PRETREATMENT PROCESSES OF LIQUID OILY PLANT BY-PRODUCTS FROM THE AGROINDUSTRY AS RAW MATERIAL FOR BIOFUEL PRODUCTION

Description

FIELD OF THE INVENTION

[0001] The present invention concerns a process for the treatment of vegetable liquid waste and slurry, by-products resulting from agro-industry, in particular the oily fraction recovered at the origin from the effluents of palm oil mills, hereinafter referred to as POME OIL.STATE OF THE ART

[0002] Most of the trees for palm oils belong to the species Elaeis guineensis native to West Africa and typically grow in soils consisting of tropical peat.

[0003] The two types of oil that can be extracted from this type of plant are crude palm oil and oil extracted from the mesocarp.

[0004] Palm oil compared to those of sunflower and rapeseed oils has much lower production and market costs.

[0005] Large-scale palm oil production also involves the production of large amounts of waste and by-products.

[0006] Production waste is both of the liquid and solid type.

[0007] Solid palm waste is, for example, the oil palm tree fronds (OPF), empty fruitless bunches (EFB), palm kernel shells (PKS).

[0008] There are four different types of liquid waste from the production of palm oil: mill waste, i.e. POME OIL, sludge palm oil (SPO), palm acid oil (PAO) and palm fatty acid distillate (PFAD). The POME consists of wastewater that is generally discharged into collection tanks and from here in some production countries discharged without particular caution into the surface waters near the mill.

[0009] SPO, PFAD and PAO are classified as residual oils and contain different percentages of free fatty acids (FFA).

[0010] POME OIL, although classified as a liquid waste, is actually a solid material at a temperature below about 50°C and consists of oils, residual water and solids, hence a material with a strong environmental impact, since it has high BOD (biological oxygen demand) and COD (chemical oxygen demand) if discharged into waterways. (https: / / tspace.library.utoronto.ca / bitstream / 1807 / 96865 / 1 / er-2018-0124.pdf).

[0011] Therefore, like other types of oil waste, it has been thought to transform POME OIL into a material that can be used as an intermediate for the production of biofuels, in particular within crude oil refining plants and bio-refineries.

[0012] For example, WO2013 / 081446 describes a process for preparing bio-diesel starting from triglyceride-containing oils by hydrolysis of said esters in neutral buffer solution in the presence of a free fatty acid biocatalyst and glycerol, removal of glycerol and transesterification of the free fatty acids to the corresponding methyl esters by methanol.

[0013] As starting natural oils in this patent application, the use of that contained in POME OIL is also envisaged, which however, before being used undergoes a series of purification and filtration treatments, to achieve the parameters required for the subsequent treatment in the refinery.

[0014] A process for the recovery and purification of this POME OIL is disclosed for example in WO2014 / 051415 .

[0015] In any case, this waste material creates a series of difficulties in the treatment due to the considerable variability in the composition of POME OIL, linked to seasonality, the nature of the soil where the agricultural activities take place, the different characteristics of the mills, where the squeezing takes place, the different methods of treatment of the mills' wastewater, and the logistics downstream of the collection.

[0016] This results in high variability in impurity content, acidity, presence of different metals and residual water in the crude oil.

[0017] Faced with this unpredictability, the achievement of the specifications required by end users, namely the operators of the refining industry, who treat the bio-liquid charge in catalytic conversion plants, with extremely expensive and metal-sensitive catalysts, which can poison them by reducing their residual life, is therefore complex.

[0018] The aim of the present invention is to provide a process that allows obtaining from POME OIL, as well as from other similar charges, a product with constant acidity characteristics and an extremely limited metal content, comparable to that of a vegetable oil, regardless of the composition of the feed charge.SUMMARY OF THE INVENTION

[0019] The Applicant has now found a process that overcomes the aforementioned issues and comprises the following stages: i) Providing the waste material in the form of a vegetable oily liquid or slurry and consisting of: a) at least one vegetable oil, b) residual water, c) solid material having a heterogeneous particle size, comprising metals (even with concentrations greater than 1,000 ppm) and impurities already contained in the culture medium and / or incorporated during the squeezing or extraction of the oil, and / or during the stay in the collection basins of the mills and / or during the steps of storage and transport of the vegetable liquid waste material; where the typical average content of b) + c) does not exceed 10% by weight, preferably does not exceed 5% and more preferably does not exceed 3% on the total weight of said oily waste; ii) Heating, diluting said waste material with water and separating the solid material having coarser sizes, by decantation and centrifugation; iii) Subjecting the decanted liquid component exiting stage ii) to centrifugation with disc centrifuge by addition of citric and / or phosphoric acid, up to a pH comprised between 2.5 and 4.0, homogenisation of the mixture obtained, centrifugation with water to remove the solids, washing with water to remove the mineral salts formed with metals still contained in the vegetable liquid waste material, separating the aqueous phase from the oily phase; iv) drying the oily phase by evaporation of the water under vacuum; v) filtering the mixture coming from the stage iv) on filter media to remove the metals and the impurities still present. vi) reducing the acidity by esterification of the oily phase with glycerine at a temperature comprised between 210°C and 250°C,

[0020] This process is characterized in that all stages ii) -v) are conducted at a temperature comprised between 80°C and 95°C.

[0021] This type of process allows to achieve an acidity of the final product less than 2%, and an amount of metals significantly lower than that contained in the initial charge and in any case in line with the individual values agreed with the users, in general each single metal has a concentration lower than 5 ppm and the total concentration of these metals is less than 30 ppm. In addition, the process allows the complete elimination of the organic chlorine and the reduction of phosphorus below 5 ppm.DESCRIPTION OF THE FIGURES

[0022] Figure 1 reports a block diagram of a preferred embodiment of the process according to the present invention.DETAILED DESCRIPTION OF THE INVENTION.

[0023] For the purposes of the present invention, the definition "comprising" does not exclude the presence of further components or stages not expressly listed after this definition. The definition "constituted by" or "consisting of" excludes the presence of such components not expressly listed after this definition.

[0024] Preferably, in the process of the invention, as processing liquid vegetable waste use is made of the oily fraction of the waste coming from the mills for the squeezing of the palm oil, i.e. POME OIL.

[0025] For the purposes of the present invention, the definition of "heterogeneous particle size"means that said particles of solid material have dimensions comprised between 100µm and 5 cm.

[0026] For the purposes of the present invention, POME OIL is understood to mean a solid material at room temperature and a liquid material at a temperature above about 50°C. Therefore, in the process of the invention, the POME OIL in stage i) is liquid since it comes from tanks and pipes that are heated and maintained above the aforesaid temperatures. The tanks and the loading and unloading pipes must be tracked and insulated, in order to avoid the passage in solid phase, and provide for the possibility of cleaning the lines with ease in case of unexpected solidifications.

[0027] Preferably in stage ii) the POME OIL is sent to a heating section and subsequently diluted with water and centrifuged in a screw centrifuge decanter at a temperature comprised between 85 and 95°C.

[0028] In the centrifuge decanter, the screw is fully ducted, arranged horizontally and operates continuously.

[0029] The high centrifugal forces being developed separate the solids from the liquid suspension.

[0030] The sediment (solid phase) has a higher density and gathers on the drum wall. The screw conveyor continuously conveys the solids up to the discharge.

[0031] The centrifuge decanter is adjusted on the basis of the different characteristics of the POME OIL by dosing of the dilution water, the regulation of the relative speeds and an accurate temperature control, which must be between 85° and 95°C, in order to have the most suitable viscosity values.

[0032] The feed flow rate can vary considerably between 40% and 100% of the design flow rate.

[0033] The percentage of abatement of the metal content is significant, greater than 50%, for example for a charge of POME OIL containing 1000 PPM a metal content of around 500 PPM is obtained in output, it also allows to protect the rest of the plant with the removal of significant solid sediments.

[0034] The centrifugation contemplated in stage iii) of the process according to the present invention is conducted in one or more disc centrifuges.

[0035] Stage iii) is preferably conducted at a temperature comprised between 80° and 85°C, the feed flow rate of the POME OIL coming from stage ii) can vary considerably between 40% and 100% of the maximum allowed flow rate, and the optimal operation is above 60%.

[0036] Stage iii) provides for washing in water in the presence of citric and / or phosphoric acid on the basis of a model based on the characteristics of the plant supply as well as the output from stage ii).

[0037] The centrifugation with separation of the liquid phase from the solid phase can therefore take place in a single centrifuge, by keeping the second centrifuge ready to start in case of excessive fouling of the machine; or, according to another preferred embodiment of the process of the invention, it is possible that this phase is conducted in a first disc centrifuge, while in a second disc centrifuge the removal of metals is carried out after the addition of neutralization soda and washing water.

[0038] The oily fraction exiting stage iii) has a quantity of metals of around 5%. Starting, for example, from a content of metals exiting from stage ii) of 1000 ppm at the end of stage iii), a metal content of about 50 ppm is obtained.

[0039] Therefore, by carrying out stages ii) - iii) of the process of the invention it is possible to obtain a reduction of metals by about 95% with respect to the typical content of the starting POME OIL and of phosphorus up to 10 ppm, but also to break the bonds of the metals still bound to facilitate their subsequent removal. In stage iii) the separation of the oily phase from the aqueous phase also takes place.

[0040] In stage iv) the oily phase is subjected to drying by vacuum removal of the aqueous phase, at residual pressure preferably comprised between 120 mbar and 180 mbar, more preferably 150 mbar.

[0041] The filtration stage v) is conducted to achieve the desired levels of metal content and ensure uniformity of product quality, which is carried out with the addition of filtration earths, possibly activated for attack to specific metals, based on the characteristics of the oily fraction of supply, and subsequent passage in industrial filters, which can be of various type.

[0042] These filters are operated with several steps in sequence: formation of a filtration panel, filtration until maximum pressure drops are reached, panel unloading and preparation for a new cycle.

[0043] The operating temperature of stage v) is comprised between 80 and 90°C.

[0044] Stage v) allows a further reduction of metals to reach the specifications typically agreed with end users, i.e. below 30 ppm. Typically, starting from a quantity in the product coming from stage iii) of 50 ppm, a metal value of less than 30 ppm is obtained.

[0045] In conclusion, with the process of the invention, in addition to a reduction in metal content by more than 30 times compared to the typical values of POME OIL, a complete removal of all impurities contained in the fed oily matrix is obtained.

[0046] The oily phase filtered and coming from stage v) has all the quality characteristics required for final use except for the high acidity. Thanks to stage vi) of esterification with glycerine, the acidity, initially always higher than 40%, can be reduced to values lower than 2% by converting said oily phase into mono-, di- and tri-glycerides, depending on the specific requests of the end users.

[0047] Stage vi) of discontinuous esterification is preferably conducted in a reactor typically heated to 230°C, by means of high-pressure steam.

[0048] In this way the water produced is removed from the reaction environment in the form of water steam, shifting the equilibrium in favour of the formation of glyceride chains. The water steam is preferably condensed, and the liquid obtained consists mostly of an aqueous phase and an oily phase. The latter is recycled to the reactor.

[0049] Stage vi) has a variable duration depending on the temperature and dosage of glycerine; the entire cycle of preheating / loading of the reagent / actual reaction / unloading has a duration of less than 8 hours.

[0050] According to a preferred embodiment, the reaction product exiting the reactor is cooled by heat exchange with the reactive oily phase coming from stage v) and fed to the reactor.

[0051] The reaction product exiting stage vi) thus cooled is sent to storage and is ready to be shipped to refinery or biorefinery.

[0052] For example, it can be transformed into biodiesel, as described in the international patent application cited above in WO2013 / 081446, or it can be used as an intermediate in the preparation of diesel, naphtha and aviation fuels in co-processing units, for example as described in WO2021050271A1, or it can be used as an intermediate in the preparation of HVO.

[0053] Figure 1 reports the block diagram representing a preferred embodiment of the process of the invention.

[0054] According to this figure stage ii) is conducted in the centrifuge decanter in the first block indicated in the figure as CENTRIFUGE DECANTER in which the raw material of vegetable waste is introduced. At this stage the coarsest impurities are eliminated. The liquid component exiting the centrifuge decanter is subjected to stage iii), i.e. which comprises two stages, the first of centrifugation with a disc centrifuge in the presence of citric acid and / or phosphoric acid, this first step of stage iii) is indicated in figure 1 with the block DISC CENTRIFUGE 1. The liquid component exiting this block is sent to washing in a disc centrifuge indicated in the figure with DISC CENTRIFUGE 2 with a soda solution to remove the metals. The sludge that is formed at the end of these steps is collected for recovery and recycling of the residual oily phase.

[0055] The liquid phase exiting the washing consists essentially of the oily phase and water, which is subsequently removed by vacuum drying, in stage iv). The water exiting this stage is in the form of steam and is recycled in the process.

[0056] The material exiting stage iv) is subjected to stage v), i.e. to filtration with filtration earths, if necessary activated to capture the metals still present in the oily phase exiting stage iv).

[0057] Based on the diagram reported in the figure, stage v) comprises a first stage, in which the oily phase coming from stage iv) is mixed with filtration earths, and a second stage of actual filtration.

[0058] The filtered oil coming from stage v) is finally subjected to stage vi) of glycerolysis.

Claims

1. Process for the treatment of a vegetable liquid waste material or slurry comprising the following stages: i) Providing the waste material in the form of a vegetable oily liquid and consisting of: a) at least one vegetable oil, b) residual water, c) solid material having a heterogeneous particle size, comprising metals and impurities already contained in the culture medium of the palms and / or incorporated during: the squeezing of the palm oil, the stay in the collection basins of the mills and the steps of storage and transport of the vegetable liquid waste material; wherein the typical average content of b) + c) does not exceed 10% by weight, preferably does not exceed 5% by weight, more preferably does not exceed 3% by weight on the total weight of said oily liquid waste; ii) Heating, diluting said liquid waste material with water and separating the solid material having coarser sizes, by decantation and centrifugation, and iii) subjecting the decanted liquid component exiting stage ii) to disc centrifugation by addition of citric and / or phosphoric acid, up to a pH comprised between 2.5 and 4.0, homogenisation of the mixture obtained, centrifugation with water to remove the solids, washing with water to remove the mineral salts formed in the centrifugation phase with the metals, separating the aqueous phase from the oily phase; iv) drying the oily phase by evaporation of the water under vacuum; v) filtering the mixture coming from the previous stage on filter media to remove the metals and the impurities still present, vi) reducing the acidity by esterification with glycerine of the oily phase coming from stage v) at a temperature comprised between 210°C and 250°C, wherein all stages ii) -v) are conducted at a temperature comprised between 80 and 95°C.

2. Process according to claim 1, wherein said material is a vegetable oily liquid byproduct resulting from agro-industry, preferably the oily fraction or POME OIL coming from the processing of the palm oil in the mill.

3. Process according to claim 2 wherein stage i) provides that vegetable liquid waste material is sent to stage ii) at a temperature higher than or equal to 60°C.

4. Process according to any one of claims 2-3, wherein in stage ii) vegetable liquid waste material is sent to a heating section where it is heated to a temperature comprised between 80° and 95°C and subsequently diluted with water and centrifugation is carried out in a centrifugal screw decanter.

5. Process according to any one of claims 1-4, wherein in stage ii) the reduction of the metals exceeds 50% by weight with respect to the metals contained in the initial charge.

6. Process according to any one of claims 1-5, wherein in stage iii) centrifugation takes place in one or more disc centrifuges and at a temperature comprised between 80 and 85°C7. Process according to claim 6, wherein the recycled water coming from stage ii) is added as a washing water of the residue.

8. Process according to any one of claims 1-6 wherein stage ii) is conducted at a temperature comprised between 80 and 85°C.

9. Process according to any one of claims 1-8, wherein stage iii) is conducted in one or more stages at a temperature comprised between 80 and 85°C, more preferably 80°C, the feed flow rate of the vegetable liquid waste coming from stage ii) can vary considerably between 40% and 100% of the maximum allowed flow rate, and the optimal operation is above 60%.

10. Process according to claim 9, wherein in stage iii) the washing, the centrifugation in water and the separation of the liquid phase from the solid phase is carried out in a single centrifuge, maintaining a second centrifuge ready to start in case of excessive fouling of the first centrifuge.

11. Process according to claim 9, wherein stage iii) is conducted in a first disc centrifuge, while in a second disc centrifuge the removal of the metals is carried out after the addition of neutralization soda and in the washing water.

12. Process according to any one of claims 1-11 wherein at the end of stage iii) the amount of the metals present in the oily fraction is about 5% by weight on the weight of the quantity of the metals present in the initial material of liquid waste.

13. Process according to any one of claims 1-12 wherein at the end of stage v) the concentration of metals is less than 5%, preferably it is 3% with respect to the initial quantity of metals present in the material of initial liquid waste.

14. Process according to any one of claims 1-13, wherein stage vi) is conducted in a reactor heated to 230°C by means of high-pressure steam, and the water is removed in the form of steam and subsequently condensed giving rise to a liquid consisting of an oily phase and an aqueous phase which is recycled to the reactor.

15. Process according to any one of claims 1-14, wherein the heat of the reaction product exiting the reactor is used to heat the oily phase coming from stage vi) and fed to the reactor16. Process according to any one of claims 1-15, wherein the oily fraction of the liquid waste material after stage vi) has an acidity lower than 5%, preferably lower than 2%.