What Is a Hydrocarbon Processing Reactor: Types, Design and Refinery Applications Answering the core question: What is a hydrocarbon processing reactor? A hydrocarbon processing reactor is a pressure vessel in which a petroleum or petrochemical feedstock is chemically converted into higher-value products by cracking, reforming, hydrotreating, alkylation or isomerisation, almost always over a solid catalyst and under controlled temperature and pressure. The major classes are