Method and system for producing biodiesel

Abstract

The present invention relates to a method and system for producing biodiesel at a supercritical condition and operating the transesterification reactor in a continuous operation mode.

Description

[0001] Method and system for producing biodiesel

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method and a system for producing biodiesel. The present invention relates more specifically to an improved method and system producing biodiesel at a supercritical condition in a continuous operation mode.

[0004] BACKGROUND OF THE INVENTION

[0005] Biodiesel is an alternative fuel for diesel engines that may be made from new or used vegetable oils or animal fats, which are non-toxic, biodegradable, renewable resources. Fat and oils are chemically reacted with an alcohol such as methanol. The reaction requires a catalyst, usually a strong base, such as sodium or potassium hydroxide, and produces chemical compounds known as fatty acid methyl esters. As by-products are produced glycerine, a raw material in the chemical and pharmaceutical industries and also potassium fertilizer used in agriculture and the fertilizer industry. Biodiesel is a very versatile transport fuel: does not require infrastructure change. The biodiesel can be produced from local raw material (or collection of used vegetable or frying oil) in rural regions in developing countries resulting in an extremely positive impact on rural development security of supply and employment and aiming to a sustainable development of society.

[0006] Conventional biodiesel production involves the catalytic triglyceride transesterification process. When using homogeneous two-stage catalysis, it is difficult to purify the resulting product from the by-products formed, and the catalysts cannot be reused. In the case of heterogeneous catalysis, the process costs are increased due to separation and regeneration of the catalysts. To solve these problems of catalytic synthesis, a noncatalytic process has been recently studied that which takes place under supercritical conditions for an alcohol or other acyl receptor.

[0007] In such biodiesel production, fatty feedstocks and alcohols are used as raw materials, with the synthesis taking place at supercritical conditions for alcohol, i.e., high temperature and pressure, thus making the process quite simple. Biodiesel is typically produced in batch reactors when producing biodiesel at supercritical conditions.

[0008] There is still needed to improve efficiency of biodiesel production specifically at supercritical conditions. BRIEF DESCRIPTION OF THE INVENTION

[0009] The object of the invention is to provide an improved method and system for producing biodiesel so as to solve or at least alleviate the prior art disadvantages.

[0010] The objects of the invention are achieved by a method and system for producing biodiesel which is characterized by what is disclosed in the independent claim 1. The objects of the invention are further achieved by a system for producing biodiesel which is characterized by what is disclosed in the independent claim 15. Preferred embodiments are disclosed in the dependent claims.

[0011] The invention is based on the idea of providing a method for producing biodiesel. The method comprises:

[0012] - providing a fatty acid feedstock and an alcohol reagent;

[0013] - mixing the fatty acid feedstock and the alcohol reagent with a mixing device;

[0014] - obtaining an intermediate composition from the step of mixing the fatty acid feedstock and the alcohol reagent;

[0015] - increasing pressure of the obtained intermediate composition with a pressure increasing device,

[0016] - feeding the intermediate composition having an increased pressure to a transesterification reactor,

[0017] - transesterifying at least a part of the intermediate composition to a first product composition in the transesterification reactor at a supercritical condition, and operating the transesterification reactor in a continuous operation mode,

[0018] - obtaining the first product composition from the transesterification reactor, and

[0019] - separating a biodiesel composition from the first product composition.

[0020] In the context of this application, the continuous operation mode means a process where the production of a product is ongoing without a defined start or endpoint.

[0021] In other words, the continuous operation mode means a continuous process.

[0022] In some embodiments, the method comprises transesterifying up to 95 wt% of the intermediate composition to the first product composition based on the total weight of the intermediate composition.

[0023] In some embodiments, the method comprises transesterifying in the range of 70 % - 95 % of the intermediate composition to the first product composition the intermediate composition based on the total weight of the intermediate composition.

[0024] In some embodiments, the method comprises transesterifying at least 95 % of the intermediate composition to the first product composition the intermediate composition based on the total weight of the intermediate composition.

[0025] In some embodiments, the transesterification reactor being a helical coil reactor comprising a helical coil surrounded by a heat transfer fluid, and the method comprises heating the heat transfer fluid with a heater and providing a flow of the heated heat transfer fluid through the transesterification reactor.

[0026] That enables efficiently heat the transesterification reactor and adjust the temperature in the transesterification reactor.

[0027] In some embodiments, the transesterification reactor being a helical coil reactor comprising a helical coil, the method comprises heating the helical coil with an induction heater.

[0028] That enables efficiently adjust the temperature in the transesterification reactor.

[0029] In some embodiments, the step of mixing the fatty acid feedstock and the alcohol reagent is carried out with a mixing device comprising a feedstock pump.

[0030] In some embodiments, the step of mixing the fatty acid feedstock and the alcohol reagent is carried out with a mixing device comprising a feedstock pump, the feedstock pump being a constant-volume pump, and the feedstock pump mixing the fatty acid feedstock and the alcohol reagent and increasing the pressure of the intermediate composition to the range of 2 - 4 barg.

[0031] In some embodiments, the step of mixing the fatty acid feedstock and the alcohol reagent is carried out with a mixing device, the mixing device comprises a first feedstock pump and a second feedstock pump, and the first feedstock pump pumping the fatty acid feedstock and a second feedstock pump pumping the alcohol reagent.

[0032] That provides efficient mixing the fatty acid feedstock and the alcohol reagent.

[0033] In some embodiments, the step of mixing the fatty acid feedstock and the alcohol reagent is carried out with a mixing device, the mixing device comprises a first feedstock pump and a second feedstock pump, and the first feedstock pump pumping the fatty acid feedstock and a second feedstock pump pumping the alcohol reagent, and the step of mixing comprises increasing the pressure of the intermediate composition to the range of 2 - 4 barg.

[0034] That provides efficient mixing the fatty acid feedstock and the alcohol reagent and at the same time increased pressure.

[0035] In some embodiments, in the step of increasing pressure the pressure of the intermediate composition the pressure of the intermediate composition is increased to the range of 220-260 barg.

[0036] In some embodiments, the step of increasing pressure of the obtained intermediate composition is carried out with a pressure increasing device comprising a pressure increasing pump, the pressure increasing pump being a constant-volume pump, and the pressure increasing pump increasing the pressure of the intermediate composition to the range of 220-260 barg.

[0037] That provides efficiently a pressure required for supercritical conditions so that required temperature may be achieved with low amount of heating energy.

[0038] In some embodiments, the alcohol reagent being methanol.

[0039] Methanol may be provided easily.

[0040] In some embodiments, the alcohol reagent comprises any combination of the following: methanol, ethanol and butanol.

[0041] In some embodiments, the fatty acid feedstock comprises fatty acids.

[0042] In should be noted, that the fatty acid feedstock may further comprise water or other substances.

[0043] In some embodiments, the fatty acid feedstock comprises fatty acids, and free fatty acids at least 75 wt% or at least 95 wt% based on the total weight of the fatty acid feedstock with the proviso that fatty acids and free fatty taken together adds up to 100 wt%.

[0044] In some embodiments, at least 75 wt% or at least 95 wt% of the fatty acids being free fatty acids based on the total weight of the fatty acids.

[0045] The method and the system according to the invention enables use of free fatty acids up to 100 wt%.

[0046] In some embodiments, operating the transesterification reactor in a continuous operation mode is carried out by simultaneously controlling the mixing device, the pressure increasing pump of the pressure increasing device and a pressure adjusting unit so that: - the mixing device and the pressure increasing pump of the pressure increasing device increasing the pressure in the transesterification reactor by increasing the pressure of the intermediate composition, the mixing device and the pressure increasing device are provided upstream from the transesterification reactor, and

[0047] - the pressure adjusting unit maintaining a constant pressure in the transesterification rector, the pressure adjusting unit is provided in a connection with an outlet of the transesterification reactor downstream from the transesterification reactor.

[0048] That provides an efficient way to operate the transesterification reactor in a continuous operation mode.

[0049] In some embodiments, operating the transesterification reactor in a continuous operation mode is carried out by simultaneously controlling the mixing device, the pressure increasing pump of the pressure increasing device and a pressure adjusting unit so that:

[0050] - the mixing device and the pressure increasing pump of the pressure increasing device increasing the pressure in the transesterification reactor by increasing the pressure of the intermediate composition, the mixing device and the pressure increasing device are provided upstream from the transesterification reactor, and

[0051] - the pressure adjusting unit maintaining a constant pressure in the transesterification rector, the pressure adjusting unit is provided in a connection with an outlet of the transesterification reactor downstream from the transesterification reactor.

[0052] That provides an efficient way to operate the transesterification reactor in a continuous operation mode.

[0053] In some embodiments, the residence time in the transesterification reactor being in the range of 20 - 80 min or up to 30 min.

[0054] That provided near 100 % conversion of the fatty acids in transesterification reactor.

[0055] In some embodiments, the temperature of the transesterification reactor being at a temperature in the range of 220 - 310 degrees C.

[0056] That provides energy efficiently a temperature required for supercritical conditions.

[0057] In some embodiments, the intermediate composition comprises 20 - 40 wt% the alcohol reagent and 60 - 80 wt% the fatty acid feedstock the alcohol reagent based on the total weight of the fatty acid feedstock and alcohol reagent with the proviso that the fatty acid feedstock and the alcohol reagent taken together adds up to 100 wt%.

[0058] In some embodiments, the intermediate composition comprises 20 - 40 wt% the alcohol reagent and 60 - 80 wt% the fatty acid feedstock based on the total weight of the fatty acid feedstock and alcohol reagent.

[0059] That provides excellent conversion of fatty acids so that an amount of remaining alcohol reagent being low.

[0060] In some embodiments, the method comprises a step of reducing the pressure of the first product composition to a pressure in the range of 1 - 2 barg with a pressure adjusting unit.

[0061] That provides efficient separation of biodiesel composition from the first product composition.

[0062] In some embodiments, the step of separating biodiesel composition from the first product composition comprises spraying the first product composition to a distillation column, and separating with the distillation column water, remaining alcohol reagent and a composition comprising esters and glycerides.

[0063] That provides efficient separation of biodiesel composition from the first product composition

[0064] In some embodiments, the step of separating biodiesel composition from the first product composition comprises: spraying the first product composition to a distillation column, separating with the distillation column water, remaining alcohol reagent and a composition comprising esters and glycerides, and feeding the composition comprising esters and glycerides to a separating vessel, and obtaining a biodiesel ester composition from the separating vessel.

[0065] That provides efficient separation of biodiesel composition from the first product composition

[0066] In some embodiments, the step of separating biodiesel composition from the first product composition comprises: spraying the first product composition to a distillation column, and separating with the distillation column any combination of the following: molecules comprising sulphur, water, remaining alcohol reagent and a composition comprising esters and glycerides.

[0067] That provides efficient separation of biodiesel composition from the first product composition In some embodiments, the step of separating biodiesel composition from the first product composition comprises: spraying the first product composition to a distillation column, separating with the distillation column any combination of the following: molecules comprising sulphur, water, remaining alcohol reagent and a composition comprising esters and glycerides, and feeding the composition comprising esters and glycerides to a separating vessel, and obtaining a biodiesel ester composition from the separating vessel.

[0068] For instance, Hydrogen Sulfide (H2S) comprises molecules comprising sulphur, and it may be separated.

[0069] That provides efficient separation of biodiesel composition from the first product composition

[0070] In some embodiments, the step of separating a biodiesel composition from the first product composition comprises removing free fatty acids from the biodiesel ester composition with a base compound.

[0071] That improves quality of the biodiesel.

[0072] In some embodiments, the step of separating a biodiesel composition from the first product composition comprises removing free fatty acids from the biodiesel ester composition with a base compound, the base compound comprises sodium hydroxide (NaOH) or potassium hydroxide (KOH).

[0073] That improves quality of the biodiesel.

[0074] In some embodiments, the method comprises feeding carbon dioxide into the transesterification reactor in the vicinity of the intermediate composition inlet.

[0075] Carbon dioxide feed promotes the transesterification reaction and thus, the transesterification reactor may be carried out at low temperature.

[0076] The present invention further provides a system for producing biodiesel. The system comprises a mixing device arranged to receive a fatty acid feedstock and an alcohol reagent and arranged to produce an intermediate composition from the fatty acid feedstock and the alcohol reagent; a pressure increasing device arranged to receive the intermediate composition from the mixing device and arranged to increase the pressure of the intermediate composition to the range of 220-260 barg; the transesterification reactor arranged to receive the intermediate composition from the pressure increasing device and arranged to transestesterify at least a part of the intermediate composition to a first product composition at a supercritical condition, the transesterification reactor being a helical coil reactor, and the transesterification reactor is arranged to operate in a continuous operation mode, and a separation arrangement arranged to separate a biodiesel composition from the first product composition.

[0077] It should be noted that the system is arranged to carry out any above disclosed embodiment of the method.

[0078] The invention provides the following advantages:

[0079] - The system is simple and efficient to build up even it provides a continuous production mode,

[0080] - Furthermore, supercritical conditions can be efficiently achieved and easily maintained with the system and method according to the present invention, and

[0081] - Furthermore, the invention enables efficient production of biodiesel.

[0082] BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The invention will now be described in detail by way of example with reference to the accompanying drawings, in which:

[0084] Figure 1 shows schematically a method according to one embodiment of the present invention;

[0085] Figure 2 shows schematically a system according to one embodiment of the present invention;

[0086] Figure 3 shows schematically a side view of a transesterification reactor according to one embodiment of the present invention; and

[0087] Figure 4 shows schematically a side view of a transesterification reactor according to one embodiment of the present invention.

[0088] DETAILED DESCRIPTION OF THE INVENTION

[0089] The present invention will now be described more fully hereinafter.

[0090] This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and for fully convey the scope of the invention to a skilled person. Although individual features may be included in different embodiments, these may possibly be combined in other ways, and the inclusion in different embodiments does not imply that a combination of features is not feasible. In addition, singular references do not exclude a plurality. In the context of the present invention, the terms "a", "an" does not preclude a plurality.

[0091] As used herein, the term "comprising" includes the broader meanings of "including", "containing", and "comprehending", as well as the narrower expressions "consisting of" and "consisting only of".

[0092] Among the different oils available for biodiesel production are fresh plant oils such as Soybean Oil, Rape Seed Oil, Palm Oil, Peanut Oil, Canola Oil, sunflower oil as well waste cooking oils or animal fats with a high content in free fatty acids.

[0093] 1 barg indicates 1 bar gauge pressure. Barg is 1 bar more pressurised than the atmospheric pressure.

[0094] In the context of this application "Biodiesel" refers to transesterified biodiesel comprising a mix of mono-alkyl esters of long chain fatty acids. The most common form uses methanol (converted to sodium methoxide) to produce methyl esters (commonly referred to as Fatty Acid Methyl Ester - FAME).

[0095] Transesterifying means exchanging the organic functional group R" of an ester with the organic group R' of an alcohol.

[0096] In other words, transesterifying means carrying out a transesterification process.

[0097] In other words, transesterifying means completing a process of transesterification.

[0098] Figure 1 shows schematically embodiments of a method according to the present invention. The present inventive concepts are, at least in part, based on unexpected realisations that biodiesel is efficiently manufactured from a fatty acid feedstock F and an alcohol reagent R with a continuously operating method and system.

[0099] The method comprises the following steps:

[0100] - providing a fatty acid feedstock F and an alcohol reagent Rl;

[0101] - mixing the fatty acid feedstock F and the alcohol reagent Rl;

[0102] - obtaining an intermediate composition I from the step of mixing the fatty acid feedstock F and the alcohol reagent Rl;

[0103] - increasing pressure of the obtained intermediate composition I, - feeding the intermediate composition, I having an increased pressure to a transesterification reactor 3,

[0104] - transesterifying the intermediate composition I to a product composition in the transesterification reactor 3 at a supercritical condition, and operating the transesterification reactor 3 in a continuous operation mode,

[0105] - obtaining a product composition from the transesterification reactor 3, and

[0106] - separating biodiesel from the product composition.

[0107] In certain embodiments, the transesterification reactor 3 being a helical coil reactor comprising a helical coil surrounded by a heat transfer fluid H.

[0108] This type of reactor uses a continuous spiral shape to transfer fluid to be converted to product and heated heat transfer fluid H around the spiral shape to heat the fluid to be converted to product.

[0109] The spiral shape is made of a tube and the intermediate composition I is fed into the tube.

[0110] In other words, the intermediate composition I flowing into the tube of the transesterification reactor 3, the tube of the transesterification reactor 3 having a spiral shape and the intermediate composition I converting in the tube at supercritical condition to the first product composition Pl by transesterification process.

[0111] Thus, in the step of transesterifying, the intermediate composition I flowing into the tube of the transesterification reactor 3 having a spiral shape, and the intermediate composition I converting in the tube at supercritical condition to the first product composition Pl by transesterification process.

[0112] A fluid at a temperature and pressure where it is no longer possible to differentiate between the liquid and gas phase becomes a supercritical fluid.

[0113] In certain embodiments, the transesterification reactor 3 being a helical coil reactor comprising an induction heater.

[0114] In certain embodiments, the helical coil reactor comprises a coil made of a tube having a diameter in the range of 50-150 mm.

[0115] In certain embodiments, the coil of the helical coil reactor comprise a coil made of a tube having a length in the range of 100 - 1000 m.

[0116] In certain embodiments, the coil of the helical coil reactor comprises a coil having an outer diameter in the range of 2000 - 5000mm.

[0117] In certain embodiments, the coil of the helical coil reactor is arranged to extend in an upright direction. In the context of this application, the upright position means a direction having an angle 80 degrees or more to ground level. Furthermore, a first round of the tube of the coil is positioned above the second round of the tube of the coil. In certain embodiments, the coil of the helical coil reactor comprises a first coil and a second coil, the first coil is arranged to surround the second coil. In other words, the first coil having a larger diameter than the second coil, the first coil having an empty core, and the second coil is positioned to the empty core of the first coil. In certain embodiment, the helical coil reactor comprises several nested coils.

[0118] In certain embodiments, the step of mixing the fatty acid feedstock F and the alcohol reagent R1 is carried out with a mixing device 1.

[0119] In certain embodiments, the mixing device 1 comprises a feedstock pump.

[0120] In certain embodiments, the feedstock pump being a constant-volume pump, and the feedstock pump mixing the fatty acid feedstock F and the alcohol reagent R1 and increasing the pressure of the intermediate composition I to the range of 2 - 4 barg.

[0121] In other words, the method comprises feeding the fatty acid feedstock F and the alcohol reagent R1 into the feedstock pump.

[0122] In certain embodiments, the step of mixing the fatty acid feedstock F and the alcohol reagent R1 is carried out with a mixing device 1, the mixing device 1 comprises a first feedstock pump 11 and a second feedstock pump 12, and the first feedstock pump 11 pumping the fatty acid feedstock F and a second feedstock pump 12 pumping the alcohol reagent Rl.

[0123] In certain embodiments, first feedstock pump 11 and a second feedstock pump 12 being a constant-volume pumps, and the first feedstock pump 11 and a second feedstock pump 12 increasing the pressure of the intermediate composition I to the range of 2 - 4 barg.

[0124] In the context of this application, "constant-volume pumps" means pumps wherein liquid is positively displaced from a fixed-volume container.

[0125] Constant-volume pumps are capable of developing high pressures while operating at low suction pressures. They are commonly referred to also as positive-displacement pumps. Unlike centrifugal pumps, their capacity is not affected by the pressure against which they operate. Flow is usually regulated by varying the speed of the pump or by recycle. Constant-volume pumps are divided into two groups: rotary and reciprocating pumps. Rotary pumps displace a fixed quantity of fluid for every revolution of the driver shaft. Rotary pumps have different pumping elements such as vanes, lobes, gears, and screws. Reciprocating pumps move liquid by means of a constant back-and-forth motion of a piston, plunger, or diaphragm within a fixed volume or cylinder.

[0126] In certain embodiments, in the step of increasing pressure the pressure of the intermediate composition I the pressure of the intermediate composition I is increased to the range of 220-260 barg.

[0127] In certain embodiments, the step of increasing pressure of the obtained intermediate composition I is carried out with a pressure increasing device 2 comprising a pressure increasing pump.

[0128] In certain embodiments, the alcohol reagent R1 being methanol.

[0129] In certain embodiments, the alcohol reagent R1 comprises any combination of the following: methanol, ethanol and butanol.

[0130] In certain embodiments, the fatty acid feedstock F comprises fatty acids.

[0131] In certain embodiments, the fatty acid feedstock F comprises fatty acids and the fatty acid feedstock F comprises free fatty acids at least 75 wt% or at least 95 wt% based on the total weight of the fatty acid feedstock F with the proviso that fatty acids and free fatty acids taken together adds up to 100 wt%.

[0132] A fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. Fatty acids are a major component of the lipids (up to 70% by weight) in some species such as microalgae but in some other organisms are not found in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and important structural components for cells. Free fatty acids are non-es- terified fatty acids that are released by the hydrolysis of triglycerides

[0133] In certain embodiments, in that operating the transesterification reactor 3 in a continuous operation mode is carried out by simultaneously controlling the feedstock pump of the mixing device 1, the pressure increasing pump of the pressure increasing device 2 and a pressure adjusting unit 4 so that: - the feedstock pump of the mixing device 1 and the pressure increasing pump of the pressure increasing device 2 increasing the pressure in the transesterification reactor 3 by increasing the pressure of the intermediate composition I, the mixing device 1 and the pressure increasing device 2 are provided upstream from the transesterification reactor 3, and

[0134] - the pressure adjusting unit 4 maintaining a constant pressure in the transesterification rector 3, the pressure adjusting unit 4 is provided in a connection with an outlet 32 of the transesterification reactor 3 downstream from the transesterification reactor 3.

[0135] In certain embodiments, the pressure adjusting unit 4 comprises a pressure reducing valve.

[0136] In certain embodiments, a residence time in the transesterification reactor 3 being in the range of 20 - 80 min or up to 30 min.

[0137] In the context of this application, the residence time means the total time that the intermediate composition I remains inside the transesterification reactor 3.

[0138] In certain embodiments, the temperature of the transesterification reactor 3 being at a temperature in the range of 220 - 310 degrees C or in the range of 220-260 degrees C.

[0139] In certain embodiments, the content of the fatty acid feedstock F being 60 - 80 wt% and the alcohol reagent R1 20 - 40 wt% based on the total weight of the fatty acid feedstock F and alcohol reagent R1 with the proviso that the fatty acid feedstock F and the alcohol reagent R1 taken together adds up to 100 wt%. In certain embodiments, the content of the fatty acid feedstock F being 60 - 80 wt% and the alcohol reagent R1 20 - 40 wt% based on the total weight of the fatty acid feedstock F and alcohol reagent Rl.

[0140] In certain embodiments, the step of separating biodiesel from the product composition comprises reducing after the transesterification reactor (3) the pressure of the product composition to a pressure in the range of 1 - 2 barg. In certain embodiments, the step of separating biodiesel from the product composition comprises spraying the product composition to a distillation column, and separating with the distillation column water, remaining alcohol reagent Rl and a composition comprising esters and glycerides. In certain embodiments, the step of separating biodiesel from the product composition comprises spraying the product composition to a distillation column, separating with the distillation column water, remaining alcohol reagent R1 and a composition comprising esters and glycerides, and feeding the composition comprising esters and glycerides to separating vessel 6, and obtaining a biodiesel ester composition P3 from the separating vessel 6.

[0141] In certain embodiments, the step of separating biodiesel from the product composition comprises removing free fatty acids from the biodiesel ester composition P3 with a base compound.

[0142] In certain embodiments, the step of separating biodiesel from the product composition comprises removing free fatty acids from the biodiesel ester composition P3 with a base compound, the base compound comprises sodium hydroxide (NaOH) or potassium hydroxide (KOH).

[0143] In certain embodiments, the method comprises feeding carbon dioxide to the transesterification reactor 3.

[0144] In certain embodiment, the method comprises feeding gaseous carbon dioxide to the transesterification reactor 3.

[0145] In certain embodiments, the method comprises feeding carbon dioxide catalyst to the transesterification reactor 3 in vicinity of the fresh intermediate composition I.

[0146] Figure 2 shows schematically a system for producing biodiesel according to the present invention. The system comprises a mixing device 1 arranged to receive a fatty acid feedstock F and an alcohol reagent R1 and arranged to produce an intermediate composition I from the fatty acid feedstock F and the alcohol reagent Rl, a pressure increasing device 2 arranged to receive the intermediate composition I from the mixing device 1 and arranged to increase the pressure of the intermediate composition I to the range of 220-260 barg, the transesterification reactor 3 arranged to receive the intermediate composition I from the pressure increasing device 2 and arranged to convert the intermediate composition I to a product composition at a supercritical condition, the transesterification reactor 3 being a helical coil reactor, and the transesterification reactor 3 is arranged to operate in a continuous operation mode, and a separation arrangement 500 arranged to separate a biodiesel composition B from the first product composition Pl. In certain embodiments, the separation arrangement 500 comprises a distillation column 5 water arranged to separate the remaining alcohol reagent R2 and a composition comprising esters and glycerides P2.

[0147] In certain embodiments, the separation arrangement 500 comprises a separating vessel 6 arranged to receive composition comprising esters and glycerides P2 from the distillation column 5 and providing a biodiesel ester composition P3 from the separating vessel 6. The biodiesel ester composition P3 comprises esters.

[0148] In certain embodiments, the separation arrangement 500 comprises pretreatment device 7 arranged to remove free fatty acids from the biodiesel ester composition P3 with a base compound, the base compound comprises sodium hydroxide (NaOH) or potassium hydroxide (KOH).

[0149] It should be noted that the system is arranged to carry out any of the above disclosed embodiments of the method.

[0150] It should be noted that the above disclosed method may be carried out with any of the above disclosed embodiments of the system.

[0151] Figure 3 shows schematically a side view of a transesterification reactor according to one embodiment of the present invention.

[0152] It should be noted that the above disclosed method may be carried out with any of the above disclosed embodiments of the system. Furthermore, embodiments of the figure 3 may be incorporated with embodiments of the figure 2.

[0153] In certain embodiments, the transesterification reactor 3 being a helical coil reactor comprising a helical coil 33 surrounded by a heat transfer fluid H, and the method comprises heating the heat transfer fluid H with a heater 13 and providing a flow of the heated heat transfer fluid H through the transesterification reactor 3.

[0154] In certain embodiments, the heater 13 being an oil heater.

[0155] In certain embodiments, the helical coil 33 is made of tube 3333 having a diameter in the range of 50 -150 mm.

[0156] In certain embodiments, the helical coil 33 is made of tube 3333 having a length in the range of 100-1000 m.

[0157] In certain embodiments, the helical coil 33 having a diameter in the range of 2000 - 5000 mm. In certain embodiments, the helical coil 33 is made of tube 3333. The tube 3333 being a hydraulic tube having a pressure capacity in the range of 350- 450 barg.

[0158] In certain embodiments, the helical coil 33 is arranged to extend and upright direction. In the context of this application, the upright position means a direction having an angle 80 degrees or more to ground level. Furthermore, a first round of the tube of the coil is positioned above the second round of the tube of the coil.

[0159] The helical coil means a coil having the shape of a helix (a curve that goes around a central tube or cone shape in the form of a spiral).

[0160] In other words, the upright position means that the central tube or cone shape extending in an upright direction.

[0161] Figure 4 shows schematically a side view of a transesterification reactor according to one embodiment of the present invention.

[0162] In certain embodiments, the coil of the helical coil reactor comprises a first coil 332 and a second coil 333, the first coil 332 is arranged to surround the second coil 333.

[0163] In other words, the first coil 332 having a larger diameter D than the second coil 333.

[0164] This means that, the first coil 332 having an empty core 3321, and the second coil 333 is positioned to the empty core 3321 of the first coil 332.

[0165] In certain embodiment, the helical coil reactor comprises several nested coils 332, 333, 334.

[0166] It should be noted that the above disclosed method may be carried out with any of the above disclosed embodiments of the system. Furthermore, embodiments of the figure 4 may be incorporated with embodiments of the figures 2 and 3.

[0167] Example 1 (Comparative)

[0168] The inventor tested biodiesel production with a batch type transesterification reactor. The reactor had a volume of 5 m3.

[0169] First, a mixture of the fatty acids and methanol was produced

[0170] The mixture was fed in the transesterification reactor at a supercritical condition to produce to produce methyl esters. At a supercritical condition, a temperature is in the range of 220 - 310 degrees C and a pressure in the range of 220-260 barg. The production required filling time min 0,5 hours, heating time min 2 hours, and production further required processing time, settling time and cooling time. A magnetic stirrer was used to provide even temperature in the reactor which was complicate.

[0171] Example 2 (According to the invention)

[0172] The inventor tested biodiesel production with a helical coil type reactor operating in continuous mode. The reactor had a volume of 1 m3. In other words, the transesterification reactor was a helical coil reactor operating in a continuous operation mode.

[0173] First, a mixture of the fatty acids and methanol was produced with constant-volume pumps.

[0174] Then, a pressure of the mixture was increased with the mixing pump and a pressure increasing pump. The pumps were constant-volume pumps. The pressure was increased to a pressure of the supercritical condition upstream from the reactor.

[0175] The mixture having increased pressure was fed into the transesterification reactor. The helical coil reactor comprised a helical coil which was surrounded by a heat transfer fluid. The heat transfer fluid was heated with a separate heater and it was flowing through the transesterification reactor.

[0176] The system comprised a pressure adjusting unit provided in a connection with an outlet of the transesterification reactor downstream from the transesterification reactor.

[0177] The pressure adjusting unit comprised a pressure reducing valve. The continuous operation mode is carried out by simultaneously controlling the pumps and the pressure reducing valve.

[0178] The inventor surprisingly found out that a spiral reactor having 0,2 times the volume of a batch reactor having more yield than a batch reactor.

[0179] The inventor surprisingly found out that the reactor may be constructed from a hydraulic tube having a pressure capacity in the range of 350-450 barg having a remarkable thinner wall than the batch reactor. Furthermore, the heat transfer fluid surrounding the tube of the spiral reactor provided an evenly distributed temperature in the spiral reactor. Thus, an entire content or at least almost the entire content in the reactor were at the supercritical condition. Furthermore, the inventor found out that the method and the system was very efficient as processing time the range of 20 - 80 min or very short processing time such as less than 30 min was enough for producing more biodiesel than in the batch reactor. It is to be understood that the above description and the accompanying Figures are only intended to teach the best way known to the inventors to make and use the invention. It will be apparent to a person skilled in the art that the inventive concept can be implemented in various ways. The above-described embodiments of the invention may thus be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings.

[0180] It is therefore to be understood that the invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

Claims1. Method for producing biodiesel, characterized in that the method comprises:- providing a fatty acid feedstock (F) and an alcohol reagent (Rl);- mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) with a mixing device (1);- obtaining an intermediate composition (I) from the step of mixing the fatty acid feedstock (F) and the alcohol reagent (Rl);- increasing pressure of the obtained intermediate composition (I) with a pressure increasing device (2),- feeding the intermediate composition (I) having the increased pressure to a transesterification reactor (3),- transesterifying at least a part of the intermediate composition (I) to a first product composition (Pl) in the transesterification reactor (3) at a supercritical condition, and operating the transesterification reactor (3) in a continuous operation mode,- obtaining the first product composition (Pl) from the transesterification reactor (3), and- separating a biodiesel composition (B) from the first product composition (Pl).

2. Method for producing biodiesel according to claim 1, characterized in that:- the transesterification reactor (3) being a helical coil reactor comprising a helical coil (33) surrounded by a heat transfer fluid (H), and the method comprises heating the heat transfer fluid (H) with a heater (13) and providing a flow of the heated heat transfer fluid (H) through the transesterification reactor (3); or- the transesterification reactor (3) being a helical coil reactor comprising a helical coil (33), the method comprises heating the helical coil (33) with an induction heater.

3. Method for producing biodiesel according to claim 1 or 2, characterized in that:- the step of mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) is carried out with a mixing device (1) comprising a feedstock pump; or- the step of mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) is carried out with a mixing device (1) comprising a feedstock pump, the feedstock pumpbeing a constant-volume pump, and the feedstock pump mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) and increasing the pressure of the intermediate composition (I) to the range of 2 - 4 barg; or- the step of mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) is carried out with a mixing device (1), the mixing device (1) comprises a first feedstock pump (11) and a second feedstock pump (12), and the first feedstock pump (11) pumping the fatty acid feedstock (F) and a second feedstock pump (12) pumping the alcohol reagent (Rl); or- the step of mixing the fatty acid feedstock (F) and the alcohol reagent (Rl) is carried out with a mixing device (1), the mixing device (1) comprises a first feedstock pump (11) and a second feedstock pump (12), and the first feedstock pump (11) pumping the fatty acid feedstock (F) and a second feedstock pump (12) pumping the alcohol reagent (Rl), and the step of mixing comprises increasing the pressure of the intermediate composition (I) to the range of 2 - 4 barg.

4. Method for producing biodiesel according to any of preceding claims, characterized in that:- the step of increasing pressure of the obtained intermediate composition (I) is carried out with a pressure increasing device (2) comprising a pressure increasing pump, the pressure increasing pump being a constant-volume pump, and the pressure increasing pump increasing the pressure of the intermediate composition (I) to the range of 220-260 barg; or- in the step of increasing pressure, the pressure of the intermediate composition (I) the pressure of the intermediate composition (I) is increased to the range of 220- 260 barg.

5. Method for producing biodiesel according to any of preceding claims, characterized in that:- the alcohol reagent (Rl) being methanol; or- the alcohol reagent (Rl) comprises any combination of the following: methanol, ethanol and butanol.

6. Method for producing biodiesel according to any of preceding claims, characterized in that:- the fatty acid feedstock (F) comprises fatty acids; or- the fatty acid feedstock (F) comprises fatty acids, and free fatty acids at least 75 wt% or at least 95 wt% based on the total weight of the fatty acid feedstock (F) with the proviso that fatty acids and free fatty taken together adds up to 100 wt%.

7. Method for producing biodiesel according to any of preceding claims, characterized in that operating the transesterification reactor (3) in a continuous operation mode is carried out by simultaneously controlling the mixing device (1), the pressure increasing pump of the pressure increasing device (2) and a pressure adjusting unit (4) so that:- the mixing device (1) and the pressure increasing pump of the pressure increasing device (2) increasing the pressure in the transesterification reactor (3) by increasing the pressure of the intermediate composition (I), the mixing device (1) and the pressure increasing device (2) are provided upstream from the transesterification reactor (3), and- the pressure adjusting unit (4) maintaining a constant pressure in the transesterification rector (3), the pressure adjusting unit (4) is provided in a connection with an outlet (32) of the transesterification reactor (3) downstream from the transesterification reactor (3).

8. Method for producing biodiesel according to any of preceding claims, characterized in that:- the residence time in the transesterification reactor (3) being in the range of 20 - 80 min or up to 30 min.

9. Method for producing biodiesel according to any of preceding claims, characterized in that:- the temperature of the transesterification reactor (3) being at a temperature in the range of 220 - 310 degrees C.

10. Method for producing biodiesel according to any of preceding claims, characterized in that:- the intermediate composition (I) comprises 20 - 40 wt% the alcohol reagent (Rl) and 60 - 80 wt% the fatty acid feedstock (F) based on the total weight of the fattyacid feedstock (F) and alcohol reagent (Rl) with the proviso that the fatty acid feedstock (F) and the alcohol reagent (Rl) taken together adds up to 100 wt%; or- the intermediate composition (I) comprises 20 - 40 wt% the alcohol reagent (Rl) and 60 - 80 wt% the fatty acid feedstock (F) based on the total weight of the fatty acid feedstock (F) and alcohol reagent (Rl).

11. Method for producing biodiesel according to any of preceding claims, characterized in that the method comprises a step of reducing the pressure of the first product composition (Pl) to a pressure in the range of 1 - 2 barg with a pressure adjusting unit (4).

12. Method for producing biodiesel according to any of preceding claims, characterized in that:- the step of separating biodiesel composition (B) from the first product composition (Pl) comprises: spraying the first product composition (Pl) to a distillation column (5), and separating with the distillation column (5) water, remaining alcohol reagent (R2) and a composition comprising esters and glycerides (P2); or- the step of separating biodiesel composition (B) from the first product composition (Pl) comprises: spraying the first product composition (Pl) to a distillation column (5), separating with the distillation column (5) water, remaining alcohol reagent (R2) and a composition comprising esters and glycerides (P2), and feeding the composition comprising esters and glycerides (P2) to a separating vessel (6), and obtaining a biodiesel ester composition (P3) from the separating vessel (6); or- the step of separating biodiesel composition (B) from the first product composition (Pl) comprises: spraying the first product composition (Pl) to a distillation column (5), and separating with the distillation column (5) any combination of the following: molecules comprising sulphur, water, remaining alcohol reagent (R2) and a composition comprising esters and glycerides (P2); or- the step of separating biodiesel composition (B) from the first product composition (Pl) comprises: spraying the first product composition (Pl) to a distillation column (5), separating with the distillation column (5) any combination of the following: molecules comprising sulphur, water, remaining alcohol reagent (R2) and a composition comprising esters and glycerides (P2), and feeding the compositioncomprising esters and glycerides (P2) to a separating vessel (6), and obtaining a biodiesel ester composition (P3) from the separating vessel (6).

13. Method for producing biodiesel according to any of preceding claims, characterized in that the step of separating a biodiesel composition (B) from the first product composition (Pl) comprises:- removing free fatty acids from the biodiesel ester composition (P3) with a base compound; or- removing free fatty acids from the biodiesel ester composition (P3) with a base compound, the base compound comprises sodium hydroxide (NaOH) or potassium hydroxide (KOH).

14. Method for producing biodiesel according to any of preceding claims, characterized in that:- the method comprises feeding carbon dioxide (C) into the transesterification reactor (3) in the vicinity of the intermediate composition inlet (31).

15. System for producing biodiesel, characterized in that the system comprises:- a mixing device (1) arranged to receive a fatty acid feedstock (F) and an alcohol reagent (Rl) and arranged to produce an intermediate composition (I) from the fatty acid feedstock (F) and the alcohol reagent (Rl);- a pressure increasing device (2) arranged to receive the intermediate composition (I) from the mixing device (1) and arranged to increase the pressure of the intermediate composition (I) to the range of 220-260 barg;-the transesterification reactor (3) arranged to receive the intermediate composition (I) from the pressure increasing device (2) and arranged to transestesterify at least a part of the intermediate composition (I) to a first product composition (Pl) at a supercritical condition, the transesterification reactor (3) being a helical coil reactor, and the transesterification reactor (3) is arranged to operate in a continuous operation mode,- a separation arrangement (500) arranged to separate a biodiesel composition (B) from the first product composition (Pl).

16. System for producing biodiesel according to claim 15, characterized in that:- the system is arranged to carry out a method according to any of the claims 1 -14.

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