Newswise – Collaborative research that combined experiments at Yale University and molecular dynamics simulations at the Department of Energy’s Oak Ridge National Laboratory is providing new insights into solving a major technical barrier to efficient and sustainable industrial operations.
Silicon is the second most abundant element in the Earth’s crust and is often found in the form of dissolved silica in natural water sources. Under certain pH and temperature conditions in industrial feed water, the acid can become supersaturated and insoluble, causing a substance called silica deposits to precipitate, which crusts the equipment. This undesirable coating contaminates the surfaces of various technical systems, such as: B. Water treatment membranes for reverse osmosis desalination, heat exchanger components and system piping.
“One way to combat the silica is to adjust the pH of the water, but this process is quite expensive and exacerbates other forms of inorganic deposits such as gypsum and calcite,” said ORNL’s Vyacheslav “Slava” Bryantsev. “More recently, silicon oxide inhibiting polymers or antiscalants have been used, all of which are proprietary. We know that these antiscalants may be a class of polyamine-like systems that provide some hindrance to silica deposition, but how they work and how their existing properties can be improved remain poorly understood.”
Previous studies on the performance of polymeric silica antiscale agents have ranged from preventing to accelerating the formation of silica scale. “We have conducted the first systematic study of the role of molecular structures and functional groups of polymeric antiscalants in the stabilization of supersaturated silica solutions,” said Bryantsev.
An article entitled “Molecular Design of Functional Polymers for Silica Scale Inhibition” published in Environmental Science and Technology provides details about the study.
The Yale scientists synthesized a series of nitrogen-containing polymers as silica antiscalants and tested their performance in a supersaturated silica solution. They discovered huge differences in effectiveness between similar types of antiscalants.
“Working closely with our colleagues at ORNL, we were able to determine that the differences were due to the specific physical and chemical properties of the polymers,” said Masashi Kaneda of Yale. “The approach and result are remarkable because we have provided an understanding of the mechanisms involved in mitigating silica deposits through the use of polymeric antiscalants in water treatment processes.”
A polymer is a large molecule made up of repeating units called monomers that are linked together by chemical bonds to form a structural chain or backbone. When monomers with functional groups participate in a polymerization reaction, they fuse into a larger polymer and impart certain functionalities to the resulting structural chain.
Water-soluble chemical compounds called amines and amides are incorporated into polymers to form anti-scaling agents due to their ability to stabilize and suspend silica. When a positively charged hydrogen ion is added to an amine molecule, the amine is said to be protonated. Protonation can increase the water solubility and reactivity of the molecule.
In the Yale-ORNL study, scientists discovered that polymers with charged amine and uncharged amide groups in their backbones exhibited superior performance in inhibiting silica deposition, keeping up to 430 parts per million of reactive silica intact for eight hours under neutral pH conditions remain. However, monomers of these amine- and amide-containing polymers showed insignificant inhibition along with polymers containing only amine and amide functions.
“We had to answer why the polymers we developed for the experiment worked but the monomers didn’t,” said ORNL’s Deng Dong. “To identify the design parameters, we performed molecular dynamics simulations that we believed would allow us to understand the mechanisms behind the phenomena.”
The simulations showed a strong bond between the deprotonated silica and a polymer when the amine groups in the polymer were protonated.
“Through ORNL’s contribution, we were able to discover that certain functional groups in the polymer chain contribute synergistically to the process of deposition inhibition,” said Mingjiang Zhong of Yale.
Zhong added that silica scaling is significantly different from other scaling processes.
“Although current efforts are focused on solving the silica scale problem through the water treatment process, the ideal case will be to add some kind of anti-scaling agent to prevent all types of scale formation, not just silica,” Zhong said. “However, to the best of our knowledge, no such antiscalant exists to date. The molecular understanding we have gained through our research will help us discover a universal solution.”
This study was supported by the National Alliance for Water Innovation and funded by DOE’s Office of Energy Efficiency and Renewable Energy, Industrial Efficiency and Decarbonization Office. This research utilized resources from the Oak Ridge Leadership Computing Facility at ORNL and resources from the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory. OLCF and NERSC are user facilities of the DOE Office of Science.
UT-Battelle manages ORNL for the DOE’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.