Formation Of Carbonaceous Compounds Research Articles

Highly selective hydrodeoxygenation of wood pallet sawdust pyrolysis oil to methyl phenol derivatives using cobalt and iron on activated carbon supported catalysts

• Effect of Co, Fe, and Co-Fe on AC support was investigated for WPS bio-oil upgrading. • 20 wt% 4Co-1Fe/AC catalyst was optimal with HHV (34.16 MJ/kg) and liquid yield (68.85%) at 350 °C and 60 bar. • Methyl Phenol derivates was the main component in upgraded bio-oil. • The deactivation was occurred by external coke formation and oxidation of metals. The catalytic hydrodeoxygenation (HDO) processes for upgrading pyrolysis bio-oils from wood pallet sawdust (WPS) were studied using activated carbon (AC) as a support of mono- (Co/AC and Fe/AC) and bi-metallic (Co-Fe/AC) catalysts. The effects of the reaction temperature and hydrogen pressure on products and high heating value (HHV) were systematically investigated. At 350 °C and 60 bar, 20 wt% Co/AC showed the highest liquid yield (70.46 wt%) along with HHV of 34.22 MJ/Kg. Among the tested bimetallic catalysts, comparable liquid yield (68.85 wt%) and HHV (34.16 MJ/kg) were achieved with 20 wt% 4Co-1Fe/AC catalyst. Methyl phenol derivatives were found to be the main component in upgraded bio-oil. The carbon number of the upgraded bio-oil was mainly distributed in C 5 –C 11 fraction, especially with the C 8 component (20.40 wt%). The catalysts were deactivated by the formation of carbonaceous compounds on the external surface, oxidation of metal species, and blocking of active sites on catalysts.

Conversion of biogas to synthesis gas over NiO/CeO2–Sm2O3 catalysts

The main objective of this work has been to study the catalytic activity in the conversion of biogas to Syngas of a Ni/Ce0.82Sm0.18O1.91 oxide system, which could be used as a component in the anode material of a SOFC directly fed with biogas.The solids were active without need of pretreatment with a stable behavior during a time on stream of six hours for a carbon dioxide to methane molar ratio of 2.3. This feed composition maximize the production of synthesis gas, with stable catalytic behavior without formation of carbonaceous compounds and involving CO2 capturing, contributing to the reduction of greenhouse gases.It can be concluded that NiO/CeO2Sm2O3 catalysts exhibited promising catalytic performance for their use in the composition of anode material of solid oxide fuel cells fed with biogas.

Phase transformation of unpromoted and promoted Fe catalysts and the formation of carbonaceous compounds during Fischer–Tropsch synthesis reaction

Precipitated Fe catalysts with or without additives (Zn, K, Cu) were prepared, pretreated by CO, and then time-dependent behaviors of their FTS activities were investigated at 503 K and 1.6 MPa in a fixed bed reactor. Over the catalyst without additives, CO conversion showed a maximum at ca. 8 h on stream and then decreased monotonically with increasing time on stream. When Zn, K and/or Cu were added, respectively, similar behaviors were observed. However, an increasing CO conversion was observed during on stream (29 h) when Zn, K and Cu were added simultaneously. X-ray diffraction (XRD) analysis of these catalysts showed the formation of Fe carbides (Fe 5C 2 and Fe x C) after the CO pretreatment irrespective of the catalyst composition. In the case of the catalyst without additives, these carbides were oxidized to Fe 3O 4 during on stream. The oxidation of the carbides was more significant on the catalyst charged near the outlet of the reactor. For the catalyst containing all the additives simultaneously, however, the Fe carbides were only phases detected by XRD analysis even after the long time on stream (29 h). In addition, the formation of amorphous carbonaceous compounds was observed by laser Raman spectroscopy (LRS) for the catalysts after the CO pretreatment and/or the FTS reaction. So-called a graphite-like carbonaceous compound was not observed by LRS, which was considered as one of reasons for the catalyst deactivation in the previous studies. Therefore, it is suggested that the oxidation of the Fe carbides by H 2O vapor is a main reason for the deactivation of the Fe FTS catalyst. Because the Zn, K and Cu containing catalyst showed a higher CO 2 selectivity, the combination of these additives improves the water-gas shift activity, thereby suppresses the oxidation of the Fe carbides.

Selective isomerization of n-butenes into isobutene over aged H-ferrierite catalyst : nature of the active species

The nature of the active species responsible for butene isomerization over aged HFER samples is reexamined in the light of the change in the product yields at very short time-on-stream and of the reversible and irreversible increases in weight of the zeolite during the reaction. At very short time-on-stream, the selectivity of butene isomerization is that expected from a dimerization-cracking process, in particular simultaneous formation of isobutene, propene and pentenes. A rapid decrease of all the yields is observed with time-on-stream; however, for isobutene but not for the other products, the initial decrease is followed (after 10 minutes-on-stream) by an increase. The decrease in the yield can be related to the formation of carbonaceous compounds (``coke'') which block the access to the pores, while the increase in isobutene yield can be explained by the development of a new isomerization mode which is very selective to isobutene. This new mode could be catalyzed by carbonaceous compounds and/or by reaction products which are shown to be retained inside the pores during the reaction. It is proposed that at short time-on-stream the increase in isobutene yield is due to an autocatalytic reaction, n-butene isomerization occurring on t-butyl carbenium ions formed by adsorption of isobutene molecules (which are slowly desorbed from the pores) on the protonic sites of the zeolite. At long time-on-stream, the active species would be benzylic carbocations formed from carbonaceous compounds trapped in the pores near the outer surface of the crystallites.

Formation of Carbonaceous Compounds from Propene and Isobutene over a 5A Zeolite. Influence of Temperature on Their Compositions and Locations

The formation of carbonaceous compounds (“coke”) from propene and isobutene on a 5A zeolite and their effects on the capacity for nitrogen adsorption were investigated in a microbalance system. The operating conditions of coking were as follows: 100−420 °C, pressure of alkene of 0.97 bar, 0.085 g of the 5A zeolite, and operating time from 5 min to 100 h. At low temperatures (100−150 °C), coke constituted mainly of oligomers formed on the acid sites of the zeolite. These oligomers located in the α cages can be removed by thermal treatment in vacuum at high temperatures. The effect on the adsorption capacity was more pronounced for coke formed from isobutene due to the preferential location of oligomers in α cages near the outer surface of the crystallites. At high temperatures (350−420 °C), aromatics and polyaromatics were formed which cannot be removed by a simple thermal treatment. The effect of coke on the adsorption capacity showed that whatever their origin, these coke molecules (most likely the poly...

Formation from propene of carbonaceous compounds responsible for the deactivation of a 5A adsorbent. Removal through pyrolysis and oxidative treatment

The formation of carbonaceous compounds (coke) from propene was investigated by microgravimetry at 423 K on a 5A adsorbent (80% zeolite, 20% binder) for propene pressures of 6.5, 30 and 97 kPa. First, oligomers and their position and skeletal isomers are formed on the protonic sites of the 5A zeolite. These branched compounds are trapped in the α cages. They can be removed as propene (after cracking) by simple vacuum treatment at 423 K. These compounds (reversible coke) undergo afterwards other reactions, in particular hydrogen transfer and cyclization with the formation of dienes, trienes and naphthenes, as shown by gas chromatographic-mass spectrometric (GC-MS) analysis. Part of these latter compounds can only be cracked at high temperatures leading to olefinic products which rapidly transform into aromatics. These aromatics cannot be transformed into linear products, which explains that part of the coke cannot be removed from the adsorbent by thermal vacuum treatment. All the carbonaceous compounds can be removed through treatment under oxygen at 773 K. The adsorption capacity decreases linearly with the increase in the irreversible coke content. This decrease is independent of the propene pressure used for coke formation. The total blockage of the access of nitrogen to the zeolite pores occurs for a number of coke molecules close to the number of α cages.