Lurgi recycle process

L. Seglin Why has Lurgi selected the hot gas recycle process for methanation rather than the isothermal reactor (ARGE) design which they used for the Fischer-Tropsch plant in SASOL s plant in South Africa ... 

Ruhrchemie-Lurgi—recycle experiments. The production of synthetic hydrocarbons with a high content of olefins (mono-olefins) is desirable in many cases. The olefins increase the octane number of the gasoline and can be used as valuable raw material for many processes (polymer gasoline, lubricating oils, oxo-synthesis, etc.). 

Lurgi CFB Process. In this SO2 removal process, hydrated lime is injected into a circulating fluid bed (CFB) reactor located ahead of the particulate removal system. Water is also injected into the reactor to cool and humidify the gas and increase the SO2 removal efficiency. A mixture of fly ash and reacted and unieacted sorbent particulate in the gas from the CFB reactor is collected in a special downstream mechanical dust collector curtain followed by an ESP. Most of the collected particulate is recycled to the CFB reactor (Keetii et al., 1991B). In 1993, eight systems of this type were operating or were under construction in Europe, and two were under construction in the U.S. (Moore, 1993B). 

This section reviews the Lurgi MTF technology for production of propylene from methanol on a proprietary ZSM-5 type catalyst MTPROP supplied from Slid Chemie [12,13]. Lurgi started the development of methanol to propylene (MTP ) in 1993. The proprietary zeolite-based MTP catalyst is exclusively supplied by Slid Chemie [47]. The process begins with a vapor phase dehydration of methanol to DME to produce an equilibrium mixture of DME, methanol, and steam. This mixture is then converted to propylene in a fixed-bed MTP reactor at 400-500°C in the presence of steam and recycled C -C olefins. By-products of the Lurgi MTP process are gasoline, LPG, and fuel gas. The ethylene could be recycled back or used as a copolymer. 

The chapter by Eisenlohr et al. deals with the results of large scale pilot operations using a newly developed high-nickel catalyst with hot-gas recycle for temperature control. This and other work, conducted by Lurgi Mineraloeltechnik GmbH, with South African Coal and Oil Limited (SASOL), are the bases of the methanation process which Lurgi is proposing for commercial plants. 

This fall, the closed-loop Evergreen Nylon Recycling plant will start up in the US, a joint venture of DSM Chemicals North America and AlliedSignal. The facility will recover 45,000 m.t./year of caprolactam by depolymerising the fibres from 100,000 m.t./year of discarded nylon-6 carpets. Meanwhile in Germany, Lurgi is building the Polyamid 2000 AG facility. It will process 120,000 m.t./year of carpet waste and recover 10,000 m.t./ year of caprolactam from nylon-6 carpets and 13,000 m.t./ year of nylon-6-6 from nylon-6-6 carpets. 

In this process developed by Lurgi [17], the phenolic effluent is contacted with the solvent in a multistage mixer-settler countercurrent extractor (Fig. 10.8). The extract, containing phenol, is separated into phenol and solvent by distillation and solvent is recycled to the extractor. The aqueous raffinate phase is stripped from solvent with gas, and the solvent is recovered from the stripping gas by washing with crude phenol and passed to the extract distillation column. 

The process has been demonstrated on a pilot scale by Lurgi and Statoil. Sufficient propylene has been produced to make polypropylene resin product by Borealis. This process appears to use an oxide doped ZSM-5 zeolite catalyst in fixed bed reactors. The oxide doping promotes the methanol conversion to olefins. All olefins, other than propylene, are recycled to extinction or purged as fuel gas or produced as naphtha. The flow sheet is illustrated in the Figure 11.8. 

The Eastman process was the first modem coal-to-chemicals facility. Coal is converted to synthesis gas (CO + H ) by reaction with water in a Lurgi reactor. The synthesis gas is then purified and converted to methanol in a heterogeneous process. Reaction of methanol with acetic acid (which is recycled from applications of acetic anhydride) produces methyl acetate, which is the starting material for the Eastman carbonylation 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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