The SUPRATHERM Process

The cooler 5 and the reduced pressure in the cyclone both serve to increase the furfural concentration in the vapor fraction. The latter enters the first distillation column without intermediate condensation, thus conserving its high enthalpy. Contrary to conventional processing, this vapor is entirely free of particles, so that encrustation problems, a well-known plague of orthodox furfural plants, are reliably avoided. 

The underflow of the cyclone 7 is withdrawn by an eccentric worm pump 8 and delivered to a belt filter press 9 yielding a highly dewatered cake and a filtrate consisting essentially of water but loaded with small concentrations of sulfuric acid, furfural, and by-products. This filtrate is recycled to tank 1 for preparing the feed stock slurry. Due to this scheme, most of the sulfuric acid is recovered and reutilized, the only loss being the quantity contained in the cake. This loss is replaced in tank 1. Analogously, the water leaving the system with the cyclone vapor and the cake is also replenished in tank 1 so that the overall mass balance is satisfied. 

Due to the recycle system, very little furfural is lost, and the furfural concentration in the cyclone vapor increases until it reaches a steady state limit. Undesirable nonvolatile byproducts such as sugars cannot build up to a prohibitive concentration as a certain portion of them continuously leaves the plant with the cake. Thus, the cake discharge represents the stabilizer stream always required in recycle systems. 

As compared to conventional furfural plants, the SUPRATHERM process is seen to feature the following advantages  

The only disadvantage is the high cost for the investment and maintenance of the belt filter press, and for a drier to make the cake burnable. 

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The SUPRATHERM process developed by KRUPP [35, 36, 37, 38] is a continuous hydrolysis where by using a high temperature between 200 and 240 C the reactor is reduced to a simple pipe. An outline of the process in its original form is shown in Figure 23. 

Needless to say, what has been described for the continuously operating ROSEN-LEW reactor also applies to the continuously operating reactor of QUAKER OATS. It, too, generated significant quantities of diacetyl. By contrast, in the continuous SUPRATHERM process, where the air of the raw material is eliminated in the slurry preparation, diacetyl is... 

In the light of all the facts now available from many independent sources, new furfural processes, as the SUPRATHERM and STAKE processes, aim at the increased yields obtainable at high temperatures, even without removal of the furfural from the scene of the reaction. Although this leads to somewhat uncomfortable high pressures, it is certainly a correct route towards higher yields, based on a fundamental principle of thermodynamics, and in hindsight the circumstances at the birth of the furfural industry must be deplored. 

Inasmuch as all industrial furfural processes are carried out at elevated pressures, they all involve a depressurization (flashing) of the residue. In the case of processes where the raw material is steam-stripped to the point of exhaustion, the flashing of the residue yields very little if any furfural, but in the case of non-stripped single pass processes, such as the SUPRATHERM and STAKE processes, the flashing of the residue is an important part of the overall process in that it yields a vapor stream containing most of the furfural produced, and a residue still containing some furfural in its liquid phase. This is illustrated schematically in Figure 123. 

To obtain a comprehensive picture of the yield situation, diagrams of the type shown in Figure 132 must be drawn for various temperatures. In this fashion, it is found that the condensation loss decreases markedly with increasing temperatures. This is strong support for the high temperatures advocated in the SUPRATHERM and STAKE processes. 

Another suprathermal process that is used for suppression of unwanted ions is kinetic energy discrimination (KED). It was first used by Rowan and Houk to prevent polyatomic ions formed in-cell from entering the analyzer, by providing a potential energy barrier between the cell and the analyzer. Ions formed in the cell originate at a potential that is close to the cell rod bias (I CRo) and have little residual kinetic energy (which may be acquired from the precursor ion). 

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