Abstract: A process is described for the manufacture of .beta.-ionone by the sulphuric acid-catalyzed cyclization of pseudoionone in a two-phase solvent system comprising concentrated sulphuric acid and a second solvent essentially immiscible with water, which process comprises using carbon dioxide liquefied under pressure as the second solvent. This process is carried out, inter alia, under a pressure of about 50 bar to about 150 bar and at temperatures from about -15.degree. C. to about +15.degree. C. prior to the subsequent stopping (quenching) of the cyclization reaction. The process in accordance with the invention is preferably carried out continuously and is an important intermediate stage in the synthesis of vitamin A.

Abstract: By the process of the present invention the activity of heterogeneous catalysts for reactions at normal and low pressures is restored or maintained. These catalysts can lose their activity as a result of the deposition, physisorption or chemisorption of organic or inorganic deactivating substances which are carried over into the reaction system or are formed as the result of side reactions in a chemical synthesis carried out with the aid of the catalyst. The activity is restored or maintained by using a pressure greater than the critical pressure of the fluid phase and a temperature higher than or equal to the critical temperature of the fluid phase. In this process, the pressure and temperature are applied for a period such that the deactivating substances are either removed from the catalyst or are not initially deposited thereon or absorbed or formed.

Abstract: By the process of the present invention the activity of heterogeneous catalysts for reactions at normal and low pressures is restored or maintained. These catalysts can lose their activity as a result of the deposition, physisorption or chemisorption of organic or inorganic deactivating substances which are carried over into the reaction system or are formed as the result of side reactions in a chemical synthesis carried out with the aid of the catalyst. The activity is restored or maintained by using a pressure greater than the critical pressure of the fluid phase and a temperature higher than or equal to the critical temperature of the fluid phase. In this process, the pressure and temperature are applied for a period such that the deactivating substances are either removed from the catalyst or are not initially deposited thereon or absorbed or formed.