Energy Fuels 2010, 24, 3710–3712 Published on Web 06/03/2010
: DOI:10.1021/ef9012664
Response to “Comments on ‘Thermochemical Catalytic Liquefaction of the Marine Microalgae Duanaliella tertiolecta and Characterization of Bio-oils’ by Zou et al.” )
Shuping Zou,† Yulong Wu,*,‡ Mingde Yang,*,‡ Imdad Kaleem,§ Juanjuan Zhou,§ Chun Li,†,§ and Junmao Tong † School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, People’s Republic of China, § School of Life Science and Technology, Beijing Institute of Technology, Beijing 100081, People’s Republic of China, and Food College, Shihezi University, Shihezi 832000, Xijiang, People’s Republic of China )
‡
Received November 2, 2009 . Revised Manuscript Received May 10, 2010 We sincerely appreciate the comments1 on our work on the thermochemical catalytic liquefaction (TCL) of the marine microalgae Duanaliella tertiolecta and characterization of bio-oils.2 In our paper, we introduced a new thermochemical solvolysis process to convert microalgae D. tertiolecta into liquefied products with acidified ethylene glycol and investigated the physical and chemical characteristics of its bio-oils dissolved in chloroform. We recognize that TCL is one of the excellent methods to liquefy microalgae biomass because of the high liquefaction yield (>95%) obtained in our experiments, and these bio-oils are presented as an eco-friendly feedstock candidate for the biofuels and chemicals. In his comment, Weber made a comparison of the specific heating values of the starting D. tertiolecta and that of bio-oils and argued that there are potential problems in the energy balance, in that the product oils appear to contain more heating value than the starting algae. In addition, Weber also felt “ambiguous” to the reaction mechanism of “alcoholysis” in the liquefaction process. After careful consideration of Weber’s objection and re-examination of our own work, we respond to Weber’s comments. One of Weber’s main points is that there are problems related to the energy balance in our system. He stated: “Zou et al. reported that they were able to convert the algae nearly quantitatively into a bio-oil, whose specific heating value was 28.4 MJ/kg, i.e., nearly 50% greater than the estimated specific heating value of the starting algae”.1 However, we think there is a misunderstanding of our work, which is probably because of author’s neglection on the definition of term “liquefaction yield”, the separation procedure, and distribution of liquefaction products. In our paper, we used the term “liquefaction yield” as the evaluation parameter for liquefaction but not “oil yield”. Our aim is to comprehensively evaluate the feasibility of providing valuable chemicals or liquid fuels via TCL of marine microalgae D. tertiolecta. We consider that it might not be essential to use the bio-oils yield as a comprehensive evaluation parameter for liquefaction of microalgae because some valuable products are water-soluble compounds and can be used in the
chemical industry. For example, the water-soluble products from the solvolysis liquefaction of wood materials have great potential to supply raw material for the polyurethane resin industry.3 The procedure for liquefied product separation from the TCL of the marine microalgae D. tertiolecta was showed in Figure 1. As we have already mentioned in our paper, “after the preset time, the flask was cooled in cold water to room temperature. The crude oil was filtered, the liquid portion comprising ethylene glycol acidified with H2SO4 was recovered as a liquefacient for the next cycle, and the residual solid was washed with chloroform and dried at 105 °C for 1 day; the chloroform solution fraction was dried at 40 °C to obtain the bio-oils”.2 This procedure shows that the bio-oils obtained are only one part of liquefied products, and these bio-oils are water-insoluble and chloroform-soluble fractions (Figure 1), while the rest of the liquidied products obtained are watersoluble liquid portions and solid residues (Figure 1). Moreover, the liquefaction product yield is determined by the following ratios: liquefaction yield ðwt %Þ ¼
bio-oil yield ðwt %Þ ¼
weight of residue weight of raw material
100
ð1Þ
weight of bio-oil 100 ð2Þ weight of raw material
aqueous portion yield ðwt %Þ ¼ liquefaction yield ðwt %Þ - bio-oil yield ðwt %Þ ð3Þ The liquefied products include bio-oils, solid residues, and the aqueous phase. In our experiment, the bio-oil, residue, and aqueous phase yields of microalgae were about 19, 3, and 78% (Table 1), respectively, at the optimized reaction conditions, i.e., an added amount of 2.4% H2SO4 and a reaction temperature of 170 °C, with a 33 min reaction time. In other words, around 19% of the composition of feedstock algae was changed into bio-oil, around 3% of the composition became residual solids as byproduct, and around 78% of the composition remained in the aqueous phase or evaporated as light
*To whom correspondence should be addressed. Telephone: 86-01089796088. Fax: 86-10-69771464. E-mail:
[email protected] (Y.W.);
[email protected] (M.Y.). (1) Weber, R. Comments on “thermochemical catalytic liquefaction of the marine microalgae Duanaliella tertiolecta and characterization of bio-oils” by Zou et al. Energy Fuels 2009, 23 (12), 6575–6276. (2) Shuping, Z.; Yulong, W.; Mingde, Y.; Chun, L.; Junmao, T. Thermochemical catalytic liquefaction of the marine microalgae Dunaliella tertiolecta and characterization of bio-oils. Energy Fuels 2009, 23, 3753–3758. r 2010 American Chemical Society
1-
(3) Kurimoto, Y.; Takeda, M.; Koizumi, A.; Yamauchi, S.; Doi, S.; Tamura, Y. Mechanical properties of polyurethane films prepared from liquefied wood with polymeric MDI. Bioresour. Technol. 2000, 74, 151– 157.
3710
pubs.acs.org/EF
Energy Fuels 2010, 24, 3710–3712
: DOI:10.1021/ef9012664
Figure 2. Correlation by Soehr and Milner between the heat of combustion and the degree of reduction of biomass-derived materials.
Figure 1. Procedure for liquefied product separation from the thermochemical catalytic liquefaction of the marine microalgae D. tertiolecta.
Because the thermochemical catalytic liquefaction of biomass is a very complicated process4-6 and its reaction mechanism is still unknown, we are unable to explain its reaction chemistry. We totally agree with the comment regarding the alcoholysis, which is involved in not only depolymerization but also other chemical reactions, such as dehydration, decarboxylation, transetherification, etc. However, we disagree with Weber’s explanation that ethylene glycol is involved in the depolymerization by “insertion”. We calculated the mass of ethylene glycol recovered by reduced pressure distillation at the optimized TCL conditions, and a average recovery rate of 94.2% was found. Moreover, according to some data obtained from the distribution and characterization experiments of liquefaction products, we suggest that, on one hand, similar to water in hydrothermal liquefaction, ethylene glycol is mainly used as a liquefacient or a reaction medium in liquefaction with ethylene glycol. On the other hand, part of ethylene glycol was involved in esterification with organic acid from liquefied products to form fatty acid hydroxyethyl ester, which is similar to biodiesel. The recycling of ethylene glycol is quite important for reducing the cost of the TCL of microalgae. If the ethylene glycol acidified with H2SO4 is reused for the next cycle after the separation of bio-oils by the extraction of chloroform, the renewable value of ethylene glycol will substantially increase. To answer the comment that “the composition and specific heating value of the bio-oil are in good accordance with the functional form developed 60 years ago by Spoehr and Milner, which relates the heat of combustion of biomassderived materials to a quantity they call R, an approximation of the degree of reduction of the material”,1 we suggest that not all kinds of microalgae biomass and their bio-oils2,7,8 are close to the trend line (Figure 2), indicating that Spoehr and
Table 1. Yield of Liquefaction Productsa yield (wt %) product
run 1
run 2
run 3
average
bio-oil residue aqueous phaseb
18.22 3.17 78.61
20.01 2.84 77.06
17.85 3.45 78.70
18.70 3.15 78.12
a Obtained at the optimized reaction conditions: added amount of 2.4% H2SO4, reaction temperature of 170 °C, reaction time of 33 min, and feedstock ratio of materials/ethylene glycol of 1:5. b Calculated by the difference.
Table 2. Molar Mass Characteristics of the Water-Soluble Portion by High-Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (HPLC-ESI-MS) Analysis number
retention time (min)
molar mass (Da)
area (%)
1 2 3 4 5 6 total
12.35 13.04 15.89 15.90 18.53 29.08
139.2 146.3 153.2 179.1 194.0 229.3
3.7 5.3 12.7 16.2 8.5 2.3 48.7
organic fractions during the liquefaction process. The main compounds of bio-oils detected from D. tertiolecta were benzofuranone, fatty acid methyl ester, and fatty acid hydroxyethyl ester with a long chain from C14 to C18 with a high calorific value of 28.42 MJ/kg, which is higher than the calorific value of the microalgae material (20.08 MJ/kg). The main compounds of the water-soluble portion were amino acid and ammonia from the degradation of protein in D. tertiolecta, with a molar mass of 130-230 Da (Table 2). The carbon and hydrogen contents of the solid residual product, 32.71 and 4.11%, respectively, are lower than that of the feedstock (39 and 5.37%). The oxygen content of the solid residual product, 61.48%, is higher than that of the microalgae material (53.02%), indicating that the solid residual product has a lower energy density, which can be confirmed by the heating value of the feedstock and solid residual product (20.08 and 12.48 MJ/kg, respectively). We suggest that the mass and energy of products will be consistent with the starting feedstock if we keep in consideration all products (bio-oils, aqueous-phase portion, and solid residues) and not only bio-oils.
(4) Zou, X. W.; Yang, Z.; Qin, T. F. FTIR analysis of products derived from wood liquefaction with 1-octanol. Spectrosc. Spectrom. Anal. 2009, 29 (6), 1545–1548. (5) Kleinert, M.; Barth, T. Towards a lignincellulosic biorefinery: Direct one-step conversion of lignin to hydrogen-enriched biofuel. Energy Fuels 2008, 22 (2), 1371–1379. (6) Kleinert, M.; Gasson, J. R.; Barth, T. Optimizing solvolysis conditions for integrated depolymerisation and hydrodeoxygenation of lignin to produce liquid biofuel. J. Anal. Appl. Pyrolysis 2009, 85 (1-2), 108–117. (7) Miao, X. L.; Wu, Q. Y.; Yang, C. Y. Fast pyrolysis of microalgae to produce renewable fuels. J. Anal. Appl. Pyrolysis 2004, 71 (2), 855– 863. (8) Miao, X. L.; Wu, Q. Y. High yield bio-oil production from fast pyrolysis by metabolic controlling of Chlorella protothecoides. J. Biotechnol. 2004, 110 (1), 85–93.
3711
Energy Fuels 2010, 24, 3710–3712
: DOI:10.1021/ef9012664 neglecting other elemental contents. However, it can be justified from the results of the elemental analysis that we obtained after TCL, in which the carbon and hydrogen contents of bio-oils were 59.36 and 7.58%, respectively, which were higher than that of the raw material (39 and 5.37%). This indicates that the increase of carbon and hydrogen contents in the bio-oil also improved its specific heat of combustion, in addition to its oxygen content.
Milner’s function may be appropriate for some lignocellulosic biomass materials, such as wood7 (Figure 2), but not for all biomass, particularly microalgae. The main reason may be the difference in composition of various biomasses. For example, microalgae biomass is mainly composed of protein, fat, and raw cellulose, and the protein content exceeds 60%, while lignocellulose biomass is mainly composed of cellulose, semi-cellulose, and lignose, with these three components accounting for more than 95% of the composition. As for the increase of the specific heating value of bio-oils, Weber’s explanation that “a decrease in the concentration of oxygen in the bio-oil increases its specific heat of combustion” is focused only on the effect of the oxygen content while
Acknowledgment. We thank the referees for many valuable comments that have improved this paper and appreciate the financial support of this work that was provided by the National Basic Research Program of China (973 Program) (G2006CB705809) and the Science and Technology Innovation foundation of CNPC.
3712
