瓦斯浓度影响下水合物晶体结构Raman光谱特征

Raman Characterization of Hydrate Crystal Structure Influenced by Mine Gas Concentration

在初始温压2℃,5 MPa条件下开展了三种瓦斯混合气（CH_4—C_2H_6—N_2,G1=54∶36∶10,G2=67.5∶22.5∶10,G3=81∶9∶10）水合实验,利用可见显微拉曼光谱仪获取水合产物拉曼光谱,通过水合物相中C_2H_6 C—C键伸缩振动特征峰拉曼位移判断水合物晶体结构,利用谱图特征峰分峰拟合方法计算出瓦斯水合物孔穴占有率、水合指数等。研究发现：气样G1和G2水合产物为I型水合物、G3为Ⅱ型,气样中C_2H_6浓度改变导致水合物晶体结构转变;Ⅰ型结构水合物相中CH_4和C_2H_6含量受气样浓度影响较小,G1和G2体系中CH_4含量分别为34.4%和35.7%、C_2H_6含量分别为64.6%和63.9%,而G3体系中CH_4和C_2H_6含量分别为73.5%和22.8%,晶体结构对水合物相客体分子含量控制作用明显;G1~G3体系水合物相大孔穴的CH_4—C_2H_6占有率分别为98%,98%和92%,小孔穴的CH_4占有率分别为80%,60%和84%,N2由于分压较低且吸附能力较弱其小孔穴占有率不高于5%。

CH_4/C_2H_6/N2 mixed hydrate formation experiments were performed at 2 ℃ and 5 MPa for three different mine gas concentrations（CH_4/C_2H_6/N2,G1=54∶36∶10,G2=67.5∶22.5∶10,G3=81∶9∶10）.Raman spectra for hydration products were obtained by using Microscopic Raman Spectrometer.Hydrate structure is determined by the Raman shift of symmetric C—C stretching vibration mode of C_2H_6 in the hydrate phase.This work is focused on the cage occupancies and hydration numbers,calculated by the fitting methods of Raman peaks.The results show that structureⅠ（sⅠ）hydrate forms in the G1 and G2gas systems,while structureⅡ（sⅡ）hydrate forms in the G3 gas system,concentration variation of C_2H_6 in the gas samples leads to a change in hydrate structure from sⅠto sⅡ;the percentages of CH_4 and C_2H_6in sⅠ hydrate phase are less affected by the concentration of gas samples,the percentages of CH_4 are respectively 34.4% and 35.7%,C_2H_6 are respectively64.6% and 63.9%for gas systems of G1 and G2,the percentages of CH_4 and C_2H_6are respectively 73.5% and 22.8%for gas systems of G3,the proportions of object molecules largely depend on the hydrate structure;CH_4and C_2H_6 molecules occupy98%,98% and 92% of the large cages and CH_4 molecules occupy 80%,60% and 84% of the small cages for gas systems of G1,G2 and G3,respectively;additionally,N2 molecules occupy less than 5% of the small cages is due to its weak adsorption ability and the lower partial pressure.