Residual catalyst content

An understanding of the residual catalyst content of prepared materials is important as it could potentially influence materials ageing and reliability. For FeCl3, the co-ordination by water to the Fe3+ will result in the formation of acidic species that could induce hydrolysis and scission of the Si—O—Si linkage. We have utilised Mossbauer spectroscopy to assess the nature of the FeCl3 catalyst in the final polymer. Our work in this area is quite original, as there are no reports of any such studies being performed previously on these materials. 

Azeotropic dehydration and condensation polymerization (route 2 in Figure 8.2) yields directly high molar mass polymers. The procedure, patented by Mitsui Toatsu Chemicals [13, 14], consists of the removal of condensation water via a reduced pressure distillation of lactic acid for 2-3h at 130°C. The catalyst (in high amounts) and diphenyl ester are added and the mixture is heated up to reflux for 30-40 h at 103°C. Polycondensated PLA is purified to reduce residual catalyst content to the ppm range [5,10,15]. 

Of the three worldwide manufacturers of poly(ethylene oxide) resins. Union Carbide Corp. offers the broadest range of products. The primary quaUty control measure for these resins is the concentrated aqueous solution viscosity, which is related to molecular weight. Specifications for Polyox are summarized in Table 4. Additional product specifications frequendy include moisture content, particle size distribution, and residual catalyst by-product level. 

The Ticona materials are prepared by continuous polymerisation in solution using metallocene catalysts and a co-catalyst. The ethylene is dissolved in a solvent which may be the comonomer 2-norbomene itself or another hydrocarbon solvent. The comonomer ratio in the reactor is kept constant by continuous feeding of both monomers. After polymerisation the catalyst is deactivated and separated to give polymers of a low residual ash content and the filtration is followed by several degassing steps with monomers and solvents being recycled. 

Either acid or base catalysis may be employed. Alkaline catalysts such as caustic soda or sodium methoxide give more rapid alcoholysis. With alkaline catalysts, increasing catalyst concentration, usually less than 1% in the case of sodium methoxide, will result in decreasing residual acetate content and this phenomenon is used as a method of controlling the degree of alcoholysis. Variations in reaction time provide only a secondary means of controlling the reaction. At 60°C the reaction may takes less than an hour but at 20°C complete hydrolysis may take up to 8 hours. 

To accelerate the polymerization process, some water-soluble salts of heavy metals (Fe, Co, Ni, Pb) are added to the reaction system (0.01-1% with respect to the monomer mass). These additions facilitate the reaction heat removal and allow the reaction to be carried out at lower temperatures. To reduce the coagulate formation and deposits of polymers on the reactor walls, the additions of water-soluble salts (borates, phosphates, and silicates of alkali metals) are introduced into the reaction mixture. The residual monomer content in the emulsion can be decreased by hydrogenizing the double bond in the presence of catalysts (Raney Ni, and salts of Ru, Co, Fe, Pd, Pt, Ir, Ro, and Co on alumina). The same purpose can be achieved by adding amidase to the emulsion. 

The effect of synthesis gas composition on conversion, catalyst life, carbon black formation, etc. was determined in numerous tests. Characteristic variables in the synthesis gas composition are the H2/CO ratio, residual C02 content, and content of trace components in the form of higher hydrocarbons and catalyst poisons. 

Residual catalyst (expressed as ash content). The actual residues depend on the manufacturing process used and on the characteristics of the polymer. The so-called new generation HD-PE processes such as the Solvay process use superactive catalysts which produce polymers with a low ash content and, hence, low or negligible odor. Some narrow MWD (Molecular Weight Distribution) resins also have lower catalyst residues than their wide MWD counterparts. 

Fig. 3.3.2 Relaxation dispersion T7(v) for (a, b) n-heptane and (c, d) water at room temperature in catalyst pellets at various stages of coking and regeneration. Numbers indicate weight-percentages of coke (a, c) and residual coke content during regeneration (b, d).

Fig. 3.3.11 Partially regenerated, coked Al203 catalyst samples with the same residual coke content of 7.65% left, regenerated at 550 °C right, regenerated at 400 °C. (a) Optical photographs of cut samples (b) NMR images with...

The second group was characterized by well-performing catalysts with high naphtha yields combined with low yields of coke and gas. At that time this was rather unexpected, since it was commonly accepted in those days that a residue catalyst should have a medium zeolite content and a high matrix surface area [15]. Obviously more studies were necessary within this held. 

In the present context, heavy oils and residua can also be assessed in terms of sulfur content, carbon residue, nitrogen content, and metals content. Properties such as the API gravity and viscosity also help the refinery operator to gain an understanding of the nature of the material that is to be processed. The products from high-sulfur feedstocks often require extensive treatment to remove (or change) the corrosive sulfur compounds. Nitrogen compounds and the various metals that occur in crude oils will cause serious loss of catalyst life. The carbon residue presents an indication of the amount of thermal coke that may be formed to the detriment of the liquid products. 

If a Low Temperature Shift (LTS) converter is installed (see Figure 5.35), the gas from the HTS is cooled to increase the conversion, and then it is passed through the LTS converter. The LTS converter is fdled with a catalyst containing copper oxide, zinc oxide, and aluminum oxide. It operates at about 200-220°C. The residual CO content in the converted gas is about 0.2% to 0.4% (on a dry gas basis)53. Some LTS reactors operate with an inlet temperature of 190-210°C and reduce the CO level to 0.1 to 0.2 mole % (dry). Again, the catalyst takes the reaction to equilibrium at as low a temperature as possible because this favors the hydrogen production70. 

Figure 3.8 Comparison of k0forthe hydrolysis of albumin (S0 = 1.50 x KT6 m) by [lmc]22PCDMe° (C-22), [lmc]5PCDMe° (C-5), [lmN]16PCDMe° (N-16), and [lmN]63PCDMe° (N-63) (Q = 0.115 m) at pH 7.00 and 25°C. In the nomenclature ofthe catalysts, superscript C or N indicates that imidazole was attached via the C or N atom, respectively, and the subscript is the residue mol% content of imidazole attached to PCD.

Figure 4. Relative metallic or acidic activity as a function of relative residual carbon content on the "burned1 catalyst. The unity of catalytic activity is the percentage of cyclohexane produced by hydrogenation of benzene (a), or i-pentane produced by n pentane isomerization (b), over the completely decoked catalyst. The unity of residual carbon is the percentage of carbon in the initial catalyst (Table 1). I, catalyst I burnt with ozone-air II, catalyst II burnt with 02-N2 III, catalyst III burnt with 02-N2.

The gas from the HTS is cooled to increase the conversion, and then it is passed through the low temperature shift (LTS) converter. The LTS converter is filled with copper oxide/zinc oxide-based catalyst and operates at about 200-220°C. The residual CO content is about 0.2 to 0.4 percent (on a dry gas basis).53... 

The control of key quality parameters is made easier the particle size distribution, the bulk density and the residual moisture content It produces the most homogeneous product for multicomponent systems and the catalyst particles have the same chemical composition as the feed, therefore affording a very high recovery (99+%) and a minimal level of pollution... 

In this reaction the residual C02 content can be tolerated. Another major H2 consuming process is the manufacture of ammonia. This requires pure H2 carbon oxides are poisons for the ammonia catalyst and have to be removed, C02 by scrubbing, and residual CO (as well as traces of C02) by catalytic conversion to CH4 (methanation) which is recycled. 

High-temperature conversion employs catalysts based on iron oxides (80 to 95 per cent weight) and chromium (5 to 10 per cent wei t) which can withstand the presence of small amounts of sulfur products without an excessive loss of activity. They operate between 300 and 450 C, and as high as with volume hpuily space velodties of 300 to 3000 h and lead to residual CO contents of 1 to 2 per cent volume. 

This is practically total above 300°C and, even at atmospheric pressure, lowers the residual CO content to less than 20 ppm and to a few ppm under pressure. It takes place in the presence of nickel base catalysts deposited on alumina and doped with chrominm oxide. The exothennicity of the reaction (Ar from 70 to 80 C/per cent CO converted) requires operation with two catalyst beds and intermediate effluent cooling. 

In the traditional plant concept, the gas from the secondary reformer, cooled by recovering the waste heat for raising and superheating steam, enters the high-temperature shift (HTS) reactor loaded with an iron - chromium catalyst at 320 - 350 °C. After a temperature increase of around 50 - 70 °C (depending on initial CO concentration) and with a residual CO content of around 3 % the gas is then cooled to 200-210 °C for the low-temperature shift (LTS), which is carried out on a copper - zinc - alumina catalyst in a downstream reaction vessel and achieves a carbon monoxide concentration of 0.1-0.3 vol%. 

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