NOVELTY - A continuous process for neutralizing (P1) tall oil soap involves feeding tall oil soap, water and carbon dioxide into a reactor; causing a reaction between the soap, carbon dioxide and water to provide a mixture of soap oil and aqueous bicarbonate brine; during the reaction, controlling the partial pressure of carbon dioxide in the gas phase of the reactor; and discharging the mixture of soap oil and brine from the reactor.    USE - As continuous process for neutralizing tall oil soap, where the tall oil is distilled and/or fractionated to provide tall oil fatty acids, tall oil rosin and valuable chemical compounds useful in industrial, pharmaceutical and food compositions (claimed). The tall oil and/or the soap oil are utilized as fuel as such or it is converted to various other forms of biofuel mimicking the present day diesel fuels.    ADVANTAGE - The process provides improvements in the production of soap oil and ultimately in the production of tall oil and the recovery of useful chemicals from black liquor. The improvement relates specifically to the maintaining of efficient partial pressure of the carbon dioxide in the gas phase of the reactor. This is done by controlled removal of released gases collected in the gas phase of the reactor. The process shows that the key to the proper functioning of the reaction lies in the partial pressure of carbon dioxide. When there is sufficient carbon dioxide in the gas phase of the reactor, the reaction proceeds. The soap oil provided according to the process contains less brine, is cleaner and has higher dry substance content than that of comparable prior art process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) apparatus (A1) for the continuous neutralization of tall oil soap, comprising reactor with units for maintaining a pressure, where the reactor has controlled inlet units for tall oil soap, water and carbon dioxide, outlet units for the discharge of a mixture of soap oil and bicarbonate brine, and mixing units; and the reactor is provided with units for controlling the partial pressure of carbon dioxide in the head space of the reactor; and    (2) use of partial pressure control in a process for neutralizing tall oil soap with carbon dioxide, involving reacting tall oil soap with carbon dioxide and water in a reactor and continuously and/or intermittently removing gases collected in the gas phase of the reactor for maintaining the partial pressure of carbon dioxide in the reactor above a minimum level.