Hydrogen Transfer Capacity Research Articles

A novel production of aromatic hydrocarbons via dielectric barrier discharge assisted one-stage pyrolysis-catalysis of biomass: Insights into modified HZSM-5 selectivity and stability

Dielectric barrier discharge (DBD) was employed to assist to convert biomass into aromatic hydrocarbons under the vacuum pyrolysis and zeolite catalysis conditions. This study was to investigate the selectivity and stability of HZSM-5 modified by Ti, Ni, and Ni-Ti. The texture and acidity of different modified catalysts varied greatly. Ti modification strengthened the cracking removal of carbon and oxygen, while Ni-modified version improved hydrogen transfer capacity. Bimetallic modification increased the HHV to 36.93 MJ/kg, and obtained a compromised yield of 28.10%. Hydroxyl was difficult to completely remove due to hydrophilicity, carbonyl removal was better, and refined bio-oils had a high aromatic degree, of which, bimetallic modification increased the selectivity of MAHs to 76.61% and the refined bio-oil was more suitable to be used as gasoline additives. Although the aromatization performance of Ti-modified version was weaker than that of Ni-modified version, its anti-coking performance was better. The acidity adjustment of bimetallic modification cooperated with the synergistic effect of metal species and discharge, so that the difficulty of carbon deposition was increased significantly. The high-temperature catalytic coke was not distinguished and the low-temperature thermal coke mainly deposited on the outer surface was further reduced for bimetallic modified catalyst. Therefore, the Ni-Ti/HZSM-5 assisted by DBD exhibited better potential in improving the selectivity of aromatic hydrocarbons and enhancing the stability of zeolite catalyst.

Promoting asphaltene conversion by tetralin for hydrocracking of petroleum pitch

The effects of tetralin as an H-donor on the reactivity of asphaltenes in a petroleum pitch were investigated under thermal cracking or catalytic hydrocracking conditions at 693 K and 10.0 MPa N2 or H2. Reaction temperatures, pressures, and tetralin contents were varied to examine the reactivity of asphaltenes. Thermal cracking of the petroleum pitch led to a considerable amount of coke formation, close to 53.7 wt%, but the addition of tetralin reduced the coke formation down to 23.6 wt%. The coke formation was considerably reduced to 10.3 wt% in the catalytic hydrocracking condition, and was not formed in the presence of tetralin. Kinetic studies on the catalytic hydrocracking of petroleum pitch in the absence or presence of tetralin demonstrated that the addition of tetralin, showing an increase in the hydrogen transfer capacity, contribute to the marked performance of hydrocracking of the petroleum pitch in the presence of dispersed MoS2 catalyst.

Hydrogen and Atom Transfer Activity of Saffron Extracts by Square Wave Voltammetry

AbstractSaffron is an edible spice with highly appreciated sensory and antioxidant properties. One of the most representative redox species found in saffron extracts is crocin, whose content is used to evaluate the quality and value of the resulting spice. In this study, a voltammetry method based on the direct detection of crocin at a bare glassy carbon electrode is presented. The principle of the method is based on the monitoring of the anodic wave exhibited by crocin (0.1–1.0 mM) after its mixing with the azo radical initiator AAPH (20 mM) in ethanol:acetonitrile (1 : 1) solution. The decay rate of the anodic peak (E=+434 mV vs. Ag/Ag+), as a result of the consumption of crocin by AAPH, was used as index of the hydrogen transfer capacity and, thus, of its antioxidant activity. With a decay rate of k=0.02 h−1, crocin exhibits only a weak antioxidant activity in comparison with tocopherols (k=0.13 h−1), but still sufficient to protect against the oxidation of safranal, a further redox species found in saffron extracts and mainly responsible for its flavor. The proposed approach was finally applied to discriminate saffron extract samples from different geographical origins. The proposed approach is suitable to characterize the quality of saffron extracts and estimate its antioxidant properties.

Adsorption of Thiophenic Compounds in the Gasoline Boiling Range over FCC Catalysts under Process Conditions

Experiments on commercial FCC equilibrium catalysts with different hydrogen transfer properties and content of Ni and V contaminant metals were performed in a CREC Riser Simulator reactor to study the behavior of thiophenic compounds in the gasoline boiling range. Thiophene and alkylthiophenes were used as test reactants dissolved in aromatic and paraffinic solvents in usual concentrations of the process, from about 150 to 400 ppm of each compound. The experiments were performed under conditions similar to those of the industrial operation (510 º C, contact time 5 to 20 s). The reaction effluents were analyzed by on-line gas chromatography using two detectors simultaneously: FID (hydrocarbons) and PFPD (sulfur). The results showed that a higher hydrogen transfer capacity in a catalyst favors the decrease of the concentration of sulfur compounds in gasoline by adsorption and / or coke formation. These results were more pronounced as the molecular weight of the alkylthiophene increased. Reductions in total sulfur concentration in the gas phase as high as 65 % were observed. Among contaminant metals, Ni seemed to have an important contribution to this effect.

Novel coal-based precursors for cokes with highly oriented microstructures

The suitability of new environmentally-friendly coal-based products for the preparation of cokes with a highly oriented microstructure is investigated. These products (AO-A and AO-B) are obtained from two different stages of the processing of an industrial anthracene oil. The composition and degree of polymerization determine their ability to produce cokes with highly oriented textures. The transformation of AO-A into a highly oriented coke requires pyrolysis temperatures of 450–460°C, residence times of 8–20h and a pressure of 5bar, whereas AO-B, which is more polymerized, requires lower temperatures (420–440°C) and shorter residence times (8h) without the application of any external pressure. The larger extent of highly oriented microstructures present in cokes from AO-A is explained from the greater hydrogen transfer capacity during the coking process.

Efecto del uso de Catalizadores Ácidos Sobre la Distribución de Productos en la Pirólisis de Neumáticos

The thermal and catalytic pyrolysis of tyres in a high heating rate commercial microreactor has been studied by following two reaction strategies: in situ catalytic and thermal pyrolysis followed by on-line catalytic pyrolysis. The catalysts have been prepared based on HZSM-5, HY and HBeta zeolites and they have been used in situ in the pyrolysis reactor and on-line, in a fixed bed reactor. The use of the catalyst in situ decreases the pyrolysis temperature by 50 K (from 773K to 723 K) and significantly increases the yield of gas and C10- light aromatics. The shape selectivity of HZSM-5 zeolite and the higher micropore size and hydrogen transfer capacity of HY zeolite significantly affect product distribution. The HBeta zeolite catalyst has an intermediate behaviour. The yields of gases, C10aromatics and tar increase in the catalytic reforming of thermal pyrolysis.

Effect of acid catalysts on scrap tyre pyrolysis under fast heating conditions

A study has been carried out on the effect of acid catalysts prepared based on HZSM-5, HY and HBeta zeolites on the distribution of volatile products (gas, non-aromatic C 5–C 10 fraction, aromatic C 10 − and tar), in the pyrolysis of tyre material carried out in a fast heating microreactor. The results have been compared with those of thermal pyrolysis. The strategies of using the catalyst in situ and reforming the volatiles generated in thermal pyrolysis have also been compared. The use of a catalyst in situ lowers the pyrolysis temperature by 50 K (to 723 K) and produces a significant increase in the yield of gases and light aromatic C 10 − , at the expense of a decrease in the yield of non-aromatic C 10 − . The yield of tar increases only slightly. The shape selectivity of each zeolite has a significant effect and, consequently, HY zeolite leads to the formation of heavier structures that make up the tar and to aromatic C 10 − , which is favoured by hydrogen transfer capacity. HZSM-5 is more efficient for the formation of gases, although it contributes only to decreasing the molecular weight of aromatic C 10 − fraction. HBeta zeolite catalyst has an intermediate behaviour. Reforming pyrolysis volatiles at 723 K using a HZSM-5 zeolite catalyst efficiently increases (from 2 to 20 wt%) the yield of gases, with a high yield of ethene and propene. The yields of BTX fraction are also very high (around 11.5 wt%).

Effect of catalyst properties on the cracking of polypropylene pyrolysis waxes under FCC conditions

The catalytic cracking of polyolefin pyrolysis waxes has been studied under conditions that mimic the operation of a catalytic cracking unit (FCC). Two commercial catalysts of different properties were used. Yields and compositions of the lumps (dry gases, LPG, gasoline and coke) were compared with those corresponding to the actual feed in the refinery (vacuum gas-oil). The effect of process operating conditions (temperature and contact time) is significant. Catalyst acidity has a significant effect on conversion (at a temperature around 525 °C) and on yields and compositions of lumps (in the 500–550 °C range). The main effect of increasing catalyst acidity is an increase in coke content on the catalyst by decreasing the yield to dry gases. Due to the higher hydrogen transfer capacity, the gasoline obtained using the catalyst with higher acidity has a higher aromatic (especially C 6–C 8) and paraffinic content, and lower olefin content, being these two latter fractions less branched. An increase in catalyst acidity leads to a lower yield of light olefins and to an increase in the yield of paraffins.

Effect of HZSM-5 catalyst addition on the cracking of polyolefin pyrolysis waxes under FCC conditions

A study has been carried out on the effect of catalyst acidity and composition (mixtures of base catalyst and catalysts provided with HZSM-5 zeolite of different acidity) on the catalytic cracking of polyolefin pyrolysis waxes carried out under standard conditions in a refinery FCC. The experiments have been carried out in a riser simulator, in the 500–550 °C range. The results show that the yields and composition of product stream are acceptable and controlable by refineries without any special adaptation of process conditions. The acidity of the catalysts has a relevant effect on hydrogen transfer capacity, which contributes to decreasing the concentration of olefins in the gases and in the gasoline. The incorporation of HZSM-5 zeolite is very efficient for increasing the yield of gasoline. This gasoline and LPG are more olefinic than those obtained with the base catalyst, given that hydrogen transfer capacity of the catalyst is inhibited.

1-Hexene isomerization and n-hexane cracking over HMCM-22

Isomerization of 1-hexene and cracking of n-hexane over HMCM-22 were carried out in a continuous flow glass reactor. The results were compared with those obtained over HZSM-5 under similar conditions of conversion. The catalyst HMCM-22 caused much more double bond shift and less skeletal isomerization in 1-hexene isomerization than HZSM-5. Also, in n-hexane cracking, HMCM-22 gave a higher yield of olefins and a lower yield of aromatics than HZSM-5. The results can be explained on the basis of the lower acidic strength and the inferior hydrogen transfer capacity of HMCM-22 compared to those of HZSM-5.

Stereospecificity of hydrogen transfer by phosphoglycerate dehydrogenase

Phosphoglycerate dehydrogenase (EC 1.1.1.95) has been shown to be A site specific in its hydrogen transfer capacity unlike other dehydrogenases which use phosphorylated substrates. The experiments have been carried out using a coupled assay system with yeast alcohol dehydrogenase. The specific activity measurements of the reaction products indicate the possible influence of an isotope effect on this system.

Effect of cell-free extracts from Mycobacterium tuberculosis H37Rv on lung succinoxidase.

SEGAL AND BLOCH showed that non-proliferating suspensions of human tubercle bacilli grown in vivo (LRv) exhibited different biochemical properties as compared with the same strain of tubercle bacilli grown in vitro: (a) they had a lower hydrogen transfer capacity; (b) glucose and its intermediates failed to cause an increase over their endogenous respiration1.

Studies on the metabolism of murine leprosy bacilli. I. Stimulating effect of mitochondria extract of rat liver on the metabolism of bacilli.

Biochemical study on the metabolism of murine leprosy bacilli was first commenced by Hanks (1951) . According to his report, the hydrogen transfer capacity of the bacilli was so feeble that only 0.8μmole of TTC (Triphenyl Tetrazolium Chloride) was reduced per mg nitrogen of the bacilli after 24 hours' incubation at 37°C. Soon after, Gray (1952) has found by manometric method that only 5 cmm of oxygen was consumed per mg nitrogen of the bacilli after 1 hour incubation at 37°C. Ito and Sonoda (1957 a) reported that asparagine and yeast extract stimulate the respiration of the bacilli, and also succinate stimulates it in the presence of liver or testicle extract of rats. Later, the same authors (1957 b) have concluded that aspartic-α ketoglutaric transaminase exists in the bacilli. On the other hand, Tamemasa and Tsutsumi (1958) found that the bacilli reduced tetrazolium chloride under anaerobic condition in the presence of o-aminophenol, higher fatty acid such as lauric or myristic acid and indol or skatol.The author has entered the metabolic study of murine leprosy bacilli, bearing in mind that this bacilli might highly be dependent on the host. Reported in the following are the results demonstrating that the heated mitochondria extract of ratliver stimulates the endogeneous metabolism and D-glucose or succinate oxidation of the bacilli.