Browsing by Subject "Glycerol"

Now showing 1 - 6 of 6

Open Access
Differential effects of nitrogen and sulfur deprivation on growth and biodiesel feedstock production of Chlamydomonas reinhardtii
(2012) Cakmak, T.; Angun P.; Demiray, Y.E.; Ozkan, A.D.; Elibol, Z.; Tekinay, T.
Biodiesel production from microalgae is a promising approach for energy production; however, high cost of its process limits the use of microalgal biodiesel. Increasing the levels of triacylglycerol (TAG) levels, which is used as a biodiesel feedstock, in microalgae has been achieved mainly by nitrogen starvation. In this study, we compared effects of sulfur (S) and nitrogen (N) starvation on TAG accumulation and related parameters in wild-type Chlamydomonas reinhardtii CC-124 mt(-) and CC-125 mt(+) strains. Cell division was interrupted, protein and chlorophyll levels rapidly declined while cell volume, total neutral lipid, carotenoid, and carbohydrate content increased in response to nutrient starvation. Cytosolic lipid droplets in microalgae under nutrient starvation were monitored by three-dimensional confocal laser imaging of live cells. Infrared spectroscopy results showed that relative TAG, oligosaccharide and polysaccharide levels increased rapidly in response to nutrient starvation, especially S starvation. Both strains exhibited similar levels of regulation responses under mineral deficiency, however, the degree of their responses were significantly different, which emphasizes the importance of mating type on the physiological response of algae. Neutral lipid, TAG, and carbohydrate levels reached their peak values following 4 days of N or S starvation. Therefore, 4 days of N or S starvation provides an excellent way of increasing TAG content. Although increase in these parameters was followed by a subsequent decline in N-starved strains after 4 days, this decline was not observed in S-starved ones, which shows that S starvation is a better way of increasing TAG production of C. reinhardtii than N starvation. © 2012 Wiley Periodicals, Inc.
Open Access
Dry reforming of glycerol over Rh-based ceria and zirconia catalysts: New insights on catalyst activity and stability
(Elsevier B.V., 2018) Bulutoğlu, P. S.; Say, Zafer; Bac, S.; Özensoy, Emrah; Avcı, A. K.
Effects of reaction temperature and feed composition on reactant conversion, product distribution and catalytic stability were investigated on syngas production by reforming of glycerol, a renewable waste, with CO2 on Rh/ZrO2 and Rh/CeO2 catalysts. For the first time in the literature, fresh and spent catalysts were characterized by in-situ FTIR, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis techniques in order to unravel novel insights regarding the molecular-level origins of catalytic deactivation and aging under the conditions of glycerol dry reforming. Both catalysts revealed increased glycerol conversions with increasing temperature, where the magnitude of response became particularly notable above 650 and 700 °C on Rh/ZrO2 and Rh/CeO2, respectively. In accordance with thermodynamic predictions, CO2 transformation occurred only above 700 °C. Syngas was obtained at H2/CO ∼0.8, very close to the ideal composition for Fischer-Tropsch synthesis, and carbon formation was minimized with increasing temperature. Glycerol conversion decreased monotonically, whereas, after an initial increase, CO2 conversion remained constant upon increasing CO2/glycerol ratio (CO2/G) from 1 to 4. In alignment with the slightly higher specific surface area of and smaller average Rh-particle size on ZrO2, Rh/ZrO2 exhibited higher conversions and syngas yields than that of Rh/CeO2. Current characterization studies indicated that Rh/CeO2 revealed strong metal-support interaction, through which CeO2 seemed to encapsulate Rh nanoparticles and partially suppressed the catalytic activity of Rh sites. However, such interactions also seemed to improve the stability of Rh/CeO2, rendering its activity loss to stay below that of Rh/ZrO2 after 72 h time-on-stream testing at 750 °C and for CO2/G = 4. Enhanced stability in the presence of CeO2 was associated with the inhibition of coking of the catalyst surface by the mobile oxygen species and creation of oxygen vacancies on ceria domains. Deactivation of Rh/ZrO2 was attributed to the sintering of Rh nanoparticles and carbon formation.
Open Access
Exceptionally active and stable catalysts for CO2 reforming of glycerol to syngas
(Elsevier, 2019) Bac, S.; Say, Zafer; Koçak, Yusuf; Ercan, Kerem E.; Harfouche, M.; Özensoy, Emrah; Avcı, A. K.
CO2 reforming of glycerol to syngas was studied on Al2O3-ZrO2-TiO2 (AZT) supported Rh, Ni and Co catalysts within 600–750 °C and a molar inlet CO2/glycerol ratio (CO2/G) of 1–4. Glycerol and CO2 conversions decreased in the following order: Rh/AZT > Ni/AZT > Co/AZT. Reactant conversions on Rh/AZT exceeded 90% of their thermodynamic counterparts at 750 °C and CO2/G = 2–4 at which the activity of Ni/AZT was boosted to ˜95% of the thermodynamic CO2 conversion upon increasing the residence time. The loss in CO2 conversions was below 13% during the 72 h longevity tests confirming the exceptional stability of Rh/AZT and Ni/AZT. However, Co/ AZT suffered from sintering, carbon deposition and oxidation of Co sites, demonstrated via TEM-EDX, XPS, XANES and in-situ FTIR experiments. Characterization of Rh/AZT revealed no significant signs of deactivation. Ni/AZT preserved most of its original metallic pattern and gasified carbonaceous deposits during earlier stages of the reaction
Open Access
A highly active and stable Ru catalyst for syngas production via glycerol dry reforming: Unraveling the interplay between support material and the active sites
(Elsevier, 2022-04-25) Ozden, M.; Say, Zafer; Kocak, Yusuf; Ercan, Kerem Emre; Jalal, Ahsan; Ozensoy, Emrah; Avci, A. K.
Glycerol dry reforming (GDR) was studied on Ru/La2O3, Ru/ZrO2, and Ru/La2O3–ZrO2 catalysts. Impacts of the support on morphological, electronic and surface chemical properties of the catalysts were comprehensively characterized by TEM, in–situ DRIFTS, XPS, ATR–IR and XRD. Initial (5 h) CO2 conversion at 750 °C and CO2–to–glycerol ratio of 1–4 was ordered as Ru/La2O3 < Ru/ZrO2 < Ru/La2O3–ZrO2. During 72 h stability tests, Ru/ZrO2 deactivated by ~33% due to Ru sintering, structural deformation of the monoclinic zirconia support, and strong metal–support interaction. Under identical conditions, CO2 conversion on Ru/La2O3 decreased by 27% mainly due to dehydroxylation/carbonation of lanthana and severe coking. Lanthana–stabilized tetragonal zirconia phase of Ru/La2O3–ZrO2 led to finely dispersed small oxidic Ru clusters which deactivated by 15% after 72 h and demonstrated unusually high catalytic performance that was on par with the significantly more expensive Rh–based catalysts, which are known with their exceptional activity and stability in GDR.
Open Access
Induction of triacylglycerol production in Chlamydomonas reinhardtii: comparative analysis of different element regimes
(Elsevier, 2014) Çakmak, Z. E.; Ölmez, T. T.; Çakmak, T.; Menemen, Y.; Tekinay, T.
In this study, impacts of different element absence (nitrogen, sulfur, phosphorus and magnesium) and supplementation (nitrogen and zinc) on element uptake and triacylglycerol production was followed in wild type Chlamydomonas reinhardtii CC-124 strain. Macro- and microelement composition of C. reinhardtii greatly differed under element regimes studied. In particular, heavy metal quotas of the microalgae increased strikingly under zinc supplementation. Growth was suppressed, cell biovolume, carbohydrate, total neutral lipid and triacylglycerol levels increased when microalgae were incubated under these element regimes. Most of the intracellular space was occupied by lipid bodies under all nutrient starvations, as observed by confocal microscopy and transmission electron micrographs. Results suggest that sulfur, magnesium and phosphorus deprivations are superior to nitrogen deprivation for the induction triacylglycerol production in C. reinhardtii. On the other hand, FAME profiles of the nitrogen, sulfur and phosphorus deprived cells were found to meet the requirements of international standards for biodiesel.
Open Access
Multiphase flow displacement application of novel green nanoparticle synthesis in glycerol and reconfigurable nanoemulsions in reservoir-on-a-chip
(2024-01) Jahangir, Robab
Nanofluids and oil in water (O/W) nano/micro emulsions have been extensively investigated for their potential in multiphase displacement applications such as enhanced oil recovery (EOR). However, the potential of metal nanofluids and water-in-oil nanoemulsions (W/O) has not been readily studied and the under-lying mechanisms are yet to be investigated. Moreover, most nanofluids pose toxicity risks to reservoirs, and a high polydispersity index of conventionally syn-thesized nanofluids adversely impacts displacement efficiencies. Hence, in this study, we synthesized two injection fluids including, a novel green nanofluid comprising of ultra-small silver nanoparticles (NPs) in glycerol and reconfigurable nanoemulsions to investigate their impact on displacement efficiencies. We have carried out the synthesis of green nanofluid comprising silver NPs in a customized microfluidic (Mf) chip, with 18 omega-shaped micromixers, by using glycerol as a promising green solvent and reducing agent at various concentrations (10-80 %), and simultaneous comparison of the results from batch synthesis. Interestingly, the experimental findings depicted that by varying different parameters, the spherical silver nanoparticles with an average ultra-small particle diameter of < 2nm were obtained at all glycerol concentrations (10-80 %) and variables, as compared to batch synthesis (giving a yield of 10-fold larger particles). The synthesis was then confirmed by Dynamic Light scattering (DLS), UV-visible spectroscopy, and Tunnelling Electron Microscope (TEM). Subsequently, the dis-placement efficiencies were then investigated in a reservoir-on-a-chip platform (filled with fluorescence-doped oil) for real-time visualization, quantification and pore-scale investigation. The measurement data for green nanofluid revealed the wettability alteration and IFT reduction with the increase in viscosity and size of NPs. No significant effect of the IFT on sweep efficiencies was observed, however, the contact angle of the injection fluids shifted from an oil-wet state (101◦-113◦) towards an intermediate wettability state (90◦-97◦) over 2 minutes. A shift to-wards intermediate wettability in a short time indicated the influence of AgNPs in displacing oil ganglia by structural disjoining pressure. It was reported that a critical glycerol viscosity (30 %) was essential to increase the sweep efficiency by 5 % in microfluidics-synthesized nanofluid (1.7 nm) and by 8 % in benchtop synthesized nanofluid (3.3 nm). Finally, the NPs-surfactant assemblies between SiO2 and Poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] copolymer were in-vestigated for the synthesis of reconfigurable nanoemulsions. The buckling phenomena was confirmed between pH 5 and 6 and nanoemulsions were synthesized with 3 different Oil: NPs concentrations i.e., 80:20, 70:30 and 60:40 at pH 3, 5, 6, and 8 (pH 3 and 8 taken as control groups). The sweep efficiency gradually increased in the order of 60:40 < 70:30 < 80:20, with the highest sweep efficiency obtained in the case of 80:20 nanoemulsions at pH 5, pH 6 and pH 5 in case of 70:30 nanoemulsions respectively, due to the displacement of oil because of formation of wedge film and in-situ emulsification.