Second-Stage Operation

Newly developed second-stage catalysts which increase their ability to resist either sulfur spikes in the second-stage feed or overall higher sulfur levels will greatly enhance the economics of the process. Criterion26 developed a more poison-resistant catalyst that in one plant extended the catalyst cycle length to 3.5 years from 6 months attained by the previous nickel catalyst. 

The second-stage catalyst must also have essentially no acidity to prevent cracking of the feedstock and generation of light ends. It is normal to have a stripper at the end of the process to remove small amounts of light ends formed and correct the product flash point, but any further cracking would lead to unnecessary yield loss. 

It is appropriate to point out here that since catalyst technology is a rapidly advancing art, it is to be expected that more recently developed catalysts for both first- and second-stage reactors will significantly outperform any mentioned here. 

To address any concerns that there might be chemical differences between white oils produced by the acid process and hydrotreatment, the mass spectra of Lyondell Duotreat products were compared with those from acid treatment.8 The authors concluded that there was indeed little difference at the same viscosity level (Table 11.3). White oils made by acid treating can have higher sulfur levels than those that are produced by hydrotreating.27 

Mass Spectrometry Analyses of Food Grade Oils Produced by Acid Treatment and by the Duotreat Process 

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W the second stage operates at temperatures between 8 and 20K with cooling powers in the range 2 to 10 W) are more convenient to use in routine applications for pumping speeds up to 104Ls 1. 

Residual carbamate and CO2 are recovered downstream of the stripper in two successive stages. The first stage operates at 17 bar, and the second stage operates at 3.5 bar. Ammonia and CO2 vapors from the stripper top are mixed with the recovered carbamate solution from the High Pressure (HP) / Low Pressure (LP) sections, condensed in the HP carbamate condenser and fed to the reactor. The urea solution that leaves the LP decomposition stage is concentrated in the evaporation section to make a urea melt110. 

TwinRec A two-stage process for recovering energy and materials from various industrial wastes. The first stage, operated at 500 to 600°C in a reducing atmosphere, separates combustible materials from metallic and inert materials. The second stage, operated at 1350 to 1450°C, produces a molten ash, which solidifies to a granular material suitable for the construction industry. Developed by Ebara Corporation and commercialized in 20 plants in Japan by 2004. 

For the third stage of the typical process when the vehicle is methanol or water, the same automatic perforated basket centrifuge described under the second stage would be applicable and the capacity and performance would be substantially identical to those reported under second stage operation. 

The flexibility of the bath smelting furnace permits the operation to adapt quickly to the prevailing economic situation. A higher rate of treated battery paste, achieved by lowering the amount of concentrates processed, results in a lower tonnage of primary slag produced. The latter is either processed in a second stage operation or is sold. 

The first stage of the Spheripol process consists of polymerization in liquid propylene. Usually, two loops are used in series to narrow the residence-time distribution of the catalyst particles. For the ethylene-propylene copolymer (EPR) stage, the Spheripol process (Fig. 2.33) utilizes a gas phase fluidized bed reactor (FBR). The liquid propylene/ polymer suspension from the first reactor is flashed to gas/solid conditions prior to entering the second stage. The second stage operates at pressures of 15-35 atm, which is often close to the dew point of the gas. Elevated temperatures of approximately 80°C are used to provide a reasonable amount of copolymer contents in the final product. 

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