Article pubs.acs.org/IECR
Rapid Optimization of Typha Grass Organosolv Pretreatments Using Parallel Microwave Reactors for Ethanol Production Chandana Janaka Abeywickrama,† Yakindra Prasad Timilsena,† Sudip Kumar Rakshit,‡ Laurent Chrusciel,§ and Nicolas Brosse*,§ †
Asian Institute of Technology, 58 Moo 9, Km. 42, Paholyothin Highway, Klong Luang, Pathumthani 12120, Thailand Lakehead University, Thunder Bay, Ontario Canada P7B 5E1 § Laboratoire d’Etude et de Recherche sur le MAteriau Bois, Faculté des Sciences et Technologies, Université de Lorraine, Bld des Aiguillettes, BP 70236, 54506 Vandoeuvre-lès-Nancy cedex, France ‡
ABSTRACT: A comparative study of organosolv process was performed at laboratory scale using traditional stainless steel batch reactor with parallel microwave (MW) reactors. Ethanol (with sulfuric or soda catalyst), formic acid, and performic acid organosolv processes were first optimized for the pretreatment of Typha capensis using MW reactors. The best conditions based on mass balance and Klason lignin content were reassessed using a traditional pressure steel reactor. The enzymatic hydrolysability of soda process revealed better results (reducing sugar yields = 77−87%) as compared to the sulfuric acid process (reducing sugar yields = 57−66%). Substantially higher delignification and better enzyme hydrolysability were observed for the formic acid process with hydrogen peroxide catalyst. This process produced a pulp with very low residual lignin (85%). It can be concluded from this study that parallel microwave technology could be used for rapid optimization of biomass pretreatment to narrow down the range of process parameters studied before a final optimization using a classical pressure reactor.
1. INTRODUCTION Lignocellulosic feedstock is the most abundant biomass resource on the planet and contains three main biopolymers: cellulose, hemicellulose, and lignin. Cellulose and hemicellulose sugars contained in such feedstocks can be utilized as a platform for the production of ethanol as well as other industrially important products.1 Cellulosic bioethanol produced from plant biomass is one of the many renewable energy alternatives to fossil resources.2 The use of bioethanol has raised considerable interest due to depleting fossil fuel reserves and increased air pollution caused by petroleum fuels.3 Although lignocellulosics contain carbohydrate-based polymers (cellulose and hemicellulose) to levels of more than two-thirds of the entire biomass dry weight, these sugars are often difficult to convert to useful derivatives mostly due to the impervious and protective lignin seal. Pretreatment by various physical, chemical, and biological techniques have been developed to disrupt the lignocellulose structure thus releasing the cellulose from the lignin.2 The purpose of pretreatment is to remove lignin and hemicellulose, reduce crystallinity of cellulose and increase porosity of the biomass to facilitate the subsequent bioconversion processes. Among the different steps involved in biomass to ethanol conversion, pretreatment is one of the most essential and difficult steps. Several pretreatment methods including steam explosion, sulfuric acid, sulfur dioxide, organosolv, ammonia, aqueous lime, sodium hydroxide, and wet oxidation have been developed for different biomass.24 However, pretreatment still remains the most expensive and time-consuming step in biomass conversion. Furthermore, it is very difficult to generalize the process conditions even for a similar kind of biomass owing to the broad variability with feedstock composition, nature, variety of species, conditions of © 2012 American Chemical Society
production, and even between batches. Several methods have been used for designing the optimization experiments including response surface methodology (RSM), central composite design (CCD), factorial design, etc.4−6 Use of microwave irradiation is an alternative approach for heating substances and is highly effective with many moist materials. The heating mechanism of a microwave can accelerate reaction rate, provide better yields, provide uniform and selective heating, and achieve greater reproducibility of reactions.25 The application of microwaves for biomass pretreatments have been reported for rice straw and bagasse immersed in water7 and used with acid or alkali as catalyst for the pretreatment of other feedstocks.8,9 Typha (Typha capensis) is a monoecious, perennial leafy aquatic plant, reaching up to 2 m in height. It spreads and grows very fast in slow-flowing waters, canals, ponds, stream banks, and marshes. It is considered as a weed or even as a pest due to its fast growing rate and because it invades arable lands and irrigation systems. Typha has considerable potential to be used as feedstock for the production of biofuel owing to its high productivity (50−60 ton/ha/year), easy delignification (high S/ G ratio), and its noncompetitive nature with food and feed production systems.10 In this paper optimization of different kinds of organosolv processes (ethanol, formic and performic acid) using typha grass and microwave treatment is described. The objective was to determine the optimal conditions for time, temperature, and Received: Revised: Accepted: Published: 1691
July 26, 2012 December 12, 2012 December 12, 2012 December 12, 2012 dx.doi.org/10.1021/ie3019802 | Ind. Eng. Chem. Res. 2013, 52, 1691−1697
Industrial & Engineering Chemistry Research
Article
Figure 1. Scheme of the reacting devices. (Device A) SER = spiral electrical resistance, Th1 and 2 = temperature sensors, V1 to 4 = valves, P = pressure sensor). (Device B) MO = microwave oven, PS = pressure sensor, QR = quartz reactor, RC = rotating carrousel, RP = reacting phase, TS = temperature sensor (only 2 quartz reactors are represented).
this equipment was its ability to test eight different reaction mixtures in a single run with automatic controlling and recording of the experiment conditions. 2.2. Pretreatment Using Microwave Reactor and Pressure Reactor. 2.2.1. Autohydrolysis. Typha samples of particle size 200 μm, 15 g (dw) for the steel pressure reactor (device A) and 3 g (dw) for the microwave reactor (device B), were supplemented with an appropriate amount of deionized water to make a final solid to liquid ratio of 1: 9 taking into account the moisture content of the sample. The mixture was heated to 200 °C with continuous stirring (device A by agitation and device B by rotation) for 1 h (see the temperature profile of the treatment in Figure 2). At the end of each
catalyst concentration for the pretreatment of typha grass under constant microwave radiation exposure and compare it with a classical pressure reactor system.
2. MATERIALS AND METHODS Typha straw (Typha capensis) was harvested in October 2011 from Pathum Thani, Thailand. The air-dried typha (moisture content 0.5%), the effect of temperature was lower and mass losses around 40−45% were obtained, whatever the conditions used. Figure 5B gives the effect of temperature and soda concentration on Klason lignin content of resulting pulp. The observed lignin content was high at lower concentration of soda (0.5%). It was observed that at 150 and 170 °C, the removal of lignin was increased rapidly with the increase in sodium hydroxide concentration. At 190 °C, a further increase in lignin content was observed for soda concentration of 1% but is not significant (in terms of the standard deviation). Formic acid-based pretreatments are among the most successful allowing efficient delignification of nonwoody materials.19 When used in the presence of catalytic amounts of hydrogen peroxide, the process relies on the action of peroxyformic acid generated in situ which degrades, solubilizes, and oxidizes lignin into small fragments.20,21 An initial set of experiments, designed to evaluate the influence of formic acid concentration, was carried out by setting values for a number of variables (temperature, 80 °C; time, 120 min). Previously published results showed that delignification was poor for formic acid levels in liquor below 70%,22 and for this reason this value was considered as the lowest level in our tests. Figure 6A gives the Klason lignin contents and the mass loss of the recovered solids. The mass loss trend is the result of two opposite processes, namely, the lignin and polysaccharides deconstruction at high hydronium ion activity (low formic acid concentrations) and solubility of lignin fragments at medium to high formic acid concentration. A minimal mass loss was observed with a concentration of 80% formic acid, whereas the maximum delignification was at a concentration of 90%. The latter concentration which corresponds to a good compromise between hydronium activity and lignin solubility was adopted for the next series of experiments dealing with hydrogen peroxide concentration. A variation of H2O2 concentration in the range of 0−6% was employed in the pretreatment process. The results (Figure 6B)
Figure 4. Ethanol organosolv pretreatments with acid catalyst using microwave-based device B. (A) Yields based on dry weight of raw materials. Standard deviations: 0.8−1.8% w/w. (B) Percent w/w of Klason lignin in the pretreated pulp. Standard deviations: 0.7−2.8% w/ w.
expected, the mass loss increases with the temperature of the treatment and with the sulfuric acid concentration. Similar results were previously described in the literature for the ethanol organosolv treatment of empty palm fruit bunch (EFB) where xylans removal increased with the severity of the treatment.17 Almost complete removal of hemicelluloses from the pulp was observed for a treatment performed at 190 °C at a sulfuric acid concentration of 1.6%.17 The slight decrease in mass loss observed between 0.7% and 1.2% of catalyst for the series at 150 and 170 °C were not significant and had a standard deviation of
