Most process engineers are chemical engineers. A process engineer is an engineer linked with the smooth working and operation of the process. A process engineer can be a chemical engineer, mechanical engineer, petroleum engineer, instrument engineer and also an electrical engineer. Since most engineering core concepts (fundamentals) are common, a process engineer can belong to any discipline and can grow in to multifunctional roles. Modern industrial development after 1950's is attributed to chemical industries so you will find more chemical engineers working as process engineers. A few decades back, the role of the process engineer was contributed usually by a mechanical engineer. Now you will find this role being demanded from chemical engineers.