Hydrocarbons synthesis from methanol

It is clear that these catalysts will provide a very rewarding area for both fundamental and applied research in catalysis as they give rise to a route to hydrocarbon synthesis from methanol and ethanol as an alternative to oil-based routes. 

Sulfur poisoning is a key problem in hydrocarbon synthesis from coal-derived synthesis gas. The most important hydrocarbon synthesis reactions include methanation, Fischer-Tropsch synthesis, and methanol synthesis, which occur typically on nickel, iron, or cobalt, and ZnO-Cu catalysts, respectively. Madon and Shaw (2) reviewed much of the early work dealing with effects of sulfur in Fischer-Tropsch synthesis. Only the most important conclusions of their review will be summarized here. 

It can also be obtd as a by-product of hydrocarbon synthesis from CO and H2, and as a by-product of methanol synthesis from these gases. The oldest method of alcohol prepn is by fermentation of grains, molasses and carbohydrates. It can also be prepd by fermentation of sulfite pulp. Alcohol prepd from grains is known as grain alcohol and it is used in prepn of beverages (Refs 1, 11 12)... 

We studied hydrocarbon synthesis from CO2 using Cu-Zn-Cr (3 3 1)/HY and Fe-ZnO /HY composite catalysts[2 6]. In this case, first CO2 converted to methanol, and then methanol converted to hydrocarbon over zeolite. The main products formed among hydrocarbons was ethane, propane and butane, and hydrocarbon distribution was different from Schulz-Anderson-Flory rule. In MTG reaction, methanol converted to dimethyl ether, then to ethene, and ethene converted to higher hydrocarbons or ethane. In order to obtain higher hydrocarbons, it is important to find active catalysts which have no hydrogenation activity of olefin. 

Hydrocarbon synthesis from syngas (Fischer-Tropsch reactions) can be carried out over the catalysts prepared from Co- and Cu-containing LDHs. The products include methane, higher paraffins, and olefins as well as methanol. The loading of Co and Cu determines the selectivity for each compound. For instance, Co-rich catalysts give more paraffins, while Co-poor ones lead to methanol (615). 

By selection of appropriate operating conditions, the proportion of coproduced methanol and dimethyl ether can be varied over a wide range. The process is attractive as a method to enhance production of Hquid fuel from CO-rich synthesis gas. Dimethyl ether potentially can be used as a starting material for oxygenated hydrocarbons such as methyl acetate and higher ethers suitable for use in reformulated gasoline. Also, dimethyl ether is an intermediate in the Mobil MTG process for production of gasoline from methanol. 

Synthesis gas is an important intermediate. The mixture of carbon monoxide and hydrogen is used for producing methanol. It is also used to synthesize a wide variety of hydrocarbons ranging from gases to naphtha to gas oil using Fischer Tropsch technology. This process may offer an alternative future route for obtaining olefins and chemicals. The hydroformylation reaction (Oxo synthesis) is based on the reaction of synthesis gas with olefins for the production of Oxo aldehydes and alcohols (Chapters 5, 7, and 8). 

As mentioned in Chapter 2, methane is a one-carhon paraffinic hydrocarbon that is not very reactive under normal conditions. Only a few chemicals can he produced directly from methane under relatively severe conditions. Chlorination of methane is only possible by thermal or photochemical initiation. Methane can be partially oxidized with a limited amount of oxygen or in presence of steam to a synthesis gas mixture. Many chemicals can be produced from methane via the more reactive synthesis gas mixture. Synthesis gas is the precursor for two major chemicals, ammonia and methanol. Both compounds are the hosts for many important petrochemical products. Figure 5-1 shows the important chemicals based on methane, synthesis gas, methanol, and ammonia. ... 

From a prachcal standpoint, formic acid or its salts are the least valuable reaction products. The energy content of formic acid upon its reverse oxidation to CO2 is insignificant, and its separation from the solutions is a labor-consuming process. At present, maximum effort goes into the search for conditions that would ensure purposeful (with high faradaic yields) synthesis of methanol, hydrocarbons, oxalic acid, and other valuable products. 

The liquid hydrocarbon yield from the BTL production via gasification and FT synthesis is about 42% based on the LHV, which is similar to the production of BTL via gasification, methanol synthesis and the MtSynfuel process (Dena, 2006). 

According to another important and promising technology, hydrocarbons are produced from methanol, which, in turn, is synthesized from synthesis gas. Called the methanol-to-gasoline process, it was practiced on a commercial scale and its practical feasibility was demonstrated. Alternative routes to eliminate the costly step of synthesis gas production may use direct methane conversion through intermediate monosubstituted methane derivatives. An economic evaluation of different methane transformation processes can be found in a 1993 review.1... 

Thus a variety of hydrocarbons, ranging from natural gas to coal, are used in methanol production. Regardless of the feedstock used to prepare the synthesis gas, it is necessary to remove sulfur so that the converter catalyst is not poisoned. Before natural gas or naphtha is reformed, the feedstock is desulfurized. In the partial oxidation and coal gasification processes, the feedstock is first oxidized and the resulting synthesis gas is desulfurized before entering the converter. 

The production of gasoline from methanol is a parallel process to the Fischer-Tropsch synthesis of hydrocarbons from syngas (Section 4.7.2). A shape-selective zeolite (ZSM-5) was the catalyst of choice in the process put on stream in 1987 by Mobil in New Zealand however the plant was later closed. The zeolite was used at ca. 400°C in a fluid catalyst reactor, which allows prompt removal of the heat of reaction. 

The recent interest in chemical production is based on a higher return expected for chemical [uoducts versus fuels. For example, biomass gasification can be used to produce a synthesis gas of hydrogen and carbon monoxide. This gas can be used in catalytic synthesis of a range of chemicals, from methanol and formaldehyde to higher hydrocarbons, in the same way that synthesis gas derived from natural gas can be used. However, by breaking down the biomass to the basic building blocks all product differentiation relative to fossil fuels is lost. 

Hydrogenation of CO2 to produce valuable chemicals has received much attention in recent years. Not only synthesis of methanol as the energy carrier but also syntheses of hydrocarbons and higher alcohols as the carbon resources will be possible. CO is usually formed as a side product at the same time. Therefore, the control of the product distribution is important. We have carried out hydrogenation of COj over copper-based catalysts [1-4]. These results showed that the formate species formed on copper was a common reaction intermediate to both methanol and CO and that CuO-ZnO/TiOj was the most effective for methanol from the viewpoint of activity and selectivity [1,2,4]. Furthermore, we have found that Fe added catalyst reduced CO with increasing hydrocarbon products [3]. 

Figure 2 shows the effect of method of Fe addition on product distributions. Cu0-Zn0/Ti02 (cat. A) was active for methanol synthesis, but it was not effective for the synthesis of hydrocarbons. This indicates that Cu species alone is not enough to produce hydrocarbons. On the contrary, Fe-based catalysts are known as hydrocarbon synthesis catalysts from CO, that is, Fischer-Tropsch reaction. However, Fe/TiOj catalyst (cat. C) showed poor... 

Performances of each catalyst is shown in Figure 1. The ethanol synthesis catalyst (Fe-based catalyst. Cat. 1) have both functions of F-T synthesis and alcohol synthesis. The main products were hydrocarbons, ethanol and methanol. With the increase of CO in reaction gas, the yield of ethanol increased[l]. The Cu-based catalyst (Cat. 2) converted CO2 to CO with selectivity more than 70% at a temperature range from 270 to 370°C, and other products were methanol and a slight amount of methane. Ethanol and C2 hydrocarbons were not produced. In order to harmonize the three functions, C-C bond growth, partial reduction of CO2 to CO, and OH insertion to products, the mixed ratio of Fe-based catalyst to Cu-based catalyst was coordinated at the range from Cu/Fe =... 

In order to produce ethanol by COj hydrogenation, the catalyst should have two functions C-C bond formation and C-0 bond partial preservation. In the case of the CO/Hj feed gas system, the former is industrially performed in Fischer-Tropsch synthesis, while the latter in methanol synthesis. K/Fe oxides catalyst, being effective in Fischer-Tropsch synthesis, was found to produce C-C bond in COj hydrogenation. It converted COj into CO, alcohols, and hydrocarbons. Cu-Zn oxides catalyst, practically used in methanol synthesis from CO/CO2/H2 mixture, was found unable to produce C-C bond it converted CO, to CO and methanol without any other detected compounds. 

In order to elucidate the role of CO in COj hydrogenation, activity tests were carried out with the feed gas, in which CO2 was partly replaced with CO. The results are illustrated in Figure 3. It shows that the ratios of the yields of ethanol, methanol, and hydrocarbons (C1 C5) scarcely changed with the replacement of CO2 by CO. The total yield of the products increased with an increase in the CO/CO2 ratio. The total yield dependence on the CO/CO, ratio is attributable to the difference of reactivity between CO and CO2. In Figure 2 CO selectivity remained low in the whole range. These results shown in Figure 2 and 3 suggest that ethanol was produced directly from CO2 as well as CO. In methanol synthesis from CO/CO2/H2 mixture, it was reported that methanol is produced directly both from CO and CO, [3]. 

Dimerization and codimerization reactions are widely used on an industrial scale either to provide chemicals of high added value or to upgrade by-product olefinic streams coming from various hydrocarbon cracking processes (steam or catalytic cracking) or hydrocarbon forming processes (Fischer-Tropsch synthesis or methanol condensation) (e. g., according to eq. (1)). 

---