3 kg of ammonium heptamolybdate and

2.6 kg of cobalt nitrate solution (15X of CoO) are mixed ;n a kneader, and the mixture is kneaded, with the addi~
tion of water, until the material is capable of being molded. It is then extruded through a star-shaped matrix ._ ~L9~

~ 10 - O.Z. 0050/35958 (diame-ter of circumscribed circle: 4 mm) and the mater;al obtained is dried heated at 550C and then ;mpregnated ~;th potassium oxalate solution. To do this 1.8 kg of potassium oxalate are dissolved in 7 liters of water and the above catalyst precursor is impregnated w;th this solueion. The catalyse is then dried and heated (550C).
Pressure loss per m of height at a gas velocity of 1 m/sec.: ~ P = 600 mmWS
H m The procedure described in Example 5 ;s followed except that a circular matr;x of ~ mm d;ameter ;s used for molding the catalyst.
Pressure loss per m of height at a gas velocity of 1 m/sec. ~P = 6Z0 mmWS
H m The activ;ty ;s tested as described in ~xample 3 under the follo~ing conditions:
COE = 10X; steam/gas = 1.0; pressure: 30 bar; space velocity = 6 ûO0 liters per liter of catalyst per hour.

~olume-% or C0 in the exit gas T ( C~ 4 mm star 4 mm extrudate Equ;l;brium as described as described in Example 5 in Example 6 250 0.95 ~.~0 0.36 Z75 0.85 0.95 0.62 300 0.85 0.90 0.76 ~ O.Z. OOS0/359S8 The activity is tested as described in Example 3, under the following conditions:
COE = 1Q~; steam/gas ~ 1.û; pressure: 10 bar: space velocity = 3,ûO0 liters per liter OT catalyst per hour.

250 0.75 1.12 0.34 275 0.70 0.98 0.51 30û 0.85 0.92 0.73 To determine the mechanical properties of the resulting catalysts under operating conditions, these catalysts are treated with a 1 : 1 gas/steam mixture for 100 hours under 50 bar and at 300C (cf. section on cata-lyst testing).

~ 9~Q~2 - 12 - O.Z. OOS0/35958 Hardness Rubbings (%) X-ray analysis (kg/extrudate) before after before after before after treatment treatment treatment 4 mm star (Example I) 14.7 13.0 6.5 4.7 spinel spinel 4 mm extru-date (Example 2) 8.2 7.1 9.2 4 spinel spinel 4 mm Al203 bead (conven-tional catalyst carrier) 8.7 1.6 0.3 41 eta- boehmite Al203

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A catalyst which can be used for converting carbon monoxide and steam in sulfur-containing gases to carbon dioxide and hydrogen and comprises an oxide, a sulfide or a mixture thereof of at least one metal selected from the group consisting of cobalt, nickel and molybdenum, an alkali metal salt and a carrier composed of magnesium aluminum spinel, wherein the catalyst molding possesses a star-shaped cross-section, star-shaped cross-sectional surfaces with rounded points or a clover leaf-shaped cross-section.

2. A process for the preparation of a catalyst as claimed in claim 1, wherein the carrier material is mixed with the active components, and the material is brought to a moldable consistency and is then extruded or tabletted.

3. A process for the preparation of a catalyst as claimed in claim 1, wherein the carrier material itself is converted to moldings, and the active components are applied onto the moldings in one or more steps, by impregnation.

4. A process for the preparation of a catalyst as claimed in claim 1, wherein the carrier material together with some of the active components are converted to moldings, and the remainder of the active components are applied onto the moldings in one or more steps, by impregnation.