Sciencemadness Discussion Board

Acid neutralizing on industrial scale

Broken Gears - 12-4-2022 at 03:29

I manage a process where an ethylene oxide scrubber is a part of it.
EO is washed through a 5% sulfuric acid solution. When the ethylene glycol content reaches 30%, the efficiency falls, and the emission goes up.

Disposing of the mixture is expensive. Mostly because of the corrosive properties. I don’t have a separate tank to do a neutralizing with a base; soda lime, NaOH or maybe Na-Carbonate.

But can I do the neutralizing when the tank is drained? If I know the volume and the acid conc. I can calculate the amount of base needed, according to whatever base is chosen. But can it be mixed by or in a mixing valve, or is that too risky?
Any ideas on how this could be managed?

BromicAcid - 12-4-2022 at 03:45

What volume are you talking about? You could do a slick setup with two metering pumps going to a inline mixing element with an inline pH probe and quench it in a continuous flow process or a skid mounted setup. I mean, if you're saying you don't have a mixing tank and adding one is not an option then this might be your best bet.

Broken Gears - 12-4-2022 at 04:18

We are talking about 9000 L
No a bad idea :-) I'll do some research on that setup.
Heat could be a concern. Could it reach 100 degrees celsius resulting in pressure in the pipes?

[Edited on 12-4-2022 by Broken Gears]

draculic acid69 - 12-4-2022 at 18:30

Quote: Originally posted by Broken Gears  
We are talking about 9000 L
No a bad idea :-) I'll do some research on that setup.
Heat could be a concern. Could it reach 100 degrees celsius resulting in pressure in the pipes?

[Edited on 12-4-2022 by Broken Gears]


Neutralization of h2so4 produces lots of heat
Depending on concentration,solvent,water content, solution
temperature,speed of mixing, possibility of cooling etc etc 100'c is definitely
a possibility but not a certainty.

Tsjerk - 12-4-2022 at 23:12

Can't you take 10 liters or so and dump in the NaOH to see what happens?

Metacelsus - 13-4-2022 at 07:42

I would do some very careful calculations and a few smaller scale experiments before doing anything at 9000L scale!

And I wouldn't rely on this forum for chemical engineering advice.

clearly_not_atara - 13-4-2022 at 07:58

Using NaHCO3 for neutralization will reduce the heat production significantly, but also releases plenty of gas. Foam is the major concern, though; gas can be vented.

Olivine - MgSiO3 - has been proposed for neutralization of waste acids; it is / can be very cheap and not too exothermic, but it produces silica powder as a byproduct and can self-passivate under the wrong conditions:
https://www.sciencedirect.com/science/article/abs/pii/S03756...

Ordinary magnesium oxide/hydroxide might do well enough to limit ∆H, and has neither of the above concerns, though I'm not sure of the price. Probably still cheaper -- and definitely easier to handle -- than NaOH. Not sure if it's worth trying to recover/sell MgSO4.

Sulaiman - 13-4-2022 at 08:34

maybe obvious;
if neutralizing with KOH or NaOH the heat of solution (enthalpy of dissolution) is massive,
(easier to boil water than with Az. sulphuric acid)
so use a pre-cooled solution, rather than dumping in solid base.

Tsjerk - 13-4-2022 at 22:43

Quote: Originally posted by clearly_not_atara  
Using NaHCO3 for neutralization will reduce the heat production significantly, but also releases plenty of gas. Foam is the major concern, though; gas can be vented.

Olivine - MgSiO3 - has been proposed for neutralization of waste acids; it is / can be very cheap and not too exothermic, but it produces silica powder as a byproduct and can self-passivate under the wrong conditions:
https://www.sciencedirect.com/science/article/abs/pii/S03756...

Ordinary magnesium oxide/hydroxide might do well enough to limit ∆H, and has neither of the above concerns, though I'm not sure of the price. Probably still cheaper -- and definitely easier to handle -- than NaOH. Not sure if it's worth trying to recover/sell MgSO4.


He wants to neutralize inline with a mixing valve, how would solids or gas releasing agents work there?

If heat is the problem, use colder or more dilute NaOH.

unionised - 14-4-2022 at 05:55

You could, in principle, just run the effluent through a trough full of limestone chippings.
That will strip out most of the acidity and allow the CO2 to escape.

Is it possible to recover the glycol by distillation?

WGTR - 14-4-2022 at 07:00

I have a 6000L tank, and my neighbor has a 9000L one, so I have an idea of how much solution this is. :D

How quickly must the tank be drained? In one hour, overnight, one week, etc.?

What pH range is required for the "cheaper" disposal? It is likely not exactly 7.000, but a range I would think. This would be useful to know.

One idea is to continuously pump the tank volume through a mixing valve, and then run the mixed solution through a heat exchanger before it is circulated back to the tank. If neutralizing with NaOH (for example), mix in much less than what is stoichiometrically required for the solution flow rate through the mixer. Continuously monitor the pH of the tank over hours/days. When it achieves your target range then you're ready for disposal. The tank itself may need some mixing/circulation.

Bmoore55 - 14-4-2022 at 07:43

You should strongly consider not using either NaOH or Soda Lime as you could push this too far and risk creating a strongly basic solution that can cause stress corrosion cracking in the base metal of your tank. Sodium bicarbonate will release a lot of CO2, but the end result should be much safer for your tank metal and it will mitigate the thermal release when mixing.

clearly_not_atara - 14-4-2022 at 19:01

Quote: Originally posted by Tsjerk  

He wants to neutralize inline with a mixing valve, how would solids or gas releasing agents work there?

If heat is the problem, use colder or more dilute NaOH.

I may not have considered the situation carefully enough.

Rainwater - 15-4-2022 at 13:00

Im no expert but i like recycling in my processes. Saves money.
it sounds as if a distillation apparatus would be useful.
First the spent solution has the water removed @ 100c and returned to the start of the process, then around 150c the ethylene glycol distills out.
Next the cruid sulfuric acid can be purified or simply returned to the system.

As a result you have a useful by product to sell, less of a mess to pay disposal fees for, and less neutralizing agents to purchase.
Your basicly exchanging neutralizing reagents for distillation energy

Maybe vacuum distillation might save on the energy requirements.
There could be another method to separate these compounds.
What are your other perdicted/observed byproducts?

Edit: just did a little more research and discovered my suggestion will result in dioxane perduction as well as a lot of other byproducts

[Edited on 16-4-2022 by Rainwater]

Texium - 15-4-2022 at 21:15

Also, distilling 9000 liters of liquid requires a tremendous amount of energy...

Tsjerk - 15-4-2022 at 21:29

Besides the tremendous amount of energy, a 9000 liter distillation rig is huge and expensive. OP mentioned he doesn't have a vessel where he can do the neutralization, I doubt he has the right standing by.

draculic acid69 - 15-4-2022 at 22:55

I think the only way forward was suggested above: take 10 liters of solutin, get a few 20L buckets and a thermometer & try a few different neutralization products & get some data. There's no going forward without doing this to see what works best for you and what doesn't & what can be managed with what you got.

[Edited on 16-4-2022 by draculic acid69]

unionised - 16-4-2022 at 01:56

Quote: Originally posted by Rainwater  
Im no expert but i like recycling in my processes. Saves money.
it sounds as if a distillation apparatus would be useful.
First the spent solution has the water removed @ 100c and returned to the start of the process, then around 150c the ethylene glycol distills out.
Next the cruid sulfuric acid can be purified or simply returned to the system.

As a result you have a useful by product to sell, less of a mess to pay disposal fees for, and less neutralizing agents to purchase.
Your basicly exchanging neutralizing reagents for distillation energy

Maybe vacuum distillation might save on the energy requirements.
There could be another method to separate these compounds.
What are your other perdicted/observed byproducts?

Edit: just did a little more research and discovered my suggestion will result in dioxane perduction as well as a lot of other byproducts

[Edited on 16-4-2022 by Rainwater]


If you boil glycol with acid it turns into dioxane which is carcinogenic.
(Not dioxin which is more famous).

But if you neutralised it first then that's a much better approach.
Selling the glycol, together with savings on waste disposal costs might pay for the still.

Incidentally, the heat evolved is well documented.
https://en.wikipedia.org/wiki/Enthalpy_of_neutralization


[Edited on 16-4-22 by unionised]

Tsjerk - 16-4-2022 at 02:45

Quote: Originally posted by unionised  


Incidentally, the heat evolved is well documented.
https://en.wikipedia.org/wiki/Enthalpy_of_neutralization


[Edited on 16-4-22 by unionised]


I was just doing some calculations on the back of an old envelope and the solution won't get close to boiling, even if you would dump in solid NaOH. Unless you start at ridiculously high temperatures of course.

Broken Gears - 21-4-2022 at 00:14

Thank you all so much for all the input.
I think I have underestimated the extent of this project...

With a pH at pH 6-9 we can deliver it to a Biogas-plant free of charge, and it will be converted to district heating = helping the local community.

Another solution is to neutralize it and dump it in the industrial sewer and it would be the wastewater plants problem. It's all within the law, but it seems backwards thinking to me.

The neutralization tank I can manage, but I think the inline model will be more favorable. Does that kind a equipment come ready-made? What would be the process time for pumping and neutralizing 9000 L with out too much heat generated?
The current downtime is 4 hours for draining the scrubber tank, refilling with water and adding conc. H2SO4. In 6 mouths time the sterilization process is doubled, add pressure to the scrubber system, but it give me a possibility to have accepted downtime of 24 hours.

Rainwater - 21-4-2022 at 02:52

You have the potential to produce a lot of very profitable products or a lot of very toxic pollution. I hope you figure out a good method for dealing with your byproducts.

The local market will help determine the best end products.
If you're in the farming area, neturalizeing with ammonia, then purifying the ammonia sulfate could be an option, and the pure product would be a great fertilizer.

A city or industrial area, neturaling with aluminum, will produce aluminum sulfate, which is a common chemical used in waste water treatment. Which seams a little arronic taking your waste water and using it to treat waste water.

Hopefully, you'll get this worked out before you produce all that waste

Rainwater - 21-4-2022 at 04:51

After some more research into industrial practices and making a few phone calls, calcium hydroxide is the standard neturalizeing reagent due to the easy use of a settling tank to separate the products.

Why is the scrubbing solution being acidified? To encrease the conversion of Eo to ethylene glycol.

The separation and treatment time/cost would be greatly reduced if the acid was not present. As well as eliminating the production of several byproducts.

A greater surface area would be required to react ethylene oxide with water at an equally efficient rate, but the problem with neturalizeing the wash water would be eliminated.
An additional problem that arises is self solving with a properly designed production process. That is the purity of the scrubbing media. For the greatest efficiency, the water should be free from glycol.

For example
Screenshot_20220421-081742_Samsung Notes.jpg - 158kB

At that point, a continuous distillation apparatus could be used to consentrate ethylene glycol and return the purified water back to the scrubbing reactor.

The apparatus could be constructed of common items such as old car radiators and copper tubing. Which would result in high thermal loss but could still be cost effective.

Proper heat exchangers would preheat the stage 1 solution with heat from stage 3, recycling energy and saving money



Temperature monitoring would ensure proper separation.

Further optimizing the system to a 2-stage reaction would result in less energy required and produce a less pure ethylene glycol solution but greatly reduce initial investment cost and construction requirements.

Also, by using a continuous recycling method, and by controlling the rate of glycol production to match removal, you can create a non-stop process that will increase overall production.

Edit:
if co2 emissions are not a consequence, conversion by acid catalyzed reactions to volatile products followed by combustion could supplement the distillation heat source.
Properly controlled with appropriate safety measures, complete combustion of the byproducts can occure and sulfuric acid can be recovered and recycled.

[Edited on 21-4-2022 by Rainwater]

SWIM - 21-4-2022 at 20:27

Well yeah, but if the OP is trying to avoid buying (or doesn't have room for)a neutralization tank it sounds like these more elaborate setups are off the table.

Looks like simple is a big priority here.

Bonee - 22-4-2022 at 03:35

Could try multi stage reverse osmosis or electrodialysis as well. Although the ethylene glycol may complicate things.
see patent.
https://patents.google.com/patent/US7976710B2/en

WGTR - 22-4-2022 at 05:41

Quote: Originally posted by Broken Gears  
Thank you all so much for all the input.
I think I have underestimated the extent of this project...

With a pH at pH 6-9 we can deliver it to a Biogas-plant free of charge, and it will be converted to district heating = helping the local community.

Another solution is to neutralize it and dump it in the industrial sewer and it would be the wastewater plants problem. It's all within the law, but it seems backwards thinking to me.

The neutralization tank I can manage, but I think the inline model will be more favorable. Does that kind a equipment come ready-made? What would be the process time for pumping and neutralizing 9000 L with out too much heat generated?
The current downtime is 4 hours for draining the scrubber tank, refilling with water and adding conc. H2SO4. In 6 mouths time the sterilization process is doubled, add pressure to the scrubber system, but it give me a possibility to have accepted downtime of 24 hours.


Your reply is helpful and helps with understanding the scope of what you are trying to do. Yes, unfortunately this sounds like a big project, because 4 hours is very little time to empty and refill a tank of this size if we add a neutralization step. This can be done of course, but there is so little room for error that no solution that I can offer will likely be useful, and it may take an engineer to design the process (due to the lack of room for error).

Anyway, is the tank pumped out, or is it emptied via gravity flow? If by gravity, the simplest method that I can conceive would be to have a second, equally-dimensioned tank, that is at the same height as the process tank. The second tank would contain pre-mixed neutralization solution (whether this is NaOH or something else) with a calculated concentration. The two tanks are joined with a 'Y' fitting through valves at their outputs for mixing. The output of the mixer would need to go to a small retention tank so that the pH could be constantly monitored as the tanks empty. Beyond this I wish you success.

Deathunter88 - 22-4-2022 at 10:19

Quote: Originally posted by Tsjerk  
Quote: Originally posted by unionised  


Incidentally, the heat evolved is well documented.
https://en.wikipedia.org/wiki/Enthalpy_of_neutralization


[Edited on 16-4-22 by unionised]


I was just doing some calculations on the back of an old envelope and the solution won't get close to boiling, even if you would dump in solid NaOH. Unless you start at ridiculously high temperatures of course.


Remember that's assuming perfect homgeneity and perfect mixing, which is very different from reality. If you want to prove this to yourself, fill a large graduated cylinder with water and dump in a couple hundred grams of NaOH. What you'll get is a geyser of boiling hot caustic solution spewing out. And that's just from the heat of solvation.

[Edited on 22-4-2022 by Deathunter88]

Rainwater - 22-4-2022 at 15:07

I have really enjoyed the challenge this problem has presented. I've read almost 20 papers and patent on the subject as well as provided a pretext for contacting some old friends I haven't spoken to for too long. The methods for dealing with this type of waste are well documented.

Quote: Originally posted by SWIM  
Well yeah, but if the OP is trying to avoid buying (or doesn't have room for)a neutralization tank it sounds like these more elaborate setups are off the table.

Looks like simple is a big priority here.



The 6 P's should be applied here.

Methods of disposing waste products should be well studied before any reaction is run. This constitutes proper and ethical chemistry. The methods to neturalize the waste product in question are presented in many posts of this thread.

From the impression I got, this reaction will be run again. Neturalizeing and shipping the waste is the most expensive solution I have seen.

For the first 9kL, this may be acceptable, but after this waste is disposed of, their will be more generated. Thus increasing cost. And there is no guarantee that the disposal company will do the work properly.

The original question was answered in the first few replies. But the problem, at least it is my opinion, was not solved.
The question I chose to answer is "How can this waste be dealt with in a manner that will improve process profitability with minimal cost, labor and environmental impact?".

Thus, the initial setup will be more expensive than paying someone else to dispose of the material. Because their is no need for additional reagents or labor, in my opinion, for a continuous process, continuous waste treatment is advisable.

Edit:
Quote: Originally posted by Bonee  
Could try multi stage reverse osmosis or electrodialysis as well. Although the ethylene glycol may complicate things.
see patent.
https://patents.google.com/patent/US7976710B2/en

If you could get this to work. That would be your best option

Edit:
Detailed instructions and analysis of pva membranes amd their properties.
www.mdpi.com/2073-8994/12/6/960/htm
Attachment: Pva membrane study.pdf (7.4MB)
This file has been downloaded 258 times

Easy to follow video tutorial on making a membrane
http://www.sciencemadness.org/talk/viewthread.php?tid=158099


[Edited on 23-4-2022 by Rainwater]

OR

Sulaiman - 23-4-2022 at 13:05

Maybe better for future runs to scrub the ethylene oxide by condensing (and collecting) it?

Edit : buying/leaasing/renting and running costs of refrigeration/heat exchanger plant may be overall economical?
producing products instead of waste,
... I have no idea of costs involved, markets, regulations etc.

[Edited on 24-4-2022 by Sulaiman]

SWIM - 23-4-2022 at 22:08

Rainwater,

I don't think using home-made membranes is on the table either.

However I am impressed that you can come up with cost-benefit analyses from the information presented.

You got a nice big crystal ball back home to help out with that?

The impression you got is that this reaction will be run again.
If you read and understood the posts you shouldn't have to rely on any impressions.

You're also getting pretty didactic for a "not an expert"
I've found this to be a common reaction from posters when they realize they're in over their head and soiling their union suits. :P

Tsjerk - 24-4-2022 at 01:45

Quote: Originally posted by Deathunter88  


Remember that's assuming perfect homgeneity and perfect mixing, which is very different from reality. If you want to prove this to yourself, fill a large graduated cylinder with water and dump in a couple hundred grams of NaOH. What you'll get is a geyser of boiling hot caustic solution spewing out. And that's just from the heat of solvation.

[Edited on 22-4-2022 by Deathunter88]


Yes, although I wasn't really suggesting to use solid NaOH, here you would only need relatively little NaOH, as the sulfuric acid is only 5% (w/w?). With 2 molar eq. NaOH dissolved that would only raise the temperature by about 15 degrees, not taking any water in account that was used to dissolve the NaOH. Without dissolving it first you would raise the temperature by about 30 degrees.

But 10% NaOH mixed in with a mixing valve, with a continuous pH probe down the line sounds reasonable to me. That way the mixing is practically homogeneous and you would have a realtime view on how the mixing is going.

Rainwater - 24-4-2022 at 05:34

The more research I read, the more I think distillation is the completely wrong approach,
Here is a paper explaining the use of co2 to produce ethylene glycol,

But, as for a running process, it seems to be much more efficient than anything else I've suggested, as well as working at temperatures less than 80c.
It appairs the running cost would consist of maintaining the operating temp, and the production of co2 for the reaction.

Tho the OP request a method to neturalize the scrubbing solution for proper disposal, this method, if it works, will achieve the same end effect, with minimal alterations to the existing apparatus

Attachment: EP0776890A2.pdf (261kB)
This file has been downloaded 309 times

Tsjerk - 24-4-2022 at 13:06

@Rainwater: that process would require a new gas feed, CO2, and a catalyst. That would be a complete new process which would have to be set up, optimized and what not. While OP states that he doesn't even have access to a neutralization container; a mixing valve is what could be done.

Rainwater - 24-4-2022 at 14:22

Just throwing out ideas that will not cause the problem of acidity
Loving the research im finding.
Mr Gears. What is the rate of EO entering the scrubber?
Is it a closed loop system or open to the atmosphere?

Broken Gears - 25-4-2022 at 04:04

Quote: Originally posted by WGTR  

Anyway, is the tank pumped out, or is it emptied via gravity flow?

The scrubber consist of 14 cells. Each cell have to be pump. Which also means that it would not be a continuous flow of all 9000 L through a inline neutralizer.

Quote: Originally posted by Rainwater  

Mr Gears. What is the rate of EO entering the scrubber?
Is it a closed loop system or open to the atmosphere?


5,58 kg of EO is added to a 12 m3 vacuum chamber, which is at that time at 120 mbar and of relative humidity of 60%. It's topped of with nitrogen to 930 mbar. That's somewhere about 400mg/L EO.
After dwell time, the 12 m3 mix of EO, N2 and water vapor is emptied over an a period of 60 min.


Alternatively the the whole waste disposal could be eliminated by burning off the EO, but the Sterigenics incident put an end to that discussion, despite the fact that it was human error.
https://www.youtube.com/watch?v=_2UnKLm2Eag

Tsjerk - 25-4-2022 at 08:10

Quote: Originally posted by Broken Gears  

Alternatively the the whole waste disposal could be eliminated by burning off the EO, but the Sterigenics incident put an end to that discussion, despite the fact that it was human error.
https://www.youtube.com/watch?v=_2UnKLm2Eag


Well... That surely was not just an human error, because it shouldn't be possible to blow up a building with a single password.

Rainwater - 25-4-2022 at 21:03

Thinking out loud again.

When neturalizeing the solution within the reactor, percipitates can be a problem.
Solubility tables will be less accurate due to the 30% EG solution.

The temperature of the neturalizeing is another issue.
The byproducts and side reactions will be another issue.

Inline mixing valves and manifolds only work with fluidsliquids/gases, increasing the total volume/pressure. So, head space within the apparatus would be required.

Solid neturalizeing agents would create a long list of problems, stearing away from those for now.

This is a gas scrubber. So, adding gas would be rather simple. But, pressure and time become an issue.
Time for the reaction to proceed and the extra pressure from the gas to drop as it is absorbed and reacted.

Ammonia comes to mind as it acts as a base when it encounters water, but ammonia sulfate is insoluble in alcohol. So, with a 30% mass of glycol, percipitate may cause an issue requiring a rinse cycle of the reactor.

I'm not sure what other gases are alkaline or if ammonia would be a compatible choice because of reactions with other products in the mix.
A complete list of all known compounds in the scrubbing solution would aid in perducting side reactions

unionised - 25-4-2022 at 23:20

Quote: Originally posted by Tsjerk  
Quote: Originally posted by Broken Gears  

Alternatively the the whole waste disposal could be eliminated by burning off the EO, but the Sterigenics incident put an end to that discussion, despite the fact that it was human error.
https://www.youtube.com/watch?v=_2UnKLm2Eag


Well... That surely was not just an human error, because it shouldn't be possible to blow up a building with a single password.

The error was made by the human who designed the system.