Synthesis and optimization of modified amino acid as chelating agent for barium sulphate and calcium carbonate dissolution / Aimi Asyiqin Abu Kassim

Faculty of Chemical and Process Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2022

Includes bibliographical references

In the oil and gas industry, the precipitation, and the accumulation of solid scales such as barium sulphate (BaSO4) and calcium carbonate (CaCO3) in the oil well pipelines causing a loss of US$1100 million. As a remediation for the scales problem, chelating agent has been widely used due to its high ability to dissolve the scales and able to form stable complex metal ion. In previous studies, most of proposed methods used a cyano-methylation method to synthesize amino poly-carboxyl chelating agents. However, there is still lack of study for using Michael Addition method to synthesize a chelating agent. Therefore, this study focused on developing a new chelating agent using green materials, such as amino acid and sodium acrylate under Michael addition in the presence of ceric (IV) ammonium nitrate (CAN) catalyst. A preliminary study was conducted to obtain an optimum synthesize parameters such as stirring rate, reaction time, and temperature using One-Factor-at-Time (OFAT) and Response Surface Methodology (RSM). The study found that a stirring rate at 350 rpm with 150 min reaction time at 85℃ is the most significant condition for synthesis reaction with the regressions (R2) obtained being more than 90 % (p<0.005). The highest dissolution at 16.09 % (BaSO4) and 21.6% (CaCO3) were achieved with error less than 0.05%, comparing experimental results to mathematical model from the RSM. Design of Experiment (DoE) was conducted by varying four significant factors such as concentration of amino acid, type of amino acid, ratio base to amino acid and type of base in Full Factorial Design (FFD) and the model was optimized via Centre Composite Design (CCD) in Design-Expert software. The developed models for BaSO4 and CaCO3 dissolution were significant where N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent was successfully synthesized at p <0.005. The concentration of amino acid and type of amino acid played a vital role towards the dissolution. N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent’s yields have obtained more than 80 %, with pH achieved higher than 12. The highest BaSO4 and CaCO3 dissolutions in FFD were achieved at 30.45 and 52.98 %, accordingly. In the optimization, the optimized N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent dissolved BaSO4 at 40.58 %, approximately 33.28 % of increment of dissolution. Meanwhile, the dissolution of CaCO3 scale was at 64.68 %, with 22.08 % increment. These results indicated that the optimization managed to optimize and increase the N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent’s chelation ability at p < 0.05. In data validation, the errors less than 10 % which indicated the prediction equation from the ANOVA analysis was acceptable. The molecular structure of N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent was proved based on NMR and FTIR analysis. N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent exists in amorphous solid and Differential Scanning Calorimetry (DSC) analysis found that N, N- (Dicarboxylethyl) glutamic trisodium salt chelating agent has 195.64 ℃ melting point with viscosity at 12.02 cp. A comparison of N, N- (Dicarboxylethyl) glutamic trisodium salt and commercial DTPA-K and EDTA-K found that the synthesized chelating agent able to obtain less than 20% difference dissolution performance.