[Hoffman_711]

We are in discussion with a customer and they do not want to use a Di or RO system for the water treatment. My question , since I am not a Chemical Engineer, which one would remove the mineral to prevent precipitation of the hard water mixture with water?

[Arkcon]

Its a little hard to follow your application.  Let's try, however:

We are in discussion with a customer and they do not want to use a Di or RO system for the water treatment.

No distillation or reverse osmosis.  OK.  Then ion exchange columns only, correct?  They are quote common in industry.

My question , since I am not a Chemical Engineer, which one would remove the mineral

Both.  I mean, all three, but you don't want the first two.  Or, what?

to prevent precipitation of the hard water

How hard and what kind.  I mean to say, how much minerals are dissolved, and which ions in particular.  As an example,

Temporary hardness is caused by dissolved calcium hydrogen carbonate (which is removed by boiling). Permanent hardness is caused by dissolved calcium sulfate (which is not removed by boiling).

ref: http://www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_gateway/chemistry_out_there/hardness_of_water/revision/1/  Depending on your particular situation, answers and results will vary.

mixture with water?

Annnd this bit makes no sense.  Precipitation of hard water with more water?  That's also hard, or maybe it isn't?  That shouldn't happen at all.

[silverz89]

if by "Di" you mean deionization, then i think your best option is going to be some thermodynamic treatment such as distillation/condensation or MVC. I could understand their desire to avoid RO and Deionization, as they will potentially separate out the methanol from the mixture (which based off your OP it seems they would like to keep in the mixture). However it is important to note that due to vapor pressure differences between H2O and MeOH you are going to likely end up with a higher concentration of methanol in the resultant product if you distill it. Which I'm not sure based off your OP is acceptable or not. Please provide some more information and possible solutions you have been working on with your team and we can try to help you more.