Dechlorination process of vegetable and animal fats and oils

Abstract

A process for reducing the chlorine content and, possibly, also the sulphur and phosphorus content in vegetable and animal fats and oils, wherein a flow of said fats and oils is heat-treated with a dechlorinating agent consisting of fatty acid salts with alkali metals from the first group of the Periodic Table of Elements. The process includes a reaction step for the elimination of organic chlorine and of any other heteroatoms such as sulphur and phosphorus contained in said flow of fats and oils, by means of said dechlorinating agent, and a washing step for removing from said fats and oils the obtained reaction products and the excess of said dechlorinating agent.

Description

[0001] DECHLORINATION PROCESS OF VEGETABLE AND ANIMAL FATS AND OILS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a specific process for removing chlorine, and in particular organic chlorine, from vegetable and animal fats and oils in general.

[0004] PRIOR STATE OF THE ART

[0005] Biofuel production, for example by means of the HVO (Hydrotreated Vegetable Oils) process, is obtained from vegetable or animal fats and oils of various origins. These raw materials can either be virgin, i. e., directly derived from the primary source (e. g., soybean oil, sunflower oil, palm oil), or derived from secondary products of primary production (e. g., POME = Palm Oil Mill Effluents), or be waste and recovered raw materials, such as oils recovered from spent bleaching earths (SBEO = Spent Bleaching Earth Oils), as well as UCO (Used Cooking Oils), which are residual oils from cooking processes (e. g., frying oils). Similarly, this last category of waste and recovered raw materials also includes animal fats, such as fats classified in risk categories 1, 2 and 3, and tallow. In the biofuel production according to HVO process, all these raw materials are subjected to an extremely intense hydrogenation process which transforms the triglycerides into hydrocarbons producing water as a by-product [Zeman, P., et al. " Hydrotreated vegetable oil as a fuel from waste materials", Catalysts, (2019) Vol. 9, art. 337 ]. Any free fatty acids are also transformed into hydrocarbons suitable as fuels.

[0006] To ensure a proper operation of hydrogenation catalysts for HVO production, the aforementioned fats must contain extremely low residual contents of chlorine, sulphur, and phosphorus. In other words, it is necessary to preliminarily remove these three elements, and most of all chlorine, as much as possible to prevent poisoning thehydrogenation catalysts which convert fats and oils into HVO. Failure to perform such a preliminary purification can cause a serious damage to HVO production, ranging from a reduced efficiency in converting raw materials into HVO to a reduction in catalyst life resulting in increased costs due to frequent replacement of the catalysts themselves. Furthermore, the fuels produced through the HVO process have stringent technical specifications to comply with, as regards their chlorine and sulphur content. Indeed, the presence of chlorine and sulphur in these fuels implies then the emission of such elements into the atmosphere as HCl and SO2, respectively, when used in internal combustion engines and jet engines. Therefore, it is evident that the chlorine and sulphur content in HVO must be minimized as much as possible. As a matter of fact, the produced fuel quality is just assessed, in addition to other technical parameters, but precisely by its residual amount of chlorine and sulphur.

[0007] WO2023 / 187628 " Process for removing organic chlorine from used cooking oils (UCO), animal and vegetable recovery fats (AVR), and pyrolysis oils (PO) derived from waste", in the name of the same Applicant, discloses the use of several dechlorinating chemicals, which at the same time also have the effect of lowering the sulphur and phosphorus content in the raw material substrates to be sent to an HVO hydrogenation process to produce biofuels.

[0008] TECHNICAL PROBLEM

[0009] The dechlorinating chemicals discloses in patent application WO2023 / 187628 have proven to be highly effective in treating pyrolysis oils, with a very high yield in the final product, and no process issues. Instead, about treatment of UCO and fats and oils in general, although the dechlorination efficiency using the chemicals disclosed in WO2023 / 187628 has consistently proven to be more than satisfactory, some secondary problems arose that prompted the Applicant in studying new technical solutions for thedechlorination treatment of UCO and vegetable and animal fats and oils in general. Said secondary technical problems comprise both process issues during the dechlorination reaction (e. g., excessive foaming) and composition changes of the finished product due to transesterification and / or hydrolytic cleavage undesired reactions in the treated triglycerides.

[0010] The object of the present invention is therefore finding a dechlorinating agent for UCOs and vegetable and animal fats and oils in general to be used in a dechlorination process of the type described in WO2023 / 187628 - which contents are hereby incorporated by reference - which is nevertheless free from the secondary technical problems described above, i. e., which does not produce foaming during the dechlorination reaction and which is substantially inactive in promoting the unwanted reactions of transesterification or hydrolytic cleavage, while being effective in the dechlorination action and simultaneous reduction in the sulphur and phosphorus content.

[0011] US-2024 / 327749 discloses a heat treatment of vegetable and animal fats and oils upon prior addition to the same, where applicable, of potassium soap, NaOH / KOH, or potassium acetate or sodium acetate or mixtures thereof, in amounts which are just sufficient to achieve and maintain the reagent "alkalinity" (defined as the sum of Na, Mg, K, Ca, and Fe in ppm) equal to 500 ppm, to facilitate the reduction in organic phosphorus and chlorine content. Conversely, when the "natural alkalinity" of treated fats and oils is equal to or greater than 500 ppm, no additive is considered necessary. Furthermore, among the additives cited by US-2024 / 327749, the most preferred are sodium acetate and potassium acetate rather than soaps, since - as explained in this document - the low molecular weight of acetates allows for minimizing the mass increase with an equal numberof moles, compared to soaps which have much higher molecular weights than acetates.

[0012] In contrast, the present invention provides for a heat treatment (200 °C-230°C) of vegetable and animal fats and oils exclusively performed under vacuum (10-50 mbar), wherein a dechlorinating agent is added in significantly higher amounts than in US-2024 / 327749, namely from 1.5% to 3. 0% (15, 000-30, 000 ppm) of the oil or fat mass. This heat treatment allows for a high effectiveness in reducing the content of polluting elements, in the case of UCO and POME, without the need for any additional treatment. Known pretreatments such as degumming and / or bleaching are useful instead in treating fats and oils with a higher content of polluting elements, such as in the case of SBEO and animal fats.

[0013] SUMMARY OF THE INVENTION

[0014] The process problems mentioned in the previous paragraph have been surprisingly overcome by new dechlorinating agents for UCO and other fats and oils, consisting of both saturated and unsaturated fatty acids salts with alkali metals, also known as alkali soaps, which therefore form the subject-matter of the present invention. Alkali metals useful for the present invention are all the alkali metals of the first group of the Periodic Table of Elements, but preference is given in particular to the second and third elements of said first group, i. e., sodium and potassium, due to their large availability, low cost, and effectiveness. The best results in terms of dechlorination efficiency, and absence of the aforementioned secondary technical problems, are achieved with potassium salts of fatty acids and, in particular, with potassium oleate and / or potassium soaps of commercial mixtures of saturated and unsaturated fatty acids.

[0015] In developing this invention, the inventors surprisingly discovered that standard soaps, i. e., (saturated and unsaturated) fatty acids salts with alkalimetals, are effective dechlorinating agents for UCO and for vegetable and animal fats and oils in general, also overcoming the aforementioned secondary technical problems related to the dechlorination process itself and to any possible subsequent alteration of the treated substrate.

[0016] It is well known that elimination reactions of halogens, as well as of sulphur derivatives, generally involve the use of strong bases such as the carbonates, the alcoholates, or certain finely divided powdered metals discloses in WO2023 / 187628. However, the inventors surprisingly discovered during their testing that standard soaps (i. e., fatty acids salts with alkali metals ) which certainly cannot be defined as "strong bases" are even more effective than the latter, as dechlorinating and desulphurising agents for UCO and vegetable and animal fats and oils in general. Moreover, said soaps exhibit the further advantages of not giving rise to secondary technical process problems, of stabilizing the chemical composition of the substrate by preventing transesterification and de-esterif ication reactions, and of being easily removable from the substrate at the end of the treatment. Potassium salts of fatty acids have proven to be particularly effective in a dechlorination process compared to salts with other alkali metals, which nevertheless fall within the scope of protection of the present patent.

[0017] EXAMPLES

[0018] In Examples 1-11 below, three different UCO qualities were used, featuring different initial content of chlorine, sulphur, and phosphorus, as shown in Table 1. In particular, UCO " A" is characterized by an initial total chlorine content of 43.3 ppm, UCO " B" by an initial chlorine content of 60.5 ppm, and, finally, UCO " C" by an initial chlorine content of 613 ppm. All elemental analyses relating to contents of chlorine, sulphur, and phosphorus were performed using an X-ray fluorescence spectrometer.

[0019] EXAMPLE 1Example 1 is a comparative example wherein 120 g of UCO " A" are washed with double-distilled water at 90°C without having been previously subjected to heat treatment with a dechlorinating agent.

[0020] UCO " A" (120 g) is heated to 90 °C and stirred in a separating funnel maintained at 90°C, with 400 ml of hot double-distilled water at 90 °C containing 20 ml of concentrated formic acid. After the two phases have settled, the aqueous phase is removed, and a further washing step is performed with 400 ml of neutral double-distilled water at 90 °C. After removing the washing water, UCO " A" is cooled to room temperature and analysed with an X-ray fluorescence spectrometer. The results of this analysis are reported in Table 1 below and show that only a negligible amount of chlorine, sulphur, and phosphorus can be removed by two successive washing steps with hot water and this amount is essentially related to the inorganic fraction which can be extracted with water.

[0021] EXAMPLES 2-10

[0022] The typical process used for these Examples involves pouring 120.0 g of UCO into a 250 ml " Duran" glass flask equipped with a magnetic stir bar and placing such flask into a 250 ml heating mantle equipped with a magnetic stirrer. A thermocouple for monitoring the actual temperature is inserted into the gap between the heating mantle and the flask outer bottom. The dechlorinating agent is a (sodium or, preferably, potassium) soap (see Table 1) which, in preferred embodiments, is added in an aqueous medium to UCO at a rate of 1.5% by weight of the UCO mass. Typically, 21% aqueous potassium soap solutions are used; therefore, 8. 6 ml of 21% potassium soap solution (corresponding to 1.8 g of potassium soap) is added to the 120 g of UCO. However, a dechlorinating agent in solid form can be used as well, as in Example 2 where sodium octoate was added in powder form and, similarly, in Examples 3 and 4 for potassium stearate and oleate. Only in the case ofUCO " C" (Examples 9-10), which has a particularly high chlorine content, the dechlorinating agent concentration was doubled to 3% by weight of sodium or potassium soap, as indicated in Table 1.

[0023] The thus loaded flask is connected to a vacuum distillation apparatus, at a pressure ranging from 0.5 mbar to 90 mbar, and preferably from 10 mbar to 50 mbar. Said distillation apparatus consists of a distillation head with thermometer connected to a condenser, a collecting flask, a Woulff bottle for vacuum regulation, a cold trap and, finally, an attachment to the high vacuum pump equipped with an electronic manometer to measure the actual vacuum.

[0024] Heating is started, by gradually applying vacuum and operating under stirring at 500 rpm. At approximately 100 °C-115 °C all the water used as a vehicle to bring the soap into the UCO is removed by distillation. At this point, the vacuum is brought to 10 mbar and the temperature is gradually brought to 180°-250 °C, preferably to 200°C-230°C or, in any case, to the temperature reported in Table 1, around 200°C. Such conditions are maintained for a time scale of 0.5-10 hours, and preferably of 1-7 hours. The specific reaction times for each example are reported in Table 1 and vary depending on the activity of the dechlorination chemical agent, and the chlorine concentration in the substrate to be treated. Obviously, substrates with high chlorine concentrations, which are therefore more difficult to treat, need longer treatment times. Once the heat treatment is finished, the flask is left to cool to 90°C, keeping the content constantly stirred and the vacuum level at 10 millibars.

[0025] At this point, if the UCO mass viscosity is deemed sufficiently low, the UCO mass is transferred to a separating funnel (maintained at 90 °C) and washed under stirring with 400 ml of hot double-distilled water at 90°C containing 20 ml of concentrated formic acid. After phase separation, the aqueous phase is discarded, the UCO mass isdirectly added with other 20 ml of concentrated formic acid, stirred, and then washed again with 400 ml of hot doubledistilled water at 90 °C.

[0026] After phase separation is completed, the aqueous phase is discarded, and a final washing step is performed using 500 ml of hot double-distilled water at 90°C.

[0027] After stirring and phase separation, the final washing water is also discarded, and the UCO mass is subjected to a final vacuum stripping (110°C and 50 millibars) to remove the last traces of water. Finally, the sample is analysed using an X-ray fluorescence spectrometer. The results of these analyses are reported in Table 1 below.

[0028] As an alternative to directly washing with hot water as described, it may be necessary to treat the UCO mass with 130 ml of n-hexane if the UCO is very viscous. In this case, the UCO is left to cool to 60 °C before treating it with n-hexane (pesticide grade, i. e., free of chlorine, sulphur, and phosphorus ). The same washing steps with the same volumes of double-distilled water and formic acid as described in the previous paragraph are then performed, with the only variation that all washing steps are made at 55 °C. Furthermore, at the end of all washing steps, the n-hexane is completely removed by distillation under reduced pressure. Normally, distillation of n-hexane also removes the last traces of water from the UCO mass.

[0029] It is important to point out that, surprisingly, the use of alkaline soaps as dechlorinating agents does not lead to any evident foaming in the UCO mass during heat treatment, contrary to what happens with some of the dechlorinating chemicals described in WO-2023 / 187628. Furthermore, a careful analysis by FT-IR (infrared spectroscopy) of the dechlorinated UCO obtained according to Examples 2-10 allowed inventors to verify a complete lack of ester cleavage following the described treatments.

[0030]

[0031] From a comparison between Examples 2-10 and Comparative Example 1, it clearly appears that substantial removal of both chlorine and phosphorus only occurs in the presence of one of the inventive dechlorinating chemicals, which in the above Examples is selected from sodium octoate, potassium stearate, potassium oleate, sodium soap from a mixture of fatty acids as well as potassium soap from a mixture of fatty acids. In the preferred embodiments of the invention the above-mentioned dechlorinating chemicals have been used, but it is understood that any alkaline soap — this term referring to an alkaline salt of any type of fattyacid or mixture of fatty acids — falls within the scope of protection of the present invention.

[0032] The dechlorinating chemicals of the present invention are also particularly effective in dechlorination treatments of substrates other than UCO. To prove this statement, treatment tests with the inventive dechlorinating chemicals have been performed on other oily substrates such as: POME (Palm Oil Mills Effluents ), which are a waste product of palm oil processing (Examples 11-12 ); SBEO ( Spent Bleaching Earths Oils ) (Examples 12-13 ); animal fats (Animal Fats Cat. 3 ) (Examples 14-15).

[0033] EXAMPLES 11-12

[0034] In Examples 11 and 12, potassium oleate and a potassium soap from a mixture of fatty acids were used as POME dechlorinating chemicals.

[0035] The process is exactly as detailed in Examples 2-10, the only change being the use of 120 g of POME instead of UCO. Once the reaction and the washing steps are ended, the residual content of chlorine, sulphur, and phosphorus in the purified POME is determined using an X-ray fluorescence spectrometer. The results of these analyses are reported in Table 2 below. The analytical data show a more than satisfactory reduction in the chlorine content to minimum values, together with a significant reduction in the sulphur and phosphorus content.

[0036] EXAMPLES 13-14

[0037] The chlorine and especially sulphur and phosphorus content in SBEOs is very high, as shown in Table 2. Therefore, prior to the dechlorination treatment of the present invention, the SBEOs were subjected to a conventional treatment with adsorbent and bleaching earths, a process known to those skilled in the art as "bleaching". After bleaching, X-ray fluorescence analysis shows a reduction in the content of chlorine, sulphur, and phosphorus (see Table 2 ) to levels more suitable for thefinishing dechlorination by means of the dechlorinating agents of the present invention.

[0038] The process is exactly as detailed in Examples 2-10, the only change being the use of 120 g of SBEO (previously subjected to bleaching) instead of UCO. Once the reaction and the washing steps are ended, the residual content of chlorine, sulphur, and phosphorus in the purified SBEO is determined using an X-ray fluorescence spectrometer. The results of these analyses are reported in Table 2. Also in this case, the analytical data show an excellent reduction in the chlorine content to minimal values, together with a significant reduction in the sulphur and phosphorus content.

[0039] EXAMPLES 15-16

[0040] The chlorine and especially sulphur and phosphorus content in Animal Fats Cat. 3 is very high as shown in Table 2. Therefore, prior to the dechlorination treatment of the present invention, the Animal Fats Cat. 3 were subjected to a conventional treatment with 1% citric acid, a process known to those skilled in the art as "degumming". After degumming, X-ray fluorescence analysis shows a reduction in the content of chlorine, sulphur, and phosphorus (see Table 2 ) to levels more suitable for the finishing dechlorination by means of the dechlorinating agents of the present invention.

[0041] The process is exactly as detailed in Examples 2-10, the only variation being the use of 120 g of Animal Fats Cat. 3 (previously subjected to degumming) instead of UCO. Once the reaction and the washing steps are ended, the residual content of chlorine, sulphur, and phosphorus in the purified Animal Fats Cat. 3 is determined using an X-ray fluorescence spectrometer. The results of these analyses are reported in Table 2 below. Also in this case, the analytical data show an excellent reduction in the chlorine content to minimal values, together with asignificant reduction in the sulphur and phosphorus content.

[0042]

[0043] Even with these other types of recovered oils, the use of alkaline soaps as dechlorinating agents surprisingly resulted in the absence of any noticeable foaming in the bulk oils during heat treatment. Furthermore, careful FT-IR (infrared spectroscopy) analysis of the dechlorinated oils obtained according to Examples 11-16 confirmed the complete lack of ester cleavage following the described treatments.

[0044] From the preceding description it is therefore evident how the present invention has fully achieved its intended object, having identified a particular class of chemical dechlorinating agents which are very effective in dechlorinating and simultaneously reducing the content of sulphur and phosphorus in oils, while being surprisingly inactive in promoting unwanted transesterification or hydrolytic cleavage reactions.

Claims

CLAIMS1 ) A process for reducing the chlorine content, and possibly also the sulphur and phosphorus content, in vegetable and animal fats and oils, comprising a reaction step wherein a flow of said fats and oils is heat-treated with a dechlorinating agent, resulting in an elimination reaction of the organic chlorine and, possibly, other heteroatoms such as sulphur and phosphorus contained in said flow of fats and oils by means of said dechlorinating agent, followed by a washing step to remove from said fats and oils both the thus obtained reaction products and the excess of said dechlorinating agent, characterized in that said dechlorinating agent comprises fatty acid salts with alkali metals of the first group of the Periodic Table of Elements and is added in a percentage by weight ranging from 1.5% to 3. 0% (w / w) of the weight of the flow of vegetable and animals fats and oils to be treated.2 ) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to claim 1, wherein said oils belong to the classes UCO (Used Cooked Oils ), POME (Palm Oil Mills Effluent) or SBEO (Spent Bleached Earths Oil), and said fats are animal fats of Categories 1, 2 and 3.3) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to claims 1 or 2, wherein said alkali metals are selected from sodium and potassium.4 ) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to claim 3, wherein said dechlorinating agent is selected from the group consisting of sodium octoate, potassium octoate, sodium oleate, potassium oleate, sodium stearate and potassium stearate.5) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to claim 3, wherein said dechlorinating agent isselected from the group consisting of sodium salt of a mixture of fatty acids and potassium salt of a mixture of fatty acids.6) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to any one of claims 1 to 5, wherein the dechlorination reaction is performed at a temperature ranging from 180°C to 250°C, and preferably from 200°C to 230°C.7 ) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to any one of claims 1 to 6, wherein the dechlorination reaction is performed at a vacuum level ranging from 0.5 to 90 mbar, and preferably from 10 to 50 mbar.8 ) The process for reducing the chlorine, sulphur and phosphorus content in vegetable and animal fats and oils according to any one of claims 1 to 7, wherein the dechlorination reaction is performed on a time scale ranging from 0.5 to 10 hours, and preferably from 1 to 7 hours.

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