Continuous conversion of methanol to higher hydrocarbons at ambient pressure

Available online at www.sciencedirect.com| Joumal ofScienceDirect7I Natural GasChemistryEL SEVIERJournal of Natural Gas Chemistry 19(2010)461-462www.elsevier.com/locate/jngcCommunicationContinuous conversion of methanol to higherhydrocarbons at ambient pressureWilliam W. Porterfieldl*，Gordon M. Zrelak2，L. Avery Moncure IMatthew D. Huff3I. Hampden-Sydney College, Hampden Sydney, VA 23943, USA; 2. Pensylvania State University, University Park, PA 16802, USA;3. UNC-Charlote, Charlotte, NC 28223, USA[ Manuscript reeved April 16, 2010; revised July 29, 2010]JomdAbstractAn iodozincate ionic liquid solvent and catalyst is used to convert methanol continuously to a wide variety of hydrocarbons at atmosphericpressure.Key wordsmethanol conversion; zinc iodide; hydrocarbon formalionRecent discoveries of extensive shale- gas depfosits and td FOfficuly of carrying out the reaction ina v(technology to retrieve them have made expandep use of natliscdus med rtUm all further trials were carried out at the Zn3I8ral gas, and more specifically methane, a matfer of natiqyt!interest Inasmuch as methanol is commercNy bprolpuevI mV lethylpiperidinium iodide was prepared by warmingfrom methane, chemical interest has revived whh respect toN-ethylpiperidine with iodoethane in acetone solvent, and theprocesses for the production of liquid hydrocarbon fuels fromsolid product was filtered and dried under vacuum. The ionicmethanol. Several such processes have been well establishedliquid was prepared by combining the appropriate stoichio-[1], but one of the most interesting has been recently reportedmetric quantities of diethylpiperidinium iodide and zinc io-using solid ZnI2 as a Lewis acid catalyst for dehydration [2].dide and heating to about 90 °C until mutual dissolution wasThis reaction occurs in liquid methanol at 200。C, requiring acomplete.sealed tube and approximately two hours. It would be desir-The methanol reaction was carried out using a conveable to have a continuous process, preferably at atmospherictional distillation apparatus with a one-meter column loosepressure, which requires a solvent other than methanol.packed with Raschig rings, heated externally to an internalToward this end, the ionic liquid N,N-diethylpiperidiniumtemperature of 200 °C and flld to a depth of about 50 cmiodozincate ((C2Hs)2NCsH$oZnI3), was investigated, func-with the ionic liquid. The distillation flask was chosen totioning as both solvent and catalyst. The ionic liquid has, typ-make practical volume the smallest, heated by a mantle toically, no significant vapor pressure at high temperatures andprovide a continuous heated column of ionic liquid, and had aoffers a very high concentration of catalyst reactive sites. Theside arm with a septum cap to allw syringe injection of smallionic liquid is prepared simply by melting the piperdinium i0-quantities of methanol into the bottom of the heated columndide with zinc iodide, and the Lewis acidity of the liquid canof ionic liquid. All joints were sealed by Teflon sleeves tobe controlled by adjusting the iodide(base): Znl2(acid) ratio.avoid hydrocarbon contamination. The collection flask was .Most of the work reported here was done in a liquid with 50%vented into a cold trap cooled by acetone slush, and the prod-excess ZnI2, corresponding to a stoichiometric Zn3I8. Otheruct was observed to accumulate both in the flask and the trap.stoichiometries were investigated by increasing ZnI2 up to aNo precautions were taken with respect to the atmosphere, but200% excess, corresponding to Zn3I7; at higher ZnI2 acidity, .the assembly was dried with a heat gun before the ionic liquida slightly wider variety of hydrocarbons was observed, but thewas added.viscosity of the ionic liquid increased and made foaming aVisible condensate appears within 20- 30 min of first in-problem. In view of the very modest change in reaction prod-jection and can be| 中国煤化工distillate in the' Corresponding author. Tel: 434-223-6179; Fax: 434-223- 6024; E mail: wporerfield@ hsc.eduTYHCNM HGCopyrightO2010, Dalian Institute of Chemical P, Chinese Academy of Sciences. All rights reerved.doi:10. 1016/S 1003-9953(09)60114-6Cnemnicalw.st,462William w. Porterfield et al./ Journal of Natural Gas Chemistry Vol. 19 No.52010cqlection flask is in two phases because the reaction (shown; analysis, show-b9ow in its simplest form) produces water and a hydrocarboning aromatic, unsaturated, and saturated H and C atoms withinproduct:extremely complicated spectra.The condensate collecting in the cold trap was a sin-3CH;OH一+ C3H6 + 3H2Ogle phase, primarily propene with a small amount of butenesand iodomethane. The relative quantities of low- and higher-It will be apparent from the form of the reaction equa-molecular-weight products in the cold trap could be shiftedti4h that even with a mixture of hydrocarbon products thesomewhat by changing the ionic-liquid column height and in-mass balance and similar densities of hydrocarbons dictatesjection rate. A longer column and slower injection rate canthe relative volumes of the polar and nonpolar phases. Evenreduce the amount of low-molecular-weight products.as a mixture, the hydrocarbon layer should have a volume ofThe degree of methyl branching in the hydrocarbon mix-about 1.2 ml/mlH2o, and this ratio was consistently seen whenture was studied by 'H NMR on a 400-MHz JEOL instru-hydrocarbons in the cold trap were included.ment. Quantitative mixtures of straight-chain and methylated2 The polar phase in the collection flask is primarily wa-saturated hydrocarbons were prepared and it was verified thatter, with a small amount of unreacted methanol. The nonpolarintegration areas of the CH3, CH2, and CH peaks matched thephase is a mixture of over 20 hydrocarbons, plus a small butknown abundance ratios to within about 2%. On this basis, forvariable amount of CH3I. Conversion of methanol appears toexample, n-octane has a CH3 : CH2 : CH area ratioof 1:2:0be larger than 95% but is not quantitative. The iodomethaneand triptane (2, 2, 3-trimethylbutane) has a ratio of 15:0:1.can be suppressed by using a greater depth of ionic liquid andOur product mixtures varied in degree of branching, but wereaojightly longer reaction temperature, and most injections .usually near a ratio of5 : 2 : 3, indicating considerable branch-wefe made at 210- 220°C. A GCMS chromatogram of aing but not to the degree shown by triptane. Major componenttypical nonpolar phase, taken on a Varian Saturn 2200 ionstructures are indicated in Chart 1 below.trap instrument, is shown in Figure 1. Most peaks could be .tentatively identified from the NIST AMDIS database, making allowances for differences between quadrupole and ion-->+HtYtrap spectra. Identifiable peaks ranged from methylpentenest&hexamethylbenzene, as indicated in Chart 1.>00cb14( 12Chart 1. Major components of methanol reformation as indicated by GC-MSIn summary, the use of the ionic liquid diethylpiperi-dinium iodozincate as a reaction medium allows the conve-nient and continuous catalytic conversion of methanol to acomplex mixture of hydrocarbons, most having a high degreeof methyl branching. The reaction is carried out at atmo-spheric pressure and a convenient elevated temperature, andL Jwwbbwlcan be carried out on a continuous basis.' minAcknowledgementsFigure 1. GC of nonpolar layer from typical product of methanol reformationGMZ thanks Hampden-Sydney College for summer support,in iodozincate liquid, collcted as condensate at room temperature hydrocar-and the department is grateful to many alumni whose donations have(ollection flask)b2provided the instrumentation for this work.It is interesting that this procedure does not appear toReferences .give triptane in unusual amounts, since the procedures of bothPearson [1] and Bercaw [2] yield up to 50% triptyls in their[1] (a) PearsonD E. J C s Chem Comm, 1974, 397. (b) Kim L,hydrocarbon product. It may be speculated that the solutionWald M M, Brandenbergers G. J Org Chem, 1978, 43: 3432cqngditions, in which the solvent is the catalyst and the sub-[2] (a) Bercaw J E, Hazari N, Labinger J A, Scott V J, Sunley GJ.stMate methanol is present in relatively small quantities in anyJ Am Chem Soc, 2008, 130: 11988. (b) Bercaw J E, Diaconescugiven region, may drive the reaction to different products evenP L, Grubbs F-ringer J A,Li X,if the mechanism is basically similar. NMR spectra for the hy-Mehrkhodava中国煤化工VgeP:J0Orgdrocarbon mixtures are consistent with the general character10Chem, 2006YHCNMHG2046[4|b18t/min