Methylnaphthalene isomers separation

We, at Sun Oil Co., are greatly interested in separating 2,6-dimethyl-naphthalene from 2,7-dimethyInaphthalene (2,7-DMN). These 2 di-methylnaphthalene isomers are too close-boiling (262.0°C for 2,6-DMN and 262.3°C for 2,7-DMN) to allow separation via fractional distillation. Furthermore, both isomers are solid at room temperature (mp 111°-112°C for 2,6-DMN and 96°-97°C for 2,7-DMN). Only a small fraction of the naturally-occurring 2,6-DMN in a refinery stream can be crystallized before a binary eutectic containing 42% 2,6-DMN and 58% 2,7-DMN begins to precipitate. 

After CLD modification, the zeolites exhibit excellent shape selectivity for separation and purification of various isomers. For instance, the pore-size-adjusted NaY zeolite after Si(OCH3)4 modification is very effective for the separation of methylnaphthalene and trimethylbenzene isomers. Because the pore size of NaY itself is large, before modification the zeolite shows no shape selectivity for the two methylnaphthalene isomers, and the adsorption capacities for 1-methylnaphthalene and 2-methylnaphthalene are similar. However, as the pore size decreases, the zeolite exhibits increasing adsorption capacity... 

Methylnaphthalenes are also found in petroleum-derived feedstocks, such as pyrolysis tar from ethylene production and cat-cracker residues (see Chapter 9.2.2). The l-/2-methylnaphthalene isomer ratio, which is around 1 2.5 for methyl-naphthalenes in coal tar, is higher in this case, because of the lower temperature exposition of the raw material, and is close to 1 1. Recovery of methylnaphthalenes from these sources is generally only carried out on a small scale, since it can be extremely intricate to separate co-boiling compounds petroleum-derived methylnaphthalenes has served as a feedstock for naphthalene production by dealkylation, especially in the USA in the 1960 s and 70 s. 

While steric effects of alkyl groups may be present in the hydrogenation of alkylnaphthalenes they are by no means the only effect. Competitive hydrogenation of 2-methyl- and 2-t-butylnaphthalene showed that the latter was hydrogenated somewhat more slowly. In experiments with Raney nickel catalyst at 1000 psig and 200°, the ratios of tetralin isomers were the same whether the methylnaphthalene and i-butylnaphthalene were hydrogenated separately or competitively ... 

Since 2-acetylnaphthalene 50) forms an inclusion compound with 7 a and the 1-isomer 49 does not, both isomers can be separated easily. 1-Methylnaphthalene (57, bp 240-243 °C) which forms an inclusion compound with 23 can be separated from the 2-isomer 52, bp 245 °C) which does not The X-ray crystal structure of the 1 1 inclusion of 57 with 23 (Fig. 8) showed that this compound is formed by van der Waals... 

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