Carbonaceous residue

Carbonization. Next to combustion, carbonization represents one of the largest uses of coal (2,24—26). Carbonization is essentially a process for the production of a carbonaceous residue by thermal decomposition, accompanied by simultaneous removal of distillate, of organic substances. 

One area of cat cracking not fully understood is the proper determination of carbon residue of the feed and how it affects the unit s coke make. Carbon residue is defined as the carbonaceous residue formed after thermal destruction of a sample. Cat crackers are generally limited in coke burn capacity, therefore, the inclusion of residue in the feed produces more coke and forces a reduction in FCC throughput. Conventional gas oil feeds generally have a carbon residue less than 0,5 wt for feeds containing resid, the number can be as high as 15 wt lf. 

BONE CHAR A decolorizing and de-ashing filtration material made from dried cattle bones that have been crushed and retorted (at >550°C) to activate their alkaline calcium phosphate crystalline structure and carbonaceous residue. 

A platinum electrode pretreated in the way as is described in Section 1.2 may show some minimal desorption of carbonaceous residues which may come from C-atoms diffusing from the bulk of Pt or from the rest of the gas in the UHV. A blank desorption experiment carried out by transferring a Pt electrode which was held at 450 mV in H2S04 for 120 s is shown in Fig. 2.4(a). 

Methylcyclopentane is a powerful probe molecule for the study of metal surfaces. The product distribution on platinum depends on the following factors particle size 491 reaction conditions 492-494 carbonaceous residues,492,493,495 and the extent of the interface between the metal and the support.492,493,495 The hydrogenolysis rate of methylcyclopentane depends on the hydrogen pressure.496,497 The rate exhibits a maximal value as a function of hydrogen pressure on EuroPt catalysts.498 The hydrogenolysis of methylcyclopentane has also been studied over Pt-Ru bimetallic catalysts.499... 

The MDA experiments were performed in a continuous down-flow fixed bed reactor at 700°C, atmospheric pressure, and a space velocity of 1500 em3/(gcat h). Catalysts were pretreated in He flow at 700°C for 30 min before feeding a CH4 N2 mixture in a 9 1 voEvol ratio (N2 used as internal standard). Unreacted methane, the reference N2, and the reaction products were analyzed on line in a gas chromatograph (HP-GC6890) as detailed in [6]. Product selectivities are given on a carbon basis. The use of N2 as internal standard allows to obtain the amount of carbonaceous residues as the amount of carbon required to close the mass carbon balances to 100%. 

Autotrophic activity. Because of the low C N ratio and its declining value as carbonaceous residues are degraded there is substantial ammonification. With all mean treatment times greater than the doubling time of Nitrobacter sp. nitrification will occur provided that oxygen is not limiting. Smith and Evans (19) found that with DO levels above 15% of saturation, nitrification continued until the culture was limited by a fall in pH level. Up to 40% of the slurry ammonia was oxidised. The autotrophic activity never achieved steady state and cycled between periods of activity when the pH value was above about 5.5 and periods of inactivity when the pH value fell below 5.5. Complete nitrification of all ammonia only occurred if the pH value was controlled at about 7 by the addition of alkali. When the DO level was held within the range of 1 to 15% of saturation a system of simultaneous nitrification and denitrification was established. The reduction of nitrate allowed the pH value to remain above 6 and nitrification to continue. Thus more than 70% of the ammonia was oxidised. If the DO level was held below 0.1% of saturation, nitrification was inhibited (unpublished). 

Another coke formed in a FCC unit is occluded or residual coke. In a commercial unit this coke corresponds to coke formed on catalyst porosity and its content depends on textural properties of the catalyst (pore volume and pore size distribution) and the stripping system capacity in the reaction section. Finally on the FCC catalyst rests some high-molecular weight of nonvaporized hydrocarbons. These molecules do not vaporize or react at the reactor conditions and accumulate in the catalyst pores like a soft carbonaceous residue with high hydrogen content. 

Before TPO analysis it was necessary to Soxhlet extract the FCC samples to remove nonvaporized hydrocarbons and avoid their accumulation in the pores of the catalyst as carbonaceous residue with high hydrogen content. As a result, the interference during TPO analysis caused by the desorption and decomposition of these compounds at high temperatures was eliminated. In this study it was observed that this type of coke is directly related to the Conradson carbon content of the feedstock. 

Note As chlorides such as NaCl are volatile, part of them may be lost during the heating of carbonaceous residue either with a burner or... 

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