[labnetwork] DI water Question

Wed Jun 5 12:59:44 EDT 2019

I just had the annual PM done I will look at the DI mixed bed rinsing.

Rick

From: Rehn, Larry A [mailto:lrehn at tamu.edu]
Sent: Tuesday, June 04, 2019 3:39 PM
To: Morrison, Richard H., Jr <rmorrison at draper.com>; labnetwork at mtl.mit.edu
Subject: RE: DI water Question

Hello Richard,

We recently had our DI system sanitized by our service provider with a chlorine treatment.  They used a chlorine color drop test indicator to determine that the chlorine was present at all drops in our system, and then later to determine that it was rinsed to around < 1ppm.  After that I was told that the DI resin beds would continue to remove remaining chlorine as indicated by the resistivity getting back into the Mohm range.  We experienced a gradual climb in DI resistivity from about 15Mohm up.  Our service provider offered the following explanation (of why it did not immediately climb back to 18Mohm), which might be useful to answer your question about chlorine.  The numbers he mentions refers to data in the attachment.

....Usually, it means that a longer rinse should have been done on the regeneration, meaning that a very slight amount of regenerant hasn't been fully rinsed out. I've attached one for the purpose of explanation. Six Megohm is equal to 83 ppb and eight megohm is equal to 63 ppb, so we're talking about t 20 ppb difference overnight. The difference between 14 megohm and 16 megohm is only 5ppb. I honestly believe that the quality will continue to climb very slowly and reach it's highest quality in the course of a few days. I've just seen this scenario too many times over the 30 plus years I've been working with high purity water.

FYI: When we regenerate the resin in our shop, we recirculate DI water for typically 24-48 hours through the separately regenerated cation and anion beds before we achieve the quality we desire, prior to mixing it. I suspect very strongly that a batch didn't get fully rinsed. Going back to the paragraph above, it comes down to ppb levels of regenerants (HCl and NaOH) that haven't been fully removed through the resin. If you consume water throughout the day (which in essence is the same as rinsing), along with constant recirculation, I truly believe the quality will climb.

So, my interpretation is that maintaining high DI resistivity essentially guarantees that you will not have much chlorine in your water.  Therefore, there may not be a need to make a separate measurement for Cl-.

I agree that the ppm numbers you cite below seem high.  Maybe I am missing something.

Regards,
Larry A Rehn
Technical Lab Manager
AggieFab Nanofabrication Facility
Texas A&M University
979 845-3199
lrehn at tamu.edu<mailto:lrehn at tamu.edu>
[cid:image001.jpg at 01CEC37D.FAF8C9E0]

From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Morrison, Richard H., Jr
Sent: Tuesday, June 04, 2019 9:25 AM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] DI water Question

Hi,

I have a question about Chloride in DI water, the E1 water spec states 0.1ppm for Chlorides, have any of your operations monitor for this?

I had a test done and my6 redcir tank is 10ppm and the RO output is 25 these seem high to me, any data out there

Rick

Richard H. Morrison
Principal Member of the Technical Staff
Draper
555 Technology Square
Cambridge, MA
02139-3573

Work  617-258-3420
Cell  508-930-3461
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