EP0131563A1 - Method for hydrolyzing starch to produce a saccharified mash - Google Patents

Abstract

In this process, starchy raw materials are brought into contact with liquefaction enzymes or with acid above the gelatinization temperature of the starch at atmospheric pressure and the digested mixtures are saccharified after cooling with the addition of a saccharification enzyme. In order to avoid pretreatment and cleaning of the crushed raw materials as well as long heating and dwell times and to achieve complete starch digestion with a correspondingly lower energy requirement, it is provided that - as starchy raw materials crushed cereals, such as crushed corn, are used, - these crushed cereals be stirred into an aqueous receiver liquid kept at a temperature of 85 to 100 ° C, preferably 90 to 95 ° C, in a digestion vessel, acid being added before stirring or the liquefaction enzyme - especially amylase - is added during stirring . - And the resulting digested mixture is cooled to 60 to 65 ° C. in the digestion vessel without dwell time and is fed to the saccharification stage.

Description

The invention relates to a process for the digestion of starch for the production of saccharified mash, in which starchy raw materials are brought into contact with liquefaction enzymes or with acid above the gelatinization temperature of the starch at atmospheric pressure and the digested mixtures are saccharified after cooling with the addition of a saccharification enzyme.

Various methods of starch digestion are currently in use. However, they often have disadvantages, in particular the starch is either not fully digested or they require a large amount of energy.

All of these processes have in common that retention times for mashing, digestion or liquefaction must be observed during the implementation.

DE-A-20 18 031 describes a two-stage process in which starch is gelatinized at temperatures between 85 to 170 ° C. in the first stage (A). Up to 100 ° C this step can be carried out in the presence of CU amylase. The known process primarily uses so-called "sticky starches", i.e. starches with a high content of amylopectin. If so-called "above-ground starches" such as corn starch are used, larger amounts of enzyme must be used and after liquefaction, heating to 130 ° C. is necessary.

According to DE-A-20 18 031, however, it is necessary for all embodiments to use suspensions of thoroughly cleaned starches as starting products, which are gradually heated. The gelatinization is preferably carried out under pressure, even in the presence of cx-amylase, with residence times of 20 min and longer being provided. The necessary cleaning of the starches before they are digested is associated with losses and increased energy expenditure. The application of pressure and compliance with heating up and dwell times also affect the economics of the process. In the second stage (B) according to DE-A-20 18 031, the bonds of the branched parts of the amylopectin molecules are selectively cleaved with cx-1,6-glucosidases.

The present invention has for its object to provide a process for digesting starchy cereals, in which process can be carried out without pretreatment of the comminuted raw materials and without observing the abovementioned residence times and accordingly with considerably less energy expenditure, but a complete starch digestion is nevertheless achieved .

• - als stärkehältige Rohstoffe zerkleinerte Körnerfrüchte, wie zerkleinerter Mais, eingesetzt werden,
• - diese zerkleinerten Körnerfrüchte in eine auf einer Temperatur von 85 bis 100°C, vorzugsweise 90 bis 95°C, gehaltene, in einem Aufschlußgefäß befindliche, wässerige Vorlageflüssigkeit eingerührt werden, wobei vor dem Einrühren Säure oder während des Einrührens das Verflüssigungsenzym - insbesondere Amylase - zu- gegeben wird
• - und die erhaltene aufgeschlossene Mischung ohne Verweilzeit im Aufschlußgefäß auf 60 bis 65°C abgekühlt und der Verzuckerungsstufe zugeleitet wird.

This object is achieved according to the invention in a method of the type defined in the introduction by

• - crushed grains, such as crushed corn, are used as starchy raw materials,
• - These crushed cereals are stirred into an aqueous stock liquid, which is kept at a temperature of 85 to 100 ° C., preferably 90 to 95 ° C., in a digestion vessel, acid being added before stirring or the liquefying enzyme - especially amylase - during stirring. is added
• - And the digested mixture obtained without Ver cooled down to 60 to 65 ° C in the digestion vessel and passed on to the saccharification stage.

The surprising effect, namely the complete saving of the usual digestion or liquefaction dwell times, is probably achieved by the fact that, as a result of the high mashing temperature (between 90 and 95 ° C) immediately reached, a considerably more intensive and faster gelatinization of the starch granules, i.e. Dissolution of the grain structure takes place and therefore the added thermostable oc-amylase or the added acid can liquefy the starch much faster.

Up until recently, the starch digestion was almost exclusively based on various high-pressure steaming. procedure, using temperatures between 150 and 160 ° C and pressures of 5 to 6 bar.

In addition to the inefficiency of these processes resulting from constantly increasing energy costs, caramel substances and melanoidines also result from the Maillard reaction, which reduces the yield.

When starch is digested in pressure in the known hen damper, about 250 to 300 kg of steam / hl of alcohol, which is obtained by fermenting the digested saccharified starch, are required. According to the further customary continuous high-pressure process, a steam consumption of about 150 to 200 kg must be expected per hl of alcohol.

The long-known so-called cold mashing process, which is carried out without pressure at temperatures below 65 ° C, is particularly suitable for cereals with a natural amylase content, such as wheat and rye. It is hardly carried out today - especially because of the risk of infection due to the low temperature. In addition, the degree of disintegration of starch that can be achieved with this is usually unsatisfactory.

The process according to the invention avoids side reactions which, inter alia, lead to the aforementioned caramelization, which has an advantageous effect on the yield, in particular when the sugars are subsequently fermented to alcohol. The expenditure on equipment for carrying out the method is very low, in many cases it can be found to be sufficient with existing, slightly modified plants.

Thermostable a-amylases, which can expediently be used for the process according to the invention, are easily accessible, are available in large quantities and are commercially available at any time.

When using acid as a disintegrant, the pH can preferably be adjusted to 1.5 to 3.5, preferably to 1.5 to 2.5, and when using liquefying enzyme as disintegrant to a value from 4.0 to 8, 0, preferably 6.0 to 7.0.

In the case of a batch or semi-continuous process, the comminuted cereals are expediently added within 5 to 20 minutes, preferably within 10 to 15 minutes.

According to an advantageous embodiment of the process according to the invention, at least some of the stillage from the distillative work-up of the saccharified mash subjected to alcoholic fermentation is used without cooling, optionally after separation of solids. Since the stillage without this occurs at high temperature, in this case you save a large part of the heat that is otherwise required to heat up the supply liquid.

According to a further preferred embodiment, the digestion and the saccharification stage are carried out continuously.

The invention is explained in more detail using a system diagram shown in the drawing and by the following examples.

The cereals are crushed in a mill 1 and temporarily stored in a storage container 2. From this container 2, the shredded cereals reach the digestion vessel 4 via a dosing screw 3, which is equipped with a stirring element 5 and with a feed line 6 for enzyme solution and is connected via a line 7 to a mixing vessel 8. In the mixing vessel 8, water from feed line 9 or recirculated stillage from line 10 is prepared by ^admixing Ca ^{2 +} ions from line 11, alkali from line 12 or acid from line 13 or adjusted to the desired pH. The aqueous feed liquid obtained in this way is, if necessary, brought to the desired process temperature by introducing live steam from line 14 and drawn off via line 7 into the digestion vessel 4. A further steam supply line 15 for keeping constant the temperature during the digestion process, leading to the _A ufschlußgefäß 4. The digested mixture by opening a shut-off member 16 from the outlet at the conical bottom of the vessel 4 by means of a. Pump 17 is pumped via a first heat exchanger 18 into a saccharification tank 19. In the heat exchanger 18 can be used for the original liquid water preheated and introduced into the mixing vessel 8 via the feed line 9. Feeds for enzyme 6 ', for acid 12' and for alkali 13 'in the case of acid digestion again lead into the saccharification tank. A stirring element 5 'is also provided in the tank. The saccharified mash by means of a second pump 20 via a second heat exchanger 21 by setting the desired concentration with water mash or slurry to an unillustrated Gärstation ^g eför- changed from the tank 19th In the Schlempeleitung 10 is a Absetzvorrich- do 22 ^g (eg decanter) for the optionally contained in the stillage solid residues incorporated. After decantation, the aqueous supernatant reaches the mixing vessel 8.

Example 1: 2500 to 3000 l of water or decanted stillage with a temperature between 90 and 95 ° C. are introduced. This aqueous ^{receiving liquid} is previously ^adjusted in the mixing vessel 8 by ^adding base (OH ^⊖ ions) to a pH value between 6 and 7 and ^mixed with Ca ^2⊕ ions up to a content of 50 to 70 ppm. 1 t of ground maize is stirred in over the course of about 10 minutes, the digestion mixture being kept between the specified temperature limits by introducing live steam from line 15. After stirring in about 20 to 30% of the total amount of ground maize, thermostable α-amylase is added. Immediately after the addition of maize has ended, the digested mixture is passed into the saccharification tank 19 while flowing through the first heat exchanger 18, the mixture cooling to about 60 ^° C. The pH of the mixture now in the saccharification tank is adjusted to 4.5 to 5.0 by adding acid and then amyloglucosidase is added. After a dwell time of at least 30 minutes, the partially saccharified mash is transported to the fermentation station changes, where it cools in the second heat exchanger 21 to about 30 ° C. After setting the desired mash concentration with water or stillage, the saccharified mash is then mixed with yeast mash in the fermentation tank. The cooling water preheated in the heat exchangers 18 and 21 from an initial temperature of approximately 15 ° C to approximately 80 ° C is either fed directly to the mixing vessel 8 for the production of the original liquid or - if mainly decanted thin slurry is used after the preparation as the original liquid - as process water in the company or used for space heating.

Example 2: The procedure is analogous to Example 1, but the aqueous initial liquid is adjusted to a pH value between 1.5 and 2.5 in the mixing vessel 8 by adding acid and heated to 95 ° C. by means of superheated steam. No enzyme is added in the digestion vessel. The pH value in the saccharification tank is adjusted by adding lye.

• Gemahlener Mais wird aus dem Vorratsbehälter 2 über die Dosierschnecke 3 gleichzeitig mit heißer Vorlageflüssigkeit, welche zuvor im Mischgefäß 8 auf 90 bis 95°C aufgeheizt wurde, mit Base (OH^⊖-Ionen) auf pH 6 bis 7 eingestellt wurde und etwa 50 bis 70 ppm Ca^2⊕-Ionen enthält, in einem Mengenverhältnis von 1 Teil Maisschrot zu etwa 2,5 bis 3 Teilen Vorlageflüssigkeit in das Aufschlußgefäß 4 geleitet. Die vorbestimmte Menge an thermostabiler α-Amylase wird kontinuierlich in das Aufschlußgefäß zudosiert. Die Aufschlußmischung wird unter ständigem Rühren durch Frischdampfzufuhr auf 90 bis 95°C gehalten und gleichzeitig über den Auslaß am Boden des Gefäßes abgezogen. Die auf etwa 60°C abgekühlte Maische wird am Kopf des Verzuckerungstankes 19 gleichzeitig mit der zur Einstellung des pH-Wertes der Mischung auf 4,5 bis 5,0 benötigten Menge an Säure sowie mit dem Verzuckerungsenzym (Amyloglucosidase) aufgegeben. Es wird eine Verweilzeit von mindestens 30 min zur Teilverzuckerung der Maische vorgesehen. Die teilverzuckerte Maische wird kontinuierlich abgezogen, auf ca. 30°C abgekühlt und nach Einstellung der gewünschten Maischekonzentration mit Wasser bzw. Schlempe weiter zur Gärstation zwecks kontinuierlicher Vergärung geleitet. Der Einsatz von in den Wärmeaustauschern vorgewärmtem Wasser sowie von dekantierter Schlempe erfolgt wie beim in den Beispielen 1 und 2 beschriebenen diskontinuierlichen Verfahren.

Example 3: Continuous implementation of the method according to the invention:

• Ground maize is adjusted from the storage container 2 via the metering screw 3 at the same time with hot feed liquid, which was previously heated to 90 to 95 ° C in the mixing vessel 8, with base (OH ^⊖ ions) to pH 6 to 7 and about 50 to 70 ^Contains ppm Ca ^2⊕ ions, in a ratio of 1 part of ^{corn meal} to about 2.5 to 3 parts of ^{feed liquid} into the digestion vessel 4. The predetermined amount of thermostable α-amylase is continuously metered into the digestion vessel. The digestion mixture is kept at 90 to 95 ° C. with constant stirring by supplying fresh steam and, at the same time, is drawn off via the outlet at the bottom of the vessel. The mash cooled to about 60 ° C is added to the top of the saccharification tank 19 simultaneously with the amount of acid required to adjust the pH of the mixture to 4.5 to 5.0 and with the saccharification enzyme (amyloglucosidase). A dwell time of at least 30 minutes is provided for the partial saccharification of the mash. The partially saccharified mash is drawn off continuously, cooled to approx. 30 ° C and, after setting the desired mash concentration with water or stillage, is passed on to the fermentation station for the purpose of continuous fermentation. The use of water preheated in the heat exchangers and of decanted stillage is carried out as in the batch process described in Examples 1 and 2.

Example 4: The procedure is as in Example 3, with the difference that the initial liquid is adjusted to a pH between 1.5 and 2.5 and no enzyme is added to the contents of the digestion container. Instead of acid, lye (OH ^⊖ ions) is continuously fed to the saccharification tank in order to set a pH of 4.5 to 5.0.

Semi-continuous process control is also possible according to the invention if, for example, two digestion vessels are provided instead of one vessel 4 according to the drawing. While the digestion takes place in the first vessel, material which has already been digested can be withdrawn from the second vessel.

Fortsetzung der Tabelle

In der ganz linken Spalte der Tabelle ist die Art des jeweils angewendeten Aufschlußverfahrens angegeben, es bedeuten:

• D₀: kontinuierliches Druckverfahren
• D_W: kontinuierliches Druckverfahren mit Wärmerückgewinnung
• D_G: diskontinuierlicher Druckaufschluß
• K_O: Kochverfahren
• K_A: Kaltmaischverfahren
• H_O: erfindungsgemäßes Verfahren mit Verflüssigungsenzym als Aufschlußmittel
• H_A: erfindungsgemäßes Verfahren mit Säure als Aufschlußmittel
• H_S: erfindungsgemäßes Verfahren mit Verflüssigungsenzym als Aufschlußmittel und Schlemperückführung

The following table summarizes the results of comparative tests, based on 1 t, of starch in comminuted maize kernels (grain size less than 0.8 mm). The amount of alcohol obtained in the individual experiments from 1 t starch and the amounts of NaOH, conc. H ₂ SO _4, α-amylase and amyloglucosidase (A _M G) are give ^e-ix. Furthermore, the dextrose equivalent or the degree of saccharification DE - ie the amount of fermentable monosaccharides present in the saccharified mash, based on the amount of anhydroglucose units theoretically present in the starch used - is given. The α-amylase was used as an aqueous solution with 210,000 MWU / ml (modified Wohlgemut units), the AMG as an aqueous solution with 150 GAU / ml (glucosidase activity units).

Continuation of the table

The leftmost column of the table shows the type of digestion process used, meaning:

• D ₀ : continuous printing process
• D _W : continuous printing process with heat recovery
• D _G : discontinuous pressure digestion
• K _O : Cooking process
• K _A : Cold mashing process
• H _O : Process according to the invention with liquefaction enzyme as a disintegrant
• H _A : Process according to the invention with acid as a disintegrant
• H _S : Process according to the invention with liquefaction enzyme as a disintegrant and sludge return

When using the continuous high-pressure steaming process (D _O ), in addition to high energy requirements, difficulties also arise due to gelatinization of the starch, particularly in the tests with heat recovery (D _W ), which have repeatedly blocked the system.

When using the pressure-free cooking process (K _O ), according to which the digestion mixture is heated from 60 ° C (di below the gelatinization temperature) to about 90 ° C, a lower degree of saccharification is achieved, which also means that the alcohol yield is lower. As expected, even worse results were achieved with the cold mashing process (K _A ) already mentioned at the beginning of the prior art.

The experiments H _{O 12} to H _{O 17} were carried out - as can be seen from the table - with a smaller amount of α-amylase. It can be seen that a reduced enzyme input between 0.138 and 0.58 l of α-amylase Solution per t starch does not lead to a significant reduction in the alcohol yield. When using only 0.0275 1 enzyme solution, the digestion is apparently not sufficiently complete.

In experiments H _{S 1} to H _{S 6} , decanted stillage was used as the original liquid. The stillage came from the previous experiment, it was processed and used again in the following experiment. This process was repeated 6 times, ie the stillage from experiment 1 was used as the original liquid for experiment 2, the stillage resulting from experiment 2 was used for experiment 3 and so on. As the results obtained show, no negative influence on the fermentation control can be observed. The dry matter content of the stillage varied between 1 and 12.5% in the tests.

• Zur Erzeugung von 1 hl Alkohol benötigt man etwa 250 bis 260 kg gemahlenen Mais mit einem Stärkegehalt von etwa 60 bis 63 %. Um diese Menge an gemahlenem Mais von 20° C auf 95° C zu erwärmen (Δt = 75° C), benötigt man 33 bis 34 MJ Wärmeenergie, was einer Dampfmenge von 15 bis 15,5 kg entspricht.
  • A) Wird Wasser als Vorlageflüssigkeit eingesetzt, benötigt man für die angegebene Maismenge 0,6 bis 0,75 m³. Unter der Annahme, daß das Wasser von einer Ausgangstemperatur von 15° C im ersten Wärmeaustauscher auf 45° C und im zweiten Wärmeaustauscher auf 80° C vorerhitzt wird, müssen dieser Wassermenge noch 38 bis 47 MJ zugeführt werden, um sie auf eine Temperatur von 95° C zu bringen (dt = 15° C). Diese Wärmemenge wird durch Zufuhr von weiteren 17 bis 21 kg Dampf aufgebracht. Insgesamt werden somit 73 bis 82 MJ (≙ 32 bis 36,5 kg Dampf) zur Herstellung von 1 hl Alkohol benötigt.
  • B) Setzt man 0,6 bis 0,75 m³ dekantierte Schlempe, welche mit einer Temperatur von 80 bis 90° C anfällt, als Vorlageflüssigkeit ein, ergibt sich zum Aufwärmen von einer mittleren Temperatur von 85° C auf 95° C (dt = 10° C) ein Energiebedarf von nur 25 bis 31 MJ (entsprechend 11 bis 14 kg Dampf). Dabei wird noch nicht in Rechnung gestellt, daß die zum Erhitzen der Schlempe nötige Energiemenge infolge des Trockensubstanzgehaltes der Schlempe sogar geringer ist als die zum Erhitzen der gleichen Menge Wassers notwendige. Es werden somit insgesamt nur 59 bis 66 MJ, d. h. 26 bis 29,5 kg Dampf pro hl Alkohol benötigt.

The energy expenditure for the digestion process according to the invention, including the fermentation to produce 1 hl alcohol from corn, was calculated as follows:

• About 250 to 260 kg of ground corn with a starch content of about 60 to 63% are required to produce 1 hl of alcohol. To heat this amount of ground maize from 20 ° C to 95 ° C (Δt = 75 ° C), you need 33 to 34 MJ thermal energy, which corresponds to a steam amount of 15 to 15.5 kg.
  • A) If water is used as the reference liquid, you need 0.6 to 0.75 m ³ for the specified amount of corn. Assuming that the water is preheated from an initial temperature of 15 ° C in the first heat exchanger to 45 ° C and in the second heat exchanger to 80 ° C, this amount of water still needs 38 up to 47 MJ to be brought to a temperature of 95 ° C (dt = 15 ° C). This amount of heat is applied by adding a further 17 to 21 kg of steam. In total, 73 to 82 MJ (≙ 32 to 36.5 kg of steam) are required to produce 1 hl of alcohol.
  • B) If 0.6 to 0.75 m ^{3 of} decanted stillage, which is obtained at a temperature of 80 to 90 ° C, is used as the receiving liquid, the result is a warm-up from an average temperature of 85 ° C to 95 ° C (German = 10 ° C) an energy requirement of only 25 to 31 MJ (corresponding to 11 to 14 kg of steam). It is not yet taken into account that the amount of energy required to heat the stillage is even less than that required to heat the same amount of water due to the dry matter content of the stillage. A total of only 59 to 66 MJ, ie 26 to 29.5 kg of steam per hl of alcohol are required.

A comparison of these values with the corresponding data given at the beginning for the known printing methods shows the great superiority of the method according to the invention also with regard to the energy balance.

Claims (3)

1. A process for the digestion of starch for the production of saccharified mash, in which starchy raw materials are brought into contact with liquefaction enzymes or with acid above the gelatinization temperature of the starch at atmospheric pressure and the digested mixtures are saccharified after cooling with the addition of a saccharification enzyme, characterized in that - crushed grains, such as crushed corn, are used as starchy raw materials, - These crushed cereals are stirred into an aqueous stock liquid, which is kept at a temperature of 85 to 100 ° C., preferably 90 to 95 ° C., in a digestion vessel, acid being added before stirring or the liquefying enzyme - especially amylase - during stirring. is added - And the resulting digested mixture is cooled to 60 to 65 ° C. without dwell time in the digestion vessel and fed to the saccharification stage. 2. The method according to claim 1, characterized in that at least some of the stillage from the distillative work-up of the subject to alcoholic fermentation of the saccharified mash - optionally after separation of solids - is used without cooling. 3. The method according to one or both of claims l and 2, characterized in that the digestion and the saccharification stage are carried out continuously.

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