BR102020009107A2 - INTEGRATED SYSTEM FOR ETHANOL PRODUCTION BY EXTRACTIVE FERMENTATION WITH GASEOUS DRAG AND RECOVERY BY ABSORPTION AND USE OF THE SAME - Google Patents

Abstract

integrated system for ethanol production through extractive fermentation with gas entrainment and recovery through absorption and use. This document belongs to the field of chemical and biochemical engineering. The invention proposes an integrated system for producing ethanol by extractive fermentation, in which ethanol is extracted by gaseous drag with inert gas, preferably CO2, in a pneumatic bioreactor, bubble column or airlift type, and recovered in an absorption unit with absorbers configured in series. The system operates in a closed circuit with recirculation of the CO2 produced in the alcoholic fermentation itself. the application of the proposed system during the fermentation process provides significant gains in relation to the conventional alcoholic fermentation process, allowing the complete conversion of more concentrated musts into substrate with a consequent increase in total ethanol production, as well as a substantial reduction in the volume of vinasse generated . the technique can also be used in the extraction and recovery of ethanol from yeast wines obtained after separating the yeast from the fermented broth or any other hydroalcoholic solution, as well as the extraction and recovery of other volatile compounds present in fermentation broths or in mixtures of liquids with different volatilities.

Description

INTEGRATED SYSTEM FOR ETHANOL PRODUCTION BY EXTRACTIVE FERMENTATION WITH GASEOUS DRAG AND RECOVERY BY ABSORPTION AND USE OF THE SAME FIELD OF INVENTION

[001] This document belongs to the field of chemical and biochemical engineering. The invention proposes an integrated system for ethanol production by extractive fermentation, in which ethanol is extracted by gaseing with an inert gas, preferably CO2, in a pneumatic bubble column or airlift type bioreactor and recovered in an absorption unit with absorbers configured in series.

[002] The system operates in a closed circuit with recirculation of inert gas produced in alcoholic fermentation itself. The application of the proposed system during the fermentation process provides significant gains compared to the conventional alcoholic fermentation process, allowing the complete conversion of more concentrated musts into substrate with a consequent increase in total ethanol production, as well as a reduction in the volume of vinasse generated.

[003] The technique can also be used in the extraction and recovery of ethanol from spoiled wines obtained after the separation of yeasts from the fermented broth or any other hydroalcoholic solution, as well as in the extraction and recovery of other volatile compounds present in fermentation broths or in mixtures of liquids with different volatilities.

DESCRIPTION OF TECHNICAL STATUS

[004] Ethanol is the most consumed biofuel worldwide (BAEYENS et al., 2015). In 2019, the world production of ethanol was 110 billion liters, with Brazil being the second largest producer (30% of the total), only behind the United States (RENEWABLE FUELS ASSOCIATION, 2019). The ethanol industry in Brazil was based on the National Alcohol Program (Proálcool), created in the 1970s. Since then, government programs to encourage the production and consumption of ethanol and the emergence of the flexfuel car have led to the consolidation of the sector ( AMORIM et al., 2011). Currently, with the National Biofuel Policy (RenovaBio), which aims to encourage the increased participation of biofuels in the country's energy matrix, the trend is for the sector to grow and strengthen even more (ANP, 2019).

[005] Ethanol production in Brazil takes place via fermentation using sugarcane as a raw material. The process is based on the fermentation of concentrated sugarcane juice musts or molasses diluted with water or sugarcane juice, and uses the yeast Saccharomyces cerevisiae. The sugar composition of the wort is mostly sucrose and amounts of free glucose and fructose. Sugars, including free and potential fructose and glucose resulting from sucrose hydrolysis, are called total reducing sugars (ART), a process variable of great importance in distilleries, from which ethanol is generated (PEREIRA et al., 2018 ).

[006] The industrial process is conducted in fed-batch or continuous modes, being the first used by most Brazilian distilleries (85%) (GODOY et al., 2008). In both cases, the yeasts are recycled in the process, a procedure repeated several times throughout the harvest (Melle-Boinot process). In fed-batch fermentation, the process is started by feeding the must to a yeast suspension, called “cube foot”, corresponding to 10-30% of the final working volume of the fermentation vessel. The concentration of ART in the must can vary from 150 to 250 kg m-3, depending on the stage of the crop. After filling the vats, the process continues in batch mode until complete consumption of sugars (PEREIRA et al., 2018; BASSO et al., 2011). In continuous mode, distilleries employ systems with multiple fermentation vats in series that increase substrate conversion and productivity in ethanol compared to single vats (CAMARGO et al., 1990). At the end of fermentation, the fermented broth (wine), composed of water (mainly), ethanol at a concentration of 8 to 12 °GL (Gay-Lussac grade or % v v-1) and yeast is centrifuged to separate the cells. The resulting yeast suspension (cream) is treated with a sulfuric acid solution to control contamination and the dewatered wine is pumped to the distillation columns, where it is concentrated to obtain hydrated ethanol, an azeotropic mixture of approximately 95% ( v v-1) of ethanol (BASSO et al., 2011). In the first distillation column (rectification) vinasse is generated, a by-product with high biochemical oxygen demand and rich in minerals such as potassium, calcium, magnesium, nitrogen and phosphorus, which has been applied as a fertilizer in sugarcane plantations (MOHANA et al., 2009; AMORIM et al., 2011). To obtain anhydrous ethanol, it is necessary to completely remove the water, which can occur by azeotropic distillation with cyclohexane, extractive distillation with monoethylene glycol (MEG) or adsorption with molecular sieves (WHEALS et al., 1999; MORANDIN et al., 2011).

[007] Although already consolidated, the process can still be improved with the development and implementation of new technologies to reduce costs. The main limitation of the industrial alcoholic fermentation process is the toxicity of ethanol to yeast. During fermentation, ethanol accumulates in the fermentation broth, inhibiting cell growth and its own production (MAIORELLA et al., 1983).

[008] Therefore, to ensure complete conversion of the substrate within a reasonable time, it is necessary to start the process using musts relatively diluted in sugar (ART concentration generally does not exceed 250 kg m-3 or equivalent to 175 kg m-3 of consumed ART ). As a result, in addition to the need to use large-volume vats, the costs associated with energy demand for ethanol recovery are high (up to 2600 kg of steam per m3 of ethanol produced). In addition, there is the generation of large volumes of vinasse, up to 11.9 m3 for each m3 of ethanol produced, with high costs associated with its storage, transport and disposal in the field, which can reach R$ 7.80 per m3 of stillage. And even the application of vinasse in sugarcane fields requires care to avoid environmental damage due to its polluting potential (MOHANA et al., 2009; AMORIM et al., 2011; RUIZ, 2015; LOPES et al., 2016).

[009] One way to minimize the negative effects of inhibition by the product in the ethanol production process is the use of extractive fermentation, which consists of removing the inhibitory compound (ethanol) present in the fermentation broth throughout the process. There are different methods that can be applied in extractive fermentations, which include systems that use membranes, such as pervaporation, perstration and reverse osmosis; in addition to adsorption, liquid-liquid extraction, gaseous entrainment, vacuum extraction, among others. Gas drag, a technique for removing ethanol applied in the present invention, also known as stripping, consists of spraying a gas in a liquid solution so that the transfer of one or more compounds from this solution to the gaseous phase occurs. Compared to other separation methods, gaseous entrainment has advantages such as simplicity of operation and economic feasibility due to the possibility of using the CO2 produced during alcoholic fermentation, which makes it attractive for large-scale applications. Furthermore, the gaseous carryover does not remove the nutrients from the broth, since it is selective to volatile compounds, as well as it does not damage the cells during fermentation (EZEJI et al., 2003). In the scientific literature there are works that report the use of gaseous carryover in fermentation processes for the production of ethanol from corn (TAYLOR et al., 2010), sugarcane (SILVA et al., 2015; SONEGO et al. , 2014; SONEGO et al., 2016; RODRIGUES et al., 2018; SONEGO et al., 2018) and sweet sorghum (THANI et al., 2018), in addition to ABE (acetone-butanol-ethanol) fermentations (CHEN et al., al., 2018). In theory, these studies show that the application of gaseous carryover in fermentation enables the complete conversion of larger amounts of substrate, as well as the increase in total ethanol production and productivity. Thus, in the context of Brazilian distilleries, gaseous entrainment is a promising technology with the potential to reduce the size of equipment (smaller volume vats for the same production capacity), energy costs of ethanol recovery and, mainly, the volume generated of stillage.

[0010] Although gaseous entrainment can bring benefits to alcoholic fermentation, efficient methods for recovering the removed ethanol are needed in order to make the application of the technique viable. Operations that can be employed for this purpose include condensation (PONCE et al., 2016), adsorption (HASHI et al., 2010), vapor permeation (SUN et al., 2017) and absorption (RODRIGUES et al., 2019) . Despite providing good efficiency in ethanol recovery, the first three methods are not yet viable for large-scale implementation, due to the high costs with adsorbents and membranes and the energy consumption in the operation of condensers and in the production of vacuum. Among these operations, absorption proves to be the most attractive option for use on an industrial scale, with equipment that is easy to install and operate. In Brazil, some distilleries already use towers to wash the exit gas from the fermentation vats with water to minimize ethanol losses. Analogously, absorption units could be installed to recover the ethanol removed during the fermentation by gaseous drag. Glycerol and glycols, such as monoethylene glycol (MEG) and diethylene glycol (DEG) are attractive solvents for this application, as they prevent the formation of the ethanol-water azeotrope (BLACK and DITSLER, 1972). MEG, in particular, is already used in Brazilian distilleries in extractive distillation to obtain anhydrous ethanol. As such, it would be readily available for use in the process and the resulting absorption solution could be fed directly into the extractive distillation column.

[0011] Given the scenario presented, the present invention proposes an integrated process for ethanol production by extractive fermentation employing gaseous drag with CO2 for ethanol extraction from fermentation broth or fermented wine and absorption for recovery of removed ethanol. In the example shown, the system employs a pneumatic bioreactor coupled to a set of absorbers containing MEG as an absorbent and operates in a closed circuit with recirculation of CO2 produced by alcoholic fermentation.

[0012] The document PI9403246-7 refers to a process and apparatus for separating volatile compounds from fermentation liquids using gaseous drag. Initially, fermentation liquid and carrier gas, preferably nitrogen, pass through a gas-liquid mixer. The mixture formed is directed to a container, where the phases are separated. The gas is discharged to the atmosphere, while the liquid is conveyed to a second mixer, where it is again in contact with pure carrier gas. This second mixture is also directed to a vessel for phase separation. The liquid resulting from this step is the desired product and the gas can be discharged to the atmosphere or recycled in the process to start a new cycle. Although it uses gaseous drag, the process in question is only for the removal of volatile compounds, that is, it does not employ fermentation to produce a product of interest or a system for its recovery and, therefore, it does not have similarities with the process being proposed here.

[0013] The document PI0500321-0 refers to a process of production, extraction and recovery of ethanol. The invention employs a system comprising a fermentation tank, cell separation device (centrifugation or filtration), yeast treatment tank, vacuum flash tank, ethanol condensing unit, in addition to pumps. The process uses the yeast Saccharomyces cerevisiae and a must composed of molasses diluted in water. During the process, the fermentation broth is pumped from the vats to a cell separation unit, resulting in the formation of two streams, yeast cream and yeasty wine. The cream is sent to the acid treatment tank to control bacterial contamination before being recycled into the process (continuous operation mode) or starting a new fermentation cycle (batch operation mode). The dewatered wine is sent to the flash tank that operates under vacuum conditions, generating a liquid stream that may or may not be recycled to the fermentation vessel and a steam stream that is fed into a rectification column resulting in the condensation of a solution rich in ethanol. Although it comprises an integrated process for the production, extraction and recovery of ethanol, the aforementioned patent differs from the present invention in the following aspects: it uses a vacuum to remove the ethanol, the recovery is carried out by condensation and the production and extraction of ethanol takes place in separate devices.

[0014] The document PI0801209-1 proposes an alcoholic fermentation system that employs gaseous entrainment with nitrogen to remove ethanol and other volatile compounds from the fermentation broth in order to increase the fermentation reaction speed and product productivity. In the system, gaseous entrainment is done using a device referred to as in-line supersonic stripping equipment, capable of generating nitrogen microbubbles and maximizing mass transfer. The fermentation broth is pumped from the fermenter to the supersonic equipment, passes through it and the resulting liquid gas mixture returns to the fermenter, where the gaseous and liquid phases separate. The resulting gaseous stream containing nitrogen, ethanol and other volatile products leaves the fermentor at the top, is washed with water in a scrubber and released into the atmosphere. The resulting liquid stream from the washer containing ethanol, water, unfermented substrate and waste by-products is routed to a distillation unit for ethanol recovery. Although gaseous entrainment is used in alcoholic fermentation, the aforementioned patent differs from the present invention, which operates in a closed circuit with recycling of the gaseous stream to the bioreactor, does not use nitrogen as the entraining gas and does not employ supersonic equipment, with the gaseous entrainment being carried out in the bioreactor. fermentation vessel using CO2.

[0015] The document PI0803058-8 refers to a process for removing water from a hydroalcoholic mixture using membrane. In the process, the hydroalcoholic mixture is distilled and the vapor formed passes through a water-selective membrane. The steam that permeates the membrane, rich in water, is used for heating operations (energy reuse) or condensed to be used as make-up water for fermentation. The patent also describes other process configurations employing multiple stages of membrane units. The process can be used to remove water from a fermentation broth that has been partially dehydrated, for example, by one or more of a distillation column or molecular sieve. Said patent uses a distillation system coupled to vapor permeation membranes. Furthermore, it focuses on the removal and recovery of water for reuse in the process instead of ethanol and, therefore, it has no similarity with the present invention.

[0016] The document PI0806712-0 proposes an integrated process for the production and extraction of ethanol using a reactor equipped with tubular membranes selective to ethanol. The fermentation process takes place inside membranes containing yeast and a continuous supply of glucose solution (must). The application of a vacuum on the outer side of the membrane imposes a pressure gradient between the two sides of the membrane causing ethanol to flow through, being removed from the fermentation broth. Continuous removal of ethanol ensures that its concentration in the broth is kept below inhibitory levels, improving process performance. The patent in question presents clear differences in relation to the present invention, which does not use membranes, employs a pneumatic bioreactor and does not operate under vacuum conditions. In addition, the focus of this patent is only on the extraction of ethanol, while that of the present patent is on the integration between its production, extraction and recovery.

[0017] The document PI1105142-6 refers to an extractive alcoholic fermentation process using water-immiscible solvent (liquid-liquid extraction). The invention is directed to fermentation processes that use musts resulting from the hydrolysis of lignocellulosic and starch materials or containing highly depleted molasses with a high content of inhibitors. The extracting solvent has low toxicity to the fermenting microorganism and is capable of simultaneously removing the product (ethanol) and other inhibitors, in addition to cooling the fermentation broth. In the process, the solvent is fed into the fermentation vessel itself from the bottom and flows upwards because it is less dense than the fermentation broth (aqueous phase). At the top of the vats, the solvent containing the product and inhibitors is removed and sent to a recovery unit, where it is simply heated or subjected to vacuum distillation. The resulting steam stream is sent to another unit for product recovery and the recovered solvent is reintroduced into the fermentation vessel. Although it is an extractive fermentation process, said invention does not show any similarity with the present invention, which does not use solvent extraction or heating operations for ethanol recovery.

[0018] The document US4703007A refers to a system for separating volatile compounds from aqueous solutions by gaseous drag using an airlift reactor. In the system, the carrier gas is introduced in the lower part of the inner cylinder of the reactor through a tube. The gas bubbles pass through the solution in the reactor and the volatile component is transferred from the liquid phase to the gas phase. The resulting gas stream exits the top of the reactor and passes through a collection system where it is cooled to condense the volatile component. Optionally, the carrier gas can be recycled to the reactor. The passage of gas inside the reactor also provides the necessary agitation in the reaction medium. The invention also shows that the system can be adapted for fermentation processes employing, for example, Saccharomyces cerevisiae. Although the aforementioned patent also makes use of gaseous drag, a technique widespread in the literature, it does not resemble the present invention, as it does not employ solvent absorption for component recovery and does not use a high substrate load in the process.

[0019] Document US20100221802 refers to an integrated process for the production, removal and recovery of butanol, in which the production occurs via fermentation using a recombinant strain of Escherichia coli or Saccharomyces cerevisiae and removal by liquid-liquid extraction using oleic acid solvents and stearic acid. The invention proposes different process configurations in which the extraction can be carried out in the fermentor or in separate extraction tanks and can use only one of the solvents or a mixture of both. In the process, the fermentation broth is kept in contact with the solvent, forming a mixture of two phases, an aqueous phase (fermentation broth) and an organic phase (solvent). The greater affinity of butanol for the organic phase makes it possible to extract it from the fermentation broth. After extraction, the phases are separated for later recovery of butanol from the organic phase. The invention also proposes the application of gaseous drag to remove butanol concomitantly with solvent extraction. Although it is an integrated process, the patent in question is not similar to the proposed invention, which does not use the Escherichia coli bacteria, does not employ liquid-liquid extraction and focuses on ethanol.

[0020] The document GB483363 refers to an industrial alcoholic fermentation process that employs acid treatment in yeasts to control bacterial infection. At the end of fermentation, the fermented broth is pumped from the fermentation vessel to a separation unit that separates the wine from the yeast cells. The yeast-free wine is fed into the distillation unit and the yeasts are sent to a vat where the acid treatment is carried out. The treatment consists of submitting the yeast to a solution with a concentration of hydrogen ions at least ten times lower than the concentration used during fermentation (equivalent to a reduction in pH by at least one unit). After the treatment, the yeasts are transferred to a mixing tank where diluted molasses is added and the resulting suspension is pumped to a vats where a new fermentation cycle begins. At the end of this cycle, the entire procedure mentioned above is performed again. Operating cycles are repeated as often as necessary. Although said invention addresses an important step related to the control of infection in alcoholic fermentation, it does not employ any method for removing and recovering ethanol and, therefore, it does not bear any similarity with the technique proposed here.

[0021] The document CN1403579 refers to a process for production and recovery of ethanol that uses an airlift bioreactor coupled to a recovery unit composed of two adsorption/desorption columns connected in parallel and a condenser. In the bioreactor, the fermentation process itself takes place and the ethanol is removed by gaseing. The two columns are used to adsorb the ethanol present in the gas mixture while the condenser is used to collect the desorbed ethanol. The bioreactor operates under a vacuum of 4000 to 8000 Pa with the aid of a pump that also promotes the recirculation of the gas mixture in the system. Said technique presents clear differences in relation to the proposal in the present invention, which does not operate under vacuum, as well as does not use adsorbent material and condenser for the recovery of ethanol.

[0022] The document US2005089979 concerns a continuous process for the production and recovery of acetone, butanol and ethanol (ABE). The process employs a bioreactor where solvents are produced via fermentation by solventogenic bacteria of the genus Clostridium. Solvents are removed by gaseous drag in the fermentor itself, which has a perforated sprinkler for feeding a gas mixture composed of CO2 and H2, used as substrates in the production of EBA. After being removed from the fermentation broth by the gas mixture, the produced solvents (ABE) are recovered by condensation while the gas stream is recirculated in the system with the aid of a peristaltic pump. Although it describes a process for the production and recovery of fermentation products, this patent presents clear differences in relation to the invention proposed here, which does not focus on ABE fermentation, as well as does not use condensation for product recovery.

[0023] The document CN101024846 describes a method and apparatus for recovering ethanol from the vapor phase of distilled fermented broth. The recovery system employs two adsorption columns, the first consisting of a bed of hydrophobic zeolite and the second of a bed of 3A zeolite. The fermented broth containing ethanol passes through a tower where it is heated to 100-110°C to generate steam. The resulting steam feeds the first column, in which ethanol is adsorbed while water exits the top. Then, a gas, which can be N2, H2 or the CO2 produced by fermentation, is used to desorb the ethanol from the saturated adsorbent. The resulting gaseous stream feeds the second adsorption column to remove residual moisture and obtain anhydrous ethanol. This second column works as a molecular sieve, in which the adsorbent's pores are larger than the water molecule and smaller than the ethanol molecules. Said invention is able to reduce up to 50% the energy consumption in relation to the traditional distillation process used industrially. The invention in question does not employ gaseous drag, is applied only to fermented broth and uses adsorption to recover ethanol and, therefore, does not present similarity with the process proposed in the present invention.

[0024] The document CN101952451 describes a process for recovering ethanol and other liquid products produced by synthesis gas fermentation by the bacterium Clostridium ragsdalei. The process comprises a fermentor containing tubular biological films, in which the microorganism grows adhered, and a recovery system that combines vacuum distillation and vapor permeation in membranes. The components of the synthesis gas (CO/CO2/H2) flow through the interior of the tubular films, solubilizing in the fermentation broth as they pass through the films due to the existence of a driving force. During fermentation, a stream of fermentation broth from the bioreactor is pumped to the vacuum distillation column, where a steam stream containing approximately 30% (m/m) ethanol and a liquid bottom stream that is recycled is generated. to the fermenter. Finally, the vapor stream passes through two vapor permeation units containing hydrophilic membranes, resulting in a final retentate with an ethanol concentration of 99% (m/m). Although the process of that patent involves ethanol production and recovery, the application (synthesis gas fermentation), and the system as a whole, do not present similarities with the proposed invention.

[0025] Document CN101003779 refers to a system for the production, extraction and recovery of ethanol. The invention comprises a fermentation tank, where ethanol is produced and removed by gaseous entrainment with CO2, and a recovery unit composed of multiple devices, namely, gas-liquid separator, adsorption column and absorption column containing solvent . The system operates in a closed circuit, in which a vacuum diaphragm pump promotes the recirculation of the gaseous stream. Differing from that patent, in addition to not employing adsorption and not using a vacuum in the recovery step, the present invention has a simpler design, in which the recovery system employs only a unitary operation, in this case, absorption.

[0026] The document US2014356920 refers to different methods for recovering C3-C6 alcohols from dilute aqueous solutions, such as fermentation broths. Such methods make it possible to reduce energy consumption and increase the amount of alcohol produced in the process. In one of the methods employed, the fermentation broth is pumped from the fermenter to a flash distillation tank, which operates under vacuum. After distillation, the resulting liquid stream is recycled to the fermentor while the alcohol-enriched steam stream is conducted to a device referred to as a condenser. In this device, the steam comes into contact with a solvent through a spraying mechanism and the resulting liquid solution is sent to a liquid-liquid separator for subsequent recovery of the alcohol. The sprayed liquid is, preferably, the alcohol itself that is being recovered in the process. The patent also describes a recovery method in which flash distillation and condensation are coupled in the same equipment, which consists of a vessel with two compartments that communicate at the top, allowing only the passage of steam. The invention in question also addresses other process configurations, but none has similarity to the system proposed in the present invention. The patent in question employs vacuum distillation to remove ethanol from the fermentation broth and a recovery unit composed of a liquid-liquid condenser and separator and, therefore, does not resemble the system proposed in the present invention. Furthermore, the application focus of this patent is on alcohols (C3-C6) that have molecules larger than the ethanol molecule (C2).

[0027] The document US10150973 refers to an integrated process for production, separation and recovery of microbial fermentation products, including alcohols, ketones and carboxylic acids, employing a system composed of two adsorption columns. The columns contain particles of an adsorbent and are provided with stirrers that guarantee the homogenization of the system. Initially, the process is conducted in the first column, in which the product is produced via fermentation and extracted by adsorption. When the growth of the microorganism is inhibited by increasing the product concentration or the product productivity is reduced, the fermentation broth is transferred to the second column, where the production and extraction of the product proceeds. The adsorbed products in the first column are recovered by heating or using eluant compound and, later, the adsorbent can be reused. During the process, the columns are rotated whenever necessary, so that while one is used to produce and extract the product, the other is used to recover it. This strategy ensures continuous production, extraction and recovery of the product, maintaining process efficiency. The presence of a filter at the bottom of the columns prevents the passage of adsorbent material from one column to the other. Although it is a fermentation product production, extraction and recovery process, the methods and apparatus used do not show any similarity with those proposed in the present invention.

[0028] The document US9962623 relates to an integrated process for removing and recovering butanol and other alcohols from fermentation broth employing a vacuum vaporization system coupled to an absorption column. The invention can be applied to the removal and recovery of alcohols during the fermentation process as well as in fermented broths. In the process, the fermentation broth is fed into a vacuum distillation system (flash tanks) composed of one or several stages, where it is processed, forming a steam stream enriched in alcohol and a bottom liquid stream with reduced alcohol content that it is recycled to the fermentation vessel. The steam stream is fed into an absorption system, where it comes into contact with a solvent capable of absorbing alcohol, which solvent may be fatty acid, glycol, glycerol, among others. Finally, the formed absorption solution is subjected to distillation to recover the alcohol. Furthermore, the patent in question suggests, as an alternative to the described process, the injection of gas into the fermentation broth as a vacuum pre-vaporization operation in order to remove gases from the broth. Although it is an integrated process for the production and recovery of alcohols and uses absorption with glycol for recovery, the aforementioned patent presents clear differences from the invention being proposed here, which does not operate under vacuum conditions, employs gaseous drag as a method for removing ethanol , uses the CO2 produced by the fermentation itself as carrier gas, operates in a closed circuit with recirculation of the gaseous phase, and also the production and removal of ethanol occur simultaneously in the fermentation tank.

SUMMARY OF THE INVENTION

[0029] The present application reveals an integrated system for ethanol production by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, comprising a pneumatic bubble column bioreactor or airlift coupled to a gas absorption unit with absorbers configured in series .

[0030] The bioreactor disperser is of the perforated plate or crosshead type.

[0031] The extractive fermentation carrier gas of the present integrated system is an inert gas, preferably CO2.

[0032] The integrated system operates in a closed circuit with recirculation of CO2 produced by alcoholic fermentation.

[0033] The component used in the gas absorption unit of this integrated system is at least one of glycerol, monoethylene glycol, diethylene glycol or other absorbents with high affinity for ethanol.

[0034] The Carrier Gas of the present integrated system is fed to the pneumatic bioreactor through a sprinkler located at the base of the bioreactor.

[0035] The gaseous stream of CO2, ethanol and water from the output of the pneumatic bioreactor is directed to the absorption unit.

[0036] The output current of the system absorption unit containing CO2, trace water and unrecovered ethanol from the present integrated system is recycled to the bioreactor by means of a diaphragm pump.

[0037] The absorption unit of the present integrated system is composed of Dreschel type gas washer bottles, made of borosilicate glass with a total capacity of 1 L, defined as bubble column type absorbers.

[0038] The devices of the absorption unit are equipped with sprinkler located on the bases of the same.

[0039] The use of said integrated system is in the process of production, extraction and recovery of ethanol or other volatile compounds.

OBJECTIVES OF THE INVENTION

[0040] The present invention refers to an integrated system for the production, extraction and recovery of ethanol. The technique can be used during alcoholic fermentation as an extractive fermentation system, in the extraction and recovery of ethanol from fermented wines obtained after the separation of yeasts from the fermented broth or any other hydroalcoholic solution, as well as the extraction and recovery of other compounds volatiles present in fermentation broths or in mixtures of liquids with different volatilities in continuous mode in a closed system with gas phase recycling. The present patent application highlights the application of the system developed in the ethanol production process from sucrose, but the proposal can be expanded to extract and recover other inhibitor compounds obtained by fermentation or volatile compounds present in aqueous solutions.

BRIEF DESCRIPTION OF THE FIGURES

[0041] Figure 1 - Schematic drawing of the pneumatic bubble column type bioreactor applied in the example.

[0042] Figure 2 - Comparison between the performance of the conventional process and the proposed system for ethanol production: (a) concentration of ART in the must (wort volume corresponding to 70% of the useful volume); (b and c) ethanol production; (d) vinasse generation.

[0043] Figure 3 - Schematic drawing of the integrated production, extraction and recovery of ethanol from fermentation broth during extractive fermentation.

[0044] Figure 4 - Experimental values of the concentrations of ART (CART, ○), viable cells (CX, ■) and ethanol (EC, ▲) in the broth over time in the fermentations: (a) conventional and (b) extractive .

[0045] Figure 5 - Experimental values of ethanol concentration over time in extractive fermentation: (■) 1st absorber and (□) 2nd absorber. The arrow indicates the time when the exchange of absorbers was carried out.

DETAILED DESCRIPTION OF THE INVENTION

[0046] In the proposed system, the extraction of ethanol is promoted by gaseous entrainment with inert gas, preferably CO2, and the recovery is by gaseous absorption using a system of absorbers configured in series and using glycerol, glycols (mono or diethylene glycol, MEG or DEG) or other absorbents with high affinity for ethanol. The invention employs a closed system with recirculation of CO2 produced in alcoholic fermentation itself. The functioning of the system is characterized by the passage of CO2 through the bioreactor (vair) containing fermentation broth or dewatered wine obtained from centrifugation of the broth at the end of fermentation or any hydroalcoholic solution, preferably removing the ethanol. The resulting gaseous stream containing CO2, ethanol and water is routed to the recovery system. Subsequently, the output current of the recovery system containing CO2 and traces of water and unrecovered ethanol is recycled to the bioreactor, closing the circuit and avoiding losses in the process.

• - Altura total denominada como “H1”;
• - Altura da coluna de líquido denominada como “H2”;
• - Diâmetro interno denominado como “D1”;
• - Diâmetro externo denominado como “D2”;
• - Relação entre “H2” e “D1” de 2,5 < H2/D1 < 5,0.

[0047] The bioreactor used in the example of the present invention is of the pneumatic type bubble column model, which can be replaced by an airlift model of concentric cylinders or "split", with a capacity of 2 L (Figure 1). The bioreactor (1) has a jacketed cylindrical base (2), top cover (3) and sprinkler (4) made in stainless steel and body (5) in borosilicate glass, featuring the geometric characteristics:

• - Total height designated as “H1”;
• - Height of the column of liquid called “H2”;
• - Internal diameter named as “D1”;
• - External diameter named as “D2”;
• - Ratio between “H2” and “D1” of 2.5 < H2/D1 < 5.0.

[0048] The sprinkler (4), located at the bottom of the bioreactor is of the perforated plate (41) or crosshead (42) type, and contains holes for injection of inert gas, preferably CO2.

[0049] The ethanol recovery system is composed of Dreschel type gas washing flasks made of borosilicate glass, characterized as bubble column type absorbers. Devices are equipped with a sprinkler located at the bottom.

[0050] The application of the invention for the extraction and recovery of ethanol during fermentation provides a significant improvement in performance in the ethanol production process, with high substrate consumption with consequent total ethanol production around 60% higher than in the process. conventional used industrially, as well as an eventual reduction in the production of vinasse by approximately 50%, as illustrated in Figure 2. It is noteworthy that the percentage of ethanol recovery in the proposed system is approximately 100%.

[0051] From the point of view of a possible implementation on an industrial scale, the use of absorption with MEG for ethanol recovery presents great advantage. Some distilleries already use towers to wash the exit gas from the fermentation vats with water to minimize ethanol losses. Similarly, absorption units can be installed in the industrial plant to recover the ethanol removed by gaseing. In addition, MEG is already used in distilleries in the extractive distillation step to obtain anhydrous ethanol. Thus, the resulting solution of the absorbers (MEG + water + ethanol) can be fed directly into the extractive distillation column to obtain anhydrous ethanol and recover the MEG.

[0052] In order to better understand the developed process, it was decided to describe it from a detailed example, presented as follows:
Two conditions of alcoholic fermentation in fed batches were carried out, one conventional with substrate concentration in the wort of 256 kg m-3 (corresponding to 179.2 kg m-3 of consumed ART) and another with extraction and recovery of ethanol with concentration of substrate in the wort of 401 kg m-3 (corresponding to 280.7 kg m-3 of consumed ART). The experimental conditions of conventional fermentation were similar to those of the industrial ethanol production process, with no removal and/or recovery of ethanol throughout fermentation. The results were used as a reference to compare the performance of extractive fermentation integrated with the step of recovering ethanol from the fermentation broth, proposed by the present invention. Extraction was carried out by gaseous entrainment with CO2 and recovery by gaseous absorption using MEG as an absorbent. A closed system with recirculation of CO2 produced in alcoholic fermentation was used.

[0053] The lyophilized industrial strain Saccharomyces cerevisiae Y904 (AB Brasil Indústria e Comércio de Alimentos Ltda, Brazil) was used as an ethanol-producing microorganism. The must from conventional fermentation had the following composition: sucrose (243.0 kg m-3, equivalent to 256.0 kg m-3 of total reducing sugars, ART), KH2PO4 (8.0 kg m-3), MgSO4. 7H2O (2.0 kg m-3), yeast extract (9.7 kg m-3) and urea (7.6 kg m-3). The same components were used in the extractive fermentation wort, but at different concentrations, namely: sucrose (381.0 kg m-3, equivalent to 401.0 kg m-3 of ART) KH2PO4 (9.6 kg m-3 ), MgSO4.7H2O (2.4 kg m-3), yeast extract (11.7 kg m-3) and urea (9.1 kg m-3). Initial pH was adjusted to 4.6 by adding 1M HCl solution. Such musts simulated the diluted sugarcane molasses used industrially.

[0054] The fermentations were conducted in a pneumatic bioreactor bubble column model (1), shown in Figure 1, and a concentric cylinder airlift model or "split" type airlift can also be used. The yeast (40 g, dry basis) was previously hydrated in 0.6 L of distilled water, corresponding to 30% of the useful volume of the bioreactor. The suspension was acclimated for 20 minutes under agitation and then inoculated into the bioreactor. The must (1.4 L) was fed using a peristaltic pump at a constant volumetric flow until filling the bioreactor (2.0 L). The filling times used in the fermentations were different, being 5 h in conventional and 8 h in extractive. The longer filling time in extractive fermentation was necessary to avoid substrate inhibition. During fermentations, the broth was stirred using a peristaltic pump. Commercial defoamer was added, where necessary, to control excessive foaming. The temperature was maintained at 34 °C by recirculating water from a thermostatic bath to the jacket of the bioreactor. Fermentations were carried out in duplicate and carried out until the complete consumption of the substrate. Samples were periodically taken from the fermentation broths to determine substrate (ART), ethanol and viable cell concentrations, and from absorber solutions during extractive fermentation to analyze the ethanol content. The volumes of the liquid phases of the bioreactor and the absorbers were also monitored.

[0055] Figure 3 illustrates the proposed system. During the fed-batch extractive fermentation, the gaseous entrainment in the bioreactor (1) was started in the 3rd hour of the process, at which time the ethanol content in the vats begins to inhibit the yeast metabolism more intensely (SONEGO et al., 2014 ). Before starting the gaseous drag, all the air present in the system lines was removed using the CO2 generated by alcoholic fermentation during the first three hours. The bioreactor exit gas mixture (CO2 + ethanol + water) was directed to the absorption system composed of two absorbers (6) and (7) configured in series, each containing 0.80 L of MEG and kept at 25 °C by immersion in a thermostatic bath. The output current of the first absorber (6) was connected to the input of the second absorber (7). The output current of the second absorber (7) containing CO2 and traces of water and unrecovered ethanol was recycled to the bioreactor (1) through a diaphragm pump (8). The volumetric flow of CO2 used was 5 L min-1, which corresponded to a specific flow of 2.5 vvm (ratio between the volumetric flow of gas and the volume of broth), a value used in previous studies on extractive alcoholic fermentation (SONEGO et al., 2016; RODRIGUES et al., 2018). As the pump operating flow was greater than the flow required in the system, a recycle stream was introduced to control the flow, with part of the discharge current redirected to the pump suction passing through a valve (9). The flow was maintained by regulating the valve (9) and using as a basis the flow measurement of a mass flowmeter (10). A coil (11) immersed in a thermostatic bath at 25 °C was installed in the recycling stream to prevent the equipment from overheating. To relieve the pressure in the line, the excess CO2 produced during fermentation was purged using a valve (12) activated by a controller (13) equipped with a pressure sensor installed in a pressure tap (14). The valve (12) was programmed to open and close in order to ensure that the point of lowest pressure in the line (pump suction) was always maintained at a positive gauge pressure, in order to prevent the entry of air into the system during the process. . Due to the long duration of extractive fermentation, it was necessary to change the absorbers to avoid saturation of the absorption solution. In the procedure, the first absorber (6), with a higher concentration of ethanol, was removed from the process and replaced by the second absorber (7), with a lower concentration of ethanol. Another absorber containing pure MEG (15) was then inserted in place of the second absorber (7). This exchange was carried out in the 10th hour of fermentation. [0056] The concentrations of ethanol, glucose, fructose and sucrose in the fermentation broths and the concentration of ethanol in the absorber solutions were determined using methodologies based on the combination of the Fourier transform (FT-IR) medium infrared spectroscopy technique with the partial least squares multivariate regression method (RODRIGUES et al., 2018; RODRIGUES et al., 2020). The viable cell concentration was determined by the product between the total cell concentration, obtained by the gravimetric method, and the percentage of viable cells, obtained by the staining method.

[0056] The concentrations of ethanol, glucose, fructose and sucrose in the fermentation broths and the concentration of ethanol in the absorber solutions were determined using methodologies based on the combination of the Fourier transform (FT-IR) medium infrared spectroscopy technique with the partial least squares multivariate regression method (RODRIGUES et al., 2018; RODRIGUES et al., 2020). The viable cell concentration was determined by the product between the total cell concentration, obtained by the gravimetric method, and the percentage of viable cells, obtained by the staining method.

onde mERec é a massa de etanol recuperada por absorção (kg), mERem é a massa de etanol removida do biorreator por arraste gasoso (kg), NA é o número de absorvedores utilizados no experimento, CEAb é a concentração total de etanol recuperado no absorvedor “n” (kg m-3), VAb é o volume de solução no absorvedor “n” (m3), mEPro é a massa de etanol produzida (kg) calculada com base na massa de substrato alimentado e no coeficiente de rendimento em etanol (YE/ART) obtido na fermentação convencional (kgE kgART-1) e mECal é a massa de etanol no caldo ao final da fermentação (kg).[0057] The recovery performance was evaluated using the percentage of ethanol recovery (ER), according to Equation 1, in which the denominator represents the difference between the mass of ethanol produced and the mass of ethanol present in the broth.

where mERec is the mass of ethanol recovered by absorption (kg), mERem is the mass of ethanol removed from the bioreactor by gaseous entrainment (kg), NA is the number of absorbers used in the experiment, CEAb is the total concentration of ethanol recovered in the absorber “n” (kg m-3), VAb is the volume of solution in the absorber “n” (m3), mEPro is the mass of ethanol produced (kg) calculated based on the mass of substrate fed and the ethanol yield coefficient (YE/ART) obtained in conventional fermentation (kgE kgART-1) and mECal is the mass of ethanol in the broth at the end of fermentation (kg).

[0058] A synthesis of the main results of conventional and extractive fermentation is presented in Table 1. The values of viable cell concentrations (CX), ART (CART) and ethanol (CE) are shown in Figure 4.

[0059] CART-M a is the concentration of ART in the wort, bART consumed is the concentration of ART consumed considering the useful volume of the bioreactor, CEfC is the final concentration of ethanol in the fermentation broth, CETd is the total concentration of ethanol produced (for extractive fermentation it is calculated considering ethanol present in the vats plus ethanol recovered in the absorbers), PE and is the volumetric productivity in ethanol, CVf is the percentage of viable cells, ERg is the percentage of ethanol recovery and VVinhaça/VEtanolh is the relationship between the volume of vinasse generated and the volume of ethanol produced.

[0060] In conventional fermentation, complete consumption of ART occurred within 8 h. The final concentration of ethanol in the broth was 80.4 kg m-3 and the ethanol productivity of 10.1 kg m3 h-1. The ethanol yield coefficient (YE/ART), defined as the ratio between the mass of ethanol produced and the mass of ART consumed, was 0.449 kgE kgART-1, corresponding to 88% of the theoretical yield coefficient (0.511 kgE kgART -1). Overall, these results were similar to those observed in industrial alcoholic fermentations.

[0061] With respect to extractive fermentation, the complete consumption of substrate occurred in 15 h. During must feeding, even with the high sugar load fed, the substrate concentration did not exceed 120 kg m-3 and, therefore, there was no process limitation by substrate inhibition. The total production of ethanol in the process (ethanol present in the vats added to the ethanol recovered in the absorbers) was 125.8 kg m-3 (15.9 °GL), a value 56% higher than that observed in conventional fermentation. The final concentration of ethanol in the broth was 87.1 kg m-3. This value was higher than the concentration obtained in conventional fermentation, which means that the resulting wine could be directed to distillation without compromising the energy efficiency of the process. Finally, the ethanol productivity was 8.4 kg m-3 h-1, only 17% lower than the conventional process. This difference can be compensated by using a higher cell density in the process or by using strategies to optimize the wort feed and gaseous carryover. Regarding cell viability, at the beginning of extractive fermentation it was 61.2% and increased over time reaching 81.2% at the end of the process, a value higher than that observed in conventional fermentation (64.5%) .

[0062] With regard to the recovery step, the percentage of recovered ethanol (RE) in extractive fermentation was ~100% (Table 1), indicating an excellent performance of absorption as a method of recovery of the ethanol extracted during fermentation. Experimental data of ethanol concentration over time in absorbers are shown in Figure 5.

[0063] The volume of vinasse generated in the ethanol production process depends on the concentration of ethanol in the juice at the end of fermentation. In conventional fermentation, the final ethanol concentration in the broth was 80.4 kg m-3 (10.2°GL), which corresponds to the generation of 9.3 m3 Vinasse m-3 Ethanol (LOPES et al., 2016 ). In extractive fermentation, the final ethanol concentration in the broth was 87.1 kg m-3 (11°GL). The distillation of a wine with this alcohol content would generate 8.5 m3 Vinasse m-3 Ethanol (LOPES et al., 2016). However, this concentration of ethanol in terms of mass corresponds to 58% of the total ethanol produced (mass of ethanol present in the fermentation broth added to the mass of ethanol recovered in the absorbers). The remainder (42%) was recovered in the absorbers and, therefore, cannot generate vinasse once it has been removed from the broth. Therefore, the ratio between the volume of vinasse generated and the volume of ethanol produced using the proposed system is 4.9 m3 Vinasse m-3 Ethanol, representing a 47% reduction in relation to the volume of vinasse generated in conventional fermentation.

[0064] Although the application of the present invention as an extractive fermentation system has been described, it can also be used for extraction and recovery of ethanol from yeasty wine or any hydroalcoholic solution. In this case, atmospheric air can be used as a carrier gas, alternatively to CO2. Furthermore, the invention can be extended to extraction and recovery of other alcohols and/or volatile solvents present in fermented broths and other aqueous solutions. [0065] It can be said that the results obtained were very representative since in the industrial process the loss of ethanol dragged by the CO2 produced during fermentation can reach 2% if the exhaust gas from the vats is not washed, while the loss of ethanol in the proposed system was practically nil. In addition, if the global efficiency of extractive fermentation is calculated, given by the ratio between the total mass of ethanol at the end of the process (ethanol present in the broth plus the ethanol present in the absorbers) and the fed substrate mass, the value (0.448 kgEthanol kgsubstrate -1) was practically equal to the YE/ART value of conventional fermentation (0.449 kgEthanol kgsubstrate1). In other words, the overall efficiency obtained with the present invention is equal to that of the conventional process, but with the advantage of feeding a 56% wort. more concentrated in sugar than the conventional process, which implies an eventual reduction of 47% in the amount of vinasse generated, a highlight of the proposed system. Furthermore, the solution resulting from the absorption (containing ethanol, water and MEG) can be fed directly into an extractive distillation column to obtain anhydrous ethanol, as is currently done in distilleries.

Claims (11)

Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use, characterized by the fact that it comprises a pneumatic bioreactor, bubble column model or airlift, coupled to a gas absorption unit with absorbers configured in series. Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use of the same characterized by the fact that the bioreactor disperser is of the perforated plate or crosshead type. Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use thereof, according to claim 1, characterized in that the extractive fermentation carrier gas of the integrated system is CO2 or another inert gas . Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use thereof, according to claims 1 to 3, characterized by the fact that the integrated system operates in a closed circuit with recirculation of CO2 produced by alcoholic fermentation . Integrated system for ethanol production by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, according to claim 1, characterized in that the component used in the gaseous absorption unit is at least one of glycerol, monoethylene glycol, diethylene glycol or other absorbents with high affinity for ethanol. Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use thereof, according to claims 1 to 5, characterized in that the carrier gas is fed to the pneumatic bioreactor by means of a localized sprinkler at the base of the bioreactor. Integrated system for ethanol production by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, according to claims 1 to 6, characterized by the fact that the gaseous stream of CO2, ethanol and water from the output of the pneumatic bioreactor is directed to the absorption unit. Integrated system for ethanol production by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, according to claims 1 to 7, characterized by the fact that the output current of the system's absorption unit contains CO2, traces of Unrecovered water and ethanol is recycled to the bioreactor via a diaphragm pump. Integrated system for ethanol production by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, according to claims 1 to 8, characterized in that the absorption unit is composed of Dreschel-type gas washer bottles, made in borosilicate glass with a total capacity of 1 L, defined as column-bubble absorbers. Integrated system for the production of ethanol by extractive fermentation with gaseous entrainment and recovery by absorption and use thereof, according to claims 1 to 9, characterized in that the devices of the absorption unit are equipped with a sprinkler located at their base . Integrated system for ethanol production by extractive fermentation with gaseous drag and recovery by absorption and use thereof, according to claims 1 to 10, characterized in that it is applied in the production, extraction and recovery process of ethanol or other volatile compounds .

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