CA1060183A - Process for treating gases containing sulphur compounds - Google Patents

Abstract

Abstract of the Disclosure The invention concerns a process for catalytically treating re-sidual gases, containing hydrogen and carbon derivatives of sulphur, by the Claus reaction wherein the catalyst employed has a specific area of at least 80 m2/g and essentially comprises active alumina and a titanium compound.
The process enables carbon compounds of sulphur to be destroyed and the Claus reaction proper to be obtained with good yields.

Description

~ 61~83 S P E C I F I C A T I o N

rrhe invention relates to catalysts ~or treating re~
sidual gases containing hydrogen and carbon derivatives of sulphur.
It is known that gaseous mixtures of complex com-position charged with sulphur compounds, such as the gaseous mixtures resulting from the purification of gaseous or liquid ; -;
natural hydrocarbons, are frequently encountered in the chem~
ical industry, and that very large quantities of sulphur can ;;
be recovered by purifying these mixtures. The methods of re-~ 10 covering the sulphur have been generally well-known for a j long time but nevertheless have to be constantly improved so that, once the mixtures have been purified and are ready to be discharged into the atmosphere, their content of sulphur compounds can be reduced to the absolute minimum, in vLew of 1$ increasingly strict pollution standards.
I Usually the greater part of the sulphur in the gas~
I eous mixtures to be treated is in the form of hydrogen sulphide, and the recovery of the sulphur is then generally based on the well-known claus reaction, which can be obtained in a gaseous or liquid medium, between the sulphurous an-hydride which generally resuLts from oxidation of a suitable ~ ;
proportion of the hydrogen sulphide, and the remainder of the , hydrogen sulphide. The claus reaction should advantageously 3 be carried out at the lowest possible temperature as this is 3 ~-~5 helpful in obtaining sulphur. The reaction can in fact be obtained at normal te~perature provided that it is activated by suitable catalysts.
However~ the presence of other gaseous sulphur compounds, such as carbon di-sulphide and carbonyl sulphide, 3 greatly affects the application of gas purifying processes - 1- , , ~
s . ~.

~0~0~83 based on the,claus reaction, because the catal~sts which are :~

most active in the claus reaction are not those which are most ~ -.
active in destroying carbon compounds of sulphur. The de~
struction of carbon compounds of sulphur is very likely to ~ ;
. 5 operate by hydrolysis, because the optimum temperatures for these various reactions are not the same and because the very :~
~ .
presence of sulphurous gas inhibits the hydrolysis of the carbon derivatives of sulphur. ~ :
Despite the fact that, in industry, residual mixtures containing these various sulphur compounds have to be treated . in a succession of catalytic stages in order to obtain a high .
degree of purification, the amount of hydrogen sulphide and carbon compounds o~ sulphur eontained in the gases leaving the last stage is conse~uently found to exceed normally aecepted standards. Moreover, the incompleteness o the purifying :~
action becomes more and more marked with the passage of time ~
and probably has to do with the sulphating of the catalysts. ~.:
This may.be due ko the presence of traces of oxygen in the ~ :
1 gases to be treated, in which case it is gradual, although it : ~
`3. 20 may also result ~rom air being accidentally admitted over the : :
~ incompletely cooled catalysts when the plant has been shut .
down.
The catalysts previously recommended to obtain these ; ~;
various reactions involving gaseous sulphur compounds are very 25 ~ numerous. In fact many are suitable and give good results, so long as one does not have to obtain the highest possible yield -~
for a given plant and provided that one can tolerate relative ~:
i :
ly short periods of use without re-charging with fresh cata- ... `:~. .

lysts. ThUs it has been recommended to use bauxite, activated - 3 carbon, alkalised earriers, active alumina and catalysts -~:~

'' ~ ' ' ~' ., ; .... , ~ .. .. . ., , . . . . , . .. . ._ .. ~

r~
:106~L83 comprising sulphides, oxides or various compounds, including those of molybdenum, titanium, cobalt, iron and uranium deposited on various carriers.
of all these catalysts, active alumina is the most advantageous if only the claus reaction is consid~red and provided that the sulphating effect is minimised so as not to shorten the period of use. However, from the moment that the gases which have to be purified contain any appreciable pro~
portion of carbon derivatives of sulphur the above-mentioned 10 drawbacks become apparent. ;~
'! It has now been discovered that catalysts which can be given a set of properties enabling both the destruction of ¦ the carbon compounds of sulphur and a good yield to be ob~
1 A~ tained~the claus reaction proper with the further property of ! 15 long life due to their mechanica~ strength and to the absence of any sulphating effect on the yields obtained, are those es-sentially comprising active alumina and titanium compounds.
~ This is provided that the catalysts, when ready for use, have ~`
'4 a large enough specific surface area and that the proportions of active alumina and titanium compounds are defined. The chemical nature of the titanium compounds present in the cata-lysts is difficult to specify under the conditions of use, so in practice it is preferable to relate the proportions of these compounds to that of titanium oxide.
It should~be noted that activated bauxites, which :: .
were formerly recognised as being suitable for use as cata-~ lysts for these various reactions, as indicated above, often ;l~ contain oxides with an effective catalytic action,~ such as iron oxide and titanium oxide, and have a specific c;urface 3~ area which may be suitab~le~ However, the amount of active .. ~ .

. ~ -3- ~ ~

. ~ .

~' ~06~3 oxides contained in the bauxites is variable and insufficient, and the bauxites moreover contain equally variable proportions o other compounds which may be inac~ive or even ha~mful. Accordingly bauxites do not ha~e all the features which would enable the purification of sulphur-containing gases to be carried as far as is nowadays required and to be carried out with the constant action ~ ;
required.
The invention provides a process for catalytically reco~ring sulphur ~~
from a gas stream comprising hydrogen sulfide, sulfur dioxide, wa~er vapor and ~;
carbon-sulphur compounds consisting essentlally of carbon disulfide and/or car-bonyl sulfide which comprises reacting carbon-sulphur compounds consisting essentially of carb~n disulfide and/or carbonyl sulfide with water vapor to ;-produce by hydrolysis carbon dioxide and hydrogen sulfide and simultaneously reacting hydrogen sulfide and sulphur dioxide to produce water vapor and ele-mental sulphur whereby the carbon-sulphur compounds are e~iminated from the gas stream and sulphur is recovered therefrom, said reactions being carried out in the presence of a catalyst consisting essentially of activated alumina and a titanium compoundJ the titanium compound being present in an amount within the range of 1-60% by weight expressed as titanium oxide, the catalyst r~
having the specific surface area greater than 80 m /g and the temperature of the reaction zone being such that the product gases at the conclusion of the reaction have a temperature ranging from 260-335CJ and recovering the sulphur ; thus formed.
Less importantly, the catalysts may further comprise small quantities of molybdenum, cobal~J nickelJ iron and uranium compounds, although the pre-sence of these other elements does not usually give any very marked improve- ;
ment in results. `
The catalysts used in the process of the invention can be prepared in various ways. By way of example, a well-known and appropriate method con-sists of impregn~ting the carrier of active aluminaJ of the desired specific surface areaJ with solutions of metal compounds which are particularly adapted easily to provide the corresponding oxides by thermal decomposition. The con-centration of these solutions must be chosen so as to obtain the desired quan-~, .

.. . : . . . . . :

~,f~
10601~3 tity of catalytic elements in the final catalysts. The solutions which are easiest to use for introducing titanium are those containing titanium chlorides, oxychlorides or sulphates, although other compounds may be employed such as various organic salts like oxalates. Other metals, if desired, can easily be added, e.g. in nitrate form.
.

, `' :.

-'1 ' `, '`

., .

. . , J ~ ~
. ~
.

~ a- ~

:, - ;
:. :
~ . ,, , : : :, ,.

~060~3 ~:

, . . . .
other suitable methods consist of agylomerating mixtures of aluminum oxides or hydroxides, e.g. active alumina, and oxides, hydroxides or other compounds of various metals. At least some of these various metal compounds may be in the form of gels, sols or solutions. It is also pos-sible to coprecipitate the various hydroxides or other com-~ :;
pounds or to form co-gels of hydroxides or of compounds from 901s, as well as to add sols which will c~ntribute certain ~ I
metals to the compounds of other metals. ~ i The preparation of these catalysts usually ends with ~ ~
:~ . , , a drying and ~n activation process. Their subsequent use in~
, .
volves more or less firm fixing of sulphur, the exact nature ~ ;
of the bond with this element is not well understood.
The various catalysts of the invention may be used 1, 15 in a fixed bed or in a moving, fluidised or flying bed, the di-mension= of the particles making up the bed being adapt=d ac-cordingly.
, In order to illustrate the invention various =xamples i will now be given of results obtained in a fixed bed with cata~
, 20 lysts consisting of alumina and titanium in various proportions :1 , and obtained in different ways. ~he first example concerns a I catalyst which is hardly solid, without alumina, and which is `~
consequently outside the scope of the invention. It consists s~lely of titanium oxide of the desired specific surface are~
i~ 25 the purpose o this being to show the special action c tita-nium in converting carbon derivatives of sulphur. The other examples make it possible to define the limits of variations from the main parameters. In all these examples, the gases are treated by the various catalysts in a small reactor 60 mm 3 in diameter. The composition of the gases by volume is as ~: .
~ .

.~ :::
j .

- :- , : . . ............ . . . - . ~:
. .

1~60~3 - -follows:
H2S 6%
CS2 1% `, SQ2 4%
E-12 02 8% ~ :
- ~26 1%
The times of contact can vary up to 8 seconds and the temperatures on discharge vary from 2Z0 to 335C.
The gases leaving the reactor are analysed by chrom~
atography to determine the rate of ~S02 conversion relative to the thermodynamic yield, and the rate of ~ CS2 hydrolysis of the carbon sulphide.

Starting with a suspension in water with~400 g of 15 Tio2 per litre of titanium hydroxide obtainéd by precipitation -~;
with ammonia from its sulphuric solution, a titanium sol is prepared in the conv`entional way by heating to about 80C then ,:
adjusting the plI to about 1.1 with hydrochloric acid The micellae of this sol are about 400 A in diameter.
The sol is dripped into the top oE a glass column~
the upper part of which contains petroleum mixed with a chlo-rofluoro hydrocarbon and the lower part of which contains a mixture, in the ratio of 1/1 by volume, o~ a concentrated a~ueous solution of ammonia~and a saturated aqueous solution f ammonium carbonate. The temperature of the column is kept at 25C. In this way the~drops ge~ and the lower part of the colum~ receives pellets 2 to ~ mm in diameter which are then ;
dried in air at 180C. The pellets thus obtained,~of a ~;
specific surface axea of 220 m2/g, are separated into two 3 batchesO The firs batch is used as is, while the second IS
.:

-6- ~
:

~-~ ~
~6~ 33 : ~
,,:
artificially sulphated by heating to 450C for 4 hours in a mixture of 70% air and 30% S02. The two batches are used to treat the gaseous mixture of the composition indicated above.
In addition, by way of comparison, the gases are treated in the identical way over pellets of active alumina of the same ;
~.~
dimensions and the same specific surface area, in either the fresh or the sulphated state, the sulphated state being ;
.
obtained by the method used for the pellets of titanium oxide.
Table I below summarises the various results ob-tained and also gives the values (in kg) of the resistance R
to crushing of one particle by another before the various catalysts are used. ~
j T A B L E I 1~ ;
I ~, . . .
3 15 _ R Time of TLme of Time o ; Catalysts(kg) contact: 3s contact: 5s contact: 8s ~-Temperature: Temperature: Temperature:
; 320 335C 335C ;~
~S2 ~CS2 ~S02~ ~2~S02 ~CS
., _ _ ,~
A1203 pellets ~ew 15 90 45 94.578 97 98 Sulphated 15 83 15 91 35 97 80 Tio2 pellets New 3 100 100 100 100 100 lG0 Sulphated 3 98 90 100 100 100 100 :~

~ These results clearly show the superiority of tita- ~
. .
nium oxida over alumina so far as its action in converting both S2 and CS2 is concerned, and particularly after the pellets have been sulphated. However, the resistance of the titanium oxide pellets to crushing is not suficient for industrial use.

~ ~ .

This example concerns results obtained with catalysts .,,]
~l -7- ;
~:, ;.

:', .... . . .

.

which contain different quantities o titanium oxide and ~ ;
which are obtained by impregnatiny pellets of active alumina with a specific surface area of 300 m2/g and with diameters ~;
from 2 to 4 mm, with solutions of titanium chloride so that the desired oxide content is achieved after drying, and cal~
cining at 500C for 4 hours. Before the catalysts axe used - they are sulphated as described in the previous example. A11 the tests are carried out at 335C. The table below summa~
rises the results measured for ~S02 for a contact time of 5 seconds and for ~CS2 for a contact time of 5 and 8 seconds, as well as the specific surface area of the catalysts and their resistance to crushing.
1 I' A B L E II

Catalysts % by Specific _ ~, 15 weight of titanium surface Resistance oxide relative to area of to crushing ~S02 ~CS
alumina carrier catalysts m2/g kg 5s 5s 8s _ : '' ' ' ~! 0 250 15 91 35 80 1 250 1~ 95 60 95 ~hese res~ llts give a good indication of the impor-tance of titanium: even in a proportion of 1%, calculated in -;~
respect of titanium oxide, it is responsible for destroying , ~ most of the carbon sulphide. The strength of these various catalysts is adequate and results from the use of alumina pel~
lets as carriers.

This example concerns catalysts obtained by ag-i glomerating alumina powder with a gel of titanium hydroxide, 3 which is a suspension of hydrolysed titanyl sulphate 1~ :
~ -8-1 ` :

1~60~3 containing about 7% by weight of S04 -- relative to Tio2. The titanium hydroxide gel, dried and ~round and containing 79% by weight of Tio2, is intimately mixed with active alumina powder of a grain size less than 20 microns, obtained by partial de~
hydration of hydrargillite in a stream of hot gas, in propor-tions such that the final catalysts contiain 10%, 20%, 40% and 60% by weight of oxide of Tio2. The mixture is humidified and agglomerated in a rotary granulator in the form of pellets ¦ having a diameter of from 2 to 5 mm. The pellets are left to ;
¦ 10 mature for 24 hours at about lOO~C then calcined for 2 hours at 450C for activation purposes. The catalysts are sulphated j ~
by the method described in the previous examples. ~;
The results obtained are given in Table III below.
T-A B L E III

i~
Specific Resistance ~CS2 for: ~PS02 for:
, Sulph- surface to ated a~ea crushing 3s 5s 8s ls 2s 5s ca~ysts m /g kg 310C 335C 335C 260C 29oC 335 10% of al mina 190 15 20 45 97 35 65 100 ;1 Tio2 ~
alumina 195 12 30 57 98 45 72 100 Tio2 + 195 11 45 87 100 65 82 100 ;~

60% of ,. , Tio2 ~ . . ,~
alumina 190 65 95 100 66 86 100 , ,:
This table shows the importance of catalysts ~ 30 containing titanium as compared with the results obtained 3, ,, _ g_ i ~ ' !
'i ~
' " " ` '' , ,''~' , ~ ' ' ' ', 106~183 ,~
with alumina alone. It also shows that in this type of cata~
lyst, obtained by agglomeratiny the mixture of oxides, more titanium oxide has to be used if very good results are to be obtained. However, this preparation method has the advan-tage of avoiding the process of impregnating with titanium chloride, as in Example 2, which has some drawbacks owing to the difficulty of handling the product. ;

.
This example concerns catalysts which are agglom- `~
; 10 erated in the form of pellets from 2 to 5 mm in diameter and obtained from an alumina identical with that used in the pre-ceding example and from titanium hydroxide sol in proportions such as will give a Tio2 content of 10%, 20%, 30%, 40% and 60% in the ~inal catalysts. The sulphated catalysts are tested by the method described above; the résults are set out in Table IV below.
~, T A B L E rv Specific Resistance /PCS2 for: ~ S02 for:
Sulph- surface to ~ _ ated a~ea crushing 3s 5s 8s ls 2s 5s Tio2 + m /g kg 320C 335~C 335C 260C 280 33~C

Tio2 ~ 200 14 25 54 96 40 70 100 alumina 195 12 35 65 96 49 _ 76 100 30% of Tio2 ~
alumina 194 12 45 85 100 58 81 _ 100 _ .
.~ 4%2f ~ alumina 198 10 50 94 100 69 86 100 ,~,. Ti/2+ ' . ~
~l alumina 191 8 70 96 100 65_ 90 100 ~''i . ' ' " ' :
'' ' - 10- , ~ .

. ~ . , , ,. . -::

~60183 The results obtained here come close to those ob~
tained in Example 3. ~;~

The purpose of this example is to show the effect of the specific surface area of the catalysts on the results ob~
tained. -~
The catalysts tested are all obtained by the im- ~ ;
pregnation method described in Example 2, so that they finally contain 5% by weight of Tio2 oxide. The impregnated pellets of `~

active alumina vary in their specific surface area, so that the final catalysts also vary in this respect. The catalysts are tested in the sulphated state with a contact time of 5 seconds to determine the ~ S02 and for 5 and 8 seconds to determine the ~CS2.
The results obtained are recorded in Table V below.
T A B L E V

Specific surface ~S0 area of catalysts _ in m2/g 5s 5s 8æ

,j _ _ 62 90 ; ~
~,~ :

.~ _ . : , .~, .
This table shows the need for an adequate specific surface area, 80 m2/g being the limit below which yields drop sharply.
The above examples do not restrict the invention to , . , treatments for gases of the composition mentioned. ThiS com-position was used solely because the main purpose of the " -11- , ~. :

~L060~1L83 ..
invention is'the joint destruction of hydrogen sulphide, of sulphurous gas and of carbon derivatives of sulphur. The catalysts of the invention can obviously be us0d to treat gas-eous mixtures which are far richer in sulphur compounds and ,~
which may further comprise, e.g. carbondioxide and ammonia, which do not react. ~

, ':

,, , .~ ~, ~0 ";
" ~ .

.j :
~

~. !
.. . . .
;,;,, ...
,1 i 30 `
:::i ;`' ' ~ ' ~` -12-, . , 1 , . . ..

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for catalytically recovering sulphur from a gas stream comprising hydrogen sulfide, sulfur dioxide, water vapor and carbon-sulphur compounds consisting essentially of carbon disulfide and/or carbonyl sulfide which comprises reacting carbon-sulphur compounds consisting essentially of carbon disulfide and/or carbonyl sulfide with water vapor to produce by hydro-lysis carbon dioxide and hydrogen sulfide and simultaneously reacting hydrogen sulfide and sulphur dioxide to produce water vapor and elemental sulphur whereby the carbon-sulphur compounds are eliminated from the gas stream and sulphur is recovered therefrom, said reactions being carried out in the pre-sence of a catalyst consisting essentially of activated alumina and a titanium compound, the titanium compound being present in an amount within the range of 1-60% by weight expressed as titanium oxide, the catalyst having the speci-fic surface area greater than 80 m2/g and the temperature of the reaction zone being such that the product gases at the conclusion of the reaction have a temperature ranging from 260-335°C, and recovering the sulphur thus formed.

2. A process as defined in claim 1 wherein the titanium compound is titanium oxide.

3. A process for catalytically recovering sulphur from a gas stream comprising hydrogen sulfide, water vapor, sulphur dioxide and carbon-sulphur compounds consisting essentially of carbon disulfide and/or carbonyl sulfide comprising contacting said gas stream with a catalyst consisting essentially of activated alumina and a titanium compound, said titanium compound being present in an amount within the range of 1-60% by weight expressed as titanium dioxide and the catalyst having a specific surface area greater than 80 m2/g, the temperature of the reaction being such that the product gases at the con-clusion of the reaction have a temperature ranging from 260-335°C, whereby said carbon-sulphur compounds present in said gas stream are converted to carbon dioxide and hydrogen sulfide, the hydrogen sulfide present in the gas stream reacting with sulphur dioxide to form water vapor and sulphur, and recovering the sulphur.

4. A process as defined in claim 3 wherein the titanium compound is titanium oxide.