Evaluation of CO2 as an Acid Catalyst Precursor for Promoting a Nitrogen-Generating System

Abstract

Summary Nitrogen-generating systems (NGSs) are mainly used in the oil industry to fluidize low melting point organic deposits and gas hydrate buildups. They are exothermic reactions between two nitrogenous salts in acidic catalytic media. This work investigates the use of CO2 to promote NGS reactions instead of commonly used acids such as acetic and citric acids, which can be problematic for corrosion control. Sodium nitrite and ammonium chloride were the reactants, and CO2 performance was evaluated for up to 4 hours at 5 and 25°C, and either under autogenous pressure at 10, 25, and 50 bar of CO2 or pressurized at 10 bar of CO2 by adding 40 bar of nitrogen (totaling 50 bar). The nitrite conversion was determined by measuring the concentration of residual nitrite using titration. Thus, it was verified that the CO2 effectively promoted the NGS at various experimental conditions. The nitrite conversion increased with increasing CO2 pressure and increasing temperature. Moreover, the nitrite conversion was enhanced in the pressurized system (PS) because the high pressure enabled the dissolution of CO2 in the aqueous medium, and therefore, the constant formation of carbonic acid, favoring the acidic catalytic medium at the reaction. This advantage was confirmed by carrying out an NGS catalyzed by acetic acid, in which the pH increases as reagents are consumed, and therefore, a lower nitrite conversion is achieved. The use of CO2 also converts the NGS in a process more suitable for flow assurance applications in offshore oil production, particularly in the Brazilian presalt fields where the coproduced CO2 can be used.