The RHT- Biodiesel process is optimized to produce biodiesel from palm oil, rape-seed oil, vegetable and animal products that contain fatty acids with even number of carbon atom (12 to 22). The lack of sulfur in the biodiesel enables complying with many international fuel specifications.
The biodiesel is comparable to petroleum-based diesel. Triglycerides are reacted with methanol, ethanol or higher alcohols to yield biodiesel within the acceptable boiling range. Methanol is most commonly used for the biodiesel production since it is the most cost-effective of alcohols, and it can provide better economics for the biodiesel producers. Biodiesel is produced by reacting vegetable oils and animal fats (triglycerides) with methanol in the presence of highly alkaline heterogeneous catalyst at moderate pressure and temperature. Pretreatment may be equired if the vegetable oil has a high free-fatty acids content to optimize methyl esters yield. If free fatty acids are present in the feed, first step is esterfication of the free-fatty acid with methanol. However if the free-fatty acids concentrations are low, then this step can be deleted.
The triglycerides and methanol are converted by transesterfication reaction to yield methyl esters of the oils and fats, and glycerine is produced as a byproduct. The glycerine is separated from the methyl esters (biodiesel) by phase separation via gravity settling. The methyl esters and glycerine are purified to meet the product specifications.
In the simplified process flow diagram (1), the feed—vegetable oil or animal fats—is pumped from storage and is mixed with methanol in the required molar ratio vegetable/methanol at moderate operating pressure. The feed is heated to the reaction temperature and is sent to esterification reactor. Free-fatty acids are pretreated if the concentration exceeds 3% percent of the feed. The reactor contains an acid catalyst for this reaction and can remove 99.9 % of free-fatty acids from the vegetable oils. (Note: the pretreatment is only required when the feed contains free-fatty acids; otherwise, this step can be omitted.
The effluent from the first reactor (if free-fatty acids are present) or the heated feed is sent to the transesterfication reactor, where 3 moles of methanol react with the triglyceride to produce 3 moles of methyl ester oil (biodiesel) and one mole of glycerine. The transesterfication reactor uses a highly alkaline heterogeneous catalyst and provides essentially 100% conversion. The transesterification reactor effluent is sent to gravity separator/settler. The biodiesel product is taken from the top of the separator, and is water washed. The washed biodiesel product is taken from the top of the drum. Water washing removes excess methanol from the reaction products, which is recovered by normal distillation; the pure methanol is recycled back to the reactor. The bottoms from the separator/settler are sent to the purification unit to remove impurities and residual methanol, which is recycled back. Pure glycerine product is sent to storage.
Fig. 2 is an alternate flow scheme; a spare transesterification reactor is added to remove glycerine from the reactor to sustain reaction rates. Once the reaction rates are reduced the reactor is switched and washed with hot solvent to remove residual glycerine and biodiesel. This extra reactor patented mode of operation provides higher reactions rates and onstream capability while enhancing yield and productivity. Glycerine purity can exceed 99.8% after distillation.
Reaction chemistry: Transesterification reactions:
Triglycerides + 3 Methanol –> Methyl Ester of the oil (biodiesel) + Glycerol
Licensor: Refining Hydrocarbon Technologies LLC.