Directed discovery of greener cosolvents

3 minute read

 Graphical abstract

This was a fun paper to talk about, because I described it to the general public as ‘saving the world, by finding better ways to dissolve all of the trees!’.

So, cellulose is the most abundant molecule found in plants and trees. It’s made from sugar molecules stuck together, and that’s the molecule that cows can digest that we can’t (to us, it’s fibre). It’s useful stuff to make things like paper and biodegradable plastics out of. And a good source of it is not actually trees, but bagasse, which is the woody part of sugarcane that is left over after the sugar cane crop has been fermented to make bioethanol (a green fuel).

To process cellulose, you first have to dissolve it, and this is done using something called ionic liquids, which are cool as they are liquids which are also salts. Note, this is not salt dissolved in a liquid, but a salt that is a liquid. The chemical structure of the ionic liquid is the orange and green chemical formulae in the left hand side of that diagram. Now, we know that cellulose doesn’t dissolve easily (for example, cellulose is also a large constituent of wood, and wood doesn’t dissolve in water, even salty water, which is why it’s used to make boats), but an ionic liquid can do it. Ionic liquids are considered to be very green, as they have zero vapour pressure, which means that the ionic liquid doesn’t evapourate, so if you use them in a chemical process, they can’t escape into the atmosphere. However, they are very corrosive (you do not want to put your hand into them) and expensive, and when you start to dissolve a huge polymers like cellulose in it, the ionic liquid and cellulose mixture becomes very thick and hard to process. So, the ionic liquids are mixed with what are called co-solvents, which help the dissolution. These dissolving mixtures of ionic liquids and co-solvents are called organic electrolyte solutions (OESs). The problem with co-solvents is they tend to be rather nasty chemicals, and this paper is about finding greener and better co-solvents for use in the paper and plastics industries.

Directed discovery of greener cosolvents

new cosolvents for use in ionic liquid based organic electrolyte solutions for cellulose dissolution

Citation Gale, E, Wirawan, RH, Silveira, RL, Pereira, CS, Johns, MA, Skaf, MS & Scott, JL, 2016, ‘Directed discovery of greener cosolvents: new cosolvents for use in ionic liquid based organic electrolyte solutions for cellulose dissolution’. ACS Sustainable Chemistry and Engineering, vol 4., pp. 6200-6207

Abstract:

Cellulose is an abundant, cheap, renewable, yet recalcitrant, material, which, if dissolved, may be formed into a wide range of materials, composites, and mixtures. Much attention has recently been focused on the use of mixtures of ionic liquids and some solvents (so-called organic electrolyte solutions, OESs) as efficient cellulose dissolution solvents, but many of the cosolvents used lack green credentials - a perennial problem where dipolar aprotic solvents are the solvents of choice. We present a rational approach, based on definition of ranges of solvent parameters gathered together in recently published databases, to find “greener” cosolvents for OES formation. Thus, γ-butyrolactone is identified as a suitable OES former for dissolution of microcrystalline cellulose and biobased γ-valerolactone as a marginally less efficient, but significantly safer, alternative. Comparison of cosolvent efficiency reveals that previous use of measures of mass, or concentration, of cellulose dissolved may have masked the similarities between 1-methylimidazole, dimethyl sulfoxide (DMSO), N,N-dimethylformamide, N-N′-dimethylimidazolidinone, N,N-dimethylacetamide, N-methylpyrrolidinone, and sulfolane (seldom considered), while comparison on a molar basis reveals that the molar volume of the solvent is an important factor. Reference-interaction site model (RISM) calculations for the DMSO/1-ethyl-3-methylimidazolium acetate OES suggest competition between DMSO and the acetate anion and preferential solvation of cellulose by the ionic liquid.

Citation:

Gale, E, Wirawan, RH, Silveira, RL, Pereira, CS, Johns, MA, Skaf, MS & Scott, JL, 2016, ‘Directed discovery of greener cosolvents: new cosolvents for use in ionic liquid based organic electrolyte solutions for cellulose dissolution’. ACS Sustainable Chemistry and Engineering, vol 4., pp. 6200-6207

Link to paper on the journal site