The Vanishing Bio-Diaper

Superabsorbent disposable diapers have been a world changer for the ladies who cheerfully don't hunt diaper pail door busters on Black Friday ( as Ms. Rabett puts it, any store that opens on Thanksgiving, is a store she will not set paw in) and for bunnies like Eli who are moving into the Alzheimer generation.  The key is polyacrylic acid, made, guess what, from acrylic acid.  And what, say the bunnies, is acrylic acid made from?  Well propylene.  And what is propylene made from, well oil, specifically as a byproduct from ethylene crackers in Texas and LA, e.g. heavy oil.

A recent article in C&E News, the American Chemical Society social magazine (they have obits and promotions, but sorry, pay wall), discusses the possibility of superabsorbent bio-diapers, which comes down to whether there is a route from plants to acrylic acid which is cheap enough to compete..

As with any commodity chemical the question is price.  That is the only question as far as substitution.  Worse, it is not a question of whether something is cheaper now, as whether it will be cheap enough  in the future to justify investment in plant and equipment now. 

The situation is not simply whether you can produce cheaper acrylic acid from propylene wrested from tar sands or Orinoco basin oil, but even that is being displaced by even cheaper propylene from ethane separated from natural gas which is increasingly cheap given the expansion of cracking.  So the propylene price point at which it pays to invest in bio-acrylic acid is also a bet on how long fracking will provide cheap natural gas, and to an extent a bet on the ethane content of what comes up in the future.

While bio-acrylic acid may get a bit of a lift from those who want to be as sustainable as possible and  the iPhone effect (eg be the first on your block), that soon wears off and babies and the incontinent get through a mess of diapers.  So price is indeed the only point and early enthusiastic adopters would be a help at the introduction of the product but should not be counted on long term

A good illustration of how this all doesn't work is the glycerin route which has fallen victim to the bio-fuel bust. Glycerin comes from fats and oils in plants extracted in the processing of bio-fuels.  While that business was growing great guns in the early part of this century, growth has slowed, the price of glycerin has not fallen to where it would be competitive as a feed stock for acrylic acid.

There are two solutions, and probably both.  First, the price of oil and gas can be increased by a tax or a market mechanism to increase the price of fossil fuels.  A point for though is that at least as far as commodity chemicals made from oil and gas, the market mechanism and taxes have to hit at the well head and not at the point of emissions.  Second, the price of the bio-routes can be lowered.  Right now they are moving out of the lab to pilot plant and some progress might be anticipated, but probably not enough to completely close the price gap.

BTW, for bunnies who want to paint the town red, about half of the 5 million tons of acylic acid made ever year go into acrylic paints, most of the rest is for the diaper trade.