There is no universal definition for chemical engineering. The problems which chemical engineers face are too diverse to fall into one category.
Chemical engineers solve problems ranging from mathematical analysis to plumbing.
Another question you are probably asking is what is the difference between a chemist and a chemical engineer. The difference is the chemical engineer will design the process using the reaction the chemist found and make the product in a profitable way. For example, a chemist discovers that if he mixes two reactants at a high temperature, he will obtain a more valuable product. The company wants to invent a process to make this product using this reaction. From here on is the engineering part of the problem.