The Effects of carboxylic Acids on Homo-geneous CaCO3 Scale Formation studied by Dynamic Light Scattering

CO2 emission in the Netherlands must be reduced by 40% in 2030 compared to 2015. A large contributor to the CO2 emissions is the heating sector. To meet these emission goals the heating sector needs to achieve a reduction of 20 megatons CO2 by 2030. A promising alternative heat source in the Netherlands is geothermal energy which can meet 23% of the total heat energy demand in 2050. To make geothermal energy a viable option the operation costs have to be low. One major obstacle in the development of geothermal energy is the formation of scale. Scale is the formation of inorganic sparingly soluble salts present in subsurface waters. These salts precipitate in pipe lines and heat exchangers, decreasing energy production. The most common scale is calcium carbonate (CaCO3) and has been widely studied. However, little is know about the interaction between reactive organic compounds and the formation of scale. The goal of this research is to investigate the effect of several common Carboxylic acids on the homogeneous nucleation and precipitation of Calcium Carbonate. These effects were measured by Dynamic Light Scattering (DLS) at several saturation ratio's (SR) and acid concentration. To investigate the effects of the carboxylic acids a DLS ow loop was developed to measure the scale formation over time. With the use of Scanning Electron Microscopy (SEM) the effect on the crystal morphology were investigated. To improve the DLS experiments and to research the effect of particulates on scale formation several experiments were conducted with addition of silica nanoparticles. It was found that due to a large particle size variation of the formed CaCO3 particles the DLS is not able to measure a representative mean particle size. Nevertheless this method allowed us to study important aspects of homogeneous nucleation like induction time and relative amounts of precipitate formed by using the scaled count rate. Experimental data shows that Acetic acid, Malonic acid, Benzoic acid and Citric acid all had an inhibiting effect on the formation of Calcium carbonate precipitation. Both induction time and relative amount of precipitate were influenced by the carboxylic acids. No signifcant change in CaCO3 crystal morphology was observed due to the addition of low concentrations of the acids. Several relatively high acid concentration experiments showed the formation of aragonite crystals, normally only observed at high temperatures. DLS and SEM results showed that silica nanoparticles increased the formation of CaCO3 precipitation. By using nanoparticles the reaction can be steered to produce smaller crystals which also might make the particles size analysis by DLS possible.