Summary for naoh resistant tanks Discussion
Chemical resistant tanks for NaOH sol. up to 90% are discussed mainly in terms of temperature limits rather than alkali strength. Amir Koorosh Zarrabi asked whether PVC, PE, or PP tanks/linings that handle about 30% caustic at room temperature would also survive 80% solution at 90°C. Freeman replied that PE is out because of temperature limits, and that PVC and PP by themselves are also out; however, he said professionally bonded FRP over PVC could work to about 80°C and FRP over PP to about 90°C, provided the bonding technique is done correctly and PP uses cloth- or glass-backed sheet. He also noted that PVDF:FRP or FEP:FRP could handle even higher temperatures, but at much higher cost, and added that mild steel might possibly work at the stated concentration and temperature. A later question asks about vinyl versus bisphenol resin for a lime scrubber at elevated temperatures, but no answer is shown in the excerpt.
Q. Dear Sir /Madam,
I know that PVC, PE and PP tanks and linings withstand NaOH sol. up to about 30 % at room temp. But will they do the same for higher concentrations (e.g. 80 % ) and temperature ( 90 Deg. Cent. ). Please advise in details.
Thank you in advance.
Amir Koorosh Zarrabi
– Isfahan, Isfahan, Iran
A. Hi Amir!
You have a problem temperature-wise not, I think, with the alkali concentrations.
Pe is out. Max. continuous temp. is l60 degr. Fahrenheit for Engel process rotationally moulded tanks and LESS for fabricated tankage.
(some say l50, others l70, I chose the middle)
PVC (i.e., unplasticized PVC, tpe 1, grade 1) and PP by themselves are totally out. HOWEVER, If one ‘professionally’ bonded fibreglass (frp) to them, then PVC would be OK to 80 Centigrade and PP to 90 °C.
…if you had lots of $$$ and went to PVDF:FRP or FEP:FRP, then you can hit l40 or 200 °C
The key to success with dual laminates (I used to call them armoured thermoplastics) is the bonding technique. And for PP it is necessary to use sheet having a cloth or glass backing. It is totally useless to have the best FRP fabricator in the world to fibreglass thermoplastics if he is not familiar with this technique … (I recall a chemical Company asking ‘us’ to make two identical PVC tanks, one of which went to a very competent frp fabricator. Both had to be frp reinforced. His failed!)
Lastly, Amir, due to the relatively highish concentration & temperatures, I have a gut feeling that good old ordinary mild steel might well work.
Freeman Newton [deceased]
R.I.P. old friend (It is our sad duty to
advise that Freeman passed away 4/21/12)
Dear Freeman,
Thank you for your detailed response.
BEST WISHES,
Amir Koorosh Zarrabi
– Isfahan, IRAN
Q. RESPECTED SIR,
I want to know which type of resin is suitable for the lime scrubber (FRP) at elevated temperatures. Is vinyl resin or bisphenol suitable?
SOUMYA SARANGAN
CASE STUDY – Kollam, Kerala, India
April 20, 2013