Conversion to Hydrocarbons

Methanol Conversion to Hydrocarbons. The conversion of methanol to hydrocarbons requires the elimination of oxygen, which can occur in the form of H20, CO, or C02. The reaction is an exothermic process the degree of exothermicity is dependent on product distribution. The stoichiometry for a general case can be written as in Eq. (3.45)  

The products may be alkenes, cycloalkanes, or mixtures of alkanes and aromatics. 

When alkanes are the sole products, Eqs. (3.46)-(3.49) represent the principal reactions with the formation of water, hydrogen, coke, and carbon oxides as byproducts eq. (3.49) describes the formation of aromatics  

Methanol can be converted to hydrocarbons over acidic catalysts. However, with the exception of some zeolites, most catalysts deactivate rapidly. The first observation of hydrocarbon formation from methanol in molten ZnCl2 was reported in 1880, when decomposition of methanol was described to yield hexamethylbenzene and methane.414 Significant amounts of light hydrocarbons, mostly isobutane, were formed when methanol or dimethyl ether reacted over ZnCl2 under superatmo-spheric pressure.415 More recently, bulk zinc bromide and zinc iodide were found to convert methanol to gasoline range (C4-C13) fraction (mainly 2,2,3-trimethyl-butane) at 200°C with excellent yield ( 99%).416 

P205 was also reported to decompose methanol to mixtures of hydrocarbons with widely varying compositions.417 418 Polyphosphoric acid is unique in effecting the transformation of methanol under comparatively mild conditions (190-200°C)418 Superacidic TaF5 and related halide catalysts419 420 condense methanol to saturated hydrocarbons of the gasoline range at 300°C. 

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Methanol conversion to hydrocarbons over various zeolites (370X, 1 atm, 1 LHSV)... 

As shown in Scheme 1 (17,19,21), rapid catalytic addition of to I produces Ilia and Illb. The presence of Ilia and the absence of Illb in the products is at least qualitatively consistent with the fact that the former is kinetically favored while the latter is thermodynamically favored (17,19,21). Structure-reactivity relationships provide a preference for hy-drogenolysis of the N-C(2) bond rather than the C(8a)-N bond in Ilia producing V rather than 3-phenylpropylamine. Both Ilia and Illb are converted to decahydroquinoline (VI), mass 139 the rate constant for the latter conversion is significantly greater than the one for the former (17,19,21). The absence of significant amounts of VI in the products is consistent with its facile conversion to hydrocarbons and NH (17,19,21,35). 

The turnover frequencies reported for the Fischer-Tropsch synthesis are small. In the publication of Vannice (2) the turnover frequencies for CO-conversion to hydrocarbons range from... 

By using the steady state kinetic equations, it is then possible to express k and k3 as a function of the overall turnover frequency for CO-conversion to hydrocarbons (Nco), the overall turnover frequency for methane formation (NCH ), the probability for chain growth (a), the steady state coverage of the precursor A and the value of the equilibrium constant K. In table I the expressions for the kj and k are given. 

Direct Methane Conversion to Hydrocarbons and Chemical Derivatives... 

AIPO4 is isoelectronic with silica and, as such, readily forms glasses and Si02-like crystalline materials. As well, framework stmctmes similar to zeolites may be prepared by the use of amines as templates. Like zeolites, these are active in catalytic reactions such as methanol conversion to hydrocarbons (seeZeolites) As a ceramic material, AIPO4 is an infusible material that is insoluble in water but is soluble in alkali hydroxides. It is often used with calcium sulfate and sodium silicate for dental cements. AIPO4 is also used as a white pigment that also acts as a corrosion inhibitor. 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

We also studied the effect of ion exchange with on the catalytic activity of acid-treated Bent (H -Bent ), sometimes called activated clay. The results are given in Table IV. H" -Bent is virtually the same as H -Bent in catalytic activity. However, the catalytic activity of Ti -Bent for methanol conversion to hydrocarbons is much higher than that of Ti -Bent. The hydrocarbon yield reaches 90%, and the products, in addition to methane, are primarily olefins lower than Ce. The selectivity for olefin formation is estimated to be 90% or higher based on C2 and C3 hydrocarbon product distribution. Ti -Bent appears to surpass the phosphorus compound-modified zeolite proposed by Kaeding and Butter (31) in selective activity for olefin formation, and has the potential to exceed H-Fe-silicate (32) and Ni-SAPO-34 (33), proposed recently by Inui et al. 

Dithiolanes, also named five-membered 1,3-dithioacetals or A,3 -acetals, find wide applications in organic synthesis, particularly in protection of carbonyl functions and their reductive conversion to hydrocarbons or olefins. Due to the stability of 1,3-dithiolanes toward various reagents and reaction conditions, they have attained an important position in this area despite the fact that dedithioacetalization to the corresponding carbonyl compounds is sometimes not an easy process. There are three general strategies that can be used for deprotection of 1,3-dithiolanes involving... 

Lefebvre et al. (170) have conducted the high pressure CO + H2 reaction (30 atm, 503-523 K) over Rh-NaY catalysts. Whatever the rhodium precursors [e.g., Rh -NaY and Rh (CO)2-NaY], the reaction data were similar. This is in agreement with the fact that all the precursors were ultimately converted to Rh6(CO),6 under catalytic conditions. The external Rh crystals deposited on the zeolite surface exhibit significant activity for hydrocarbons, mainly methane, whereas the carbonyl clusters gave lower conversion to hydrocarbons with a small amount of oxygenates such as methanol and ethanol. 

It would seem that a more practical approach to the upgrading of pyrolytic liquids from biomass is to utilize what is already on hand, namely, the oxygenated product liquids. Instead of conversion to hydrocarbons, which usually requires severe reaction conditions, why not convert the liquids by simple chemistry to other liquids that are suitable for use as motor fuels or additives Although not directly related to pyrolysis, this approach has been pursued in... 

Thiophene HDS was performed at 673 K in a microflow reactor with on-line gas chromatography (GC) analysis. The catalyst samples (200 mg) were pre-sulfided in situ using conditions described in the preparation section. The reaction mixture consisting of 4.0 mol% thiophene in H2 was fed through the reactor and was analyzed every 35 min (flow rate 50 ml min , 673 K, 1 bar). First order rate constants for thiophene conversion to hydrocarbons (Khds) and the consecutive hydrogenation of butene (knyo) were calculated as described elsewhere [8]. 

Methanol conversion to hydrocarbons has been studied In a flow micro reactor using a mixture of C-methanol and ordinary C-ethene (from ethanol) or propene (from Isopropanol) over SAPO-34, H-ZSM-5 and dealumlnated mordenlte catalysts In a temperature range extending from 300 to 450 °C. Space velocities (WHSV) ranged from 1 to 30 h. The products were analyzed with a GC-MS Instrument allowing the determination of the Isotopic composition of the reaction products. The Isotope distribution pattern appear to be consistent with a previously proposed carbon pool mechanism, but not with consecutive-type mechanisms. 

On the other hand, it was proposed that acid catalyzed reactions such as skeletal isomerization of paraffin [2], hydrocracking of hydrocarbons [3] or methanol conversion to hydrocarbon [4] over metal supported acid catalysts were promoted by spillover hydrogen (proton) on the acid catalysts. Hydrogen spillover phenomenon from noble metal to other component at room temperature has been reported in many cases [5]. Recently Masai et al. [6] and Steinberg et al. [7] showed that the physical mixtures of protonated zeolite and R/AI2O3 showed high hydrocracking activities of paraffins and skeletal isomerization to some extent. 

Catalytic hydrogenation of CO2 to hydrocarbons is classified into two categories. The one is direct hydrogenation fix)m H2/CO2 to hydrocarbons. The other is indirect process which includes methanol sjmthesis fix>m H2/CO2, followed by in situ methanol conversion to hydrocarbons using sohd acid catalyst in H2/CO2 feed. Study on indirect hydrocarbon synthesis is now popular. 

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