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Should I dilute sulfonic acid before neutralizing it with Sodium hydroxide ?
If I add concentrated linear alkyl benzene sulfonic acid (thick, dark brown liquid) to a Sodium hydroxide solution
it takes days to react.
It forms an insoluble white powder that doesn’t seem to dissolve, or takes several days to do so.Then I tried dissolving sulfonic acid in 3X it’s volume of water (it remains a bit thick, it doesn’t become really water thin after diluting), then add it to Sodium hydroxide
it reacts and becomes a light yellow liquid in about 1 day.How much to dilute the sulfonic acid?
Should I add the dilute sulfonic acid to the Sodium hydroxide solution, or viceversa for large scale convenience and reduced tank time?
Readymade Sodium sulfonate is unavailable here, BTW.
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86 Replies
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@Gunther for dissolving Sulfonic acid it will be easier to add NaCl but few quantity cause much of Nacl will make your final product with low viscosity, and i see that for 1:3 dilution the concentration of Sulfonic acid is too high so it is normal to have very thcik product .
The neutralization with NaOh i prefer to diluate NaOh in water then i will add it to sulfonic acid that for me make operation easier.
good luck friend. -
@Fekher did you get the dreaded white powder precipitate when adding concentrated sulfonic acid without diluting it first?
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@Gunther i never get white powder
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I wonder what the white powder is
it ain’t supposed to be thereLinear Sulfonic acid shouldn’t precipitate out of solution (and ain’t a white powder AFAIK)
Sodium sulfonate. While the powder can be white, it should be soluble, and make a pale yellow solution.
The only thing I can think of, is that Sodium hydroxide has some Sodium carbonate in it, but it still should react to make Sodium sulfonate,
and no CO2 like bubbles are seen either.At first I thought sulfonic acid was reverting EDTA Na-4 to EDTA free acid, but then I just reacted water + NaOH with sulfonic acid (nothing else added), and the white precipitate remains
The mistery remains.
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Gunther what exactly are your trying to do here??? Making the neutralized salt or doing a finished product. I can share my dish wash liquid experience where I am doing the neutralization in-situ and adjust the final pH as per the benchmark. I never had any precipitation in such dishwash liquids and I don’t use any hydrotropes as well.
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The white powder is most likely salt. It
shouldn’t happen at all.Wait, are you mixing pure LAS with pure NaOH?.
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@Chemist77 @DAS I’m trying to make Sodium dodecylbenzene sulfonate out of Linear alkylbenzene sulfonic and Sodium hydroxide (in water solution).
Then will use the Sodium sulfonate for several products, like dishwash and laundry detergent liquid.distilled or deminaralized water 50% vol
Sodium hydroxide flakes 1.31% or 2.31% wt
I wait for the NaOH flakes to fully dissolve, before adding the sulfonic acid. IDK if this makes any difference.
Linear alkylbenzene sulfonic acid 10% vol
Then I get the dreaded white powderThe above formula doesn’t add up to 100% as some ingredients will be added later, but I can’t get past the neutralization stage unless I predilute sulfonic acid:
Phase A
water 10% vol
NaOH 1.31% wt (or 2.31% if additional acids like citric acid (to get Sodium citrate builder), or oleic acid (for laundry detergent suds control) will be added later)Phase B
water 40% vol
Linear alkylbenzene sulfonic acid 10% vol
even the sulfonic acid takes a couple days to fully dissolve (it forms a brown gunk) and you can’t stir it much as bubbles appear.Finally add phase B to A
I prefer to handle the sulfonic acid larger volume solution, instead of NaOH smaller volume but more dangerous to handle. -
I never had to dissolve it, just add it and stir. What kind of agitation are you using?.
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@Gunther I generally use 96% LABSA and never had any kind of precipate falling out. In fact it goes into water easily and then I would adjust the pH at the end of the process. Of course I do have other surfactants in between. If you want I can pm you the formulation we use and which sells pretty much good in my region. But again I would say that there is something wrong with your LABSA I suppose. Can you arrange a fresh small sample from your supplier and do a lab trial. The starting process is same as you have mentioned in your post.
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Update:
Prediluting LABSA still made a milky white solution, albeit now it seems fully dissolved, unlike the previous white powder precipitate.
Phase A
distilled or demineralized water 10 % vol
NaOH 2.31% wtPhase B
water 40% vol
LABSA 10% volAllow for each phase to be fully dissolved
Then pour phase B to A.Maybe LABSA decomposes when touching large amounts of concentrated Sodium hydroxide?
Next time I’ll try slowly pouring phase A to B, pouring it real slow, while allowing ample time for it to react, and get fully dissolved.
Sometimes I got the white powder precipitate, sometimes it didn’t and worked perfectly with the same batch,
but my experimentation notes only mention ‘Phase A+B’ and I don’t quite remember how the phases were added together. -
Pour slowly and mix it.
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Gunther did you check the pH when the solution is milky. IDK but maybe you need more alkali there for complete neutralization. There is no fixed ratio for such neutralizations and this is what I have learnt in lab. Everytime such reactions need a final pH adjustments.
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@Gunther is not too much 2,31% NaOh for 10% Labsa ? Ratio depend on Labsa purity or degree but it seems whatever the degree of Labsa it is more then needed quantity of NaOh.
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Update:
This time I prediluted LABSA (makes a thick, pale brown liquid)
Then poured NaOH little by little, like 1/10th of the total NaOH amount at a time.At first, LABSA form a white swirl, which seems to dissapear after stirring.
But in the last NaOH additions, it formed the dreaded milky white solution
so it seems that excess NaOH degrades LABSA.I found some literature that says that sulfonic acids may react with excess NaOH may create Sodium phenoxide, but high temperature was supposed to be required.
http://staff.um.edu.mt/ratk1/BenzeneSulphonicAcids.htm
https://chemistry.tutorvista.com/organic-chemistry/benzenesulfonic-acid.html@Fekher
The 2.31% NaOH was used because it will neutralize some other acids in the formula too (citric and oleic acids)
Next time I’ll add LABSA the last thing, as to avoid excess NaOH. -
@Gunther actually i think that who have lower moleculaire mass should be added the last here meant soda and my explication that litel access of it in addition it is high base will give more exess mole cause (n= masse / moleculaire masse ) so the lower moleculaire mass the more access of moles”n” so as conclusion exess of LABSA will be more tolareted then excess of Soda.
One more other reasons to make soda as final add, you will neutralize many acids so it will be easier to add them all then neutralize them by soda.
For heating dissolving soda is very exothermic so that dissolving will abe to heat you blend. -
Gunther even if the pH shoots up, the back acid neutralisation brings it back under control. Honestly you need to switch the supplier here. The LABSA you are using is probably a batch full of problematic impurities.
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I have never had any problem with precipitation when neutralising LABSA with NaOH when making detergents and dishwashing liquids. However it can look milky if you have not got the ratio correct.We add the NaOH to the water and then add in the LABSA. -
Update: adding citric acid to lower pH to 6, it didn’t redissolve the milky white precipitate.
@Chemist77 will do. I definitely need to switch suppliers to see if it gets better.
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Try using LABSA to adjust the pH down if it is too high.
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Completely agree with @ozgirl, I mean its always manageable with either LABSA neutralzation or alkali. Generally pH drop brings in milky appearance in my dish wash and alkali troubleshoots it.
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It’s not a good idea to throw in a mixture of acids and let them fight. If you want to add a buffer, make the citrate separately and add it later. The same goes for the rest. Try neutralizing the LABSA fist and then add the rest one by one. If you do have a problem with LABSA+NaOH then you do have a problem with the material like @Chemist77 said.
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Update:
I bought LABSA from another supplier
the liquid is a bit thinner and goes into solution slightly faster (still takes hours or evernight), but the cloudiness problems remain.I’m conducting tests, changing all the variables and taking detailed notes.
@Fekher what % of salt would you use to speed up LABSA dissolution?
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@Gunther it depends on the concentration of your actives , from my experiences when LABSA is used the optimum % of NaCl for maximum of viscosity will be between 1.5 and 2.
for the Clarity reducing % of LABSA will increase the Clarity. -
Upon diluting by half with water
most (but maybe not all) test formulations became crystal clear light yellow
so it looks like they’re too concentrated and some of it it’s precipitating out of solution.Not for nothing they advise to use Potassium hydroxide in premium, more concentrated formulations:
The potassium analogue (potassium carbonate, potassium silicate and potassium hydroxide) is used for the liquid detergents due to their higher solubility.
http://surfactantschemistry.blogspot.com/2013/07/laundry-detergents-formulation.htmlHow It WorksFor the surfactant part of the formula we need a well-rounded and balanced combination that can clean various kinds of soils. I suggest we use a combination of linear alkyl benzene sulfonate (Pilot’s LAS-99 neutralized with potassium hydroxide)…Let us go to the lab and prepare a sample of the premium 3X liquid laundry detergent. First add deionized water (29.15%), followed by potassium hydroxide 45% solution (6.1%)
https://www.happi.com/contents/view_features/2012-04-02/formulating-liquid-laundry-detergents -
I think the precipitate you are having is the neutralized salt, SDBS, which is usually used in detergent powders.
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