(Glycerolysis Reactor system to convert Brown Grease to Yellow Grease)
Glycerolysis is an old oleochemicals technique (early to mid-20th Century) that has been used for many decades. It has been used to prepare, for example, mono-glycerides via reactions of fatty acids and glycerin, or mono-glycerides from glycerin reactions with tri-glycerides. Mono-glycerides have been used as emulsifying agents in foods for humans and animals, in cosmetics, and many other products.
Glycerolysis can also be used to process high FFA waste oils, such as trap grease and brown grease (with FFA’s as high as 50 to 75% or more) and upgrade them to yellow grease which, by definition, contains less than 15% FFA’s. A batch reactor for this purpose was installed by Superior Process Technologies at a Baker Commodities rendering site several years ago.
Based on our oleochemicals industry experience, the Superior Process engineering team recognized (more than 10 years ago, in 2002) that Glycerolysis could be used as a pretreatment step for the production of biodiesel from high FFA waste oils. Glycerolysis reactions have demonstrated over and over again, that yellow greases with 15% FFA, beef tallow with 20% FFA, and trap greases with 50 to 75% FFA, can all be pretreated to produce glycerized oils with 1% FFA or less, and made suitable for biodiesel feed stock.
For more than six years, Superior Process Technologies has been doing process development work to produce biodiesel fuel from high FFA waste oils (such as yellow grease, brown grease, rendered oils, beef tallow). Glycerolysis seemed to be a “natural” step in preparing free fatty acids to be transesterified to methyl esters. In fact, since glycerin is a by-product of biodiesel production, it seemed obvious to simply recycle some of this glycerin to pretreat high FFA feed oils. Keep in mind, however, there are a few important processing steps required to prepare the crude glycerin before it can be recycled.
SPT has studied the chemical kinetics of glycerolysis reactions in the laboratory (see attached kinetic data) and then used this kinetic data to design, not only commercial “batch” glycerolysis systems, but also “continuous” systems. Continuous “G” systems have the advantage of much higher annual throughput, since they avoid the batch cycle time periods of filling, heating, cooling, and discharging a batch system; continuous systems can operate constantly, and never waste any process time that is typical of batch systems. When processing 5 to 10 million gallons per year of feed oils (or more) it becomes advantageous to install a continuous system rather than a batch system.
Chemical Kinetics of Glycerolysis
FA + G -------- > MG + W at Rate Constant K1
TG + G -------- > MG + DG at Rate Constant K2
FA + MG ------ > DG + W at Rate Constant K3
dFA/dt = -K1xFAxG - K3xFAxMG
dG/dt = -K1xFAxG - K2xTGxG
dMG/dt = +K1xFAxG + K2xTGxG - K3xFAxMG
dDG/dt = + K2xTGxG + K3xFAxMG
dTG/dt = - K2xTGxG
dW/dt = + K1xFAxG + K3xFAxMG