Sciencemadness Discussion Board - Amount of SO2 released from Sodium Bisulfite solution

Amount of SO2 released from Sodium Bisulfite solution

jus_thom - 25-2-2019 at 00:51

Hi everyone,

I am currently working on determining the amount of SO2 that would be released in a Sodium Bisulfite chemical storage room. The tanks usually vent outside the building, so the only credible scenario (in my opinion) is if you ever had a spillage from the tank (via overflow pipework).

So, my question is how do i determine the amount of SO2 that would be released from a known spillage volume (lets say 1m3) of 40% w/w Sodium Bisulfite solution at room temperature and atmospheric pressure?

j_sum1 - 25-2-2019 at 02:31

What makes you think any will be released?

Of course SO2 will be given off if you react with an acid. But, (and I might be wrong here) I am not aware that solid sodium bisulfite decomposes significantly at all.

woelen - 25-2-2019 at 03:10

A solution of sodium bisulfite indeed releases some SO2. You can easily smell the gas.
If you want to test, I would say you create 1 liter of the 40% solution and put this in a closed vessel of e.g. 5 liter. From this, suck in 1 liter of air and then bubble this through a solution of dilute NaOH. This solution then will contain sodium sulfite, which can be titrated against an oxidizer.

j_sum1 - 25-2-2019 at 03:28

Thanks woelen. I did not read carefully enough. I did not notice it was a solution.

jus_thom - 25-2-2019 at 04:06

Thank you Woelen. I appreciate the experimental method but not the route I can go for. I was looking for more of a theoretical way to determine this. I have data on vapor pressure exerted by the solution (0.9kPA SO2 @RTP) but cannot relate this to the final answer I need.

streety - 25-2-2019 at 15:53

The simple answer is: all of it.

Assuming the store room is not air tight and given enough time the bisulfite will be entirely converted to sulfur dioxide.

What you are probably more interested in is the concentration of sulfur dioxide in the store room at a particular time. That would be more challenging to calculate and I'm not sure I have the answer. It may be simplest to think about upper bounds.

Complete conversion is your absolute/improbable maximum.

Sulfur dioxide at the vapor pressure is your reasonable maximum.

Beyond that you would want to know the rate at which sulfur dioxide is produced (probably dependent on the area of the spill), the volume of the store room, and the number of air changes per hour.

happyfooddance - 26-2-2019 at 14:29

Quote: Originally posted by streety

The simple answer is: all of it.

Assuming the store room is not air tight and given enough time the bisulfite will be entirely converted to sulfur dioxide.

What you are probably more interested in is the concentration of sulfur dioxide in the store room at a particular time. That would be more challenging to calculate and I'm not sure I have the answer. It may be simplest to think about upper bounds.

Complete conversion is your absolute/improbable maximum.

I agree with this. If this is a safety thing then this is how you should look at it, if it is just a theoretical thing then any number greater than 1 and less than your theoretical max should work.

I happen to be very sensitive to SO2, much more sensitive than any compound that I work with regularly.

So much so, that if I have to prepare sat. solution of bisulfite I usually have to get a co-worker to do it. I start coughing as soon as the lid comes off the (dry) metabisufite.

I am pretty confident that if you spilled a hundred liters of 40% bisulfite, you would have a mess that you are much less prepared for than you are this math.

Also, this is not a compound that is ideal to "store" as an aqueous solution, if I am not mistaken? Maybe for some uses but not any of mine.

[Edited on 2-27-2019 by happyfooddance]

woelen - 27-2-2019 at 02:56

An aqueous solution of bisulfite is not ideal on storage. It loses SO2 easily (much more so than the dry solid metabisulfite) and it also easily is oxidized by oxygen from the air. I once had a bottle of sulphurous acid (appr. 6% SO2 by weight). After I had used half a liter of this, I had the impression that in the remaining liquid half of the available SO2 was lost. Part of the SO2 was oxidized to H2SO4 in the bottle and part of the SO2 simply was lost into the air, each time when the bottle was opened again.

jus_thom - 27-2-2019 at 08:46

Thank you for you comments so far everyone .

So, I have carried out a series of calculations to come up with the required air change rate. I think most of it makes sense except for step 2; where I have multiplied the molar concentration by the spillage volume instead of the SO2 gas volume. I'm not too sure how to solve this.

1. Molar concentration of SO2 ; n/V = P/RT = ( 900 (Pa) / 8.314 * 293 (K) ) = 0.37 moles/m3

2. Total SO2 release; SO2 Molar concentration * Spillage Volume* SO2 Molar Mass = 0.37 (moles/m3) * 1 (m3) * 64 (g/mole)= 23.7 g

3. SO2 concentration in room; Total SO2 release (mass) / Room free volume = 23.7 (g)/ 175 (m3) = 0.136 g/m3 = 51 ppm

4. Min. required ventilation rate; (ln( SO2 concentration / COSHH limit) * Room Free Volume ) / Time = (ln(51/1)*175)/1 = 805 m3/hr

5. Air Change required = Ventilation Rate / Room free Volume = 805/175 = 4.6 air changes.

streety - 27-2-2019 at 17:49

For the total release it is the volume of the room rather than the volume of spill that should be used.

For the concentration, using the 0.9 kPa partial pressure mentioned earlier I think that would correspond to 9000 ppm (0.9 kPa / 101 kPa).

jus_thom - 1-3-2019 at 08:03

The volume over the room is around 200 m3. Won't that be a massive overestimation to say the SO2 released by 1 m3 Sodium Bisulphite will take up that much volume ?

Same goes for the SO2 concentration that you worked out from the vapour pressure. The SO2 pressure would only be there for the small bubble around the spillage. Would it be correct to assume the whole room has the same vapour pressure ?

Thanks

happyfooddance - 1-3-2019 at 11:21

Quote: Originally posted by jus_thom

The volume over the room is around 200 m3. Won't that be a massive overestimation to say the SO2 released by 1 m3 Sodium Bisulphite will take up that much volume ?

No.

I don't know where you are getting these equations and ideas from, but I suggest do more research and definitely don't work with chemicals on this scale until you have more experience and understanding of the properties of the chemicals you are handling.

Is this schoolwork or something? Post the actual problem. One cubic meter of saturated Na bisulfite ontains about 40 kilos of NaHSO3. That is 40000 grams. Molar mass is 104 so: 40000/104= 384 mol
384*22.4L= 8,601 L or 86m*3

So a spill of that size will kill all living things in your storeroom, even the microscopic ones, and you need to find a better solution.

Now, with most compounds there is a point in calculating vapor pressure such as you are. However, as it has been mentioned, this compound decomposes readily and rapidly, so the only sensible way to treat it is as if it will all be released upon spillage.

morganbw - 1-3-2019 at 18:06

Contact the manufacturer of the Sodium Bisulfite solution. If you mix in-house the info might be a little harder to find.
I did just now read at a producers website that the saturated solution is not considered an environmental hazard.

If you have a spill, I promise all of the SO2 is not going to immediately jump out of solution. You will have time to protect your employees.

Contact the people who know. Manufacturer

AJKOER - 2-3-2019 at 06:20

A possible safety measure would be to have the HSO3- solution in presence of inexpensive Washing Soda (Na2CO3) or perhaps hydrated Lime (Ca(OH)2), or more interesting (a war of chemical fumes, but less appealing), ammonia fumes for a loosely closed bottle of ammonia water (perhaps in a box storing also the aqueous HSO3-). The interaction of NH3, SO2 and water vapor may produce a white cloud of solid particles. Some of the author's comments at https://pubs.acs.org/doi/abs/10.1021/ie050734q include:

"The solid products are analyzed by thermal gravimetric analysis, the element analysis, and the wet chemical analysis. The results show that the reactions are very fast and the products are mixtures of various types of ammonium−sulfites with (NH4)2SO3 as the main component."

Note, using a carbonate (Na2CO3, CaCO3,...) basically coverts SO2 to CO2, so I would open the door to the storage room and allow some time for any CO2 to pour out before entering.

[Edited on 2-3-2019 by AJKOER]

Sulaiman - 2-3-2019 at 06:51

You could have multiple sensor levels,
. safe = no action required
. not safe = fan on low speed
. Danger = fan on high speed but still insufficient ventilation

The fan high speed should be sized for emergency ventilation,
at low vapourisation rates the fan will only operate briefly and rest most of the time.
or similar.

I think that knowing the gas concentration and warning (or alarming) for unacceptable levels before opening the door is a 'nice' idea.
(the overall design would be similar for any gas/vapour that has a sensor available, preferably dual/redundant)
EDIT: monitors/alarms should be 'fail-safe'

P.S. I have hdpe bottles of ammonia and HCl in the same plastic tub,
It seems to work well - in my well-ventilated hobby environment,
but I think that it is a poor choice for a shared storage space.

[Edited on 2-3-2019 by Sulaiman]

AJKOER - 2-3-2019 at 07:09

I sort of like the concept of my chemically automated approach using an ammonia source over a mechanical ventilation system (as discussed above) from a cost/simplicity perspective. Further, I would guess that the loss of ammonia from solution in the closed box with stored bisulfite would likely automatically increase as SO2 concentration rises!

Also, the generation of white dust particles brings attention to a leakage issue!

In the event of total leakage of the aqueous HSO3- (from say a storm or some accident), one can calculate the volume of a 5% aqueous ammonia needed to neutralize.

On the down side, any formed ammonium sulfite is not exactly itself without health risks (see, for example, http://www.emdmillipore.com/Web-US-Site/en_CA/-/USD/ProcessM... ), but is likely stable in an atmosphere containing NH3 (removing acid gases).

I repeat Sulaiman's comment above:

Quote: Originally posted by Sulaiman

......
P.S. I have hdpe bottles of ammonia and HCl in the same plastic tub,
It seems to work well - in my well-ventilated hobby environment,
but I think that it is a poor choice for a shared storage space.

[Edited on 2-3-2019 by Sulaiman]

[Edited on 2-3-2019 by AJKOER]

jus_thom - 4-3-2019 at 06:21

Quote: Originally posted by happyfooddance

Quote: Originally posted by jus_thom

The volume over the room is around 200 m3. Won't that be a massive overestimation to say the SO2 released by 1 m3 Sodium Bisulphite will take up that much volume ?

What do you mean by post the actual problem? I have stated the problem along with available data in my first post.

How did you come up with 1m3 of Sodium Bisulphite contains 40 kg of NaHSO3 ? The density of a 40% Sodium Bisulfite sol is 1480 kg/m3. If I calculate it based on the room volume, the air change required would be around 20 per hour!

Also, this solution does not easily and readily decompose. There was a study carried out which showed a 1.5% change in NaHSO3 concentration (40% - 38.5% w/w) during a 140 day time period. So, it is rather a slow reaction.

jus_thom - 4-3-2019 at 06:28

Quote: Originally posted by morganbw

Contact the manufacturer of the Sodium Bisulfite solution. If you mix in-house the info might be a little harder to find.
I did just now read at a producers website that the saturated solution is not considered an environmental hazard.

If you have a spill, I promise all of the SO2 is not going to immediately jump out of solution. You will have time to protect your employees.

Contact the people who know. Manufacturer

Hi, I have contacted the manufacturer who does not have this information. Previously, we have just gone with a fan that's designed to 10 air changes per hour which is based on nothing. So, I want to come with up the ventillation design based on actual chemical properties.

morganbw - 4-3-2019 at 08:32

You may have this but it gives some info that may or may not help.
It does offer some info on storage and handling.

Attachment: sulfur_handbook.pdf (1.8MB)
This file has been downloaded 602 times

happyfooddance - 4-3-2019 at 12:51

Quote: Originally posted by jus_thom

Also, this solution does not easily and readily decompose. There was a study carried out which showed a 1.5% change in NaHSO3 concentration (40% - 38.5% w/w) during a 140 day time period. So, it is rather a slow reaction.

Thas is with spontaneous hydrolysis conditions (anaerobic), not exposure to atmospheric oxygen, under which conditions hydrolysis is rapid.