Separation of mixed aromatics into individual constituents

3 Separation of mixed aromatics into individual constituents 

It is also possible to produce benzene by crystallization Newton-Chambers method) a pre-requisite is the absence of thiophene, since this sulfur compound, unlike the co-boiling paraffins which are present, cannot economically be separated by crystallization. However, in contrast to the recovery of other aromatics by crystallization, there is presently no large-scale application of benzene crystallization. 

Since the boiling points of the Cg-isomers lie close together, their separation is more difficult than for benzene and toluene. The separation of ethylbenzene by distillation alone requires a system of columns with some 300 theoretical trays, with reflux ratios of around 100 1.The yield of ethylbenzene from this superfractionation is over 95%, with 99.8% purity. 

Since it is basically more economical to synthesize ethylbenzene from benzene and ethylene (see Chapter 5.1.2), distillation is used only in isolated cases, particularly in the USA (Cosden), 

The crystallization point of p-xylene is markedly higher than that of the other Cg-aromatics it is therefore possible to separate p-xylene by crystallization. Since p-xylene can be better adsorbed than the accompanying Cg-aromatics, adsorption can also be used in its recovery. 

---