Heterogeneous catalysis for sustainable biodiesel production via esterification and transesterification

Concern over the economics of accessing fossil fuel reserves, and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change from combusting such carbon sources, is driving academic and commercial research into new routes to sustainable fuels to meet the demands of a rapidly rising global population. Here we discuss catalytic esterification and transesterification solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels to meet future societal demands.

Physicochemical properties of WOx/ZrO2 catalysts for palmitic acid esterification

A series of WOx/ZrO2 with various tungsten loadings was prepared via incipient-wetness impregnation of zirconium hydroxide. The resulting thermally processed materials were characterised by XRD, XPS, porosimetry, NH3-TPD and pyridine FTIR spectroscopy to elucidate their composition, morphology and acidity, and subsequently tested in the esterification of palmitic acid with methanol. Catalytic performance was strongly dependent upon calcination temperature and W surface density. Esterification activity increased with increasing surface W density, reaching a maximum at 8.9Wnm-2 corresponding to near monolayer coverage. Subsequent growth of crystalline WO3 lowered activity, consistent with a decrease in the density of active surface sites. Calcination temperatures as high as 800°C increased surface acidity and hence catalytic activity. The formation of polymeric tungstate species on zirconia is necessary to generate the Brönsted acid sites responsible for palmitic acid esterification under mild conditions. © 2014 Elsevier B.V.

Tunable KIT-6 mesoporous sulfonic acid catalysts for fatty acid esterification

We report the first catalytic application of pore-expanded KIT-6 propylsulfonic acid (PrSO H) silicas, in fatty acid esterification with methanol under mild conditions. As-synthesized PrSO H-KIT-6 exhibits a 40 and 70% enhancement in turnover frequency (TOF) toward propanoic and hexanoic acid esterification, respectively, over a PrSO H-SBA-15 analogue of similar 5 nm pore diameter, reflecting the improved mesopore interconnectivity of KIT-6 over SBA-15. However, pore accessibility becomes rate-limiting in the esterification of longer chain lauric and palmitic acids over both solid acid catalysts. This problem can be overcome via hydrothermal aging protocols which permit expansion of the KIT-6 mesopore to 7 nm, thereby doubling the TOF for lauric and palmitic acid esterification over that achievable with PrSO H-SBA-15. © 2012 American Chemical Society.

Zirconium phosphate supported tungsten oxide solid acid catalysts for the esterification of palmitic acid

A series of zirconium phosphate supported WOx solid acid catalysts with W loadings from 1–25 wt% have been prepared on high surface area zirconium phosphate by a surface grafting method. Catalysts were characterized by N2 adsorption, FTIR, Raman, UV-Vis, 31P MAS NMR, pyridine TPD and X-ray methods. Spectroscopic measurements suggest a Keggin-type structure forms on the surface of zirconium phosphate as a ([triple bond, length as m-dash]ZrOH2+)(ZrPW11O405−) species. All catalysts show high activity in palmitic acid esterification with methanol. These materials can be readily separated from the reaction system for re-use, and are resistant to leaching of the active heteropolyacid, suggesting potential industrial applications in biodiesel synthesis. © The Royal Society of Chemistry 2006.

Assessment of the astrogliotic responses of three human astrocytoma cell lines to ethanol, trimethyltin chloride and acrylamide

The astrogliotic responses of the CCF-STTG1, U251-MG, and U373-MG human astrocytoma lines were determined after exposure to ethanol, trimethyltin chloride (TMTC), and acrylamide over 4, 16, and 24 h. Basal glial fibrillary acidic protein (GFAP) expression in the U-251MG and U373-MG cells was 10-fold greater than the CCF-STGG1 line. Ethanol treatment over 24 h, but not at 4 and 16 h, resulted in significant increases in GFAP in all three glioma lines at sub-cytotoxic levels; the GFAP responses in the CCF-STTG1 line were the most sensitive, as concentrations of 0.1 and 1 mM led to increases in GFAP expression compared with control of 56.8 ± 15.7 and 58.9 ± 11.5%, respectively (P < 0.05). Treatment with TMTC (1 μM) over 4 h showed elevated GFAP expression in the U251-MG cell line to 28.0 ± 15.7% above control levels (P < 0.01), but not in the other U373-MG or CCF-STTG1 cells. At 4 h, MTT turnover was markedly increased compared with control, particularly in the U373-MG line at concentrations as low as 1 μM (17.1 ± 2.3%; P < 0.01). TMTC exposure over 16 and 24 h resulted in reduction in GFAP expression in all three lines at concentrations; at 24 h incubation, the reduction was >50% (P < 0.01). There were no changes in GFAP expression or MTT turnover in response to acrylamide except at the highest concentration ranges of 10-100 mM. This study underlines the significance of period of exposure, as well as toxin concentration in astrocytoma cellular response to toxic pressure. © 2007 Elsevier Ireland Ltd. All rights reserved.

Effects of dihydrolipoic acid (DHLA), α-lipoic acid. N-acetyl cysteine and ascorbate on xenobiotic-mediated methaemoglobin formation in human erythrocytes in vitro

α-Lipoic acid, dihydrolipoic acid (DHLA), N-acetyl cysteine and ascorbate were compared with methylene blue for their ability to attenuate and/or reduce methaemoglobin formation induced by sodium nitrite, 4-aminophenol and dapsone hydroxylamine in human erythrocytes. Neither α-lipoic acid, DHLA, N-acetyl cysteine nor ascorbate had any significant effects on methaemoglobin formed by nitrite, either from pre-treatment, simultaneous addition or post 30 min addition of the agents up to the 60 min time point, although N-acetyl cysteine did reduce methaemoglobin formation at 120 min (P<0.05). In all three treatment groups at 30, 60 and 120 min, there were no significant effects mediated by DHLA or N-acetyl cysteine on 4-aminophenol (1 mM)-mediated haemoglobin oxidation. Ascorbate caused marked significant reductions in 4-aminophenol methaemoglobin in all treatment groups at 30-120 min except at 30 min in the simultaneous addition group (P<0.0001). Neither α-lipoic acid, nor N-acetyl cysteine showed any effects on hydroxylamine-mediated methaemoglobin formation at 30 and 60 in all treatment groups. In contrast, DHLA significantly reduced hydroxylamine-mediated methaemoglobin formation at all three time points after pre-incubation and simultaneous addition (P<0.001), while ascorbate was ineffective. Compared with methylene blue, which was effective in reducing methaemoglobin formation by all three toxins (P<0.01), ascorbate was only highly effective against 4-aminophenol mediated methaemoglobin, whilst the DHLA-mediated attenuation of dapsone hydroxylamine-mediated methaemoglobin formation indicates a possible clinical application in high-dose dapsone therapy. © 2003 Elsevier B.V. All rights reserved.

Catalytic upgrading of bio-oils by esterification

Biomass is the term given to naturally-produced organic matter resulting from photosynthesis, and represents the most abundant organic polymers on Earth. Consequently, there has been great interest in the potential exploitation of lignocellulosic biomass as a renewable feedstock for energy, materials and chemicals production. The energy sector has largely focused on the direct thermochemical processing of lignocellulose via pyrolysis/gasification for heat generation, and the co-production of bio-oils and bio-gas which may be upgraded to produce drop-in transportation fuels. This mini-review describes recent advances in the design and application of solid acid catalysts for the energy efficient upgrading of pyrolysis biofuels.

Methyl chloride purification for the silicone industry

This study experimentally investigated methyl chloride (MeCl) purification method using an inhouse designed and built volumetric adsorption/desorption rig. MeCl is an essential raw material in the manufacture of silicone however all technical grades of MeCl contain concentrations (0.2 - 1.0 % wt) of dimethyl ether (DME) which poison the process. The project industrial partner had previously exhausted numerous separation methods, which all have been deemed not suitable for various reasons. Therefore, adsorption/desorption separation was proposed in this study as a potential solution with less economic and environmental impact. Pure component adsorption/desorption was carried out for DME and MeCl on six different adsorbents namely: zeolite molecular sieves (types 4 Å and 5 Å); silica gels (35-70 mesh, amorphous precipitated, and 35-60 mesh) and granular activated carbon (type 8-12 mesh). Subsequent binary gas mixture adsorption in batch and continuous mode was carried out on both zeolites and all three silica gels following thermal pre-treatment in vacuum. The adsorbents were tested as received and after being subjected to different thermal and vacuum pre-treatment conditions. The various adsorption studies were carried out at low pressure and temperature ranges of 0.5 - 3.5 atm and 20 - 100 °C. All adsorbents were characterised using Brunauer Emmett Teller (BET), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA) to investigate their physical and chemical properties. The well-known helium (He) expansion method was used to determine the empty manifold and adsorption cell (AC) regions and respective void volumes for the different adsorbents. The amounts adsorbed were determined using Ideal gas laws via the differential pressure method. The heat of adsorption for the various adsorbate-adsorbent (A-S) interactions was calculated using a new calorimetric method based on direct temperature measurements inside the AC. Further adsorption analysis included use of various empirical and kinetic models to determine and understand the behaviour of the respective interactions. The gas purification behaviour was investigated using gas chromatography and mass spectroscopy (GC-MC) analysis. Binary gas mixture samples were syringed from the manifold iii and AC outlet before and after adsorption/desorption analysis through manual sample injections into the GC-MS to detect and quantify the presence of DME and ultimately observe for methyl chloride purification. Convincing gas purification behaviour was confirmed using two different GC columns, thus giving more confidence on the measurement reliability. From the single pure component adsorption of DME and MeCl on the as received zeolite 4A subjected to 1 h vacuum pre-treatment, both gases exhibited pseudo second order adsorption kinetics with DME exhibiting a rate constant nearly double that of MeCl thus suggesting a faster rate of adsorption. From the adsorption isotherm classification both DME and MeCl exhibited Type II and I adsorption isotherm classifications, respectively. The strength of bonding was confirmed by the differential heat of adsorption measurement, which was found to be 23.30 and 10.21 kJ mol-1 for DME and MeCl, respectively. The former is believed to adsorb heterogeneously through hydrogen bonding whilst MeCl adsorbs homogenously via van der Waal’s (VDW) forces. Single pure component adsorption on as received zeolite 5A, silica gels (35-70, amorphous precipitated and 35-60) resulted in similar adsorption/desorption behaviour in similar quantities (mol kg-1). The adsorption isotherms for DME and MeCl on zeolite 5A, silica gels (35-70, amorphous precipitated and 35-60) and activated carbon 8-12 exhibited Type I classifications, respectively. Experiments on zeolite 5A indicated that DME adsorbed stronger, faster and with a slightly stronger strength of interaction than MeCl but in lesser quantities. On the silica gels adsorbents, DME exhibited a slightly greater adsorption capacity whilst adsorbing at a similar rate and strength of interaction compared to MeCl. On the activated carbon adsorbent, MeCl exhibited the greater adsorption capacity at a faster rate but with similar heats of adsorption. The effect of prolonged vacuum (15 h), thermal pre-treatment (150 °C) and extended equilibrium time (15 min) were investigated for the adsorption behaviour of DME and MeCl on both zeolites 4A and 5A, respectively. Compared to adsorption on as received adsorbents subjected to 1 h vacuum the adsorption capacities for DME and MeCl were found to increase by 1.95 % and 20.37 % on zeolite 4A and by 4.52 % and 6.69 % on zeolite 5A, respectively. In addition the empirical and kinetic models and differential heats of adsorption resulted in more definitive fitting curves and trends due to the true equilibrium position of the adsorbate with the adsorbent. Batch binary mixture adsorption on thermally and vacuum pre-treated zeolite 4A demonstrated purification behaviour of all adsorbents used for MeCl streams containing DME impurities, with a concentration as low as 0.66 vol. %. The GC-MS analysis showed no DME detection for the tested concentration mixtures at the AC outlet after 15 or 30 min, whereas MeCl was detectable in measurable amounts. Similar behaviour was also observed when carrying out adsorption in continuous mode. On the other hand, similar studies on the other adsorbents did not show such favourable MeCl purification behaviour. Overall this study investigated a wide range of adsorbents (zeolites, silica gels and activated carbon) and demonstrated for the first time potential to purify MeCl streams containing DME impurities using adsorption/desorption separation under different adsorbent pre-treatment and adsorption operating conditions. The study also revealed for the first time the adsorption isotherms, empirical and kinetic models and heats of adsorption for the respective adsorbentsurface (A-S) interactions. In conclusion, this study has shown strong evidence to propose zeolite 4A for adsorptive purification of MeCl. It is believed that with a technical grade MeCl stream competitive yet simultaneous co-adsorption of DME and MeCl occurs with evidence of molecular sieiving effects whereby the larger DME molecules are unable to penetrate through the adsorbent bed whereas the smaller MeCl molecules diffuse through resulting in a purified MeCl stream at the AC outlet. Ultimately, further studies are recommended for increased adsorption capacities by considering wider operating conditions, e.g. different adsorbent thermal and vacuum pre-treatment and adsorbing at temperatures closer to the boiling point of the gases and different conditions of pressure and temperature.

Disinfection of clinical materials using photo-activated tolonium chloride solution

Photo-activated disinfection is beginning to be used in dental surgery to treat deep seated bacterial infection. It works by combining a photosensitiser and light of a specific frequency to generate singlet oxygen which is toxic to many types of bacteria. It is suggested that this technique could be used as a means to help treat infection more generally. To do so, it needs to work with materials and geometries exhibiting different physical and optical characteristics to teeth. In these trials, samples of stainless steel and polymethylmethacrylate were exposed to bacterial solutions of Staphylococcus aureus and Staphylococcus epidermis. These were treated with tolonium chloride-based photo-activated disinfection regimes showing positive results with typically 4 log10 reductions in colony forming units. Tests were also carried out using slotted samples to represent geometric features which might be found on implants. These tests, showed disinfectant effect however to a much lesser degree. © 2011 Inderscience Enterprises Ltd.

Mesoporous sulfonic acid silicas for pyrolysis bio-oil upgrading via acetic acid esterification

Propylsulfonic acid derivatised SBA-15 catalysts have been prepared by post modification of SBA-15 with mercaptopropyltrimethoxysilane (MPTMS) for the upgrading of a model pyrolysis bio-oil via acetic acid esterification with benzyl alcohol in toluene. Acetic acid conversion and the rate of benzyl acetate production was proportional to the PrSO3H surface coverage, reaching a maximum for a saturation adlayer. Turnover frequencies for esterification increase with sulfonic acid surface density, suggesting a cooperative effect of adjacent PrSO3H groups. Maximal acetic acid conversion was attained under acid-rich conditions with aromatic alcohols, outperforming Amberlyst or USY zeolites, with additional excellent water tolerance.

New organogermanium substrates for palladium-catalyzed cross-coupling reactions. Application of organogermanes towards the synthesis of carbon-5 modified uridine analogues

The diverse biological properties exhibited by uridine analogues modified at carbon-5 of the uracil base have attracted special interest to the development of efficient methodologies for their synthesis. This study aimed to evaluate the possible application of vinyl tris(trimethylsilyl)germanes in the synthesis of conjugated 5-modified uridine analogues via Pd-catalyzed cross-coupling reactions. The stereoselective synthesis of 5-[(2-tris(trimethylsilyl)germyl)ethenyl]uridine derivatives was achieved by the radical-mediated hydrogermylation of the protected 5-alkynyluridine precursors with tris(trimethylsilyl)germane [(TMS)3GeH]. The hydrogermylation with Ph3GeH afforded in addition to the expected 5-vinylgermane, novel 5-(2-triphenylgermyl)acetyl derivatives. Also, the treatment with Me3GeH provided access to 5-vinylgermane uridine analogues with potential biological applications. Since the Pd-catalyzed cross-coupling of organogermanes has received much less attention than the couplings involving organostannanes and organosilanes, we were prompted to develop novel organogermane precursors suitable for transfer of aryl and/or alkenyl groups. The allyl(phenyl)germanes were found to transfer allyl groups to aryl iodides in the presence of sodium hydroxide or tetrabutylammonium fluoride (TBAF) via a Heck arylation mechanism. On the other hand, the treatment of allyl(phenyl)germanes with tetracyanoethylene (TCNE) effectively cleaved the Ge-C(allyl) bonds and promoted the transfer of the phenyl groups upon fluoride activation in toluene. It was discovered that the trichlorophenyl,- dichlorodiphenyl,- and chlorotriphenylgermanes undergo Pd-catalyzed cross-couplings with aryl bromides and iodides in the presence of TBAF in toluene with addition of the measured amount of water. One chloride ligand on the Ge center allows efficient activation by fluoride to promote transfer of one, two or three phenyl groups from the organogermane precursors. The methodology shows that organogermanes can render a coupling efficiency comparable to the more established stannane and silane counterparts. Our coupling methodology (TBAF/moist toluene) was also found to promote the transfer of multiple phenyl groups from analogous chloro(phenyl)silanes and stannanes.

Novel approaches for the synthesis of C-5 modified pyrimidine nucleosides

The antiviral or anticancer activities of C-5 modified pyrimidine nucleoside analogues validate the need for the development of their syntheses. In the first half of this dissertation, I explore the Pd-catalyzed cross-coupling reaction of allylphenylgermanes with aryl halides in the presence of SbF 5/TBAF to give various biaryls by transferring multiple phenyl groups, which has also been applied to the 5-halo pyrimidine nucleosides for the synthesis of 5-aryl derivatives. To avoid the use of organometallic reagents, I developed Pd-catalyzed direct arylation of 5-halo pyrimidine nucleosides. It was discovered that 5-aryl pyrimidine nucleosides could be synthesized by Pd-catalyzed direct arylation of N3-free 5-halo uracil and uracil nucleosides with simple arenes or heteroaromatics in the presence of TBAF within 1 h. Both N3-protected and N3-free uracil and uracil nucleosides could undergo base-promoted Pd-catalyzed direct arylation, but only with electron rich heteroaromatics. ^ In the second half of this dissertation, 5-acetylenic uracil and uracil nucleosides have been employed to investigate the hydrogermylation, hydrosulfonylation as well as hydroazidation for the synthesis of various functionalized 5-vinyl pyrimidine nucleosides. Hydrogermylation of 5-alkynyl uracil analogues with trialkylgermane or tris(trimethylsilyl)germane hydride gave the corresponding vinyl trialkylgermane, or tris(trimethylsilyl)germane uracil derivatives. During the hydrogermylation with triphenylgermane, besides the vinyl triphenylgermane uracil derivatives, 5-[2-(triphenylgermyl)acetyl]uracil was also isolated and characterized and the origin of the acetyl oxygen was clarified. Tris(trimethylsilyl)germane uracil derivatives were coupled to aryl halides but with decent yield. Iron-mediated regio- and stereoselective hydrosulfonylation of the 5-ethynyl pyrimidine analogues with sulfonyl chloride or sulfonyl hydrazine to give 5-(1-halo-2-tosyl)vinyluracil nucleoside derivatives has been developed. Nucleophilic substitution of the 5-(β-halovinyl)sulfonyl nucleosides with various nucleophiles have been performed to give highly functionalized 5-vinyl pyrimidine nucleosides via the addition-elimination mechanism. The 5-(β-keto)sulfonyluracil derivative has also been synthesized via the aerobic difunctionalization of 5-ethynyluracil analogue with sulfinic acid in the presence of catalytic amount of pyridine. Silver catalyzed hydroazidation of protected 2'-deoxy-5-ethynyluridine with TMSN3 in the presence of catalytic amount of water to give 5-(α-azidovinyl)uracil nucleoside derivatives was developed. Strain promoted Click reaction of the 5-(α-azidovinyl)uracil with cyclooctyne provide the corresponding fully conjugated triazole product.^

New Organogermanium Substrates for Palladium-Catalyzed Cross-Coupling Reactions. Application of Organogermanes towards the Synthesis of Carbon-5 Modified Uridine Analogues

The diverse biological properties exhibited by uridine analogues modified at carbon-5 of the uracil base have attracted special interest to the development of efficient methodologies for their synthesis. This study aimed to evaluate the possible application of vinyl tris(trimethylsilyl)germanes in the synthesis of conjugated 5-modified uridine analogues via Pd-catalyzed cross-coupling reactions. The stereoselective synthesis of 5-[(2-tris(trimethylsilyl)germyl)ethenyl]uridine derivatives was achieved by the radical-mediated hydrogermylation of the protected 5-alkynyluridine precursors with tris(trimethylsilyl)germane [(TMS)3GeH]. The hydrogermylation with Ph3GeH afforded in addition to the expected 5-vinylgermane, novel 5-(2-triphenylgermyl)acetyl derivatives. Also, the treatment with Me3GeH provided access to 5-vinylgermane uridine analogues with potential biological applications. Since the Pd-catalyzed cross-coupling of organogermanes has received much less attention than the couplings involving organostannanes and organosilanes, we were prompted to develop novel organogermane precursors suitable for transfer of aryl and/or alkenyl groups. The allyl(phenyl)germanes were found to transfer allyl groups to aryl iodides in the presence of sodium hydroxide or tetrabutylammonium fluoride (TBAF) via a Heck arylation mechanism. On the other hand, the treatment of allyl(phenyl)germanes with tetracyanoethylene (TCNE) effectively cleaved the Ge-C(allyl) bonds and promoted the transfer of the phenyl groups upon fluoride activation in toluene. It was discovered that the trichlorophenyl,- dichlorodiphenyl,- and chlorotriphenylgermanes undergo Pd-catalyzed cross-couplings with aryl bromides and iodides in the presence of TBAF in toluene with addition of the measured amount of water. One chloride ligand on the Ge center allows efficient activation by fluoride to promote transfer of one, two or three phenyl groups from the organogermane precursors. The methodology shows that organogermanes can render a coupling efficiency comparable to the more established stannane and silane counterparts. Our coupling methodology (TBAF/moist toluene) was also found to promote the transfer of multiple phenyl groups from analogous chloro(phenyl)silanes and stannanes.

N-acetoxy-N-acetyl-2-aminofluorene binding sites on [phi] X174 and SV40

Restriction enzyme inhibition and lambda exonuclease studies indicate that carcinogen N-acetoxy-N-acetyl-2 aminofluorene (AAAF) binds to sequences on ɸX174 RF and SV40 plasmids DNA that are similar to the eight preferred binding sites previously located on pBR 322. Both DNAs were digested with enzyme Hinf I and resultant fragments 32P end-labeled. Labeled fragments were reacted with the carcinogen to give one to sixteen bound moieties per DNA. Fragments were isolated and restriccion enzyme and lambda exonuclease inhibition assays were performed. Inhibition detected occurred at selected sites and was not specific for a certain enzyme or certain size of recognition sequence. Results of these assays allow mapping of the location of high affinity binding sites of the carcinogen on both DNAs. All sites have common sequence elements: the presence of either the sequence T(G/C)TT(G/C) or the sequence T(G/C) CTT(G/C).

Effect of acetyl resin retentive arms on the retentive force ofcircumferential clasps: an in vitro study.

PURPOSE: To compare and to evaluate the stability of the retentive force of cobalt-chromium (Co-Cr) circumferential clasps (control) to those with an acetyl resin retentive arm. METHODS: Sixteen specimens with a couple of circumferential clasps were made using Co-Cr over a metal model providing 0.25 mm undercuts. Eight specimens were fabricated without the anterior retentive arm, which was made later using acetyl resin (Dental D). Insertion and removal simulation test was performed through 7250 cycles. The retentive force was recorded in Newtons (N) for periods corresponding to 0, 1, 2, 3, 4, and 5 years. The data were subjected to ANOVA and Tukey test to compare periods and to Student's t test to compare groups (α=0.05). RESULTS: Mean (SD) is presented for Co-Cr and resin groups, respectively: 8.09(3.05) and 2.79(1.57) in period 0; 10.48(4.25) and 3.32(1.92) in 1 year; 10.09(4.15) and 3.47(1.81) in 2 years; 9.87(4.30) and 3.46(1.87) in 3 years; 9.46(3.93) and 3.27(1.59) in 4 years; 9.63(3.79) and 3.41(1.59) in 5 years. There were significant differences for Co-Cr between periods of 0 and 1 (p<0.001), 0 and 2 (p<0.01) and 0 and 3 (p<0.05). In the resin group, no significant differences were found between periods (p>0.05). Comparisons between the groups showed statistical differences for all tested periods: 0 (p=0.0012), 1 (p=0.0013), 2 (p=0.0019), 3 (p=0.0031), 4 (p=0.0027) and 5 years (p=0.0014). CONCLUSIONS: Acetyl resin retentive arms, even if only in the anterior clasps, can significantly reduce the retentive force, but this force remained stable after 5 years of simulated use.