Processes and Synthesis Reactors

Processes for catalytic conversion of syngas into methanol can be divided into three classes according to reaction pressure, temperature, and catalyst composition. Today, high-pressure processes (250-350 bar, 300-450 °C, Cr/Zn) are no longer economic. Medium-pressure (100-250 bar, 220-300 °C, Cu/Zn) and low-pressure (50-100 bar, 200-300 °C, Cu/Zn) processes are operated, with the latter being much more attractive owing lower investment and operating cost 

In an isothermal single bed reactor the developed heat is removed from the reactor by transfer to a heat removing medium (e.g., water). 

The following subsection briefly describes current industrial processes for methanol production with adiabatic multi-bed and isothermal single-bed reactor design. We will refer to the ICI (adiabatic multiple-bed reactor) and to the Lurgi process (isothermal single-bed reactor), which are important representatives of the different ways of producing methanol commercially nowadays. 

Other examples of methanol production processes using adiabatic multiple-bed reactor concepts are the Haldor Topsoe process and the Kellogg process. 

The Lurgi process is a famous example of a process operating with an isothermal single-bed reactor (50-100 bar, 230-265 °C, copper catalyst). The catalyst is contained in fixed tubes and the tubes are cooled by a continuous boiling water flow. The temperature of the water is controlled by a steam pressure control valve that is adjusted to the pressure corresponding to the set-point temperature in the reactor. The reactor can achieve high syngas conversions and, therefore, the recycle ratio is low. 

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Boodhoo, K. (2013) Spinning disc reactor for green processing and synthesis, in Process Intensification for Green Chemistry Engineering Solutions for Sustainable ChemicalProcessing (eds K. Boodhoo and A. Harvey), John Wiley Sons Ltd., Chichester U. K. pp. 59-87. 

Extensive research efforts have been made incessantly in this field during the past few years. Recent advances in the design and fabrication of microreactors, micromixers, microseparators, and so on show that they represent a cheap alternative for the production of special fine chemicals by a continuous process to observe simpler process optimization and rapid design implementation. It is possible to predict that in the near future chemical, pharmaceutical, and biological laboratories will change radically toward considerable improvement of process and synthesis efficiency at essential miniaturization of reactor devices. 

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268]. 

Toyo Engineering-AGES Process. The synthesis section of the ACES process (Fig. 8) consists of a reactor, a stripper, two carbamate condensers, a scmbber and operates at 17.5 MPa (175 bars). The reactor is operated at 190°C with a NH /CO2 ratio of 4.0 (mol/mol). Liquid NH is fed directly into the reactor by a centrifugal ammonia pump. Gaseous CO2 is sent from the centrifugal CO2 compressor to the bottom section of the falling-film type stripper. 

The use of a fluidized-bed reactor is possible only when the reactants are essentiaUy in the gaseous phase. Eluidized-beds are not suitable for middle distiUate synthesis, where a heavy wax is formed. Eor gasoline synthesis processes like the MobU MTG process and the Synthol process, such reactors are especiaUy suitable when frequent or continuous regeneration of the catalyst is required. Slurry reactors and ebuUiating-bed reactors comprising a three-phase system with very fine catalyst are, in principle, suitable for middle distiUate and wax synthesis, but have not been appHed on a commercial scale. 

These products can be fairly easily processed into high-quality diesel and jet fuel in theory, any source of carbon can be used to generate synthesis gas. These facts along with the growing need for petroleum alternatives have renewed interest in FT synthesis. During the twentieth century, the FT process was used to produce fuels from coal in large and costly reactors. Recently, this megasize approach has been applied to world-scale GTL plants in Qatar. However, to tap abundant biomass resources and stranded natural gas reserves, a smaller scale, yet economically viable, FT process is needed. 

Many reports confirm notable reductions in reaction times when carrying out reactions under micro flow conditions. Concerning p-dipeptide synthesis, for example, a comparison between batch and micro-reactor processing was made for the reaction of Dmab-P-alanine and Fmoc-i-P-homophenylalanine [158]. While the micro reactor gave a 100% yield in 20 min, only about 5% was reached with the batch method. Even after 400 h, only 70% conversion was achieved. 

Many examples of safe processing in micro reactors have been reported. Among them, the formation of the poisonous hydrogen cyanide is often mentioned [5], Rinard and Saha refer to the non-oxidative Degussa variant [174] of this synthesis [85], while a micro reactor has performed the oxidative formation of hydrogen cyanide [175] via the Andrussov process [176,177]. 

Hessel V, Lowe H, Muller A, Kolb G (2005d) Chemical micro process engineering—processing and plants. Wiley-VCH, Weinheim Hessel V, Hofmann C, Lob P, Lowe H, Parals M (2007) Micro-reactor processing for the aqueous Kolbe-Schmitt synthesis of hydroquinone and phloro-glucinol. Chem Eng Technol 31, (in press)... 

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