Carbohydrate-Mediated Purification of Petrochemicals

Abstract

Metal−organic frameworks (MOFs) are known to facilitate energy-efficient separations of important industrial chemical feedstocks. Here, we report how a class of green MOFsnamely CD-MOFsexhibits high shape selectivity toward aromatic hydrocarbons. CD-MOFs, which consist of an extended porous network of γ-cyclodextrins (γ-CDs) and alkali metal cations, can separate a wide range of benzenoid compounds as a result of their relative orientation and packing within the transverse channels formed from linking (γ-CD) 6 body-centered cuboids in three dimensions. Adsorption isotherms and liquid-phase chromatographic measurements indicate a retention order of ortho-> meta-> para-xylene. The persistence of this regioselectivity is also observed during the liquid-phase chromatography of the ethyltoluene and cymene regioisomers. In addition, molecular shape-sorting within CDMOFs facilitates the separation of the industrially relevant BTEX (benzene, toluene, ethylbenzene, and xylene isomers) mixture. The high resolution and large separation factors exhibited by CD-MOFs for benzene and these alkylaromatics provide an efficient, reliable, and green alternative to current isolation protocols. Furthermore, the isolation of the regioisomers of (i) ethyltoluene and (ii) cymene, together with the purification of (iii) cumene from its major impurities (benzene, n-propylbenzene, and diisopropylbenzene) highlight the specificity of the shape selectivity exhibited by CD-MOFs. Grand canonical Monte Carlo simulations and single component static vapor adsorption isotherms and kinetics reveal the origin of the shape selectivity and provide insight into the capability of CD-MOFs to serve as versatile separation platforms derived from renewable sources. ■ INTRODUCTIONWith the expanding global demand for petrochemical feedstocks, the development of novel, low-cost materials that reduce the impact of chemical processing on the environment is critically important. Improving the efficiency of the refinement and separation of aromatic hydrocarbons is of particular importance, given the large volumes on which these compounds are produced. The sustained interest in metal− organic frameworks 1 (MOFs) as adsorbents and sequestering agents for industrially important gases, 2−4 e.g., H 2 , CH 4 , CO 2 and N 2 , as well as for the liquid-phase separation of larger molecular compounds, which include (1) constitutional isomers, 5 (2) chiral compounds, 6 (3) aliphatic hydrocarbons, 3b,5b,7 and (4) pharmaceuticals, 8 is leading to MOFs being investigated as alternatives to zeolites 9 and activated carbon 10 as separation media. The improvements 5−7 in separation efficiencies using MOFs over traditional size-and shape-selective materials can be attributed primarily to (i) the physiochemical properties imbedded in their diverse building blocks, (ii) their higher surface areas, and (iii) their larger adsorption capacities, which reduce the amount of adsorbent required for industrial processes. 7a,11 Consequently, MOFs represent emergent materials f...

Biologically derived metal organic frameworks

“…[215] Monte Carlo molecular simulations suggest the γ-CD rings enable selectivity for o-xylene through a favorable host-guest interaction, and efficient packing of the isomer in the framework, which is confirmed by the host-guest interactions from virial equation analysis of vapor isotherms. [215] For isomers such as cymene, their larger size and steric bulk can decrease their ability to form favorable orientations thereby culminating in weaker interactions with the framework, the unctional materials, but they materials. A new artificial elices in the crystalline state helices are arranged threeion.…”

“…[215] One of the most challenging separations in the chemical industry is that of BTEXbenzene, toluene, ethylbenzene, and the regioisomers of xylene, and while they act as antiknocking additives in gasoline, they are also critical chemical feedstocks, thus the need to separate and process them is essential. [216][217][218][219][220][221] Terephthalate-based MOFs with 1-dimensional channels have been the most widely investigated in the separation of aromatic hydrocarbons, [222][223][224][225][226] in particular, both MIL-47 and MIL-53 have demonstrated high o-xylene selectivity based on entropic differences and molecular packing.…”

“…[35,223,229] Stoddart et al recently reported a high selectivity of CD-MOFs (γ-CD) (see section 3.4), which exhibited high shape selectivity, for separation of aromatic hydrocarbons using alkali metal cations. [215] The retention order of o-> m-> p-xylene separation was determined through adsorption isotherms and liquid-phase chromatographic measurements, with impressive regioselectivity of ethyltoluene and cymene regioisomers during the liquid-phase chromatography. [215] Furthermore, this work highlights the specificity of shape selectivity exhibited by CD-MOFs through the isolations of regioisomers of i. ethyl toluene, ii.…”

“…[215] The retention order of o-> m-> p-xylene separation was determined through adsorption isotherms and liquid-phase chromatographic measurements, with impressive regioselectivity of ethyltoluene and cymene regioisomers during the liquid-phase chromatography. [215] Furthermore, this work highlights the specificity of shape selectivity exhibited by CD-MOFs through the isolations of regioisomers of i. ethyl toluene, ii. cymene together with the purification of cumene from major impurities such as benzene, n-propylbenzene, and diisopropylbenzene and iii.…”

Application of Metal-Organic Frameworks in Chromatographic Separation

“…为 此, MOFs 广泛应用于气体吸附 [5,6] 、物质分离 [7,8] 、提 纯 [9] 、催化 [10,11] 等领域, 以及作为模板制备各种功能材 料 [12,13] . 特别是在分离方面, 由于金属-有机骨架材料 的特殊金属位点, 孔道 [14] 和粒径 [15] 的可调性, 使得…”