a b s t r a c t a r t i c l e i n f oIn the US, biodiesel producers usually follow the 19.8:1 methanol-to-FFA molar ratio for free fatty acid (FFA) esterification, as suggested by the National Renewable Energy Laboratory (NREL) without optimization studies. In this paper, both laboratory studies and industrial practices of the esterification process were compared, and an optimization study of a used vegetable oil with 5% FFA was conducted. The optimal conditions of this oil, i.e., methanol-to-FFA molar ratio of 40:1, and sulfuric acid usage of 10%, fell out of the suggested range of 19.8:1. The activation energy of the esterification reaction is 20.7 kJ/mol at the optimized condition and 45.9 kJ/mol at the 19.8:1 methanol to FFA ratio. It was found that the 19.8:1 methanol-to-FFA molar ratio worked well only within the FFA range of 15-25% while the suggested 5% sulfuric acid worked well only within the FFA range of 15-35%. Outside these ranges, especially at FFA levels less than 15%, optimization study is necessary. Regression models of methanol and acid dosing have been utilized in two industrial scale biodiesel producing facilities and have successfully reduced the FFA level to less than 0.5%.
A photochemically active dithiazolethene BN was designed and synthesized, exhibiting a specific gated photochromism. That is, the photochromic reactivity of BN is prevented to a great extent by BF(3), showing a "Lock" gate.
A photochromic terarylene (BTO) containing a benzo [b]thiophene-1,1-dioxide unit as a central ethene bridge was synthesized and characterized, and exhibits good thermal stability and fatigue resistance both in solution and bulk crystals. When triggered by chemical ions, protons and light, BTO can behave as an absorbance and fluorescence switch, leading to a multi-addressable system. The different color changes of BTO upon adding Cu 2+ and Hg 2+ ions arise from the relative binding stoichiometry and the association affinities. The titration of the Job plot indicates that BTO forms a 1 : 1 complex with Hg 2+ , whereas in the case of Cu 2+ , the Job plot exhibits a maximum at about a 0.33 mole fraction, indicating that BTO forms a 2 : 1 complex with Cu 2+ . Moreover, the conversion yield of BTO can be modulated with chemical ions. Impressively, an increase in conversion yield was observed by adding Hg 2+ to the solution of BTO, that is, the conversion yield and cyclization quantum yield are increased from 77.6% and 28.5% (for BTO only) to 99.8% and 43.1% (BTO-Hg 2+ ), respectively. A series of molecular logic gates such as a half-adder, half-subtractor, 4-to-2 encoder, 2-to-4 decoder, and a 1 : 2 demultiplexer were constructed on the unimolecular platform by employing absorption and emission properties at different wavelengths as outputs, with the appropriate combination of chemical and photonic stimuli, which is a further step towards data processing on the molecular level with potential applications in sensing and labeling as well as for data manipulation.
An open and closed case: The photochromic bisthienylethene BTTE based on benzobisthiadiazole exhibits excellent photochromic performance in both solution and single crystals (see picture). BTTE shows excellent thermal stability, which is comparable to the widely known five‐membered hexafluorocyclopentene‐based counterpart.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.