Patent Description:
The present invention, in some embodiments thereof, relates to biodiesel production and, more particularly, but not exclusively, to a novel process of generating an alkyl ester of a fatty acid from a free fatty acid-containing substance. In some embodiments, the process is usable for generating biodiesel from liquid waste such as Brown Grease.

Massive use of fossil fuels has led to an increase in the CO<NUM> concentration in the atmosphere, and this has caused global climate changes. In contradistinction, biofuels which are produced from plant sources, and in particular biodiesel, do not affect the greenhouse gas balance.

Recently, biodiesel has become one of the most potential renewable energy sources. The use of biodiesel instead of conventional diesel fuel can reduce emissions of greenhouse gases and other environmental pollutants (ash, soot, sulfates), protect the environment and improve air quality.

Herein throughout, and in the art, the term "biodiesel" describes a fuel that is made from natural elements such as lipids and fats that originate from plants, vegetables, and/or animals, and/or from re-usable materials such as liquid waste. Biodiesel is typically biodegradable, renewable and non-toxic, and is devoid of petroleum or petrodiesel.

The renewable and biodegradable biodiesel is typically produced by transesterification of vegetable oils and animal fats. The process duration and reaction conditions depend on catalysts, yet currently practiced processes typically require heating and pressure.

Conventional sources of biodiesel are agricultural crops, such as corn, soybean, canola, cotton, mustard and palm. However, use of these crops for biodiesel leads to depletion of global food resources.

Brown grease (BG) is the fat layer of liquid waste generated during cooking and processing of food, which typically included in wastewater from industrial kitchens, food processing facilities, banquet halls, restaurants etc.). Direct disposal of fats, oils and grease (FOG) to sewage collection system (SCS) is illegal. Lipids may precipitate on the walls of pipes in SCS, leading to pipe fouling, clogging, and sewer overflows (He et al. Removal of BG is usually carried out using grease traps, which are mechanical devices, in which gravitational separation takes place, when effluents flow with a velocity, allowing to float or precipitate the wastes. The fat content in the waste traps depends on the type of industry and can reach up to <NUM> % vol. (Suto et al. , <NUM>; Gabel et al.

One option for BG treating is anaerobic digestion of fats with methane gas formation (Long et al. , <NUM>; Wang et al. Another option is to use FOG energy more directly by separating the lipids and converting them into biodiesel, an alternative renewable fuel source (Chakrabarti et al. The cost of raw materials is very low and even negative, since collection and disposal of wastes is refunded. Thus, even with additional processing costs, FOG can provide a cost-effective alternative to fossil fuels, in addition to minimizing the negative effects of FOG on wastewater treatment systems (Chakrabarti et al.

Biodiesel can be produced by the chemical reaction of triglycerides or free fatty acids (FFA) with an alcohol (usually, methanol), to form alkyl esters of fatty acids, as a result of trans-esterification reaction in the case of triglycerides, as depicted in Scheme <NUM> below, and of an esterification reaction in the case of FFA, as depicted in Scheme <NUM> below. <CHM>
<CHM>.

Both reactions require the use of various catalysts, typically traditional alkaline catalysts such as KOH, NaOH, NaOCH<NUM>, KOCH<NUM> and others.

The basic (alkaline) catalysts have a number of advantages, such as the ability to promote the reaction at moderate temperature and atmospheric pressure conditions, high conversion in a relatively short time and a low catalyst cost (Talha & Sulaiman, <NUM>, Canakci & Gerpen, <NUM>). However, there is a high sensitivity of the process to even negligible amounts of water and to the presence of FFA in the feedstock. FFA reacts with an alkaline catalyst to form soap (fatty acid salt) and water. As a result, the consumption of the catalyst increases, and the emulsion formed due to the presence of the soap makes it difficult to separate the biodiesel from the glycerin formed by trans-esterification of triglycerides (Talha & Sulaiman <NUM>, Canakci & Gerpen <NUM>). The high FFA content in BG therefore restricts the use of alkaline catalysts when producing biodiesel therefrom (Talha & Sulaiman <NUM>).

Acid catalysis, which is usually carried out with sulfuric acid, is not sensitive to the presence of free fatty acids and trace amounts of water, but this method is less efficient due to a slow reaction rate (Talha & Sulaiman <NUM>). Thus, acid-catalyzed reactions require higher temperatures, large amounts of catalysts and a longer reaction time in order to achieve the same conversion rates as with basic catalysis (Lam et al.

One solution to the above-described limitations is the use of a two-phase process in which the first phase is the conversion of FFA to methyl esters with an acid catalyst, and the second phase is basic/alkaline transesterification (Canakci & Gerpen <NUM>, Banerjee & Chakraborty <NUM>, Chai et al. , <NUM>) of triglycerides. However, such a process involves increased costs of designing and operating the infrastructure.

Another trend in the development of catalysts for the esterification and transesterification is the use of heterogeneous catalysts (basic or acidic), which facilitate the separation and purification of the product (Romero et al. Heterogeneous catalysts can also be re-used and allow performing a continuous process. As in the case of homogeneous catalysts, the activity of the alkaline heterogeneous catalysts is higher than that of the acid catalysts, and the reaction proceeds under more moderate conditions, but the limitations posed by the presence of water and FFA still render such processes inefficient (Talha & Sulaiman <NUM>).

FFA esterification can also be performed in the presence of Lewis acid catalysts (Santos et al. These catalysts can be used homogeneously (Santos et al. , <NUM>) and heterogeneously (as a solid phase) (Barbosa et al. <NUM>; Casas et al. <NUM>), and allow performing the reactions under mild conditions (Sun et al.

Esterification and transesterification reactions are typically activated thermally, by heating the mixture of reactants and the catalyst at elevated temperatures (Meher et al.

Recently, it has been reported that esterification reactions can be activated by the use of ultrasound, without application of heat and at high rate and yield (Teixeira et al. , <NUM>; Hingu et al. These reactions were carried out using basic catalysts: NaOCH<NUM>, KOCH<NUM> (Cintas et al. , <NUM>), KOH (Hingu et al. , <NUM>, Rajkovic et al. , <NUM>, Encinar et al. , <NUM>) or SrO (Salamatinia et al. , <NUM>), which are not suitable for esterification of FFA-rich substances such as BG.

Heterogeneous catalysts (K<NUM>PO<NUM>, Na<NUM>PO<NUM>, Na<NUM>HPO<NUM>, NaH<NUM>PO<NUM>, KH<NUM>PO<NUM>) were investigated with ultrasonic activation, and were shown to be effective for transesterification of used cooking oil, which also has a very law FFA content (Pukale et al.

Document <NPL> discloses a process wherein lauric acid is reacted with glycerol in the presence of ultrasounds and ZnCl<NUM> as Lewis acid catalyst which is solid and is added in a continuous manner to the mixture.

Document <NPL> discloses an alkyl ester of fatty acids, obtained from an oil with at least <NUM>% free fatty acids which has been esterified with BF3 as catalyst, in toluene.

Document <CIT> discloses an alkyl ester of fatty acids, obtained from a waste oil with free fatty acids which has been esterified with an acid catalyst, with ultrasounds.

Document <CIT> discloses alkyl esters of fatty acids.

The present inventors have designed and successfully practiced processes and systems for executing thereof which can be utilized for processing liquid waste such as Brown Grease by esterification of free fatty acids (FFAs) optionally together with transesterification of triglycerides using a Lewis acid for promoting the reaction (e.g., BF<NUM>, AlF<NUM> and others). The newly designed process utilize ultrasound for activating the chemical reactions and can be used to produce biodiesel at ambient temperatures during several minutes with high efficiency and without additional heating. The newly designed process can be performed in a continuous regime, using solid or gaseous Lewis acid, and/or while recycling the Lewis acid.

According to an aspect of some embodiments of the present invention there is provided a process of generating an alkyl ester of a fatty acid from a free fatty acid-containing substance, the process comprising: contacting a mixture of the free fatty acid-containing substance and a respective alcohol with a Lewis Acid; and during said contacting, exposing said mixture to ultrasound energy, wherein said free fatty acid-containing substance comprises a free fatty acid in an amount of at least <NUM> % by weight, and wherein said contacting and said exposing is at room temperature ± <NUM>.

According to some of any of the embodiments described herein, the free fatty acid-containing substance further comprises a triglyceride, the process being further of generating alkyl esters of one or more fatty acids corresponding to the triglyceride.

According to some of any of the embodiments described herein, the free fatty acid-containing substance is a liquid waste.

According to some of any of the embodiments described herein, the free fatty acid-containing substance is a Brown Grease.

According to some of any of the embodiments described herein, the mixture is devoid of an alkaline substance.

According to some of any of the embodiments described herein, the mixture comprises water.

According to some of any of the embodiments described herein, the mixture further comprises an organic solvent.

According to some of any of the embodiments described herein, the alcohol and/or said free fatty acid-containing substance is immiscible with said organic solvent and the alkyl ester of the fatty acid is dissolvable or miscible in said organic solvent.

According to some of any of the embodiments described herein, the organic solvent is an aprotic solvent.

According to some of any of the embodiments described herein, the Lewis acid is in a solid form, and said contacting comprises continuously introducing said mixture into a reactor comprising said Lewis acid in a non-dispersible solid form.

According to some of any of the embodiments described herein, contacting is performed in a continuous manner and said Lewis acid is in a gaseous form, and wherein said mixture and a liquid form of said Lewis acid are introduced to a reactor that is in acoustic communication with an ultrasound transducer, and wherein following said exposing, a liquid phase comprising said alkyl ester of said fatty acid is separated from a gaseous phase comprising said Lewis acid in a gaseous form, and said gaseous form of said Lewis acid is condensed into said liquid form and is re-contacted with said mixture.

Moreover, according to actual instrumentation and equipment of embodiments not being part of the method of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.

For example, hardware for performing selected tasks according to embodiments not being part of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments not being part of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment not being part of the invention, one or more tasks according to exemplary embodiments of method and/or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions.

The present inventors have designed and successfully practiced an improved process of esterification of free fatty acids, which can be used efficiently in production of biodiesel from, for example, liquid waste, and, importantly, in the production of biodiesel from free fatty acid-containing substances such as, for example, Brown Grease. The disclosed process can advantageously replace fossil energy sources by renewable biofuels, decrease greenhouse gas exhausts and contribute to wastewater treatment.

As discussed in the Background section hereinabove, fats-containing liquid wastes generated by the food industry and which are known as Brown Grease (BG), are accumulated in grease traps of e.g., restaurants and food plants. BG is classified as waste, and it must be properly treated and disposed. On the other hand, BG contains vegetable oils and animal fats, which can be converted into biodiesel. All these factors make BG an attractive raw material for biodiesel production.

However, the content of water, detergents and other pollutants, as well as a high content of free fatty acids in BG, does not allow the use of BG in conventional biodiesel production processes. In Example <NUM> and Table <NUM> and <FIG> referred to therein, the high content of free fatty acids in BG collected from various sources has been demonstrated by the present inventors.

As discussed in the Background section hereinabove, while BG can serve as promising feedstocks for biodiesel production using reactions of esterification and transesterification, it cannot be processed in the presence of conventional basic catalysts due to adverse saponification reactions. In addition, basic catalysts are sensitive to even negligible presence of water (which is typically present in BG). Although conventional acid catalysts do not lead to saponification and are less sensitive to the presence of water, the reaction rates are very low and the process requires high temperatures.

The present inventors have recognized the benefits of using Brown Grease (BG), which has a high free fatty acid (FAA) content, for producing biodiesel, yet, have further recognized that while the esterification and triglyceride trans-esterification of BG can be performed under thermal activation and classical homogeneous catalysis, such processes cannot be practiced efficiently, and are time, cost and energy consuming.

In a search for an improved process for biodiesel production from liquid waste such as BG, the present inventors have uncovered that esterification of free fatty acids (FFAs) can be performed using a Lewis acid for promoting the reaction (e.g., BF<NUM>, AlF<NUM> and others), that such Lewis acids can be used also for transesterification of triglycerides and that these reactions can be activated efficiently by means of ultrasound. The newly designed process can be used to produce biodiesel at ambient temperatures during several minutes with high efficiency and without additional heating.

The newly designed process can be performed in a continuous regime, using solid or gaseous Lewis acid, and/or while recycling the Lewis acid.

As demonstrated in the Examples section that follows, and is shown in <FIG>, esterification of free fatty acids and transesterification of triglycerides can be efficiently performed in the presence of a Lewis acid, without addition of NaOH, and while using ultrasonic activation, at ambient temperature in several minutes.

For example, under such conditions, esterification of the oleic acid yielded <NUM> % of conversion after only one minute of the reaction and <NUM> % after <NUM> minutes, thus demonstrating a fast and efficient process of biodiesel production from FFA-rich feedstocks at ambient conditions.

Esterification of oleic acid using Lewis acid catalysts immobilized in a sol-gel matrix, and recycling of the immobilized catalyst, was also successfully demonstrated, as shown in <FIG>.

Embodiments of the present invention relate to a novel process of generating or producing an alkyl ester of a fatty acid (biodiesel) from a free fatty acid-containing substance such as brown grease, which supersedes currently practiced methodologies for biodiesel production.

The process of the present embodiments can be advantageously employed in the production of fatty acid alkyl esters (biodiesel), by being characterized by high conversion rate, high yield, high efficiency, ease of use (e.g., at ambient conditions), using heterogeneous catalysis which allows a continuous process, and is cost effective.

According to an aspect of some embodiments of the present invention there is provided a process of generating an alkyl ester of a fatty acid from a free fatty acid-containing substance.

Herein and in the art, the phrase "an alkyl ester of a fatty acid" describes a compound, or a mixture of compounds, which are each independently represented by the Formula I:.

Alternatively, R can be an alkylene chain of a triglyceride that is represented by Formula III:
<CHM>
in which each of R<NUM>, R<NUM> and R<NUM> is independently as defined herein for R.

When the alkyl ester is of a triglyceride as represented by Formula III, one, two or each of R<NUM>, R<NUM> and R<NUM> is replaced by R' as defined herein (by trans-esterification).

Representative examples of fatty acids may include, without limitation, saturated or unsaturated fatty acids that have <NUM> or more carbon atoms, preferably <NUM> or more carbon atoms, for example, <NUM>-<NUM> carbon atoms, such as, but not limited to, lauric acid, sebacic acid, myristic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, palmitoleic acid, erucic acid, etc. The variable "R" in Formula I, II or III can be an alkylene chain of the above-mentioned fatty acid.

Herein, the phrase "free fatty acid-containing substance" encompasses a compound which is a free fatty acid (e.g., have a Formula II as described herein), or a mixture of two or more different free fatty acids, as defined herein, and any substance which contains a free fatty acid or a mixture of free fatty acids, and optionally other components, including other fatty (oily) components such as, for example, a triglyceride (e.g., having a Formula III as defined herein), or a mixture of two or more triglycerides, liquid components, solid components, aqueous solutions, water, etc..

The process as described herein can therefore be utilized for the esterification of free fatty acids when present per se or when forming a part of a mixture of various materials and/or substances.

The process as described herein can be utilized for producing biodiesel as defined herein and in the art, by means of, inter alia, esterification of free fatty acids. The process of producing biodiesel can further include generation of alkyl esters of fatty acids by other reactions, for example, by trans-esterification of triglycerides.

In some embodiments, the free fatty acid-containing substance is a waste material and the process as described herein is utilized for producing biodiesel from the waste material. In some embodiments, the process is utilized for producing biodiesel from a waste material by, inter alia, esterification of free fatty acids, and optionally also by transesterification of triglycerides if such are present in the waste material.

In some of these embodiments, the waste material is a liquid waste material, that is, a waste material that may comprise a liquid substance (comprising one or more liquid components) and optionally also a solid substance (comprising one or more solid components).

A liquid waste material typically comprises oils and optionally further comprises other organic components, water and/or other aqueous components.

In some embodiments, the free fatty acid-containing substance is a liquid waste. The free fatty acid-containing substance may comprise an oily or organic phase of a liquid waste. A waste material that comprises a liquid waste is used as is in the process as the fatty acid-containing substance. Alternatively, the waste material is first processed so as to remove solid components (e.g., by filtration) and optionally non-organic (e.g., water and water-soluble components) or non-fat liquid components (e.g., by extraction or by a simple phase separation), and the processed material which comprises only liquid components of the waste material or only fatty substances of the waste material is used as a free fatty acid-containing substance.

The process may comprise processing a waste material so as to remove solid components, if present, and optionally non-organic or non-fat liquid components, if present, as described herein, and using the thus processed waste material as the free fatty acid-containing substance (e.g., as a feedstock).

In some of any of the embodiments described herein, the waste material is Brown Grease (BG), as described herein. The brown grease can be used as is (e.g., upon being collected from an oil trap), or upon being processed to remove solid components, if present, and optionally non-organic or non-fat liquid components, if present.

Herein throughout, the free fatty acid-containing substance is or forms a part of a feedstock, from which a biodiesel is obtained by the process as described herein.

The process of the present embodiments, for preparing an alkyl ester of a fatty acid, can be regarded as a process of preparing or producing biodiesel from a free fatty acid-containing substance, as defined herein.

The process of the present embodiments, for preparing an alkyl ester of a fatty acid, can be regarded as a process of an esterification of a free fatty acid in a fatty acid-containing substance, as defined herein.

According to some of any of the embodiments described herein, the fatty acid-containing substance comprises one or more free fatty acids and one or more triglycerides.

The fatty acid-containing substance comprises one or more free fatty acids in an amount of at least <NUM>, or at least <NUM>, or at least <NUM>, or at least <NUM> % by weight of the total weight of the free fatty acid-containing substance (the feedstock).

The fatty acid-containing substance comprises one or more free fatty acids in an amount of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> % by weight, including any intermediate values and subranges between these values of the total weight of the free fatty acid-containing substance (the feedstock).

In some of any of the embodiments described herein, the free fatty acid-containing substance comprises one or more of oleic acid and linoleic acid. In these embodiments, a total concentration of these one or more free fatty acids in the feedstock is at least <NUM> %, or at least <NUM> %, or at least <NUM> %, and in some embodiments, the total amount ranges from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, or from <NUM> to <NUM> %, by weight, of the total weight of the feedstock, including any intermediate values and subranges therebetween.

In some of any of the embodiments described herein, the free fatty acid-containing substance (e.g., the feedstock) comprises water. The amount of water may be at least <NUM> %, or at least <NUM>%, or at least <NUM> %, and can be even higher, e.g., at least <NUM> %, at least <NUM> % or higher. In case of feedstock that is unprocessed waste material, the amount of water can be of <NUM> %, <NUM> %, <NUM> % or higher.

According to the present embodiments, a process as described herein comprises contacting a mixture of the free fatty acid-containing substance, as described herein in any of the respective embodiments, and a respective alcohol (also referred to herein as a mixture of reagents, as a reagents mixture or simply as a mixture) with a catalytic amount of a Lewis Acid.

By "respective alcohol" it is meant a R'OH compound from which R' in Formula I is derived (see, for example, Scheme <NUM> above). R' may be a short alkyl, of, for example, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>, carbon atoms in length. The alcohol may be a short alcohol, for example, methyl, ethyl, n-propyl or n-butyl, alcohol (namely, methanol, ethanol, n-propanol, n-butanol, respectively), however, other alcohols, in which R' is, for example, a branched and/or substituted alkyl, and/or is an alkyl of more than <NUM> carbon atoms in length) are also contemplated. The alcohol may be methanol and the alkyl ester of the fatty acid is a methyl ester. The alcohol may be ethanol and the alkyl ester of the fatty acid is an ethyl ester.

By "Lewis acid" it is meant, as commonly accepted in the art, a compound or species with is an acceptor of a pair of electrons.

An amount of the Lewis acid is selected so as to promote the reaction(s) and reduce their duration, and can be determined by those skilled in the art by known means.

The Lewis acid may be used in an amount which is no more than <NUM> mol % relative to the total amount of a mixture of the free fatty acid in the free fatty acid-containing substance, the respective alcohol and the Lewis acid (e.g., a total amount of the reagents mixture and the Lewis acid).

Exemplary Lewis acids that are usable are based on metals such as aluminum, boron, silicon, tin, titanium, zirconium, iron, copper, and zinc, which are typically substituted by one or more electron withdrawing groups, most commonly one or more halo atoms (e.g., fluoro, chloro, or bromo). Exemplary Lewis acids include BF<NUM>, Al<NUM>Cl<NUM>, TiCl<NUM>, ZnCl<NUM>, BCl<NUM>, and more complex Lewis acids, including any other Lewis acid known in the art as promoting esterification or transesterification of fatty acids and/or triglycerides. Such Lewis acids are also referred to herein and in the art as Lewis acid catalysts or simply as catalysts.

According to the present embodiments, the process further comprises sonication of the reaction mixture, that is, subjecting the mixture of the free fatty acid-containing substance and the respective alcohol, and optionally an organic solvent, when contacted with the Lewis acid, to sonication.

By "sonication" it is meant application of a sound energy. The sonication may comprise application of ultrasound energy, or ultrasonication, at frequencies of, for example, higher than <NUM>, for example, of from <NUM> to <NUM>, or from <NUM> to <NUM>, including any intermediate values and subranges therebetween. Higher values are also contemplated. In some embodiments, the process is effected by exposing the mixture of reagents, when contacted with the Lewis acid, to ultrasound energy, as described herein.

Contacting a mixture of the fatty acid-containing substance, the alcohol and the Lewis acid may be for a time period in the range of minutes, that is, for example, from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM> minutes, including any intermediate value and subranges therebetween.

The application of sonication may be for a time period in the range of minutes, that is, for example, from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM> minutes, including any intermediate value and subranges therebetween.

The contacting and the sonication may be effected substantially at the same time. Contacting and sonication may be effected substantially at the same time for a time period as indicated herein.

It is to be noted that a time period of the contacting and/or the sonication can be longer than <NUM> minutes, and may depend, inter alia, on the amount and/or phase of the Lewis acid. For example, when a Lewis acid is dissolved or dispersed in the reaction mixture, or is in a gaseous form, the time period is lower than <NUM> minutes and can be even lower than <NUM> minutes. When a Lewis acid is in a non-dispersible solid form, the time period is typically higher than <NUM> minutes, and can be even higher than <NUM> minutes. Time periods of the contacting and/or sonication can be manipulated by increasing or reducing the amount of the Lewis acid.

The contacting and/or the sonication are performed at room temperature ± <NUM>.

The mixture of the fatty acid-containing substance and the respective alcohol may be devoid of an alkaline substance, and in some embodiments, may be devoid of an alkaline substance that is usable in esterification and/or transesterification reaction of fatty acids and triglycerides, respectively.

By "devoid of" it is meant that the alkaline substance (e.g., NaOH) is in an amount that does not exceed <NUM> %, or <NUM> %, or <NUM> %, or <NUM> %, by weight, of the total weight of the respective mixture or product, or is completely absent therefrom.

In some of any of the embodiments described herein, the mixture of the free fatty acid-containing substance (e.g., the feedstock) and the respective alcohol further comprises an organic solvent, preferably an aprotic and/or hydrophobic organic solvent. Such solvent may be a liquid alkane (e.g., hexane, heptane, octane, and the likes).

In some of any of the embodiments described herein, the organic solvent, when present, is such that is immiscible with the alcohol (R'OH) and/or the free fatty acid and/or the free fatty acid-containing substance as described herein, at least at room temperature and/or without subjecting a mixture of the organic solvent and the reagents mixture to sonication as described herein.

In some of any of the embodiments described herein, the organic solvent is such that the alkyl ester of the fatty acid (the biodiesel) is dissolvable or miscible therewith, at room temperature and without subjecting a mixture of the organic solvent and the reagents mixture to sonication as described herein.

Exemplary such solvents include aprotic, preferably hydrophobic, organic solvents as described hereinabove, for example, an alkane, or a mixture of alkanes, or alkenes, alkynes or a mixture of one or more of an alkane, alkene and alkyne. The organic solvent is preferably non-volatile at room temperature, that is, has a boiling temperature that is higher than <NUM>, or higher than <NUM>, °C. An exemplary organic solvent is n-hexane. A use of such organic solvents provides for a biphasic system, at least at room temperature and/or when sonication is not applied, in which one phase contains the feedstock, the alcohol and optionally the Lewis acid (if and when dissolved in the reagents mixture), and the other phase contains the organic solvent and the produced biodiesel. Such a system enables efficient separation of the organic solvent that comprises the biodiesel product from the reaction mixture. Such a system further enables "shifting" the reaction's equilibrium towards the biodiesel production, as the formed biodiesel continuously moves from the reaction mixture phase that contains the feedstock and the alcohol to the organic solvent phase.

In the context of an organic solvent, an amount of the organic solvent may range from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, by volume, relative to an amount of the reagents mixture, including any intermediate values and subranges therebetween.

In some of any of the embodiments described herein, the process is performed in a reactor to which the reagents (e.g., the feedstock and the respective alcohol, and optionally an organic solvent) are fed. The reactor preferably may further comprise, or is in acoustical communication with, an ultrasound transducer, for generating ultrasound energy in the reactor.

The ultrasound transducer can be in acoustical communication with an ultrasonic bath which in turn is in acoustical communication with a reaction vessel to which the reagents are fed. In such embodiments, the ultrasound transducer forms a part of the reactor. Alternatively, the ultrasound transducer is external to the reactor and is in acoustical communication with the reactor, or with a reaction vessel within the reactor which comprises the reagents, during the process. Other configurations for application of sound energy are also contemplated.

The Lewis acid may be contacted with the mixture to form a solution. For example, BF<NUM>, which is a gas at room temperature, is dissolved in the respective alcohol or a portion thereof, or otherwise in an organic solvent as described herein, and the process is performed as a homogeneous reaction (in terms of the catalyst and the reagents mixture being both in a liquid phase). In another example, AlCl<NUM>, which is solid (e.g., powder) at room temperature, is dispersed in the reagents mixture, and the process is performed as a heterogeneous reaction.

The process may be performed in a batch-wise manner. For example, a feedstock and a respective alcohol (herein also referred to as reagents or reagents mixture) and optionally an organic solvent are fed into a reactor as described herein, the Lewis acid (e.g., as a solution or a powder) is added (either before, after or together with introducing the mixture to the reactor) and sonication is applied (e.g., by an ultrasound transducer as described herein). The resulting mixture is then removed from the reactor and a new batch of a feedstock, a respective alcohol and a Lewis acid, and optionally an organic solvent, is added, and so forth.

The Lewis acid may be in a form that allows performing a heterogeneous catalysis, such that the Lewis acid and the reagents (the fatty acid-containing substance and the respective alcohol and optionally an organic solvent) are in separate phases (e.g., solid and liquid or gaseous and liquid, respectively), during the contacting, such that the Lewis acid is not dissolved or dispersed in the reagents mixture for at least a certain time period during the contacting.

The Lewis acid may be in a solid form, preferably a non-dispersible solid form. Exemplary such Lewis acids include, for example, all Lewis acids that are solid at room temperature, and which are immobilized by being entrapped within a liquid-permeable matrix or by being attached or absorbed onto and/or into a matrix.

A non-limiting exemplary matrix is a porous silica matrix, for example, a matrix prepared by a sol-gel process using an orthoester silicate, in which a solid Lewis acid catalyst is entrapped (immobilized). Any other porous or otherwise liquid-permeable matrices are contemplated.

In some of any of the embodiments described herein, the Lewis acid is in a gaseous form. Exemplary such Lewis acids include, for example, BF<NUM>.

In some of any of the embodiments described herein, the contacting is performed in a continuous manner. In some of these embodiments, the mixture of the fatty acid-containing substance and the respective alcohol and optionally an organic solvent, is continuously fed into a reactor that comprises the Lewis acid. In some of these embodiments, the reactor is in acoustical communication with an ultrasound transducer, as described herein.

The Lewis acid may be in a solid form, as described herein, and the contacting comprises continuously introducing the mixture of the reagents and optionally an organic solvent into a reactor comprising the Lewis acid in a non-dispersible solid form.

In some of these embodiments, the reactor further comprises, or is in acoustical communication with, an ultrasound transducer that generates ultrasound energy in the reactor, as described herein.

Exemplary such reactors are schematically illustrated in <FIG> in a non-limiting way.

<FIG> presents a reactor <NUM>, which comprises an ultrasonic bath <NUM>, and an ultrasound transducer <NUM> configured for generating ultrasonic energy in bath <NUM>. The reactor further comprises a reaction vessel <NUM> which is positioned in (or is in contact with or is in acoustical communication with) bath <NUM> and contains a non-dispersible solid form of a Lewis acid <NUM>. Preferably, Lewis acid <NUM> is in an immobilized form (e.g., entrapped within a porous silica matrix such as, for example, a sol-gel matrix). Preferably, but not limiting, Lewis acid <NUM> and vessel <NUM> are configured such that Lewis acid <NUM> is positioned close to transducer <NUM>. The reactor further comprises an inlet port <NUM> for introducing the mixture of the fatty acid-containing substance and the respective alcohol to reaction vessel <NUM>, and an outlet <NUM> from which a mixture containing the alkyl ester product flows out of reactor <NUM>. The mixture of the feedstock and the respective alcohol can be flowed continuously through reaction vessel <NUM> via inlet <NUM> and outlet <NUM> by means of, for example, a pump, or by application of pressure. The flow rate can be controlled so as to achieve high reaction efficiency. Inlet <NUM> and outlet <NUM> can include valves for controlling the flow of the reagents mixture through reaction vessel <NUM>. Exemplary flow rates are such that provide a retention time of the reagents mixture in the reactor that correspond to the contacting and/or exposing as described herein, e.g., <NUM>-<NUM> minutes, or <NUM>-<NUM> minutes). For a reactor volume of <NUM>, a flow rate of <NUM>-<NUM>, or <NUM>-<NUM>/minute may be practiced.

It is noted that the configuration presented in <FIG> is an exemplary illustration and that any other configurations in which a reaction vessel <NUM> contacts bath <NUM> and allows contacting the reaction mixture continuously with Lewis acid <NUM> are contemplated.

<FIG> presents another exemplary configuration of a reactor <NUM> which comprises reaction vessel <NUM> in which a solid form of the Lewis acid <NUM> is positioned. Reactor <NUM> comprises an external ultrasound transducer <NUM> which, when the process proceeds, is introduced to reaction vessel <NUM>, and preferably, is positioned close to Lewis acid <NUM>. Reactor <NUM> further comprises inlet <NUM> and outlet <NUM> for continuously flowing the mixture through reaction vessel <NUM> and contacting it with Lewis acid <NUM>. Reaction vessel <NUM> may have a rectangular shape, for the effective distribution of ultrasonic waves. Any other configuration suitable for employing an external US transducer is contemplated.

In some embodiments in which the contacting is performed continuously, the Lewis acid is in a gaseous form, and the contacting comprises continuously introducing to a reactor that is or is capable of being in acoustic communication with an ultrasound transducer, the reagents mixture and a condensed or dissolved liquid form of the gaseous Lewis acid.

<FIG> presents an exemplary, non-limiting, configuration of a reactor <NUM> for performing a continuous process with a gaseous form of a Lewis acid (not shown in <FIG>).

Reactor <NUM> comprises an ultrasonic bath <NUM>, and an ultrasound transducer <NUM> configured for generating ultrasonic energy in bath <NUM> (being in acoustical communication with bath <NUM>). The reactor further comprises a reaction vessel <NUM> which is positioned in (or in contact with or in acoustical communication with) bath <NUM>. Reactor <NUM> further comprises an inlet port <NUM> for introducing the mixture (not shown) of the fatty acid-containing substance and the respective alcohol to reaction vessel <NUM>, and an outlet <NUM> from which a mixture containing the alkyl ester product flows out of reactor <NUM>. The mixture of the feedstock and the respective alcohol can be introduced continuously through reaction vessel <NUM> via inlet <NUM> and removed via outlet <NUM> by means of, for example, a pump, or by application of pressure. The flow rate can be controlled so as to achieve high reaction efficiency. Inlet <NUM> and outlet <NUM> can include valves for controlling the flow of the reagents mixture through reaction vessel <NUM>. The flow rate can be as described herein for reactor <NUM>.

A gaseous form of the Lewis acid (not shown in <FIG>) is introduced to the reactor via inlet <NUM>, either before, after or together with introducing the reagents mixture. Reaction vessel <NUM> further comprises unit <NUM> which is preferably positioned between bath <NUM> and outlet <NUM>. Unit <NUM> is configured such that a liquid phase which comprises a mixture containing the alkyl ester product flows out through outlet <NUM> and a gaseous form of the Lewis acid is generated and continues flowing within reaction vessel <NUM>. Preferably, unit <NUM> is configured to effect minor heating and/or reduced pressure for obtaining a separated gaseous form of the Lewis acid, optionally together with excess of the respective alcohol. The formed gaseous phase is then flowed through a condensing unit <NUM>, which is positioned between unit <NUM> and inlet <NUM>. When the gaseous Lewis acid flows through condensing unit <NUM>, it liquefies and then flows in a liquid form to the portion of reaction vessel <NUM> that is in contact (as described herein) with bath <NUM>.

It is noted that the configuration presented in <FIG> is an exemplary illustration and that any other configurations in which a gaseous form of the Lewis acid continuously contacts the reagents mixture while being exposed to sonication are contemplated.

The chemical composition of the obtained alkyl ester is determined by the chemical composition of the feedstock.

The obtained product is devoid of, as defined herein, an alkaline substance or of cations derived from the alkaline substance, as defined herein. In exemplary embodiments, the product is devoid of NaOH or of sodium salts or of any other cations that form alkaline substances usable in esterification of free fatty acids as described herein and in the art.

The product may be devoid of, as defined herein, one or more, and preferably all of KOH, NaOH, NaOCH<NUM>, KOCH<NUM>, K+, Na+, NaOR', KOR', with R' being as defined herein, and salts of sodium and/or potassium.

It is expected that during the life of a patent maturing from this application many relevant Lewis acid catalysts, including solid (e.g., immobilized) and gaseous forms of such catalysts will be developed and the scope of the term Lewis acid is intended to include all such new technologies a priori.

It is expected that during the life of a patent maturing from this application many relevant alkaline substances usable for esterification of free fatty acids will be developed and the scope of the term alkaline substance is intended to include all such new technologies a priori.

As used herein the term "about" refers to ± <NUM> % or ± <NUM> %.

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion.

HPLC (UHPLC UltiMate <NUM>, Dionex, Germany) equipped with a Corona ultra RS (Thermo scientific, Germany) detector, and a PolyRP-<NUM>-Sepax (Technologies, Inc. , USA) <NUM>, <NUM>Å, <NUM>. 6x250 mm column was used in all measurements unless otherwise indicated. The column temperature was <NUM>, the flow rate was <NUM>/minute and the injected volume was <NUM>µl. The HPLC mobile phase consisted of <NUM> % acetonitrile.

All reagents were purchased from known vendors unless otherwise indicated.

The chemical composition of the oil phase of brown grease collected from oil traps positioned at various locations was tested using HPLC as described hereinabove, and while using reference standards of oleic acid and linoleic acid.

The oil phase of the collected brown grease was obtained by heating the collected brown grease sample up to <NUM> for <NUM> minutes, followed by centrifugation for <NUM> minutes at <NUM> rpm.

<FIG> and Table <NUM> below present the chromatograms obtained for the brown grease oily phase collected from a cafeteria (<FIG>), poultry slaughter house (<FIG>), and two event halls (<FIG>). As can be seen, the fats composition in all the tested samples was similar. The total amount of the FFA oleic and linoleic acids in the tested samples is <NUM>-<NUM> % by weight, while the amount of each of these fatty acids was similar and ranges from <NUM>-<NUM> % by weight. It is noted that as opposed to liquid waste, cooking oils typically include triglycerides of these fatty acids in an amount of <NUM>-<NUM> %.

In additional tests it was found that smaller amounts of these fatty acids were present in the solid and aqueous phase of the collected brown grease samples (data not shown).

Esterification of <NUM> oleic acid and linoleic acid (reference standards) (see, Scheme <NUM> above) with methanol was performed using BF<NUM>-MeOH (<NUM> %, <NUM>, Lewis acid and reactant), NaOH (<NUM> in methanol, <NUM>, catalyst) and <NUM> n-Hexane while heating the reaction mixture at <NUM> for <NUM>-<NUM> minutes.

The mixtures were tested in HPLC as described hereinabove before and after the reaction, and the obtained chromatograms are presented in <FIG>. As can be seen, most of the fatty acids were converted to their methyl esters and formed a biodiesel.

In additional studies, the same reaction conditions were applied to a mixture of oleic acid and glyceryl trioleate (GTO), but without NaOH: <NUM> oleic acid or glyceryl trioleate, <NUM> BF<NUM>-MeOH (<NUM> %), <NUM> methanol and <NUM> n-Hexane were mixed while heating the reaction mixture at <NUM> for <NUM>-<NUM> minutes.

After the reaction, two phases are present (methanol lower phase and n-hexane upper phase), and at least most of the product (biodiesel) is in the upper phase.

<FIG> present comparative HPLC chromatograms of the lower phase with (<FIG>) and without (<FIG>) NaOH, and of the upper phase with (<FIG>) and without (<FIG>) NaOH. As can be seen, the upper phase, which contains the biodiesel, is not affected by the absence of NaOH.

<FIG> present chromatograms of GTO (<FIG>), of the mixture obtained after the trans-esterification reaction (<FIG>) and of a commercially available methyl ester of GTO (<FIG>). As can be seen, the reaction proceeds towards biodiesel production in high yield in the absence of NaOH.

The esterification of oleic acid in the presence of BF<NUM> as a Lewis acid catalyst (without NaOH) was tested at ambient temperature while sonicating the reaction mixture for <NUM>, <NUM>, <NUM>, <NUM> and <NUM> minutes.

The reaction was performed in a batch tank reactor by addition of <NUM> oleic acid, <NUM> of <NUM> % (by weight) BF<NUM> in MeOH, <NUM> methanol and <NUM> n-Hexane, using a Sonicator ultrasonic processor (QSUNICA, USA), with a frequency of <NUM> or ultrasonic bath WUG-AO2H (Wise Clean Company, Korea) with a frequency of <NUM> or ultrasonic bath Elmasonic (Elma, Germany) with multifrequency <NUM>/<NUM>.

The obtained data is shown in <FIG> and it can be seen that the reaction proceeds efficiently under sonication, in a time-independent fashion.

The reaction was further tested using varying amounts of the BF<NUM> catalyst, and the obtained data is shown in <FIG>. As can be seen, the reaction yields depend on the catalyst amount, and <NUM> % yield is obtained at a catalyst concentration of <NUM> % by weight and upon a reaction time of <NUM> minutes.

Esterification of FFAs using solid catalysts, which avoid or reduce solubilisation of the catalyst during the reaction and thereby enable re-use of the catalysts and/or performing a continuous process, was practiced. The Lewis acid catalysts were incorporated into silica matrices by applying the sol-gel synthetic route.

Tetraethyl orthosilicate (TEOS) (<NUM>, <NUM> mol) was dissolved in ethanol (<NUM>) and a mixture of H<NUM>O (<NUM>) and HCl <NUM> % (<NUM>) was added dropwise to this solution. The obtained mixture was stirred for <NUM> minutes. A catalyst aqueous solution was prepared by adding a desired amount of the catalyst (<NUM> grams, <NUM> mol or <NUM> grams, <NUM> mol of ZnCh) to <NUM> of water and added to the TEOS solution. The mixture solution was stirred for <NUM> minutes. The suspension was kept for gelation and drying at room temperature for <NUM> weeks. The matrix obtained was then dried in vacuum oven for six hours (<NUM>, <NUM> Hg), and the obtained dried matrix was kept in a desiccator. The matrix was ground into powder by pestle and mortar prior to use.

TEOS (<NUM>, <NUM> mol) was dissolved in ethanol (<NUM>) and a mixture of H<NUM>O (<NUM>) and HCl <NUM> % (<NUM>) was added dropwise to this solution. The obtained mixture was stirred for <NUM> minutes. Then <NUM> of BF<NUM>-Me solution (<NUM> % BF<NUM> in methanol) was added. The mixture solution was stirred for <NUM> minutes. The obtained suspension was kept for gelation and drying at room temperature for <NUM> weeks as described hereinabove and was treated prior to use as in described hereinabove.

TEOS (<NUM>, <NUM> mol) was dissolved in ethanol (<NUM>) and a mixture of H<NUM>O (<NUM>) and HCl <NUM> % (<NUM>) was added dropwise to this solution. The obtained mixture was stirred for <NUM> minutes. The suspension was kept for gelation at room temperature for <NUM> weeks until most of the water evaporated and a viscous gel was obtained. <NUM> grams (<NUM> mol) of AlCl<NUM> dissolved in <NUM> of ethanol was added to the gel and the mixture was vigorously stirred for <NUM> minutes. The wet gel was kept for drying for <NUM> weeks and further treated, as in described hereinabove.

The esterification of oleic acid in the presence of the immobilized Lewis acid catalyst (without NaOH) was tested at ambient temperature while sonicating the reaction mixture for <NUM> minutes. The reaction was performed in a batch tank reactor in which a sol-gel matrix entrapping a catalyst was placed and to which <NUM> oleic acid, <NUM> methanol and <NUM> n-Hexane, were added. Sonication was performed using a Sonicator ultrasonic processor (QSUNICA, USA), with a frequency of <NUM> or ultrasonic bath WUG-AO2H (Wise Clean Company, Korea) with a frequency of <NUM> or ultrasonic bath Elmasonic (Elma, Germany) with multifrequency <NUM>/<NUM>.

After the reaction, two phases are present (methanol lower phase and n-hexane upper phase), and the product (biodiesel) is in both the upper and lower phases.

The obtained data is shown in <FIG> and it can be seen that all the immobilized Lewis acids showed an ability to catalyze the esterification reaction already after <NUM> minutes of ultrasonic treatment without additional heating and can be used for biodiesel production. Catalyzing the reaction by immobilized AlCl<NUM> under these conditions gained biodiesel production at a yield of about up to <NUM> % and by immobilized BF<NUM> at a yield of up to <NUM> %. The yield can be increased by elongation to of the reaction time, that is, the time at which the reagents mixture and the immobilized catalyst are contacted under sonication (data not shown).

The immobilized catalyst was thereafter separated from the reaction mixture, contacted again with <NUM> oleic acid, <NUM> methanol and <NUM> n-Hexane, and the same sonication was applied. As shown in <FIG> (dashed bars), the re-used (recycled) catalyst remained active in generating biodiesel, and a decrease of less than <NUM> % and up to <NUM> % was observed from the immobilized BF<NUM> and AlCl<NUM>, respectively.

Claim 1:
A process of generating an alkyl ester of a fatty acid from a free fatty acid-containing substance, the process comprising:
contacting a mixture of the free fatty acid-containing substance and a respective alcohol with a Lewis Acid; and
during said contacting, exposing said mixture to ultrasound energy,
wherein said free fatty acid-containing substance comprises a free fatty acid in an amount of at least <NUM> % by weight,
and wherein said contacting and said exposing is at room temperature ± <NUM>.