Improvements to Quality-related Limitations to Market Growth of Biodiesel and Renewable Hydrocarbon Diesel Produced from Low-value Feedstocks

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Commodities

Practices

• Education and Training: demonstration, workshop
• Energy: biodiesel

Feedstocks for biodiesel production are vegetable oils, animal fats and short chain alcohols. Amongst the most common oils are soybean, rapeseed, palm oil, linseed oil, sunflower oil, safflower oil, animal oil and peanut oil. Feedstock constitutes about 80% of the total cost of biodiesel production which has limited the world market growth of biodiesel production. Thus, the use of non-edible vegetable oil and low-value feedstocks has become a subject of intense research in recent years. Brown grease lipids (BGL), the primary component of dewatered grease trap waste (GTW) and sewage scum grease (SSG) is a potential low-value feedstock for biodiesel production. Market limitations of these feedstocks include high sulfur (S) content. A combination of analytical techniques including GC-FID, GC-PFPD, and GC-MS have been previously used to elucidate the identity of thiophene derivatives (C4H4S-X), thiolane derivatives (C4H8S-X) and other S-bearing compounds in BGL-derived biodiesel. These compounds do not exist in the MS library; therefore, a small degree of uncertainly surrounds their identification. Therefore, this project was designed to synthesize the S-bearing compounds believed to be found in BGL-derived biodiesel in quantities sufficient to characterize them by analytical methods such as NMR. We have developed strategies to synthesize thiophene and thiolane and preliminary results indicate they can be produced in yields sufficient to assist in their characterization in biodiesel. The identification of S-bearing compounds in BGL-derived biodiesel is necessary to devise effective desulfurization protocols needed to reduce the concentration of S-bearing impurities in biodiesel to < 15 ppm, as specified by ASTM.

1. Detection, Quantification, Identification and Removal of Sulfur-bearing impurities in biodiesel produced from brown grease lipids. This study is proposed to synthesize some sulfur-bearing compounds as surrogate species in order to fully understand the nature of the sulfur impurities present in biodiesel produced from BGL. Identifying individual sulfur-bearing compounds in brown grease lipid derived fatty acid methyl ester (BGL-FAME) should aid in developing more effective desulfurization technologies to reduce these sulfur-containing impurities in BGL-FAME and other BGL derived bio-lubricants as a potential strategy for market growth of biodiesel.

2. Synthesis and Analysis of Cold Flow Enhancers. Biodiesel produced from low-value feedstocks generally has poor cold flow properties: poor performance in cold weather such as North America and Europe and thereby limiting the biodiesel market growth. Biodiesel of bio-based oils are biodegradable, favorable environmental properties, low toxicity to aquatic life and safe to store and handle. As a consequence of their high molecular weights, they possess inherent properties such as low volatilities and high viscosity indices. The viscosity of oil usually increases with decreasing temperature. Thus, biodiesel is considered to have performance limitation with regards to cold flow properties. Most of the bio-based oil crystallize at low temperatures and thereby affecting biodiesel performance during cold weather. Biodiesel based on palm oil, peanut oil, sesame oil, soybean oil or rapeseed oil have start-up and operability problems when ambient temperatures fall below the cloud point (CP) of the fuel. The performance limitations can be overcome by chemical modification, genetic modification of plants, processing technology, blending with petrol diesel and treatment with cold flow improver additives.

3.Identify and develop new feedstocks and accompanying technologies to produce biodiesel and renewable hydrocarbon diesel (RHD) from fats and oils. Alternative lipids sources such as fats, oils and greases from brown grease lipids (BGL), poultry fat, tallow, distillers’ corn oil and other sources have not been proven as suitable feedstocks for either biodiesel or renewable hydrocarbon diesel. Elevated sulfur content in these feedstocks results in biodiesels that do not meet the ASTM specification for sulfur. Production of RHD from such feedstocks is also unproven. In order to overcome these challenges, in this work we will (1) take a combined approach to chemically and physical remove sulfur from biodiesel and provide structural identification of the sulfur-bearing compounds, and (2) evaluate the process of converting fatty acids derived BGL into RHD.