Much appreciated comments.
As I am looking at 97% purity at the top, and moderate volumes in the process, the responses regrading pervaporation are maybe not relevant.
The links to the biodiesel sites is an intuitive leap. Yes, it's biodiesel, but this process is for the waste methanol and chemical water from an esterification stage.
Based on VLE, Methanol seems to behave ok at these purities, so the reasoning behind picking an average volatility is well taken, and I have assigned a higher relative volatility, say 4.0 in some rough calculations for the process. I can see where at .99+ it becomes very important.
This column design has evolved to some fairly safe numbers mostly because we can choose our feed point and our feed temperature, the unit is relatively small, and it is a side-stream process at a biodiesel plant meant for recovery of waste methanol-water from an esterification stage. The diameter and stage calcs are converging with the recommendations of the packing manufacturers, a good sign.
My study of Kister's "Distillation Design" confirms my basic design, and has given me confirmation for some assumptions, and adds a good foundation for designing and operating this monster. Not a whole lot on rebolier duty, though.
I am interested in the comments of member MYRDALE who has an operating methanol still, much larger than this unit. Although scaling is a risky method, his setup does confirm that I am within the tolerances for this separation. His/Her quoting of energy duty was very useful.
I am somewhat agog of the rigor of this sort of design process and am on my knees in front of professional chemical engineering.
My recent challenge is refining the heat requirements to drive this beast. I've got some basics, but I will post a query separately.