TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Apparatus: In the apparatus (A1), the units for controlling the partial pressure comprise a controlled outlet for the removal of gases from the head space of the reactor. The gas outlet is provided with units for monitoring the partial pressure of the carbon dioxide and units for continuously and/or intermittently removing gas from the head space of the rector. The outlet units for the mixture are connected to a separator having its head space in gas connection with the head space of the reactor.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In the process (P1), an overpressure is maintained in the reactor and the overpressure comprises an overpressure of more than 0.2, or 0.5-10 or 1-5 bars. The controlling of the partial pressure involves continuous and/or intermittent controlled removal of gases from the gas phase of the reactor. The controlling includes removal of gaseous carbon dioxide from the reactor. Controlling the partial pressure involves monitoring the concentration of carbon dioxide or another gas in the gas phase and/or monitoring the pH of the reaction mixture. The content of gases other than carbon dioxide in the gas phase is monitored and maintained below 75% or below 60%, or 10-50% calculated on the volume of the gas. The removed gas is conveyed to a tall oil soap treatment step preceding the neutralization reaction. The mixture of soap oil and bicarbonate brine is transferred to a separator in which brine is separated from soap oil, and where the gas phase of the separator is maintained in gas flow contact with the gas phase of the reactor. The partial pressure of carbon dioxide in the separator is maintained at the same level as in the reactor. The soap oil is acidified with a strong acid to provide tall oil and the tall soap is optionally processed into products selected from fuel, fatty acids, rosins and chemicals for industrial, pharmaceutical and food compositions. EXAMPLE - No suitable example given.