carbon nanotubes with different diameter distributions were produced examples are listed in table 1 the raw carbon nanotubes were purified by mixing 3 4 g of them with 300 ml of 1m h 2 so 4 stirring for about 5 h to eliminate the catalyst particles leaching the solution then dispersing the nanotubes in isopropyl alcohol by sonication leaching again washing with de ionized water and drying at 473k in a flow of n 2 400 mg of ni 4 mo 1 mg 4 700 catalyst was put into fluidized bed reactor for carbon nanotube fabrication after reduction by hydrogen with flow rate 17l h for 30 min and reaction with pure methane flow rate 11 5l h for 2 h 3 394 g of carbon nanotubes was obtained by analyzing the record of a gas chromatogram the average conversion of methane was calculated to be about 30 mg no 3 2 h 24 mo 7 n 6 o 24 sample ni no 3 2 6h 2 o 6h 2 o 4h 2 o citric acid price 116 7s kg 51 8s kg 323 9s kg 59 3s kg gas methane hydrogen price 82 3s m 3 5 15 m 3 according to the above market price of each reagent and gas we calculated the value of multi wall carbon nanotubes.