AU2011226731B2

AU2011226731B2 - Lipid removal from suspensions

Info

Publication number: AU2011226731B2
Application number: AU2011226731A
Authority: AU
Inventors: Eduard Lack; Franz Lang; Helmut Siedlitz; Martin Sova
Original assignee: Natex Prozesstechnologie GmbH
Current assignee: Natex Prozesstechnologie GmbH
Priority date: 2010-03-11
Filing date: 2011-03-11
Publication date: 2014-03-27
Anticipated expiration: 2031-03-11
Also published as: BR112012022863A2; TW201130965A; KR20130033364A; EP2545149B1; PT2545149E; AT509525B1; ZA201207422B; BR112012022863B1; TWI457436B; AU2011226731A1; WO2011109852A1; ES2547882T3; CL2012002498A1; AT509525A1; EP2545149A1

Abstract

In a process for extracting lipids from aqueous suspensions of biomass, especially from digested algal suspensions, using water-immiscible solvents, the algal suspension with an algal content of 50% by weight is supplied continuously to a thin-film extruder and contacted as a thin film with the solvent present in the liquid or supercritical state in the thin-film extractor, and then the solvent is recovered by expanding the solution composed of solvent and lipids, and the extracted lipids are removed.

Description

Lipid removal from suspensions The invention relates to a method for extracting lipids from aqueous suspensions of biomass, in particular disrupted algal suspensions, using water-immiscible solvents. In recent times, algae of various kinds have to an increasing extent attracted interest as raw materials. For the production of biofuels from lipids of algae, no agricultural areas which are needed to cultivate plants for food are required, the cultivation of algae being extremely simple as compared to the cultivation of plants on the mainland. The cultivation of algae can be performed both in the coastal regions of the earth and also on the mainland in algal farms, and produces large amounts of biomass merely by virtue of solar energy while applying small amounts of nutrients or fertilizers and utilizing CO 2 , whereby, due to the rapid growth of algae, based on the surface area, an unequally higher amount of lipids will be obtained, which can be processed to biofuels or the like. A method of the initially defined kind has already become known from WO 93/25644. That method for recovering lipids uses single celled algae (microalgae) as raw materials, yet also macroalgae having water contents of < 50% by weight. According to the specification of that document, water-miscible organic solvents like short-chain alcohols are, above all, used for the extraction of the lipids, wherein, however, even compressed gases such as for instance propane, which represents a water immiscible gas, are mentioned. Although WO 93/25644 cites water contents of the extraction material of up to 50% by weight in the claims, the exemplary embodiments of that application refer to applications in which the water content of the algal material, which is generally comprised of algal meal from macroalgae, is substantially lower. It is particularly pointed 2 out that macroalgae are dried prior to milling in order to reach a water content of below 50% by weight. In those examples, the water contents, thus, apparently relate to the water contents of the algal cells themselves. In this 5 connection it is however problematic that algae from aquacultures, for their extraction, have to be dried under considerable energy and time expenditures in order to achieve the required water contents and enable the extraction to be operated economically. 10 The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these 15 matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 20 Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, 25 integers, steps or components, or group thereof. It is an object of the present invention to improve a method of the initially defined kind to the effect that aqueous suspensions of biomass and, in particular, disrupted algal 30 suspensions can be extracted without preceding drying steps by using water-immiscible solvents in order to obtain lipids, whereby an enhanced economic efficiency of the lipid recovery from algae is to be achieved.

3 To solve this object, the method of the initially defined kind according to the invention is further developed to the effect that the suspension having a biomass portion of up to 50% by weight is continuously supplied to a thin-film extractor and 5 contacted as a thin film with the solvent present within the thin-film extractor in the liquid or supercritical state, whereupon the solvent is recovered from the solution of solvent and lipids either in isobaric form by a phase change or by depressurisation, and the extracted lipids are separated. Other 10 than in the prior art, a smaller portion of algae or biomass may be contained in the suspension according to the present invention, and the portion may, in particular, be so low that it will suffice to merely perform a sedimentation of the algae after the harvest of the algae and to use the sedimented algae 15 directly for the extraction after cellular disruption, wherein the disrupted algae, according to the invention, are supplied to a thin-film extractor, in which the algal suspension or a different biomass suspension is applied on a surface in the form of a thin film so as to make the disrupted algae, and 20 hence the lipids contained in the algae, available for the access of the solvent. By using a thin-film extractor which is continuously operated, the inherently problematic high water portion will thus be compensated, since, due to the huge surface enlargement within the thin-film extractor, the solvent 25 will readily be able to reach the fat globules from the algal macerate. By choosing a solvent that is immiscible with water, said solvent being present in the thin-film extractor in the liquid or supercritical state, no solvent will be lost in the large amount of water provided in the thin-film extractor, 30 which would definitely be the case, for instance, when using carbon dioxide. Thus, the total solvent used for the extraction of the lipids can practically be recovered and recycled to the thin-film extractor for reuse. The lipids of the algae will 3a thus remain in a separator system by evaporation or depressurisation and can be further processed accordingly. In one embodiment, the present invention provides a method for 5 extracting lipids from aqueous suspensions of biomass, in particular disrupted algal suspensions, using water-immiscible solvents, characterized in that the suspension having a biomass portion of up to 50% by weight is continuously introduced to a pressure-proof thin-film extractor, a thin film of the 10 suspension is formed at the cylindrical inner periphery of the extractor, the thin film is contacted with the solvent present within the thin-film extractor in the liquid or supercritical state, the thin-film is mechanically impacted with the help of a rotor, which is arranged in the extractor, whereupon the thin 15 film of the suspension is continuously renewed by mechanical impact at least over a portion of the film thickness of the thin film, the suspension being pressed downwards in the annular gap provided between the inner periphery of the extractor and the outer periphery of the rotor and the solvent 20 loaded with the extracted lipids being subsequently drawn off from the extractor, whereupon the solvent is recovered from the solution of solvent and lipids either in isobaric form by a phase change or by depressurisation, and the extracted lipids are separated. 25 By a thin-film extractor as used in the present invention, a device as can, for instance, be taken from WO 2004/018070 Al is to be understood. Such a thin-film extractor comprises a pressure-proof reactor including at least one charge opening 30 for the biomass suspension or algal suspension to be treated and the compressed solvent as well as appropriate discharge openings, wherein the charge opening for the algal suspension to be treated opens on the inner jacket of the reactor and, in the interior of the reactor, a rotor is arranged, whose radial 3b arms cooperate with the algal suspension film on the inner jacket of the reactor. The use of a reactor in whose interior a rotor is arranged provides the possibility of effecting the mechanical action by the additional exposure to centrifugal 5 forces, whereby an accordingly rapid rotation for the application of the desired centrifugal force is enabled. At the same time, the rotor forms 4 tools for the mechanical processing of the thin film, which, in the simplest case, may be formed by wipers, rollers, doctor blades or the like. Such thin-film extractors are basically suitable for the processing of raw materials having relatively high solids contents, wherein, according to the teaching of WO 2004/018070, carbon dioxide is above all provided as a solvent. For the raw materials to be processed according to the invention, which, for the achievement of the desired economy of the extraction of algal suspensions, have very low solid contents, it is, however, provided according to the invention to replace carbon dioxide, which mixes to some extent with water, in such an extractor with a water-immiscible solvent in order not to loose any solvent in the. large amount of water. A positive side aspect of the use of such solvents, moreover, resides in that, due to the substantially more moderate extraction conditions, the technical expenditures and hence the process costs will be lowered. The thin-film extractor to be used according to the invention, as against the device according to WO 2004/018070, can be provided with special fixtures to be discussed further below. In order to achieve a simple separation of the solvent from the extracted lipids, the method according to a preferred embodiment of the present invention is further developed to the effect that short-chain alkanes, particularly propane, are used as said solvent. Short-chain alkanes such as, for instance, propane exhibit excellent solution properties for the lipids to be extracted under the conditions provided by the invention in the thin-film extractor and, in particular, conditions under which the solvent is present in the liquid or supercritical state, while, at the same time, offering the advantage that only a very low solubility of the solvents in the extracted lipids will be observed if the solution of solvent and extracted lipids is 5 depressurised, so that a simple recovery of the solvent and a practically complete separation of the desired lipids will be ensured by the solvent passing into the gas phase. When using even more lipophilic solvents, equally good extraction results will be achieved, yet a separation of solvents and lipids would only be possible at increased expenditures, for instance elevated temperatures and/or reduced pressures. The method of the invention according to this preferred embodiment thus offers the option to use algal suspensions without previous drying for the extraction of lipids, wherein the solution of solvent and lipids merely need to be depressurised in order to separate the lipids and recover the solvent for a new use at an extraction. In principle, the method according to the invention can be applied to any algal or biomass suspension that exhibits a suitable degree of fineness or has undergone suitable cellular disruption, wherein, in a preferred manner, the method is, however, further developed to the effect that microalgae are used as algal raw material. Microalgae having dimensions of about 20 pm and less are particularly simple and space-saving to cultivate and can be supplied to cellular disruption to liberate lipids without requiring mechanical disintegration. Microalgae have particularly high lipid portions of about 50% by weight, and partially even more, and the increase in the algal or solids portion of the algal suspension, which is sought for the extraction, can, for instance, be effected by mere sedimentation and decantation of the supernatant water after the harvest of the algae from a cultivation basin. As already mentioned above, it is essential to the economy of the method that the expenditures involved in the preparation of the algae prior to their extraction will be kept as low as possible. The method according to the invention is, therefore, advantageously further developed such that the algal portion of the algal suspension is 5-40% by weight, in particular 10-35% by weight, preferably 15- 6 30% by weight and, in a particularly preferred manner, 20-25% by weight, wherein such algal or solids portions can readily be achieved by the above-described sedimentation of the algae from the culture solution or, optionally, by applying coarse filtration or similar measures. As already pointed out above, the method according to the invention provides that algae or any other biomass are subjected to cellular disruption in order to liberate the lipids contained in the cells for the access of the solvent. In a preferred manner, it is proceeded such that the cellular disruption of the algae is effected enzymatically using cellulases, wherein it may also be provided according to a preferred embodiment of the present invention that the algae are mechanically disrupted, if macroalgae are to be processed. During the application of the method according to the invention, valuable lipids occur as extracts, wherein the use of the lipids as food additives would call for the thorough removal of solvent residues possibly left in the lipids after depressurisation. Such cumbersome refining can, however, be omitted if, as in accordance with a preferred embodiment of the present invention, the extracted lipids are further processed to biodiesel by esterification and/or to other fuels by cracking. Short-chain alkane residues, such as propane or butane, contained in the extracted lipids do not cause any problems when processed to fuels such that an even further enhancement of the economy of the method according to the invention will be achieved. Further processing to the cited fuels is performed according to methods known from the prior art. According to an embodiment of the present invention, it is preferably proceeded in a manner that the extraction residues are further processed to bioethanol or biogas by fermentation.

7 As already mentioned before, the cultivation of algae produces extremely large amounts of biomass, - wherein the lipids merely constitute a fraction of the usable substance. The extraction residues, which, above all, are comprised of carbohydrates, yet also of other cell-wall components and cell organelle components, can also be exploited by other known methods so as to again provide an increased benefit. In the thin-film extractor used according to the invention, a thin film of the material to be extracted is applied on a surface, wherein it is according to the invention preferably provided that the thin film of the algal suspension in the thin film extractor is continuously replaced by mechanical impact at least over a portion of the film thickness of the thin film. The continuous replacement of the film, and its mechanical treatment by shearing and rolling forces, which are exerted on the film by the rotating tools of the thin-film extractor, ensure that, despite the low solids portion, the algal components from the disrupted algae will again and again come to the surface and hence into contact with the liquid or supercritical solvent so as to enable a more or less quantitative extraction of the lipids. In the following, the invention will be explained in more detail by way of an exemplary embodiments illustrated in the drawing. Therein, Fig. 1 is a schematic illustration of the method according to the invention; and Fig. 2 is a schematic illustration of the thin-film extractor employed by the invention. In Fig. 1, an alga cultivation basin (Sl) is symbolized. Such a basin may be located in a flat region near the coast, e.g. in a former salt basin, yet any other type of aquatic culture is conceivable. In particular, attempts have recently been made to 8 cultivate algae in tubes, wherein the tubes are to define the layer thickness of the algal suspension in order to enable the access of sunlight to the algae in the total suspension volume. In addition to a few nutrients, which are available in seawater without the help of man, algae also need carbon dioxide for their growth, which can be taken from the air. After a sufficient phase of growth, the algae can be harvested, which may, for instance, take place once a week. The algae are subsequently enriched, for instance, by sedimentation or filtration (S2) in order to increase the solids content of the algal suspension. The supernatant water can, for instance, be decanted off so as to provide a suitable algal pulp for extraction (S5). Prior to the extraction, a homogenization (S3) and, above all, a cell disruption (S4) are performed in order to liberate the lipids for the access of the solvent. In the subsequent step, the extraction (S5) takes place in a thin-film reactor as already described and illustrated in more detail in Fig. 2. During the extraction (S5), the lipids are extracted from the disrupted algal suspension and, after the depressurisation of the solution comprised of solvent and lipids, the lipids are obtained in the form of oil (S6), wherein the solvent is released and recycled into the thin-film extractor. Lipophilic bioactive substances will occur as by products (S7). The deoiled algae form an extraction residue (S8) whose biomolecules such as carbohydrates can, for instance, be further processed to bioethanol (SlO) or biogas (Sll) by fermentation (S9). The residues left can be used as animal feed (S12). Alternatively, the extraction residue can be recycled into the alga cultivation basin (Si). From the extracted oil (36) can be obtained either biodiesel (S14) by esterification (S13) or other fuels (S16) by cracking (S15). Fig. 2 depicts in more detail the thin-film extractor used according to the invention. In Fig. 2, a pressure-proof reactor 9 is denoted by 1, which is designed to be cylindrical or tubular. The reactor 1 can be closed in a pressure-proof manner by a lid portion 2 and a bottom portion 3, the connection being provided via flanges 4 and 5. In the lid portion 2, an agitator 6 is arranged, which comprises a magnetic coupling for rotationally driving an agitator shaft 7. The agitator shaft 7 is in turn connected with a rotor 8, which is mounted in the interior of the reactor 1 so as to rotate about an axis of rotation 9. The respective guidance and centering of the rotor are realized via a mandrel 10, which is firmly connected with the bottom portion 3. The rotor 8 carries several guide rods 11 arranged in a circularly distributed manner and serving to guide rotationally mounted rollers 12 in such a manner as to enable the rollers 12 to roll off along the inner periphery 13 of the reactor 1 at a rotation of the rotor 8 about the axis of rotation 9. A charge opening 14 for the suspension to be treated is provided in the lid 2. The charge opening opens into the cylindrical reactor volume in the region of the inner periphery 13 of the reactor 1. By introducing the algal suspension to be treated via the charge opening 14, the algal suspension will then be conveyed in the direction toward the discharge opening 15 within the interior of the reactor 1, with the algal suspension being pressed downwards in the annular gap provided between the inner periphery 13 of the reactor 1 and the outer periphery of the rotor 8. In this region, the algal suspension is mechanically acted upon by the rotating rollers 12 in such a manner as to form an extremely thin liquid film between the rotating rollers 12 and the inner periphery 13 of the reactor 1. The thickness of the liquid film is determined by the preset distance of the rollers 12 relative to the inner jacket 13 of the reactor 1. The rollers 12 may have a helical-line-shaped profiling, yet may also be designed to be conical, concave or convex, said profiling during rolling off along the liquid film, at the same 10 time, promoting the downward movement of the liquid film in the direction of the discharge opening 15. The solvent is introduced into the reactor in counter-flow to the algal suspension, the respective charge opening being formed in the bottom portion 3 and denoted by 16. The solvent rises in the interior of the reactor 1 while intimately contacting the liquid film, at which the liquid film surface exposed to the solvent being constantly replaced by the milling or kneading procedure caused by the rotating rollers 12. The solvent loaded with the extracted lipids can subsequently be drawn off through the discharge opening 17 provided in the lid 2. Additionally provided is a closeable opening 18, via which samples can be taken during operation, or various operating parameters can be checked. A further such opening can also be provided in the bottom portion 3. Furthermore, the pressure-proof reactor 1 is surrounded by heating and cooling jackets 19 and 20, respectively, through which respectively a heating or cooling fluid and, in particular, water can flow in co-current flow with, or in counter-flow to, the liquid or dispersion to be treated. Figs. 3, 4, 5 and 6 depict modified thin-film reactors operating according to the same principle as the above-described one. Where provided, identical components bear identical reference numerals. The modifications primarily relate to different configurations of the rotor 8, wherein helical geometries are of particular advantage for conveying the material to be extracted through the extractor. The installations further developed according to Figs. 3, 4, 5 and 6 in addition to the optimized alga extraction enable the likewise continuous processing of any type of suspensions containing, for instance, yeasts, fungi, egg 11 yolks or even ground and finely suspended spices and herbs. Moreover, also other suspensions of vegetable origin can be processed to obtain essential oils and/or oleoresins, and suspensions of ground oil-bearing seeds or their pressing residues as well as fruit pulp like avocado puree can be processed to obtain fruit oils.

Claims

1. A method for extracting lipids from aqueous suspensions of biomass, in particular disrupted algal suspensions, using 5 water-immiscible solvents, characterized in that the suspension having a biomass portion of up to 50% by weight is continuously introduced to a pressure-proof thin-film extractor, a thin film of the suspension is formed at the cylindrical inner periphery of the extractor, the thin film is contacted with the solvent 10 present within the thin-film extractor in the liquid or supercritical state, the thin-film is mechanically impacted with the help of a rotor, which is arranged in the extractor, whereupon the thin film of the suspension is continuously renewed by mechanical impact at least over a portion of the 15 film thickness of the thin film, the suspension being pressed downwards in the annular gap provided between the inner periphery of the extractor and the outer periphery of the rotor and the solvent loaded with the extracted lipids being subsequently drawn off from the extractor, whereupon the 20 solvent is recovered from the solution of solvent and lipids either in isobaric form by a phase change or by depressurisation, and the extracted lipids are separated.

2. A method according to claim 1, wherein short-chain alkanes 25 are used as said solvent.

3. A method according to claim 1 or claim 2, wherein propane is used as said solvent. 30

4. A method according to any one of claims 1 to 3, wherein microalgae are used as algal raw material.

5. A method according to any one of claims 1 to 4, wherein the algal portion of the algal suspension is 5-40% by weight. 13

6. A method according to any one of claims 1 to 4, wherein the algal portion of the algal suspension is 10-35% by weight. 5

7. A method according to any one of claims 1 to 4, wherein the algal portion of the algal suspension is 15-30% by weight.

8. A method according to any one of claims 1 to 4, wherein the algal portion of the algal suspension is 20-25% by weight. 10

9. A method according to any one of claims 1 to 8, wherein the cellular disruption of the algae is effected enzymatically using cellulases. 15

10. A method according to any one of claims 1 to 9, wherein the algae are mechanically disrupted.

11. A method according to any one of claims 1 to 10, wherein the extracted lipids are further processed to biodiesel by 20 esterification and/or to other fuels by cracking.

12. A method according to any one of claims 1 to 11, wherein the extraction residues are further processed to bioethanol or biogas by fermentation. 25

13. Extracted lipids obtained by a method according to any one of claims 1 to 12.

14. A method according to claim 1, substantially as 30 hereinbefore described, with reference to any one of the examples.