Coke-forming propensity

Data reporting (i.e., the statement of the results of the proximate analysis test methods) usually includes (in some countries but not in all countries) descriptions of the color of the ash and of the coke button. As an interesting comparison, the test for determining the carbon residue (Conradson), the coke-forming propensity of petroleum fractions and petroleum products (ASTM D-189 ASTM D-2416), advocates the use of more than one crucible. A porcelain crucible is used to contain the sample, and this is contained within two outer iron crucibles. This corresponds to the thermal decomposition of the sample in a limited supply of air (oxygen) and the measurement of the carbonaceous residue left at the termination of the test. 

The carbon residue (ASTM D-189 and ASTM D-524) of a crude oil is a property that can be correlated with several other properties (Figure 2-14). The carbon residue presents indications of the volatility or gasoline-forming propensity of the feedstock and, for the most part in this text, the coke-forming propensity of a feedstock. Tests for carbon residue are sometimes used to evaluate the carbonaceous depositing characteristics of fuels used in certain types of oil-burning equipment and internal combustion engines. 

As noted, in any of the carbon residue tests, ash-forming constituents (ASTM D-482) or nonvolatile additives present in the sample will be included in the total carbon residue reported, leading to higher carbon residue values and erroneous conclusions about the coke-forming propensity of the sample. 

Thus a feedstock map can be used to show where a particular physical or chemical property tends to concentrate on the map. For example, the coke-forming propensity, that is, the amount of the carbon residue, is shown for various regions on the map for a sample of atmospheric residuum (Fig. 2.7 Long and Speight, 1998). In addition, a feedstock map can be very useful for predicting the effectiveness of various types of separations processes as applied to petroleum (Fig. 2.8 Speight, 2001). 

Carbon Residue—amount left after evaporation and pyrolysis to provide some indication of relative coke-forming propensity (ASTM Test Method D189, Conradson Carbon Residue of Petroleum Products, ASTM Test Method D524, Ramsbottom Carbon Residue of Petroleum Products, or ASTM Test Method D4530, Determination of Carbon Residue (Micro Method)), ASTM Method D4530 having gained wide acceptance. 

Note 4—In diesel fuel, the presence of alkyl nitrates such as amyl nitrate, hexyl nitrate, or octyl nitrate causes a higher residue value tlum observed in untreated fuel, which can lead to erroneous conclusions as to the coke forming propensity of the fuel. The presence of alkyl nitrate in the fUel can be detected by Test Method D 4046. 

This test method covers the determination of the amount of carbon residue (Note 1) left after evaporation and pyrolysis of an oil, and is intended to provide some indication of relative coke-forming propensity. This test method is generally applicable to relatively nonvolatile petroleum products which partially decompose on distillation at atmospheric pressure. Petroleum products containing ash-forming contituents as determined by Test Method D 482, will have an erroneously high carbon residue, depending upon the amount of ash formed (Notes 2 and 3). 

CCR content. The content of CCR is the most important property of the feed to the coker unit since it determines the amount of coke produced, which is why CCR is a direct measurement of the coke-forming propensity of the feedstock. Feeds with high content of CCR produce more coke. Hence, to maximize the production of liquid products low CCR content feeds are desired. 

Carbon residue the amount of carbonaceous residue remaining after thermal decomposition of petroleum, a petroleum fraction, or a petroleum product in a limited amount of air also called the coke- or carbon-forming propensity, often prefixed by the terms Conradson or Ramsbottom in reference to the inventor of the respective tests. 

Lubricating oil is not usually considered to be used under the extreme conditions under which coke is formed from, for example, fuel oil. Nevertheless, the tests that are applied to determine the carbon-forming propensity of fuel oil (and other petroleum products) are also available for application to lubricating oil should the occasion arise. 

For example, all of the carbon in coal is determined by ultimate analysis and it is not an indication (or determination) of the carbon-forming propensity (i.e., the coke-producing ability) of the coal as is the case with the test for the volatile matter content of coal. Thus, just as there has been the need to develop standard methods for the proximate analysis of coal, there has also been the necessity to develop standard methods for the ultimate analysis of coal. 

CO2 reforming of methane can be used to adjust the H/CO ratio and provide the correct H2/CO ratio for Fischer-Tropsch synthesis and could potentially be used to reduce CO2 emissions from other processes however, it is even more endothermic than steam reforming. Partial oxidation is exothermic and has the correct H2/CO ratio for methanol synthesis, but requires a pure oxygen source, adding to the cost. In addition to the individual drawbacks, all of these processes must be run with 0/C ratios of greater than 1 to prevent coking of the catalyst. This makes the processes more expensive in practice than would be expected under optimized conditions for the stoichiometric reactions. The propensity of these processes to form carbon at low 0/C ratios is even more pronounced at... 

The carbon residues of petroleum and petroleum products serve as an indication of the propensity of the sample to form carbonaceous deposits (thermal coke) under the influence of heat. 

The carbon residue of a petroleum product serves as an indication of the propensity of the sample to form carbonaceous deposits (thermal coke) under the influence of heat. In the current context, carbon residue test results are widely quoted in diesel fuel specifications. However, distillate diesel fuels that are satisfactory in other respects do not have high Con-radson carbon residue values, and the test is chiefly used on residual fuels. 

The carbon residue of a petroleum product gives an indication of the propensity for that product to form a carbonaceous residue under thermal conditions. The carbonaceous residue is correctly referred to as the carbon residue but is also often referred to as coke or thermal coke. 

Two aspects of these results will be discussed here, namely the low platinum dispersion and the presence of significant amounts of coke on alumina and zeolite catalysts after testing. The latter finding is prohahly due to a combination of test tenq>eratures below 2S0°C and the propensity for toluene to form coke. In any event, coke formation did not seem to inhibit the oxidation reaction to any significant extent. The low platinum diversions, confirmed by XRD measurements, indicate that the active reside outside the zeolite micropores on... 

The main problem with the nickel-based anodes is their propensity to coke, that is to become coated with a carbon layer on reacting with hydrocarbon fuel. This carbon layer has two deleterious effects it can disrupt the anode by pushing the nickel particles apart and it can form a barrier at the nickel surface, preventing gas reactions. Typically, if a hydrocarbon such as methane is fed directly into an SOFC anode, then it may not remain functional after as little as 30 minutes as the coking proceeds. Additives to the Ni+YSZ cermet such as 5% ceria or 1% molybdena can inhibit this process [19]. Alternatively, metals other than nickel can be employed [20]. 

---