Method and apparatus for producing biodiesel and products obtained therefrom

Abstract

A method and apparatus for economically producing a biodiesel product from a feedstock. Some embodiments include using at least one of a crude feedstock pretreatment process and a free fatty acid purification process prior to transesterification and the formation of crude biodiesel and glycerin. The free fatty acid purification process can include subjecting the feedstock to glycerolysis to obtain glycerolysis products, and then stripping the glycerolysis products to produce a fatty acid distillate and a stripped feedstock. The fatty acid distillate is recycled to the glycerolysis process to produce higher molecular weight glycerides, and the stripped feedstock (primarily di- and triglycerides) proceeds to transesterification to produce biodiesel.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on U.S. Provisional Patent Application No. 63 / 401,012, filed August 25, 2022, the entire disclosure of which is expressly incorporated herein by reference.

[0002] The present invention relates to the efficient processing of low-cost feedstocks into high-quality biodiesel that meets a variety of commercial biodiesel specifications. More specifically, the present invention relates to a method for producing biodiesel that includes a stripping step after the glycerolysis step to separate unreacted free fatty acids (FFA) from glycerides, where the unreacted FFA are recycled to the glycerolysis step and the glycerides undergo transesterification. [Background technology]

[0003] Biodiesel is a renewable, generally less polluting, and low-carbon alternative to petroleum diesel that increases independence from imported oil, helps reduce greenhouse gas emissions, supports agricultural and rural economies, and creates jobs. While biodiesel offers many benefits, its production must be efficient to remain competitive and economically viable.

[0004] To reduce costs and adapt to changing market conditions, many biodiesel producers strive to use lower-cost (and therefore higher-FFA) feedstocks. However, lower-cost feedstocks contain various low-level impurities that can adversely affect biodiesel quality. In other words, it is more difficult to produce high-quality biodiesel when using feedstocks containing more contaminants or particulates. High-FFA feedstocks are generally difficult to process into biodiesel via base-catalyzed transesterification due to the conversion of FFAs to soaps, resulting in undesirable processing results (e.g., emulsion formation and increased catalyst costs), lower yields, and slower production rates. Furthermore, meeting ever-changing quality standards for biodiesel end products is more difficult when using high-FFA feedstocks. To ensure product consistency and consumer safety, current practice is to regulate biodiesel quality according to various commercial standards, including ASTM D6751, EN 14214, CAN / CGSB 3.524, and numerous customer-specific specifications. The aforementioned specifications require biodiesel to be produced to strict standards for many properties, including flash point, residual alcohol, water and sediment, kinematic viscosity, sulfated ash, oxidation stability, sulfur, copper strip corrosion, cetane number, cloud point, carbon residue, acid number, cold soak filterability, monoglycerides, total and free glycerin, phosphorus, 90% distillation temperature, calcium and magnesium, sodium and potassium, particulate contamination, and ester content. The 2012 revisions of ASTM D6751 and D6751-12 introduced multiple biodiesel grades with varying limits on cold soak filtration test time and monoglyceride content, further increasing the importance of these two properties in biodiesel customer acceptance. As biodiesel specifications become more stringent and the demand for low-cost and non-food feedstocks increases, biodiesel producers need improved production processes that increase the efficiency of producing new and / or low-cost feedstocks to remain competitive and economically viable.

[0005] Chemical inputs, such as catalysts, are expensive but necessary parts of the biodiesel production process. Optimizing and ultimately reducing the catalysts and other reactants used is a desirable way to make the biodiesel production process more efficient, as it reduces the cost of producing the components. Furthermore, biodiesel production allows for the recovery and reuse of some catalysts and other reactants, while others are converted to other chemicals and / or cannot be recovered or reused. Therefore, by optimizing and reducing chemical inputs and recovering and reusing reaction products, biodiesel producers can reduce the cost and increase the efficiency of their biofuel production process.

[0006] Two methods that allow for the production of biodiesel from high-FFA feedstocks at lower cost are FFA stripping and glycerolysis. FFA stripping is a distillation process in which FFAs are thermally separated from the feedstock, resulting in a low-FFA feedstream or feedstock and a high-FFA distillate stream. FFA stripping is often characterized by high temperatures and low pressures, which favor the evaporation of FFAs from the feedstream. These conditions also favor the vaporization and carryover of monoglycerides (MG) from the feedstream. MG carryover is undesirable because MG vapors degas or reduce the vapor capacity of the fatty acid distillation column, resulting in increased heat input requirements. However, due to the similar boiling points of FFAs and MG, carryover of some MG vapors is unavoidable while MG is present in the feedstock.

[0007] Another major method for FFA reduction is glycerolysis, in which FFAs are reacted with glycerol to produce a product stream characterized by low FFAs. The glycerol reactant can originate from an external source, be added to a high-FFA feedstock, and / or be inherently present in the feedstream. Available hydroxyl sites may also be present in the form of mono- and diglycerides present in the original feedstock composition. Due to the excess glycerol in the reactor, glycerolysis products can typically be characterized by an overall high MG concentration compared to conventional fat, oil, and grease feedstocks. The artificially high MG concentration generally results in a glycerolysis product stream that is undesirable as a feed for FFA stripping. Therefore, there is a need for a more efficient and economical biodiesel production process that can produce high-quality biodiesel from low-cost feedstocks. Summary of the Invention

[0008] One embodiment of the present invention relates to a method for purifying a feedstock in a biodiesel production process. The method includes introducing the feedstock into a first processing unit and subjecting it to a glycerolysis process and a separation process, such as FFA stripping. The output stream from the first processing unit is then introduced into a second processing unit, which performs the other of the glycerolysis process and the separation process. The glycerolysis process converts FFAs and glycerol into a glycerolysis product having a mixture of mono-, di-, and triglycerides, as well as unreacted FFAs and glycerin. The separation process separates the glycerolysis product into a stripped feedstream rich in di- and triglycerides and a fatty acid distillate stream rich in FFAs and MGs. The fatty acid distillate is then introduced into a glycerolysis process to convert the FFAs and MGs into di- and triglycerides. The method continues as a loop, with the fatty acid distillate being recycled upstream of the glycerolysis process until di- and triglycerides are produced and separated into a stripped feedstream.

[0009] Another embodiment of the present invention relates to a method for purifying a feedstock in a biodiesel production process. The method includes introducing a feedstock stream into a glycerolysis process, which converts FFAs in the feedstock into glycerolysis products. The glycerolysis products include at least a portion of unreacted FFAs and glycerin, as well as mono-, di-, and triglycerides. The glycerolysis products are then introduced into a separation process, such as an FFA stripping process, which separates the glycerolysis product stream into a refined feedstock containing di- and triglycerides and a fatty acid distillate containing FFAs and MGs. The fatty acid distillate is either recycled upstream of the glycerolysis process or introduced into a subsequent glycerolysis process that converts additional FFAs and MGs into di- and triglycerides. In some embodiments, the glycerolysis process is "starved" by introducing less glycerin than is required to convert all of the FFAs and MGs into di- and triglycerides. Depletion of glycerolysis reactions helps increase production of di- and triglycerides while minimizing production of MG.

[0010] Another aspect of the present invention relates to a method for purifying a feedstock in a biodiesel production process. The method includes removing free fatty acids from the feedstock in a first free fatty acid stripping process to produce a stripped feedstock and a fatty acid distillate. The stripped feedstock contains di- and triglycerides and continues the process for transesterification to produce biodiesel. The fatty acid distillate contains FFAs and MGs. The fatty acid distillate is introduced into a glycerolysis process to convert some unreacted FFAs and glycerolysis products having mono-, di-, and triglycerides. The glycerolysis products are then recycled upstream of the fatty acid stripping process or introduced into a subsequent fatty acid stripping process that separates the stream into the stripped feedstock and the fatty acid distillate again. The stripped feedstock continues for transesterification, and the fatty acid distillate is introduced back into the glycerolysis process to further convert unreacted FFAs and MGs into di- and triglycerides. In some embodiments, the glycerolysis process is "starved" by introducing less glycerol than is required to convert all of the FFAs and monoglycerides to di- and triglycerides. Starving the glycerolysis reaction serves to increase di- and triglyceride production while minimizing MG production.

[0011] The advantages of the described technology may be better understood by referring to the following description in conjunction with the accompanying drawings. The drawings are not to scale and represent exemplary configurations illustrating basic principles of the technology; they are not intended as an exhaustive description of, or limitation on, broader aspects of the invention. Dotted lines in the figures represent various embodiments that may be included as part of the process. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a process flow diagram illustrating several embodiments of a method for biodiesel production. [Figure 2-1]FIG. 2 is a process flow diagram illustrating a more specific embodiment of the method for biodiesel production shown in FIG. 1. [Figure 2-2] This is a process flow diagram (continuation of [Figure 2-1]) showing a more specific embodiment of the method for producing biodiesel shown in Figure 1. [Figure 2-1] and [Figure 2-2] are collectively referred to as Figure 2. [Figure 3] FIG. 3 is a process flow diagram illustrating a more specific embodiment of the free fatty acid purification step shown in FIG. 2. [Figure 4] FIG. 1 depicts the glycerolysis reaction network. [Figure 5] FIG. 1 is a process flow diagram of the laboratory-scale batch reactor configuration used for glycerol degradation experiments. [Figure 6] 1 is a graph showing the effect of glycerin dose on the FFA and MG content of glycerolysis products. [Figure 7] 1 is a graph showing the effect of glycerin dosage on the concentration of FFAs and the corresponding latent heat of vaporization, assuming complete removal of FFAs and MGs during FFA stripping. DETAILED DESCRIPTION OF THE INVENTION

[0013] The apparatus, devices, systems, products, and methods of the present invention will now be described in detail with reference to various non-limiting embodiments, which are by way of example only, including the drawings.

[0014] Unless otherwise indicated, all numbers expressing dimensions, volumes, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." "About" is understood by those of ordinary skill in the art and will vary to some extent depending on the context in which it is used.

[0015] The present invention may be practiced by performing the process steps in an order other than that specifically set forth herein. All references to a "step" may include multiple steps (or sub-steps) within the meaning of a step. Similarly, all references to the plural "steps" may be construed as a single process step or various combinations of steps.

[0016] The present invention may be practiced by performing the process units in an order different from that specifically set forth herein. All references to a "unit" may include multiple units (or sub-units) within the meaning of the unit. Similarly, all references to the plural "units" may be interpreted as a single process unit or various combinations of units.

[0017] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0018] As used herein and in the appended claims, the term "fats and oils" refers to any material of biological origin, both plant and animal, that is useful as a feedstock for producing biodiesel. Feedstocks may be in a crude form containing impurities and are considered "crude stock" or "crude oil." Alternatively, feedstocks may be pre-processed using other equipment to remove impurities. The pre-processing process may occur at the biodiesel production facility, at the source, or both, to produce a "pre-treated feedstock" or "pre-treated oil." The term "refined feedstock" refers to a feedstock with a free fatty acid content low enough to be used directly in transesterification. Refined feedstocks may contain crude alkyl esters. The term "free fatty acids" refers to aliphatic carboxylic acids with carbon chains containing from about 6 to about 24 carbon atoms. Free fatty acids may be found in 0 to 100% by weight of fats and oils and are susceptible to forming esters upon reaction with alcohols under esterification conditions. The term "ester" refers to organic esters, including monoesters, diesters, triesters, and more commonly, multiesters. The term "biodiesel" refers to a fuel composed of fatty acid alkyl esters of long-chain fatty acids derived from fats and oils. The term "alcohol" generally refers to organic alcohols, including monohydric, dihydric, and polyhydric alcohols.

[0019] The term "acid number" refers to a general measurement of the amount of acid functionality on molecules in a sample. It specifically refers to the amount of strong base (typically KOH) required to titrate the acid functionality in a sample. Acid number is conventionally expressed as milligrams of potassium hydroxide per gram of sample.

[0020] The term "sulfur" refers to the total amount of sulfur in a liquid fuel, defined as mg / kg or parts per million (ppm). The term "unsaponifiable matter" refers to compounds in fats and oils that do not contain fatty acid moieties that can be converted to alkyl ester molecules, thereby reducing the ester content and / or yield of biodiesel. The term "cold soak filterability test" refers to test methods contained in commercial specifications such as ASTM D7501, CAN / CGSB 3.524 Appendix A, and EN 14214, which are used to evaluate the potential cold weather performance of biodiesel and biodiesel blends.

[0021] The terms "glycerin" or "glycerol" or "free glycerin" refer to the molecule propane-1,2,3-triol (CAS number 56-81-5). The term "crude glycerin" refers to a stream consisting primarily of glycerin and dilute impurities such as methanol, salts, water, and non-glycerin organic matter. The term "total glycerin" refers to glycerin present either as free glycerin or as glyceryl moieties bound to fatty acids as glycerides.

[0022] The method of the present invention can accommodate a wide range of feedstocks. In some embodiments of the present invention, non-exclusive examples of feedstocks are oils and fats, including coconut oil, palm oil, palm kernel oil, cottonseed oil, rapeseed oil, peanut oil, olive oil, linseed oil, babassu oil, tea oil, tallow oil, olive kernel oil, meadowfoam oil, kaulmo okra oil, coriander oil, canola (rapeseed) oil, soybean oil, corn oil, camelina oil, castor oil, pennycress oil, lard oil, jatropha oil, sunflower oil, algae oil, used cooking oil, bacon grease, premium white grease, yellow grease, brown grease, poultry fat, beef tallow, lard, fish oil, or combinations thereof. Furthermore, the feedstock may include clarified or distilled oils and fats containing fatty acid distillates, such as palm fatty acid distillates. Other feedstocks containing significant concentrations of FFAs, such as greater than about 1% by weight, may also be suitable, such as acid soap scum. In some cases, distillation bottoms may be considered low-grade crudes, including bottoms from crude biodiesel distillation. Additional oils suitable for biodiesel production may be recovered from grain ethanol processes, including corn oil, sorghum oil, wheat oil, etc., depending on the feedstock of the ethanol production process.

[0023] The present invention generally relates to a method for purifying a feedstock in a biodiesel production process by subjecting the feedstock to a glycerolysis process followed by a separation process, such as FFA stripping, prior to transesterification. While the present invention is primarily directed to a method for purifying a feedstock, the present application also describes additional exemplary steps in the biodiesel production process.

[0024] An exemplary method 100 for processing crude feedstock 105 into glycerin 145 and purified biodiesel 160 that meets commercial specifications is described with reference to FIG. 1. Crude feedstock 105 arrives at a biodiesel production facility and is discharged into crude stockpile 105. Compatible feedstocks may be combined and stored in a common tank before being processed. Crude feedstock 105 may first undergo a feedstock pre-treatment process 110, depending on its FFA content and other characteristics, to produce pre-treated feedstock 115.

[0025] 2, the pre-treated feedstock 115 may then be subjected to an FFA purification process 120 that converts the FFAs to glycerides via glycerolysis 250. The FFA purification process 120 includes a loop in which the FFAs and MGs are introduced into glycerolysis 250 to convert them primarily to di- and triglycerides, and the stream then undergoes FFA stripping to separate the fatty acid distillate 240 (rich in FFAs and MGs) from the stripped feedstock 245 (rich in di- and triglycerides). The fatty acid distillate 240 is recycled back to glycerolysis 250, and the stripped feedstock 245 is the refined feedstock 125 that proceeds to transesterification 130. In some embodiments, the feedstock 115 is introduced into an FFA stripping process 235 prior to glycerolysis 250. Regardless, processes 235 and 250 are connected in a loop, with fatty acid distillate 240 from FFA stripping process 235 being directed to glycerolysis 250 and stripped feedstock 245 proceeding to transesterification 130. Refined feedstock 125 undergoes transesterification process 130 to produce crude biodiesel 150 and crude glycerin 135. Crude glycerin 135 is refined in glycerin purification unit 140 to produce glycerin 145, which may be recycled to FFA purification process 120 for glycerolysis 250. Crude biodiesel 150 undergoes final biodiesel refinery process 155 to produce commercially acceptable purified biodiesel product 160. Wet alcohol from biodiesel refinery 155 and glycerin refinery 140 is sent to alcohol recovery unit 165 to separate water 175 and recover dry alcohol 170. An embodiment of the unit operations of FIG. 1 is described in more detail in FIGS. 2 and 3.

[0026] FIG. 2 illustrates a process embodiment similar to that illustrated in FIG. 1, except that FIG. 2 illustrates additional embodiments and process steps in more detail. Crude feedstock 105 is stored at a biodiesel production facility. Suitable feedstocks may be combined and stored in a common tank before further processing. Crude feedstock 105 is pre-treated and refined as dictated by its FFA content and other feedstock characteristics. Pre-treated feedstock 115 requires further processing to convert the FFAs to glycerides before transesterification. FFAs in crude feedstock 105 are generally undesirable in transesterification process 130 because they form soaps in the oil when they react with the base catalyst used to drive transesterification. As described in more detail below, free fatty acid purification process 120 involves chemical conversion of FFAs by glycerolysis 250. Glycerolysis is a subcategory of esterification that uses glycerol, or alcohol, to convert FFAs into glycerides, which are fatty acid esters of glycerol. U.S. Patent No. 7,087,771 (Luxem) contains a more detailed description of glycerolysis and is expressly incorporated by reference. An advantage of the present invention over the prior art is that feedstocks having any FFA content (0-100 wt%) can be processed by appropriate feedstock pre-treatment embodiments 110 and / or FFA purification 120 processes. More specifically, feedstocks 105 containing any amount of FFAs can be processed by at least one of the pre-treatment 110 and FFA purification 120 methods described herein, in which the FFAs are removed in chemical purification unit 205, physical purification unit 235, and / or converted by glycerolysis in FFA conversion unit 250.

[0027] The embodiment shown in Figures 2 and 3 includes an FFA purification process 120 with a recycle loop in which a pre-treated feedstock 115 is introduced into a first process unit, which includes an FFA stripping process 235 and a glycerolysis process 250. The stream from the first processing unit is then introduced into a second process unit having the other of the FFA stripping process 235 and the glycerolysis process 250. A fatty acid distillate 240 stream from the stripping process 235 is recycled back to the glycerolysis process 250. In one embodiment, shown by the solid line in the FFA purification process 120, the pre-treated feedstock 115 is stripped of FFAs and other components with lower molecular weights than di- and triglycerides (e.g., MG) in a physical FFA purification step using distillation 235. While the FFA stripping step can be performed on feedstocks with any FFA level, a preferred FFA level is between about 0.2% FFA by weight and about 30% FFA by weight. The FFA stripping step 235 may heat the crude feedstock using steam, hot oil, or other thermal fluid. Distillation may be performed under vacuum pressure to remove FFAs from the oil phase by evaporation within unit 235. The FFA stripping step 235 may utilize a distillation column, wiped film evaporator, or other such equipment and may optionally include injection of steam into the distillation unit to facilitate separation of the FFAs from the remainder of the feedstock. Two product streams can be produced from FFA stripping 235: a relatively pure fatty acid distillate 240 made of greater than about 50% by weight FFAs along with some MG, and a stripped feedstock 245 containing di- and triglycerides and less than about 0.5% by weight FFAs. FFA stripping 235 purifies the stripped feedstock stream 245 sufficiently to enter the transesterification process as refined feedstock 125. The fatty acid distillate stream 240 is directed to an FFA conversion unit 250 where it undergoes glycerolysis to form mono-, di-, and triglycerides. The stream resulting from the glycerolysis unit 250, along with any unreacted FFAs, is referred to herein as the "glycerolysis product."In this embodiment, the glycerolysis product is introduced into another FFA stripping unit or recycled through FFA stripping unit 235 (shown in FIGS. 2 and 3) to produce second stripped feedstock 245 and second fatty acid distillate 240. Note that the reference numbers for second stripped feedstock 245 and second fatty acid distillate 240 are the same as those for first stripped feedstock 245 and first fatty acid distillate 240, respectively, because the process creates a flow loop in which each stream can be directed to the same process unit. FFA Stripping 235 unit receives streams from two different locations: from pre-treated feedstock 115 on the one hand and from the FFA Conversion 250 unit on the other. To accommodate the second (recycled) stream, some embodiments increase the volumetric capacity of the FFA Stripping 235 unit.

[0028] The glycerolysis products may be returned to the pre-treatment feedstock unit 115 prior to the FFA stripping unit 235 or may be introduced directly into the FFA stripping unit 235. The stripped feedstock 245 is separated from the fatty acid distillate 240 during FFA stripping 235, as described above. The first and second stripped feedstocks 245 are passed to the refined feedstock 125 and directed to transesterification 130 as described herein. The crude biodiesel 150 produced during transesterification 130 may be subjected to biodiesel refinery 155 as described below. The second fatty acid distillate 240 separated in the FFA stripping unit 235 is then reintroduced into the FFA conversion unit 250 to undergo glycerolysis, which converts more FFAs and monoglycerides to di- and triglycerides and reduces the FFAs in the refined feedstock 125. The fatty acid distillate 240 is continuously separated from the stripped feed 245 and introduced into the FFA conversion unit 250, and then recycled through the FFA stripping unit 235 to reduce the amount of FFAs in the refined feed 125. In some embodiments, the stripped feed 245 (product stream) is less than about 5%, 4%, 3%, 2%, 1%, 0.5%, 0.3%, or 0.1% by weight of FFAs before entering the transesterification as the refined feed (125).

[0029] A second embodiment, shown by dashed lines in Figures 2 and 3, is similar to the above-described embodiment, except that refined feedstock 115 is first introduced into glycerolysis unit 250 to convert FFAs and MGs into di- and triglycerides. The glycerolysis product stream is then introduced into stripping 235, where higher molecular weight glycerides are removed as stripped feedstock 245 and proceed toward transesterification, while fatty acid distillate 240 is recycled to glycerolysis unit 250 as described above. The method continues as a loop, with fatty acid distillate 240 being recycled back into glycerolysis process 250 until di- and triglycerides are produced and separated into stripped feedstream 245. The loop continues for FFAs and other low molecular weight compounds, while higher molecular weight glycerides are separated during stripping 235 and continue toward transesterification 130.

[0030] In some embodiments, the glycerolysis process 250 described above can be optimized to increase di- and triglyceride production using less glycerin while minimizing the combined concentration of FFAs and MG in the glycerolysis product. Glycerin optimization involves "starving" the glycerin reaction, or using less glycerin than would be required to convert all of the FFAs to glycerides. Glycerolysis proceeds according to the reaction network shown in Figure 4, with reaction conditions such that each of the five reactions proceeds primarily in the forward direction.

[0031] There are three forward reactions (R1, R4, and R5) that result in the production of MG. These are the only reactions that require free glycerol (FG) as a reactant. Furthermore, because reaction R1 is the primary reaction in the conversion of FFAs, glycerolysis reaction conditions are traditionally set to favor reaction R1 to produce the lowest possible FFA content. However, the subsequent implementation of the FFA stripper in the present invention reduces the FFA concentration in the refinery feedstock, regardless of the degree of FFA conversion in glycerolysis. Therefore, the implementation of the FFA stripper in the present invention allows for the use of a more optimized, lower glycerol dosage for the glycerolysis product stream fed to the FFA stripper. This optimized glycerol dosage "starves" the FG reaction and favors the forward reactions R2 and R3. The forward reactions R2 and R3 then favor the production of di- and triglycerides. After separation in step 235, the MG and unreacted FFAs are recycled back into the glycerolysis where they have another opportunity to react with glycerin to form higher molecular weight (di- and tri-)glycerides. The FFA purification process 120 of the present invention allows for less glycerin to be used during glycerolysis because it is not necessary to react all of the FFAs in a single glycerolysis process 250.

[0032] Once the feedstock is pre-treated 110 and refined 120, it enters a transesterification process 130 and then a biodiesel refinery process 155. There are several processes that can be used to produce biodiesel from fats and oils, including base-catalyzed transesterification, acid-catalyzed transesterification, and enzymatic transesterification.

[0033] In one embodiment, after crude biodiesel 150 and crude glycerin 135 are separated in unit 275, crude glycerin 135 may be treated with an appropriate acid from acid dilution vessel 285 to neutralize residual catalyst, and crude biodiesel 150 may be subjected to a water wash in unit 295 to remove glycerin, salts, and soaps. To remove any remaining alcohol, the separated crude glycerin 135 may be subjected to further purification in an evaporation step. One such distillation and drying step is performed in unit 290. Glycerin alcohol stripper 290 removes alcohol and water, which are collected in wet alcohol unit 315. Removal of the alcohol and water results in a glycerin product comprised of about 78% to about 98% pure glycerin. This glycerin 145 can be further refined to about 99% purity or greater using additional processing techniques to make the glycerin product suitable for use in high-purity applications such as cosmetics and pharmaceuticals. Alternatively, if the FFA conversion 250 process is glycerolysis, glycerin 145 may be used as a reactant (shown in dashed lines) for glycerolysis.

[0034] The crude biodiesel 150 exiting the phase separation unit 275 still contains impurities and must be purified in one or more unit operations. The order and number of these operations can vary depending on the crude feedstock characteristics, pre-treatment processes, transesterification processes, and economic feasibility. However, combining an appropriate biodiesel purification process 155 with appropriate feedstock pre-treatment 110 and FFA purification 120 processes will result in purified biodiesel 160 that meets commercial specifications, regardless of the initial feedstock characteristics.

[0035] The present invention is illustrated in more detail below with reference to examples, but is not limited to these examples.

[0036] example Example 1: Effect of glycerol dose on glycerolysis A high-FFA feedstock blend was prepared from approximately 79 wt% used cooking oil (UCO) and approximately 21 wt% fatty acid distillate (FAD). Key properties of the high-FFA feedstock blend are summarized in Table 1 below. Purified glycerin was produced by distilling crude glycerin from biodiesel production in a wiped-film evaporator at approximately 180 °C and 16 mbar. The composition of the purified glycerin is shown in Table 2. The effect of glycerin dosage on glycerolysis performance was evaluated by dosing the high-FFA feedstock blend with purified glycerin at dosage rates ranging from 0 to 0.31 molar equivalents (MEq-TFA) relative to the total fatty acids present in the high-FFA feedstock blend. The glycerin dosage rate was determined on an MEq-TFA basis according to the following formula:

number

number

[0037] The glycerin-dosed feedstock was then reacted in a laboratory-scale stirred batch reactor at 230 °C and 300 mbar for approximately 4 hours. Figure 5 shows a block flow diagram of the laboratory-scale reactor system used in this study. The stirred batch reactor consisted of a 1000 mL round-bottom flask placed on an electric heating mantle, and the liquid temperature was maintained by a PID controller. A magnetic stir bar was added to the flask and stirred at approximately 500 rpm by magnetic drive throughout the reaction. A glass-tube-in-tube heat exchanger was connected downward to the outlet of the stirred batch reactor so that all condensate collected in the heat exchanger flowed into the cold trap. Chilled water, maintained at 10 °C, was pumped through the shell side of the heat exchanger. The cold trap was a three-port 500 mL round-bottom flask with the heat exchanger entering through one port and a vent line connected to another port. The third port was plugged. The vent was plumbed to a vacuum pump. The vacuum pump discharge was routed to a fume hood. [Table 1] [Table 2]

[0038] After conducting the glycerolysis experiments as described above, the effectiveness of the glycerolysis treatment was determined by analyzing the composition of the glycerolysis products for FFAs and glycerides. The results of these analyses are shown in Table 3 below. Interestingly, a 6.7 wt% reduction in FFAs was observed even when no glycerin was added to the reactor. As the dosage rate of purified glycerin increased, the FFA content of the glycerolysis products decreased, as shown in Figure 6, until the FFA content decreased to less than approximately 1 wt%, which occurred at glycerin dosage rates above approximately 0.10 MEq-TFA. From Figure 6, it can be seen that once the FFA content of the glycerolysis products decreased to less than 1 wt%, the MG concentration began to increase substantially. [Table 3]

[0039] Traditionally, glycerolysis is optimized to produce feedstocks characterized by low concentrations of FFAs. However, in the present invention, when glycerolysis is optimized to feed FFA distillation, the latent heat of vaporization (LHOV) of the glycerolysis products must also be considered. Figure 4 illustrates the tradeoff between low FFAs and low latent heat of vaporization (LHOV) of the feedstock, with the LHOV increasing substantially as the FFA content decreases to optimal levels (e.g., less than 1 wt%). The LHOVs for the volatile components FFA and MG were calculated based on their respective compositions and LHOVs. The undiluted LHOVs for the FFA, assumed to be oleic acid, and the MG, assumed to be monoolein, were 163.5 BTU / lb and 142.7 BTU / lb, respectively. Using a high (>0.18 MEq-TFA) glycerin dosage, the LHOV of the glycerolysis products increased to more than 37 BTU / lb. This trade-off between FFA reduction and MG production becomes problematic when attempting to distill FFAs from glycerolysis products because the low volatility of MGs also results in MG carryover in the FFA distillation step, thus increasing the LHOV load.

[0040] As a result of the wide variation in the identity and amount of impurities found in biodiesel feedstocks, particularly low-cost crude feedstocks, several process steps disclosed in embodiments of the present invention may be utilized as disclosed to convert impure feedstocks into high-quality, fully acceptable biodiesel. These various embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, and it will be understood that modifications to the various disclosed embodiments may be made by those skilled in the art.

[0041] While the methods and steps described above indicate certain events occurring in a certain order, those skilled in the art will recognize that the order of certain steps may be varied and still be in accordance with the principles of the present invention. Additionally, certain steps may be performed simultaneously in a parallel process where possible, as well as sequentially.

[0042] All publications, patents, and patent applications cited in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in this specification.

[0043] The above-described embodiments, variations, and drawings demonstrate the utility and versatility of the present invention. Other embodiments that do not provide all of the features and advantages set forth in this application may be utilized without departing from the spirit and scope of the present invention. Such modifications and variations are deemed to be within the scope of the principles of the present invention as defined by the appended claims.

Claims

1. 1. A method for producing biodiesel from a feedstock containing free fatty acids (FFA) and monoglycerides, comprising: a. introducing the feedstock into a first process, the first process being one of a glycerolysis process and a separation process, wherein the first process produces a product stream; b. introducing the product stream into a second process, the second process being the other of a glycerolysis process and a separation process; c. wherein the glycerolysis process converts free fatty acids (FFAs) and monoglycerides into glycerolysis products having a mixture of mono-, di-, and triglycerides and unreacted FFAs; d. the separation process separates one of the feedstock and the glycerolysis products into a stripped feed stream and a fatty acid distillate stream; e. introducing the fatty acid distillate into the glycerolysis process of step (a) or step (b); A method comprising:

2. 10. The method of claim 1, wherein the separation process is a free fatty acid (FFA) stripping process.

3. 2. The method of claim 1, wherein the first process is the glycerolysis process and the second process is the separation process.

4. The method of claim 1 , wherein the feedstock is a pre-treated feedstock.

5. 10. The method of claim 1, wherein the stripped feed stream is enriched in di- and triglycerides.

6. 10. The method of claim 1, wherein the fatty acid distillate stream is enriched in FFAs and monoglycerides.

7. 10. A product produced by the process of claim 1.

8. 1. A method for producing biodiesel from a feedstock containing free fatty acids (FFA), comprising: a. converting the FFAs in said feedstock to glycerolysis products using a glycerolysis process; b. separating the glycerolysis product into a fatty acid distillate and a stripped feed using a free fatty acid stripping process; c. introducing the fatty acid distillate into either the glycerolysis process of step (a) or a subsequent (second) glycerolysis process; A method comprising:

9. 10. The method of claim 8, further comprising converting the stripped feedstock to a first crude biodiesel using a transesterification process.

10. 9. The method of claim 8, wherein the feedstock and the glycerolysis products are introduced simultaneously into the fatty acid stripping process.

11. 10. The method of claim 9, further comprising distilling the first crude biodiesel to produce a clarified biodiesel and a distillation bottoms.

12. 10. The method of claim 8, further comprising pre-treating the feedstock to produce a pre-treated feedstock, and using the pre-treated feedstock as the feedstock in step (a).

13. 10. The method of claim 8, wherein the feedstock comprises at least one of distiller's corn oil, palm oil, fatty acid distillate, biodiesel still bottoms, yellow grease, brown grease, poultry fat, used cooking oil, pennycress oil, algae oil, soybean oil, beef tallow, premium white grease, canola oil, and combinations thereof.

14. 9. The method of claim 8, wherein the glycerolysis products include mono-, di-, and triglycerides, and unreacted FFAs.

15. 9. A product produced by the process of claim 8.

16. 1. A method for producing biodiesel from a feedstock containing free fatty acids (FFA), comprising: a. converting FFAs in said feedstock to glycerolysis products using a glycerolysis process; b. separating the glycerolysis product into a stripped feedstock and a fatty acid distillate; c. introducing the fatty acid distillate into the glycerolysis process of step (a); d. Transesterifying the stripped feedstock to produce a first crude biodiesel; A method comprising:

17. 17. The method of claim 16, further comprising distilling the first crude biodiesel to produce a purified biodiesel and a distillation bottoms.

18. 17. The method of claim 16, further comprising pre-treating the feedstock to produce a pre-treated feedstock, and using the pre-treated feedstock as the feedstock in step (a).

19. 17. The method of claim 16, wherein the feedstock comprises at least one of distiller's corn oil, palm oil, fatty acid distillate, biodiesel still bottoms, yellow grease, brown grease, poultry fat, used cooking oil, pennycress oil, algae oil, soybean oil, beef tallow, premium white grease, canola oil, or combinations thereof.

20. 17. A product produced by the process of claim 16.

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