Jul 2015, Volume 9 Issue 2

Cover illustration

  • (See Kathryn A. MUMFORD, Yue WU, Geoffrey W. STEVENS. pp 125-141)
     The capture of carbon dioxide (CO2) from large point sources and subsequent storage underground, utilization for enhanced oil recovery processes or use in chemical synthesis, is essential if CO2 emissions to the atmosphere are to be reduced in the short term. Amongst all CO2 capture technologies currently available, solvent absorption is regarded as the most likely [Detail] ...

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    Kathryn A. MUMFORD,Yue WU,Kathryn H. SMITH,Geoffrey W. STEVENS

    Currently, a large proportion of global fossil fuel emissions originate from large point sources such as power generation or industrial processes. This trend is expected to continue until the year 2030 and beyond. Carbon capture and storage (CCS), a straightforward and effective carbon reduction approach, will play a significant role in reducing emissions from these sources into the future if atmospheric carbon dioxide (CO2) emissions are to be stabilized and global warming limited below a threshold of 2 °C. This review provides an update on the status of large scale integrated CCS technologies using solvent absorption for CO2 capture and provides an insight into the development of new solvents, including advanced amine solvents, amino acid salts, carbonate systems, aqueous ammonia, immiscible liquids and ionic liquids. These proposed new solvents aim to reduce the overall cost CO2 capture by improving the CO2 absorption rate, CO2 capture capacity, thereby reducing equipment size and decreasing the energy required for solvent regeneration.

    Alan J. McCue, James A. Anderson

    Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic properties for monometallic and bimetallic Pd catalysts. Activity/selectivity of Pd catalysts can be modified by controlling particle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers (i.e., species adsorbed onto Pd particle surface) have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO2 change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal (Cu or Au) where the reaction takes place more selectively.

    Erik C. Neyts

    While it is well-known that the plasma-enhanced catalytic chemical vapor deposition (PECVD) of carbon nanotubes (CNTs) offers a number of advantages over thermal CVD, the influence of the various individual contributing factors is not well understood. Especially the role of ions is unclear, since ions in plasmas are generally associated with sputtering rather than with growing a material. Even so, various studies have demonstrated the beneficial effects of ion bombardment during the growth of CNTs. This review looks at the role of the ions in plasma-enhanced CNT growth as deduced from both experimental and simulation studies. Specific attention is paid to the beneficial effects of ion bombardment. Based on the available literature, it can be concluded that ions can be either beneficial or detrimental for carbon nanotube growth, depending on the exact conditions and the control over the growth process.

    Andreja NEMET, Jiří Jaromír KLEMEŠ, Petar Sabev VARBANOV, Valter MANTELLI

    Heat Integration has been established over the last decades as a proven chemical engineering methodology. Two design implementations are often used in the industry: grassroots and retrofit. Although various methods have been developed for retrofit, it still needs more development to ensure simultaneously thermodynamic feasibility and economic viability. In this paper, a novel graphical approach has been developed to facilitate the understanding of the current situation and scope of improvement. The Retrofit Tracing Grid Diagram presents all streams and heat exchangers in temperature scale and the heat exchangers are clearly separated from each other, enabling clear visualisation of the current state. The tool incorporates the previously developed Cross-Pinch Analysis as well as path approach for retrofit. Additionally, the non-vertical heat transfer can be evaluated. The application of the developed tool has been validated on an oil refinery case study. The applicability of the tool is evident as it can reveal additional options for modification that none of the previous methods considered.

    Minhua ZHANG,Fang MENG,Zhongfeng GENG

    Shell-and-tube heat exchanger with helical baffles is superior to that with segmental baffles in reducing pressure drop, eliminating dead zone and lowering the risks of vibration of tube bundle. This paper focused on the small-angle helical baffles that have been merely reported in open literature. These baffles are noncontinuous helical baffles with a helix angle of 10° to 30°, and their shapes are 1/4 ellipse, 1/4 sector and 1/3 sector. To assess the integrative performance, α/?p is employed, and the calculated results show that among the three baffle shapes the heat exchangers with a 1/4 sector helical baffle have the lowest pressure drop. At β = 10° and 20°, 1/4 sector helical baffle heat exchangers show the best integrative performance; at β = 30°, 1/4 ellipse and 1/4 sector helical baffle heat exchangers perform almost the same. For the study of helix angles, we found that 30° has the best integrative performance at low mass flow rate, almost the same as 20° at high mass flow rate.

    Rovshan MAHMUDOV, Chinglung CHEN, Chin-Pao HUANG

    Two types of activated carbon, namely, Filtrasorb 400 and Nuchar SA, were functionalized by quaternary ammonium salts (quats), as to enhance perchlorate adsorption. Results showed that the adsorption of quats on Nuchar SA increased with increase in chain length (hydrophobicity) of quats. Filtrasorb 400, however, had limited uptake of long-chain quats such as dodecyltrimethylammonium and hexadecyltrimethylammoium (HDTMA). Results indicated that perchlorate removal by the functionalized activated carbon was directly related to the chain length of the modifying quats. Perchlorate removal by functionalized activated carbon increased with increase in chain length of the modifying quats and became less pH-dependent. Modified Nuchar SA had higher overall perchlorate removal capacity than the modified Filtrasorb F400, but was more strongly affected by pH than Filtrasorb 400. Activated carbon treated with HDTMA exhibited the best perchlorate removal capacity among all quats studied. Results indicated that tailoring the activated carbon surface with HDTMA rendered the activated carbon surface positively charged, which resulted in substantial increase in perchlorate removal compared to unfunctionalized activated carbons.

    Weikang ZHANG, Ye TIAN

    The adsorption capacities of Y zeolite and La (III)-modified Y zeolite were studied. A series of La(III)-modified Y zeolites with different La/Y zeolite mass ratios were characterized by X-ray diffraction, X-ray fluorescence and Brunauer-Emmett-Teller surface area analysis. Batch experiments were conducted to evaluate the effects of various experimental parameters, such as pH, ionic strength, coexisting anions (CO32-, Cl-, SO42- and NO3-) and temperature, on the phosphate adsorption. The capacity of the La (III)-modified Y zeolite to remove phosphate increased as the La/Y zeolite mass ratio increased and after 4 h, a phosphate removal efficiency of 95% was achieved for a La/Y zeolite mass ratio of 0.10. The equilibrium adsorption isotherm data correlated better to the Langmuir model than the Freundlich model and the data followed a pseudo-second-order kinetic equation.

    Xiaoxue SUN,Yuzhu SUN,Jianguo YU

    The process of activating coal spoil (CS) in order to recover aluminum as a high value product was investigated. The CS was first characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) in order to determine the chemical and mineral compositions of the CS. Then a mechanothermal activation method was adopted to increase the aluminum activity in the coal spoil. Over 95% of the aluminum in the CS could be extracted using this activation method. The mechanothermal activation process promoted the destruction of kaolinite structures and hindered the formation of amorphous γ-Al2O3. This resulted in a high aluminum leaching activity in the mechanothermally activated CS.

    Pengzhen CHEN, Shouying HUANG, Jijie ZHANG, Shengping WANG, Xinbin MA

    CuCl supported on molecular sieves has attracted increasing attention in catalyzing oxidative carbonylation of ethanol to diethyl carbonate. Mesoporous MCM-41 has been widely used as catalyst support due to its large surface area and well defined mesoporous structure. Considering its intrinsic weak acidity, MCM-41 was modified by a simple impregnation method to incorporate Al. The incorporation of Al components resulted in the high dispersion of Cu species and the increase of acid sites without changing the mesoporous structure of MCM-41, and thus enhanceed the catalytic activity of CuCl/MCM-41for diethyl carbonate synthesis.

    Zimeng HE,Ling YUE,Meng LI,Yazhuo SHANG,Honglai LIU

    We report on the rheological behavior of wormlike micelles constructed by ionic liquid surfactant [C8mim]Br (1-octyl-3-methylimidazolium bromide) and anionic surfactant sodium oleate (NaOA) in aqueous solution. The effects of surfactant composition, total surfactant concentration, added salts, and temperature were investigated. The prevailing surfactant effect at lower concentration and the leading cosolvent effect at higher concentration of [C8mim]Br may be the main reasons for appearance of well-established maximum in key rheological parameters with variation of surfactant composition and total surfactant concentration. The Cole-Cole plots demonstrate that the systems (total surfactant concentration falls within 0.17–0.35 mol·L-1 and molar ratio 0.33≤R≤0.50) fit the Maxwell’s mechanical model as linear viscoelastic fluid. The addition of NaBr or sodium salicylate decreases significantly the viscosity and the relaxation time of the wormlike micelle solution but cannot change the value of plateau modulus G0. The present system has low rheological tolerance to temperature. The increase of temperature decreases the average contour length and viscosity of wormlike micelles and thus strengthens the relaxation progress of diffusion and weakens the relaxation progress of reptation. Increasing the temperature also decreases the value of plateau modulus G0 and shifts the minimum value of the loss modulus Gmin to higher frequencies.

    Mingyu LIN,Yao Hsiang TSENG,Chin-Pao HUANG

    Nano-sized titanium dioxide (nano-TiO2) has wide industrial applications and therefore considerable chances of exposure are created for human beings and ecosystems. To better understand the interactions between nano-TiO2 and aquatic organisms, we first studied TiO2 uptake by algae exemplified by Pseudokirchneriella subcapitata. P. subcapitata were exposed to nano-TiO2 in a series of concentrations and at various pH. TiO2 uptake was quantified using a sedimentation curve analysis technique. After exposure of algae to TiO2, the variation of zeta potential was measured and the morphology of algae-TiO2 aggregate was observed with scanning electron microscopy and the optical microscopy. The steady-state TiO2 uptake was found to be pH-dependent and the isotherms can be described well by Freundlich model. TiO2 deposited on algal surfaces causes the shift of pHzpc of TiO2-covered algae from that of algae toward that of TiO2. The attraction between TiO2-covered algal cells induces the agglomeration of algae and TiO2 and thus the formation of algae-TiO2 aggregates in the size of 12 to 50 μm. The 2-D fractal dimension of the aggregates is pH-dependent and ranges from 1.31 to 1.67. The theoretical analysis of the Gibbs energy of interaction indicates that both TiO2 uptake by algae and the formation of algae-TiO2 aggregate are influenced by the interaction between TiO2 particles.