CA1108822A - Gas purification process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for purifying gases containing hydrogen sulfide and/or hydrogen cyanide is provided wherein said gases are contacted with an absorbing solution containing naphthols or their salts as a catalyst having a nitroso group at .alpha.- position or .beta.- position, acidic group(s) and a standard redox potential in the range of 0.4 V to 0.7 V.
Hydrogen sulfide and/or hydrogen cyanide are removed by converting the former mainly into thiosulfuric acid and the latter mainly into thiocyanic acid. According to this process, no trouble is caused by sulfur deposit as in conventional methods. The scale of the purification appa-ratus is smaller, and the amount of catalyst required for purification is reduced. Further by pretreating the absor-bing solution, this process becomes even more advantageous.

Description

The present invention relates to a gas purification process by causing an absorbing solution containing speci-fied napthols or their salts to absorb hydrogen sulfide and/or hydrogen cyanide contained in a gas to xemove hydro-gen sulfide and/or hydrogen cyanide in the ~orm of thio-sulfuric acid and thiocyanic acid converted therefrom, respectively.
Heretofore, in the so-called wet o~idation process a ; hydrogren sulfide-containing gas is contacted with a cata~
lyst-containing absorbing solution to remove hydrogen sulfide in the form of sulfur as shown in the ~ollowing equation. Various processes have been proposed:
H2S + 0 - _ S(deposition) ~ H2O

For example, a process wherein naphthoquinone-sulfonic acid is employed as catalyst ITakahax Process), a process wherein picric acid is employed as catalyst (Fumaks Process) and a process wherein anthraquinonedisul~onic acid and metavanadic acid are employed as catalyst (Stretford Pro-cess), are known.
However these processes are directed mainly to con-verting H2S into S as in the above equation. There have been disadvantages in that it is necessary for circulating the absorbing solution to remove the resulting sulfur from the solution. This re~uires a large capacity apparatus such as decanter, ~ilter press, etc., and, besides, the resulting sulfur adheres onto packing, etc. in the absorption tower to cause trouble. Foaming can also make the operation dif-~ic~lt.

.
, :
~ 2 ~8~

The present inventors have found that when an absorbing solution containing certain catalytic compounds is employed, it is possible to carry out an extremely effective gas purification wherein absorbed hydrogen sulfide gas is converted mostly into thiosulfuric acid, and yet decyani~a-tion is almost completely carried out together with desul-furization. Various troubles brought by sulfur are also removed. The catalytic compounds mentioned above are naphthols or their salts, which have a nitroso group at ~-position or~ -position, at least one acidic group in their molecule and of which the standard redox potential is in the range oE 0.4V to 0~7V. As such compounds, those having the following formulas are mentioned. The standard redox poten-tial referred to herein are values measured at a temperature of 25C and pH of 9Ø

OH

~ ~ 2-Nitroso-l-naphthol-4-S03M ~ sulfonic acid and its salts ~ ~ J 2 OH
~

COOM
OH 2-Nitroso-l-naphthol-4-NO~ carboxylic acid and i s salts

2~

~o .

~IIO~jS ~;,J~J 503~ t~oso-2~n~phthol-r ~1 1 3 5, ~di sul ~on~ c cl c id and ~0 1 ~OH ~ MII it~ salts 03S'~ S()~ ~ _ ~,~0~1 10MIOOC ~J""~J~ J`COOMI . ,? l-Nltroso--?-naphtho-L-N0 3 9 ~-clicarboxylic ~c:Ld and ,~"O~I ~II its sal ts ooc,~J.~., coo ~

~-\~ ~r-S03ML `

t,H ~ Ni~roso-4~ ph~hol-2~
I!J0 sulfonic acid and it~> s~l ~;s 20 l ~/O~rl J2 ' ~0 C~ I
~"~ , 0~ ~ i-troso~4 -na~ thol~2-- . f rN c~rboxylic æid ancl its salts OU M

~0 ~`' l)il ~

I ~
03M ~ l-Ni-troso-2-naphthol-4 ~ JEI sulf~nlc acid ~n~ it.s salts ~' I
COOM l-Nitroso-2-naphthol-4-NO OH carboxylic acid and its salts / ~II

. 00 2 In the above-mentioned formulas, MI represents H, ~H~
X r or an alkali metal and M ' means an alkaline ear~h metal.
These compounds function as a redox catalyst, and oxi-dize hydrogen sulfide into thiosulfuric acid and h~drogen cyanide into thiocyanic acid in the presence of oxygen~ , :
Now~ with regard to the oxidation reaction of hydrogen sulfide and the formation reac-tion of thiosulfuric acid, the standard redox potentials ~o in the reactions will be re-ferred to below.
S ~ 2H+ + 2e = H2S(aq) ~o = 0.142 V
S20~- + 6H+ -~ 4e = 2S ~ 3H20 Eo = 0.~65 V
0~ the other hand~ the standard redox po-tentials Eo of oxygen are as follows:
2 ~ 2~I + 2e = H202(a~) Eo = 0.6~2 H202 + 2H + 2e = 2H2 ~0 - 1.776 V
Accordingly, i-t i9 conceivable tha-t as the ca-talyst employed for conver-ting hydrogen sulfide into thio~ulfuric acid9 a catalyst having a standard redox potential ~0 in the range of 0.465 - 0.682 V is preferable.
Based on -this finding, -the lnventors have made stre-nu.-~us studies on various compounds useful as a desulfurlza-tion-decyanization ca-talyst, and as a result have found tha-t naph-thols or their salts as shown in the following ~able 1 are preferable, and have at-tained the present inven-tion.

1~ ' ~ ~ ro 1- 0 ~ Co ~ ~ ~ ' O
- ------ - - - -- --- - - - -- -- -r~ ~n rnrn rn rn rnrn V~ rnrn Q ~n r~ Q
o o o o o o o o o o o P~ o !2 c~

1~ ~ ~ ~ ~ Ul ~, ~ o Q
I' I'~ 1'- 1'- ~'- 1'-IJ- ~'- 1~-I'- 1'- ~ ~'- ~--c+ ct ct ~ c* c+ ct ~ c~ 1 t~, J ~ ~1 O O O o o o ` O O o O o ~ O ~ o n u~ I rn rn ~n u~ n o rr~ ;d ,_ o o ~ o o o o o o o o a~ o ~ ~
I I I I I I I I I I I O I ct ~ 1 P ~ ~d1~
P~ I
-rd ~d ct ~ 'd ~d ~d~d ~d ~drd p~ ~d ~ .
~ ~ ~ tS' tS' 15 t~ d PJ I
c~ ~t o ~ ~t c~ c+~t c-t c~~t ~ n ~ ~ I- ~ ~ ~ P' ~ ~ ~ ~ c+ ~ ~
o C~ I o o o o o o o o ~ o ~--1~ O 1~
~ 1 ~ V p~ I I I ~>~. _ .. I ,,t~ I ~J.
~J ~ ~ o I - I Cl' ~ ~ O 1 u~ q o o o u~ o 1-~ 0 1-~
O
1-- 1-- p~ p~
~ G' ~ I~ P~ c~
O O tDtD p~ tD O O O O p~ c~ tD
t~ ~ C l- t~ tD
p~ P~ tD p~p~ Cq p~tD
c+ c+ ~ I ~.
tD tD tDtD p~ tD
tD ~3 ¦
' _ P~ I
~Oc~+ ~D
tD ~} 1--O O O O O O O O O O O O O O t~ ~
. . . . , . . . . . . . . . c+ p~
~n ~n ~ n ~n ~n~n ~n ~ ~ ~ ~ IJ- Ii I- ~ O ~ ~ ~ ~ 1- ~ ~ ~ 00 0~ C

____ __ ~ P~ ~
I~ C-~
6~;n ~J ~ ~ ~ ~ ~ ~ ~n ~n ;n E~

_ _ _ ct b ~
1- ~ O ~ O
~Q ~O ~ O ~O O ~O ~ ~O ~ ~ ~
O~ Jl CO tP ~rl t ~ ~ O O O ~- ~ ~æ,- 1'- ct ~ b O

Note l: Measurement of s-tandard. redox potential was carried ou-t at a pH of 9.
Note 2: Percentage :Eormation of thiosulfuric acid Weight o~ S in thiosulfuric acid _rmed x 100(%) Weigh-t of S in H2~ absorbed into absorbing solution Note 3: Oxidation rate means reduction rate of HS- per unit time in batch test of absorbing solution5 and is expressed by reduc-tion of HS (mol)/absorbing solution (m3)/test time (min.) Any of the compounds in the above ~able have a ni-troso group at ~-position or ~-position and also one or two aci.dic group such as -SO 3, -COO , etc. in their molecule, and their standard redox potentials are in the range of 0.4 V or higher but less -than 0.7 V.
~urther, for effectively carrying ou-t desulfuriza-tion-: decyaniza-tion in the presence of catalyst~ it is preferable that the oxidation rate of HS- be.high~ since the high ra-te thereof results in reduction of the amount of catalys-t used, as well as reduction of the amoun-t of absorbing solution used, which makes it possible to reduce -the scale of appara-tus and affords a very advantageou~s practical operation.
In this respect, too, since any Or the catalyst com pounds employed in the present invention have a larger oxi-dation rate, as shown in Table 19 their catalytic acti~i-ties are so high that the object can be fully attained.
On the o-ther hand, compounds which are similar to those employed in -the present invention but not within the scope of the present invention are enumerated as compa~ative examples in ~able 2.
3o ~ ~ ~ -- ---1- 0 ~ n o~
.. ~ ___ ~3 ~ rn ~n rn ~n ~ O O O O
o ~ .
o ~
p p~ 10 ~- ~
~. P I ~ p p, e~' ~ t ~;t P~
O O Ol_ t ~ ' ~
t ~ t t b ~:1 .-t~ .
~D ~
.

':~ C:~ r~ ~.3 i 0 ,0 0 ,0 ,0 0 0 ~ t~
w O (~ ,`1 10 ~ ~O I

.~. l l ~ ~ ~qo ll o o o o ~ o ~ & i, co ~n O co ~ ~ o' ~ l~

-~ d o~

p~ o ~ ~
n ~ , ~
o ' O ~ ~n ~1~ 1' t ~o~ ~ aq I
Lo~l Compounds of No. 18 and No. l9 having an Eo of 0.7 V or higher and No. 15 having an Eo of lower than 0.4 V are much lower in oxidation rate than the compounaLs shown in Table 1.
Other compounds are generally lower in the percentage formation of thiosulfuric acid, although the compound of No.
16 is exceptionally high is oxidation rate alone. As a result, it is impossible for the compounds in Table 2 to attain the desired effectivenesses. Thus, the catalyst compounds which sufficiently satisfy two requirements of the percentage formation of thiosulfuric acid and the oxidation rate are limited to those employed in the present invention.
Further, it is an indispensable requirement for the catalyst cornpounds employed in the present invention to introduce at least one acidic group such as -SO 3, -COO , etc. into the molecule. This is effective in enhanciny the solubility of the catalyst in the absorbing solution wherein the catalyst of the present invention is employed, and also for lowering the redox potential down to an optimal poten-tial to increase the percentage formation of thiosulfuric acid. It does not matter if chelating agent, reaction-promoter, surfac-tant or other modifier or additive is added to the absorbing solution in an amount in the range where the reaction is not hindered. Further it is also possible to employ two or more of the catalyst compounds.
In the present invention, it is a further specific feature to activate the catalyst compound and employ the absorbing solution containing this activated catalyst compound in the reaction. The absorbing solution containing the catalyst compound of the present invention, exhibits its activity initially when specified naphthols or their sal-ts ~,dr;3 ~i~32~

have been dissolved, but usually insufficient activity is exhibited unless the solution is used for 20 hours or longer.
The inventors have made various studies with a view to S imparting a sufficient activity to the absorbing solution so that the activity may be exhibited from the beginning of its use. As a result it has been found that if an aqueous solution of the catalyst compound is subjected to an ad-equate pretreatment by blowing air into the aqueous solu-: 10 tion, before dissolving the aqueous solution in an alkaline absorbing solution, then the catalyst is immediately ac-. tivated at the time oE its use.
The drawings illustrate the invention. In the drawings:
Figure 1 is a graph illustrating this activation of the catalyst compound of the present.invention, and Figure 2 is a diagram illustrating a preferable produc-tion apparatus by means of which the process of the present invention is carried out.
In Figure 1, the abscissa shows a pretreatment time (hour) for catalyst and the ordinate. shows a activation rate of catalyst through the pretreatment thereof (%).
A pretreatment was carried out by blowing air at a rate of ~5~ hour into 2~ of an aqueous solution containing 2-nitroso-l-naphthol-4-sulfonic acid as an example of the catalyst compound, in an amount of 70 mols/m3, maintained at a temperature of 30C~ An adequate amount of the resulting aqueous solution of the catalyst compound was added to an ammonia aqueous solution maintained at a pH of 0.2, 50 as to give a concentration of 2 mols/m . Further, NH~HS was added so as to give a concentration of 65 mols/m3. There-after, air was blown into the resulting solution with stirring, and the liquid phase oxidation rate of NH4HS in the presence of 2-nitroso-1 naphthol 4-sulfonlc acid was measured to obtain the activation rate (%). As a result it was observed that the solution subjected -to the pretrea-tment of 4 hours was completely activated. Such a pretreatment yields the advantages that it is possible to fully make use of the performance of the catalyst and obtain a higher percentage desulfurization decyanization with a smaller amount of the catalyst.
As another specific feature of the present invention, there is mentioned a method wherein the absorbing solution 15 is regenerated by contacting it with air or oxygen in a gas- `
liquid contact manner, in a counter flow tower. In this case, since the catalyst employed in the present invention catalyzes the oxidation of hydrogen sulfide into thiosul-furic acid, no trouble is brought about by adherence of sulfur onto packing material, etc. Thus, it i5 possible to employ a counter flow tower having a packing material packed therein as an apparatus for regenerating the absorbing solution whereby the gas-liquid contact efficiency is further enhanced and also the scale of the apparatus is made smaller. Thus, this regenerating process is an excellent advantage.
This process, however, has a drawback that hydrogen sulfide and/or hydrogen cyanide in the solution are driven off due to the stripping effect of air or oxygen for oxi-dation and contained in the exhaust gas from the top of the counter flow tower, which is ~ery undesirable from the vie~point of environmental conservation.
~hus the inventors have made various studies or over-coming this drawback, and as a result have found that iE a process is emplo~ed wherein the absorbing solution is intro- ;
duced into a middle stage of the counter flow tow~r~ air or oxygen is introduced into the tower at its bo-t-tom~ and the absorbingr solution withdrawn from the bottom of the tower is partly circulated to the top of the -tower, then it is possible to reduce the conten-t of hydrogen sulfide and/or hydrogen cya-nide in the exhaust gas from the counter flow tower, do~m to substantially zero. Namely, accordin~ to the above-mentioned process, the upper part of the counter flow tower functions as a zone for absorbing hydrogen sulfide and/or h~drogen cya-nide, and it is possible to reduce the concentration of hyd-rogen sulfide and/or hydrogen cyanide in the exhaust gas.
The above-mentioned gas purification process of the presen-t invention will be illustrated referring to ~ig. 2.
In Fig. 2~ an unpurified gas 1 is introduced into the absorption tower 2 at its bo-ttom part, ascends through the tower 2 and is con-tac-ted with an absorbin~ solutlon falling from the top of the tower. ~he absorbing solution absorbs hydrogen sulfide and/or ~ydrogen cyanide and the resulting purified gas 4 is discharged outside the tower.
~he absorbing solution having hydrogen sulfide and/or hydrogen cyanide absorbed therein and accumulated at the botto~ of the tower is sent -through a conduit 5 to a middle s-tage 7a o~ a counter flow tower 7 ~or regenerating the absorbing solution, having a packing material such as R~-schig ring packed therein~ by means of a pump 6~ ~rhile air is blo~n through a conduit 11 into the tower 7 at i-ts bottom by means of a blower 12 and con-tacted with t,he ab-sorbing solution in a counter flow manner to regeneratc the absorbing solution.
A part 8 of the resul-ting regenerated absorbing solution is circulated -through a conduit 9 to the top of the to~ler by me~ans of a pump 10, flows down and completely removes hydrogen sulfide and/or hydrogen cyanide contained in the ascending air~ while the resulting air is discharged through a conduit ~10 13 to the outsideO ~he mos-t part of -the resulting regenerated absorbing solution is sent to the absorption tower 2.
'The process of the present inve~tion will be described below in more detail by way of ~amples.
Exampl.e l An absorption tower is constructed by providing a glass tube having an inner diameter of 70 mm and a height of 1000 mm -~
and ~aGkin~ there.i~ chi~ rin~ having a di~metor of lQ ~m ~;
up to a height of 800 mm, and separatel~ a glas~ tube having an inner diameter of 100 mm and a length of 1800 mm is employed as a regenera-tion tower for an abso.rbing solutionO
An absorbing solution (at 30C) consisting of an alkaline aqueous solution having 2-nitroso-1-naphthol-4-sulfonic acid dissolved therein in a proportion of 5 mols/m3t was ~lowed down from the top of the absorption tower at a rate of 50 ~/hr while a nitrogen gas containing 0~8 % by volume of hydrogen sulfide and 0.65 % by volume of ammonia was in.s-troduced into the tower at its bottom at a rate of 1 Nm~/hr and contacted with the solution.
~he resulting absorbing solution having absorbed a part ~0 of ammonia contained in the nitrogen ~as and almost all of %
;

hydrogen sulf1àe also corl-tain~d therein wa~ Sellt ~0 the rec,fenera-ti.on to~er a-t l-ts bot~om part at a rate o:~ 50 ~/hour~
whl 1~ air was blown i~. to the to .~3er a t 1ts bot to~D pax ~ at: a ra-te o~ 60 ,e~ho~lr to effec~ ~a~-liquid c:on~clc t O
~s a resul-t, the ~ost part o f h~y~rogen sulfid~ ln ~h~
absorblng solutlon v~as ox:idiz~d in-i,o thlosul:~uric aoid~ and the x-esulting ab~30rbin~, solu-t~ on was reCJ,enera ted ancl aga1n sent to the top part of the absorpti3n tower~ During -the op~ra-tion, no ~oaming phenomen3n c,aus~d ~y for~nativn o:E
0 3UlfUr W3S observed a~ the top part of the reger~eration tower~ and also sul~ur part1cl~ was hardly observe~l~ The resul-ts are sho~n In Table ~.
Table 1~ j J~fter i Concent~ation of ~-l2S Percentfl~e I P~rcerl^~age ¦ start ~f I in gas (pp~n) ~esul.~uri~ Ifo.rMa-tion o;~ ~ I
op2r~tion L .. ~ . . z.~ion ( j6~ t~io~ulfuric ~I t inle-t Q:~ at exit of acld (',~) ¦ absorption ab~orption to~ r to~ r ~ __~ ____~ __~__ ~
2 6 hours ~3ûO0 800 90 . O 5o O 13 hours 8000 350 95 ., 6 70 20 hour5 ¦ ~JO()O 7 99 / 9 90 '. 27 ho~rs I 8000 5 99~ 9 g Exa~ 2 'XWO liters o: arl aqueous ~,olution containin~ 2-ni .r o~;o-l-naphthol-4-~;ulfor~ acid in a proportion of 70 mol~/rn~
w~s pr~r~ate~ by blo~.~ing air i~ltO the solution at a rate ot' 15 ~/~lOUX' for 2 hours, and ~herea~t~r arl ~.dequa~ amo~ t ~.
~rhi~ solution was di~solY~d in 20 ,P of ~n alkaline solut.ioi~
~at a ~olut:~Gn te~nperc~ture o~ 30C) so a~ to gilJ.~ a concentration w 15 ~

of 5 mols/m3. ~es-t was carried out under the same conditions and employing the same gas as in case oE Example 1 excep~t for -the above-mentioned pretreatment. ~he results are shown in ~able 4 'rable L~

. ~ ~ j , . ~ . ~ _ _ - ~;~ After Concentration of H2~ Percentage Percen-tage start of in gas (ppm) desulfuri- of forma-operation _ _ ~ zation (%) tion thio-at inlet of at exit of sulfuric absorption absorption acid (%) -tower tower ~ . _ _ _ _ . .
I 6 hour~ 8000 8 99.9 90 13 hours 8000 8 99.9 90 20 hours 8000 7 99.9 90 27 hours 8000 ~ 99.9 ~ 91 Example 3 A test was carried out under the same conditions as in Example 1 except that the composition of gas -to be purified i was varied.
A gas to be purified contained 0.8 % b-y volume of hyd-rogen sulfide, 0.1 % by volume of hydrogen cyanide and 0.65 %
by volume oE ammonia. After 27 hours since star-t o:E the operation, the percentage desulEuriza-tion, the percen-tage dec~anization and -the percentage formation of thiosulfuric acid were 99.9 %, 99.0 % (all of product was thiocyanic acid) and 91 %, respec-tively.
Exam~le 4 A tes-t was carried out under -the same condltions and employing the same gas as in Example 1, except that sodium l-nitroso-2-naphthol-3~6-dicarboxylate was substi-tuted as catalyst. ~he results are shown in ~able 5 q'a~ 5 jAf-ter Concen-tration of H2S Percen-tage> Percen- I
star-t of in gas (ppm) desulfuri- ta~e of ¦
operation :~ . zation (%) forma-a-t inlet of at exi-t o.~ t~on absorp-tion absorption .u -tower tower acid (%) . . _. _ _ _ . _. _ 13 hours 8000 820 89~9 100 20 hours 8000 89 98.9 100 27 hours 8000 80 99.0 100 E~ample 5 A single type desulfurization tower which is able to absorb and regenerate simultaneously~was constructed by providing a glass tube having an inner diameter of 70 ~n and a height oE 1000 mm and packing therein Raschi.~ xings ihaving a diameter of 10 mm up to a height of 800 mm~ -~went~J
liters of an alkaline aqueous ~olution (~H : 9) having sodiu~
l-nitroso-4-naphthol-2-sul:~onate dissolved therein in a proportion of 5 mols/m3, was flowe~ down Erom the top part of said sin~le type desulfllrization tower at a rate o:E 50 .~/hr~
while N2 gas containing 0.65 % by volume of a~monia and 0.
b~ volume o:~ hydro~en sulfide was blown into the tower at its bottom part at a rate of 60 ~/hr. and at the same time air was blown thereinto at a rate of 1 m~/hr. to subjec-t them to gas-liquid contact whereb~ desulfurization together with re-genera-tion were carried out~ The results are shown in Table 6~

~able 6 I
. .
. _ _ _. , After Concentration of H2S Percentage Percen-tage start of in gas ~p~m) desulfuri- of forma-operation ~ zation (%) tion thio-at inlet of a-t exit of sulfuric absorption absorption acid (%) tower tower . . ~_ . ~ ... ._ .. _ _ . . ... ..
1~ hours 8000 500 93.8 95~2 20 hours 8000 1~5 98.3 97.o 27 hours 8000 92 98.9 98~3 At the initial period of the opera-tion, a foaming phenomenon was observed to a certain extent, bu-t it was scarcely observed after 20 hours.
~xam~
A test was carried out under the same conditions and employing -the same apparatus as in ~xample 1 excep-t tha-t an alkaline aqueous solution containing sodium 2-nitroso-1-naphthol-4 carboxyla-te as ca-talyst in a proportion of 5 mols/
m~ was su~s-tituted. ~he results were as follows: After 20 hours, the percentage desulfuriza-tion was 99 /~, and the percen-tage forma-tion of thiosul~uric acid was 90 %.
Comparative example A test was carried ou-t under the same conditions and employing the same apparatus as in Example 1 except -that an aqueous solution having ammonium l~i-naphthoquinone~2-sulfonate as catalyst in place of 2-nitroso-1-naphthol-4-sulfonic acid, dissolved therein, in a propor-tion of 5 mols/
m3, was employed. Regeneration was carried out u~der the s~me conditions and employing the same apparatus as in ~xample 1. ~he results are shown in ~a~le 7.

~able 7 ~ . .
~fter Concentra-tlon of H2S Percen-tage Percentage s-tart of in gas (ppm) desulfuri- of forma-operation za-tion tion thio-a-t inlet of at exit of (%) sulFuric absorption absorption clCiC~ (%) -tower tower __ _ . . , _ _ . . _ _ . ~D _ . __._ _ 1~ hours 8000 6 99.9 63 20 hours 8000 30 99.6 65 27 hours 8000 9_ 98.6 65 . . _ In this comparative example~ although the percentage desulfurization was high, formation of sulfure was con-siderabl~. Namely~ a :~ew hours after star-t of the o~eratlon, Eorrnation of sulfur particles oc~urr~d and they adhered onto the packinK material. Particularly at the top part of the regeneration tower, a violent foaming was observed.
~xamPle 7 An absorption tower was constructed by providing a tower having an inner diarneter of 900 mm and a height of 9 m and packing -therein a packing material of Tellere-tte type up to a height of 5 m, and separately a counter flow tower was constructed by providing a tower having an inner diameter of 750 mm and a height of 12 m and packing therein a packing material of ~ellere-tte L type in two stages9 the height of the upper stage being 2.2 m and -that of the lower being 4.6 m.
~ `wo hundred liters of an aqueous solution containing 2-nitroso-1-naph-thol-4-sulfonic acid in a propor-tion of 70 mols/rn3 was pretreated by blowing air therein for l~ hours at a rate of 500 ~/hr~ and thereafter ~n adequate amount * TRADE MARK

~ 19 ~

of the resulting solution was dissolved in 5 m3 of an a~monia aqueous solution so as to give a concentration of 2 mols/M3.
The resulting solution wasflowed down from the top of the ~bsorption tower a-t a rate of 22m3/hr~, while a coke oven gas containing 0.3 % by volume of hydrogen sulfide~ O.J2 %
by ~olume of hydrogen cyanide and 1.0 % by volume of ammonia was introduced in-to the bottom of -the a~sorption tower at a rate o~ 1000 Nm3/hr. to bring them into contac-t.
'~he resulting absorbing solution withdrawn from the bottom of the absorption tower was fed between the upper stage and the lower s-tage of the packed parts of the counter flow tower at a rate of 22 m3/hru and flowed down~ while air was blown into the bottom of the coun-ter flow tower at a rate of 60 Nm3/hrO to effect gas-liquid contact. The results are shown in ~able 8.

2~
~able 8 ~, . . . . . ... , . _ _ ._ _ After star-t6 Hours 13 Hours 20 Hours 27 Hours of opera-tion . .... _. . . ., _ .. __.. ....
Percentage desulfuriza- 99.9 99.9 99.9 99.9 tion (%) _ ._ . . . ~ _.

Percentage 99~0 99.0 99.0 99.0 decyaniza-tion (%) ___ _ ~ .
Percentage formation of -thio- 90 91 91 91 sulfuric acid ~%) . _____ A_ _ _ . . __ H2S con-centra-tion in exhaus-t 180 180 180 180 gas from coun-ter flow tower (ppm) _ !

Example 8 A teæ-t was carried out under the same conditions and empl;oying the same gas as in ~xample 7 excep-t that a part o~ -the solu-tion withdrawn from -the bo-t-tom of the counter flow tower was sen-t to the -top o~ the counter flow tower at a rate o~ 4 m3/hr. and flown down, while the absorbing solution wi-thdrawn from the bottom of the absorp-tion -tower was sen-t be-tween -the upper s-tage and the lower s-tage of the packed par-ts of the counter flow tower at a rate of 22 m3/hr.
and flown down. ~he resul-ts are shown in ~able 9.

~ p~

~able 9 .. _~ _.. ..... _ . ~ _ .. . , ~ ___ __ _ After star-t of operation 6 Hours 13 Hours 20 Hours 27 Hours . . . . .. . ._ _ ....
Percentage desulfuriza~tion 99.9 99.9 99.9 99.9 .
- ._, Percen-tage clecyc~nization 99.0 99.0 99.0 99.0 . I

__ _ _ r __ .. _ _ _ _ _ _ ._ _ . _ ___ ~ . . _.__ _ __~ __ _ Percentage formation of 9 91 91 - 91 -thiosul~uric acid (%) _ ~ _ , ,. .
H2S concentra-- .
tion in exhaust gas from 5 5 L~ 2 counter ~low tower (ppm) .

. _ .... ..

Claims (6)

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

1. A process for purifying a gas containing hydrogen sulfide and/or hydrogen cyanide which comprises contacting a gas containing hydrogen sulfide and/or hydrogen cyanide with an absorbing solution con-taining at least one of naphthols or their salt(s) having a nitroso group at .alpha.-position or .beta.-position, at least one acid group in the molecule thereof and a standard redox potential in the range of 0.4V to 0.7V, to cause said absorbing solution to absorb the hydrogen sulfide and/or the hydrogen cyanide contained in said gas, and thereafter contacting air or oxygen with the resulting absorbing solution in a gas-liquid contact manner, to convert hydrogen sulfide mainly into thiosulfuric acid and hydrogen cyanide mainly into thiocyanic acid to remove hydrogen sulfide and/or hydrogen cyanide, and at the same time regenerate the absorbing solution.

2. A process according to claim 1, wherein said at least one of naphthols or their salt(s) is selected from the group consisting of 2-nitroso-1-naphthol-4-sulfonic acid, 2-nitroso-1-naphthol-4-carboxylic acid, 1-nitroso-2-naphthol-3, 6-disulfonic acid, 1-nitroso-2-naphthol-3, 6-dicarboxylic acid, 1-nitroso-4-naphthol-2-sulfonic acid 1-nitroso-4-naphthol-2-carboxylic acid, 1-nitroso-2-naphthol-4-sulfonic acid, 1-nitroso-2-naphthol-4-carboxylic acid and their salts.

3. A process according to claim 1, wherein said absorbing solution is alkaline.

4. A process according to claim 1, wherein said absorbing solution is obtained by pretreating an aqueous solution containing said at least one of naphthols or their salts(s) by blowing air into said aqueous solution.

5. A process according to claim 1, wherein said gas-liquid contact of said absorbing solution containing absorbed hydrogen sulfide and/or hydrogen cyanide with air or oxygen consists of a gas-liquid contact of said absorbing solution introduced into a counter flow tower at its middle stage, with air or oxygen introduced into said tower at its bottom and a gas-liquid contact of a part of said absorbing solution circulated from the bottom to the top of the tower, with air or oxygen ascending inside the tower.

6. A process according to claim 5, wherein said counter flow tower contains a packing material.