SystemOpen@Export["C3H8_CH4_1_1.xls",Table[{p,x/.FindRoot[6.67222*1.95092*Log[1+0.21977*(p*0.5/x)^(1/1.95092)]45.39602*1.01257*Log[1+1.41285*
-4
10
*(p*0.5/(1-x))^(1/1.01257)],{x,0.01,0.98}]},{p,2,100,2}]~Prepend~{p,x}]