Hydrothermal liquefaction of agricultural and forest biomass residue: Comparativestudy
Rawel Singh, Bhavya Balagurumurthy, Aditya Prakash, and Thallada Bhaskar*
Bio-Fuels Division, CSIR-Indian Institute of Petroleum (IIP), Dehradun, India* Corresponding author. Tel: +91 135 2525820, Fax: +91 135 2660202, E-mail: tbhaskar@iip.res.in

Abstract
Biomass is a promising feedstock for the chemical industry due to the presence of wide range of functionalities available withthe lignocellulosic biomass (the natural polymer). Hydrothermal liquefaction is an attractive approach for the conversion of
lignocellulosic biomass feedstocks because it obviates energy intensive drying steps. The objective of this study is toinvestigate the distribution of products, i.e. liquid, gas and solid from forest (pine wood, deodar) and agricultural (wheatstraw, sugarcane bagasse) biomass, produced by hydrothermal treatment (280 ᴼC for 15 min) under non-catalytic andcatalytic (KOH, K2CO3) conditions and analysis of bioresidue obtained as well as liquid hydrocarbons (oils) for the differencesin the bio-oil composition with respect to feed material. Agricultural biomass showed higher conversion rates under thermaland catalytic conditions compared to forest biomass. Sugarcane bagasse showed the highest conversion (95 %) among thefour samples investigated. Pine wood and deodar has similar conversions. The compositions of bio-oils from agricultural andforest biomass residue contained both phenolic compounds and furans. FTIR and Powder XRD analysis of lignocellulosic
biomass as well as bioresidue samples showed that the peaks due to cellulose, hemicellulose and lignin became weak in bio
residue samples.

Keywords: Lignocellulosic biomass, hydrothermal liquefaction, subcritical water, thermochemical conversion, bio-oil

1. Introduction
Biomass is an abundant and carbon-neutral renewableenergy resource for the production of biofuels andvaluable chemicals. Energy production from biomass has
the advantage of forming smaller amounts of greenhousegases compared to the conversion of fossil fuels, as thecarbon dioxide generated during the energy conversion
is consumed during subsequent biomass regrowth [1].
Abundant and inexpensive lignocellulosic biomass does
not compete with the production of food crops. Cellulose
is a polydisperse linear homopolymer consisting of regioand stereo-selectively β-1, 4-glycosidic linked Dglucopyranose units [2]. Hemicellulose (copolymer of anyof the monomers glucose, galactose, mannose, xylose,arabinose, and glucuronic acid), the second mostabundant component of lignocellulose, are plant cell wall
polysaccharides that are not solubilized by water but aresolubilized by aqueous alkali. Lignin is a three
dimensional amorphous polymer consisting of
methoxylated phenyl propane structures. The three
primary monolignols p-coumaryl alcohol, coniferyl
alcohol, sinapyl alcohol are the building blocks of lignin.
There are several methods of biomass conversion which
can be either biochemical or thermo-chemical routes.
Biochemical routes involve several steps such as
pretreatment, fermentation and separation of products by
various unit processes. Thermochemical routes also
require feedstock pretreatment steps such as moisture
reduction, size reduction. Superior to pyrolysis
technology, hydrothermal process (high-pressure directliquefaction technology) has the potential to produce
liquid oils that is not miscible in water, with much higher
calorific values and a range of chemicals including
vanillin, phenols, aldehydes, and organic acids, etc [3-5].
The process is especially best suited for wet materials as
the drying of feedstock is not necessary and water isused as one of the reactants. Hydrothermal liquefaction
involves the reaction of biomass in water at hightemperature and pressure with or without the presence ofa catalyst. The products include a bio-crude, an aqueous
fraction and a gaseous fraction. Hydrothermal
technologies are broadly defined as chemical andphysical transformations in high-temperature (200–600⁰C), high-pressure (5–40 MPa) liquid.
The objective of this study is to investigate thedistribution of products, i.e. liquid, gas and solid fromforest (pine wood, deodar) and agricultural (wheat straw,sugarcane bagasse) biomass, produced by hydrothermaltreatment (280 ᴼC for 15 min) under non-catalytic andcatalytic (KOH, K2CO3) conditions and analysis of liquidhydrocarbons (oils) for the differences in the hydrocarbon
composition as well as bioresidue obtained with respect
to feed material.

2. Materials and MethodsHydrothermal liquefaction experiments were conductedin a 500 ml high pressure autoclave (AutoclaveEngineers) at 280 ⁰C for 15 min using solutions of KOHand K2CO3. The reaction conditions were selected basedon our earlier investigations [6-8] In a typicalhydrothermal liquefaction experiment, the reactor was

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

loaded with lignocellulosic biomass and H2O/alkaline
solutions (1:6 by weight). Then the reactor was purged
five times with nitrogen to remove the inside air. Thetemperature was then raised up to 280 ⁰C at heating rateof 5 ⁰C min-1 and kept for 15 min at 280 ⁰C. Afterreaction, the reactor was left to cool down to the roomtemperature. The gaseous products were vented. The
liquid portion was then extracted with equal quantity ofdiethyl ether. The etheral solution thus obtained wasdried over anhydrous sodium sulfate, filtered andevaporated in a rotary evaporator at room temperature.
Upon removal of diethyl ether, this fraction was weighedand designated as bio-oil1. After extraction, theremaining water phase contained the water-solublehydrocarbons. Solid products were extracted withacetone in a Soxhlet extraction apparatus until thesolvent in the thimble became colorless. After removal of
the acetone under reduced pressure in a rotary
evaporator, this fraction was weighed and designated as
bio-oil2. Acetone insoluble fraction was dried at 80 ⁰Cthen weighed, called as bioresidue (solid residue).

3. Results and Discussion
Thermal and catalytic hydrothermal treatment oflignocellulosic biomass was carried out at 280 ⁰C for 15
min in the presence of various alkaline catalysts (KOHand K2CO3). Fig 1 shows the conversion of various
agricultural and forest biomass residue under thermaland catalytic conditions.

Fig 1: Effect of feedstock type on Conversion rates underthermal and catalytic conditions.

wood and deodar was almost same. 0.5 N K2CO3
solution showed greater conversion and bio-oil yields incase of pine wood compared to deodar. In case of bothpine wood and deodar 0.5N KOH showed great
conversion rates(86 %) and bio-oil yields (34%). Bothbio-oil yield as well as conversion rates were higher with
0.5N K2CO3 for agricultural (wheat straw and sugarcanebagasse) biomass compared to forest (pine wood anddeodar) biomass. From all the four tested feedstocks
sugarcane bagasse showed highest conversion (95 %)and bio-oil yields (36 %). The yield of gaseous products
were very less in all cases. The compositions of bio-oilsfrom agricultural and forest biomass residue contained
both phenolic compounds and furans. Use of different
types of biomass (agricultural and forest) have an
important effect on the formation of various compounds
in oil fraction. The ratio of biomass components differs inagricultural and forest biomass. Thus, the composition of
the functional hydrocarbons in bio-oil was different in all
the samples. FTIR and Powder XRD (X-ray diffraction)
analysis of lignocellulosic biomass as well as bioresidue
samples show that the peaks due to cellulose,
hemicellulose and lignin became weak in bio residue
samples which suggest that these components haveundergone hydrolytic cleavage/decomposition.

4. Conclusions
Agricultural biomass (wheat straw and sugarcanebagasse) showed higher conversion rates under thermaland catalytic conditions compared to forest biomass(pine wood and deodar). Alkaline catalysts (KOH andK2CO3) have found an important effect on thedecomposition of both agricultural and forest biomass
residue in terms of both bio-oil yield and conversion.
Product distribution of Pine wood and deodar was almost
same. 0.5N K2CO3 showed higher catalytic activity interms of both bio-oil yield as well as conversion rates for
agricultural (wheat straw and sugarcane bagasse)biomass compared to forest (pine wood and deodar)
biomass. The compositions of bio-oils from agriculturaland forest biomass residue contained both phenolic
compounds and furans.

References
1.

Agricultural biomass (wheat straw and sugarcanebagasse) showed higher conversion rates under thermaland catalytic conditions compared to forest biomass(pine wood and deodar). In case of liquefaction of wheat
straw using distilled water bio-oil yield was 29 % withoutcatalyst. The bio residue yield was 24 % and theconversion was 76 %. Using 0.5N KOH and K2CO3
solutions the bio-oil yield and conversion was increased.
The maximum bio-oil (35 %) yield was observed with 1N
KOH for wheat straw. In case of liquefaction ofsugarcane bagasse with distilled water the bio-oil yieldwas 25 %. The bio residue yield was 22 % andconversion was 78 %. Greater than 90 % conversion wasobserved with the alkaline catalyst in case of liquefactionof sugarcane bagasse. The product distribution from pine

2.
3.
4.
5.
6.
7.
8.

Stocker; Angew Chem Int Ed 47:92009211(2008)
Yang et al.; Chin J Catal 32:716-22(2011)
Appell et al.; Report of Investigation No. 7560,U.S. Bureau of Mines: Washington, D.C. (1971)
Huber et al.; Chem. Rev. 106: 4044–4098(2006)
Yokoyama et al.; Liquid Fuels Technol. 2: 115163(1984)
Bhaskar; Energ Fuel 18:234-241(2004).
Bhaskar; Chem Eng J 108:127-137 (2005).
Bhaskar; Bioresource Technol.97:90-98(2006)

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013