6 replies to this topic

[curious_cat]

Is anyone buying bulk Caustic in 30% (w/w) grades? I know that the typical grade is 50% and that's what we have been buying. But it's a hassle to then dilute  / cool it down to 30% which is what we really need for our process. 

 

Reading about the ChlorAlkali route reveals that the manufacturing process itself produces 12% or 30% caustic depending on what type of electrolytic cell they use? Am I right here? 

 

If so the subsequent concentration by the seller to 50% and then re-dilution  at our end back to 30% seems a waste.

 

I spoke to our regular supplier and he doesn't offer bulk shipments as 30% grade.  Was wondering if others know anything more about this?  Good idea or destined to fail? Our consumption is not huge so I doubt the manufacturer  will jump through hoops for us but if it's done already by others we might have options. 

 

I do realize that my shipping  costs will go up but the savings in dilution equipment / storage and cooling utility might compensate. The lower freezing point of the 30% solution is also a plus.

 

Any comments? 

 

[breizh]

_{Curious cat ,}

_{In China I was using 30% solution , it may depend about your location and risk for freezing  . In Thailand we are using 50% .}

_{Safety is key with this kind of chemicals.}

_{Hope this helps}

_Breizh

[curious_cat]

_{Curious cat ,}

_{In China I was using 30% solution , it may depend about your location and risk for freezing  . In Thailand we are using 50% .}

_{Safety is key with this kind of chemicals.}

_{Hope this helps}

_Breizh

 

Thanks @breizh

 

I had the Dow Handbook but that mostly mentions the 50% grade alone. Glad to know someone was selling you the 30% grade at least in China. So my plan may not be entirely unfeasible. 

 

This plant I'm designing for is in a sub-tropical zone with a yearly low of ~0 C. The relative delivered cost of 30% versus 50% will be the key factor for us. The plant is located ~300 miles from the Caustic manufacturer. 

[Mole Chaser]

The process group I'm in fairly routinely designs chloralkali plants using different electrolytic cell manufacturers. The caustic produced is typically in the 30% to 33% range. The reason it is mostly shipped as 50% is so the customer isn't paying for shipping as much water, and there are fewer railcars required for a given amount of shipment.

 

If you have a use for the Chlorine produced you could potentially benefit from putting in your own captive chloralkali unit. We typically combine the CA unit with a bleach plant, and sometimes also have a caustic evaporator and an HCL synthesis unit if there is a need for the acid also.

[curious_cat]

The process group I'm in fairly routinely designs chloralkali plants using different electrolytic cell manufacturers. The caustic produced is typically in the 30% to 33% range. The reason it is mostly shipped as 50% is so the customer isn't paying for shipping as much water, and there are fewer railcars required for a given amount of shipment.

 

If you have a use for the Chlorine produced you could potentially benefit from putting in your own captive chloralkali unit. We typically combine the CA unit with a bleach plant, and sometimes also have a caustic evaporator and an HCL synthesis unit if there is a need for the acid also.

 

Thanks @MoleChaser:

 

That's a very interesting idea. I had no clue a captive Chloralkali unit was an option. What's the smallest reasonable unit size you guys design? Our scale isn't huge.

 

Right now we don't have any use for the Chlorine but if an HCl synthesis unit is an option that's viable because we indeed do have a process feed stream that's HCl. 

 

On a longer term though a Chloralkali unit might be a perfect fit for us because: One of our reactions uses H2O2 + HCl currently for a halohydration but the same step is indeed possible via direct chlorination as well. And a different reaction step uses the 30%NaOH. 

 

So we may be able to use the Chloralkali unit without needing the addons of Caustic Evaporators and HCl units. 

 

I'm intrigued. I'll definately follow up on this. Any tips you might offer are always welcome. What's the economics of a captive unit versus purchased from a huge Chloralkali plant? 

[Mole Chaser]

Good Morning, @Curious_Cat!

 

If you were to go to a CA unit the Hydrogen that is produced can either be vented or in some cases blended into a fuel gas stream. The other products are the Cl2 and caustic.

 

A standard "module" of electrolysis varies in capacity by the cell supplier, but we typically go down to 100 STPD of Cl2, and can go lower if needed. (Some cell suppliers go considerably lower even.) That is 100 STPD as 100% Cl2. As it comes off the cell it is typically about 84%(w) and ~4 - 4.5 psig. After condensing the excess water vapor with tower water in a heat exchanger the vapor is typically 98.5%(w) Cl2 and ~4 psig.

 

The economics vary considerably depending on location, local supplier costs for the materials, and especially electric power cost. As an electrolytic process it consumes a lot of power, which is the single largest operating cost for a unit.

 

I hope this helps. We would be glad to discuss this offline as a potential project if you like. I'm not familar with how to do make contact offline with this forum.

[curious_cat]

If you were to go to a CA unit the Hydrogen that is produced can either be vented or in some cases blended into a fuel gas stream. The other products are the Cl2 and caustic.

 

I hope this helps. We would be glad to discuss this offline as a potential project if you like. I'm not familar with how to do make contact offline with this forum.

 

Thanks! Ah! Even better, we actually have significant hydrogenation reactions on site for which we currently use a combination of merchant gas and methanol reforming. Better than venting or fuel.

 

It sure helps. I've sent you a PM (personal message) see if you get it and we can discuss more offline.