Catalytic Hydrothermal Liquefaction of Solid Food ...

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and other emerging technologies like pyrolysis and HTL (hydrothermal liquefaction). ... HTL of solid restaurant waste into light bio-oil is a sustainable renewable ...

Journal of Biofuels DOI : 10.5958/0976-4763.2015.00006.9

Vol. 6 Issue 1, January-June 2015 pp. 38-43

Catalytic Hydrothermal Liquefaction of Solid Food Waste for Light Bio-oil Production: Process Optimisation Yahaya Alhassan1,2*, Naveen Kumar1 1

Centre for Advanced Studies and Research in Automotive Engineering, Delhi Technological University, New Delhi-110042, India 2 Petrochemicals and Allied Department, National Research Institute for Chemical Technology, P.M.B. 1052, Basawa-Zaria, Nigeria *Corresponding author email id: [email protected]

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ABSTRACT Feedstocks availability has posed a big question on sustainability of biodiesel, bioethanol and biogas production. FWs (food wastes) are emerging sustainable renewable energy feedstocks, especially with the bio-refinery concept and other emerging technologies like pyrolysis and HTL (hydrothermal liquefaction). In this research work, process optimisation for the production of light bio-oil from solid restaurant waste is been reported. Solid restaurant waste was thermally liquefied using hot water under highpressure condition. Effects of heating temperature (150°C, 200°C and 250°C), biomass to solvent ratios (1:5, 1:10 and 1:15) as well as catalyst loading (5 wt%, 7.5 wt% and 10 wt%) are investigated. From the results as expected, increasing reaction temperature improved the production of light biooil and its fuel quality as well, with an optimum reaction temperature of 225°C. In contrast, increasing biomass to solvent ratiofrom 1:10 to 1:15 did not increase the oil yield. As such, the optimum biomass to solvent ratio was 1:10. Similarly, catalyst concentration of 5 wt% (weight of slurry) gives the best oil production. It could be concluded that HTL of solid restaurant waste into light bio-oil is a sustainable renewable energy source. Keywords: Food wastes, Fuel properties, Lightbio-oil, Liquefaction

1. INTRODUCTION Recently, there are vigorous developments in different countries and regions leading to industrialisation and consequently, issues of waste generation and management emanated. In the light of this, renewable fuels from different sources are been investigated by researchers. However, feedstocks availability has posed a big question on sustainability of biodiesel, bioethanol and biogas production especially, during largescale production of these fuels[1,2]. Interestingly, one emerging feedstocks source is FW (food waste) has superior advantages over other lignocellulosic materials. For example, they are widely available worldwide; they are non-seasonal unlike other feedstocks and most importantly, do not compete with the food chain. FW includes specific energy rich chemical components other than cellulose, hemicelluloses and lignin[3]. These include ketones and aldehydes, which have great tendencies to undergo thermal degradation during high temperatures reactions like pyrolysis and HTL (hydrothermal liquefaction). HTL is one of the most widely used and efficient thermally processes to obtain liquid fuel from FW and other lignocellulosic containing materials at moderate temperature range from 150°C to 350°C. HTL is a thermal conversion process of heating organic matter in the absence of oxygen and supported by catalyst, forming biochar, bio-crude or heavy oil and gaseous products including CO, CH 4 and H2 are produced[4], in the ratio depending on the extent of heating. The factors that affect HTL conversion of FW materials into bio-oil include reaction temperature, heating rate, material residence time, moisture content and catalyst concentration/loading[5]. It is imperative to note that, not all biomass and FW materials are suitable for HTL. The liquefaction of pinewood waste[4], microalgae[5] and wheat straw showed varying yields. For example,


Catalytic Hydrothermal Liquefaction of Solid Food Waste for Light Bio-oil Production: Process Optimisation

maximum reducing sugar yield (60.80%) was obtained during hydrolysis of wheat straw as reported by Ji et al.[6]. The use of ILs (ionic liquids), as non-aqueous solvents with unique properties and advantages such as low vapor pressure, high dissolution ability to wide range of compounds, ionic conductivity and most interestingly high thermal and chemical stability has been reported[7,8]. However, in order to effectively replace them (conventional ILs) with more promising ones, DES (deep eutectic solvents) otherwise called RTILs (room temperature ionic liquids) have emerged. They showed additional advantages with regards to their simple preparations, low toxicity, low cost, and low-temperature stability than conventional ILs[9,10].

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According to literature surveyed, HTL of several wastes materials has been investigated. For examples, Tungal and Shende[4], investigated the HTL of pinewood (Pinus ponderosa) reported maximum bio-crude yield of 55 wt % obtained at heating temperature of 250°C and 200 psi Nitrogen gas pressure. They noted that increasing reaction temperature from 225°C to 250°C results in increasing bio-crude yield from 24.02 wt % to 30.5 wt %, while higher temperatures favoured H2 production and low residue formation. Similarly, marine microalgae liquefaction was reported with an optimum sulphonic acid functionalised ion exchange resin (Amberlyst-15) of 15 wt% within 150 min and biomass to solvent ratio of 1:7.5, reporting highest reducing sugar yield of 61 g/ L[11]. The authors reported increasing active sites of catalysts and its expanded surface area as the major reasons behind the increasing reducing sugar production obtained with 20 wt % catalyst loading. In this research work, catalytic HTL of solid food waste from college restaurantusing alternative ILs as catalysts is presented. Reaction parameters suitable for the maximum production of light bio-oil are also reported. In addition, fuel properties of the produced oil are evaluated with the view for ensuring fuel quality. 2. MATERIALS AND METHODS 2.1. Materials and Methods Solid restaurant FW were obtained from the Delhi technological university canteen, New Delhi, India. Chemical reagents used were Central Drug House chemicals purchased from a chemical store in Delhi, India. All chemicals and reagents were analytical grade chemicals except otherwise stated. In addition, glasswares, containers and other laboratory instruments were initially washed and rinsed with diluted nitric acid and distilled water. Thereafter, allowed to dry in an oven overnight. 2.2. Preparation of DES (Deep Eutectic Solvents) For each DES, one mole of ChCl (139.63 g) was mixed with different molar ratio of HBD. DES 1 is formed by mixing ChCl and Urea 1:2; DES 2 is formulated by mixing ChCl and TsOH in the ratio 1:4 and DES 3 by mixing ChCl and Glycerol in the ratio 1:3, respectively. Other reaction conditions are: temperature 120°C, reaction time 180 min, stirring speed of 750 rpm and initial pressure of 5.0 MPa. 2.3. Production of light Bio-Oil A 100 mL capacity laboratory scale reactor unit (Figure 1) was used. Nitrogen gas was initially supplied into the reactor through a control valve. HTL was conducted at 150°C for 30 min reaction time. Other conditions included the catalyst concentration of 5 wt% and biomass to water ratio was 1:10, while the initial pressure was 6.0 MPa. After reaction completion, the supernatants were filtered, while the residue was used for the light biooil extraction. The acetone extraction was conducted. Other reaction conditions are reaction temperature of 150°C or 250°C, and reaction time was 60 min while stirring speed was 750 rpm. 2.4. Analyses Light bio-oil yield was by measured using the formula reported by Alhassan et al.[12]. Mass of oil (g) Yield =

x 100% Mass of feedstock used (g)

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Yahaya Alhassan, Naveen Kumar

Figure 1: Schematic reactor diagram for HTL 3

Density (g/cm ) was measured using density metre at 15.5°C [Antonn-parr, Germany]; whereas calorific value (MJ/Kg) was measured using an oxygen bomb calorimeter. All analyses were conducted based on ASTM standards. 2.5. Statistical Analyses All experiments were conducted in triplicates and values reported were statistical mean of triplicate analyses for which the experimental error was evaluated as the SD was computed. 3. RESULTS AND DISCUSSION Results for the optimisation of the reaction conditions is presented in this section. It was obvious from the results that the reaction conditions affected the products yield differently. For example, the optimal biomass to solvent ratio obtained was 1:9 as shown in Figure 2. It was reported that the solvent was required for the effective dissolution of the residue for insolvent. Excess solvent addition did not significantly improve the yield. This was similar to the finding revealed by Pali et al.[13]. In contrast, catalyst loading was found to be one of the most significant factors in the production of light bio-oil. During HTL of different lignocellulosic materials, catalyst type, its loading and selectivity are found to be very vital in the liberation of the carbohydrates (i.e., cellulose and hemicelluloses), free from the lignin surrounding it. Strong mineral acids catalysts have issues associated with their corrosion, expensive reactor specification and large waste-water generation[14]. While base catalysts show excellent delignification ability, decreased polymerisation and crystallinity index, which was found to be suitable for feedstocks containing low lignin content[15]. Figure 3 presents the effect of catalysts loading on the product yield. In Figure 4, the effect of reaction time is presented. Accordingly, the effect of reaction time was found to be less effective as compared to other reaction parameters. This could be attributed to the fact that, since the reaction time was recorded after attaining the required temperature, which takes an hour, some significant conversion could have been reached within this period. As regards to the effect of reaction temperature, it could probably be the most influential factor. Since HTL is a thermo-chemical process, this was expected. Figure 5 presents the effect of reaction temperature on the product yield for heavy oil production. 40

Vol. 6 Issue 1, January-June 2015

Catalytic Hydrothermal Liquefaction of Solid Food Waste for Light Bio-oil Production: Process Optimisation


conversion (% wt)

Yield (wt %)

Percentage product (%)

100 80 60 40 20 0 3


9 Biomass : solvent



Figure 2: Effect of biomass to solvent ratio on the product yield

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Yield (%)

80 70

Yield (%)

60 50 40 30 20 10 0 1

2 3 4 Catalyst concentration (% wt)



Figure 3: Effect of catalyst loading on the product yield


Yield (%)


Product yield (%)

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80 70 60 50 40 10


40 50 Reaction time (min)



Figure 4: Effect of reaction time on the product yield Journal of Biofuels


Yahaya Alhassan, Naveen Kumar


Yield (%)


Product yield (%)

60 50 40 30 20 10 0 110







Reaction temperature (oC)

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Figure 5: Effect of reaction temperature on the product yield

Increasing reaction temperature significantly increases the light bio-oil production. Although, thermal decomposition has been reported, it could be suggested that the thermal degradation temperature has not been attained yet. The decomposition temperature was reported to be around 350–550°C[16]. 4. CONCLUSION The paper herein reports the hydrothermal liquefaction of solid restaurant waste into light bio-oil as a potential burning fuel. The reaction conditions suitable for the production of the oil are herein reported. Optimal reaction conditions include reaction temperature of 225°C and reaction time of 30 min. The optimum catalysts concentration was 4 wt% and the biomass to solvent ratio of 1:10, as the best conditions for the production of light bio-oil. It is suggested that the most influential factors are temperature and catalysts concentration. ACKNOWLEDGEMENT The principal author is grateful to the support of the management of the National Research Institute for Chemical Technology, Zaria-Nigeria. REFERENCES [1]

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