METHOD FOR OBTAINING A CONCENTRATED PROTEIN-RICH PHASE FROM RESIDUES OF BIOETHANOL PRODUCTION

Description

Definitions:

[0001] The term "mashing" describes the process in which grain flour is mixed with liquid, whereby the liquid is a mixture of process liquids and possibly water.

[0002] In this invention, the term "thin stillage" encompasses the liquid phase produced by a solid-liquid separation of the stillage.

[0003] For the purposes of this invention, "dissolved dry matter content" refers to the dry matter present in dissolved form in the filtrate after centrifugation and fine filtration (pore size 0.2 µm) of a diluted starting sample, such as stillage. The dissolved dry matter content is expressed as a percentage by mass.

[0004] The "cold mashing process" refers to the pressureless enzymatic digestion of the mashed grain flour at a temperature below the gelatinization temperature of the starch, preferably in the range between 45°C and 66°C. This breaks down the starch molecules and the starch-enveloping proteins, and some of the starch is saccharified.

[0005] In this invention, the term "clear phase" refers to the aqueous phase that results from the separation of the diluted thin stillage.

[0006] The term "concentrate" refers to the protein-rich phase produced from the diluted stillage.

[0007] In this invention, the term "process fluid" includes all solid-containing and all solid-free fluids that arise in the process.

[0008] For the purposes of this invention, "crude protein content" refers to the proportion of crude protein in the dry matter. It is expressed as % dry matter (w / w).

[0009] In this invention, the term "stillage" refers to the residue from the distillation of a grain mash containing ethanol.

[0010] The term "spent grain" in this invention refers to the solid phase that is separated from the stillage by a solid-liquid separation.

[0011] The "separation particle size" describes the particle size that is present after the separation of an initial sample with different particle size fractions, such as stillage, with 50% each in the coarse phase, such as spent grain, and 50% in the fine phase, such as thin stillage.

[0012] The term "feed" refers to the diluted thin stillage, which is separated into clear phase and concentrate. STATE OF THE ART

[0013] The production of bioethanol from plant-based raw materials is well known. In Germany, the amount of bioethanol produced has more than doubled in the last 10 years. The future trend is positive, as further reductions in CO2 emissions from fuels will be legally mandated in the coming years, which can be achieved by blending with bioethanol. Globally, small-grain cereals such as rye, wheat, and triticale, along with corn, represent one of the main raw materials for bioethanol production.

[0014] For bioethanol production, the grain is milled, mashed, and fermented with the addition of yeast. The fermented mash is then distilled, where the ethanol is separated to form stillage. This stillage consists of components not converted to ethanol, salts, and yeast. The stillage typically undergoes a solid-liquid separation process, in which the solid grain residues are separated from the liquid phase, the thin stillage. The separated solids are often referred to as spent grain. Thin stillage and spent grain are used in various forms, either individually or in combination, primarily as animal feed.

[0015] A well-known and widely used feed, especially in the USA, is DDGS (Dried Distillers Grains with Solubles), which consists of dried spent grain and dried thin stillage concentrate and has a dry matter content of approximately 90%. Drying concentrate concentrates the nutrients contained in the grain compared to liquid stillage, resulting in a higher-quality feed. The condensate produced during drying or evaporation is recycled into the mashing process, thus reducing or completely covering the fresh water requirement.

[0016] The crude protein content in DDGS is approximately 30% dry matter, meaning that with a dry matter content of 90%, the crude protein accounts for 27% of the original substance. In comparison, liquid stillage contains only approximately 2-4% crude protein based on the original substance. However, due to the high fiber content in DDGS, this feed can only be fed to ruminants.

[0017] Crude protein content is a key criterion in the evaluation of a feed. The higher the crude protein content, the more valuable the feed. For this reason, increasing the crude protein content is the goal to enhance the feed. At the same time, the fiber content should be kept to a minimum so that the feed's use is not limited to ruminants.

[0018] Various processes for separating proteins from stillage or for enriching the proteins in individual stillage fractions are known to the person skilled in the art.

[0019] One possible method for obtaining proteins from stillage is by extraction. EP2874503 A1 describes a process for extracting proteins from spent grain using ethanol. For this purpose, the spent grain is volumetrically diluted with 50% ethanol. After a residence time of approximately 20 minutes at approximately 49°C, the solid is separated from the protein-containing solvent. The solvent must then be removed to isolate the proteins.

[0020] This process is disadvantageous because it only separates the small amount of protein contained in the spent grain, ignoring the proteins in the thin stillage. Furthermore, the high ethanol demand and the additional step for ethanol removal negatively impact the process costs.

[0021] Another process, in which protein separation occurs with the addition of a chemical, is part of the complex process for processing stillage described in patent US9516891 B1. In this process, thin stillage is mixed with cationic and anionic copolymers, such as acrylamide-acrylic acid copolymers, which cause the proteins to flocculate. The flocculated proteins can then be separated using a tricanter.

[0022] Disadvantages include the cost of the flocculant and the limited usability of the protein product due to the flocculant it contains. The patent does not specify whether and how the flocculant is separated from the proteins, and therefore the product cannot be used as animal feed without further treatment.

[0023] Processes for protein separation from stillage that do not require the addition of chemicals or flocculants are most suitable for the product's use as animal feed. In this case, the protein product contains no chemical contaminants, and no additional process step is required to separate the chemicals.

[0024] The process described in WO2016019374 A2 involves a temperature treatment of the stillage in the range of 93°C to 177°C for a duration of 3 to 180 minutes. This temperature treatment denatures the proteins and forms agglomerates that can be more easily separated, for example by gravity sedimentation or centrifugation.

[0025] A major disadvantage here is the high energy requirement for the temperature treatment of the stillage.

[0026] EP2481293 B1 discloses a temperature-controlled process for producing a protein-containing product from thin stillage (dry matter content approximately 4%). The thin stillage is concentrated in a filtration system, e.g., an ultrafiltration system. A partial stream of the retentate from the filtration system is returned to the filtration storage tank to achieve a dry matter content of approximately 7% for the optimal operating point of the filtration system. Optionally, the protein product can be subsequently dried and pelletized at a temperature-controlled rate.

[0027] The high equipment and operational expenditure due to the filtration system is to be considered a disadvantage here.

[0028] Those skilled in the art are aware that disc centrifuges are frequently used to separate proteins from thin stillage. Examples can be found, among others, in EP2699655 A1 and EP2741615 A2.

[0029] If not all of the thin stillage is to be processed into dried animal feed, or if the plant design does not generally include drying of the thin stillage, the freshwater requirement can be reduced by recycling at least a portion of the thin stillage into the mashing process. However, the recyclable portion is currently limited due to several factors, or it requires special treatment.

[0030] EP2864460 A1 describes that, while the proteins and nutrients contained in the thin stillage have a positive effect on fermentation when recycled, the suspended dry matter it contains is a far greater negative aspect. This limits the amount of fresh flour that can be added to the mash. It also increases viscosity, which impairs pumpability. As an alternative, after temperature treatment of the thin stillage (93°C - 177°C, 3 - 180 min), an aqueous fraction is separated from the thin stillage in a further separation process, the so-called stick water, which contains less than 1% suspended dry matter and is more suitable for recycling. However, this process is very complex in terms of equipment and energy-intensive.

[0031] Part of the process disclosed in EP2847341 A1 involves recycling thin stillage (TS approx. 10%) or stillage (TS approx. 16%) up to a proportion of 45% into the mash. Before fermentation, the mash is subjected to jet cooking, i.e., high-temperature digestion (100°C - 150°C) under pressure (3 bar - 5 bar) to liquefy the starch and reduce viscosity.

[0032] The disadvantages here are the high costs for the equipment and the high energy consumption.

[0033] US 2015 / 0305370 A1 describes a method for controlling the protein content of by-products of a fermentation process, which in turn is part of a process for producing bioethanol from grain. The method comprises the step of separating the stillage obtained after distilling the grain mash into spent grain and thin stillage. Protein-rich by-products are then removed from the thin stillage, resulting in a protein-reduced thin stillage. Subsequently, further non-protein components are removed from the protein-reduced thin stillage, and all or part of the thus-treated protein-reduced thin stillage is added to at least part of the spent grain.

[0034] US 2019 / 0119711 A1 describes a process for producing a highly concentrated syrup using a dry milling process. The process describes a separation process of the stillage, in which the coarse solids are ground, and the liquid is subjected to a centrifugation process using high-speed centrifuges and subsequently evaporated.

[0035] Currently, no processes are known that achieve targeted protein enrichment in the mash and, consequently, in the stillage by returning the stillage to the mashing process. Protein enrichment simplifies protein separation and increases the value of the resulting product due to the increased crude protein content. Likewise, the return of significant quantities of stillage without an additional energy-intensive treatment step in an economical production process has not been described. SUMMARY OF THE INVENTION

[0036] It is therefore the object of the invention to specifically enrich the proteins in an efficient, energy- and resource-saving fermentation process, to separate them simply and cost-effectively and to produce a protein product with higher value and improved marketability.

[0037] The object is achieved by a process for obtaining a concentrated protein-rich phase from residues of bioethanol production according to claim 1, which is characterized in that: a) milled grain is mashed before fermentation in a cold mashing process, b) the fermented mash is fed to a distillation, which produces stillage as a residue, c) the stillage from b) is fed to a solid-liquid separation, whereby spent grain is produced as the solid and thin stillage as the liquid phase, and the resulting solid is removed from the process, d) the thin stillage from c) is proportionally returned to the mashing, whereby at least 0.15 kg of thin stillage DM per kg of grain DM is returned and by returning the thin stillage to the mashing, the crude protein content is increased, whereby a pH < 4.0 is maintained throughout the process, and e) at least a portion of the liquid phase from c) thin stillage is diluted with an aqueous process liquid and fed to a further separation process, whereby the aqueous phase separated in this process, the clear phase,predominantly the dissolved dry matter and the produced concentrated phase, the concentrate, predominantly contains the protein-rich suspended dry matter.

[0038] The advantages achieved with this invention are in particular that due to the process conditions (low pH, low temperatures) the proteins are present as small particles in the thin stillage, these are enriched by the proportional return of the thin stillage to the mash, whereby the crude protein content is significantly increased and the proteins can be easily separated without the addition of chemicals and without an energy-intensive treatment step.

[0039] Advantageous further developments are mentioned in the dependent claims. The wording of all claims is incorporated into the description by reference.

[0040] In a preferred embodiment, the method according to the invention is designed such that the grain is subjected to dry grinding.

[0041] In a further preferred embodiment, the process according to the invention is designed such that the mashing is carried out per kg of grain DM preferably with at least 0.25 kg of thin stillage DM and particularly preferably with at least 0.35 kg of thin stillage DM.

[0042] In a further preferred embodiment, the process according to the invention is designed such that the crude protein content of the thin stillage is increased by at least 5% relative, and preferably by at least 10% relative, compared to the crude protein content of the grain less the starch, by the proportional return to the mashing.

[0043] In a further preferred embodiment, the process according to the invention is designed such that, due to the special procedure, ie the recycling of significant amounts of thin stillage into the mash and thus the multiple passage through the still, the predominant proportion of particles in the thin stillage has a size of less than 50 µm.

[0044] In a further preferred embodiment, the process according to the invention is designed such that the thin stillage has a dry matter content of at least 8%.

[0045] In a further preferred embodiment, the process according to the invention is designed such that non-protein-containing suspended substances are cleaved and dissolved by the targeted use of enzymes, e.g. cellulases, hemicellulases, trehalase, xylanase, amylases, lipases, phytase and / or combinations thereof.

[0046] In a further preferred embodiment, the process according to the invention is designed such that the solid-liquid separation of the stillage takes place in a filter press or in a decanter.

[0047] In a further preferred embodiment, the process according to the invention is designed such that the separation grain size in the solid-liquid separation of the stillage is in the range 150 - 500 µm, preferably 200 - 300 µm.

[0048] In a further preferred embodiment, the process according to the invention is designed such that the thin stillage is exposed to a maximum temperature of 90°C throughout the entire process.

[0049] In a further preferred embodiment, the process according to the invention is designed such that the thin stillage can be subjected to an enzymatic treatment for the cleavage of non-protein-containing suspended substances before the separation process.

[0050] In a further preferred embodiment, the process according to the invention is designed such that the proportionate dilution of the thin stillage is carried out with a suitable process liquid, such as condensate from the thin stillage evaporation.

[0051] In a further preferred embodiment, the process according to the invention is designed such that the thin stillage is diluted with a suitable process liquid in a ratio of 1:5, preferably 1:3 and particularly preferably 1:1 before separation.

[0052] In a further preferred embodiment, the process according to the invention is designed such that the feed is subjected to a pre-cleaning step before the separation step.

[0053] In a further preferred embodiment, the method according to the invention is designed such that the pre-cleaning of the inlet is carried out using a rotary brush sieve or an edge gap filter.

[0054] In a further preferred embodiment, the process according to the invention is designed such that the separation of the diluted thin stillage into clear phase and concentrate is carried out by means of a separator at at least 2800xg, preferably at least 3500xg and particularly preferably at least 5000xg.

[0055] In a further preferred embodiment, the process according to the invention is designed such that the concentrate has a crude protein content increased by at least 15% relative compared to the thin stillage.

[0056] In a further preferred embodiment, the process according to the invention is designed such that the concentrate has a crude protein content of at least 44% TS and preferably at least 48% TS.

[0057] In a further preferred embodiment, the process according to the invention is designed such that a maximum of 1 / 3 of the TS in the concentrate is present in dissolved form.

[0058] In a further preferred embodiment, the process according to the invention is designed such that the clear phase is at least partially returned to the process, e.g. into the thin stillage evaporation.

[0059] In a further preferred embodiment, the process according to the invention is designed such that the clear phase can be fed at least partially to an ultrafiltration unit in order to increase the protein yield.

[0060] In a further preferred embodiment, the process according to the invention is designed such that the concentrate is at least partially used directly as a high-quality protein feed or is fed to further treatment steps.

[0061] In a further preferred embodiment, the process according to the invention is designed such that the concentrate can be subjected to an enzymatic treatment with subsequent solid-liquid separation in order to increase the crude protein content.

[0062] The method according to the invention also relates in particular to all combinations of the preferred embodiments described above. Description of the solution

[0063] The crude protein content depends on the grain type. It is approximately 10–15% dry matter in small-grain grains such as wheat, rye, triticale, and barley, and approximately 9% dry matter in corn. Grains are essentially composed of hulls, endosperm, and germ. The proteins contained in grains are found primarily in the endosperm, which accounts for approximately 70% of the protein. This applies to wheat, rye, and corn. In small-grain grains, approximately 10% of the protein is found in the germ, whereas in corn, approximately 20% is found, since the germ is much larger. The remaining proteins are distributed among the other components.

[0064] When processing grain into bioethanol, the proteins contained in the starch are not broken down by the yeast during fermentation but are retained. Complete conversion of the starch to ethanol would result in a concentration of the crude protein content by a factor of approximately three compared to the starting material. Furthermore, the yeast cells themselves also contain and produce proteins. At the end of fermentation, or after the separation of the produced ethanol from the mash, the stillage contains both grain and yeast proteins.

[0065] Stillage typically has a dry matter content of at least 10% and a crude protein content of at least approximately 25% dry matter. The dry matter content is composed of suspended and dissolved components, which are present in approximately equal proportions.

[0066] Those skilled in the art are aware that the stillage is at least partially subjected to a solid-liquid separation process in order to evaporate or dry the thin stillage. The separated solid, often referred to as spent grain, is used either untreated or dried, primarily as cattle feed due to its high fiber content.

[0067] It is desirable to produce a competitive, protein-rich, low-fiber product from the stillage using a cost-effective, simple and efficient process, which has a higher added value due to its higher nutritional value and has a wider application.

[0068] Surprisingly, it was discovered that the recycling of significant amounts of thin stillage can be economically implemented in combination with the cold mashing process. For mashing, at least 0.15 kg, preferably at least 0.25 kg, and especially preferably at least 0.35 kg of thin stillage dry matter is recycled per kg of grain dry matter. This procedure results in ethanol contents in the fermented mash in the range of 5–8 wt%. Previously, it was known that such a high recycling rate could only be achieved in combination with jet cooking.

[0069] Furthermore, it was determined that the main potential for producing a protein-rich product lies in the thin stillage, since more than 70% of the crude protein in the stillage is contained in particles smaller than 50 µm and these particles remain in the thin stillage to at least 70% during the solid-liquid separation. Fig. 1The distribution of crude protein in the individual particle size fractions is shown using a stillage from the current process as an example. In this example, particles < 50 µm contain approximately 90% of the crude protein. The proportion of proteins separated with the spent grain is therefore low.

[0070] The combination of solid-liquid separation and high recirculation of thin stillage results in the enrichment of protein-rich particles, which significantly increases the crude protein content.

[0071] In addition, the high recirculation rate results in a significant reduction in freshwater requirements, making the process more efficient and resource-efficient. The overall freshwater requirement can be reduced to a minimum or even completely covered by partially recycling other process fluids, such as condensate from the thin stillage evaporation or liquor from distillation, back into the mashing process.

[0072] A comparison of the particle sizes of the stillage from the present process with those of stillage from an external bioethanol production plant shows that the particles in the stillage from the described process are significantly smaller (Table 1). On average, these particles are only about half the size of those in the external stillage. It is also clear that the thin stillage from the present process predominantly contains only very small particles, as 50% of the particles are ≤ 10 µm (D10). These small particle sizes are a clear indication that the special operating procedure, i.e. the recycling of significant amounts of thin stillage to the mash and thus the multiple passage through the still, reduces the particle sizes. Tab. 1 Stillage external Stillage Thin stillage Average value [µm] 485,7 260,0 37,0 D10 [µm] 10,3 6,2 4,6 D50 [µm] 412,2 60,7 10 D90 [µm] 1188,8 783,3 119,3

[0073] The invention is explained below on the basis of the extraction of a concentrated protein-rich phase from stillages from bioethanol production.

[0074] Grains such as rye, wheat, triticale, barley, corn, and / or combinations thereof are dry-milled and processed into bioethanol in an efficient, energy- and resource-saving fermentation process. The milled grain is mashed with a mixture of process liquids. If the available process liquids are insufficient and / or contain substances that interfere with fermentation, e.g., high concentrations of acetic acid, additional water is added to the mash. The mashed grain flour is digested using the cold mashing process, i.e., below the gelatinization temperature of the starch, preferably between 45°C and 66°C. These low temperatures are particularly advantageous due to the low energy requirements.

[0075] By adding enzymes in the ethanol process, such as cellulases, amylases, trehalase, phytase, hemicellulases, lipases and / or combinations thereof, non-proteinaceous substances are split and dissolved, thus converting them from the suspended to the dissolved fraction, which is then specifically separated.

[0076] A temperature of 66°C is not exceeded until distillation, and a maximum of 90°C is reached for a limited time during the further course of the process. The pH value is constantly < 4.0. Due to the low pH value, the low temperatures, and the resulting partial denaturation, the proteins are present as small particles that remain in the thin stillage during the solid-liquid separation of the stillage. This allows for targeted protein enrichment through the partial recirculation of the thin stillage. The low pH value also means that small proteins are predominantly undissolved and can therefore be separated more easily. A particular advantage of this process, due to the low temperatures, is the particularly low energy requirement.

[0077] After separating the produced ethanol from the mash, at least a portion of the stillage is subjected to a solid-liquid separation process. A decanter or filter press, for example, is used for this separation. The particle size required for this separation process is in the range of 150–500 µm, preferably 200–300 µm. The separated solids, which contain a maximum of 15% of the total crude protein, are discharged and used as feed, primarily for cattle.

[0078] The resulting thin stillage has a dry matter content of at least 8% and a crude protein content of at least 30%. The proportions of dissolved and suspended dry matter are approximately equal. At least 70% of the total crude protein in the thin stillage is contained in particles < 50 µm, and thus in the suspended dry matter.

[0079] It is particularly advantageous to carry out the mashing with a significant proportion of thin stillage, i.e. at least 0.15 kg, preferably at least 0.25 kg and particularly preferably at least 0.35 kg of thin stillage DM per kg of grain DM, which results in an enrichment of the small, protein-rich particles. After several cycles with the described thin stillage recirculation, the concentration of these particles reaches a constant value. The crude protein content of the thin stillage increases significantly by at least 5% rel. compared to the grain less the starch, i.e. compared to the crude protein content that would result after complete conversion of the starch, and is kept constant at this level with constant recirculation.

[0080] Fig. 2shows an example in which, with a constant return of 0.19 kg of thin stillage DM per kg of grain DM to the mash, the crude protein content in the thin stillage is increased by approximately 20% relative compared to the crude protein content in the grain less the starch.

[0081] Before the thin stillage is subjected to separation, an enzymatic treatment of at least a portion of the thin stillage with cellulases, hemicellulases, lipases and / or amylases or combinations thereof can be carried out in order to cleave undissolved non-proteinaceous substances and transfer them into the dissolved fraction, thereby further increasing the crude protein content of the suspended dry matter.

[0082] In a particularly efficient process, the enzymatic treatment takes place directly under the conditions (temperature, pH) existing in the thin stillage. Alternatively, the pH of the thin stillage can be adjusted to an optimal value for the enzymes by adding alkali, such as NaOH, KOH, or NH 4 HCO 3 , to ensure optimal enzyme activity. The temperature can also be adjusted to the enzymes' requirements. Simultaneous adjustment of pH and temperature is advantageous.

[0083] To obtain a protein-rich phase from at least a portion of the thin stillage, it is advantageous to dilute it with an aqueous process liquid before the separation step. This reduces the viscosity. Furthermore, the dilution reduces the dissolved dry matter content and thus the salt content, such as sulfate. An aqueous process liquid that contains virtually no dissolved dry matter is most suitable.

[0084] Such an aqueous process liquid originates, for example, from the evaporation of thin stillage, in which a thin stillage concentrate is produced from at least part of the resulting thin stillage, which has a dry matter content approximately twice as high as that of the starting material.

[0085] This process fluid is particularly advantageous because it has a similar temperature to the thin stillage itself, resulting in a temperature of approximately 50°C during dilution, which also has a positive effect on viscosity and thus on the subsequent separation. The process fluids can therefore be used energetically efficiently at their initial temperature without the need for temperature control.

[0086] The thin stillage should preferably be diluted in a ratio of 1:5, preferably 1:3, and especially preferably 1:1. In general, the more the thin stillage is diluted, the easier it is to separate the suspended protein-rich particles in the subsequent separation process. However, the proportion of thin stillage must be large enough to separate significant amounts of suspended dry matter. The dilution should therefore be chosen so that the process is economically viable.

[0087] To ensure optimal separation, the diluted thin stillage, known as the feed, should be subjected to pre-cleaning to remove any coarse particles and foreign matter that might impair the separation or contaminate the protein product. Pre-cleaning can be performed, for example, in the form of a solid-liquid separation using a coarse filter.

[0088] A separator is used to separate the feed. In this step, the suspended solids accumulate in the concentrated phase, known as the concentrate, while the dissolved solids are primarily discharged via the aqueous phase, the so-called clear phase.

[0089] One way to optimize separation is to temper the feed stream to temperatures in the range of 50°C - 90°C, which reduces viscosity and allows for a smaller particle size. The smaller the particle size, the fewer protein-rich particles are separated with the clear phase. Whether tempering above 50°C is advisable must be evaluated based on the protein yield and the required energy consumption.

[0090] Multi-stage separation is also possible and advantageous for increasing the crude protein content and reducing the salt content. For this purpose, the concentrate is diluted again after the first separation step with an aqueous process liquid, e.g., condensate from the thin stillage evaporation, and fed to a further separation stage, e.g., a separator.

[0091] Optionally, the concentrate can be treated with enzymes, e.g., cellulases, hemicellulases, lipases, and / or amylases, or combinations thereof, prior to this separation step to break down undissolved non-proteinaceous substances and convert them into the dissolved fraction. Enzymatic treatment at this stage of the process is particularly advantageous because, due to the lower flow rates, less enzyme is required, and any necessary retention tanks can be smaller.

[0092] In the clear phase, the dissolved dry matter content accounts for at least two-thirds of the total dry matter content. The concentrate has a dissolved dry matter content of a maximum of one-third of the total dry matter content, and the crude protein content is at least 15% relative higher than in the thin stillage.

[0093] To increase the efficiency of the entire process and the protein yield, it is advantageous to feed at least a portion of the clear phase to an ultrafiltration unit to recover any remaining proteins. The resulting permeate can be recycled to the thin stillage evaporation stage.

[0094] Alternatively, the clear phase can be evaporated or added to the thin stillage evaporation. The resulting condensate can be returned to the mashing stage and / or used to dilute the thin stillage or the concentrate in multi-stage separation. Direct return of the clear phase to the mashing stage is not advisable to avoid enrichment of the non-protein-containing dissolved dry matter.

[0095] The protein-rich concentrate can be used directly as a high-quality protein feed or can be subjected to subsequent treatment steps for further concentration, such as evaporation or spray drying. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0096] FIG. 1 shows the distribution of the crude protein in the individual particle size fractions using the example of stillage from the present process. FIG. 2 shows an example of standardized crude protein contents of grain less starch and of a thin stillage at a constant recycle of 0.19 kg thin stillage-dry matter / kg grain-dry matter (standardized to crude protein content of grain less starch). FIG. 3 shows a flow diagram of a possible embodiment according to the invention. 4 shows a flow diagram of a possible embodiment according to the invention in the form of a two-stage separation DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS EXAMPLE 1

[0097] The possibility of a technical implementation of the process is illustrated below by the extraction of a concentrated protein-rich phase from triticale-rye thin stillage ( Fig. 3 ).

[0098] A triticale-rye mixture contains the following ingredients: Tab. 2 dry matter 85% OS Strength 67%TS crude protein 11%TS OS - original substance

[0099] If the starch is fully converted, the crude protein content would be 34% TS.

[0100] Before fermentation, a triticale-rye mixture is dry-milled and mashed with 0.24 kg of thin stillage DM per kg of grain DM and water in a ratio of 1:4.0, i.e., one part grain to four parts liquid. Enzymatic digestion of the mash takes place at approximately 47°C. Fermentation is initiated by adding yeast, which lasts approximately 60 hours. The ethanol produced is then separated from the fermented mash in a distillation process.

[0101] The resulting stillage is fed to a solid-liquid separation process in a decanter at a mass flow rate of approximately 71 t / h. The decanter's particle size is approximately 250 µm. All particles larger than 390 µm are completely removed in this step and contain 5% of the crude protein originally present in the stillage. Approximately 76% of the protein-rich particles < 50 µm remain in the thin stillage. The mass flow rate of the separated solids that is discharged is approximately 7 t / h, and the thin stillage mass flow rate is approximately 64 t / h.

[0102] The thin stillage has a dry matter content of approximately 13%, of which approximately half is in suspended and half in dissolved form. The average particle size is 38 µm, with three-quarters of the particles smaller than 20 µm. Particles < 20 µm contain approximately 90% of the crude protein.

[0103] A thin stillage mass flow of 31 t / h is returned to the mashing (in Fig. 3shown in dashed lines), 19 t / h go into the evaporation. The remaining thin stillage is led into a collecting tank and from there into a stirred tank, into which the condensate from the thin stillage evaporation is simultaneously led (in Fig. 3 shown dashed). The thin stillage and the condensate are mixed in a ratio of 1:1.

[0104] The diluted stillage, referred to as the feed, has a temperature of 50°C and is first pre-cleaned in a rotary brush screen to remove coarse particles and impurities. The screen gap width is 0.4 mm.

[0105] At a mass flow rate of 12 t / h, the pre-cleaned feed is fed to the nozzle separator. This contains 12 nozzles arranged on the underside of the drum and each having a diameter of 0.7 mm. The feed is separated in the separator at approximately 5500 x g, with the clear phase flowing out via the grab in the upper section. The solids collect at the edge and are discharged through the nozzles on the underside, which limit the concentrate flow and thus ensure enrichment.

[0106] Table 3 compares the mass flow, dry matter content, and crude protein contents of the individual jet separator streams. The crude protein content of the concentrate demonstrates that the protein-rich particles could be successfully enriched under the stated process conditions. The crude protein yield in this example is 47%. Tab. 3 Inflow Clear phase concentrate mass flow [t / h] 12,0 9,8 2,2 Dry matter content [Ma%] 6,2 4,6 13,3 Crude protein content [%TS] 41 36 50

[0107] The separated clear phase is returned to the evaporation stage (in Fig. 3 (shown dashed) and the resulting condensate is then used as a dilution medium for the thin stillage. The resulting protein-rich concentrate is collected and used either directly or after evaporation or spray drying as a high-quality protein feed.

[0108] Compared to feed currently available on the market that was produced from residues of bioethanol production (Table 4), the concentrate has a significantly higher value due to the significantly increased crude protein content. Tab. 4 TS [%TS] Crude protein content [% DM] ProtiGrain ®(1)< 90 29 Wheat / barley stillage (2)< 90 38 Press stillage (3)< 34,5 27 GrainPro (4)< 27 37 (1) HTTP: / / WWW.CROPENERGIES.COM / DE / DOWNLOADS / BROSCHUEREN / BROSCHUEREN-DATEIEN / DATENBLATT_PROTIGRAIN / DATENBLATTPROTIGRAIN_JULI_2016.PDf (ACCESSED 13.03.19) (2) HTTPS: / / WWW.LFL.BAYERN.DE / MAM / CMS07 / ITE / DATEIEN / TROCKENSCHLEMPE_MERKBLATT.PDF (ACCESSED 13.03.19) (3) HTTP: / / FUTTERMITTEL-GETREIDETECHNIK.DE / PAGES / PRODUKTE / PRESS-SCHLEMPE.PHP (ACCESSED 13.03.19) (4) HTTP: / / FUTTERMITTEL-GETREIDETECHNIK.DE / PAGES / PRODUKTE / PRESS-SCHLEMPE.PHP (ACCESSED 13.03.19) EXAMPLE 2

[0109] Another possible technical implementation of the process is illustrated below by the extraction of a concentrated protein-rich phase by a two-stage separation in a jet separator ( Fig. 4 ).

[0110] Thin stillage from the ethanol process is mixed in a stirred tank with condensate from the thin stillage evaporation in a ratio of 1:1. This stream, referred to as feed 1, is fed to the nozzle separator at a mass flow rate of 10.8 t / h and separated at approximately 5500xg into 8.4 t / h of clear phase 1 and 2.4 t / h of concentrate 1.

[0111] The relevant measured values ​​of the streams of the first separation stage are listed in Table 5. The yield of crude protein is 50%. Tab. 5 Inlet 1 Clear phase 1 Concentrate 1 mass flow [t / h] 10,8 8,4 2,4 Dry matter content [Ma%] 8,0 6,2 14,3 Crude protein content [%TS] 41 34 52

[0112] Concentrate 1 is initially collected in a storage tank, as a minimum feed to the nozzle separator is required for the second separation step. Once the tank is full, concentrate 1 is fed into a stirred tank where it is diluted with condensate from the thin stillage evaporation in a 1:1 ratio. This stream, referred to as feed 2, is fed to the nozzle separator at a mass flow rate of 10.8 t / h and separated at approximately 5500xg into 8.4 t / h of clear phase 2 and 2.4 t / h of concentrate 2.

[0113] The relevant measured values ​​of the streams of the second separation stage are listed in Table 6. The yield of crude protein in the second separation stage is 62%. Tab. 6 Inlet 2 Clear phase 2 Concentrate 2 mass flow [t / h] 10,8 8,4 2,4 Dry matter content [Ma%] 6,8 3,7 17,4 Crude protein content [%TS] 53 47 58

[0114] The crude protein content in Concentrate 2 demonstrates that a two-stage separation results in a significant improvement in the protein product. The overall crude protein yield from a two-stage separation in this example is 31%. EXAMPLE 3

[0115] Another possibility of implementing the process on a laboratory scale is illustrated below by the production of a concentrated protein-rich phase starting from a concentrate produced according to Example 1 and subsequently treated enzymatically.

[0116] The concentrate used has a dry matter content of 13.7% and a crude protein content of 48% dry matter.

[0117] For the enzymatic treatment, 250g of the concentrate is weighed into a 500ml fermentation flask. A preparation with cellulase, hemicellulase, and xylanase activity is used as the enzyme at a dosage of 0.1% dry matter. In the reference batch, no enzyme is added to the concentrate. The fermentation flasks are sealed with a fermentation tube and incubated in a shaker at 150 rpm and 33°C for 72 hours.

[0118] After the incubation period, 100g of the treated material (from the flask with enzyme or from the flask without enzyme) is mixed with 100g of tap water, previously tempered to 33°C, and then centrifuged at 4770xg for 15 min. The crude protein content of both pellets is determined.

[0119] For comparison, the concentrate used as starting material for the experiments was tempered to 33°C and diluted 1:1 with tap water as described above. The resulting pellet was centrifuged for 15 minutes at 4770xg.

[0120] The dry matter and crude protein contents of the pellets are summarized in Table 7. Tab. 7 Pellet from concentrate Pellet from treatment without enzyme Pellet from treatment with enzyme Dry matter content [Ma%] 25,0 25,2 24,4 Crude protein content [%TS] 56 56 61

[0121] Enzymatic treatment significantly increases the crude protein content in the pellet. The dry matter content decreases because the enzymes break down undissolved non-protein substances and dissolve them, which remain in the supernatant after centrifugation.

Claims

1. A method for obtaining a concentrated protein-rich phase from waste products of bioethanol production, characterised in that: a) a ground cereal is mashed in a cold mashing process before fermentation; b) the fermented mash is fed to a distillation process, which produces thick stillage as waste product; c) the thick stillage from b) is fed to a solid-liquid separation, wherein spent grains are produced as the solid and thin stillage is produced as the liquid phase, and the resulting solid is discharged from the method; d) the thin stillage is partially returned to the mashing process, with at least 0.15 kg thin stillage DM per kg of cereal DM being returned and the raw protein content of the thin stillage being increased by recirculating the thin stillage to the mashing process, wherein a pH value < 4.0 is maintained throughout the method; and e) at least part of the thin stillage is diluted with an aqueous process liquid and fed to a further separation process, wherein the aqueous phase separated in this further separation process, the clear phase, containing predominantly the dissolved dry matter, and wherein the concentrated protein-rich phase produced in this further separation process, the concentrate, containing predominantly protein-rich suspended dry matter.

2. The method according to claim 1, characterised in that the mashing process is carried out with at least 0.25 kg thin stillage DM per kg of cereal DM and particularly preferably with at least 0.35 kg thin stillage DM per kg of cereal DM.

3. The method according to any one of the preceding claims, characterised in that the solid-liquid separation of the thick stillage takes place in a filter press or in a decanter.

4. The method according to any one of the preceding claims, characterised in that, by the partial recirculation to the mashing process, the raw protein content of the thin stillage is increased by at least 5%rel. and preferably by at least 10%rel. compared to the raw protein content of the cereal less starch.

5. The method according to any one of the preceding claims, characterised in that the partial dilution of the thin stillage is carried out with a suitable process liquid, such as condensate from the thin stillage evaporation.

6. The method according to any one of the preceding claims, characterised in that the thin stillage is diluted with a suitable process liquid in a ratio of 1:5, preferably 1:3 and particularly preferably 1:1 before separation.

7. The method according to any one of the preceding claims, characterised in that the further separation of the diluted thin stillage into the clear phase and the concentrate is performed with the aid of a separator and takes place at least at 2800xg, preferably at least 3500xg and particularly preferably at least 5000xg.

8. The method according to any one of the preceding claims, characterised in that, by a targeted use of enzymes selected from the group of cellulases, hemicellulases, trehalases, xylanases, amylases, lipases, phytases and / or combinations thereof, non-protein-containing suspended substances are cleaved and dissolved.

9. The method according to any one of the preceding claims, characterised in that the concentrate has a raw protein content increased by at least 15%rel. compared to the thin stillage.

10. The method according to any one of the preceding claims, characterised in that the concentrate has a raw protein content of at least 44%DM and preferably at least 48%DM.

11. The method according to any one of the preceding claims, characterised in that the clear phase is at least partially returned to the process, for example to the thin stillage evaporation.

12. The method according to any one of the preceding claims, characterised in that the concentrate is at least partially used directly as a high-quality protein feed or is fed to further treatment steps.