Biodiesel is defined as monoalkyl fatty acid ester and produced by the transesterification of the grease, vegetable oils or animal fats with short chain alcohols. Compared with the traditional fuels, it has lots of advantages: excellent environmental performance, low-temperature startup, stability, and renewable. It has been proven to be a promising alternative fuel for the mineral diesel fuel. But the grease and alcohols are not miscible with each other. So the reaction only takes place in the interphase boundary, and it will reduce the reaction conversion and reaction rate. Some researchers proposed that the addition of the cosolvent in reaction system can create a single homogeneous phase, and the cosolvent and surplus alcohols can be separated from the reaction system after the reaction for recycling. This new method overcome the disadvantage of traditional technology in mass transfer and greatly accelerates the reaction conversion and reaction rate.
The mutual diffusion coefficients of short chain alcohols with the cosolvent strongly affect the catalytic reaction and separation processes in the process of biodiesel production. Thus the accurate data of the mutual diffusion coefficient is useful for the design of processing equipment.
In this work, the mutual diffusion coefficients of different short chain alcohols (methanol, ethanol, and propanol) with the cosolvent (t-pentanol) were measured by digital holographic interferometry. The mass fraction and temperature range are from 0.1 to 0.9 and from 283.15 K to 313.15 K. The combined measurement uncertainties of mass fraction and temperature are 0.002 and 0.24 K, respectively. The relative combined uncertainty of the mutual diffusion coefficient is not greater than 0.2 %. For all the investigated mixture, the mutual diffusion coefficient increases with the increasing temperature. At the same concentration and temperature, the mutual diffusion coefficient was as follow: methanol + t-pentanol > ethanol + t-pentanol > propanol + t-pentanol. This behavior is consistent with the order of the molecular weight of alcohols. A new correlation was proposed for the experimental data.
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