So, the bane of my life right now is water.  You see, the planetary atmosphere that presses down upon us is dilute, wet, oxygen. Given that the planet is generally damp, providing a customer with an anhydrous product requires some care.  For solids, it resolves to the removal of lattice water and/or coordinated water originating from the process and then keeping the dried material from humidity.

Lattice water is the easiest to remove. Azeotropic methods or good old-fashioned vacuum goes a long way to remove this troublesome aqua. Coordinated water is a different issue, however.

Inorganic materials form aqua complexes that are often quite stable. Removal of this ligand opens a coordination site which begs to be refilled with a donor.  Removal of coordinated water may change the stuctural nature of the material and affect its application. Rare earth materials, for instance, often have coordination numbers of 7 to 9, so there are lots of extra coordination sites for water to park. OK, so what?

As a chemical merchant, one has to decide on the specifications of a product either in response to a query or as part of a collection. In the matter of dehydration, the issue that is front and center is how far to go with that dehydration.  How much water can you keep and still have a saleable product? It is quite possible to work way too hard to provide product purity that no one asked for.  Excess quality, call it.

Excess quality is excess expense. This seems contrary to the prevailing work ethic taught by our parents. But, for a given application, there will be a threshold material purity above which further purification affords little or no increase in benefit. Resources spent to obtain or use this excess quality is a type of loss.

Generally speaking, a chemical company will offer what it can make with reasonable effort to meet the needs of the market. If a customer comes along who wants a higher grade, then the manufacturer has to communicate with the customer to determine if the higher grade is really necessary and if so, make a decision as to the merits of kicking up the grade a bit. 

Many times a customer will develop a process based upon material obtained from Aldrich, Strem, Alfa Aesar, etc. These catalog houses provide R&D materials and are often quite pure.  Part of the reason for the purity is that many of the compounds are prepared in 5 or 12 liter flasks and are subject to benchtop processing that is difficult to duplicate in large metal reactors. In particular, tight fractional distillations or the handling of intractable solids, emulsions, or oils, is easier on the benchtop than in a plant. So, sub-kilogram quantities can be easier to prepare in a purer state, generally. Obviously, well engineered bulk manufacturing produces high quality goods as well. But remember, a large fraction of what you see in a catalog has not been scaled up.

It is often a shock for a customer to find that a material will have a different or exaggerated contaminant profile at scale because of their work with commercial R&D materials.  If you need to obtain a material at scale, it is best to work with a manufacturer as early as possible in the commercialization timeline to qualify samples of the needed compound. The assumption that process development with Aldrich samples is good enough could be a trap.  In reality, a user will have to consider to what extent they can live with residual process solvents, suspended solids, water, color, and side products.  Higher purity generally means lower manufactured yields and as a result, fewer kgs of product to dilute the costs. Somewhere the needs curve crosses the wants curve and you’re in business.