Thermo-Cognitive Advanced Process Control (TC-APC) models, simulates and optimizes your process in real time to improve yield, conversion and throughput, and reduce energy use, with a quick payback.
Solvent recovery, DMSO and DMF
The solvent is back in the tank. How much went to residue, and how much decomposed on the way, appears in no reading.
Recovery is treated as a utility, run to a recipe, and judged by whether the tank filled up.
It is a distillation with a thermal limit, and it is decided in the last hour.
Every extra kilogram you recover is bought with heat.
The last part of the batch is where the money is. The solvent left in the residue is the most expensive part of the charge to get out, and getting it out means more duty, more time, and a hotter and more concentrated pot than anything earlier in the run.
That is also precisely when the solvent is least able to take it. DMSO and DMF both degrade thermally, and both degrade faster in the presence of the things that concentrate in a residue: water, acid, base, and whatever your reaction left behind.
So there is a point where the next kilogram recovered costs more in degradation than it is worth. Every plant is somewhere either side of it, and nothing on the panel says which side.
Engineering proposal. Begins with a data audit on one column.
The science under TC-APC
A column's result is decided in the vapor and the liquid.
Which compounds leave at the head, and when, is settled between the vapor and the liquid on every tray, not by the temperature read at the top. That's the science TC-APC is built on, and AI makes it sharper.
The curve is the same shape every time and the peak is never in the same place. It moves with the water in the charge, with what the reaction left behind, and with how long the batch has already been hot.
A fixed end-point cannot sit on a moving optimum. It can only sit safely short of the worst case.
And being wrong costs differently on each side.
Push past the optimum
Color, odor, acidity. The recovered solvent fails its specification or needs polishing it should not have needed. Somebody finds out, there is a discussion, and everyone remembers it.
Stop short of it
Good solvent leaves with the residue and goes for incineration. It appears in no alarm, no analysis and no shift log, because nobody assays the residue for the thing they are throwing away.
One failure is loud and the other is silent, so after a few years the practice settles on one side.
Weigh the residue and assay it. The answer is in your own drum.
Four reasons the end point will not stay put.
01
The charge is not the same twice
Water content and residual acidity depend on what the reaction did upstream and how the work-up went. Both move the point at which degradation takes over, and both are usually known, on a certificate nobody feeds into the recipe.
02
The damage is autocatalytic
What degradation produces accelerates further degradation. So an excursion early does not cost you an excursion. It seeds the rest of the batch, and the residue that has already been round once is worse again.
03
It is heat history, not temperature
What matters is the accumulated exposure, not the reading at any moment. A pot that has been held near the limit for two hours is in a different condition from one that touched it once, and the panel shows the same number for both.
04
Under vacuum, the reading itself moves
A small pressure drift shifts the apparent boiling point by several degrees, so the temperature you are steering by changes without the composition changing at all. The same problem as any vacuum column. Set out in full here.
This is the same problem as every other application on this site. The variable that determines the money is not measured, so the plant runs a fixed recipe with a margin built into it.
What TC-APC does about it
It works out where the peak is today, and stops there.
It estimates both ends
Purity of what is coming over, and how much solvent is still in the pot, continuously, from the instruments the column already has rather than from a new analyzer.
It carries a heat budget
Accumulated thermal exposure is tracked through the batch, so the limit that applies in the last hour reflects what the charge has already been through.
It uses the assay you already paid for
The incoming water and acidity figures position the column before the batch starts, instead of being filed while the batch runs the same recipe as the one before it.
It reads from your existing DCS, PLC or SLC and writes setpoints back to it. Nothing is replaced, and it writes setpoints only after you have watched its estimate track your own laboratory results, for as long as you want. The deployment sequence in full.
What this cannot do.
It cannot undo degradation
Solvent that has already broken down is gone, and so is whatever it catalyzed. The gain is in not making it, which means the value is in the batches ahead rather than the drums behind.
It cannot clean up the feed
If the charge arrives wet, acidic or loaded with the wrong residues, that is a work-up problem upstream. The engine will tell you what it is costing you, which is often the argument that gets it fixed.
It cannot beat the vacuum system
If the pump and condenser cannot hold pressure, the operating window is set by them. The estimate will report that accurately, and it is a mechanical answer, not a control one.
It does not replace your laboratory
Your purity, color and acidity results stay the reference. The estimate is checked against them every time they arrive, and the bias between the two is on the screen.
The mark
Find the optimum. Hold it while it moves.
The curve is a yield or selectivity response. The amber point is the optimum, and the dashed drop is where it sits on the operating axis.
The second half of the line is the part that matters. Finding an optimum is a study, and studies end up in drawers. Holding one while the feed, the fouling, the weather and the wear keep moving it is a control problem, and that is the work.
Start with the residue
Weigh one residue drum and assay it for solvent
It costs almost nothing and it answers the question before we do. If there is little solvent in it, your column is being run close to its limit and there is nothing here worth pursuing. If there is, the size of it is now a number rather than an argument.
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Or start with the note
Cut-point determination in the vacuum fractionation of odour-critical products
Written for an aroma column, and the measurement argument underneath it is the same one. Three pages. Free, no form, and we do not ask for your email address.