Comparison and optimisation of biodiesel production from <Emphasis Type="Italic">Jatropha curcas</Emphasis> oil using supercritical methyl acetate and methanol

In this study, biodiesel has been successfully produced by transesterification using non-catalytic supercritical methanol and methyl acetate. The variables studied, such as reaction time, reaction temperature and molar ratio of methanol or methyl acetate to oil, were optimised to obtain the optimum yield of fatty acid methyl ester (FAME). Subsequently, the results for both reactions were analysed and compared via Response Surface Methodology (RSM) analysis. The mathematical models for both reactions were found to be adequate to predict the optimum yield of biodiesel. The results from the optimisation studies showed that a yield of 89.4 % was achieved for the reaction with supercritical methanol within the reaction time of 27 min, reaction temperature of 358°C, and methanol-to-oil molar ratio of 44. For the reaction in the presence of supercritical methyl acetate, the optimum conditions were found to be: reaction time of 32 min, reaction temperature of 400°C, and methyl acetate-to-oil molar ratio of 50 to achieve 71.9 % biodiesel yield. The differences in the behaviour of methanol and methyl acetate in the transesterification reaction are largely due to the difference in reactivity and mutual solubility of Jatropha curcas oil and methanol/methyl acetate.     

Reductive Alkylation Causes the Formation of a Molten Globule-Like Intermediate Structure in <Emphasis Type="Italic">Geobacillus zalihae</Emphasis> Strain T1 Thermostable Lipase

A thermostable lipase from Geobacillus zalihae strain T1 was chemically modified using propionaldehyde via reductive alkylation. The targeted alkylation sites were lysines, in which T1 lipase possessed 11 residues. Far-UV circular dichroism (CD) spectra of both native and alkylated enzyme showed a similar broad minimum between 208 and 222 nm, thus suggesting a substantial amount of secondary structures in modified enzyme, as compared with the corresponding native enzyme. The hydrolytic activity of the modified enzymes dropped drastically by nearly 15-fold upon chemical modification, despite both the native and modified form showed distinctive α-helical bands at 208 and 222 nm in CD spectra, leading us to the hypothesis of formation of a molten globule (MG)-like structure. As cooperative unfolding transitions were observed, the modified lipase was distinguished from the native state, in which the former possessed a denaturation temperature (T _m) in lower temperature range at 61 °C while the latter at 68 °C. This was further supported by 8-anilino-1-naphthalenesulfonic acid (ANS) probed fluorescence which indicated higher exposure of hydrophobic residues, consequential of chemical modification. Based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, a small number of lysine residues were confirmed to be alkylated.     

Optimizing departure times in vehicle routes

Most solution methods for the vehicle routing problem with time windows (VRPTW) develop routes from the earliest feasible departure time. In practice, however, temporary traffic congestion make such solutions non-optimal with respect to minimizing the total duty time. Furthermore, the VRPTW does not account for driving hours regulations, which restrict the available travel time for truck drivers. To deal with these problems, we consider the vehicle departure time optimization (VDO) problem as a post-processing of a VRPTW. We propose an ILP formulation that minimizes the total duty time. The results of a case study indicate that duty time reductions of 15% can be achieved. Furthermore, computational experiments on VRPTW benchmarks indicate that ignoring traffic congestion or driving hours regulations leads to practically infeasible solutions. Therefore, new vehicle routing methods should be developed that account for these common restrictions. We propose an integrated approach based on classical insertion heuristics.     

Atomic carbon adsorption on Ni nanoclusters: a DFT study

Atomic carbon is a key intermediate interacting with transition metal clusters during the growth of carbon nanotube (CNT). Present density functional calculations studied the initial carbon adsorption on four Ni nanoclusters (N₁₃, N₁₅, N₃₈, and N₅₅). Our results show that carbon atoms preferentially adsorb on high-coordination sites, and carbon adsorption energies are larger on smaller Ni clusters. Ni cluster reconstruction plays an important role in creating more stable subsurface adsorption sites. The migration of adsorbed carbon atom on the surface threefold hollow site into the underlying interstitial subsurface positions is thermodynamically and kinetically feasible. The results indicate that the investigation of CNT growth mechanism should include both surface and subsurface carbon atoms, coupled with surface reconstruction of Ni nanoclusters.     

ZIF-Induced d-Band Modification in a Bimetallic Nanocatalyst: Achieving Over 44 % Efficiency in the Ambient Nitrogen Reduction Reaction

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst–H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d-band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of >44 % with high ammonia yield rate of >161 μg mg_cat⁻¹ h⁻¹ under ambient conditions. The strategy lowers electrocatalyst d-band position to weaken H adsorption and concurrently creates electron-deficient sites to kinetically drive NRR by promoting catalyst–N₂ interaction. The ZIF coating on the electrocatalyst doubles as a hydrophobic layer to suppress HER, further improving FE by >44-fold compared to without ZIF (ca. 1 %). The Pt/Au-N_ZIF interaction is key to enable strong N₂ adsorption over H atom.     

Synthesis and light‐emitting properties of platinum‐containing oligoynes and polyynes derived from oligo(fluorenyleneethynylenesilylene)s

A series of blue‐light‐emitting oligo(fluorenyleneethynylenesilylene)s (OFESs) of the general formula HC?CRC?C(EC?CRC?C)_mEC?CRC?CH (E = SiPh₂, SiMe₂, or SiMe₂? SiMe₂; m = 0–2; R = 9,9‐dihexylfluorene‐2,7‐diyl) and their phosphorescent platinum‐containing oligoynes and polyynes were synthesized and characterized. The solution properties and regiochemical structures of this new structural class of organosilicon‐based polyplatinayne polymers {trans‐[? Pt(PBu₃)₂C ?CRC?C(EC?CRC?C)_mEC?CRC?C? ]_n} were studied with IR and NMR (¹H, ¹³C, ²⁹Si, and ³¹P) spectroscopy. The optical absorption and photoluminescence spectra of these metallopolymers were examined and compared with their discrete oligomeric model complexes. Our studies led to a novel approach of using the sp³‐silyl moiety as a conjugation interrupter to limit the effective conjugation length in metal polyynes, which could boost the phosphorescence decay rates essential for light‐energy harvesting from the triplet excited state. The influence of the heavy platinum atom and the group 14 silyl unit possessing different side‐group substituents on the thermal and phosphorescence properties was investigated in detail. We also established the goal of studying the evolution of the lowest singlet and triplet excited states with chain length m of OFESs and the nature of E in these metallopolymers. This work indicated that the phosphorescence emission efficiency harnessed through the heavy‐atom effect of platinum in the main chain did not change very much with oligomer chain length m but generally decreased with the E group in the order SiMe₂ > SiMe₂? SiMe₂ > SiPh₂. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4804–4824, 2006