Methods using a simple approximation for the exponential integral

2 Methods using a simple approximation for the exponential integral 

Van Krevelen et al. [529,530] in rising temperature studies of coal pyrolysis, used the rate equation 

From plots of In g(a) against In T with n = 0, 1 and 2, the plot which gives the best straight line identifies the value of n and from the slope Um and hence E is calculated. (This approach can also be regarded as a reference temperature method , see also Sect. 6.2.4). 

Alternative simple approaches to approximations for the exponential integral exploit the linearity of the log P(t/) against U relation over short ranges [533,542,543] 

E may be found from a plot of log g(a) against T 1 if / is given the appropriate value. 

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