Hydrocarbons through Methanol

HYDROCARBONS THROUGH METHANE DERIVATIVES 3.5.1. Hydrocarbons through Methanol 

Methanol Synthesis. The transformation of synthesis gas to methanol [Eq. (3.3)] is a process of major industrial importance. From the point of view of hydrocarbon chemistry, the significance of the process is the subsequent conversion of methanol to hydrocarbons (thus allowing Fischer-Tropsch chemistry to become more selective). 

Since other possible transformations, such as, formation of dimethyl ether, higher alcohols, and hydrocarbons, are accompanied with higher negative free-energy change, methanol is thermodynamically a less probable product. Therefore, solely on a thermodynamic basis, these compounds as well as methane should be formed in preference to methanol. To avoid the formation of the former compounds, the synthesis of methanol requires selective catalysts and suitable reaction conditions. Under such conditions, methanol is the predominant product. This indicates that the transformations leading to the formation of the other compounds are kinetically controlled. In the methanol-to-hydrocarbon conversion, dimethyl ether generally is converted similarly to methanol. 

An industrial process to produce methanol from carbon monoxide and hydrogen was developed by BASF in 1923 using a zinc oxide-chromia catalyst.361 362 Since this catalyst exhibited relatively low specific activity, high temperature was required. The low equilibrium methanol concentration at this high temperature was compensated by using high pressures. This so-called high-pressure process was operated typically at 200 atm and 350°C. The development of the process and early results on methanol synthesis were reviewed by Natta 363 

The low-pressure methanol synthesis process utilizes ternary catalysts based on copper, zinc oxide, and another oxide, such as alumina or chromia, prepared by coprecipitation. Cu-Zn0-Al203 and Cu-Zn0-Cr203 are usually the most important industrial catalysts. A significant advance was made when a two-stage precipitation was suggested in which ZnAl2C 4, a crystalline zinc aluminate spinel, was prepared prior to the main precipitation of copper-zinc species.372 This alteration resulted in an increase in catalyst stability for long-term performance with respect to deactivation. Catalyst lifetimes industrially are typically about 2 years. 

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Another approach to biomass-derived chemical production is the two-plat-form concept where the production of syngas (synthesis gas) from biomass gasification, or other technologies, is used to produced methanol or hydrocarbons through Fischer-Tropsch technology. ... 

Surprisingly, we found that the reaction of an alcohol with 1-chloroethyl-N,N-dialkylcarbamates can proceed through B mechanism to give alkylation rather than acylation (Ref. 195). This result appears to be a violation of the HSAB theory. In a typical example, N-(1-chloroethyloxy-carbonyl) piperidine was added to a stirred mixture of sodium hydrocarbonate and methanol at 25°C. The reaction was instantaneous. Solids were removed by filtration, excess alcohol was then distilled off and the resulting product was isolated by flash chromatography in 96% yield [Scheme 139]. 

On a weight basis acetic acid yields only 40% as much hydrocarbon as methanol. The lower yield in ZSM-5 processing results primarily from acetic acid s carbon loss due to oxygen rejection through decarboxylation to COg. 

Type 5A (five angstroms). Molecular sieve is the calcium form of the zeolite. Type 5A adsorbs molecules having a critical diameter of less than five angstroms (e.g., methanol, ethane, propane). Type 5A sieves can be used to separate normal paraffins from branched-chain and/cyclic hydrocarbons through a selective adsorption process. 

Emonts reported the operation of catalytic burners for hydrocarbons and methanol/ anode off-gas dedicated to fuel processing operations [555]. The burners were designed for thermal loads of up to 11.5 kW. Palladium catalyst deposited onto porous ceramic fibre was used for natural gas combustion. Only 0.5 g palladium was required for the burner, which was water-cooled by a concentric tube-bundle cooler mostly through radiation losses. At 11.5-kW power output, carbon monoxide emissions were below 10 mgkWh , while NOj emissions were around 2 mgkWh . The methanol burner worked with a platinum catalyst and showed lower NOj emissions of 0.4mgkWh. ... 

Thus, under ordinary reaction conditions, methanol is almost exclusively consumed by the reaction with olefins. Once certain amounts of olefins are formed in the zeolite cavities, they undergo various reactions such as dimerization and isomerization of olefins, and cracking of higher hydrocarbons through carbenium intermediates. For example, the formation of aromatic hydrocarbons from lower olefins csm be expressed by the following scheme. ... 

By proper selection of catalyst and reaction conditions, hydrocarbons and oxygenates ranging from methane and methanol through high (> 10,000) molecular weight paraffin waxes can be synthesized as iadicated ia Figure 11 (44). 

As a constituent of synthesis gas, hydrogen is a precursor for ammonia, methanol, Oxo alcohols, and hydrocarbons from Fischer Tropsch processes. The direct use of hydrogen as a clean fuel for automobiles and buses is currently being evaluated compared to fuel cell vehicles that use hydrocarbon fuels which are converted through on-board reformers to a hydrogen-rich gas. Direct use of H2 provides greater efficiency and environmental benefits. ... 

The resulting synthesis gas can subsequently be converted into methanol (Reaction 3) or polymerized to a mixture of hydrocarbons via the Fischer-Tropsch synthesis (Reaction 4) [37, 38]. These conversions usually require a H2/CO molar ratio close to 2 (Reactions 3 and 4), which contrasts with the H2/CO ratio of 0.5 that is delivered upon biomass gasification (Reaction 2). It can therefore be suitable to adjust the H2/CO ratio through the water-gas shift reaction (Reaction 5) ... 

A few LNG spill tests on organic liquids carried out at Conoco by Yang (1973) led to reproducible explosions. When saturated hydrocarbons from Cj through Cg (including many isomers) were used, immediate explosions were noted. Delays of 5 sec or longer were recorded before they occurred on methanol, acetone, or methyl ethyl ketone. Few or none were recorded for higher alcohols or for hydrocarbons above Cg (or benzene). 

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