Not getting good solutions for large problem

[mchlshort]

At the moment the second example has very poor solutions and extremely long solve times. There are a number of potential fixes that may work and would be good to get going in Pyomo:

1. Initialize the problem with a smaller subset of the discrete variables to make the B&B less time-consuming
2. Try and get a better implementation for the big-M constraints
3. Check that the model is working properly regarding the lean stream "L" - currently the model does not guarantee that lean process streams are utilized fully. Fixing the L value of the process streams results in infeasible model
4. Input the non-isocompositional mixing equations
5. Try and get BARON or COUENNE working for the problem

These are all potential fixes that would make a good first issue for someone.