Sciencemadness Discussion Board - catching H2S

catching H2S

hkparker - 22-12-2010 at 21:33

Hey everyone, I'm going to be doing a reaction soon that produces a quantity of H2S, what's the best way to absorb it? I don't want it floating around so I want to absorb it with something. Some solution I can pass it through or some salt that will react with? Thanks!

NurdRage - 22-12-2010 at 21:56

bubble it into a concentrated solution of sodium hydroxide.

hkparker - 22-12-2010 at 22:05

Yea I figured neuralizing it with something would do it, just didn't know what was most effective, thanks!

Magpie - 22-12-2010 at 22:05

It could also be bubbled into one of the many heavy metal soluble salts that form insoluble sulfides. Eg, Zn or Fe. That way you would have a sulfide as a byproduct if you wanted it.

Use an intermediate trap to avoid suckback.

mnick12 - 22-12-2010 at 22:09

I have seen alot of people use lead nitrate to absorb hydrogen sulfide, but then you have to deal with lead. Just out of curiosity what reaction are you going to do?

hkparker - 22-12-2010 at 22:11

Thanks, making an insoluble sulfide could be useful, though id rather deal with zinc then lead lol. I'm going to be trying to synthesize carbon disulfide by passing acetylene through molten sulfur.

aonomus - 22-12-2010 at 22:15

From my experience the easiest and cheapest way to deal with H2S and other thiols is to run it through 1-2 basic bleach traps. Then you don't have to deal with heavy metal sulfides, etc; the waste stream is simply a solution of sulfonic acids (or rather their sodium salts). A bit of sodium hydroxide and commercial/household bleach makes for an easy trap to get rid of thiols, especially volatile gaseous ones (MeSH, EtSH, nBuSH, AcSH, etc).

woelen - 22-12-2010 at 23:53

A mix of a solution of NaOH and bleach indeed is the best I can think of. The NaOH binds the free H2S and the bleach destroys the sulfide by means of oxidation. You might get a turbid liquid, containing finely dispersed sulphur. But certainly part of the sulfide will be oxidized further, all the way up to sulfate. Dissolve the NaOH in plain household bleach (4% active chlorine) and use that as the scrubbing solution.

Put a flask between your reaction vessel and the scrubbing bottle. If production of H2S stops or becomes very slow, then there may be suck-back.

[Edited on 23-12-10 by woelen]

hkparker - 22-12-2010 at 23:56

Awesome info, thanks. What's the problem with sodium sulfide though? If I don't have bleach on hand

woelen - 23-12-2010 at 02:40

Sodium sulfide still releases quite some H2S. The compound H2S is such a weak acid that even from alkaline solutions still quite some H2S can escape. A solution of Na2S has a strong smell of rotten eggs.

Instead of bleach, you can also use dilute H2O2 (e.g. 3% H2O2 mixed with a solution of NaOH).

aeacfm - 23-12-2010 at 03:13

a month ago i was going to make a post like that but asking about if the sample contain sulfides how can determine the sulfide it self not through the metal (stoitiometric) , and no loss in sulfides occure

[Edited on 23-12-2010 by aeacfm]

blogfast25 - 23-12-2010 at 05:31

Beware also that H2S is seriously toxic, more toxic than HCN apparently.

There's a thread about someone who managed to poison himself with it and ended up in hospital, you might want to look it up for inspiration... It was member 'fluke' IIRW...

NaOH + hypochlorite is my choice also. Make sure your scrubbers contain enough chemicals to comfortably absorb the H2S you'll be generating and make sure your apparatus is air tight!

BromicAcid - 23-12-2010 at 07:47

During one of my attempts at CS2 I was trying to react sulfur with carbon to get my desired product. I figured some H2S would be generated from any other organics in my carbon so I put a trap in line just of a concentrated CuSO4 solution in water which I figured would make the sulfide and maybe some sulfuric. The fact that sulfides are not a fan of acidic conditions didn't cross my mind since I added it at the last moment. The trap quickly turned dark and it became apparent I had grossly underestimated the amount of toxic gas that would issue fourth from the reaction. The copper solution was being reduced to copper metal or some other thick beautiful precipitate which began to collect.

About 45 minutes into the experiment my grandmother (whom I lived with at the time) came out of the house and yelled at me for making everything smell like rotten eggs. I never smelled a thing, there was no wind, my sense of smell had died somewhere along the way. Traps don't fail suddenly... and neither does the sense of smell, but the two can fail in step with one another and create a disastrous situation.

For safety prepare an indicator solution by dipping some paper in lead nitrate solution and drying, cut in strips and hang these papers around your work area with more on hand. These will give you the visual you need if you have a leak or a trap fails, they can also be used to troubleshoot as the response time can be rapid depending on preparation. Note that there are no commercial gas cartridges (at the time I last checked) that protect against hydrogen sulfide except for emergency escape cartridges. This is a supplied air only issue and one of the elite groups of chemicals that won't just injure you, it has the capacity to remove your conscious from this Earth with ease.

hkparker - 23-12-2010 at 17:48

Ok, I didnt know H2S was so toxic, or more worrisome that it numbs the nose. Tell me if this setup sounds safe then. A glass tube coming from my reaction carrying all the H2S will be bubbled through bleach/NaOH then into CaCl2 soln. If I get the black ppt of CaS in the CaCl2 soln. then I know the bleach/NaOH soln. isnt catching everything and I will have to add another bleach/NaOH gas washer.

bbartlog - 23-12-2010 at 18:23

CaS isn't black, and I don't think it exists as such in aqueous solution, and in any case with CaCl2 the reaction runs the other way (i.e. rather than going CaCl2 + H2S -> CaS + 2HCl, it goes CaS + 2HCl -> CaCl2 + H2S). I don't know what the easiest/best indicator solution would be (lead nitrate has been mentioned, I think copper acetate should also work), but CaCl2 isn't it.

hkparker - 23-12-2010 at 18:26

Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?

blogfast25 - 24-12-2010 at 07:22

Quote: Originally posted by hkparker

Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?

Yes, CaS hydrolyses immediately in water: CaS + 2 H2O === > Ca(OH)2 + H2S. Can't be used for capturing H2S. Solid it's white, BTW...

The reason why CaS hydrolyses has to do with solubility: CaS is quite soluble compared to most other sulphides, so you get:

CaS (s) (in water) === > Ca2+ (aq) + S2- (aq)
The S2- then reacts with the water, forming first HS-, then H2S and driving the first equilibrium to the right.

Lead really is your best bet, second to the even better silver (forms black Ag2S). Haven't you got a piece of lead from an old battery, pipe or (car wheel) balancing weight you can dissolve in some nitric?

[Edited on 24-12-2010 by blogfast25]

[Edited on 24-12-2010 by blogfast25]

Eclectic - 24-12-2010 at 08:23

How about some kind of burner, followed by SO2 scrubber? It would also get rid of acetylene,CS2, and any other organics that make it past the condenser.

Jor - 24-12-2010 at 08:46

Quote: Originally posted by blogfast25

Quote: Originally posted by hkparker

Ok thanks, yea my bad. Copper acetate I do have, so ill use that. I would go with lead if I had it, but I dont. Any other good indicators?

No, why use lead compounds when there so much better, safer compounds? Also lead is very environmentally unfriendly.
Just use something like bleach, that is very safe. If you decide to use a metal, don't use lead. I mean people should avoid using those toxic metals if possible, so that means you are not going to use it for srubiing something right?

DJF90 - 24-12-2010 at 09:13

Jor, the point of the lead nitrate was to make indicating strips. For detecting H2S in your workspace these would be indispensable. Bleach of course would be fine for the wash trap, but it'd be unsafe not to be sure theres no leaks in the system. The amount of lead nitrate required to make such indicating strips would be very small. I agree its nice to avoid toxic heavy metals wherever possible, but this is one case where theres no decent substitute, at least to the best of my knowledge.

Nicodem - 24-12-2010 at 09:15

Quote: Originally posted by hkparker

Thanks, making an insoluble sulfide could be useful, though id rather deal with zinc then lead lol. I'm going to be trying to synthesize carbon disulfide by passing acetylene through molten sulfur.

In such case H2S is not the only thing to worry about! Acetylene can easily explode even without oxygen/air admixed. Passing a current of acetylene through molten sulfur sounds extremely hazardous. Pure acetylene explodes if heated or compressed. I have seen it explode at normal pressure. The explosion is much less violent than the explosion of acetylene/air mixtures, forms red flames and lot's of sooth, but is still violent enough to cause damage and injuries.

I would recommend you to do what you should have done already in the first post, to provide the reference for this process so that other members can evaluate the hazards involved.

Otherwise, aqueous sodium hypochlorite efficiently scrubs and oxidises H2S, but it is obviously not compatible with traces of unreacted acetylene.

Jor - 24-12-2010 at 09:24

Quote: Originally posted by DJF90

Jor, the point of the lead nitrate was to make indicating strips. For detecting H2S in your workspace these would be indispensable. Bleach of course would be fine for the wash trap, but it'd be unsafe not to be sure theres no leaks in the system. The amount of lead nitrate required to make such indicating strips would be very small. I agree its nice to avoid toxic heavy metals wherever possible, but this is one case where theres no decent substitute, at least to the best of my knowledge.

Sorry, my fault, I didn't read all the posts well enough.
I was just suprised that someone was recommending the use of a lead nitrate scrubber, but this was not the case. My excuses.
Ofcourse for test strips you should use lead, it gives a very clear black color in contact with H2S.

DJF90 - 24-12-2010 at 09:38

I thought so... don't worry about it! But yeah, I suspect a 0.01M solution (if not more dilute) of lead nitrate would make adequate test strips, the colour change is very obvious and I suspect very sensitive also. Bear in mind the test strips would likely need to be moistened before use, to allow good interaction with any H2S in the atmosphere.

The WiZard is In - 24-12-2010 at 10:16

Quote: Originally posted by woelen

A mix of a solution of NaOH and bleach indeed is the best I can think of.

[snip]

Clorox Proresults Outdoor bleach (Lowe's among others)
in a strong bleach solution w/ sodium hydroxide.

The MSDS for their Proresults Deck Cleaner shows the same
ingredients/ %'s.

Attachment: Cloroxproresultsoutdoorbleachcleaner_6-07_.pdf (32kB)
This file has been downloaded 515 times

A short history of hydrogen sulfide

The WiZard is In - 24-12-2010 at 10:32

American Scientist
98:6-9 January-February 2010

http://tinyurl.com/2bv9d6f

Timing is everything. Just the other day a removed this
dis-bound article from the night stand to one of my file cabinets.

No sense saving the entire magazine when I can access it online,
however, like Nature, JAMA, The Lancet, &c., if I let my
subscriptions lapse I lose access.... 'bout 8-years back I took
my Bobcat dug a hole and filled it with 1200+ pounds of journals...
and never looked back.

The AAAS offered up a discount — so I renewed my membership
and now can access back issues of Science.

hkparker - 24-12-2010 at 11:24

Ill look up the reference, I got it from an article attached to another thread on here. I do have plenty of silver nitrate, so I will be using that as my test strip. But I think the reaction will be over acetylene's auto ignition point, so I might have to re-think that.

hkparker - 24-12-2010 at 12:20

Heres the pdf of the source, it seems like burning acetylene is inevitable, but according to this paper they got decent yields.

Attachment: <a href="http://www.sciencemadness.org/talk/files.php?pid=153376&aid=7799" onclick="window.open(this.href); return false;">jr9280002068.pdf</a> (193kB)

blogfast25 - 25-12-2010 at 06:49

The only thing with AgNO3 indicators is that due to extreme sensitivity it might lead to false positives: silver metal often darkens just from small amounts of H2S in the air. Stick a clean silver (or electropated silver nickel) spoon in a hard boiled egg and Ag2S forms on the silver's surface...

hkparker - 29-12-2010 at 16:11

OK so I think I have my final set up down for this reaction. Ill explain my procedure, tell me if this sounds ideal.

Ill make an acetylene generator by adding water from a dropping funnel to a flask with calcium carbide in it with a vacuum takeoff adapter. The acetylene will travel to an erlenmeyer flask with a two holed rubber stopper on top. The acetylene will bubble under the molten sulfur in the heated flask producing CS2 and H2S (along with other impurities). The products will go out a glass tube on top to the next flask, which is a smaller erlenmeyer flask with another stopper with two holes in it in a beaker with salt/ice in it. This will condense the CS2. The H2S will travel out the flask through the other hole into an anti-suck back flask and then into the bleach/NaOH soln. Finally, a glass tube coming from that solution will go into a flame from an alcohol burner, to burn away any remaining C2H2 or H2S. Also, before I begin I will add dry ice where the calcium carbide is and wait for it to sublime completely. That will fill the whole set up with CO2. Not saying that will prevent the C2H2 from exploding, but it wont hurt. What do you all think?

Magpie - 29-12-2010 at 16:39

I will not comment on the chemistry, but instead the hydraulics:
Keep in mind where in the system you are building pressure, or creating vacuum. Be sure your sealing is adequate to handle these pressures, positive or negative.

Is your "dropping funnel" a pressure equalizing type? You will be building pressure in the acetylene generator in order to sparge this gas into the liquid sulfur. I don't know the hydraulic head required here but I would minimize it; and the P-E type dropping funnel would be the best.

You will be creating a vacuum when you condense the CS2. Analyze what effect, if any, this will have on the system.

Then you are going to build pressure (or possibly vacuum?) when you absorb the H2S.

Your layout may function just fine, I'm just recommending that you give the hydraulics some thought before firing it up.

hkparker - 29-12-2010 at 17:40

Good insight, thanks! I drew out what this would all look like on paper and thought about it, and it seems fine. Condensing might suck back the bleach/NaOH solution, but thats the only thing ill seriously have to worry about, and ill have a flask ready to catch any suck back. The only thing im pretty worried about is how acetylene will handle in these conditions, but ill be extremely safe, I think its ready to try.

Rogeryermaw - 1-1-2011 at 12:12

when you start your reaction you may want to inert your setup first. the small amount of air in your glass will become bomb conditions when you pass acetylene through it. think: series of glass vessels and tubes with acetylene and atmospheric air running toward an open flame...FLASHBACK!!! also i doubt you will reach this pressure under the conditions you describe but bear in mind that acetylene, in a non-baffled container explodes spontaneously when it reaches over 15+ lbs. pressure. but the flashback is a more worrisome event in the setup you describe. positive system pressure won't give you mechanical advantage when dealing with a gas as volatile as acetylene. if it is mixed with air from inside the glassware, the acetylene will try to burn back to the source. i suggest you purge everything VERY well before you start and then take steps to be sure that your system does not drop below atm and pull air in where it can mix with flammables.

hkparker - 1-1-2011 at 12:17

I said I was going to add dry ice to the acetylene generator first, to flood the setup with CO2. That won't solve the problem of acetylene exploding at 15psi but it will prevent it from burning. Also, directly behind that flame is the washing solution, so the flame could backtrack the whole setup, actually it couldn't backtrack any of the setup.

Rogeryermaw - 1-1-2011 at 12:28

just so long as you have safety protocols in place. safety first! happy sciencing.

hkparker - 1-1-2011 at 12:30

Yep, thanks! Weather is pretty bad where I am right now but I'm hoping to try this as soon as I can