Applied Petrochemical Research (v.4, #2)
Environmental impacts of ethylene production from diverse feedstocks and energy sources by Madhav Ghanta; Darryl Fahey; Bala Subramaniam (167-179).
Quantitative cradle-to-gate environmental impacts for ethylene production from naphtha (petroleum crude), ethane (natural gas) and ethanol (corn-based) are predicted using GaBi® software. A comparison reveals that the majority of the predicted environmental impacts for these feedstocks fall within the same order of magnitude. Soil and water pollution associated with corn-based ethylene are however much higher. The main causative factor for greenhouse gas emissions, acidification and air pollution is the burning of fossil-based fuel for agricultural operations, production of fertilizers and pesticides needed for cultivation (in the case of ethanol), ocean-based transportation (for naphtha) and the chemical processing steps (for all feedstocks). An assessment of the environmental impacts of different energy sources (coal, natural gas and fuel oil) reveals almost similar carbon footprints for all the fossil fuels used to produce a given quantity of energy. For most of the environmental impact categories, the GaBi® software reliably predicts the qualitative trends. The predicted emissions agree well with the actual emissions data reported by a coal-based power plant (Lawrence Energy Center, Lawrence, KS) and a natural gas-based power plant (Astoria Generating Station, Queens, NY) to the United States Environmental Protection Agency. The analysis shows that for ethylene production, fuel burning at the power plant to produce energy is by far the dominant source (78–93 % depending on the fuel source) of adverse environmental impacts.
Keywords: Ethylene; Environmental impact analysis; Fossil fuels; Corn ethanol; Life-cycle assessment
Highly active and selective catalyst for synthetic natural gas (SNG) production by Yu Huang; Haoyi Chen; Jixin Su; Tiancun Xiao (181-188).
A novel nickel-based methanation catalyst has been prepared and tested for CO and CO2 hydrogenation to synthetic natural gas under various conditions. The catalysts before and after reaction have been characterized using XRD, Laser Raman and IR spectroscopes. It is showed that the novel catalyst can give high methane selectivity and yield at a very broad ranges of temperature and H2/CO ratios, although the selectivity to methane increase with the H2/CO ratio, which, however, increases with the temperature rising from 200 to 350 °C, then gradually decrease. The characterization results showed that the there is surface carbons forming over the catalyst surface, and the nickel crystalline structure changes during the reaction. Despite this, the catalyst still gives the same performance, which suggested that the catalyst can operate in a very broad range conditions.
Keywords: Nickel catalyst preparation; Co-precipitation; Methanation; Synthetic natural gas
The time-on-stream stability of some selected bifunctional nanoporous-based catalysts in n-heptane hydroisomerisation by Faisal M. Alotaibi; Raed H. Abudawood; Hamid A. Al-Megren; Mohammed C. Al-Kinany; Arthur A. Garforth (189-207).
In this work, some commercial nanoporous-based catalysts, such as USY, beta and mordenite zeolites loaded with Platinum metal acting as bifunctional catalysts, were used for hydroisomerisation experiments in a fixed-bed reactor at the atmospheric pressure and at feed space time 5.12 h−1 to hydroisomerise n-heptane over a temperature range of 210–270 °C. The study aimed to evaluate the changes with time-on-stream in the catalytic activity, product selectivity and manner of deactivation of metal-loaded zeolite catalysts, at constant contact time of 5.13 h−1 and a hydrogen-to-n-heptane molar ratio fixed at 9. Various analytical techniques were used to characterise fresh and aged catalysts. Results show that pore architecture is the most important factor affecting coke formation and deactivation in zeolite catalysts, and those catalysts with three-dimensional pore structures lacking cavities or cages were best able to resist deactivation. In addition, it was found that those catalysts with high Si/Al ratios and those which had been acid-leached or steamed showed better activity, higher selectivity towards isomeric products and better time stability. Moreover, the balance between the number of metal sites and the number of acid sites played an important role in determining the activity, selectivity and stability of the bifunctional catalysts.
Keywords: The time-on-stream stability; Alkanes hydroisomerisation; Catalyst deactivation; Zeolites; Bifunctional catalysts; Nanoporous catalysts
Preparation of novel mesoporous Ce-Ni2P/SBA-15 catalysts and their catalytic performance for hydrodesulfurization of dibenzothiophene by Qingyuan Li; Pingyi Wu; Ling Lan; Ni Wei; Shengfu Ji (209-216).
Ni2P/SBA-15 precursors with Ni2P loadings of 25 wt% and initial P/Ni of 0.8 were prepared using nickel nitride as nickel source, diammonium hydrogen phosphide as phosphorus and mesopore molecular sieve SBA-15 as support. Then Ce was introduced into the Ni2P/SBA-15 precursor. The novel mesoporous Ce-Ni2P/SBA-15 catalysts were prepared after temperature-programmed reduction in flowing H2. The structure was characterized by X-ray diffraction, N2 adsorption–desorption isotherms, NH3 temperature-programmed desorption and X-ray photoelectron spectroscopy. The catalytic activities for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were evaluated. The results showed that only Ni2P phase was formed in Ce-Ni2P/SAB-15 catalysts with Ce loadings of 0–5 wt%. Ni2P and Ni12P5 phases were existed in 7 wt% Ce-Ni2P/SBA-15 catalyst. The surface area and pore volume increased when Ce was added to Ni2P/SBA-15 catalyst. The strength of the acid sites and total acid amount of Ce-Ni2P/SBA-15 catalysts increased with increasing Ce loadings. Ce existed in the form of Ce3+and Ce4+, Ni existed in the form of Ni2+ and Niδ+, and P existed in the form of Pδ− and P5+. The addition of Ce to the Ni2P/SBA-15 catalyst decreased Niδ+ concentration in Ni2P/SBA-15 catalyst. The activity for HDS of DBT over Ni2P/SBA-15 catalysts was affected by the addition of Ce at 300–340 °C. The catalysts exhibited a good catalytic performance of deep hydrodesulfurization of dibenzothiophene and the conversion of DBT can reach 98.9 % at 380 °C. Biphenyl was the main product over Ce-Ni2P/SBA-15 catalysts and cyclohexylbenzene was the main product over Ni2P/SBA-15 catalyst at 380 °C.
Keywords: Ce; Ni2P; SBA-15; Hydrodesulfurization; Dibenzothiophene
Effect of N2 and O2 on selective disproportionation of xylene mixed ethylbenzene over highly active silylated HZSM-5 by Kakasaheb Y. Nandiwale; Vijay V. Bokade (217-223).
The influence of carrier gases such as nitrogen and air (78 % N2 and 21 % O2) on catalytic activity and its stability etc., over modified H-ZSM-5 (pore size regulated by silylation) for the selective formation of Para-diethylbenzene (p-DEB) by xylene mixed ethylbenzene (EB) disproportionation is discussed. The comparison of plane and modified HZSM-5 catalysts using different carrier gases viz., nitrogen and air on pure EB and xylene mixed EB feeds are presented. The disproportionation reaction with xylene mixed EB feed in the presence of air over HZSM-5TS (8 % silica deposited) is observed to be more active and selective as far as p-DEB formation is concerned. Reaction kinetics of EB disproportionation with first-order power law model at different temperatures and W/F (weight of the catalyst/reactant feed rate), with pure EB and xylene mixed EB feed are also discussed. The reaction rate constants are within 0.0668–0.0969 dm3/g h and the activation energy of the reaction is calculated to be 30.16 kJ/mol. The catalyst stability (100 h) in the presence of carrier gas is also studied in detail.
Keywords: H-ZSM-5; Silylation; Ethylbenzene; Disproportionation; Carrier gas; Kinetics
Acyclic diene metathesis polymerization and precision polymers by Nicolas F. Sauty; Lucas Caire da Silva; Michael D. Schulz; Chip S. Few; Kenneth B. Wagener (225-233).
The history of and major advances in the acyclic diene metathesis (ADMET) reaction are described. Because precise branch identity and frequency can be achieved by ADMET polymerizations of symmetrical α,ω-dienes, polyethylenes with precisely spaced alkyl branches of specified length have been prepared. Investigations of their morphologies and thermal properties have provided valuable insight into the behavior of polyethylene. ADMET preparation of ethylene copolymers and telechelic oligomers, as well as the properties of these materials, is also discussed.
Keywords: ADMET polymerization; Olefin metathesis; Precision polymers; Polyethylene
Modeling an industrial sodium bicarbonate bubble column reactor by Ataallah Soltani Goharrizi; Bahador Abolpour (235-245).
This paper deals with the study of the gas–liquid mass transfer, coupled with chemical reactions, the gas–liquid-solid mass transfer, and crystallization. Sodium bicarbonate is produced in a bubble column reactor which contains a solution of carbonate and bicarbonate and carbon dioxide gas injected into this column. In this mathematical modeling, a mole balance has been instituted on flows and components through the bubble column. A population balance is utilized to obtain the nucleation and growth formula for the solid phase. Danckwerts theory is utilized for mass transfer between gas and liquid phases. This model can predict the effects of several parameters on the production and size distribution of sodium bicarbonate crystals and also conversion of carbon dioxide. The mathematic simulator model results are compared with the experimental results to valid this model. Effects of different parameters on the production and size distribution of sodium bicarbonate crystals and also absorbent of carbon dioxide are investigated.
Keywords: Sodium bicarbonate; Bubble column; Triple phase mass transfer; Crystallization; Modeling