Research On Performance Of Protic Ionic Liquids For Capturing H₂S And CO₂

With the adjustment of the energy consumption structure,natural gas is gradually entering into people's life.However,the acid gas such as H2S and CO2 existing in natural gas not only corrodes the equipment and pipes,but also brings potential threat to gas security and environmental safety.Therefore,the removal of acid gas is the key of natural gas purification process.However,the common deacidification methods used in the industry have several disadvantages,such as secondary pollution,corrosion,intensive energy consumption and high cost.As for the problems of secondary pollution and corrosion,the application of ionic liquids(ILs)with low vapor pressure in deacidification process may serve as a good alternative methodology.However,the high cost,high viscosity and high energy consumption of the ILs are the serious obstacles to its practical application.In order to solve these problems,the protic ionic liquids(PILs)with low cost,low viscosity and low energy consumption were designed and synthesized in this thesis.Their absorption mechanism and thermodynamic performance was also investigated.The detailed researches are summarized as follows:The first part of this study is on the absorption of H2S.Three multiple Lewis base functionalized protic ionic liquids(MLB-PILs)were synthesized by one-step method.They were[TMDAPH][Ac],[PMDPTAH][Ac]and[TDMAPAH][Ac].The H2S solubilities in the aqueous MLB-PILs solutions were up to 0.65—1.92 mol/mol at 1 bar and 313.2 K,which was much higher than other reported H2S absorbents.Impressively,the materials of these MLB-PILs were cheap and the synthetic process was simple,and their viscosities were even lower than 25 mPa·s at room temperature!Therefore,the MLB-PILs aqueous solutions were superior to other H2S absorbents on the aspects of absorption capacity,cost and viscosity.In addition,we correlated H2S solubility in the MLB-PILs solutions with RETM to obtain their combination mode and the thermodynamic parameters.According to the enthalpy change,the entropy change and the regeneration efficiency,it was considered that the MLB-PILs aqueous solutions were renewable desulphurizer with low energy consumption.Secondly,we focused on the absorption of CO2.The diamino protic ionic liquids(PILs)have many advantages,such as low cost and low regeneration energy consumption.However,the stability of the pure PILs is relatively poor and their viscosities are pretty high.Faced with these problems,we mixed the diamino PIL made from 3-(dimethylamino)-1-propylamine(DMAPA)and acetic acid(HAc)with N-methyldiethanolamine(MDEA)aqueous solution to formulate the new CO2 absorbents,i.e.,PIL-MDEA formulated solutions.The formulated solutions had many advantages,such as fast absorption rate,low energy consumption,high absorption capacities,good thermal stability and so on.When studying its absorption mechanism,we found that the PIL took a key role in the absorption process.It acted as a'messenger' like mRNA in biochemistry.CO2,as the 'message',was carried by the PIL and then passed to the main absorbent MDEA.The PIL could be regenerated by the intramolecular hydrolysis and continued the next absorption cycle.We introduced the concept of TON in catalytic chemistry to represent the recycle number of PIL.The dynamic and thermodynamic performance of the PIL-MDEA solutions were also studied in detail.In consideration of the low cost and energy consumption of the diamino PIL,as well as the good affinity of DMAPA to CO2,we synthesized a series of aqueous 3-(dimethylamino)-1-propylamine(DMAPA)cation-based diamino PILs with different anions.It was found that CO2 solubility in the aqueous[DMAPAH][F]reached up to 3.62 mol/kg.A novel absorption mechanism was proposed and verified by 13C NMR and 19F NMR spectra,indicating that it was the F-anion rather than the primary amine that bonded with CO2.It should be noted that all the reported absorption mechanism of fluoro based functionalized ionic liquids with CO2 had been investigated by theoretical calculation.This was the first report that verified the mechanism by experimental data.The influence of temperature and concentration on the absorption was also studied and the absorption performance was evaluated by the thermodynamic parameters and regeneration efficiency.The third part of this investigation was about the simultaneous absorption of H2S and CO2.It is usually required to remove H2S and CO2 simultaneously during the natural gas purification process.Therefore,the absorbent should be able to efficiently trap both H2S and CO2 at the same time.In virtue of the good affinity of PIL-MDEA formulated solutions to both H2S and CO2,their ability to simultaneously capture the two kinds of gas was determined in the thesis.It was found that after absorbing 0.24 mol/kg of H2S,the PIL-MDEA formulated solutions could still absorb 2.21—2.45 mol/kg of CO2 at 1 bar.Owing to the high absorption capacities,low cost and low viscosities,the formulated PIL-MDEA solutions were believed to have potential use in gas deacidification process.The thesis paid attention to the performance of protic ionic liquids for capturing H2S and CO2.Many novel functionalized PILs were synthesized and their absorption mechanism and thermodynamic performance were investigated in detail.It will provide theoretical guidance for designing highly-efficient ILs and optimizing natural gas desulfurization and decarbonization process in the future.