Separation of Linear and Branched Alkanes Using Host–Guest Complexation of Cyclic and Branched Alkane Vapors by Crystal State Pillar[6]arene

Abstract

Activated crystals of pillar [6]arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as ac onsequence of their gate-opening behavior.T he uptake of branched and cyclic alkane vapors by the activated crystals of pillar [6]arene induced ac rystal transformation to form one-dimensional channel structures.H owever,t he activated crystals of pillar-[6]arene hardly took up linear alkane vapors because the cavity sizeo fp illar [6]arene is too large to form stable complexes with linear alkanes.T his shape-selective uptake behavior of pillar[6]arene was further utilized for improving the researchoctane number of an alkane mixture of isooctane and n-heptane:i nterestingly,t he researcho ctane number was dramatically improved from al ow researcho ctane number (17 %) to ah igh researcho ctane number (> 99 %) using the activated crystals of pillar[6]arene.Separation of linear and branched alkanes is of significant important in the petroleum chemistry.T he branched alkanes in the 5-7 carbon number range are major components in high-octane gasoline because they have high research octane numbers (RONs). Fore xample,2 ,3-dimethylbutane,2 ,2dimethylbutane,a nd isooctane have RONs of 101.7, 91.8, and 100, respectively.Incontrast, RONs of linear alkanes are quite low.The RONs of n-hexane and n-pentane are 24.8 and 0, respectively.F urthermore,q uality of gasoline is evaluated in the RON,w hich is the volume ratio of isooctane in am ixture of isooctane and n-heptane in gasoline.H owever, the boiling point of isooctane (b.p.: 99 8 8C) is almost the same as that of n-heptane (b.p.: 98 8 8C), so the separation of these two alkanes via petroleum distillation is very difficult, and many manufacturing processes are required to produce gasoline with ahigh RON. [1] Separation of linear and branched alkanes using adsorption materials is one of the most energy-efficient strategies. This has been achieved with chromatography systems that use columns packed with microporous materials such as zeolites, [2] carbon molecular sieves, [3] and metal-organic frameworks (MOFs) also been called porous coordination polymers (PCPs). [4] However,a lkanes have low affinity with these materials because they only have low polar C À Ca nd C À H groups.T hus,s eparation of liner and branched alkanes using the chromatography systems is atime-consuming process,and an ew energy-efficient separation protocol should be developed. Separation by adsorption materials that undergo ac rystal transformation should be ap romising strategy for the separation of analogous molecules [5] because the separation with crystal transformation enables isolation of at arget compound with high purity,i se asy-to-handle,a nd energyefficient. However,tothe best of our knowledge,isolation of branched alkanes from am ixture of linear and branched alkanes by means of this sort of separation procedure has not been achieved yet.Herein, we demonstrate that isolation of branched alkanes from am ixture of linear and branched alkanes using a...

Supramolecular exfoliation of layer silicate clay by novel cationic pillar[5]arene intercalants

“…Host–guest interactions of pillar[5]arenes have been revealed by our group to not only occur in solution, but also in bulk 26 , 37 , 38 . From the interlayer distances determined by PXRD, the dense C12P5A is inclined to be present in the interlayer of the modified clay.…”

Energy‐Efficient Iodine Uptake by a Molecular Host⋅Guest Crystal

“…CO 2 ) [67] . Although not featured by high sorption capacity compared to other POC based on macrocycles for iodine capture, [68–70] PHGC‐1 are endowed with several key advantages: (i) their growth from water requires almost no energy, (ii) they are hydrated so insensitive to moisture, (iii) they capture I 2 spontaneously and selectively (compared to water) at room temperature and (iv) they do not require energy‐intensive pore activation, contrary to most porous materials, [71–75] POC, [2, 3, 8, 15, 28, 43–46] or adaptive non‐porous crystals [48, 50, 52, 55] …”

Shape Selectivity of a Metallo Cavitand Host Allows Separation of n‐Alkanes from Isooctane

“…[1] Alkanes are important industrial feedstocks obtained from fossil fuels and separated traditionally by fractional distillation, an energy intensive process. [2] Branched alkanes have high Research octane numbers (RONs), the volume ratio of isooctane in its mixture with n-heptane in gasoline. It is used to evaluate the quality of gasoline fuel.…”

“…[ 3 ] Due to their closely related boiling or freezing points (ESI Table S1) some extra effort is required for their separation. During the past decade, a number of other energy‐efficient adsorption materials – zeolites, [ 4‐5 ] carbon molecular sieves, [ 6 ] metal‐organic frameworks (MOFs), [ 7‐8 ] solid state pillar[ n ]arenes, [ 3,9 ] etc ., – have been devised for use in separation of chemical mixtures or isomers. The common adsorbing materials exist in solid state and the separation process usually involves gas‐solid interface adsorption.…”