Methanol Synthesis Reactor Systems

It has been found that the potential advantages by applying the radial flow principle in methanol syntheses cannot justify the potential risks imposed by especially the last point mentioned above, and it has as a consequence been decided to design the methanol synthesis reactor system as a series of normally three axial beds with cooling between the beds. In large plants, the reactors will be separate vessels with boilers or heat exchangers between the reactors. In smaller plants, it may be possible to have more than one catalyst bed inside the same pressure shell. 

Fig.3.3a-d. Various types of methanol synthesis reactors, (a) Cold gas quench (b) cooling by evaporation - multistage, adiabatic (c) cooling by evaporation - tubular, near isothermal (d) liquid entrained system using heat carrier liquid... 

When the calculation procedure and the mathematical model described above and in the appendix is applied for calculation of the performance of a methanol synthesis reactor, interesting results are obtained because of the special reaction system. In the mathematical model, the following 2 reactions are specified, each with its own kinetic expression ... 

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. 

A system has been constructed which allows combined studies of reaction kinetics and catalyst surface properties. Key elements of the system are a computer-controlled pilot plant with a plug flow reactor coupled In series to a minireactor which Is connected, via a high vacuum sample transfer system, to a surface analysis Instrument equipped with XFS, AES, SAM, and SIMS. When Interesting kinetic data are observed, the reaction Is stopped and the test sample Is transferred from the mlnlreactor to the surface analysis chamber. Unique features and problem areas of this new approach will be discussed. The power of the system will be Illustrated with a study of surface chemical changes of a Cu0/Zn0/Al203 catalyst during activation and methanol synthesis. Metallic Cu was Identified by XFS as the only Cu surface site during methanol synthesis. 

Figure 17.24. Types of reactors for synthetic fuels [Meyers (Ed.), Handbook of Synfuels Technology, McGraw-Hill, New York, 1984], (a) ICI methanol reactor, showing internal distributors. C, D and E are cold shot nozzles, F = catalyst dropout, L = thermocouple, and O = catalyst input, (b) ICI methanol reactor with internal heat exchange and cold shots, (c) Fixed bed reactor for gasoline from coal synthesis gas dimensions 10 x 42 ft, 2000 2-in. dia tubes packed with promoted iron catalyst, production rate 5 tons/day per reactor, (d) Synthol fluidized bed continuous reactor system for gasoline from coal synthesis gas.

To conclude our examples of Aspen Dynamics simulation of tubular reactor systems, we study a very important industrial process for the production of methanol from synthesis... 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

Another reactor system which has several attractive features for heat removal is the tubular, heat-exchange reactor. Good temperature control can be achieved in the tubular reactor if the coolant approximates an isothermal heat sink. Light gas recycle can be reduced significantly compared to fixed-bed systems. Tubular reactors have been used for Fischer-Tropsch reactions and for synthesis of methanol and phthalic anhydride, for example. 

Commodity chemicals share the same benefits of economies of scale. Typical process units are 1-2 orders of magnitude smaller than refinery units, although large methanol synthesis plants can produce up to several Mt/a (Section 4.7.1). Since a chemically pure material is being produced, often in a stoichiometric reaction, the catalyst system now becomes more specialized, the reactor may require special metallurgy, and product purification starts to be an issue. 

Using two-stage series reactor system, gasoline fraction of hydrocarbons was also synthesized. [41] As a methanol conversion catalyst, MFI-type metallosihcate such as H-Fe-sdicate and H-Ga-sdicate were optimum for gasohn fraction synthesis. 

In order to synthesize gasoline effectively from carbon dioxide through one-pass reaction system, methanol synthesis catalyst was improved. Pd and Ga were added to Cu-Zn based catalyst to optimize the state of Cu during the reaction. As the result, the space-time yield (STY) of methanol from CO2 was 1,410 gd h at 270, 80 atm and SV=18,800 /h. In second stage reactor in which H-Ga or Al-silicate was packed, methanol was converted to gasoline. Maximum selectivity to gasoline fraction was 54.4 % and STY was 312 gl h at 320 C and 15 atm. 

In a Liquid Phase Di-Methyl Ether process (LPDME), synthesis gas (syngas) is converted into dimethyl ether (DME) in a single slurry phase reactor over a catalyst system. Both methanol synthesis and methanol dehydration function as a physical mixture of a methanol synthesis catalyst and a dehydration catalyst (dual catalyst system). Three reactions take place simultaneously in the system, namely ... 

Several processing alternatives have been proposed for converting synthesis gas to methanol. The main incentives are reduced energy costs due to the ability to operate at lower temperatures, lower pressures or both. The most notable of these alternatives (in terms of recent interest) have been the alkyl formate process (ref. 27) and the Chem Systems three-phase reactor approach (ref. 28). A very recent development is the use of a gas-solid-solid trickle flow reactor.which it is proposed can be retrofitted in conventional low pressure methanol synthesis plants (ref. 29). These three alternatives will be reviewed in turn. 

Chem Systems Inc. has been developing a three phase reaction system for methanol synthesis since the mid 1970 s (ref. 28). The original concept incorporated a liquid-fluidized-bed reactor. This research, which was funded by the Electric Power Research Institute, used particles of a heterogeneous catalyst, obtained by crushing pellets of a commercial Cu-ZnO-AljO type catalyst, which was fluidized by a circulating inert hydrocarbon liquid such as a mineral oil. One of the major benefits of the process over conventional synthesis is claimed (ref. 28) to be excellent temperature control of the reactions so that higher per pass conversions can be achieved, thereby reducing... 

The reactor configuration most prevalent for methanol synthesis from syngas is the gas-phase fixed-bed reactor. It is a two-phase system in which the reacting gas flows through a bed of catalyst particles. ICI introduced its low pressure methanol process in low tonnage plants. This process typically operates at temperatures of 220-28CTC and pressures of 5—10 MPa. The exothermic nature of the methanol synthesis reaction makes the temperature control difficult. The reactor operates adiabatically and the temperature rise... 

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