Dissolving Caustic Flakes

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Dear Lyn

With all due respect, I have already done searching on internet and couldn't find sufficient info (very generic). That's why I post here.

The heat added is 44.4 kJ/mol.

So, it will depend on many unknown factors, that you will need to consider.

Ask your supplier to help you.

I am not aware of a specific guide, but I imagine one does exist, likely with the supplier of flakes.

Ring them up and ask.

GA- actually excellent, but I would be careful about #1.

I recommend lukewarm water, especially if you are aiming for 50%. The reason is that especially if the flakes are large and clumped, and if your agitation is not sufficient they may not dissolve fast and you could wind up with an excess sitting on the bottom of the tank- leading to a runaway localized reaction as it warms up. The increase in density due to concentration can offset the temperature rise more than you may think. Agitation, cooling and controlled addition are your best friends here!!

The classic method using drums of solid NaOH is to knock the ends off & submerge them just under the water surface in a cast iron basket for this very reason- as it dissolves, the density gradient induces a downward circulation of the warmer, denser solution that evenly mixes the tank.

I used to use it in the tumbling dept at a ball bearing factory. We just used to chuck a scoopful into the tumblers with cold water and let em roll.

Old Salt is right...it's harsh stuff.

For your application, I would see how fast I could add the flakes to a smaller amount of water...like a quart. Measure the amount of flakes added, time, water temperature, etc., and then multiply everything out to the capacity of your dissolving tank. You can agitate it with a spoon...wear gloves.

That way, you will know the exact numbers for your application, and be able to do it as quickly and safely as possible.

Dear All

Thanks for your valuable advice.

Old Salt, I've already seen most of the links that you posted. The main question mark is the extent of cooling required (I had envisaged extensive cooling coils for the tank) and rate of addition of the flakes. Better to be safe than sorry I guess.

lyn & piquek-

Taking what lyn has stated a little further, why dilute it yourself? There are so many variables with questionable figures your attempts to solve them could be dangerous to you and your employees. As I stated previously, the root cause most caustic accidents are operator failure types.

There chemical suppliers of custom tolling processors who will make the concentration you want. Costs more for the material but overall when labor, equipment and safety costs are considered it is much cheaper.

War Story--It worked for me and was cheaper. Our bulk storage of 50% caustic equipment needed replaced in one area of our plant. Casually mentioned it to one chemical supplier over lunch. He came back saying they would like to do it. By a month later all equipment was removed from this area and the 27% that we needed was in the warehouse. Cost savings all around. No questionable calculations, no new equipment, lower labor costs, increased efficiency, higher standards for the finished caustic, cheaper overall costs and especially safer for the operating personnel.

Purchasing premixed caustic could be your optimum solution to calculations and costs.

Good Luck, Old Salt

pjquek-

Have you considered using liquid caustic instead of the flakes/beads/solid that you yourself have to dilute and liquefy? It certainly would help to make the process easier for you therefore less costly for equipment and labor costs. Most of the caustic manufactured is 50% with water so the pricing shouldn't be much higher, especially per mole. With the liquid, available in 50% or 73%, it is easier to store in bulk tanks or drums where any open container of the solids have to be kept tightly closed because the solids are highly hydroscopic. Once it gets a little water in it from the air vapors it is much harder to handle because it clumps together into chunks whose size depends on the water content.

Dilution of the 50% material would only require putting the water in an agitated and cooled tank and pumping the caustic liquid into the tank at an appropriate rate. As the solution nears the desired concentration use a hydrometer to check the concentration. Adjust it with either more caustic or water and make your final qualitative and any final necessary adjustments if necessary.

The following is general information presented for anyone's benefit when developing your good answers. It is general information for your benefit and the benefit of the OP. No statements are implied or are to be inferred about this contributor or anyone using this information.

The type of particle makes a big difference in dissolving rate of the solid caustic forms. Large "chunks" are the slowest with next being flakes and beads about 1/3 the time of the flake. The smaller the particle the faster it dissolves because there is more surface area per mole of caustic.

When doing a bench test of the dilution process it is important to rake several things into consideration. With a cooling jacket and/or internal coils you must consider that the cooling provided in the same configuration but different size, the available cooling is less in the larger unit. It is exponentially different since: volume = pi*r²*height. As the radius doubles the volume increases by a factor of the radius squared. This should be taken into considering when considering the cooling when doing any up scaling to production processing.

The method and containers of delivery should also be considered for this processing situation. Beads or Compounders Beads have the roundest particles so they can be transferred by pneumatic piping systems. Flake particles break easily so they tend to break, form powders and clog equipment. They are also the type that most frequently goes to the bottom and forms the concentration stratification that has an explosive possibility. Liquid requires liquid transferring equipment. Materials of construction for liquids are at least black steel piping for short term use. Stainless Steel is normally used but still is not the best for caustic use although price considerations make it the most frequently used. Other more expensive metals are the most resistant.

As for standards I know of no frequently referred to standards for compounding. Most of the regulations concern the transportation and transportation containers for this product.

Good Luck, Old Salt

I hear that Gran Patron tequila does a pretty good job....

Careful! Too much and you become invisible.

Dear Old Salt

My first thought was also why dissolve caustic flake, knowing the hazards involved. Most plants nowadays just call bulk tankers. Unfortunately this is not my decision to have dissolving tanks. Either it was due to logistics concerns (plant located at remote area) or old mindsets that do not change with time.... Will see if I can do some persuasion about this matter.

Thanks!

piquek-

I'm confident your persuasive talents will overcome the obvious unfounded bias against the liquids.

Good Luck, Old Salt

Quantities? Bulk caustic soda can be delivered as a 50% solution without having to muck about with dissolving flakes. A tanker-to-storage tank solution, properly engineered-up, may be the safer technical solution.