octane enhancement by the selective separation of branched and linear paraffins in naphthas using a...

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Fuel xxx (2013) xxx–xxx

JFUE 7478 No. of Pages 7, Model 5G

23 September 2013

Contents lists available at ScienceDirect

Fuel

journal homepage: www.elsevier .com/locate / fuel

Octane enhancement by the selective separation of branched and linearparaffins in naphthas using a PVDC-PVC carbon molecular sieve

0016-2361/$ - see front matter � 2013 Published by Elsevier Ltd.http://dx.doi.org/10.1016/j.fuel.2013.09.036

⇑ Corresponding author. Tel.: +52 55 91756615; fax: +52 55 91758429.E-mail addresses: [email protected] (G.C. Laredo), [email protected] (J.L. Cano),

[email protected] (J. Castillo), [email protected] (J.A. Hernandez), [email protected](J.O. Marroquin).

Please cite this article in press as: Laredo GC et al. Octane enhancement by the selective separation of branched and linear paraffins in naphthasPVDC-PVC carbon molecular sieve. Fuel (2013), http://dx.doi.org/10.1016/j.fuel.2013.09.036

Georgina C. Laredo ⇑, Jose Luis Cano, Jesus Castillo, Jose A. Hernandez, Jesus O. MarroquinPrograma de Procesos de Transformacion, Instituto Mexicano del Petroleo, Lazaro Cardenas 152, Mexico 07730 D.F, Mexico

h i g h l i g h t s

� Separation of linear and branchedalkanes was accomplished by anadsorption process.� PVDC carbon molecular sieve

presented a higher adsorptioncapacity than silicalite-1.� PVDC carbon molecular sieve

presented better selectivityproperties than silicalite-1.� A higher octane number increment

was obtained from PVDC CMS thanfrom silicalite-1.

g r a p h i c a l a b s t r a c t

454647484950515253545556

a r t i c l e i n f o

Article history:Received 29 June 2012Received in revised form 6 September 2013Accepted 10 September 2013Available online xxxx

Keywords:GasolineLinear paraffinsMultibranchedParaffinsSilicalite-1

575859

a b s t r a c t

Silicalite-1 samples and PVDC based Carbon Molecular Sieve (CMS-IMP12) material were compared inthe separation of linear and multi-branched paraffins present in a real feedstock by fixed bed adsorptionexperiments. The CMS-IMP12 material was obtained from the pyrolysis of a poly-(vinylidene choride-co-vinyl chloride) (PVDC-PVC) polymer commercially known as Saran™. Material balances of the break-through experiments showed higher adsorption capacities for the CMS-IMP12 (5.4–8.8 g/100 g-adsor-bent) than for silicalite-1 (1.2–3.4 g/100 g-adsorbent) at the temperature range studied (175–325 �C).Additionally, the octane number increment for the CMS-IMP12 was at least 4 units higher for the sameamount of recovered non-adsorbed fraction (1.5 g/100 g-adsorbent). In order to simplify the descriptionof the hydrocarbon mixture, the alkanes were classified according to their degree of branching as: linear,monomethyl, dimethyl (non-gem), dimethyl (gem) and trimethyl alkanes. Similarly, cycloalkanes as:non-branched (cyclopentane and cyclohexane), monomethyl, dimethyl (non-gem), dimethyl (gem) andtrimethyl cycloalkanes, where gem refers to the relationship between two methyl groups that areattached to the same carbon atom. The CMS-IMP12 was able to separate gem-dimethylalkanes, gem-dim-ethylcycloalkanes and trimethylalkanes, while silicalite-1 was less selective.

� 2013 Published by Elsevier Ltd.

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1. Introduction molecular structure. The octane number for a gasoline-type fuel 67
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Gasoline is essentially a complex mixture of hydrocarbons thatboils below 200 �C (390 �F). The hydrocarbon constituents in thisboiling range are those that have 4–12 carbon atoms in their

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is measured by its anti-knocking capacity. A higher octane numberin gasoline is usually desirable. It is known that normal paraffinshave the least desirable knocking characteristics and this becomesprogressively worse as the molecular weight increases. Isoparaffinshave higher octane numbers than the corresponding normal iso-mers and the octane number increases as the degree of branchingof the chain is increased [1]. In this context, materials such aszeolites and carbon molecular sieves (CMS) have the surfacecomposition, area and porosity suitable for the shape selectivity

using a

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2 G.C. Laredo et al. / Fuel xxx (2013) xxx–xxx


23 September 2013

in separations [2]. This separation has been widely studied usingzeolites 5A, ZSM-5, mordenite, HAY, NaAY, NaAUSY, ZSM-5,ZSM-22, beta and silicalite-1, in the gas and liquid phase [3]. Aninteresting source for preparing microporous carbons are the poly-vinylidene chloride (PVDC) copolymers, these carbons have beentested for the selective separation of alkanes by degree of branch-ing by several authors [4–12]. Dacey and Thomas [4] observed thepossible separation between isopentane and neopentane. Lamondet al. [5] proved that PVDC carbons obtained by pyrolysis above1200 �C demonstrated good adsorption for isopentane excludingneopentane. According to Adams et al. [6] those molecules smallerthan 0.4–0.5 nm like n-hexane, were readily adsorbed into microp-ores whereas the bigger molecules (2,2-dimethylbutane and2,2,4-trimethylpentane) were adsorbed at a slightly lower capac-ity. Kramer [7] described that after the separation by adsorptionfrom a mixture composed by 2-methylpentane, 2,3-dimethylbu-tane, 2,2-dimethylbutane, 2,4-dimethylhexane, 2,5-dimethylhex-ane, 2,3,4-trimethylpentane and 2,2,4-trimethylpentane using aCMS material, the octane number of the non-adsorbed fractionincreased. Barton et al. [8,9] presented some heat of immersiondata at 27 �C for 3-methylpentane, 3-methylhexane, 2,3-dimethyl-butane, 2,4-dimethylpentane, 2,2,3-trimethylbutane, 2,2,4-trim-ethylpentane and 2,2,5-trimethylhexane in the liquid phase.Carbons presented a uniform array of pores in the range of0.55–0.6 nm, which are not capable of adsorbing branched alkaneswith two or more methyl groups and especially when alkyl groupsare attached to the same carbon atom. Fernández-Morales et al.[10], by comparing the heat of adsorption data for different linearand branched hydrocarbons, were able to estimate the limitingaperture size of the carbon pores to be less than 0.62 nm. It hasbeen reported by Jiménez-Cruz et al. [11] that 2-methylheptanewas better adsorbed than n-heptane into PDVC-based microporouscarbon (CMS-IMP12), which was prepared from the pyrolysis ofpoly-(vinylidene chloride-co-vinyl chloride) copolymer (PVDC-PVC).Laredo et al. [12] performed thermodynamic studies at 325, 350and 400 �C and isomers partial pressures from 6.9 to 12.8 Pa forfour C8 isomers (n-octane, 2-methylheptane, 2,5-dimethylhexaneand 2,2,4-trimethylpentane). The adsorption capacities obtainedranged from 0.5 to 3.0 g/100 g with 2,2,4-trimethylpentane to bethe least adsorbed hydrocarbon.

In this work, we report the results on the selectivity of separationby adsorption in experimental evaluations using a real feedstockconstituted by linear and branched alkanes using CMS-IMP12(a material obtained from the calcination of Saran™) and silicalite-1,a well-known material employed for performing the same task.

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2. Materials and methods

2.1. Material

CMS-IMP12 was prepared from pyrolysis of poly-(vinylidenechloride-co-vinyl chloride) (PVDC-PVC, Saran™) following the

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Table 1Physical properties of CMS-IMP12 and silicalite-1.

CMS-IMP12 Silicalite-1

Averaged channel size, nm 0.5–0.833 0.51–0.550.53–0.56

Physical properties of the particlesApparent density, g/cm3 0.95 1.06Particle density, g/cm3 1.52 1.76

Adsorbent properties calculated by the t-plot analysis14-16

BET surface area, m2/g 968 416Micropore area, m2/g 873 101External surface, m2/g 95 315Micropore volume Dubinin-Radushkevich, mL/g 0.40 0.22

Please cite this article in press as: Laredo GC et al. Octane enhancement by thePVDC-PVC carbon molecular sieve. Fuel (2013), http://dx.doi.org/10.1016/j.fue

technique described in Jiménez-Cruz et al. [11]. Detailed descrip-tion of chemical characterization is provided in the same paper.

Silicalite-1 was prepared following the technique described inGuth et al. [13]. The nature and purity of the silicalite-1 samplewas determined by X-ray powder diffraction (Siemens D500 dif-fractometer) with Cu Ka radiation.

Surface properties were obtained using a Micromeritics ASAP-2000 apparatus in agreement with the BET method at 77 K. Calcu-lations according to the t-plot analysis [14–16] are shown inTable 1.

2.2. Feedstocks preparation

The C5AC8 naphtha was obtained from La Cangrejera petro-chemical complex. Small proportions of aromatics and alkene com-pounds were eliminated by a standard hydrogenation procedure,in which the C5AC8 naphtha was hydrotreated in a fixed bed pilotplant at the following conditions: 180 �C, LHSV 2 h�1, hydrogen tooil ratio 232 m3/m3 and 3.0 MPa pressure, employing a commercialNi/SiO2 catalyst (L-3427 United Catalyst Inc.). The hydrotreatedC5AC8 naphtha was composed by a mixture of branched and cyclichydrocarbons (Table 2). Octane number data of the hydrocarbonsfrom the literature is also provided [17–21].

2.3. Characterization of feedstocks and products

Feedstocks and products were subjected to a detailed chemicalcharacterization following the ASTM 6623-01 procedure appropri-ate for gasoline distillates [22] using an Agilent 6890 series chro-matographic system. Resulting chromatograms were analyzed bya ChemStation employing the Hydrocarbon Expert, version 3 soft-ware (GC/PIANO). Octane numbers (ON) were provided by thesame software.

2.4. Breakthrough experiments

Experiments were performed in the vapor phase by pumpingupwards (5 mL/min) the naphtha from the bottom of a columnfilled with approximately 90 g of the adsorbent material alreadysieved to 80/120 mesh (silicalite-1 or CMS-IMP12), set at the tem-perature of the experiment (175, 250, 325 �C). The adsorption col-umn consists of 26.6 mm i.d. stainless steel column 395 mm inlength (220 mL). Due to the differences in bulk density of theadsorbents tested (0.68 and 0.59 g/ml for the CMS-IMP12 and sili-calite-1) the rest of the volume was filled with an inert. Pressurewas in the range of 262 kPa to 289.6 kPa. The adsorption vesselwas followed by a heat interchanger column consisting of stainlesssteel condensation column with 30 mm i.d. and 150 mm of length,cooled with an 80/20 water/propanol mixture. Time was set to zeroat the beginning of the pumping procedure and recorded when thefirst drop appeared. The adsorption was followed by condensing2 mL samples until equilibrium was reached. The pump wasstopped and then nitrogen (200 mL/min) was flushed downwardsfor draining of the remaining fluid (0.5–3 min). The temperaturewas raised to 400 �C and nitrogen (50 mL/min) was flushed down-wards through the column for desorption until no more materialcould be condensed. Desorbed product was collected andweighted. All the products were sent to analysis.

2.5. Data treatment

In order to understand the behavior of the material on the sep-aration of the feedstock, the following classification accordinghydrocarbon type and degree of branching was made:

Alkanes: linear, monomethyl, dimethyl (non-gem), dimethyl(gem), trimethyl.

selective separation of branched and linear paraffins in naphthas using al.2013.09.036


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Table 2Chemical composition of the feedstock.

Compound Short name Octane number [17–21] Wt% Compound Short name Octane number [17–21] Wt%

n-Pentane nC5 62.15 2.26 3,3-Dimethylpentane 33DMC5 83.7 0.68n-Hexane nC6 25.4 19.39 3,3-Dimethylhexane 33DMC6 79.45 0.06n-Heptane nC7 0 4.32 3,4-Dimethylhexane 34DMC6 79 0.01n-Octane nC8 �17 0.32 2-Methyl-3-ethylpentane 2M3EC5 0.02

3-Methyl-3-ethypentane 3M3EC5 84.75 0.03

i-Pentane 2MC4 91.3 0.422-Methylpentane 2MC5 73.45 21.57 2,2,3-Trimethylbutane 223TMC4 106.7 0.112-Methylhexane 2MC6 44.4 5.05 2,2,3-Trimethylpentane 223TMC5 104.75 0.012-Methylheptane 2MC7 21.8 0.33 2,2,4-Trimethylpentane 224TMC5 100 0.013-Methylpentane 3MC5 74.4 17.21 2,3,4-Trimethylpentane 234TMC5 99.2 0.013-Methylhexane 3MC6 53.9 6.40 2,3,4-Trimethylhexane 234TMC6 86.5 0.013-Methylheptane 3MC7 30.9 0.42 2,2,5-Trimethylhexane 225TMC6 89.5 0.014-Methylheptane 4MC7 32.85 0.173-Ethylpentane 3EC5 67.15 0.71 Cyclopentane CC5 93.13 1.893-Ethylhexane 3EC6 42.95 0.11 Cyclohexane CC6 80.1 0.08

Methylcyclopentane MCC5 85.65 1.48

2,2-Dimethylbutane 22DMC4 92.6 4.46 Methylcyclohexane MCC6 72.92 1.362,2-Dimethylpentane 22DMC5 94.2 0.82 Ethylcyclopentane ECC5 64.20 0.092,2-Dimethylhexane 22DMC6 74.92 0.09 1,1-Dimethylcyclopentane 11DMCC5 90.8 0.062,3-Dimethylbutane 23DMC4 98.9 4.51 1t,2-Dimethylcyclopentane 1t2DMCC5 81 0.182,3-Dimethylpentane 23DMC5 89.8 2.04 1c,2-Dimethylcyclopetane 1c2DMCC5 81 0.082,3-Dimethylhexane 23DMC6 75.1 0.11 1c,3-Dimethylcyclopentane 1c3DMCC5 76.15 0.152,4-Dimethylpentane 24DMC5 83.45 1.12 1t,3-Dimethylcyclopentane 1t3DMCC5 76.6 0.202,4-Dimethylhexane 24DMC6 67.55 0.17 1,1,3-trimethylcyclopentane 113TMCC5 85.6 0.022,5-Dimethylhexane 25DMC6 55.45 0.09 Other 0.82

Total 61.9 100

G.C. Laredo et al. / Fuel xxx (2013) xxx–xxx 3


23 September 2013

Cycloalkanes: non-branched (CC5 and CC6), monomethyl, di-methyl (non-gem), dimethyl (gem), trimethyl.

Gem refers to the relationship between two methyl groups thatare attached to the same atom. Examples of this classification areshown in Fig. 1.

Breakthrough curves were made considering this classification.Material balances were obtained by a modification of a procedureemployed by Barcia et al. [23] in the separation of a multi-compo-nent mixture. The equilibrium loadings were obtained by Eq. (1)and the integration of the adsorption curves (Bi) as shown in Fig. 2:

qi ¼Qm

� �ðqXiÞBi ð1Þ

where qi is the amount of hydrocarbon i adsorbed, Q is the hydro-carbon feed rate, m is the mass of adsorbent, q is the density ofthe feed, and Xi is the fraction of the hydrocarbon i in the mixturein weight.

Calculations were made assuming that the equilibrium wasreached shortly after the first 2 mL (1.5 g) of the feed were recov-ered as a non-adsorbed fraction.

3. Results and discussion

Properties of the CMS-IMP12 and silicalite-1 are shown in Ta-ble 1. A more detailed description of the synthesis and propertiesof the CMS-IMP12 can be seen elsewhere [11,12]. X-ray of the sil-icalite-1 (Fig. 3) coincides with published data [24].

Comparisons of adsorption selectivity of the lumped dataaccording to the classification described in the experimental part,were obtained by means of breakthrough curves of the real feedat different temperatures (175, 250 and 325 �C) with both CMS-IMP12 and silicalite-1. Values of C/C0 were calculated. Figs. 4–6show the behavior of the CMS-IMP12 at different temperatures.As we may see from these figures (Figs. 4–6), different families ofcompounds presented displacement patterns of adsorptiondepending on their structure [2]. Comparison of their selectivityat all the temperatures tested, showed that hydrocarbons havinga quaternary carbon on their structure like gem-dimethylalkanes,


gem-dimethyl cycloalkanes and trimethylalkanes diffused fasterthan branched hydrocarbons without a quaternary carbon (gemcarbon) on their structure like monomethyl alkanes, non-gem di-methyl alkanes, cycloalkanes and all non-gem-branched cycloal-kanes (mono and dimethyl cycloalkanes), and finally faster thanlinear alkanes, which were the slowest. These faster diffusing spe-cies entered first into the material but were desorbed as the slowerdiffusing species penetrated, appearing as if they were totally pre-cluded from this material. The results found here, although onlypartially in agreement with our previous experiments with singlehydrocarbons in very dilute concentrations [12] proved that theseparation of hydrocarbon mixtures using molecular sieves isstrongly dependent on the initial composition and temperatureof the experiment. According to Yonli et al. [25] in adsorptionexperiments in Na6ZSM-5, carried out with equimolar concentra-tions of monobranched and dibranched alkanes, the mono-branched isomer was preferentially adsorbed, whereas when themolar percentages of the isomers were different in the initial mix-ture the adsorption of the higher concentration isomer wasfavored.

In the case of silicalite-1, (Figs. 7–9) although some selectivitybehavior was observed, the differences between the hydrocarbonsfamilies were less significant. It seems that in silicalite-1 undiffer-entiated faster diffusing species (all families except linear alkanes)were desorbed as the slower diffusing species (linear alkanes)penetrated.

Results of the adsorption behavior of both CMS-IMP12 and sil-icalite-1 are in Tables 3 and 4. Data regarding octane number ofthe hydrocarbons involved is also provided. In the upper part ofthe Tables the chemical distribution of the non-adsorbed fractionis shown. The initial non-adsorbed fraction (1.5/100 g of adsor-bent) presented an increment of 20, 18 and 16 octane numbersdue to the 4–7 times enrichment of the highest octane hydrocar-bons. This type of enrichment was observed also with silicalite-1,but in a less important way (1.4–3). Therefore the octane numberincrements observed were from 11 to 17. In the bottom of the ta-bles, the composition of the adsorbed fraction can be observed. TheCMS-IMP12 material attained the extraordinary octane increment



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Fig. 2. Schematic diagram showing the method used to calculate the amountadsorbed from breakthrough curves of a tri-component experiment.

Fig. 3. X-ray profile from silicalite-1.

Alkanes Cycloalkanes

R

R

Linear [L] Non branched [C]

R

R

Methyl [MA] Methyl [MC]

R

R

Dimethyl (non gem) [DMA (ng)] Dimethyl (non gem) [DMC (ng)]

R

R

Dimethyl (gem) [DMA (g)] Dimethyl (gem) [DMC (g)]

R

R

Trimethyl [TMA] Trimethyl [TMC]

Fig. 1. Classification of hydrocarbons according number and type of branching (R@H, Alkyl).



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by allowing an adsorption capacity of 8.8, 7.2 and 5.3 g/100 g-adsorbent at 175, 250 and 325 �C, while the silicate was able to ad-sorb 3.4, 1.9 and 1.2 g/100 g-adsorbent. The adsorption capacitydecreased as the temperature increased for both materials.


Fig. 10 shows calculations considering values of average octanenumbers versus fraction adsorbed according to the followingequation:

fAi¼ CAi

� 100CAiþ CNAi

ð2Þ

where fAi is the fraction adsorbed of the i family, and CAi is the chem-ical composition of each family according to the description on Ta-



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Fig. 4. Breakthrough curves for the hydrocarbon separation using CMS-IMP12 at175 �C.



Fig. 7. Breakthrough curves for the hydrocarbon separation using silicalite-1 at175 �C.





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bles 3 and 4. Some of the families like non-gem-dimethylalkanesand cycloalkanes, presented similar averaged octane numberstherefore, they were lumped together. It is clear from Fig. 10


that gem-dimethylalkanes, gem-dimethylcycloalkanes and trim-ethylalkanes present the highest octane numbers and are the leastadsorbed hydrocarbons in both materials, however, CMS-IMP12



Table 3Chemical composition by hydrocarbon type for the CMS-IMP12 separation: material balance and octane number.

Short name Averaged octane number Feed Non-adsorbed fraction

175 �C 250 �C 325 �C

AlkanesLinear LA 18 26.953 3.729 6.477 9.594Methyl MA 53 53.642 37.631 41.378 44.893Dimethyl (non-gem) DMA (ng) 76 8.261 10.480 10.839 10.679Dimethyl (gem) DMA (g) 85 6.287 41.993 35.012 28.450Trimethyl TMA 100 0.150 0.946 0.791 0.636

CycloalkanesNon-branched C 87 2.018 2.523 2.753 2.980Methyl MC 74 1.974 1.686 1.853 1.926Dimethyl (non-gem) DMC (ng) 81 0.629 0.572 0.538 0.565Dimethyl (gem) DMC (g) 91 0.066 0.430 0.345 0.264Trimethyl TMC 87 0.018 0.010 0.013 0.014

Weight, g/100g-adsorbent 1.50 1.50 1.50Octane Number 61.9 82.4 80.2 77.5

Adsorbed fraction

AlkanesLinear LA 18 39.727 38.111 33.092Methyl MA 53 50.578 51.294 56.082Dimethyl (non-gem) DMA (ng) 76 5.822 6.235 6.462Dimethyl (gem) DMA (g) 85 0.456 0.826 0.837Trimethyl TMA 100 0.027 0.041 0.105

CycloalkanesNon-branched C 87 0.963 1.045 0.855Methyl MC 74 1.750 1.885 1.914Dimethyl (non-gem) DMC (ng) 81 0.651 0.530 0.615Dimethyl (gem) DMC (g) 91 0.008 0.012 0.016Trimethyl TMC 87 0.017 0.020 0.023

Weight, g/100g-adsorbent 8.75 7.17 5.34Octane Number 53.8 56.9 57.6

Table 4Chemical composition by hydrocarbon type for the silicalite-1 separation: material balance and octane number.

Short name Averaged octane number Feed Non-adsorbed fraction

175 �C 250 �C 325 �C

AlkanesLinear LA 18 26.953 2.596 9.334 11.635Methyl MA 53 53.642 55.329 57.171 58.958Dimethyl (non-gem) DMA (ng) 76 8.261 17.828 14.376 13.694Dimethyl (gem) DMA (g) 85 6.287 15.971 12.197 9.525Trimethyl TMA 100 0.150 0.421 0.323 0.262

CycloalkanesNon-branched C 87 2.018 3.743 3.082 2.682Methyl MC 74 1.974 2.762 2.386 2.250Dimethyl (non-gem) DMC (ng) 81 0.629 1.143 0.974 0.869Dimethyl (gem) DMC (g) 91 0.066 0.152 0.117 0.093Trimethyl TMC 87 0.018 0.057 0.041 0.032

Weight, g/100g-adsorbent 1.50 1.50 1.50Octane number 61.9 78.5 75.8 73.3

Adsorbed fraction

AlkanesLinear LA 18 38.375 33.995 36.800Methyl MA 53 47.932 51.786 49.313Dimethyl (non-gem) DMA (ng) 76 6.200 5.876 4.294Dimethyl (gem) DMA (g) 85 3.774 4.601 4.816Trimethyl TMA 100 0.128 0.071 0.088

CycloalkanesNon-branched C 87 0.922 1.208 2.198Methyl MC 74 1.852 1.877 1.936Dimethyl (non-gem) DMC (ng) 81 0.737 0.523 0.515Dimethyl (gem) DMC (g) 91 0.064 0.054 0.030Trimethyl TMC 87 0.018 0.009 0.010

Weight, g/100g-adsorbent 3.44 1.94 1.15Octane number 53.4 55.65 56.1



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Please cite this article in press as: Laredo GC et al. Octane enhancement by the selective separation of branched and linear paraffins in naphthas using aPVDC-PVC carbon molecular sieve. Fuel (2013), http://dx.doi.org/10.1016/j.fuel.2013.09.036


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Fig. 10. Adsorbed fractions versus hydrocarbon type at 175, 250, and 325 �C, usingCMS-IMP12 and silicalite-1. The averaged octane numbers are in brackets.



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provided a sharper separation of these hydrocarbons than silicalite-1. The final results show that the initial non-adsorbed material(1.5 g/100 g-adsorbent) with CMS-IMP12 has almost 4 octane num-bers more than the equivalent fraction obtained with silicalite-1.

Simplification of the observed breakthrough patterns and thedevelopment of a mathematical model for explaining these resultsare in course.

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4. Conclusions

Comparison of the selectivity for the separation of the hydrocar-bons from a real feedstock on a carbon molecular sieve obtainedfrom the carbonization of a Saran material (CMS-IMP12), and sili-calite-1 in gas phase is presented. Regarding adsorption, all hydro-carbons without a gem carbon in their structure are more adsorbedon the CMS than in the silicalite-1. Both higher selectivity andadsorption capacity for the CMS material allowed this material toprovide a higher octane number of the non-adsorbed fraction thanthe product from silicalite-1 at the same experimental conditions.Therefore CMS-IMP12 seems to be a promising material for highoctane-low environmental impact gasoline production by anadsorption process in gas phase.

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[3] Laredo GC, Trejo-Zarraga F, Jimenez-Cruz FJ, Garcia-Gutierrez JL. Separation oflinear and branched paraffins by adsorption processes for gasoline octanenumber improvement. Rec Pat Chem Eng 2012;5:153–73.

[4] Dacey JR, Thomas DG. Adsorption on saran charcoal. A new type of molecularsieve. Trans Faraday Soc 1954;50:740–8.

[5] Lamond TG, Metcalfe JE, Walker PL. 6 Å molecular sieve properties of saran-type carbons. Carbon 1965;3:59–63.

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octane enhancement by the selective separation of branched and linear paraffins in naphthas using a...

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