Selective CO2 - H2S Capture Using Amine Modified Silica Adsorption Onboard a Floating Production Storage and Offloading Vessel

  • Talal Al Hajeri

Student thesis: Doctoral Thesis


Floating Production Storage and Offloading (FPSO) vessels are a custom division of the offshore oil and gas industry. The block topside arrangement allows for opportunities to study the feasibility of adding a silica based adsorption module onboard. Offshore gas purification has always been limited to the marketable gas associated value where purification is onsite or sent to surface facilities for treatment. CO2 is released into the atmosphere within the acceptable emission limit of the platform or being captured using conventional physical solvents such as in selexol, rectisol, or sulfinol processes. H2S follows other approved technologies such as SULFATREAT or SULFATRAP adsorption technologies. Amine modified silica sorbents for CO2 and H2S capture have seen wider experimental application. However, industrial gas separation has not migrated towards silica sorption even with their growing potential due to rudimentary understanding of their applications in large-scale projects. The purpose of this research is to synthesise and evaluate the performance of modified silica sorbent material from experimental level to a full-scale adsorption column for the specific use on an FPSO. The adsorption module will be analysed for its ability to conduct ternary (CO2+H2S+CH4) sorption and regeneration of raw gas compositions from deep offshore fields comprising of mild CO2 and H2S content, in addition to binary (CO2+N2) sorption and regeneration of downstream flue gas from post-combustion dual fired gas turbines. CO2 Experimental work was based on novel material synthesis of precipitated silica and silicagel impregnated with polyethylenimine (PEI) amines for CO2 capture. Cited work related to additional CO2 and H2S capture tests were extended to evaluate a diverse dataset of modified silica material. All silica models were scaled up using the Vermeulen method to study its compatibility to represent the experimental methods. The linear Langmuir and the extended linear Langmuir model were rearranged to develop the model for competitive sorption. The post-combustion CO2 generation from leading Aeroderivative dual firing gas turbines were simulated on Aspen Plus and DWSIM to recreate the combustion benchmarks using the Chao-Sea and Peng-Robinson built in property methods. The large-scale adsorption module was configured to account for multi-component capture and regeneration using the purging method and cyclic regeneration. The FPSO was tested for its ability to conduct low level sorption following the routine planned operation schedule. The silica beds and adjacent modules required for the FPSO modification have been designed using Autodesk Fusion 360 and 3DS Max to give a clear representation of the proposed layout. A 28-year economic analysis was conducted to quantify the return on investment and profitability metrics from selling CO2 and H2S credit. A detailed technical comparison with non-silica based technology was carried out to compare performance against more widely used sorbents. Precipitated silica showed higher loading with higher sorption capacities from 50-90°C. Additionally, amine concentration contributes towards higher loading with the optimum case being at PEI60wt% and then dips at PEI65wt%. The performance of silicagel increased with higher loading even at PEI65wt%. The temperature effect on sorption continues to be a driving factor for higher CO2 loading but the differences in higher loading at each temperature profile was small in comparison with precipitated silica. Detailed results for H2S capture showed better performance using APTMS modified MCM-41 at 1547 mg/g saturation capacity followed by PEI800 silica xerogel at 48 mg/g at medium concentrations. At higher concentrations, TRI based silica xerogel was significantly improved reaching 65 mg/g. For CO2 capture, precipitated silica achieved a saturation capacity of 92.4 mg/g at lower PEI amine concentrations. At higher PEI, silicagel outperformed reaching saturation capacities of 174 mg/g. MCM-41 co-modification with TEPA and A amines resulted in steady CO2 saturation capacity at 40.9 mg/g. Marine gas turbines efficiency values did not exceed 53%, this resulted in huge fuel requirements and higher CO2 output amounting to 295.4 kmol/hr by Siemens SGT-A35. Furthermore, an increase in air intake improved turbine efficiency but still resulted in huge CO2 emissions. The full-scale model operating on multi-species had a considerable decrease in saturation capacity with all tested samples. Adding CH4, H2S, and CO2 from production well sorption resulted in low loading capacities. Less sorption time benefited weaker silica sets such as MCM-41 from achieving higher loading with time. The cyclic regeneration achieves a better overall loading compared to purging but requires a large number of pressure changes. The cash flow statement of a CO2 and H2S modules with 144 beds showed a turnover period after 19 years and 2 years respectively. The significance of this research deliberately acknowledges that silica sorbents could have a measurable implication in acid gas treatment. The attempt made in this research have shown that under ideal conditions silica sorbents are capable of achieving high CO2/H2S uptake that is economical. Moreover, silica proved passively superior to non-silica based materials. In multi-component capture, silica retains a high standard within solid sorbent families but more research is required to verify its performance against solvent or membrane technology. Silica key performance indicator is time; the saturation time is a decisive factor in obtaining a low or high capture volume. The use of silica beds on an FPSO vessel is inherently a more attractive solution due to low dependency on mechanical drive systems, less energy requirements, and long operational periods between maintenance cycles.
Date of AwardFeb 2022
Original languageAmerican English


  • Saturation Capacity
  • Heat of Adsorption
  • Langmuir Isotherm
  • Vermeulen
  • BET Analysis
  • Cyclic Regeneration
  • Amine Modified Silica Adsorption
  • Selective CO2+H2S Capture
  • Floating Production Storage and Offloading FPSO.

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