text: In industrial scale chemistry, many processes are catalysed by "solid acids". Solid acids do not dissolve in the reaction medium. Well known examples include these oxides, which function as Lewis acids: silico-aluminates (zeolites, alumina, silico-alumino-phosphate), sulfated zirconia, and many transition metal oxides (titania, zirconia, niobia, and more). Such acids are used in cracking. Many solid Brønsted acids are also employed industrially, including sulfonated polystyrene, sulfonated carbon, solid phosphoric acid, niobic acid, and  heteropolyoxometallates.
  A particularly large scale application is alkylation, e.g., the combination of benzene and ethylene to give ethylbenzene.  Another major application is the rearrangement of cyclohexanone oxime to caprolactam. Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids. In this role, the acid converts, OH, a poor leaving group, into a good one.  Thus acids are used to convert alcohols into other classes of compounds, such as thiols and amines.