In situ alkaline transesterification of cottonseed oil for production of biodiesel and nontoxic cottonseed meal

doi:10.1016/j.biortech.2008.04.059

Bioresource Technology

Volume 99, Issue 18, December 2008, Pages 9009-9012

https://doi.org/10.1016/j.biortech.2008.04.059 Get rights and content

Abstract

The production of fatty acid methyl ester (FAME) by direct in situ alkaline-catalyzed transesterification of the triglycerides (TG) in cottonseeds was examined. The experimental results showed that the amount of cottonseed oil dissolved in methanol was approximately 99% of the total oil and the conversion of this oil could achieve 98% under the following conditions: less than 2% moisture content in cottonseed flours, 0.3–0.335 mm particle size, 0.1 mol/L NaOH concentration in methanol, 135:1 methanol/oil mole ratio, 40 °C reaction temperature and 3 h reaction time. Further, the effects of co-solvent petroleum ether and methanol recycling on the cottonseed oil extraction and conversion were also investigated. The use of alkaline methanol as extraction and reaction solvent, which would be useful for extraction oil and gossypol, would reduce the gossypol content in the cottonseed meal. The free and total gossypol contents in the cottonseed meal obtained from in situ alkaline transesterification were far below the FAO standard. And the nontoxic cottonseed meal could be used as animal protein feed resources.

Introduction

With the increasing cost and depletion of conventional petroleum-derived fuels, the need for alternative fuels is increasing steadily and accordingly much effort has been devoted to their development. Biodiesel, an alternative diesel fuel, is made from renewable biological sources such as vegetable oils and animal fats. It is biodegradable, nontoxic, renewable, environmentally benign (Vicente et al., 2004, Encinar et al., 2005), and its use in diesel engines also shows a decrease in the emission of CO, SO_x, unburned hydrocarbons and particulate matter during the combustion process (Antolin et al., 2002, Murayama et al., 2000). Currently, semirefined and refined vegetable oils are the predominant feedstocks for the production of biodiesel. However, their relatively high costs render the resulting fuels unable to compete with petroleum-derived fuel. Therefore, it is necessary to explore raw materials and ways to reduce production costs of biodiesel.

In situ transesterification (Harrington and D’ Arcy-Evans, 1985, Siler-Marinkovic and Tomasevic, 1998, Kildiran et al., 1996, Hass et al., 2004), a biodiesel production method that utilizes the original agricultural products instead of purified oil as the source of triglycerides for direct transesterification, eliminates the costly hexane extraction process and works with virtually any lipid-bearing material. It could reduce the long production system associated with pre-extracted oil and maximize alkyl ester yield. The use of reagents and solvents is reduced, and the concern about waste disposal is avoided.

In China about 10 million tonnes of cottonseed are produced annually and due to the presence of toxic gossypol in the cottonseed, the use of non-refined cottonseed oil is very limited. And using it as a raw material for producing biodiesel could be a significant choice. Also, cottonseed is only slightly inferior to soybean as a protein source, but the toxic gossypol in the cottonseed must be removed before being eaten by monogastric animals. Thus, it is necessary for cottonseed meal to be further processed to reduce gossypol to permissible levels as animal protein feed resources. Due to the presence of excess of polar methanol during in situ transesterification, the toxic polar gossypol which exists in cottonseed could be extracted. Therefore, virtual nontoxic cottonseed meal could be produced.

Alkaline catalysis is known to achieve the transesterification of TG with high speed and efficiency, and to be more effective than acid catalysis in this capacity. And in order to minimize the cost of the raw material to produce biodiesel, the use of cottonseed instead of refined oil is an effective way to reduce the raw material cost. The conversion of cottonseed oil to FAME by alkali-catalyzed in situ transesterification has not been reported. We therefore investigated and identified optimal conditions for the in situ alkaline transesterification of cottonseed oil, and at the same time we expect to obtain nontoxic cottonseed meal as animal protein feed resources.

Section snippets

Materials

Cottonseeds were obtained from Jiangsu Jintian Group (Jiangsu, China). They were milled using an electric grinder to a mesh size of 40–60. Methanol (>98%) and petroleum ether (60–90 °C) were purchased from Nanjing Huaqingnanfang chemical Ltd. (Nanjing, China). They were distilled before being used. All other chemicals including sodium hydroxide used during this experiment were of analytical reagent (AR) grade.

In situ alkaline transesterification procedure

Milled cottonseeds (25 g) were mixed with methanol (100–200 ml) in which sodium hydroxide

Results and discussion

The presence of water could cause ester saponification under alkaline transesterification conditions (Ma et al., 1998). To determine the effect of moisture content on in situ alkaline transesterification, the cottonseed flours samples with varying moisture content were prepared by vacuum drying at 60 °C. The results showed that the cottonseed oil extraction and conversion increased with the drop of moisture content in cottonseed flours. When decreasing the moisture content from 8.7% to 1.9%, the

Conclusions

In order to minimize raw material cost to produce biodiesel, the use of cottonseed instead of refined oil is an effective way. In situ transesterification could reduce the long production system associated with pre-extracted, degumming and refining of oil and maximize alkyl ester yield. In the present work, the technique of in situ alkaline transesterification of cottonseed oil to produce biodiesel has been reported. The experimental results showed that the amount of cottonseed oil dissolved in

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Short CommunicationIn situ alkaline transesterification of cottonseed oil for production of biodiesel and nontoxic cottonseed meal

Abstract

Introduction

Section snippets

Materials

In situ alkaline transesterification procedure

Results and discussion

Conclusions

Bioresour. Technol.

Fuel

Fuel

Bioresour. Technol.

J. Mol. Catal. A: Chem.

Determination of Free Gossypol. Official Method Ba 7-58. Official and Tentative Methods of Analysis

Determination of Total Gossypol. Official Method Ba 8-78. Official and Tentative Methods of Analysis

Short Communication
In situ alkaline transesterification of cottonseed oil for production of biodiesel and nontoxic cottonseed meal