Sciencemadness Discussion Board - Ways to scrub Hydrogen Sulphide?

Ways to scrub Hydrogen Sulphide?

NEMO-Chemistry - 21-3-2018 at 18:08

What would you use in a scrubber system to take care of hydrogen sulphide?

Edit by Texium: Fixed typo in title

[Edited on 3-22-2018 by Texium (zts16)]

BromicAcid - 21-3-2018 at 20:10

Whatever strong base you have laying around should work to catch it as a salt. Bleach will help oxidize it to something less odoriferous. I used copper sulfate once in an attempt to double-wammy to sulfuric acid (the formed copper sulfide looked like copper metal). The difficult part is to ensure lots of surface area between the gas an the liquid.

Tsjerk - 22-3-2018 at 00:27

NaOH would turn it into useful Na2S

Fulmen - 22-3-2018 at 00:43

In the industry there are scrubbers based on iron oxide/hydroxide. H2S reacts with the iron to form iron sulfide which is then oxidized with air to form elemental sulfur.

clearly_not_atara - 22-3-2018 at 02:51

Iron oxide I think is used because it is absurdly cheap. However I don't think the kinetics are good for detoxifying a stream of air you will be releasing, unless it is very finely ground.

I think NaOH is good. If unavailable consider perhaps a solution of zinc acetate and sodium acetate? Pennies IIRC dissolve in vinegar.

AJKOER - 22-3-2018 at 04:50

Use friendly deodorizing hydrogen peroxide:

H2O2 + H2S --> 2 H2O + S (c)

Not as cheap as chlorine bleach (NaOCl), mentioned above, but at least not adding odors!

Using Cl2 gas (not dried) may offer good mixing properties, if you don't mind compounding toxic gases!

Cl2 + H2S --> 2 HCl + S

A safe lower cost solution but slower, pass H2S mixed in air into a soluble ferrous or cuprous salt (or even better, a cupric and a ferrous, introducing a redox couple equilibrium, Fe(ll)+Cu(ll)=Fe(lll)+Cu(l)) like citrate or ascorbate (sunlight may help recycle some of the these transition metal ions). Electrochemical reaction:

Cu(l) + O2 + 2 H+ --> Cu(ll)(OH)2

Variation of the above, replace ferrous with fine metallic powdered iron in the presence of some acid (like citric acid).

Or, just use a suspension of CaCO3 or another cheap aqueous carbonate:

Na2CO3 (aq) + H2S --> NaHCO3 + NaHS

[Edited on 22-3-2018 by AJKOER]

NEMO-Chemistry - 22-3-2018 at 08:41

Thanks guys for the replies it has given me alot to think about, some are very tempting but i need to think of the end goal...

Chlorine sounds great but defeats the purpose. The gas is being scrubbed from a bio methane reactor. Its a long long story.

Fulmen - 22-3-2018 at 10:04

I found the iron oxide method while researching biogas, so it should be proven technology. Something like sodium hydroxide would be simpler to set up, and should also scrub out CO2. It will however be consumed, so you will need to change solution regularly. The iron oxide process needs a regeneration cycle, but should last much longer.

NEMO-Chemistry - 22-3-2018 at 10:16

I need the CO2, so thats not an issue. Although as a backstop its a good plan, i would likely go with ultrasonic mist of Sodium Carbonate rather than Hydroxide for CO2.

I really appreciate the help, this is my third attempt at the form filling and my last chance to get this thing taken seriously.

AJKOER - 22-3-2018 at 11:02

Found a paper, "Caustic-scrubber-designs-for-h2s-removal-from-refinery-gas-streams" at http://www.trimeric.com/assets/caustic-scrubber-designs-for-...

DraconicAcid - 22-3-2018 at 11:26

Quote: Originally posted by AJKOER

A safe lower cost solution but slower, pass H2S mixed in air into a soluble ferrous or cuprous salt (or even better, a cupric and a ferrous, introducing a redox couple equilibrium, Fe(ll)+Cu(ll)=Fe(lll)+Cu(l)) like citrate or ascorbate (sunlight may help recycle some of the these transition metal ions). Electrochemical reaction:

Cu(l) + O2 + 2 H+ --> Cu(ll)(OH)2

Why are you trying to involve electrochemistry when the simple precipitation reaction works?

Cu(2+) + H2S = CuS + 2H(+). Buffer it with acetate and you're golden.

Magpie - 22-3-2018 at 12:51

We used FeCl3 in an aqueous system to take out the H2S in a biowaste liquid stream at a papermill. Only problem is that the piping must not be iron or steel.

What flow rate of air (and the concentration of H2S) need treatment?

Fulmen - 22-3-2018 at 13:02

Sodium carbonate should work, producing NaHS rather than Na2S. Easier to handle than NaOH and should last longer as it won't absorb CO2. However both NaHS and Na2S are a bit nasty, so disposing of them could become an issue. Corrosion could also become a problem.

AJKOER - 22-3-2018 at 14:11

Quote: Originally posted by DraconicAcid

Quote: Originally posted by AJKOER

Why are you trying to involve electrochemistry when the simple precipitation reaction works?

Cu(2+) + H2S = CuS + 2H(+). Buffer it with acetate and you're golden.

DraconicAcid:

Are you really trying to say that after the spontaneous electrochemical removal of two H+ created from the interaction of hydrogen sulfide with water:

H2S (aq) = H+ + HS-

combined with the action of a soluble cuprous and oxygen resulting in a cupric that is further capable of removing yet more H2S?

In other words, my method is even better?

By the way, see http://www.sciencemadness.org/talk/viewthread.php?tid=81370 to quote:

Quote: Originally posted by byko3y

I needed like 5 minutes reading to understand what they wanted to declare a truth. The true ions can be described with a single formula from the paper:
HS^- + OH^- + Na⁺ <-> NaS^- + H₂O
So, basically, sulfide never loses its last cation in the presense of water.

--------------------------------------------------------------------

Here is a new method (actually occurs naturally in the atmosphere, see https://books.google.com/books?id=aG8oDwAAQBAJ&pg=PA224&... ) introduce Singlet oxygen (see http://www.sciencemadness.org/talk/viewthread.php?tid=31729#... ) mixed with air containing H2S. Cited reactions:

O(1D) + O2 --> O(3P) + O2*

O(3P) + H2S --> Products

This path (like with chlorine) does not produce a lot of problematic waste. Other paths include the reported utilization of ClO2 (in diluted concentrations being otherwise explosive, see http://www.beckart.com/wastewater_treatment/chlorine-dioxide... ), my take on possible reaction paths with the chlorine dioxide (a stable radical) in water:

.ClO2 (aq) + (H+ + HS-) --> H+ + ClO2- + .HS
2 H2S + HClO2 --> 2 H2O + HCl
.HS + .ClO2 --> HCl + SO2
SO2 + H2O =H2SO3 = H+ + HSO3-
HSO3- + .ClO2 --> .HSO3 + ClO2-
H2SO3 + HClO2 --> H2SO4 + HOCl
H2SO3 + HOCl --> H2SO4 + HCl
....

I suspect that dilute concentrations of Cl2O (which will explode in contact with H2S in higher concentrations, but likely only energetic at low doses) will also work well removing 2 moles of H2S for each mole of dichlorine monoxide:

Cl2O + 2 H2S --> 2 HCl + H2O + S

Note, Cl2O can be produced in dilute amounts by passing Cl2 and air over heated beds of Na2CO3, which sort of makes this a modified chlorine method for the removal of H2S.

[Edited on 23-3-2018 by AJKOER]

DraconicAcid - 22-3-2018 at 16:53

Quote: Originally posted by AJKOER

DraconicAcid:

Are you really trying to say that .... my method is even better?

No. not even close.

Quote:

By the way, see http://www.sciencemadness.org/talk/viewthread.php?tid=81370 to quote:

Quote: Originally posted by byko3y

By the way, you couldn't find a less relevant comment if you tried.

[Edited on 23-3-2018 by DraconicAcid]

NEMO-Chemistry - 22-3-2018 at 17:09

Sorry i didnt make things clear!

Magpie its a Biomethane digester, One i been working on a long time, different in alot of ways to the design of the one or two chamber systems. The Carbonate mist is at the end as a trap. The actual CO2 i am after using and scrubbing, but if i get some on the outlet after i have done what i can, then it will be scrubbed.

The Hydrogen Sulphide hasnt been an issue i have hardly had any to worry about, But lately with some different feedstocks I have had some, so it looks like iron oxide which incidentally helps with another problem.

I will post alot more detail in a few days, thanks for the papers etc. Its been really helpful, i need to go research some of it then i will come back and detail what i have been doing.

NEMO-Chemistry - 22-3-2018 at 17:11

Quote: Originally posted by Fulmen

Sodium carbonate should work, producing NaHS rather than Na2S. Easier to handle than NaOH and should last longer as it won't absorb CO2. However both NaHS and Na2S are a bit nasty, so disposing of them could become an issue. Corrosion could also become a problem.

Sorry see above, the CO2 in an ideal world would be used up, it isnt directly connected with the scrubber. That was solely directed at something thats a recent problem.

Maybe because the feedstock has changed alot lately.

Melgar - 22-3-2018 at 21:17

Ozone would kill it pretty good. If you need an ozone generator, I have a UV-based one I'd sell. If it's from some sort of bioreactor, odds are you have more than just H2S, and have a whole bunch of nonsense mercaptans and thioethers you'll be wanting to get rid of too.

I think it's:

O3 + H2S = H2O + SO2

So you might smell some SO2, but that barely has any smell by comparison.

[Edited on 3/23/18 by Melgar]

Fulmen - 23-3-2018 at 00:08

I'm not completely sure I understand what you're goal is, but as long as you do I'm sure it's fine. The iron oxide process will require a regeneration step, so unless you can shut the scrubber down you will need a twin scrubber setup. On the plus side it uses simple materials and should reduce the H2S to a completely harmless product.
A wet scrubber would probably be simpler to implement, especially if you can find a process that can reduce the H2S to a benign end product.

Another process that hasn't been covered is bioreactors. I'm not sure how simple they are to run, but it does fit the bio-scheme quite nicely.
It might also be possible to eliminate the formation of H2S in the digester. If I'm not mistaken nitrates are used for this in sewer handling.

NEMO-Chemistry - 23-3-2018 at 01:13

I had an idea for a bioreactor to make Methane, it also does something else but that would just make things harder to explain and dosnt play a part in this.

The system is based on a cows stomach, its 6 chambers if you count the load and offload chambers. The two main ferementors sit in the middle, I have a O3 generator i used a long time back for my fish house water, but its likely it would kill off the bacteria in the reactor.

The system is a kind of prototype, the CO2 is reused to part fill the next reactor (80%H and 20% CO2), the CO2 from the bleed off part is fed and dissolved into water (Carbonic Acid) and is fed to a hydroponic system, plants take it up better as a carbon source via the roots.

Hydrogen sulphide wasnt a problem until we tried a new feedstock, the new feedstock is actually a way to deal with another problem. No one is interested around here about Biomethane, by that I mean Scotland not SM!.

But they do care about another problem, and the reactor happens to be a great way to separate out what they do care about.

I take it if I had iron powder in water swirling around, and added the gas. All I really have to do is keep enough iron powder in that chamber? Should also be a way to get rid of some O2 in the initial feed water.....

Extremely helpful, thx.

Fulmen - 23-3-2018 at 02:26

The simplest fix would be to add nitrates to the reactor. As I understand it bacteria can reduce sulfates if no other source of oxygen is available, although it's possible other sulfur-sources can cause this as well. But it's worth a try.
Trying to agitate iron powder sounds hopeless, I suspect it's too heavy. But loading a reactor with metal scrap could work, something like strips of sheet metal, wire or perhaps turnings from a machine shop.

Sulaiman - 23-3-2018 at 03:13

My chemistry knowledge is too narrow to help but a few thoughts;

Unless your process is confidential it would be better to lay out the whole scheme,
so that we get an idea of the entire process.
That way someone may be able to suggest simplifications, economies etc.

This project sounds commercial,
if so then for the sake of the environment, and to maximise usefulness and profit, ideally no waste is produced, only products.

If you can be CERTAIN of relatively low concentrations of H₂S in the methane does it matter ?
e.g. H₂S burns to SO₂ and H₂O ... a little SO₂ in the exhaust may be acceptable?
as SO₂ is an 'accepted' power generation pollutant,
that has industrial scale scrubbing solutions.
or, a little H₂S in the gas stream is an added benefit - leak detection

My limited chemistry knowledge suggests heated iron pipes stuffed with iron wool/scrap would be cheap.

AJKOER - 23-3-2018 at 05:47

I have reviewed some of the literature and the first observation is that the alluded to iron oxide for the industrial processing of H2S is Fe3O4 (reference, see "Sulphide Scavengers in Oil and Gas Industry – A Review" by M.K. Amosa, I.A. Mohammed, and S.A. Yaroor), more meaningfully, as this is a mixed valence salt, FeO.Fe2O3. Cited summary reaction (of which I chemically disagree owing to the absence of dissolved or gaseous oxygen, but the reaction may approximate observed performance of the iron oxide on hydrogen sulfide removal):

" Fe3O4 + 6 H2S → 3 FeS2 + 4 H2O + 2 H2 (10)"

The success of this salt suggests to me a cyclic process between valence states of iron. Further research led to this work: "Free Radicals and Chemiluminescence as Products of the Spontaneous Oxidation of Sulfide in Seawater, and Their Biological Implications", by DAVID W. TAPLEY,GARRY R. BUETTNER, and J. MALCOLM SHICK, in Biol Bull. 1999 Feb 1; 196(1): 52–56. available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295652/ .

Read this work, in particular reactions (2) to (10) to understand the likely underlying mechanics cited below:

HS• + O2 → HO2• + S (2)

or: HS• + O2 → HSO2• (7)
followed by: HSO2• → H+ + SO2•- (9)
SO2•- + O2 → SO2 + O2•- (10)

HS• + O2•- → S + HO2- (3)

At near-neutral pH, HO2− will immediately protonate:

HO2- + H+ → H2O2 (4)

The proposed metal-catalyzed mechanism for metal M at valence state 'n+' via metal auto-oxidation of oxygen creating the superoxide radical anion:

M(n+) + O2 → M(n+1)+ + O2•- (5)

This oxidation is complemented by the reducing HS- ion:

M(n+1)+ + HS- → M(n+) + HS• (6)

The formation of H2O2 can lead to hydroxyl radical and with H2S more HS•

Fe(ll) + H2O2 + H+ --> Fe(lll) + OH• + H2O

OH• + H2S --> H2O + HS•

In my opinion, the recycling of the valence states of Fe3O4 is the key to its success.

[Edited on 23-3-2018 by AJKOER]

NEMO-Chemistry - 23-3-2018 at 15:01

It isnt commercial as such, i have applied for funding though. Unlikely to get any but worth a shot, My reluctance is solely because at some point I would like it open source.

Nitrates are pretty slow, the scrubbing of the gas is not a huge amount and iron oxide in the system would be a good thing. Where I live i am aware of someone collecting huge amounts of what I collect, by huge i mean mechanical system by the Ton!!

But they discard alot of what is trapped in with it, I want to keep those bits as well. The main problem is I happen to know the digester they are using dosnt work. But they are paid to collect the material anyway.

The feedstock is seaweed, this should give you a very good idea what the other material in it is. It also accounts for alot of my other obscure posts especially oxidizers, I have cracked the digestion of mainly seaweed feedstock, along with FOG's and brewers grains.

Once its done its job then the crap is pulled out and thats gonna be the next bit. Funny its been in the news alot here lately and yet i been on this several years now

NEMO-Chemistry - 23-3-2018 at 15:07

Quote: Originally posted by AJKOER

I have reviewed some of the literature and the first observation is that the alluded to iron oxide for the industrial processing of H2S is Fe3O4 (reference, see "Sulphide Scavengers in Oil and Gas Industry – A Review" by M.K. Amosa, I.A. Mohammed, and S.A. Yaroor), more meaningfully, as this is a mixed valence salt, FeO.Fe2O3. Cited summary reaction (of which I chemically disagree owing to the absence of dissolved or gaseous oxygen, but the reaction may approximate observed performance of the iron oxide on hydrogen sulfide removal):

" Fe3O4 + 6 H2S → 3 FeS2 + 4 H2O + 2 H2 (10)"

The success of this salt suggests to me a cyclic process between valence states of iron. Further research led to this work: "Free Radicals and Chemiluminescence as Products of the Spontaneous Oxidation of Sulfide in Seawater, and Their Biological Implications", by DAVID W. TAPLEY,GARRY R. BUETTNER, and J. MALCOLM SHICK, in Biol Bull. 1999 Feb 1; 196(1): 52–56. available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295652/ .

Read this work, in particular reactions (2) to (10) to understand the likely underlying mechanics cited below:

HS• + O2 → HO2• + S (2)

or: HS• + O2 → HSO2• (7)
followed by: HSO2• → H+ + SO2•- (9)
SO2•- + O2 → SO2 + O2•- (10)

HS• + O2•- → S + HO2- (3)

At near-neutral pH, HO2− will immediately protonate:

HO2- + H+ → H2O2 (4)

The proposed metal-catalyzed mechanism for metal M at valence state 'n+' via metal auto-oxidation of oxygen creating the superoxide radical anion:

M(n+) + O2 → M(n+1)+ + O2•- (5)

This oxidation is complemented by the reducing HS- ion:

M(n+1)+ + HS- → M(n+) + HS• (6)

The formation of H2O2 can lead to hydroxyl radical and with H2S more HS•

Fe(ll) + H2O2 + H+ --> Fe(lll) + OH• + H2O

OH• + H2S --> H2O + HS•

In my opinion, the recycling of the valence states of Fe3O4 is the key to its success.

[Edited on 23-3-2018 by AJKOER]

Thank you for this, at first glance i didnt see it, but i think I understand where there goes now. I need a day or so to get my head around this, the reactors are lab scale at the moment around 1-1.3 ltr each, they are full blown bio reactors stainless steel and glass.

The iron powder was to try out in one chamber, if that dosnt stop formation then i switch to scrubbing, what i am trying to do is avoid Carbon and such i want to make the system use everything, hence why the CO2 is fed into a hydro system.

Also after a few weeks NOx in a fair amount seems to be tolerated in the hydro system, surprised me a bit.

I am cleaning and autoclaving the entire system this weekend, i want to reconfigure it, at the moment the sample lines are in the wrong place.

I also want to get rid of one Tri port

AJKOER - 24-3-2018 at 06:39

Assume the following system to get an indication of a possible implied net reaction (ignoring pH associated with speciation issues of active transition metal ions):

H2S + H2O = H3O+ + HS-

Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•

HS• + O2 → HSO2•

HSO2• → H+ + SO2•-

SO2•- + O2 → SO2 + O2•-

SO2 + H2O = H+ + HSO3-

HS• + O2•- → S + HO2-

HO2- + H+ → H2O2

Fe(ll)/Cu(l) + H2O2 + H+ --> Fe(lll)/Cu(ll) + OH• + H2O

OH• + H2S --> H2O + HS•

Approximate theoretical implied net reaction ignoring, not listed, problem side reactions (consuming radicals) and further oxidation of sulfite:

2 H2S + 2 O2 --Fe(ll)/Fe(lll)/Cu(l)/Cu(ll)--> S + H2O + H2SO3
------------------------------------------------------------------------------------

In addition to pH issues, transition metal(s) seemingly catalytic role and other possible catalyst (like chloride), chelates (like citric acid to promote solubility), there are questions as to choice of particle size of say FeO.Fe2O3.

[Edited on 24-3-2018 by AJKOER]

Fulmen - 24-3-2018 at 06:51

I think you're following the wrong path:
https://pubs.acs.org/doi/abs/10.1021/jp980361p?journalCode=j...
"Initially, almost all the surface sites can interact readily with H2S, to form a layer of iron sulfides. Over longer reaction times reaction occurs with deeper sites, to form bulk sulfides. Regeneration of ferric (hydr)oxide by oxidation with oxygen converts Fe2+ to Fe3+, and S2- anions are replaced by O2- with formation of elemental sulfur"

So it's a two-stage reaction, the first is formation of iron sulfide in anoxic conditions. The second regeneration stage oxidizes the sulfide to elemental sulfur.

AJKOER - 24-3-2018 at 08:39

Fulmen:

To quote from your source:

"The mechanism of the interaction of H2S with either reagent is ionic and involves heterolytic dissociation of H2S and exchange of S2- and SH- anions for O2- or OH-. Subsequently water is eliminated and, in coupled redox reactions, sulfide is oxidized to elemental sulfur and Fe3+ cations are reduced to Fe2+."

Dissociation: H2S + H2O = H3O+ + HS-

Coupled Redox reactions system:

Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•
HS• + O2•- → S + HO2-
HO2- + H+ → H2O2
Fe(ll)/Cu(l) + H2O2 + H+ → Fe(lll)/Cu(ll) + OH• + H2O
OH• + H2S → H2O + HS•

Sulfide is oxidized to elemental sulfur:
.....
HS• + O2•- → S + HO2-

Fe3+ cations are reduced to Fe2+:

Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•

Now, as to whether a 'layer of iron sulfides' is necessarily in place could be a function of complexing agents/chelates (like citric acid).

As to 'stages', note by my listing of reaction steps:

1. H2S + H2O = H3O+ + HS-

2. Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•

3. HS• + O2 → HSO2•

.......

For a discussion of the surface chemistry on the action of H2S on Fe(lll), please see, for example, https://pubs.acs.org/doi/abs/10.1021/la00042a030 .

[Edited on 24-3-2018 by AJKOER]

NEMO-Chemistry - 24-3-2018 at 12:26

I have deleted a long response...

I was unaware SEAPA discharge rules were changed, despite them sending me the paperwork i have been working to the wrong limits. Not sure it affects anything written here but it does change what i need to do.

One thing i do need to mention, the discharge goes directly to feeding crops. the solid material (is hardly any) from anything organic goes onto drying then pellets. I have to watch heavy metals ect which is kinda why i like Iron.

The scrubbers on large systems are pretty small, but they dont often handle seaweed, I also have another problem to deal with. But that can wait....

NEMO-Chemistry - 24-3-2018 at 16:52

Right we are cleaned out, I will autoclave tomorrow then reconnect. I got some different pumps to go on and a better PH probe (last one started playing up).

Should be ready to fill Monday morning, will kick it off with cow shit again. Water jackets are connected in series and central reactor has a hot plate with water jacket magnetic stirer, it also has internal stiring via outside motor. Two of the other have the internal system with outside motor as well.

If I bump the temperature a little should it shouldnt take long to gas. I cant start with seaweed it dosnt seem to work well, i will put all my notes online for download if anyone wants them.

Out of interest, any merit in using oxygen poor water to start it off? I use CO2 and H2 for flushing before i charge with the cow shit. Its collected fresh....very fresh as in dosnt reach the floor fresh.

NEMO-Chemistry - 24-3-2018 at 17:15

Found one reason i may be getting problems after storms etc.