The results of the destruction time of the sediment column structure of coal grains in alkane from hexane to hexadecane are reported. The destruction time was measured in a simple device constructed in our laboratory. The changes in the destruction time were explained by calculations of the attachment and detachment forces which result from interfacial and gravitational interactions, respectively. In equilibrium conditions, the attachment force is equal to the detachment force, and coal grains did not detach from one another. The diameter of such grains, called the critical diameter, was determined from the linear relationship between the reciprocal of the destruction time and the average diameters of the coal grains. It was found that the critical diameter of the coal grains did not depend on the length of the hydrocarbon chains. The increase in the destruction time with the length of the hydrocarbon chains is due to the decrease of the detachment forces and the increase of the perimeter of the contact plane between two coal grains in thr alkane, which was shown by calculation of the attachment force per coal grain. It was also found that the detachment of coal grains from one another occurred by disruption of the alkane film present between the coal grains.