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.


  • FekherFekher Member, Professional Chemist
    @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?
  • FekherFekher Member, Professional Chemist
    @Gunther i never get white powder
  • I wonder what the white powder is
    it ain't supposed to be there

    Linear 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.
  • Chemist77Chemist77 Member, PCF student
    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. 
  • The white powder is most likely salt. It 
    shouldn't happen at all. 

    Wait, are you mixing pure LAS with pure NaOH?. 
  • @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 powder

    The 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?.
  • Chemist77Chemist77 Member, PCF student
    @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.
  • 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% wt

    Phase B
    water 40% vol
    LABSA 10% vol

    Allow 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.
  • Chemist77Chemist77 Member, PCF student
    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. 
  • FekherFekher Member, Professional Chemist
    edited September 2018
    @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.
  • 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.

    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.

  • FekherFekher Member, Professional Chemist
    edited September 2018
    @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.
  • Chemist77Chemist77 Member, PCF student
    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. 
  • ozgirlozgirl Member, PCF student
    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.
  • ozgirlozgirl Member, PCF student
    Try using LABSA to adjust the pH down if it is too high.
  • Chemist77Chemist77 Member, PCF student
    edited September 2018
    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. 
  • 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.
  • 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?
  • FekherFekher Member, Professional Chemist
    @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.

    How It Works
    For 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%)
  • I think the precipitate you are having is the neutralized salt, SDBS, which is usually used in detergent powders.
  • GuntherGunther Member
    edited November 2018
    I just got some Potassium hydroxide to see if it's better than NaOH in case the cloudiness is from excess sulfonate concentration, as some of my cloudy formulations became clear yellow when diluting them.

    Pretty much the problem remains.

    So either LABSA must be added to NaOH or KOH real slow, over several hours.
    Adding LABSA slowly over several minutes doesn't seem to work as LABSA is a thick liquid that just sits on the bottom, slow to dissolve.

    or LABSA must be diluted in some water first (it remains a thick liquid after dilution) and then slowly add the hydroxide.

    BTW I tried switching LABSA suppliers (one LABSA is a bit darker than the other) and the problem remains.
  • What else is in your formula?.
  • DAS said:
    What else is in your formula?.
    While the formula contains SLES, EDTA, preservative,

    Only water Sodium/Potassium hydroxide and LABSA have been added at this point.

    I'll try 
    Phase A

    Phase B
    allow to hydrate and dilute overnight

    Then slowly pour Phase B into A, real slow.

    If it doesn't work, I'll try neutralizing LABSA with baking soda, to see if the highly alkaline NaOH/KOH is decomposing LABSA.
  • ozgirlozgirl Member, PCF student
    Don't try baking soda unless you want to see a volcano.

    Try neutralising with Triethanolamine (TEA) or a mix of TEA and NaOH as the neutralising agents (add NaOH to water first, then LABSA and then add TEA).

    It seems that your problem is the solubility of the neutralised LABSA. I think the TEA salt is more soluble than the sodium salt (not sure how it compares to the KOH).

    At 10% LABSA you are probably over the solubility limit of the sodium salt. Hence why when you dilute your solutions become clear.  

    Also are you stirring during neutralisation?
  • Chemist77Chemist77 Member, PCF student
    I am still dumbfounded about this problem, I would generally take the batch water. Throw in the sodium hydroxide, let it mix and slowly pour in the LABSA 96%. And there is absolutely no problems at all, why today only I made a 5 MT batch of dish wash liquid with the same procedure. Hopefully @ozgirl’s suggestions can do the trick for uou. 
  • @Chemist77 interesting that you start with naoh and not with the sulphonic. How do you then neutralise before adding the surfactants?
  • Chemist77Chemist77 Member, PCF student
    I just check the clarity and the final adjustment of pH at the end of process. 
  • Chemist77 said:
    I am still dumbfounded about this problem, I would generally take the batch water. Throw in the sodium hydroxide, let it mix and slowly pour in the LABSA 96%. And there is absolutely no problems at all, why today only I made a 5 MT batch of dish wash liquid with the same procedure. Hopefully @ozgirl’s suggestions can do the trick for uou. 
    Did you get some white streaks immediately after LABSA is poured into NaOH, even if they then disappear?

  • aaaaaa There is no problem with your material..... It happened to me as well with the same material I uses, what I think what happened was I didnt gave time to each liquid to dissolve completely and poured whole of it at once. It is better for your to divide the water that you are going to use in the process in to two and dilute the sulfuic in the water and then pour slowly the NAOH to neutralize it. don't mix it with other materials until it cools down, that's my experience 
  • white streaks are the fumes that formed due to reaction of two materials.... 
  • Chemist77Chemist77 Member, PCF student
    No Gunther there is no streaking. Its straight clear solution, I suppose my LABSA is absolutely a high grade product. That is the only explanation I can think of. 
  • I wonder if 15% LABSA is too much

    This 3X concentrated liquid laundry detergent advises to use
    'First add deionized water (29.15%), followed by potassium hydroxide 45% solution (6.1%) in an appropriate beaker. Start mixing and slowly add Calsoft LAS-99 (10%) ...'

    Pilot Chemical' Calsoft LAS-99 seems to be 97%+ pure LABSA (DDBSA = LABSA as far as I know)

    OTOH this premium dishwash formulation advises 9.60% or 19.20% DDBSA
    The chart is too small to read but the transcript can be read here

    And that using Sodium hydroxide, it doesn't mention that Potassium hydroxide is really needed (Potassium salts are usually more soluble than Sodium ones).
  • Gunther said:
    I wonder if 15% LABSA is too much

    15% isnt too much, i have used 18% labsa with naoh alone to get a viscosity similar to a famous brand in my country, and worked exccelent, it was clear and light yellow.

    Today im ussing arround 8%, ussing sles / betaine to build viscosity.

    I have found that mixing and avoiding the mixture to heat helps to get a lighter color and clearness


  • Hello I am new here and I would like to ask you about neutralising ABS Acid with NaOH. I've hot 30% ABS Acid which is yelowish, and I add drop by drop 30% NaOH. My problem is to get pH approximatelly 8. I've got at the begining pH 2 and after adding NaOH it is changing to 12 and IT is difficult to me to get pH 8. Do you know what I am doing wrong? 
  • BelassiBelassi Member, PCF student
    1. Do the stoichiometry.
    2. Add 90% of the calculated amount.
    3. Check the pH.
    4. Titrate to get the pH correct.
    5. Record the figures and use that for future batches.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • Chemist77Chemist77 Member, PCF student
    Dilute the alkali further and try again the titration as @Belassi mentioned 
  • BelassiBelassi Member, PCF student
    In late Feb last year someone noted: Here in Egypt most of us use the 2nd kind of ABS that 1 kg neutralize with NaOH 180 gram
    So 100g of ABS would need 18g of NaOH.
    May I ask how you are measuring pH?
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • Thank you @Belassi and @Chemist77, I will dilute NaOH to be more precisely.
    @Belassi I am using electronical pH meter with electrode.
    Could you tell me what pH do You obtain? And what temperature are you geting through whole process?
  • BelassiBelassi Member, PCF student
    I'm just a chemist, I don't get involved with household products.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • @Belassi ok:-) perhaps @Chemist77 could help:-)
  • I've got another question. I made neutralisation and after night I get product with pH 8. But my sample delaminate...On the top my pH is 8, and on the bottom pH is 12. Should I change the quantity of NaOH...?
  • Chemist77Chemist77 Member, PCF student
    Try mixing it, check the pH and adjust again. It should be crystal clear, no other way. Or your ABS is just not a good one here.
  • @Chemist thanks, do you think that the Sodium Lauryl Benzene sulfonate (LABSA Sodium Salt) is on the bottom or on the top of this beaker?

  • Chemist77Chemist77 Member, PCF student
    Can't say tbh, you need to do it again and see what's the problem. It's a wild pH with LABSA neutralization, go pretty slow. 
  • @Chemist I will mix it. Could you tell me did you mix 96% LABSA with diluted NaOH (eg. 30 %)?
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