CA1080205A

CA1080205A - Active and durable sulfuric acid catalyst

Info

Publication number: CA1080205A
Application number: CA258,390A
Authority: CA
Inventors: Fawzy G. Sherif
Original assignee: Stauffer Chemical Co
Current assignee: Stauffer Chemical Co
Priority date: 1975-09-11
Filing date: 1976-08-04
Publication date: 1980-06-24
Also published as: GB1526873A; BE846016A; DK405876A; FR2323633A1; JPS5233895A; FR2323633B1; DE2640169A1; NL7609923A

Abstract

ABSTRACT OF THE DISCLOSURE

A catalyst is disclosed which is suitable for the oxidation of sulfur dioxide to sulfur trioxide which comprises a diatomaceous earth support which is mixed with vanadium compounds, promoters and activators and shaped. The diatomaceous earth which is employed contains at least 40% by weight of calcined diatomaceous earth of Melosira granulata diatoms which have been calcined at a temperature of from about 960°F. to about 1850°F.

Description

~o~vzos Background of the Invention Sulfuric acid i8 a ~ackbone of industry. It i8 necessary for preparing many industrial products from fertil-izers to pharmaceuticals and from petrochemicals to steel.
In 1974 approximately 34.5 million tons of sulfuric acid were produced in the United States.
Sulfuric acid is usually prepared on a commercial scale by the gas phase oxidation of sulfur dioxide to sulfur trioxide followed by absorption of the sulfur trioxide in an aqueous medium. Modern industrial plants for preparing sulfuric acid usually utilize a supported vanadium contact catalyst for the oxidation of the sulfur dioxide to sulfur trioxide.
Throughout the history of the "contact sulfuric acid"
process there has been a diligent search for active and durable sulfur dioxide oxidation catalyst which can be commercially pre-pared at a reasonable cost. Until this time a practitioner of the art, on a commercial scale, had a choice between an active cataly8t or a durable ca~alyst. The virtues of durability and hi~h activity in a catalyst at a reasonable price have eluded the diligent searches of catalyst manufacturers.

108VZI)5 It is the object of the present invention to provide a durable and active sulfur dloxide oxldation catalyst. A further object of the present invention is to provide a durable and active sulfur dioxide oxidation catalyst which can be prepared at a~reasonable cost. It is a further object of the present invention to provide a vanadium containing, durable and active ;
sulfur dioxide oxidation catalyst which can be prepared with-out undue modification of existing equipment and procedures.
Brief Summary of the Invention According to the present invention, an active and durable vanadium containing sulfuric acid catalyst is provided which comprises shaped particles comprising vanadium compo8i-tions, promoters and activators supported on a calcined and finely comminuted diatomaceous earth which contains mainly the fresh water diatom Melosira granulata.
The vanadium compositions, promoters and activators comprise the active portion of the catalyst (herein noted as active material) and are well known in the art.
The support material comprises calcined and finely com-minuted diatomaceous earth containing preferably 50~ of thediatoms by weight of the fresh water diatom Melosira granulata.
Higher proportions of the diatom Melosira granulata provide a more active and durable catalyst.
The support is calcined at a temperature above about 95GF. and below the temperature at wlnich the structure of the silica in the diatom changes which is about 1850F. The cal-cining reduces the amount of organic matter in the diatomaceous lO~OZ05 earth and at the higher temperatures the chemical composition is changed. Temperatures between about 1200 and 1800F. are preferred.
The support must be finely comminuted since small particle size increases both the durability and activity of the catalyst prepared with the support.
Description of the Drawings Figure 1 is a diagrammatic drawing of the apparatus for determining catalyst activity.
Figure 2 is a scanning electron micrograph of the fresh water diatom Melosira granulata enlarged 3000 diameters.
Figure 3 is a graph of particle size distribution of the diatomaceous earth supports employed in the examples set forth herein as determined by a Sharples Micromerograph TM .
Detailed Description of the Invention In present day sulfuric acid practlce, the sulfur dioxide oxidation catalyst is generally a supported vanadium composition which is "promoted" or "activated" by addition of certain alkali metal moieties and minor amounts of such com-pounds as cobalt, nickel, calcium, barium, iron and the like.
The composition of such catalysts and the effect of various promoters and activators on the activity of the catalyst is well known as is discussed in Topsoe and Nielson, Transactions _f the Danish Academy of Technical Sciences, No. 1J 1948, and TandyJ "The Role of Alkali Sulphates in Vanadium Catalysts for Sulfur Dioxide Oxidation", J. Applied Chemistry, February 6, 1956, Pages 68-74.

108~05 The vanadium composition is usually supported on a carrier material for several reasons. The amount of expensive vanadium, the active material, in the catalyst can be reduced relative to the volume of catalyst required. Additionally, it 5 i9 believed that the active vanadium composition is in the molten or plastic state at the temperature at which the catalyst i9 most active for oxidation of sulfur dioxide to sulfur tri-oxide in the sulfuric acid process. The active vanadium compo-sition would fuse into a molten mass if it is not supported.
Many materials have been used as supports for vanadium compositions in sulfur dioxide oxidation catalysts. Materials such as alumina, pumice, silica gel, fullers earth, diatomaceous earth, zeolites and mixtures of these materials with various binders are disclosed in the literature as suitable supports for sulfur dioxide oxidation catalysts.
The catalyst is usually prepared in the form of dis-crete shaped particles. The particles can be in the form of spheres, cylindrical pellets, tablets or irregular particles graded to a desired particle size range. Shaping and sizing of the catalyst particles is important to minimize the pressure drop realized by the gases passing through the catalyst bed in the operation of the process.
Supported sulfur dioxide oxidation catalysts are generally prepared by two methods. In one method, a shaped support particle is prepared and the vanadium containing com-10~30Z05 position with the promoters and activators is intimately ad-mixed with the shaped support particle. The shaped catalyst support can be impregnated with a solution of the catalytically active materials or the shaped particle can be intimately ad-mixed with the active catalytic composition and the mixtureheated to a temperature at which the catalytic composition be-comes a fluid and flows over the surfaces of the shaped support. `~
Another method for preparing shaped, supported catalysts is to intimately admix the vanadium composition with the particulate support and subsequently shape the admixture to form the catalyst particles. The mixture to be shaped can be prepared by dry mixing the particulate support material with the active materials followed by the addition of a liquid to form a mixture of the proper consistency w'.~ich can be shaped and which will retain the shaped configuration. The support can be mixed with a slurry of the active material followed by the addition of a controlled amount of water to obtain a mix-ture with a consistency suitable for shaping into the desired catalyst shape. The catalyst can also be prepared by admixing the catalyst support with a solution of the catalytic composi-tions and adjusting the amount of water to obtain a mixture of the consistency suitable for shaping.
Tableting presses, briquetting mills, pellet mills and ~ .
~ the like are suitable means for shaping the mixture of the ;~ 25 catalyst support and the active catalytic compositions into : - 5 -.. .
,................... . . . .

particles of the desired siæe and shape. Shaping means are well known in the art and require no elaboration at this point.
It is preferable to use shaping means which also compact the mixture to form the shaped particles.
After the mixture containing the vanadium compounds, promoters and activators, and the support~ is shapedJ it is dried to remove the water utilized in the preparation.
The dried shaped particles are then contacted with an oxygen containing gas 9 tream containing small amounts of from about 2 to about 6~ of sulfur dioxide mixed with sulfur tri-oxide at a temperature in the range of from about 600 to 900F.
Reaction with the dilute sulfur dioxide containing gas stream activates the catalyst particles and after a suitable activa-tion period, the shaped particles are suitable for use as a catalyst in a sulfur dioxide oxidation process.
The preparation of sulfur dioxide oxidation catalysts containing vanadium is discussed on Topsoe and Nielson, Trans-action of the Danish Academy of Technical Sciences, supra.
The activation step which is sometimes called sulfating and the requirement that the catalyst be reacted with ' dilute sulfur dioxide containing gas streams to accomplish the activation is discussed in the Topsoe and Nielson article, supra.
Briefly, the activation is generally utilized since the unactivated catalyst reacts rapidly and irreversibly with ~80Z05 sulfur dioxide at the elevated temperature of the sulfur dioxide oxidation reaction. The reaction of the sulfur dioxide with the catalyst i9 exothermic and the temperature of the catalyst can increase to a point at which the catalytic activity and structural integrity of the catalyst can be severely impaired.
It is` therefore the general practice to activate a vanadium containing sulfuric acid catalyst by contact with a dilute sulfur dioxide and sulfur trioxide containing gas stream before use in a commercial operation. Activation or sulfation of sulfur dioxide oxidation catalysts is well known in the art.
The catalyst of the present invention iSJ preferably, prepared by mixing the vanadium containing compositions and various promoters and activators (active material) with the novel diatomaceous earth support. The mixture of active mater-ial with the diatomaceous earth support is then adjusted to aproper consistency by addition or removal of water, and shaped into the required form. A suitable catalyst particle can also be prepared by drying a mixture of an aqueous solution or slurry of the active material with the novel support and crush-ing and screening the dried mixture to form irregular particlesin a narrow size range. However, it is preferred to prepare the catalyst in the form of regular shaped particles since the particles provide for minimum pressure differentials through the catalyst bed.

,' ' ' . . .

: lO~OZO~
The active materials can be dry mixed with the cata-lyst support followed by the addition of water to form a mixture with the desired consistency to be shaped. Another method suitable for preparing the supported catalyst of the present invention is to admix a slurry of the active materials with the catalyst support and adjusting the consistency of the mixture to that required for shaping.
The catalyst can also be prepared by admixing a solu-tion of the active materials with the diatomaceous earth support and adjusting the amount of water in the mixture to provide a material with a consistency which can be readily formed into the desired catalytic particle shape.
It is not critical how the active materials are ad-mixed with the catalyst support as long as an intimate admixture of the catalytic compositions with the catalyst support is obtained.
The active materials are well known in the sulfur di-oxide oxidation catalyst art and the best methods for admixing the active materials with the diatomaceous earth support would be dependent upon the particular composition chosen for making the catalyst. Vanadium pentoxide is a useful vanadium contain-ing composition for preparing the sulfur dioxide oxidation catalyst of the present invention. The useful concentrations of vanadium compositions and the promoters and activators u~ilized in preparing a sulfur dioxide oxidation catalyst are well documented in the literature and will not be discussed herein.

1~30Z05 The improved properties of the catalyst of the present invention, i.e., the combination of high activity and high durability, are achieved by use of a particular diatoma-ceous earth as the catalyst support. The diatomaceous earth useful in the practire of the present invention is a diatoma-ceous earth containing a major portion of the diatoms of the fresh water diatom Melosira granulata. As is known in the artJ
diatomaceous earth is a naturally occurring material which, after removal of water, contains primarily diatoms mixed with minor amounts of clay mineral type materials and organic im-; purities. The diatoms are primarily silicon dioxide. The amount of alumina in the diatomaceous earth reflects the amount of clay minerals admixed with the diatoms. The diatomaceous earth useful in the practice of the present invention generally contains from about 55 to about 90~ by weight of the calcineddiatomaceous earth of diatoms. The catalyst support should contain at least about 40~ by weight of the calcined diatoma-ceous earth of the fresh water diatom Melosira granulata and most preferably from about 50 to about 80~ of the diatom Melo-sira ranulata. Higher proportions of the diatom Melosiragranulata in the support increase the durability of the catalyst.
The diatomaceous earth catalyst support preferably contains from about 2.5 to about 10.5~ aluminum calculated as alumina (Al203).
Figure 2 is a scanning electron micrograph showing the diatom Melosira ~ranulata enlarged to ~000 diameters.

:. _ g _ lO~VZO~

The support must be finely comminuted. The fine com-minution increases the activity and also increases the durabil-ity of the catalyst. It is preferred that the diatomaceous earth support be comminuted so that at least about 25% by weight of the particles are smaller than about 10 microns and preferably at least about 40~ by weight are smaller than 10 microns.
It is preferred that the maximum particles size be no larger than about 100 microns, but mixtures containing small amounts of particles over 100 microns can be useful in the practice of the lnvention.
The diatomaceous earth support can be readily prepared by grinding coupled with air classification methods.
The support must be calcined. The calcination in-crea9es the activity of the catalyst. The calcination is carried out by heating the diatomaceous earth to a temperature from about 950 to about 1850F. and preferably from about 1200 to about 1800F. The calcination can be carried out in a ro-tating kiln type apparatus.
The time of calcination is dependent on the temperature.
Times from about 5 minutes to about 8 hours are suitable and from about 30 minutes to about 4 hours most preferred. Methods for calcining diatomaceous earth are well known in the art.
It is believed that calcination removes certain organic impurities from the diatomaceous earth. Calcination can also decompose carbonate impurities if they are present in the diatomaceous earth. The diatomaceous earth must not be heated to a temperature high enough to change the structure of the silica which makes up the individual diatoms. Little effect on the structure of the silica in the diatomaceous earth occurs at temperatures below about 1850F.
It is preferred to calcine the diatomaceous earth sup-port before admixture with the active materials and the shaping of the particles.
The activity of the catalysts shown in the examples was determined by measuring the conversions obtained by passing a gas stream containing sulfur dioxide, sulfur trioxide, oxygen and nitrogen over the catalysts at a controlled rate and temp-erature.
The activity of the catalyst was determined by measur-ing the amount o sulfur dioxide converted to sulfur trioxidein a partially reacted sulfur dioxide containing gas stream.
A gas stream containing sulfur dioxide, oxygen and nitrogen is passed over a sulfur dioxide oxid~tion catalyst to convert from about 90 to about 97% of the sulfur dioxide to sulfur trioxide.
The sulfur dioxide content of the partially converted gas stream is determined and the partially converted gas stream is passed over the catalyst to be tested. The catalyst being tested is maintained at a controlled temperature and the flow rate of sulfur dioxide containing gas contacting the catalyst is carefully controlled. The sulfur dioxide content of the gas 108V~05 stream before and af~er contact with the catalyst being tested is mea~ured. An activity coefficient for the particular cata-lyst i8 determined from the concentration of oxygen, sulfur dioxide and sulfur trioxide in the gas stream entering the test reactor and the concentration of oxygen, sulfur dioxide and sulfu`r trioxide in the gas stream leaving the test reactor. The apparatus for catalyst testing is shown in Figure 1.
Cylinders of dry sulfur dioxide, air and nitrogen properly pressure-reduced are connected to lines 1, 2 and 3, respectively. The systems for metering the gases are the same.
The pressure-reduced gases at a pressure of about 10 pounds per square inch gauge (psig) enter the system and pass through shut-off valves 5, 6 and 7 in the sulfur dioxide, air and ni-trogen lines. The gas is metered at a pressure of about 10 psi,g through rotometers 8, 9 and 10 and low flow control means 11, 12 and 13. The gases are mixed in line 14 at a pressure be-tween 1 and 2 psig. The pressure in line 14 is monitored by pressure gauge 15. Vent valve in line 14 permits the mixture of gases to be passed to the vent until the required mixture of gases is obtained. The total flow of mixed gases passing through line 30 is measured by rotometer 19. The mixed gas stream is passed through line 31 to reactor 17. A sample can be taken through line 46 and valve 20 to determine the ratio of sulfur dioxide to oxygen in the gas stream.

10~UV2V5 Reactors 17 and 18 are electrically heated reactors and contain a sulfur dioxide oxidation catalyst. Reactors 17 and 18 are utilized to convert a portion of the sulfur dioxide in the gas stream to sulfur trioxide. One or two reactors are utilized depending upon the amount of preconversion desired for a particular run. The preconverted gas leaving reactor 17 passes through line 32 and can pass through line 33 and valve 34 to line 37 and directly to test reactor 41 through valve 42 and line 45. If additional preconversion is required the partially converted gas stream can be passed through reactor 18, line 35 and valve 36 to line 37 which passes the precon-verted gas to test reactor 41.
A sample of the preconverted gas in line 37 is removed from the system through line 44 and valve 43 for analysis. The 15 preconverted gas stream is passed through valve 42 and line 45 to test reactor 41.
Test reactor 41 is immersed in a fluidized sand bath which is temperature controlled to maintain the proper tempera-ture in the reactor. The test reactor 41 is 1 inch inside 20 diameter. Fifty cubic centimeters of catalyst is introduced into the reactor for testing. The fully converted gas stream is passed through valve 46 in line 39 and passed through valve 40 to the scrubber and the vent. A sample for analysis can be taken from the system through valve 22.
Reactor 41 can be by-passed by passing the preconverted gas through line 3~ and valve 21 to line 39.

1080ZC~S

During testing of a catalyst the sulfur dioxide con-centration in the gas stream entering the test reactor through line 45 and leaving the reactor through line ~9 are monitored.
The gas mixture entering the preconverters through line 31 is adjusted to contain about 9.5~ S0z, about 11.l~ 2 and the balance, nitrogen. The catalyst being tested is equilibrated by passing the preconverted gas stream over the catalyst at the test temperature for 2 hours before sampling the gas stream.
The sulfur dioxide concentration in the preconverted gas stream and in the gas ~tream after contact with the catalyst being tested is determined by iodometric titration.
The amount of sulfur dioxide and oxygen in the gas stream entering and leaving the test reactor is measured. The rate constant k was computed from the data using the following rate expression.

rate = k~Ps02/pso3)o-5 Po2/l-(pso3/po2o 5PS02keq) ~ where keq = equilibrium constant keq = ~ + 0.611 by TA - 6.7497 TA = temperature, K.

Pso = Partial pressure of S02 in atmospheres.

Pso = Partial pressure of S03 in atmospheres formed by contact with the catalyst being tested.
P0 = Partial pressure of 2 in atmospheres.

The rate constant k = R moles S02 converted atmos X second X gram catalyst The rate constant k reported herein = k X bulk density of sul-ated catalyst in grams per cubic centimeter.
The durability of the catalyst (Accelerated Abrasion Loss) is measured by heating 150 grams of the fresh catalyst pellets at 1500~F. for 24 hours. The cataly~t pellets after heating at 1500F. for 24 hours are contacted with a ga8 mixtuPe ~.
containing about 4.0% S02 and about 5.0~ S03 for 2 hours at 810F. A 100 gram sample of the heated and reacted cataly8t i8 shaken over a standard 20 mesh sieve, U.S. Sieve Series, for 1 hour using a Rotap shaker. The loss in weight after shaking for 1 hour indicates the durability of the cataly~t. The dura-bility of the catalyst is indicated as the percent 1099 through the 20 mesh screen. The lower number8 indicate a more durable catalyst. The Accelerated Abrasion Loss test has been found to correlate clo8ely with durability experienced with sulfur diox-ide oxidation catalysts under commercial pr,ocess operating con-ditions.
The invention will be more fully illustrated by reference to the following examples.

, A test catalyst was prepared by dry mixing 109 parts ,' of vanadium oxide with 302 parts of anhydrous potassium sulfate.
- Diatomaceous earth in an amount of 8~0 parts is admixed with . :

the dry vanadium pentoxide and anhydrous potassium sulfate.
Water is added and thoroughly mixed with the solid mixture in a sufficient amount to form a damp mixture suitable for extru-sion. The damp mixture is extruded into pellets 7/32 lnch diameter by 3/8 to 5/8 inch long. The pellets are dried at 250F. for 8 hours. The catalyst pellets are heated at 1000F.
for 4 hours and activated by contact with a dil.ute sulfur diox-ide-sulfur trioxide containing gas stream for 2 hours at 810F.
before testing.
The diatomaceous earth is a natural product containing about 63~ by weight of the calcined diatomaceous earth of the fresh water diatom Melosira granulata which has been calcined at 1600F. for 1 hour and milled to an average particle size by weight of about 9 microns. The particle size distribution of the calcined and milled diatomaceous earth is shown in Table 1.

PARTICLE SIZE DISTRIBUTION OF DIATOMACEOUS EARTH

CUMULATIVE
SIZE MICRONS DISTRIBUTION
Less than 5 20%
; Less than 10 60~
Less than 20 85%
Less than 50 95%
Less than 100 99%
The plot of a Micromerograph TM distribution of parti-cle sizes is shown in Figure 3 as curve A. The properties of 10802(15 the diatomaceous earth were as ollows:

Surface Area - meters2/gram 11 - 16 Pore Volume - cubic centimeters/gm. 0.8 Al203 9.3%
~ SiO2 86.8%
Loss on Ignition o.g~

A catalyst was prepared according to the procedure of Example 1. The support was the unmilled ca cined diatomaceous earth of Example 1. The particle size distribution as measured by Micromerograph TM appears as curve B in Figure 3.

A catalyst was prepared according to the method of Example 1. The support is an uncalcined, finely comminuted fresh water diatomaceous earth. The support contained about 63~
by weight of the diatomaceous earth of the diatom Melosira gran-ulata ton a calcined basis). The particle size distribution of the diatomaceous earth as measured by Micromerograph TM is shown as curve C in Figure ~.

A catalyst was prepared according to the method of Example 1 utilizing the diatomaceous earth of Example 3 which ......
' ' ~ 0 80 20 5 wa9 heated at about 1600F. for one hour before admixture with the active materials.

A catalyst was prepared according to the method of Example 1 except the support is an uncalcined, finely comminuted salt water diatomaceous earth. The particle size distribution of the diatomaceous earth is measured by Micromerograph TM and -shown as curve D in Figure 3.

; 10 A catalyst was prepared according to the method of Example 1 using the same diatomaceous earth as in Example 1.
Potassium sulfate was used in only 167 parts and 284 parts of Cesium sulfate were added to the formulation.
The catalysts prepared in Examples 1 through 6 were tested in an apparatus as shown in Figure 1. The sulfur diox-ide was preconverted to between 90 and 97% and passed over 50 cubic centimeters of catalyst at the rate of 21 cubic centi-meters per second. The rate constant was determined at a temperature of 760F. and 810F.
The Accelerated Abrasion Loss values (AAL) were deter-mined according to the method disclosed above.
Two samples of commercially available contact sulfur dioxide catalysts were also tested to show the advantages of the catalyst of the invention.
~ .

''' ' ., , . .,- ~ , .

1080'~05 The results of the tests of the two commercial cata-lysts are shown as Examples 7 and 8 in Table 2.
The results of the evaluation tests are set forth in Table 2.

10802~5 o .,, ~q ~ U
s~
'C '~
,~ U~ ~ Lr a) P~ ~ ~ ~ ~ ~ ~u U
~n ~q o .

U ~ o o ~ o o U~
~ ~D ~1 0 ~ O O
o~ ,, ,, ~ ~ ,/ C~
u o o ,, ~X
U " .
.,~
U
C~ o N CC
~O ~ C~

O ~ C O ~q O ~ O~ ~ ~O ~ ~
~J o o c~ aJ o a~ ~~ o o d O ~ ~d U ~ U
0 ~4 o o ~ o ~1 ~ ~O ~:q ~, u ~ u a) u b, O a) v ~ ~ ~ ~ c ~ ~ ~ c c U~ ~1 ~ ~ r~ ~ ~ ~ rl rl S~ ~1 0 h ~ C~ h ~ ~I t) h u ~ ~ u ~ v ~ v ~n J C ~D V ~ ~q U ~ ~g U ~ U V ~
o ~ s~ oa~ o h ~I1 C7 h ~ C~ h 1:~ C~ h P~ h 1 _I
a~

~ z 1080'~05 ' o C
.a a N U~
a~
a~ ~ ,~
~q oq ~ O

t; .

J O C~l ~a o~
C~
O O

O C-Xl .
E~
O
.1 N ~-I
* O O
* * JJ
C C
J JJ ~q tq Cq U~ C C
~, ~, O O
X X
J J~ I I
o a~
C~ ~ .,1 .,1 E~
a) u ~
~ ~ C~
O
.,1 rl C) t~
a O O
C.7 C~

~ C~ * **
æ

. , - .
.~ .

The test results clearly indicate that it i8 necessary to finely comminute the fresh water diatomaceous earth consist-ing primarily of Melosira granulata diatoms and calcine the .

material to obtain a catalyst with high activity and high dura-bility.
~ The catalyst prepared with the uncalcined finely com-minuted diatomaceous earth is a durable catalyst but its O.
activity is relatively low.
The calcined but coarsely ground diatomaceous earth pro-duces a catalyst with a higher activity but low durability. If the catalyst support is calcined and finely comminuted, the catalyst achieves a high activity and maintains a high dura-bility.
It is not critical that the diatomaceous earth be calcined before being comminuted as shown by Example 4 in com-parison to the catalyst of Example 1.
The catalyst of the present invention combines the durability of commercial catalysts of low activity with the activity of high activity commercial catalysts.
The catalysts utilized in the examples presented here-in were prepared using only one concentration of vanadium in the form of an oxide so that the effects of treatment of the catalyst support could be clearly shown. Concentration of active materials in sulfur dioxide oxidation catalysts and ratios of promoters and activators to vanadium are well known in the art. The support of the present invention imparts de-sirable properties to catalysts within the ranges of concentra-tion of active materials utilized in the art.
The active materials may be in soluble or insoluble form~and can be admixed with the novel calcined finely commi-nuted support in a dry state, as a solution or suspension. The form of the active materials is not important but intimate ad-mixture with the catalyst support must be achieved. Vanadium compounds, activators and promoters suitable for preparing supported sulfur dioxide oxidation catalysts are well known in the art.
The examples clearly show that active and durable catalysts can be prepared by utilizing as a catalyst support, a calcined finely comminuted fresh water diatomaceous earth containing primarily diatoms of Melosira granulata.

Claims

WHAT IS CLAIMED IS:

1. An improved catalyst for the oxidation of sulfur dioxide to sulfur trioxide wherein 8 diatomaceous earth support is mixed with vanadium compounds, promoters and activators and the support which is mixed with the vanadium compounds, pro-moters and activators, is shaped the improvement comprising providing a durable and active catalyst by utilizing as a support a finely comminuted fresh water diatoma-ceous earth, containing at least about 40% by weight of the calcined diatomaceous earth of Melosira granulata diatoms, which has been calcined at a temperature from about 950°F. to about 1850°F.

2. The catalyst of Claim 1 wherein the diatomaceous earth is calcined from 30 minutes to 4 hours at a temperature from about 1300 to about 1800°F. before admixture with the vanadium compounds, promoters and activators.

3. The catalyst of Claim 1 wherein the diatomaceous earth contains from about 50 to about 80% by weight Melosira granulata diatoms.

4. The catalyst of Claim 1 wherein the diatomaceous earth is comminuted so that at least about 25% by weight of the particles are smaller than 10 microns.

5. The catalyst of Claim 2 wherein the diatomaceous earth is comminuted so that at least about 25% by weight of the particles are smaller than 10 microns.

6. The catalyst of Claim 2 wherein the diatomaceous earth is comminuted so that at least about 40% by weight are smaller than 10 microns.

7. The catalyst of Claim 2 wherein the diatomaceous earth contains from about 50 to about 80% by weight Melosira granulata diatoms and is comminuted so that about 40% by weight of the particles are smaller than 10 microns.

8. The method for preparing a durable and active catalyst for the oxidation of sulfur dioxide to sulfur trioxide which comprises (a) calcining fresh water diatomaceous earth, containing at least 40% by weight of the calcined diatomaceous earth of Melosira granulata diatoms, at a temperature from about 1200 to about 1800°F., for from about 5 minutes to 8 hours; (b) comminuting, before or after calcining, the diatoma-ceous earth so that at least about 25% by weight of the parti-cles are smaller than about 10 microns; (c) admixing vanadium compounds, water, promoters and activators with said calcined and comminuted diatomaceous earth; (d) shaping and compacting the mixture to form a catalyst particle; and (e) drying and activating the particles to form a sulfuric acid catalyst.

9. A supported vanadium containing sulfur dioxide oxidation catalyst wherein the support is a finely comminuted fresh water diatomaceous earth which has been calcined at between 950°F. and 1850°F. and at least about 40 percent by weight of the calcined diatomaceous earth of Melosira granulata diatoms.

10. The catalyst of Claim 9 wherein the support con-tains from about 40 percent to about 80 percent by weight of Melosira granulata diatoms.

11. The catalyst of Claim 1 wherein the catalyst contains Cesium as a promoter and activator.