Synthesis methanol

Methanol or methyl alcohol (mp —97.8 C, bpi.oia — 64.6 C, d 0.792 produced by the distillation of wood accounts for only a few per cent of total production. This also applies to its production by the direct oxidation of hydrocarbons. Most methanol is synthesized from mixtures of H2, CO and COj. 

Methanol production is ciddly based on the implementation of the following reaction CO + 2H, CHjOH 

To a lesser degree, it also rdies on the conversion of carbon dioxide  

according to the proportion of CO and CO2, the gaseous mixture required for conversion must have a hydrogen to carbon molar ratio between 2 and 3 . Sudi a gas can be obtained, as mentioned above, by partial oxidation, gasification, or steam reforming. 

To convert methane (see Fig. 1J), it is theoretically possible to adjust the oxygen content to obtain an effluent in which the H2/CO ratio is dose to 2. In practicC it is necessary to consider the losses resulting from the formation of methane during the synthesis of methanol, and aim for an H2/CO ratio of aroiod 2.25, which is ideal for this conversion. 

Synthesis gas (CO/H2) manufactured by reforming of a hydrocarbon, usually natural gas. 

Methanol is one of the most important chemicals. The major application is in the chemical industry, where it is used as a solvent or as an intermediate. It is increasingly used in the energy sector. A survey of the most important reactions is given in Fig. 2.18. 

Methanol is a major bulk chemical. In 1989 the production capacity exceeded 21xl06 ton/y. 

It is clear that methanol is less stable than many possible by-products, such as methane. The catalyst has to be selective. The selectivity of modern catalysts is above 99%. The original catalysts were active only at high temperature (300-400°C). The pressure applied was 25-35 MPa. Until the end of the 1960s basically the original catalyst was used. More active catalysts were known, but they were not resistant to impurities such as sulphur. In modern plants the synthesis gas is very pure and very active catalysts can be used. This has led to low pressure plants (260°C, 50-100 bar). The temperature is critical. A low temperature is favourable from a thermodynamic point of view. 

Methanol production plants consist of three parts  

Synthesis gas can be reacted or reformed to make methanol through highly exothermic reactions  

The first reaction produces methanol with a low hydrogen consumption, but evolves significantly greater amounts of heat. The second reaction evolves less heat, but consumes more hydrogen and produces the byproduct steam. Thermodynamically, low temperatures and high pressures favor methanol formation. The reactions are carried out with copper-containing catalysts with typical reactor conditions of 260°C and 5 MPa (Probstein and Hicks, 1982). 

Three-phase reactor systems are ideally suited for methanol production because of the ability to provide intimate contact between the gaseous phase reactants and the solid phase catalysts and to remove the large amounts of heat created by the high heats of reaction. In the three-phase system, an inert liquid phase circulates between the reactor and an external 

Methanol is very important both as a produet and as a feedstock in chemical industry the total world capacity is currently over 30 Mt/a and is rising at about 3% p.a. Syngas is now the only realistic feedstock for making methanol. Major plants to make it from very cheap raw materials have been built in Trinidad, Saudi Arabia and elsewhere these use methane from oil wells, which was previously flared to waste, but can easily be converted into syngas. Such methanol plants use what is termed stranded gas which is natural gas in a remote area where it cannot be economically used for any other purpose. Very large mega-scale methanol plants 1.5 Mt/a are now built. For example in Trinidad, which is now the world s largest exporter of methanol, with a total production capacity of 6.5 Mt/a. 

The major uses of methanol are to make formaldehyde (ca. 30%) the fuel additive methyl /-butyl ether (MTBE, ca. 30%, though this may now be phased out on environmental grounds) acetic acid (ca. 10%) acetate esters as solvents, methyl methacrylate, chloromethane (to make silicones) and dimethyl ter-ephthalate (DMT, fibres) (ca. 30%). 

Commercially, methanol is produced from the hydrogenation of CO (syngas) over heterogeneous CuZn oxide based catalysts using fixed bed reactors (Equation 11). 

Other reactions that play a significant role include the hydrogenation of carbon dioxide (Equation 40), 

The form of the catalyst, its morphology, and its method of preparation vary widely and this is reflected in its catalytic properties. The actual mechanism of 

2 Methanol Synthesis. - Although some studies have suggested that MeOH 

The impact of product readsorption on Xmcoh has been examined in greater 

Under the conditions of study, x °MeOH (x Rxn) was approximately one half the value of XMeOH- This difference results in the TOF ratio based on XMeasured ((l/xMeOH)/TOFco) to be approximately one half of the value based on Xrxh ((l/x°°MeOH)/TOFco)- It is important to note that once the readsorption effect has been subtracted out, l/x°°MeOH (TOFitk) is approximately an order of magnitude larger than TOFco (TOFchem), in good agreement with what was observed for methanation on Ru, Co, Fe, and Ni catalysts. Under similar reaction conditions. 

Catalyst COirrei ( pmole/g) Rate MeOH iimole/g/s) TOFco (10- s ) TMeOH (S) MeOH (s) ll TMeOH (TOFitk) (10- s ) MeOH (TOFo%rK, 1 TOF ixK TOF %jk Ref. 

The synthesis of methanol from carbon monoxide/hydrogen mixtures is also achieved by a catalytic process according to the following stoichiometric equation (Kasem, 1979 Muetterties and Stein, 1979 Klier, 1984 Lee, 1990 Chadeesingh, 2011) or by way of a carbon dioxide/hydrogen reaction  

Conversion is thermodynamically favored by relatively low temperatures and high pressures and, in the initial attempts to produce methanol from coal, conditions were usually on the order of 300°C-375°C (570°F-705°F) and 4000-5250 psi, although recent improvements in catalyst behavior and performance have led to reductions in the operating pressure to the range 500-1500 psi. 

Even though the process is generally regarded as being highly selective, the crude methanol product still requires purification. This is usually accomplished by distillation which removes dimethyl ether and the higher molecular weight alcohols. 

About 90% of industrially produced methanol is converted in the chemical industry or used as solvent for synthetic applications. In addition, methanol has gained increasing importance as energy equivalent and fuel in recent decades. In 2012 the estimated annual world supply and demand of methanol is expected to rise to 62.1 X 10 t. 

View of a MegaMethanol plant constructed by Lurgi in Trinidad to convert natural gas into methanol. The insert depicts the function of the two reactor units shown in the center of the photograph note that the boiler is shown in the photograph on the top of the water-cooled reactor (right reactor) from the side ( Lurgi GmbH). 

Pure methanol was first isolated by Sir Robert Boyle in 1661. He produced methanol by rectification of crude wood vinegar. Later, in 1834, its elemental composition was determined by the two French chemists Jean-Baptiste Dumas and Eugene Peligot. They introduced the name methylene for the alcohol made from wood (combination of the Greek words methyl = wine and hyle =wood). Around 1840 the term methyl alcohol was created and later in 1892 this was shortened to methanol by an International Conference on Chemical Nomenclature. 

Methanol is synthesized in a catalytic gas-phase reaction from synthesis gas, which is a mixture of hydrogen and carbon monoxide. In addition, some carbon dioxide is 

Both reactions are exothermic and exhibit a decrease in volume (reduction in moles as the reaction proceeds to the right). Therefore, methanol formation is favored by increasing pressure and decreasing temperature. 

Experiments during the nineteenth century had shown that certain oxides could be used as dehydrogenation catalysts. For example, Jahn dehydrogenated methanol by passing the vapour over finely divided zinc or zinc oxide to produce a stoichiometric mixture of hydrogen and carbon monoxide.  

Subsequently, patents covering the conversion of synthesis gas to complex mixtures of organic oxygen compoimds, including methanol, were issued to BASF during 1913. This followed work by Mittasch and Schneider. Full-scale production of methanol was not attempted, however, imtil 1923. By that time high-pressure equipment had been in operation for several years in the new ammonia process. The methanol process was developed by Piers and the plant, built at Leima, used mixed zinc oxide-chromic oxide catalyst. The use of metallic iron for the internal parts of the reactor was avoided to prevent the formation of the volatile iron penlacarbonyl. The would have decomposed on the surface of the catalyst, to deposit finely divided iron metal, which in turn would have promoted the exothermic formation of methane. 

The idea to test the substitution of a B cation by copper in a perovskite structure for the methanol synthesis was first developed 30 years ago by Broussard and Wade [6], then by Brown Bourzutschky et al. [7], with the substitution of Mn by copper in a LaMnOs+s perovskite. To date, few other structures have been tested. Besides LaMni CU t03+5 described by different authors [6-9] and used with CO + H2 mixture, the reactivity of LaTii. Cu Os [10,11], YBa2Cu307 t [12,13], and La2Cu04 [14] have been studied. Few works have been performed on noble metals Pt, Rh [7], probably due to the poor methanol selectivity obtained (50-60%). Only recently, studies with CO2 + H2 have been undertaken on LaCro.sCuo.sOs [15], La-M-Cu-ZnO (M=Y, Ce, Mg, or Zr) catalysts derived from perovskites [16], or LaMni. Cu Os [17]. 

5O3) and the selectivity switches from 100% hydrocarbons to 80% methanol, independendy on the substitution rate [7]. Similar catalytic results are obtained on Cu/La20s and Cu/Mn02/La20s. This suggests a decomposition of the perovskites during the reduction and/or reaction. 

This decomposition is confirmed for LaCuOs but neither XRD nor XPS showed evidence of Cu particles for 0.2 . 0.6 in LaMni CU e03 perovskite. In this case, it is suggested that Cu° particles are present as well as ionic copper form (Cu or Cu ), ionic copper being either on the surface of Cu° particles or in close contact with their [7]. 

Some higher alcohols (10 wt %) are present and it is proposed that the basic metal oxide stabilizes oxygenated species involved in the C—C bond formation. Similar results have been obtained with LaTii. Cu Os [8-11] with a deeper characterization of the catalysts. For x = 0.5 or 0.6, the selectivity to methanol is between 78 and 83% with a drastic increase of CO hydrogenation by increasing Cu substitution (maximum of activity for x = 0.6). The understanding of the catalytic behavior has been facilitated by the comparison of the main catalysts characteristics before and after reactivity test. By XRD, LaTh. Cu Os perovskite structure appears stable for 0.3 x 0.8, in addition, reflexions attributed to CuO are evidenced, accounting for a partial rejection of copper from the perovskite. Results are similar for LaMni- cCu cOs [8,9]. However, in both cases, no further study has been made to know the real value of x in the remaining perovskite. 

Similar results were obtained with LaMni j,Cu 03. For 0 0.6, copper oxide of the structure is reduced at temperature substantially higher than 200 °C showing the increased stability of copper cation when inserted in the perovskite structure [8]. Reduction of Mn to Mn starts before copper reduction is completed. For = 0.8, the reduction profile is more complex and includes the reduction of the perovskite, of La2Cu04 at r 320°C and of CuO at T 

Brown and Bemiett [97] have studied this reaction using commercial 0.635 cm (x in.) catalyst pellets, with e, = 0.5, 130 mVs dominant pore size 2 100 to 

The mean binary difliisivity for the reaction mixture was computed from Eq. 3.1C-11  

At the experimental conditions of p, = 207 bars = 204 atm and T = 300 to 400°C, the Knudsen diffusion can be neglected, and ordinary bulk diffusivities can be used in Eq. b. It was stated that the variation (of D, with composition dependence from Eq. b) was not negligible.  

The intrinsic rate was determined by crushing the catalyst pellets into small particles the rate data could be represented by the Natta rate equation 

The results of Eqs. b and d were then introduced into the general modulus, Eq. 3.6.b-8, 

The high-pressure process, which used to be exclusively operated, is carried out with Zn0/Cr203 catalyst at 250-350 bar and 350 00°C. The development of more active, copper-based catalysts allowed the process to be carried out in the pressure range 50-100 bar and at lower temperatures. This improved the economics of the process. The low-pressure processes were developed by ICI and Lurgi and introduced in the mid-1960s. 

Let us examine the mechanism of methanol synthesis [18]. In 1962 the activating effect of CO2 in the synthesis gas was discovered. When cracked gas (CO + 3H2) from methane-rich natural gas is used, CO2 is added to the synthesis gas and it consumes more H2 than the CO (Eq. 8-3). 

Another side reaction is die water-gas shift equilibrium (Eq. 8-4). 

Thus the question of what is the actual carbon source in methanol synthesis can not be unambiguously answered. Two mechanisms have been suggested to explain the formation of methanol on the heterogeneous catalyst. In the first mechanism (Eq. 8-5), adsorbed CO reacts on active copper centers of the surface with dissocia-tively adsorbed hydrogen in a series of hydrogenation steps to give methanol. 

In the second mechanism (Eq. 8-6), the first step is the insertion of CO into a surface OH group with formation of a surface formate. This is followed by further hydrogenation steps and dehydration to give a smface methoxyl group, from which methanol is formed. 

The puipose of this open-ended problem is for the students to apply their knowledge of reaction kinetics to the prt lem of modeling the metalx lism of alcohol in humans. In addition, the students will present their findings in a poster session. The poster presentations will be designed to bring a greater 

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As an example of the application of a fixed-bed tubular reactor, consider the production of methanol. Synthesis gas (a mixture of hydrogen, carbon monoxide, and carbon dioxide) is reacted over a copper-based cat dyst. The main reactions are... 

Methanol (qv) is one of the 10 largest volume organic chemicals produced in the wodd, with over 18 x 10 t of production in 1990. The reactions for the synthesis of methanol from CO, CO2, and H2 are shown below. The water gas shift reaction also is important in methanol synthesis. 

The alkalized zinc oxide—chromia process developed by SEHT was tested on a commercial scale between 1982 and 1987 in a renovated high pressure methanol synthesis plant in Italy. This plant produced 15,000 t/yr of methanol containing approximately 30% higher alcohols. A demonstration plant for the lEP copper—cobalt oxide process was built in China with a capacity of 670 t/yr, but other higher alcohol synthesis processes have been tested only at bench or pilot-plant scale (23). 

Liquid Fuels via Methanol Synthesis and Conversion. Methanol is produced catalyticaHy from synthesis gas. By-products such as ethers, formates, and higher hydrocarbons are formed in side reactions and are found in the cmde methanol product. Whereas for many years methanol was produced from coal, after World War II low cost natural gas and light petroleum fractions replaced coal as the feedstock. 

Hydrogen is used mainly in ammonia synthesis, methanol synthesis, and petroleum refining. 

The Texaco process was first utilized for the production of ammonia synthesis gas from natural gas and oxygen. It was later (1957) appHed to the partial oxidation of heavy fuel oils. This appHcation has had the widest use because it has made possible the production of ammonia and methanol synthesis gases, as well as pure hydrogen, at locations where the lighter hydrocarbons have been unavailable or expensive such as in Maine, Puerto Rico, Brazil, Norway, and Japan. 

Because the synthesis reactions are exothermic with a net decrease in molar volume, equiUbrium conversions of the carbon oxides to methanol by reactions 1 and 2 are favored by high pressure and low temperature, as shown for the indicated reformed natural gas composition in Figure 1. The mechanism of methanol synthesis on the copper—zinc—alumina catalyst was elucidated as recentiy as 1990 (7). For a pure H2—CO mixture, carbon monoxide is adsorbed on the copper surface where it is hydrogenated to methanol. When CO2 is added to the reacting mixture, the copper surface becomes partially covered by adsorbed oxygen by the reaction C02 CO + O (ads). This results in a change in mechanism where CO reacts with the adsorbed oxygen to form CO2, which becomes the primary source of carbon for methanol. 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Methanol Synthesis. AH commercial methanol processes employ a synthesis loop, and Figure 6 shows a typical example as part of the overall process flow sheet. This configuration overcomes equiUbtium conversion limitations at typical catalyst operating conditions as shown in Figure 1. A recycle system that gives high overall conversions is feasible because product methanol and water can be removed from the loop by condensation. 

With these waste-minimization techniques, methanol synthesis is relatively clean, and poses no unique environmental hazards. The need for environmental controls is more closely associated with the synthesis gas generation process. 

Future Methanol Processes. The process route for methanol synthesis has remained basically unchanged since its inception by BASF in 1923. The principal developments have been in catalyst formulation to increase productivity and selectivity, and in process plant integration to improve output and energy efficiency while decreasing capital cost. 

Methanol Synthesis. Methanol has been manufactured on an industrial scale by the cataly2ed reaction of carbon monoxide and hydrogen since 1924. The high pressure processes, which utili2e 2inc oxide—chromium oxide catalysts, are operated above 20 MPa (200 atm) and temperatures of 300—400°C. The catalyst contains approximately 72 wt % 2inc oxide, 22 wt % chromium (II) oxide, 1 wt % carbon, and 0.1 wt % chromium (VI) the balance is materials lost on heating. 

Thermal chlorination of methane was first put on an industrial scale by Hoechst in Germany in 1923. At that time, high pressure methanol synthesis from hydrogen and carbon monoxide provided a new source of methanol for production of methyl chloride by reaction with hydrogen chloride. Prior to 1914 attempts were made to estabHsh an industrial process for methanol by hydrolysis of methyl chloride obtained by chlorinating methane. 

Methanol. Methanol is produced by stoichiometric reaction of CO and H2. The syngas produced by coal gasification contains insufficient hydrogen for complete conversion to methanol, and partial CO shifting is required to obtain the desired concentrations of H2, CO, and CO2. These concentrations are expressed in terms of a stoichiometric number, ((H2 — CO)/(H2 + CO2), which has a desired value of 2. In some cases CO2 removal is required to achieve the stoichiometric number target. CO and H2 are then reacted to form methanol in a catalytic methanol synthesis reactor. 

Its appeal Hes in the fact that synthesis gas can be produced from trash, municipal sewage, scrap wood, sawdust, newsprint, or other waste. The early work of Fischer and Tropsch on methanol synthesis showed that ethanol could be obtained in the process (165) and that by certain modifications the proportion of ethanol in the product could be increased (166). The Hterature concerning this method is extensive (167—176). The conditions that favor ethanol formation are 125—175°C and 1.42 MPa (14 atm) in the presence of reduction catalysts such as powdered iron. 

Autothermal reactor for methanol synthesis using a numerical search technique... 

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

The production of methyl acetate from synthesis gas is currently being practiced commercially. Following methanol synthesis, as shown by Reac tion (27-35), the reactions are ... 

Examples for calculated heat transfer coefficients are shown in the table on Figure 1.5.1 The physical and other properties are used from the UCKRON-1 Example for methanol synthesis. These properties are ... 

For a first test of the reactor and all associated service installations it is recommended that experiments for methanol synthesis should be carried out even if this reaction is not especially interesting for the first real project. The reason for this recommendation is that detailed experimental results were published on methanol synthesis (Berty et al, 1982) made on a readily available catalyst. This gives a good basis of comparison for testing a new system. Other reactions that have been studied in detail and for which the performance of a catalyst is well known can also be used for test reactions. 

The catalyst should be the copper-based United Catalyst T-2370 in 3/16 , reduced and stabilized, in extrudate form. Initially, 26.5 g of this should be charged to the catalyst basket. This catalyst is not for methanol synthesis but for the low temperature shift reaction of converting CO to CO2 with steam. At the given conditions it will make methanol at commercial production rates. Somewhat smaller quantity of catalyst can also be used with proportionally cut feed rates to save feed gas. 

Only parts needed above but for the vapor-phase reactor are listed here. Most of the description for the installation for methanol synthesis experiments (Figure 4.2.1) holds for this installation, too. In the mentioned unit, product was blown down while still hot, thus keeping all product in a single vapor phase. This simplifies material balance calculations. When avoiding condensation is difficult, cooling and separation becomes necessary. This method was used in the cited AIChEJ publication. 

Methanol synthesis served as the model for the true mechanism. Stoichiometry, thermodynamics, physical properties, and industrial production rates were all taken from the methanol literature. Only the reaction mechanism and the kinetics of methanol synthesis were discarded. For the mechanism a four step scheme was assumed and from this the... 

In the original announcement of the workshop the participants were told that everything was to be taken from methanol synthesis except the kinetics. Some may have interpreted this to mean that the known thermodynamic equilibrium information of the methanol synthesis is not valid when taken together with the kinetics. This was not intended, but... 

Here the integration method will be shown that was used for the workshop program (Berty et al, 1989) to integrate the UCKRON rate equations. Since this is about methanol synthesis the reaction is shown here with the stochiometric coefficients ... 

Figure 9.6.5 Experimentally measured Van Heerden diagram for low pressure methanol synthesis. ...

Here a four-step mechanism is described on the framework of methanol synthesis without any claim to represent the real methanol mechanism. The aim here was to create a mechanism, and the kinetics derived from it, that has an exact mathematical solution. This was needed to perform kinetic studies with the true, or exact solution and compare the results with various kinetic model predictions developed by statistical or other mehods. The final aim was to find out how good or approximate our modeling skill was. 

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