Any other applications of correlation gas chromatography-.ppt

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1、Any other applications of correlation gas chromatography?Suppose you had an aviation fuel and for quality control purposes you were interested in measuring the vaporization enthalpy of this fuel. How would you do it?,Figure 2. The gas chromatographic trace of RJ-4 at T = 394.8 K on a 30 m SPB-5 capi

2、llary column; the retention time of the solvent, CH2Cl2, is not shown.,RJ-4 a high energy density rocket fuel,Consider a mixture of i structurally related components. For each component detected by the gas chromatograph, either individually or as a multiple component peak, the following relationship

3、 applies:ln (1/t1a) = ln(A1) gslnHm(Tm)(1)/RT; ln (1/t2a) = ln(A2) gslnHm(Tm)(2)/RT; . ln (1/tia) = ln(Ai) gslnHm(Tm)(i)/RT Multiplying each component by its mol fraction and summing over all i components results in the following equation:,The enthalpy term on the extreme right, nigslnHm(Tm)(i), is

4、the enthalpy of transfer from solution to the vapor of the entire mixture, gslnHm(Tm)(mix). A plot of the sum of niln(1/tic) verses 1/T should result in a straight line with a slope of -gslnHm(Tm)(mix). As an example, consider the following:,Table 1. Retention times of the standards as a function of

5、 temperature.T /K: 394.8 399.9 405.0 410.1 415.1 420.1 425.1 Standards t/min CH2Cl2 2.791 2.819 2.83 2.849 2.866 2.888 2.9 n-decane 4.516 4.304 4.114 3.962 3.84 3.741 3.65 exo-THDCPD 5.733 5.367 5.048 4.786 4.57 4.39 4.231 endo-THDCPD 6.345 5.887 5.492 5.167 4.899 4.675 4.479 n-tetradecane 20.895 17

6、.53 14.868 12.76 11.103 9.766 8.679,Table. The equations resulting from a linear regression of ln(1/tc) verses 1/T /K of the standards and the corrrelation coefficient, r2, describing the quality of the fit; enthalpies in J.mol-1.Standard ln (1/tic) = -vslnH(i)/RT + ln(Ai) n-decane ln(1/tc) = (-3833

7、290.0)/RT + (11.1360.0009), r2 = 0.9999 exo-THDCPD ln(1/tc) = (-36521127)/RT + (10.0510.0012), r2 =0.9999 endo-THDCPD ln(1/tc) = (-3735226)/RT + (10.1150.0012), r2 = 0.9999 n-tetradecane ln(1/tc) = (-52567231)/RT + (13.1240.0022), r2 = 0.9999,Table 5. Correlations of enthalpies of transfer from solu

8、tion to the gas phase with vaporization enthalpies from the literature; r2, correlation coefficient, enthalpies in kJ.mol-1.a Compound gslnHm(Tm) glHm(298.15 K)lit. glHm(298.15 K)calcd n-decane 38.33 51.45 51.55 0.79 exo-THDCPD 36.52 49.14 48.99 0.75 endo-THDCPD 37.35 50.24 50.17 0.77 n-tetradecane

9、52.57 71.75 71.68 1.08 glHm(298.15 K) = (1.4140.01)gslnHm(Tm) ( 2.6540.136); r2 = 0.9999 What would be the ideal vaporization enthalpy of a 60:40 molar mixture of decane and tetradecane? Ans. 0.60*51.4+.0.4*71.7 = 59.52 kJ mol-1 What would be the ideal enthalpy of transfer from solution to the vapor

10、 of a 60:40 molar mixture of decane and tetradecane? Ans. 0.60*38.33+.0.4*52.57 = 44.026 kJ mol-1,Now consider a hypothetical compound having ln(1/tc)hc = 0.6(ln(1/tc)decane) + 0.4(ln(1/tc)tetradecane)60:40 n-decane: n-tetradecane T/K 1/T/K425.1 0.002352 -0.529 420.1 0.002380 -0.676 415.1 0.002409 -

11、0.828 410.1 0.002439 -0.982 405.0 0.002469 -1.145 399.9 0.002501 -1.313 394.8 0.002533 -1.486 60:40 n-decane: n-tetradecane ln(1/tc)hc= (-44026135)/RT+(11.93120.0013),r2 = 0.9999,Table. The value of for a 60:40 mixture of decane and tetradecane and for RJ-4; r2, correlation coefficient.,Table 5. Cor

12、relations of enthalpies of transfer from solution to the gas phase with vaporization enthalpies from the literature; r2, correlation coefficient, enthalpies in kJmol-1.Compound Hslnv(Tm) Hv(298.15 K) lit. Hv(298.15 K)calcd. n-decane 38.332 51.45 51.55 0.79 exo-THDCPD 36.52 49.14 48.99 0.75 endo-THDCPD 37.352 50.24 50.17 0.77 n-tetradecane 52.566 71.75 71.68 1.08 RJ-4 40.99 55.3 0.84 6:4 mixt 44.03 59.5Hv(298.15 K) = 1.414 0.01Hslnv(Tm) 2.654 0.136; r2 = 0.9999,