Valorization of Residual Biomasses from the Agri-Food Industry by

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

VALORIZATION OF RESIDUAL BIOMASSES FROM AGRI-FOOD INDUSTRY BY SUBCRITICAL WATER HYDROLYSIS ASSISTED BY CO2 Juliana M. Prado, Renata Vardanega, Gislaine Chrystina Nogueira, Tânia Forster– Carneiro, Mauricio Ariel Rostagno, Francisco Maugeri Filho, and M. Angela A. A. Meireles Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02670 • Publication Date (Web): 25 Jan 2017 Downloaded from http://pubs.acs.org on January 29, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

VALORIZATION OF RESIDUAL BIOMASSES FROM AGRI-FOOD INDUSTRY BY SUBCRITICAL WATER HYDROLYSIS ASSISTED BY CO2

Juliana M. Pradoa1, Renata Vardanegab, Gislaine C. Nogueirab, Tânia Forster-Carneirob, Mauricio A. Rostagnoc, Francisco Maugeri Filhob, M. Angela A. Meirelesb

a

CCN (Centro de Ciências da Natureza)/Campus Lagoa do Sino – UFSCar (Federal

University of São Carlos), Rod. Lauri Simões de Barros (SP-189), km 12,18290-000 Buri, SP, Brazil

b

DEA/FEA (School of Food Engineering)/UNICAMP (University of Campinas), R. Monteiro Lobato, 80, Campinas, 13083-862, SP, Brazil

c

FCA (School of Applied Sciences)/UNICAMP (University of Campinas), R. Pedro Zaccaria, 1300, Limeira, 13484-350, Limeira, SP, Brazil

1

Corresponding author. Phone: +55 15 3256 9000. E-mail: [email protected] 1 ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 29

Abstract In this work, four residual biomasses from the food industry (coconut husk, defatted grape seeds, sugarcane bagasse, and pressed palm fiber) were subjected to subcritical water hydrolysis assisted by CO2 (SubWH+CO2) with the objective of producing fermentable sugars. Hydrolysis kinetics were determined using a semi-batch unit equipped with a 50 mL reactor. The process was conducted at 250 °C for 30 min under 20 MPa. Total reducing sugars recovered using SubWH+CO2 were (wet basis): 13.5 % for coconut husk, 10 % for defatted grape seeds, 13.2 % for sugarcane bagasse, and 11.2 % for pressed palm fiber. For coconut husk and defatted grape seeds adding CO2 increased total reducing sugars by 15 % and 56 %, respectively. For sugarcane bagasse and pressed palm fiber, adding CO2 to the process did not alter total reducing sugars recovered. In all cases the by-products yield increased when adding CO2 to the process.

Keywords: Agri-food biomass, CO2, hydrolysis, subcritical water

2 ACS Paragon Plus Environment

Page 3 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1. Introduction The bioeconomy concept has encouraged the use of waste, as biomass, for the production of energy and other compounds of interest, not only because of the value of these products, but also due to reduction of organic disposal in the environment 1. Lignocellulosic biomass is a complex matrix composed mainly of cellulose, hemicellulose, starch and lignin. It is one of the most abundant raw materials in earth and it can be converted into marketable products, very often without competition with the food supply chain. There are several agricultural residues available in Brazil, which make over 300 million tons per year and can provide a lot of lignocellulosic material. The most representative examples include sugarcane, soybean, corn, and rice residues 2. There are also other potential raw material that could be used to produce energy and other chemical products, such as coconut husk, grape seeds and pressed palm fiber 3, 4. Coconut husk is the residue resulting from coconuts processing to produce beverages and coconut powder. Adopting healthy dietary habits by the society has increased the consumption of coconut products, leading the coconut husks to become an environmental problem 5. Due to its high content of lignin, coconut husk is considered a hard wood and it is characterized by high toughness 4. Grape seeds are a waste of winery industry, mainly composed by lignin and hemicellulose. They also present a high content of oil, which can be extracted and used in several applications, such as cosmetics and foods. After the oil fraction is extracted, the grape seeds have no other immediate use 4, 6. Sugarcane bagasse, which represents one third of the plant, is mainly constituted of cellulose and hemicellulose. It is usually burned by sugars mills to generate electricity, even though this biomass could be exploited differently to produce added-value products as a replacement for or before its combustion. The knowledge


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 29

generated about processes to produce other products from the bagasse is sufficient to indicate that this raw material can be exploited in a more sustainable way resulting in different added-value products, as fermentable sugars and phenolic compounds

7, 8

.

Pressed palm fiber is a residue from the pressing of palm fruits to produce palm oil. This residue contains a fraction of oil rich in α- and β-carotene, which can be further extracted by supercritical fluid extraction. After the oil extraction, the residue composed by cellulose and hemicellulose is ultimately disposed 9. Simple sugars are important products that can be obtained from the above mentioned agri-food residues. Such sugars could be used as fermentation substrates or as precursors for producing other bio-products, including liquid alkanes, dimethylfuran, and furfural. One of the main goals is to produce liquid energy, as secondgeneration ethanol. Biomass is constituted by a lignocellulosic complex that is difficult to break because lignin is chemically bonded to hemicellulose and cellulose, which increases the resistance of such complex to hydrolysis. The high resistance of the lignocellulosic complex requires aggressive treatments to break it and produce monomeric sugars. However, the severity of the breaking process can also produce other by-products such as organic acids, furfural, and 5-hydromethyl-furfural (5-HMF). These by-products are toxic to the fermentation microorganisms 10, but, on the other hand, products as furfural and 5-HMF can also be used in the industry as solvents or as precursors for pharmaceuticals, thermoresistent polymers, etc.

11

. Thus, depending on the desired

application, the hydrolysis conditions should be optimized so that yields of fermentable sugars are maximized, while the formation of by-products is minimized, or vice-versa. Controlling reaction rates is a difficult task because there are several parameters involved, including, time, temperature, pH, etc. 12.


Page 5 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Several techniques have been proposed to transform biomass into fermentable sugars. Regarding the environmental friendship proposal, hydrothermal processing is one of the most promising techniques

13, 14

. Water is the most abundant and one of the

most useful green solvents in the chemical industry due to its non-toxicity and nonflammability. Hydrothermal treatment in which pressurized water is used to catalyze hydrolytic reactions, is classified as subcritical water hydrolysis (SubWH) or supercritical water hydrolysis (SupWH), depending on operating conditions 3, 15-17. Regarding sugar production, SubWH and SupWH are less aggressive than conventional methods as acid and alkali hydrolysis because they degrade less sugar and do not generate solid waste. Compared to enzymatic hydrolysis, the advantage of SubWH and SupWH is the high cellulose hydrolysis rate (several hours vs. a few minutes or seconds). Hydrolysis rates and yields depend on the characteristics of the residue, including cell wall composition and structure, as well as the monosaccharides present and the type of bonds between them and lignin. Therefore, each raw material represents a technological challenge that needs to be studied individually, since the optimal process conditions can vary for different types of residues 12. Depending on equipment design, SubWH and SupWH can vary from milliseconds to about 30 min

18-20

. The longer the process takes, the higher is the

formation of by-products from sugars, which can inhibit the subsequent fermentation process. One possible solution to overcome this drawback is adding CO2 to the reactant medium 12. In aqueous medium at high pressure and temperature, CO2 reacts with water to form carbonic acid, which dissociates to increase the hydronium ion concentration of the solution, therefore acting as an acid catalyzer of the process, even if CO2 is only slightly dissolved and dissociated in water.

21

The equilibrium concentration of the

hydrogen ions, hence the pH value, and the equilibrium constant, are influenced by


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 29

variations of CO2 pressure and temperature 22. The properties of the water-CO2 mixture were reported in detail by Brunner 22. The addition of CO2 can increase hydrolysis rates, thereby reducing the reaction times. This can be due to increase in the severity of the process conditions with the presence of carbonic acid 23. The use of CO2 has also the advantage of lower corrosion when compared to conventional acid hydrolysis. Moreover, CO2 can be removed by releasing the pressure of the system, so the medium can be neutralized without generating solid residues, and it can still be recirculated in the process 21, 23, 24. The objective of this work was to evaluate the addition of CO2 to the SubWH applied to different agri-food residues: coconut husk, sugarcane bagasse, defatted grape seed and pressed palm fiber, regarding sugars and by-products yield.

2. Material and Methods 2.1 Raw materials The dry sugarcane bagasse was donated by the Brazilian Bioethanol Science and Technology Laboratory (CTBE, Campinas, SP, Brazil). The coconut husk resulting from coconut water and milk production was donated by Ducoco Alimentos (Linhares, ES, Brazil). The dry palm pressed fiber resulting from palm pressing to obtain oil was donated by Agropalma (Tailândia, PA, Brazil). The raw materials were stored at -18 °C and then they were comminuted in a knife mill (Marconi, model MA 340, Piracicaba, Brazil) equipped with a 1 mm sieve before they were used as samples in the experiments. The grape seeds were provided by Villa Francioni winery (São Joaquim, SC, Brazil). The seeds were collected after wine fermentation, and they were separated from stalks and peels by sieving and air blowing. The resulting sample was dried under the


Page 7 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

sun for 7 days. The seeds were ground frozen to preserve their vegetable oil and then they were extracted by supercritical CO2, yielding around 13% oil, before the SubWH process 6. The raw materials were characterized according to the methodologies of the National Renewable Energy Laboratory (NREL), in triplicate

25-29

. The characterization

results are presented in Table 1 4, 30.

2.2 Hydrolysis equipment Figure 1 shows the set up of the system where SubWH experiments were conducted. The system is composed by a liquid high pressure pump that runs to 40 MPa (LabAlliance, model Series III, State College, PA) for water pumping, an air driven liquid pump (Maximator GmbH, model M18, Thüringen, Germany) for carbon dioxide (CO2) pumping, a thermostatic bath (Marconi, model MA-184, Piracicaba, Brazil) operated at -10 °C to assure that CO2 is liquid before entering the pump, one static mixer (Autic, Campinas, Brazil) for water and CO2 mixing, one stainless steel heating coil (Autic, 6 m × 1/8” i.d., Campinas, Brazil) for the reaction medium heating, one stainless steel 50 mL reactor (Autic, 2.34 cm i.d. × 11.7 cm, Campinas, Brazil) with metal-to-metal fit to allow using temperatures up to 400 °C, one micrometric valve (Autoclave Engineers, Erie, PA) for pressure control, one stainless steel refrigeration coil coupled to a thermostatic bath (Marconi, model MA-184, Piracicaba, SP, Brazil) operating at 40 °C to assure that the reaction is quickly quenched after the hydrolysate exits the reactor, one glass gas-liquid separator to separate the liquid hydrolysate from the CO2, and one flow totalizer to quantify the CO2. The equipment also contains block valves, thermocouples and manometers.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 29

2.3 Hydrolysis of biomasses The equipment was operated at subcritical hydrolysis conditions: temperature of 250 °C and pressure of 20 MPa. Under these conditions the solubility of CO2 in water is 2.8 % (mol/mol) 31. Around 10 g of raw material was inserted in the reactor, which was connected to the equipment. Distilled water was pumped to the system until it reached 20 MPa. After the pressurization the pump was stopped, the micrometric valve was closed, and the heating of the coil and of the reactor was started, set at 250 and 120°C, respectively. The reactor was preheated to 120 °C to assure that there was no hydrolysis of cellulose during the pre-heating time. After stabilizing the temperature throughout the system, the dynamic period of the process was started. Water and CO2 were continuously pumped at 33 mL/min (ambient conditions) and 7 g/min, respectively. Due to the low solubility of CO2 in water at the operating conditions, the system was operated with excess of CO2, considering that only the dissolved and dissociated CO2 influences the hydrolysis process

32

. Simultaneously to pumps start the reactor

temperature was set to 250 °C. The difference of temperatures between pre-heating and dynamic period caused a temperature profile until temperature stabilization. After the reaction there was a rapid depressurization followed by cooling to 40 °C in contact with the refrigeration coil to assure reaction quenching. Samples, each one consisting of the hydrolysate obtained during 2 min of process, were collected in polypropylene vials for 30 min. The CO2 was separated from the liquid hydrolysate in the glass gas-liquid separator, quantified in the flow totalizer, and then released to the atmosphere. The experiments were performed in duplicate.

2.4 Analysis of the hydrolysates


Page 9 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

The analyses described next were performed on all the hydrolysate samples collected after depressurization and cooling.

2.4.1 Total reducing sugars content The total reducing sugars (TRS), which are sugars with an aldehyde group or a free hemiacetal group, were determined by the colorimetric Somogyi–Nelson method 33, 34

. The hydrolysate samples were subjected to acid hydrolysis to assure that all the

oligomers would be broken to monomers, and could be detected as reducing sugars 33. After the coloring reaction

34

the absorbance was recorded at 730 nm by a

spectrophotometer (Femto, model 800 XI, São Paulo, Brazil). The concentration of TRS was calculated using an external calibration curve of glucose (10–600 mg/L), and expressed as glucose equivalents.

2.4.2 Determination of pH The pH of the hydrolysates was determined using a digital pHmeter (Digimed, model DM-22, Santo Amaro, Brazil).

2.4.3 Determination of saccharides by ion exchange chromatography Prior to saccharide analysis the samples were diluted in deionized water (when necessary) and filtered through a 0.45 µm nylon membrane. Samples were identified and quantified by ion exchange chromatography (HPLC-PAD), according to the methodology described by Prado et al 30.

2.4.4 Determination

of

by-products

by

high-performance

liquid

chromatography 9 ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 29

The by-products content was determined by high-performance liquid chromatography (HPLC), according to the methodology described by Prado et al 30. The by-products

analyzed

were

furfural,

5-hydroxymethilfurfural

(5-HMF),

4-

hydroxybenzoic acid (4-HBA) and vanillin.

2.5 Hydrolysis selectivity The hydrolysis selectivity is the molar ratio between monosaccharides yield and their respective reaction products yield 9. It was estimated as the ratio between total amount of sugars (C6 or C5) and their reaction products (5-HMF and furfural, respectively) obtained at the end of the process.

3. Results and discussion 3.1 Coconut husk The solid residue left after SubWH+CO2 of coconut husk was lower than for SubWH (Table 2). The hydrolysates obtained from coconut husk by SubWH+CO2 were analyzed for TRS content and pH, and the results were compared to those obtained in the SubWH process 4. Figure 2A shows that adding CO2 to the SubWH increased both the hydrolysis rate and the TRS yield of coconut husk. The yield obtained in 30 min of SubWH was achieved in 20 min of SubWH+CO2, and CO2 addition increased by 15% the final TRS yield. The pH of the hydrolysate fractions obtained with SubHW+CO2 decreased with the increase in the concentration of soluble material, a similar behavior to the one observed in the SubWH process (Figure 2B). However, in the SubHW+CO2 the pH decreased more drastically in the beginning of the process, and in the end of the process the pH value was higher than that obtained in SubHW. van Walsum and Shi also observed higher final pH in corn stover hydrolysates obtained by SubWH+CO2 23. 10 ACS Paragon Plus Environment

Page 11 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

This happens because as the process was performed in a semi-batch equipment, the organic matter was removed progressively. After 20 min of process there was little organic matter left inside the reactor. Therefore, all the compounds later hydrolyzed were diluted, including the organic acids resulting from monosaccharides reactions. Individual sugars and their by-products in the hydrolysates were also analyzed (Table 3). SubWH+CO2 was more efficient than SubWH to break down the lignocellulosic complex of coconut husk, but the total monosaccharides content of hydrolysates decreased. Thus, acidifying the reactant medium improved the rate of depolymerization of the lignocellulosic complex into oligosaccharides, but it also increased the by-products formation rate. Therefore, considering the difference observed between the TRS and the sum of monosaccharides, even though oligosaccharides were not determined in this study, it may be assumed that compared to SubWH, SubWH+CO2 increased the yield of oligosaccharides. Although the byproducts content was approximately constant for both processes, their composition varied. Thus, SubWH+CO2 can be considered a suitable process modification to obtain hydrolysates enriched in oligosaccharides from coconut husk. Figure 2 also shows the yield of sugars (C) and by-products (D) in the hydrolysate fractions obtained during the SubWH+CO2 process. The fractions recovered at 2-12 min contained both cellulosic and hemicellulosic sugars, and at 12-26 min the fractions contained high content of fructose, which results from the epimerization of glucose derived from cellulose degradation. The production of furfural (obtained from pentoses dehydration) started at 6 min, while the production of 5-HMF (obtained from hexoses dehydration) started at 12 min. In the SubWH process, the same behavior was observed 4.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 29

3.2 Defatted grape seeds After the SubWH+CO2 of defatted grape seeds there was lower solid residue compared to SubWH (Table 2). Figure 3 shows the TRS content (A) and pH (B) of the hydrolysates obtained from defatted grape seeds by SubWH+CO2 compared to those obtained by SubWH 4. CO2 addition increased the final TRS yield by 56%. The yield obtained in 30 min of SubWH was achieved in only 10 min of SubWH+CO2. The yields of monosaccharides and by-products also increased when CO2 was added (Table 3). The pH value showed little difference from SubHW to SubWH+CO2, and it presented the same general trend of coconut husk, with less variation. The yield of sugars and by-products in the hydrolysate fractions obtained during the SubWH+CO2 process are also presented in Figure 3 (C and D, respectively). The monosaccharides formation occurred mainly in the beginning of the process, at 4 – 10 min, while the formation of furfural and 5-HMF increased after 10 min. Adding CO2 accelerated the monosaccharides formation, since in SubWH the highest concentration of sugars was recovered at 10 min and in SubWH+CO2 it happened at 4 min. The acceleration of hydrolysis rates caused by the addition of CO2 had already been demonstrated

35, 36

. This effect was most likely due to the formation of carbonic acid,

acting as an acid catalyst 37. Thus, if the process was stopped at 10 min, the production of by-products could be decreased. In fact, studies demonstrated that faster processes, even at more severe conditions, presented higher yields of glucose with lower yields of by-products20, 37. On the other hand, at around 17 min the TRS curve (Figure 3A) presented a change, which coincides with improved sugars formation (Figure 3C). Analyzing these curves for SubWH, after 17 min almost no monomers are formed 4. These facts can indicate that with CO2 addition the cellulosic fraction of grape seeds was degraded, compared to hemicellulosic fraction only in the case of SubWH. This


Page 13 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

could explain the increased TRS, monosaccharides and by-products yield, and the lower residue of SubWH+CO2 compared to SubWH.

3.3 Sugarcane bagasse Sugarcane bagasse is a raw material easier to hydrolyze than coconut husk and grape seeds, as it can be noticed by the solid residue left after the process (Table 2). The hydrolysates obtained from sugarcane bagasse by SubWH+CO2 presented no difference from those obtained by SubHW

30

in terms of TRS content, and little difference for the

pH value of the hydrolysate fractions (Figure 4, A and B, respectively). As cellulose and hemicellulose portions of sugarcane bagasse are completely liquefied at temperatures of 230 °C and 280 °C, respectively 38, the temperature of 250 °C for 30 min, used in the SubHW process, was able to break down the available cellulose and hemicellulose, as it can be noticed by the low solid residue. Because of this, the CO2 addition had little effect, and it was mostly in the by-products formation. The hydrolysates obtained by SubWH+CO2 presented lower content of monosaccharides and higher content of byproducts (Table 3). Figure 4 also shows the yield of sugars (C) and by-products (D) in the hydrolysate fractions obtained from sugarcane bagasse during the SubWH+CO2 process. It was not possible to separate the hemicellulosic and cellulosic fractions, since all sugars were recovered together. However, the significant formation of by-products started only at 12 min, differently from the observed in the SubWH process, where the significant formation of these compounds started at 4 min

30

. Thus, the higher by-

products formation observed in the SubWH+CO2 resulted from the long process. Although the yield of sugars first increased up to a maximum value and then decreased with time, the yield of by-products only increased with time. At around 12 min the


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 29

temperature outlet reached 210 °C, caused by the temperature profile inside the reactor. At this temperature, only hemicellulosic sugars were recovered. Nevertheless, if the process is conducted aiming the fermentable sugars production, it is important to control the balance between time and temperature, and the SubWH+CO2 of sugarcane bagasse could be stopped at 12 min to avoid the formation of by-products.

3.4 Pressed palm fiber For pressed palm fiber the solid residue at the end of SubWH+CO2 was the same obtained at the end of SubWH (Table 2). The hydrolysates obtained from pressed palm fiber by SubWH+CO2 presented similar TRS content to that obtained by SubWH, and the pH value of the hydrolysate fractions was quite higher after 24 min (Figure 5, A and B, respectively). Moreover, adding CO2 decreased the yield of monosaccharides in the hydrolysates, which was accompanied by the increase of by-products content (Table 3). In this case, both hexoses and pentoses reaction products increased in the SubWH+CO2 process. The yield of sugars and by-products in the hydrolysate fractions obtained during the SubWH+CO2 process are also presented in Figure 5 (C and D, respectively). For this raw material, a first fraction rich in pentoses was recovered up to 15 min, followed by a fraction rich in hexoses, which indicates hydrolysis of the cellulosic fraction of the biomass after that time. The change in the curve at 15 min in Figure 5A supports this hypothesis. The SubWH process was also able to separate the hemicellulosic and cellulosic fractions

4

. The hydrolysis of hemicellulose by SubWH+CO2 was

accompanied by the formation of furfural as a by-product of the pentoses, as well as the cellulose hydrolysis was accompanied by the production of 5-HMF, a by-product from the hexoses. On the other hand, SubWH was able to slow down the by-products


Page 15 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

formation, allowing the recovery of more fermentable sugars and less by-products (Table 3). Therefore, for pressed palm fiber, SubWH with water only at 250 °C is more advantageous than adding CO2 to the process.

3.5 General trends As expected, each raw material presented a different behavior when subjected to the SubWH+CO2 process. This may be partially related to the composition profile of the lignocellulosic complex, such as the variation of hemicellulose composition between plant types. Moreover, the hydrolysis rate varies between different carbohydrates 37. One of the main products of carbohydrate hydrolysis is glucose. The general mechanisms of glucose and other monosaccharides further reactions are presented in literature

37

. An important consideration is that glucose reversibly isomerizes into

fructose, which is a more reactive compound. When subcritical conditions are applied to glucose and fructose for short time (0.2-2 s) the reaction of glucose leads to fructose, saccharinic acids, erythrose, glyceraldehyde, 1,6-anhydroglucose, dihydroxyacetone, pyruvaldehyde and 5-HMF 39. The low pH may influence the product profile obtained by the hydrolysis of carbohydrate. For instance, dehydration, producing 5-HMF, is favored under acidic conditions 40. It was noticed that for sugarcane bagasse and pressed palm fiber, which both had their hemicellulosic and cellulosic fractions hydrolyzed by SubWH, adding CO2 accelerated the by-products formation. On the other hand, for coconut husk and defatted grape seeds the SubWH+CO2 process improved hydrolysis rates and cellulose depolymerization, leading to more oligosaccharides formation. Therefore, raw materials that were not completely hydrolyzed in SubWH can benefit from CO2 addition to the process.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 29

Figure 6 refers to the hydrolysis selectivity of a particular sugar towards its byproduct. It is known that C5 sugars react to furfural, while C6 sugars react to 5-HMF. Therefore, selectivity was determined as the ratio between the sum of C5 or C6 sugars and their respective by-products. By this criterion, the process with CO2 may result in improved selectivity in the beginning of the process, after which the CO2 addition could be stopped, and the SubWH process could be continued. After the selectivity is no longer favorable for SubWH, the process could be stopped, avoiding further formation of by-products. On the other hand, if the purpose is to obtain furfural, the addition of CO2 may accelerate the SubWH process, especially for coconut husk and pressed palm fiber. When taking into account that selectivity of 1 indicates that 50% of the sugar further reacted, it could be considered that selectivity below 1 is no longer favorable. By this criterion, for coconut husk SubWH+CO2 could be conducted up to 6 min followed by SubWH up to 10 min. For defatted grade seeds the SubWH+CO2 should be performed up to 4 min followed by SubWH up to 10 min. For pressed palm fiber SubWH+CO2 would be advantageous up to 6 min, followed by SubWH up to 16 min. Sugarcane bagasse could be subjected to SubWH+CO2 up to 10 min, and, in this case, further SubWH would result in increased by-products from C5 sugars.

4. Conclusions Total reducing sugars recovered from coconut husk, defatted grape seeds, sugarcane bagasse, and pressed palm fiber using SubWH+CO2 were up to 56% higher than for SubWH. Raw materials that did not have their cellulosic fraction hydrolyzed by SubWH benefited from CO2 addition. On the other hand, for raw materials that were completely hydrolyzed under SubWH, adding CO2 increased sugars reaction rates. One


Page 17 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

option to benefit from CO2 addition is to do so only in the beginning of the process, and then switch it to SubWH with water alone, until the selectivity is favorable. This way, sugars reaction, which occur at a later point in the process, can be prevented. Another option is to focus the production of furfural. In this case the addition of CO2 to SubWH may accelerate the process.

Ackowledgments The authors acknowledge the raw materials donation by CTBE, Agropalma, Ducoco Alimentos and Villa Francioni; and the financial support and scholarships from São Paulo Research Foundation (FAPESP, grants 2010/08684-8, 2011/19817-1, 2012/10692-4, 2013/17260-5 and 2013/10037-9), and CNPq (560914/2010-5, 160469/2011-2, 163699/2012-7, 166060/2015-1 and 152148/2016-7). M.A.A. Meireles thanks CNPq for the productivity grant (301301/2010-7).

References (1) BECOTEPS European Technology Platforms for the FP7. The European Bioeconomy in 2030. Delivering sustainable growth by addressing the grand societal challenges. http://www.epsoweb.org/file/560 (2) IPEA Diagnóstico dos Resíduos Orgânicos do Setor Agrossilvopastoril e Agroindústrias Associadas. (Aug/25/2016), (3) Cardenas-Toro, F. P.; Alcazar-Alay, S. C.; Forster-Carneiro, T.; Meireles, M. A. A. Food Pub. Health 2014, 4, (3), 123-139. (4) Prado, J. M.; Forster–Carneiro, T.; Rostagno, M. A.; Romero, L. A. F.; Filho, F. M.; Meireles, M. A. A. J. Supercrit. Fluid. 2014, 89, 89-98. (5) Cabral, M. M. S.; Abud, A. K. d. S.; Silva, C. E. d. F.; Almeida, R. M. R. G. Ciênc.Rural 2016, 46, (10), 1872-1877.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 29

(6) Prado, J. M.; Dalmolin, I.; Carareto, N. D. D.; Basso, R. C.; Meirelles, A. J. A.; Oliveira, J. V.; Batista, E. A. C.; Meireles, M. A. A. J. Food Eng. 2012, 109, (2), 249-257. (7) Vardanega, R.; Prado, J. M.; Meireles, M. A. A. J. Supercrit. Fluid. 2015, 96, 217227. (8) Goldemberg, J. Science 2007, 315, (5813), 808-810. (9) Cardenas-Toro, F. P.; Forster-Carneiro, T.; Rostagno, M. A.; Petenate, A. J.; Maugeri Filho, F.; Meireles, M. A. A. J. Supercrit. Fluid. 2014, 93, 42-48. (10)

Mlyafuji, H.; Nakata, T.; Ehara, K.; Saka, S. Fermentability of Water-Soluble

Portion to Ethanol Obtained by Supercritical Water Treatment of Lignocellulosics. In Twenty-Sixth Symposium on Biotechnology for Fuels and Chemicals, Davison, B. H.; Evans, B. R.; Finkelstein, M.; McMillan, J. D., Eds. Humana Press: Totowa, NJ, 2005; pp 963-971. (11)

Asghari, F. S.; Yoshida, H. Ind. Eng. Chem. Res. 2006, 45, 2163-2173.

(12)

Prado, J. M.; Lachos-Perez, D.; Forster-Carneiro, T.; Rostagno, M. A. Food

Bioprod. Process. 2016, 98, 95-123. (13)

Cantero, D. A.; Vaquerizo, L.; Mato, F.; Bermejo, M. D.; Cocero, M. J.

Bioresource Technol. 2015, 179, 136-143. (14)

Cantero, D. A.; Dolores Bermejo, M.; José Cocero, M. Bioresource Technol.

2013, 135, 697-703. (15)

Rostagno, M. A.; Prado, J. M.; Mudhoo, A.; Santos, D. T.; Forster-Carneiro, T.;

Meireles, M. A. A. Cr. Rev. Biotechnol. 2015, 35, (3), 302-312. (16)

Prado, J. M.; Vardanega, R.; Rostagno, M. A.; Forster-Carneiro, T.; Meireles,

M. A. A. Green Chem. Lett. Rev. 2015, 8, (1), 16-30. (17)

Berni, M.; Dorileo, I.; Prado, J.; Forster-Carneiro, T.; Meireles, M. Advances in

biofuel production. In Biofuels Production, Scrivener Publishing LLC: 2013; pp 1158. (18)

Sasaki, M.; Adschiri, T.; Arai, K. AIChE J. 2004, 50, (1), 192-202.

(19)

Sasaki, M.; Kabyemela, B.; Malaluan, R.; Hirose, S.; Takeda, N.; Adschiri, T.;

Arai, K. J. Supercrit. Fluid. 1998, 13, (1–3), 261-268. (20)

Cantero, D. A.; Sánchez Tapia, Á.; Bermejo, M. D.; Cocero, M. J. Chem. Eng. J.

2015, 276, 145-154. (21)

Brunner, G. J. Supercrit. Fluid. 2009, 47, (3), 373-381.


Page 19 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(22)

Brunner, G. Hydrothermal and supercritical water processes, Elsevier:

Amsterdam, 2014; Vol. 5, p 95-225. (23)

van Walsum, G. P.; Shi, H. Bioresource Technol. 2004, 93, 217-226.

(24)

King, J. W.; Srinivas, K.; Guevara, O.; Lu, Y.-W.; Zhang, D.; Wang, Y.-J. J.

Supercrit. Fluid. 2012, 66, 221-231. (25)

Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D.;

Crocker, D. Determination of Structural Carbohydrates and Lignin in Biomass. In NREL, Golden, CO, USA, 2011; p 11. (26)

Sluiter, A.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D. Determination of

Extractives in Biomass. In NREL, Golden, GO, USA, 2008; p 9. (27)

Sluiter, A.; Hames, B.; Hyman, D.; Payne, C.; Ruiz, R.; Scarlata, C.; Sluiter, D.;

Templeton, D.; Wolfe, J. Determination of total solids in biomass and total dissolved solids in liquid process samples. In NREL, Golden, GO, USA, 2008; p 6. (28)

Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D.

Determination of ash in biomass. In NREL, Golden, GO, USA, 2008; p 5. (29)

Hames, B.; Scarlata, C.; Sluiter, A. Determination of protein content in Biomass.

In NREL, Golden, GO, USA, 2008; p 5. (30)

Prado, J. M.; Follegatti-Romero, L. A.; Forster-Carneiro, T.; Rostagno, M. A.;

Maugeri Filho, F.; Meireles, M. A. A. J. Supercrit. Fluid. 2014, 86, (0), 15-22. (31)

Tödheide, K.; Franck, E. U. Das Zweiphasengebiet und die kritische Kurve im

System Kohlendioxid–Wasser bis zu Drucken von 3500 bar. In Zeitschrift für Physikalische Chemie, 1963; Vol. 37, p 387. (32)

Schacht, C.; Zetzl, C.; Brunner, G. J. Supercrit. Fluid. 2008, 46, (3), 299-321.

(33)

Miller, G. L. Anal. Chem. 1959, 31, 426-428.

(34)

Nelson, N. J. Biol. Chem. 1944, 153, 375-380.

(35)

Hunter, S. E.; Savage, P. E. Ind. Eng. Chem. Res. 2003, 42, (2), 290-294.

(36)

Miyazawa, T.; Funazukuri, T. Biotechnol. Progr. 2005, 21, (6), 1782-1785.

(37)

Toor, S. S.; Rosendahl, L.; Rudolf, A. Energy 2011, 36, (5), 2328-2342.

(38)

Sasaki, M.; Adschiri, T.; Arai, K. Bioresource Technol. 2003, 86, (3), 301-304.

(39)

Kabyemela, B. M.; Adschiri, T.; Malaluan, R. M.; Arai, K. Ind. Eng. Chem. Res.

1997, 36, (5), 1552-1558. (40)

Srokol, Z.; Bouche, A.-G.; van Estrik, A.; Strik, R. C.; Maschmeyer, T.; Peters,

J. A. Carbohyd. Res. 2004, 339, (10), 1717-1726.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 29

Figure captions Figure 1: Scheme of the hydrolysis equipment used for SubWH assisted by CO2.

Figure 2: Total reducing sugars in glucose equivalents (A), pH (B), yield of sugars (C) and by-products (D) obtained from sugarcane bagasse by SubWH 4 (open symbols) and SubWH + CO2 (filled symbols) processes at 250 °C.

Figure 3: Total reducing sugars in glucose equivalents (A) pH (B), yield of sugars (C) and by-products (D) obtained from coconut husks by SubWH

4

(open symbols) and

SubWH + CO2 (filled symbols) processes at 250 °C.

Figure 4: Total reducing sugars in glucose equivalents (A) pH (B), yield of sugars (C) and by-products (D) obtained from pressed palm fiber by SubWH 4 (open symbols) and SubWH + CO2 (filled symbols) processes at 250 °C.

Figure 5: Total reducing sugars in glucose equivalents (A) pH (B), yield of sugars (C) and by-products (D) obtained from defatted grape seeds by SubWH

4

(open symbols)

and SubWH + CO2 (filled symbols) processes at 250 °C.

Figure 6: Hydrolysis selectivity of saccharide production with respect to reaction products (► mol C5 sugar/mol furfural; ■ mol C6 sugar/mol 5-HMF) obtained from different raw materials by SubWH 4 (open symbols) and SubWH + CO2 (filled symbols) processes at 250 °C.


Page 21 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Figure 1


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 22 of 29

Figure 2


Page 23 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Figure 3


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 24 of 29

Figure 4


Page 25 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Figure 5


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 26 of 29

Figure 6

►C5/Furfural ■ C6/HMF 26 ACS Paragon Plus Environment

Page 27 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Table 1: Raw materials characterization (wt %, wet basis). a Reprinted from The Journal of Supercritical Fluids, Vol 89, Juliana M. Prado, Tânia Forster-Carneiro, Mauricio A. Rostagno, Luis A. Follegatti-Romero, Francisco Maugeri Filho, M. Angela A. Meireles, Obtaining sugars from coconut husk, defatted grape seed, and pressed palm fiber by hydrolysis with subcritical water, Pages 89-98, 2014, with permission from Elsevier. b Reprinted from The Journal of Supercritical Fluids, Vol 86, Juliana M. Prado, Luis A. Follegatti-Romero, Tânia Forster-Carneiro, Mauricio A. Rostagno, Francisco Maugeri Filho, M. Angela A. Meireles, Hydrolysis of sugarcane bagasse in subcritical water, Pages 15-22, 2014, with permission from Elsevier. Coconut husk a

Defatted grape seed a

Sugarcane bagasse b

Pressed palm fiber a

Moisture

10.66 ± 0.05

6.5 ± 0.2

11.05 ± 0.03

10.1 ± 0.2

Ashes

0.92 ± 0.01

5.7 ± 0.4

2.3 ± 0.2

5.7 ± 0.3

Extractives in water

3.8 ± 0.2

8.1 ± 0.5

1.82 ± 0.08

5.03 ± 0.03

Extractives in ethanol

1.5 ± 0.3

5.3 ± 0.6

3.74 ± 0.08

5.39 ± 0.05

Protein

0.9 ± 0.2

11 ± 2

1.5 ± 0.1

5.1 ± 0.2

Acid soluble lignin

1.61 ± 0.07

1.4 ± 0.7

3.2 ± 0.2

1.6 ± 0.3

Acid insoluble lignin

33 ± 3

46 ± 5

1.5 ± 0.6

30 ± 3

Glucan

15 ± 2

7±1

46 ± 2

19 ± 1

Xylan

19 ± 2

7.7 ± 0.9

25 ± 3

19 ± 4

Galactan

0.09 ± 0.02

0.29 ± 0.02

0.22 ± 0.03

0.16 ± 0.04

Arabinan

0.27 ± 0.02

0.58 ± 0.09

2.1 ± 0.3

0.68 ± 0.07

Mannan

0.020 ± 0.003

0.5 ± 0.1

--

1.1 ± 0.4

Sugars

27

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 28 of 29

Table 2: Solid residue left in the reactor after the SubWH 4, 30 and SubWH+CO2. Solid residue (%) SubWH

SubWH+CO2

Coconut husk

16

10

Deffated grape seed

35

21

Sugacane bagasse

5

3

Pressed palm fiber

16

16

28

ACS Paragon Plus Environment

Page 29 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Table 3: Monosaccharides and by-products obtained by SubWH 4, 30 and SubWH+CO2 of biomasses during 30 min (g/100 g raw material, w.b.). Coconut husk SubWH SubWH+CO2 Sugars Arabinose Galactose Glucose Xylose Mannose Fructose Total monosaccharides Byproducts Furfural 5-HMF 4-HBA Vanillin Total byproducts

Defatted grape seed SubWH SubWH+CO2

Sugarcane bagasse SubWH SubWH+CO2

Pressed palm fiber SubWH SubWH+CO2

0.26 0.16 1.13 1.31 0.19 0.25

0.19 0.09 0.32 0.25 0.14 0.66

0.12 0.09 0.14 0.23 0.05 0.11

0.21 0.11 0.52 0.14 0.21 0.26

0.32 0.05 2.01 0.69 0.12 0.87

0.16 0.03 0.46 0.21 0.09 0.39

0.34 0.10 0.76 0.87 0.12 0.24

0.21 0.05 0.22 0.21 0.14 0.15

3.39

1.65

0.69

1.45

4.10

1.34

2.43

0.99

23.33 1.88 0.80 0.07

12.73 12.33 1.14 0.04

1.28 0.09 0.04 0.03

3.28 3.92 0.06 0.04

4.6 1.14

Valorization of Residual Biomasses from the Agri-Food Industry by

Recommend Documents