The Ullmann’s Academy website compiles key concepts, methods and technologies in process chemistry and chemical engineering for teaching and learning. Short introductions to different topics are presented for free. The Read On link takes you to the corresponding article in the main Ullmann’s Encyclopedia (licensed for the Max Planck Society).

Ullmann’s Encyclopedia of Industrial Chemistry
http://onlinelibrary.wiley.com/book/10.1002/14356007/topics