Suleman Suleman

Crude oil contains many individual substances. You need to separate the lower hydrocarbons by distillation or rectification. Then dissolve the residue in benzene for crystallization, try adding benzyl alcohol. Petroleum resins are high-molecular heteroatomic components of oil, soluble in low-boiling saturated hydrocarbons. Solid or highly viscous low-volatile substances of black or brown color; average molecular weight of 400-1500, softening point in air of 35-900C. Petroleum resins mainly consist of compounds containing condensed aromatic, naphthenic and heterocyclic fragments. The most characteristic substituents in the cycles are alkyl, alkenyl (C7-C12), carbonyl, carboxyl, hydroxyl, mercapto, amino groups. Asphaltenes are the highest molecular components of oil. These are solid, brittle at room temperature substances of black or brown color. They soften in an inert atmosphere at 200-300 0C with a transition to a plastic state, their density is about 1.1 g / cm3; the average molecular weight is 1000-5000, soluble in benzene, insoluble in paraffinic hydrocarbons. The asphaltene content in oils fluctuates from 1 to 20%. The asphaltene molecule contains fragments of heterocyclic, alicyclic, condensed hydrocarbons, consisting of 5-9 cycles. Large fragments of molecules are linked to each other by bridges containing methylene groups and heteroatoms. The most characteristic substituents in the cycles are alkyls with a small number of carbon atoms and functional groups, for example, carbonyl, carboxyl, mercapto group. Asphaltenes tend to cassociate to form supramolecular structures, which are stacks of flat molecules with a distance between them of about 0.4 nm (see 2.4).

(PDF) Aqueous Hydrocarbon Systems in Science and Engineering. Available from: https://www.researchgate.net/publication/295699203_Aqueous_Hydrocarbon_Systems_in_Science_and_Engineering [accessed Apr 16 2025].

Suleman Suleman

Try to use a different Solvent or Solvent Pair Methanol and hexane may not be good. Choose a solvent pair that has better polarity difference. You can try ethyl acetate and hexane or acetone and water as your solvent structure. If a compound is oily in one solvent, it might crystallize well in another solvent. Use slow cooling from room temperature down to -20°C. You can try cooling with stirring stepwise too. Ensure the concentration is not too high. If the compound is an organic acid/base, form a salt (like hydrochloride, sodium salt) to enhance crystallinity. If moisture is an issue, try dry under vacuum or over drying agents (like MgSO₄ or silica gel). Sometimes, the presence of water can prevent crystallization.