Caulfield Brian, Abraham Juliana, Christodoulatos Christos, Prigiobbe Valentina
Department of Civil, Environmental, and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA.
Nanoscale. 2022 Sep 29;14(37):13570-13579. doi: 10.1039/d2nr03199j.
Carbonate precipitation, as part of the carbon dioxide (CO) mineralization process, is generally regarded as a high-temperature, high-pressure, and high-purity CO process. Typical conditions consist of temperatures around 120 °C and a pressure of 100 bar of pure CO, making the process costly. A major challenge facing carbonate precipitation is performing the reaction at low temperatures and low partial pressures of CO (p) such as 25 °C and CO flue gas concentration. In this work, we investigated the effect of carbonic anhydrase (CA) to favor magnesium (Mg) carbonate precipitation at low temperatures and low p. CA is an enzyme that accelerates CO hydration promoting its conversion into HCO and then CO. This increases supersaturation with respect to Mg-carbonates. A geochemical model was implemented and used to identify supersaturated conditions with respect to Mg-carbonates. Tests were run at 25, 40, and 50 °C and at 1 bar of either pure CO or 10 vol% CO and 90 vol% N. The concentration of 10 vol% CO was chosen to resemble CO concentration in flue gas. In selected tests, the CA enzyme was added directly as bovine CA or through microalgae (). Experiments were run for 48 hours; 24 hours to reach equilibrium, then another 24 hours until the supersaturated conditions were established. After 48 hours the experiments were interrupted and the solids were characterized. Results show that the addition of CA, either directly or through , enhances Mg-carbonate precipitation. Regardless of the temperature, the precipitates were made entirely of nesquehonite (MgCO-3HO) when pure CO was used. Otherwise, a solid solution containing brucite (Mg(OH)) and MgCO-3HO was formed. Overall, these findings suggest that CA can promote carbonate precipitation at low temperatures, pressures, and CO purity. The enzyme is effective when added directly or supplied through microalgae, opening up the possibility for a CO mineralization process to be implemented directly at a combustion plant as a CO storage option without preliminary CO capture.
作为二氧化碳（CO）矿化过程的一部分，碳酸盐沉淀通常被视为一种高温、高压和高纯度的CO过程。典型条件包括温度约120°C和100巴纯CO的压力，这使得该过程成本高昂。碳酸盐沉淀面临的一个主要挑战是在低温和低CO分压（p）下进行反应，例如25°C和CO烟气浓度。在这项工作中，我们研究了碳酸酐酶（CA）在低温和低p条件下促进碳酸镁（Mg）沉淀的作用。CA是一种酶，它加速CO水合，促进其转化为HCO，进而转化为CO。这增加了相对于Mg-碳酸盐的过饱和度。实施了一个地球化学模型，并用于确定相对于Mg-碳酸盐的过饱和条件。测试在25、40和50°C以及1巴纯CO或10体积%CO和90体积%N的条件下进行。选择10体积%CO的浓度是为了模拟烟气中的CO浓度。在选定测试中，CA酶直接作为牛CA添加或通过微藻添加。实验进行了48小时；24小时达到平衡，然后再进行24小时直到建立过饱和条件。48小时后中断实验并对固体进行表征。结果表明，直接添加CA或通过微藻添加CA均可增强Mg-碳酸盐沉淀。无论温度如何，当使用纯CO时，沉淀物完全由三水碳镁石（MgCO·３H₂O）组成。否则，会形成含有水镁石（Mg(OH)₂）和MgCO·３H₂O的固溶体。总体而言，这些发现表明CA可以在低温、低压和低CO纯度下促进碳酸盐沉淀。该酶直接添加或通过微藻供应时均有效，这为在燃烧厂直接实施CO矿化过程作为一种CO储存选择而无需预先进行CO捕集开辟了可能性。
