物理化学学报 >> 2016, Vol. 32 >> Issue (11): 2671-2677.doi: 10.3866/PKU.WHXB201608122

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亚临界和超临界二氧化碳-甲醇混合气相及液相区中甲醇核磁弛豫速率比较研究

程晓蒙,李宇,陈总,李宏平*(),郑晓芳   

  • 收稿日期:2016-07-14 发布日期:2016-11-08
  • 通讯作者: 李宏平 E-mail:lihongping@zzu.edu.cn
  • 基金资助:
    国家自然科学资金(21543009);国家自然科学资金(21073167);国家自然科学资金(J1210060);国家级、郑州大学大学生创新训练计划(201410459047);国家级、郑州大学大学生创新训练计划(201510459046);国家级、郑州大学大学生创新训练计划(2016xjxm259)

A Comparative Study on theNMR Relaxation of Methanol in Sub-and Super-Critical Mixtures of CO2 and Methanol

Xiao-Meng CHENG,Yu LI,Zong CHEN,Hong-Ping LI*(),Xiao-Fang ZHENG   

  • Received:2016-07-14 Published:2016-11-08
  • Contact: Hong-Ping LI E-mail:lihongping@zzu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21543009);the National Natural Science Foundation of China(21073167);the National Natural Science Foundation of China(J1210060);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(201410459047);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(201510459046);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(2016xjxm259)

摘要:

用核磁共振氢谱测量了不同温度(293.15和308.15 K)及压力高达25 MPa下二氧化碳-甲醇混合气相(超临界)及液相区(亚临界)中甲醇(羟基及甲基)的纵向弛豫时间T1,exp。本工作的目的是考察近临界区二氧化碳-甲醇混合物的压力、温度及组成对甲醇弛豫速率的影响,揭示混合物不同相区(气相及液相区)中自旋-晶格弛豫(SLR)过程的机理。此外,还对比研究了等温条件下超临界和亚临界混合气相及液相区中甲醇的SLR速率1/T1,exp随混合物密度的变化规律。研究发现,在本工作所涉及的温度及压力区间,对于纯甲醇或液相区其SLR过程是以偶极-偶极(DD)作用机理为主导,而在气相区SLR过程则是以自旋-转动(SR)作用机理占优势,也即,超临界和亚临界二氧化碳-甲醇混合物的SLR过程在不同相区有不同的作用机理控制。由于甲醇的SLR弛豫速率1/T1,exp是由甲醇分子间及分子内的DD作用和SR作用三部分共同决定的,所以研究超临界和亚临界二氧化碳-甲醇混合物的SLR弛豫速率随压力、浓度及温度的变化规律有助于提供更多该混合物不同相态区分子间相互作用的动态学信息。

关键词: 二氧化碳-甲醇混合物, 偶极-偶极作用机理, 亚临界和超临界流体, 自旋-晶格弛豫速率, 自旋-转动作用机理

Abstract:

1H NMR longitudinal relaxation times (T1, exp of the hydroxyl and methyl group) of methanol in supercritical and subcritical gas-like and liquid-like CO2+methanol mixtures were obtained as a function of pressure up to 25 MPa and at 293.15 and 308.15 K, respectively. This study was designed to investigate the mechanism of the spin-lattice relaxation (SLR) time T1 in different phase regions of CO2+methanol as homogenous gas-like, and liquid-like mixtures, and the influence of pressure, temperature, and composition on the relaxation rate was examined. Moreover, the density dependent isotherms of the SLR rates 1/T1, exp were comparatively studied between gas-like and liquid-like binary mixtures. There exists an obvious phase dependent SLR mechanism within the temperature and pressure range carried out herein, that is, the SLR process is dominated by the dipole-dipole (DD) interaction mechanism for both liquid-like mixture and methanol, whereas by the spin-rotation (SR) mechanism for gas-like mixture. Measurement of nuclear magnetic relaxation times can offer micro-dynamic and micro-structural information and are very useful for the study of fluids of strongly interacting molecules. Mutual influence of electric dipoles as well as hydrogen bonds helps determine the structure of the fluid and its molecular dynamics. The present work increases our knowledge of molecular dynamics of alcohols in sub-and supercritical CO2.

Key words: CO2-methanol mixture, Dipole-dipole interaction mechanism, Subcritical and supercritical fluid, Spin-lattice relaxation rate, Spin-rotation mechanism

MSC2000: 

  • O645