Zeolites and metal‐organic frameworks (MOFs) are considered as “competitors” for new separation processes. The production of high‐quality gasoline is currently achieved through the total isomerization process that separates pentane and hexane isomers while not reaching the ultimate goal of a research octane number (RON) higher than 92. This work demonstrates how a synergistic action of the zeolite 5A and the MIL‐160(Al) MOF leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of isomers. This innovative mixed‐bed adsorbent strategy encompasses a thermodynamically driven separation of hexane isomers according to the degree of branching by MIL‐160(Al) coupled to a steric rejection of linear isomers by the molecular sieve zeolite 5A. Their adsorptive separation ability is further evaluated under real conditions by sorption breakthrough and continuous cyclic experiments with a mixed bed of shaped adsorbents. Remarkably, at the industrially relevant temperature of 423 K, an ideal sorption hierarchy of low RON over high RON alkanes is achieved, i.e.,
n
‐hexane ≫
n
‐pentane ≫ 2‐methylpentane > 3‐methylpentane ⋙ 2,3‐dimethylbutane > isopentane ≈ 2,2‐dimethylbutane, together with a productivity of 1.14 mol dm
−3
and a high RON of 92, which is a leap‐forward compared with existing processes.
The adsorption equilibrium and kinetics of CO 2 , CH 4 , and N 2 on three types of BETA zeolites were investigated at different temperatures and a defined partial pressure range from dynamic breakthrough experiments. The adsorbed amount followed the decreasing order of CO 2 > CH 4 > N 2 for all studied materials. For the same ratio of SiO 2 /Al 2 O 3 , the Na-BETA-25 zeolite showed a higher uptake capacity than H-BETA-25, due to the presence of a Na + cationic center. Comparing the same H + compensation cation, zeolite H-BETA-25 expressed a slightly higher adsorption capacity than H-BETA-150. Regarding the selectivity of gases, based on their affinity constants, H-BETA-150 displayed the best ability. The adsorption kinetics was considered using the zero-length-column (ZLC) technique. Response surface methodology (RSM) was applied to evaluate the interactions between adsorption parameters and to describe the process.
A series of isoreticular Zr carboxylate MOFs, MIL-140A, B and C, exhibiting 1D microporous triangular shaped channels and based on different aromatic dicarboxylate ligands (1,4-BDC, 2,6-NDC and 4,4’-BPDC, respectively), were...
The performance of porous metal organic framework ZIF-8 in the separation of all five hexane isomers (nC6, 2MP, 3MP, 23DMB, 22DMB) is evaluated through a series of multicomponent breakthrough adsorption experiments, at the temperatures of 373, 423, and 473 K and up to total hexane isomers pressure of 0.5 bar. The reported data show for all experiments the following sorption hierarchy: nC6 ≫ 2MP > 3MP ≫ 23DMB > 22DMB. At the temperature of 373 K and total hydrocarbon pressure of 0.5 bar the mixture loading of hexane isomers can go up to 2.15 mol•kg −1. In addition, at the same temperature the selectivities measured by the ratio of the loadings between linear plus monobranched (nC6, 2MP, 3MP) relatively to the dibranched (23DMB, 22DMB) isomers range between 34−55. The results also show that the sorption of nC6 is equilibrium based in contrast with the sorption of branched isomers which is kinetically controlled. The dibranched isomer 22DMB is practically excluded from the framework followed closely by 23DMB. The adsorption equilibrium experimental data are modeled by the Sips isotherm and the breakthrough data are simulated through a mathematical model developed in Matlab code using the method of lines (MOL), the results being in qualitative agreement. From the numerical simulations it was found that diffusivity of the branched paraffins in ZIF-8 is 2 orders of magnitude lower than for the linear nC6, and that the diffusivity of the dibranched paraffins is three times lower than for the monobranched ones. This work shows that ZIF-8 has the ability to purely separate the linear nC6 from its branched isomers and partially separate mono-from dibranched isomers if proper experimental conditions are setup, the result being important for the octane upgrade of gasoline.
Single-
and multicomponent adsorption fixed bed breakthrough experiments
of carbon dioxide (CO2), methane (CH4), and
nitrogen (N2) on commercial binder-free beads of 4A zeolite
have been studied at 313, 373, and 423 K and a total pressure of up
to 5 bar. The ternary experiments (CO2/CH4/N2) show a practically complete separation of CO2 from CH4/N2 at all the temperatures studied,
with selectivity at 313 K of CO2 around 24 over CH4 and 50 over N2. The adsorption equilibrium data
measured from the breakthrough experiments were modeled by the dual-site
Langmuir isotherm, and the breakthrough results were simulated with
a fixed bed adsorption model taking into account axial dispersion,
mass-transfer resistances, and heat effects. The mathematical model
predicts with a good accuracy the systematic behavior of the single-
and multicomponent breakthrough results based on the independent parameters
calculated from well-established correlations and intracrystalline
diffusivities for zeolite 4A available in the literature. The results
showed in the present work evidence that the binder-free beads of
zeolite 4A can be employed to efficiently separate CO2 from
CO2/CH4/N2 mixtures by fixed bed
adsorption.
Zeolites and Metal Organic Frameworks (MOFs) have frequently been considered as “competitors” for the development of new advanced separation processes. The production of high quality gasoline is currently achieved through the energy demanding conventional Total Isomerization Process (TIP) that separates pentane and hexane isomers while not reaching yet the ultimate goal of a Research Octane Number (RON) higher than 92. Herein we demonstrate how an unprecedented synergistic action of two complementary benchmark materials of each family of porous solids, a commercially available zeolite, 5A and the bio-derived Al-dicarboxylate MOF MIL-160(Al), leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of pentane and hexane isomer mixtures into fractions of low and high research octane number (RON). This innovative mixed bed adsorbent strategy encompasses a thermodynamically-driven separation of hexane isomers according to the degree of branching by MIL-160(Al) coupled to a steric rejection of pentane and hexane linear isomers by the molecular sieve zeolite 5A. The adsorptive separation ability of this MOF/zeolite duo was further evaluated under industrial operating conditions by sorption breakthrough and continuous cyclic experiments with a mixed bed of shaped adsorbents. Remarkably, at the industrially relevant temperature of 423 K, an ideal sorption hierarchy of low RON over high RON alkanes is achieved, i.e., n-hexane >> n-pentane >> 2-methylpentane > 3-methylpentane >>> 2,3-dimethylbutane > isopentane ≈ 2,2-dimethylbutane, and an exceptional ideal productivity of 1.14 mol.dm-3 is attained for a final high RON isomers product of 92, which corresponds to a substantial leap-forward when compared with existing processes.
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