B. Brian He

Characterization of crude glycerol from biodiesel production from multiple feedstocks.

Glycerol is the principal by-product of biodiesel production. For each gallon of biodiesel produced, approximately 0.3 kg of crude glycerol accompanies. Such crude glycerol possesses very low value because of the impurities contained. As the demand and production of biodiesel grow exponentially, the utilization of the glycerol becomes an urgent topic. The make-up of crude glycerol varies depending on the parent feedstock and the biodiesel production process. Before the crude glycerol could be considered for possible value-added utilizations, it is necessary to characterize it on its physical, chemical, and nutritional properties. This article reports the characterization of crude glycerol obtained from different seed oil feedstocks of mustard, rapeseed, canola, crambe, soybean, and waste cooking oils. Batch processes of biodiesel production were used as the means of crude glycerol preparation using unrefined vegetable oils, methanol, and sodium methylate as the catalyst. After separation from biodiesel, the crude glycerol from each of the oils was analyzed using ASTM and other standard test methods. Elemental impurities, nutritional value, and other chemical properties were tested.

Process optimization of biodiesel production using alkaline catalysts.

The most commonly used method for biodiesel preparation is via transesterification of vegetable oil using alkaline catalysts. Biodiesel yield and oil conversion are affected by operating conditions including the catalyst formulation and concentration. Application of alkaline catalysts can also lead to undesired soap formation. This study evaluated the alkaline catalyst effects on biodiesel yield and soap formation in transesterifying methanol and canola oil at different catalyst concentrations, reaction temperatures, and methanol-to-oil molar ratios. Four different alkaline catalysts, i.e., potassium hydroxide, sodium hydroxide, potassium methoxide, and sodium methoxide, were studied and compared on molar basis through a 4-factor 3-level experimental design. It was observed that methoxide catalysts led to better biodiesel yields than hydroxide catalysts. The methoxide catalysts not only accelerated the reaction but also elevated the conversion equilibrium. Based on statistical optimization, the operating conditions for maximizing biodiesel yield and minimizing soap formation were potassium methoxide as catalyst at 0.2 mol/mol (1.59%wt), reaction temperature of 50.C, and methanol-to-oil molar ratio of 4.5:1. Experimental verification gave 95.8% biodiesel yield and 0.75%wt soap.

A novel continuous-flow reactor using reactive distillation for biodiesel production.

The production of biodiesel through batch and existing continuous-flow processes requires the use of a much higher excess alcohol, typically 100%, than the stoichiometric molar requirement in order to drive the transesterification reaction to completion. This excess alcohol must be recovered in a separate process, which involves additional capital and operating costs. In this study, a novel reactor system using reactive distillation (RD) was developed and investigated for biodiesel preparation from canola oil and methanol. The goal was to significantly reduce the use of excess methanol while maintaining a high methanol:glyceride molar ratio inside the RD reactor by recycling a small amount of methanol within the system. Reactant conversion rate and product yield were used as the criteria for the reactor evaluation. The effect of the methanol:glyceride ratio was studied on a laboratory-scale perforated-tray RD reactor system. Product parameters such as methyl ester content, glycerides, and methanol content were analyzed. Preliminary results showed that the RD reactor with a methanol:glyceride ratio of 4:1 (molar), in which the use of methanol was cut down by 66%, gave a satisfactory biodiesel yield and oil conversion rate at a column temperature of 65°C. Total reaction time in the pre-reactor and RD column was about 3 min, which is 20 to 30 times shorter than in typical batch processes. The productivity of the RD reactor system was about 6.6 m3 biodiesel per m3 reactor volume per hour, which is 6 to 10 times higher than that of batch and existing continuous-flow processes.

Biodiesel Blend Level Detection Using Ultraviolet Absorption Spectra

Biodiesel is often blended with regular U.S. No. 2 diesel. The blending level influences engine performance, emissions, and fuel cold-flow properties. In this article, ultraviolet (UV) absorption spectroscopy is presented as a reliable and affordable technology for blend level detection based on the absorbance patterns of the aromatic compounds in the proposed spectrum. Blends of biodiesel from six different feedstocks and U.S. No. 2 diesels from five different sources were used to test the robustness of the method. Since the absorbance of undiluted samples was too high to measure reliably, the samples were diluted with n-heptane. It was found that the feedstock and alcohol used (methyl or ethyl) did not make a significant difference in the absorbance of diluted biodiesel in the 245 to 305 nm range, while absorbance from 254 to 281 nm was correlated with blend level with R2 > 0.99. It was also observed that if the absorbance of the diesel source was known, then a single wavelength could be used to detect the biodiesel blend level. However, a single wavelength was inadequate when the diesel source was unknown because of variation in the level of aromatics in diesel fuel. Absorbances at 265, 273, and 280 nm were used to calculate the absorbance index, which was found to be independent of the diesel fuel used. Using three wavelengths captured the shape information of the absorbance curve and eliminated the variation from the aromatics content. The root mean square error in determining blend level with this method was estimated to be 2.88%, and the R2 for the linear model was 0.99. The method worked well with biodiesel from the different feedstocks tested in this research and was independent of the diesel fuel used.

EXPERIMENTAL OPTIMIZATION OF A CONTINUOUS-FLOW REACTIVE DISTILLATION REACTOR FOR BIODIESEL PRODUCTION

A comprehensive study of biodiesel preparation from canola oil was performed on a continuous-flow reactive distillation (RD) reactor system. Optimization of six process variables was studied experimentally and analyzed statistically on the overall performance of the RD reactor system. These variables include the feed methanol to triglycerides molar ratio, reaction time, reboiler temperature, catalyst concentration, methanol circulation mode, and catalyst formulation. An experimental design was used in the experiments, and statistical multiple response regression models were employed for process optimization. Under the operating conditions explored, product yields ranged from 41.5% to 94.9%, productivity ranged from 16 to 55.8 kmol/m3·h (5.6 to 19.5 m3/m3·h), and soap formation varied from 4.44 to 29.1 mol/100 mol (0.19 to 1.27%wt.). For different optimization criteria, the following optimum variable ranges were found: feed molar ratio from 3.65:1 to 4.50:1, reaction time from 3.76 to 5.56 min, reboiler temperature from 100°C to 130°C, and catalyst concentration from 0.13 to 0.24 mol/mol. Although the process variables individually affected the system performance to a certain extent, the interactive effect of the process variable combinations affected the system efficiency more significantly. When maximized, the product yields and productivity were 98.8% and 55.6 kmol/m3·h (18.5 m3/m3·h), respectively. However, when soap formation was minimized, the yield and productivity were 72% and 9.3 kmol/m3·h (3.1 m3/m3·h), respectively. It is recommended that the optimization of the RD reactor system be based on the maximization of product yield and reactor productivity.

Moisture Absorption in Biodiesel and its Petro-Diesel Blends

Biodiesel has the characteristic of absorbing more moisture than petroleum diesel. High moisture content in biodiesel can cause problems such as water accumulation and microbial growth in fuel handling, storage, and transportation equipment. Currently, there is a lack of information on moisture absorbance in biodiesel and biodiesel/diesel blends. Experiments were conducted to determine the water absorbance in biodiesel of different feedstocks (three vegetable oils and two primary alcohols) at three temperatures. The effects of temperature and blending levels were explored through a central composite experimental design. Dynamic moisture absorption was studied at three constant relative humidities. Petroleum diesel was used as a reference. It was found that there were no significant differences in moisture absorbence among the biodiesel samples of different origins at given temperatures. Saturation moisture in biodiesel ranged from 0.10 to 0.17%wt in the temperature range of 4°C to 35°C, which was 15 to 25 times higher than that of diesel. Results also showed that in biodiesel/diesel blends, both temperature and level of blending affected the moisture absorbence. Moisture content of the blends was not a simple addition of the two moisture contents of biodiesel and petro-diesel. Blending created a mixture that had a lower capacity for moisture absorption.

Biodiesel Production Using Static Mixers

Static mixers, devices used for mixing immiscible liquids in a compact configuration, were found to be effective in carrying out initial transesterification reactions of canola oil and methanol. The objective of this study was to explore the possibilities of using static mixers as a continuous-flow reactor for biodiesel production. Biodiesel (canola methyl ester) was produced under varying conditions using a closed-loop static mixer system. Sodium methoxide was used as the catalyst. Process parameters of flow rate or mixing intensity, catalyst concentration, reaction temperature, and reaction time were studied. A full-factorial experimental design was employed, and samples were analyzed for unreacted glycerides as an indicator for biodiesel quality control. It was found that static mixers can be used for biodiesel production. In fact, given enough residence time, appropriate temperature, and high mixing rate, a reactor could consist solely of static mixers and pumps in a continuous-flow design. Temperature and catalyst concentration had the most influence on the transesterification reaction. The data clearly indicates separate inverse linear relationships between temperature and catalyst concentration verses total glycerin. The ASTM D6584 specification for total glycerin (0.24% wt, max.) was met at three of the four temperatures tested, utilizing two of the four catalyst concentrations. The most favorable conditions for completeness of reaction were at 60°C and 1.5% catalyst for 30 min.

Application of ultrasonication in transesterification processes for biodiesel production

In biodiesel production, adequate mixing is required to create sufficient contact between the vegetable oil or animal fat and alcohol, especially at the beginning of the reaction. Application of ultrasonication provides sufficient mixing and energy so that the transesterification can proceed at a faster rate due to two effects. First, ultrasonic cavitation and microbubble formation, which are caused by the ultrasonic energy introduced by the sonotrode, greatly improve the interfacial contact between the immiscible methanol and plant oil/animal fat mixture, thus increasing the reaction rate. Second, the formation and bursting of microbubbles caused by ultrasonic cavitation intensifies the local energy transfer and energizes the reactant molecules, thus enhancing the overall reaction rate. The other possible beneficial aspect of ultrasonication may be ultrasonic energy-induced free radical formation, which initiates chain reactions, as has been observed in other organic systems, although it is not fully understood in transesterification yet.

Sulfur Content in Selected Oils and Fats and their Corresponding Methyl Esters

According to Environmental Protection Agency (EPA) regulations, the use of ultra-low sulfur diesel (ULSD) has been mandated for all on-highway transportation diesels since 2006. To comply with the EPA regulations, biodiesel must meet the same ULSD standard for total sulfur which is set at a maximum of 15 ppm. Generally, biodiesel contains lower sulfur than fossil diesel. However, due to the diversity of biodiesel feedstocks, questions have been raised about their sulfur content and the sulfur content of the biodiesel made from them. The objective of this research was to gain basic knowledge about how the sulfur content in biodiesel is affected by the sulfur content of different feedstocks. Sulfur in oilseeds, seed meals, oils and fats, and biodiesel were investigated according to ASTM D5453. Samples of different feedstocks for biodiesel production were investigated. Results showed that sulfur content varies greatly from one source to another. The highest sulfur in seeds and meals was found in rapeseed and mustard, at the level of 9,000 and 15,000 ppm, respectively. Oils from mechanical expeller presses contained very low levels of sulfur, although some were still higher than 15 ppm. Animal fats and waste vegetable oils contained relatively higher sulfur levels and were frequently above 15 ppm. It was observed that sulfur was significantly reduced when the oils and fats were processed into biodiesel. Results showed that most of the biodiesel samples investigated in this study contained less than 15-ppm sulfur. Feedstocks which contain a high percentage of free fatty acids (FFA) must be treated with sulfuric acid to reduce the FFA level before transesterification. In these cases, care is needed during phase separation to exclude sulfur from the fuel layer.

A Continuous-flow Reactive Distillation Reactor for Biodiesel Preparation from Seed Oils

In biodiesel preparation from vegetable oils and alcohol through transesterification process in the presence of a catalyst, excess alcohol, typically 100% more than the theoretical molar requirement, is used in existing batch and continuous-flow processes in order to drive the reversible transesterification reaction to a high enough conversion rate. The excess alcohol needs to be recovered in a separate process which involves additional operating and energy costs. In this study, a novel reactor system using reactive distillation (RD) technique was developed and studied for biodiesel preparation from yellow mustard seed oil. The main objective was to dramatically reduce the use of excess alcohol in the feeding steam, which reduces the cost in downstream alcohol recover processes, and meanwhile maintain a high alcohol-to-oil molar ratio inside of the RD reactor, which ensures the completion of the transesterification of seed oil to biodiesel. A lab scale sieve-tray RD reactor system was developed and used in this study. Process parameters were studied on the effect of reduced alcohol to oil ratio on the overall quality of biodiesel product and the efficiency of such an RD reactor. Product parameters such as methyl ester content, viscosity, total glycerol, and methanol content were analyzed as per ASTM methods. Preliminary results showed that process parameters of methanol-to-oil ratio of 4:1 (molar) and a column temperature of 65 °C produced a biodiesel that met the ASTM standards for total glycerol and viscosity.