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Yijun Liu

Bio: Yijun Liu is an academic researcher from Clemson University. The author has contributed to research in topics: Catalysis & Acid catalysis. The author has an hindex of 8, co-authored 9 publications receiving 2955 citations.

Papers
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TL;DR: A review of the research related to biodiesel can be found in this paper, where solid acid catalysts are used to replace liquid acids, reducing the corrosion and environmental problems associated with them.
Abstract: Biodiesel is synthesized via the transesterification of lipid feedstocks with low molecular weight alcohols. Currently, alkaline bases are used to catalyze the reaction. These catalysts require anhydrous conditions and feedstocks with low levels of free fatty acids (FFAs). Inexpensive feedstocks containing high levels of FFAs cannot be directly used with the base catalysts currently employed. Strong liquid acid catalysts are less sensitive to FFAs and can simultaneously conduct esterification and transesterification. However, they are slower and necessitate higher reaction temperatures. Nonetheless, acid-catalyzed processes could produce biodiesel from low-cost feedstocks, lowering production costs. Better yet, if solid acid catalysts could replace liquid acids, the corrosion and environmental problems associated with them could be avoided and product purification protocols reduced, significantly simplifying biodiesel production and reducing cost. This article reviews some of the research related to biodi...

1,606 citations

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TL;DR: In this paper, the activation/deactivation behaviors of sulfonated carbon catalysts were investigated through the esterification of free fatty acids (acetic acid and caprylic acid) and transesterification of triglycerides (triacetin, tricaprylin and soybean oil) with methanol.

271 citations

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TL;DR: In this paper, the kinetics of acetic acid esterification with methanol were investigated using a commercial Nafion/silica nanocomposite catalyst (SAC-13) and H 2 SO 4, respectively.

270 citations

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TL;DR: In this article, an investigation into the impact of water on liquid-phase sulfuric acid catalyzed esterification of acetic acid with methanol at 60°C was conducted.
Abstract: This paper reports on an investigation into the impact of water on liquid-phase sulfuric acid catalyzed esterification of acetic acid with methanol at 60 °C. In order to diminish the effect of water on the catalysis as a result of the reverse reaction, initial reaction kinetics were measured using a low concentration of sulfuric acid (1 × 10 −3 M) and different initial water concentrations. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The catalysts lost up to 90% activity as the amount of water present increased. The order of water effect on reaction rate was determined to be −0.83. The deactivating effect of water also manifested itself by changes in the activation energy and the pre-exponential kinetic factor. The decreased activity of the catalytic protons is suggested to be caused by preferential solvation of them by water over methanol. A proposed model successfully predicts esterification rate as reaction progresses. The results indicate that, as esterification progresses and byproduct water is produced, deactivation of the sulfuric acid catalyst occurs. Autocatalysis, however, was found to be hardly impacted by the presence of water, probably due to compensation effects of water on the catalytic activity of acetic acid, a weak acid.

261 citations

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TL;DR: In this paper, the use of heterogeneous base catalysts derived from Mg-Al hydrotalcite was investigated for the conversion of poultry lipids to biodiesel.
Abstract: The synthesis of biodiesel from poultry fats provides a way to convert the by-product of a renewable resource to a very important value-added biofuel. In this work, the use of heterogeneous base catalysts derived from Mg–Al hydrotalcite was investigated for the conversion of poultry lipids to biodiesel. This solid base showed high activity for triglyceride (TG) transesterification with methanol without signs of catalyst leaching. Catalytic performance was significantly affected by pretreatment and operating conditions. Calcination at optimum temperature was key in obtaining the highest catalyst activities. Rehydration of the calcined catalyst before reaction using wet nitrogen decreased catalytic activity for the transesterification of poultry fat, opposite to what has been reported for condensation reactions. Also, methanol had to be contacted with the catalyst before reaction; otherwise, catalyst activity was seriously impaired by strong adsorption of triglycerides on the active sites. Both temperature (60–120 °C) and methanol-to-lipid molar ratio (6:1–60:1) affected the reaction rate in a positive manner. The use of a co-solvent (hexane, toluene, THF), however, gave rise to a change in TG conversion profile which cannot be explained solely by a dilution effect. The catalyst underwent significant deactivation during the first reaction cycle probably due to deactivation of the strongest base sites. Subsequent reaction cycles showed stable activity. By re-calcination in air, complete catalyst regeneration was achieved.

258 citations


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Journal ArticleDOI
TL;DR: A review of catalytic strategies to produce bio-fuels from aqueous solutions of carbohydrates, which are isolated through biomass pretreatment and hydrolysis is presented in this paper.

2,008 citations

Journal ArticleDOI
TL;DR: An up-to-date review of the literature available on the subject of liquid bio-fuels can be found in this article, which includes information based on the research conducted globally by scientists according to their local socio-cultural and economic situations.

1,948 citations

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TL;DR: In this paper, the authors reviewed the source of production and characterization of vegetable oils and their methyl ester as the substitute of the petroleum fuel and future possibilities of Biodiesel production.
Abstract: The world is confronted with the twin crises of fossil fuel depletion and environmental degradation. The indiscriminate extraction and consumption of fossil fuels have led to a reduction in petroleum reserves. Petroleum based fuels are obtained from limited reserves. These finite reserves are highly concentrated in certain region of the world. Therefore, those countries not having these resources are facing a foreign exchange crisis, mainly due to the import of crude petroleum oil. Hence it is necessary to look for alternative fuels, which can be produced from materials available within the country. Although vegetative oils can be fuel for diesel engines, but their high viscosities, low volatilities and poor cold flow properties have led to the investigation of its various derivatives. Among the different possible sources, fatty acid methyl esters, known as Biodiesel fuel derived from triglycerides (vegetable oil and animal fates) by transesterification with methanol, present the promising alternative substitute to diesel fuels and have received the most attention now a day. The main advantages of using Biodiesel are its renewability, better quality exhaust gas emission, its biodegradability and the organic carbon present in it is photosynthetic in origin. It does not contribute to a rise in the level of carbon dioxide in the atmosphere and consequently to the green house effect. This paper reviews the source of production and characterization of vegetable oils and their methyl ester as the substitute of the petroleum fuel and future possibilities of Biodiesel production.

1,250 citations

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TL;DR: In this paper, a review of the methods for the transesterification of waste cooking oil and the performance of biodiesel obtained from waste cooking oils in a commercial diesel engine is presented, and the effects of the products formed in the frying process on biodiesel quality are examined.
Abstract: Biodiesel (fatty acid methyl ester) is a nontoxic and biodegradable alternative fuel that is obtained from renewable sources. A major hurdle in the commercialization of biodiesel from virgin oil, in comparison to petroleum-based diesel fuel, is its cost of manufacturing, primarily the raw material cost. Used cooking oil is one of the economical sources for biodiesel production. However, the products formed during frying, such as free fatty acid and some polymerized triglycerides, can affect the transesterification reaction and the biodiesel properties. Apart from this phenomenon, the biodiesel obtained from waste cooking oil gives better engine performance and less emissions when tested on commercial diesel engines. The present paper attempts to review methods for the transesterification of waste cooking oil and the performance of biodiesel obtained from waste cooking oil in a commercial diesel engine. The paper also examines the basic chemistry involved during frying and the effects of the products formed in the frying process on biodiesel quality.

1,166 citations