Liquefaction Waste carob and Potato. Ana Patrícia Viana Ventura. Instituto Superior Técnico. June 2016

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1 Liquefaction Waste carob and Potato Ana Patrícia Viana Ventura Instituto Superior Técnico June 2016 Abstract: In this work, the potato and sweet potatoes skin, and carob pod liquefaction were studied. These biomasses are embodied of considerable interest since they are industrial wastes, which almost none interest, utility but mostly with no value what so ever. Belonging to traditional Portuguese agriculture crops sweet potato, and carob waste, the local industry would be beneficiated with the development of a solution that uses those residues to produce added value products. The solution developed under this work was to depolymerize such wastes. The outcome of the referred process resulted is a brownish viscous liquid. The yield oil is the product of the reaction of the mixture of 20% biomass, 60% of 2-ethyl hexanol, 20% of diethylene glycol (DEG) and 3% w/w of an acid catalyst, p-toluenesulfonic acid (based on the total reactional mixture weight). For all biomasses, the reactions were carried out at 160 C. The liquid obtained products were subjected to several characterization experiments: hydroxyl number, acid value, ATR-FTIR, elemental analysis and SEM. The total content of phenolic compounds, antioxidant activity and the evaluation of the presence of maltose, sucrose, and D-glucose sugar in the extracts were also conducted. Keywords: Liquefaction, potato, sweet potato, carob, liquefied. 1. Introduction Since the 1970s, with the energy crisis installed many countries that have shown interest in using biomass as a fuel source for power generation reducing environmental impacts caused by fossil fuels 1. Fossil fuels are still the largest source of energy used, around 80% of energy consumption worldwide. Petroleumderived fuels have the advantage not only from the standpoint of being energy efficient but also due to the fact that it is easy to extract and to process making it an economically and still more advantageous when compared with the other alternatives. However, fossil fuel reserves are limited and its use is harmful to the environment. Biomass can be defined as the amount of organic material produced in a given area. Those tyoe of matter englobes products 1

2 like wood, corn stover, paper wastes, wood bark, etc. This renewable and sustainable energy source generates low amounts of pollutants, and contributes to reduce the greenhouse effect and global warming 2. At present the alternatives to petroleumbased fuel, the so-called bio-fuel, can be divided into three categories, commonly knonw as fisrt, second and third generation Thermochemical conversion The biomass energy transformation processes can be grouped into two types: biochemical conversion and thermochemical conversion (combustion, gasification, pyrolysis and liquefaction) (Figure 1). Biomass Conversion Technology The first generation biofuels are produced from agricultural crops (such as sugarcane, corn, sunflower, sugar beet, wheat). The major problem of this solution is its competition with the use of land for human food production. Biogas, bioethanol, vegetable oils and biodiesel made from cooking oils are examples of firstgeneration biofuels 2. Biochemical Conversion Thermochemical Conversion Combustion Gasification Pyrolysis Liquefaction Second generation biofuels have their origin in wood cellulosic materials such as vegetable fiber in wood or non-edible parts of plants (straw, wood waste, plant residues). This type of lignocellulosic biomass can be converted into fuel by biochemical or thermochemical procedures. This type of biofuels, unlike the first generation do not compete with human food 2. Finally, the third generation biofuels are based on fast-growing plant species, especially of microalgae. 2 Figure 1 Biomass conversion technologies 3 (adapted). Combustion is the burning of biomass in furnaces. This type of process is inefficient due to the moisture of the biomass and low energy density of fuel involved in this type of power generation. Gasification is the conversion of biomass by heat treatment into gaseous products, small amounts of carbon and ash. It can be classified according to the gasifying agent to be used (air, steam or oxygen) and is performed at elevated temperatures (> 800ºC) 4. The gases obtained are CO, CO 2, H 2O, H 2, CH 4, N 2, H 2S, SO 2, etc. and rely 2

3 manly on the gasifying agent, the operating conditions of the process and in the compostion of the biomass 5. Pyrolysis is the thermal degradation of biomass by heat in the absence of oxygen affording charcoal (solid) with greater energy density, bio-oil and fuel gas 1. Bio-oil may be used as fuel in diesel engines, boilers or gas turbines for the generation of heat and electricity. The temperature used in the pyrolysis is very important because for the production of bio-oil is required a lower temperature than for charcoal production. Depending on the operating conditions, the pyrolysis process can be divided into three subclasses: conventional pyrolysis, rapid pyrolysis and flash pyrolysis. Conventional pyrolysis is defined as the slow of the biomass, with large residence times (from 7.5 to 9.2 minutes) under temperature ranging from 277 to 677ºC. It is associated with the productio of charcoal. In the fast pyrolysis biomass is rapidly heated to high temperatures ( ºC) in the absence of air (oxygen) with short residence times (0,5-10s). It is recommended for the productiob liquid and / or gaseous products. The yields of this process are 60-75% (w/w) to liquid bio-oil, 15-25% (w/w) of solid coal and 10-20% (w/w) of non-condensable gases depending on the biomass used. To maximize the yield of liquid products resulting from the pyrolysis, it uses lower temperatures than those previously described, rapid heating and short residence times. If the objective is to maximize the yield of the gas resulting from pyrolysis higher temperatures must be used than those previously described, larger residence times and slow heating 1. In Flash Pyrolysis the main product are designated liquid bio-oil. The biomass undergoes towards a very rapid heating (residence time <0.5s) and at temperatures ranging ºC 1. Afterwards. the resulting mixture is quenched affording condensed intermediates before suffering decomposition giving gaseous products prior to the reaction or the formation of products with high molecular weight. The bio-oil obtained have 15-20% moisture content, an oxygen content of 35-40% and ash content and very low sulfur. The conversion of biomass, for example wood, is obtained has a range of 72-80% 6. The liquefaction of biomass will be described in the next section Liquefaction of lignocellulosic biomass Pyrolysis and liquefaction are two thermochemical processes in which the raw material is converted into a liquid product and are sometimes confused with each other. In the case of liquefaction the 3

4 macromolecules of lignocellulosic raw material (biomass) are broken down into smaller fragments in the presence of a catalyst. In pyrolysis, usually, there is no use of a catalyst and the decomposed fragments obtained are converted into biooil by homogeneous gas phase reactions. The liquefaction product has a high calorific value with low oxygen content and high conversion efficiency. The lowest oxygen content causes the fuel to be more chemically stable and requires less posttreatments 3. The direct liquefaction can be performed in different operative conditions: a temperature in the range of ºC and high pressures ( bar), in case of hydrothermal upgrading method (HTU) or solvolysis processes with organic solvents, with or without catalyst, at moderate temperatures ( ºC) and atmospheric pressure 3, 7. Solvolysis is defined as "chemical reaction between a substracte with a solvent. In a solvolysis mechanism may occur nucleophilic substitution or elimination reaction in which the nucleophile is the solvent molecule. The liquefaction of lignocellulosic materials in polyhydric alcohols combines the solvolysis reactions, depolymerization, thermal degradation and hydrolysis, by the following steps: o The solvolysis affords a micellar structure; o Depolymerization of the smaller, soluble molecules; o The thermal decomposition leading to new molecular rearrangements by dehydration, decarboxylation, C- O and C-C and breaking connections; o Hydrogenolysis the (a connecting C- C is replaced by hydrogen) in the presence of hydrogen; o The hydrogenation of functional groups. The lignocellulosic biomass has as main constituents cellulose (40-45%), hemicellulose (25-35%), lignin (15-30%) and up to 10% of other compounds (Figure 2). These components decompose into smaller molecules during the process of liquefying 7. Figure 2 Cellulose, hemicellulose and lignin arrangement, within the cell walls of the biomass Potato The potato can be found mainly in Asia (51.4%) and worldwide it occupies a harvested area up to 19,463,041 hectares in 4

5 2013. The production area in Portugal is hectares. In the following figure it can be seen how this area is distributed on the several continents in Europe 29,9% Oceania 0,2% Africa 10,1% America 8,4% Carob Carob can be found mainly in Europe (78.8%) and occupies an area up to 82,181 hectares in 2013 worldwide, while in Portugal that area is 9,800 hectares. The distribution of carob is depicted In figure 5, in Africa America Asia Europe Oceania Asia 51,4% Asia 7,8% Africa 13,4% Figure 3 Potato area of distribution in the various continents in 2013 (FAOSTAT data) Sweet Potato Having crop area of around 8,240,969 hectares in 2013, all over the world, sweet potato can be found mainly in Asia (50.9%) and Africa (45.4%). In Portugal reserved to this particular agriculture product is hectares. In the figure 4 it can be seen how this crop is distributed, in 2013, in the various continents. Europe 0,1% Asia 50,9% Oceania 1,7% Africa 45,4% Europe 78,8% Africa Asia Europe Figure 5 Carob area of distribution in the various continents in 2013 (FAOSTAT data). 2. Experimental work 2.1. Biomass Liquefaction This section describes the experimental procedure which was used for the liquefaction potato and sweet potato peeling waste, and carob. DEG, 2- Ethylhexanol from the chemical company Sigma Aldrich were used as solvents. p- toluenesulfonic acid was the catalyst. America 1,9% Africa America Asia Europe Oceania Figure 4 Sweet potato area of distribution in the various continents in 2013 (FAOSTAT data) Characterization In order to performed the characterization of the liquefied wood and its polyols, the following experiments were accomplished: hydroxyl number, acid value, ATR-FTIR, elemental analysis, SEM, total phenolic compounds content, the 5

6 Yield (%) antioxidant activity and estimating the presence of maltose, sucrose and D-glucose sugar in the extracts Acid value and OH number OH value and the acid value is calculated with the following expressions: OH number = PM KOH N (V B V KOH ) m sample + VA value acid (VA) = PM KOH N V KOH m sample ATR FTIR FTIR spectra were recorded on a BOMEM FTLA , ABB CANADA in the cm -1 range. 3. Results 3.1. Liquefaction of biomass The liquefaction trials were carried out in a 100 ml reactor. Various assays for each biomass with different reaction times were performed. It was also evaluated how temperature influences the reaction with sweet potato. The results will be further presented Potato The liquefaction of potato skin was evaluated at 0, 30, 60, 90 and 120 minutes at a temperature of 160 C (Figure 6). It can be seen most when the reaction time, the higher the yield obtained SEM Scanning electron microscopy (SEM) observations of wood powder and liquefaction residue and polyurethane foam, were micrographed on a Hitachi S equipment, with a 15 kv beam. Samples were sputter coated with a thin Time reaction (min) layer of gold to avoid electrostatic charging during scanning Quick tests Other tests of liquefied and corresponding extracts for each biomass were performed. The tests were as follows: elemental analysis (outsourcing), determining the total content of phenolic compounds, the antioxidant activity and determining the presence of maltose, sucrose and D-glucose Figure 6 - Effect of reaction time on potato liquefaction Sweet Potato Regarding sweet potato skin the liquefactions were performed at 0, 20, 30, 40, 50, 60, 70, 90 and 120 minutes at a temperature of 160 C (Figure 7). It can be seen that the reaction time increased with time. sugar in the extracts. 6

7 Yield (%) Yield (%) Figure 7 - Effect of reaction time on sweet potato liquefaction Carob As for carob the studies times were set at 0, 30, 60, 90, 120, 150 and 180 minutes at a temperature of 160 C (Figure 8). The reactional profile was almost the same as for sweet potato Time reaction (min) Table 1 OH value and acid value for different biomasses and extracts. Biomass Potato Sweet Potato Carob Product Value OH (mg KOH/g) Value acid (mg KOH/g) Liquefied 293 0,5 polyols 304 1,8 sugar ,8 Liquefied 411 7,2 polyols 284 3,8 sugar 565 5,5 Liquefied 390 2,5 polyols 288 3,3 sugar , Time reaction (min) Both the acid value and the hydroxyl numbers are in accordance with to Hu et al., 2012, Chen and Lu ATR-FTIR In next subchapters the ATR-FTIR spectra resulting from potato and sweet potatoes peel, and crob liquefaction will present Potato Figure 8 - Effect of reaction time in carob liquefaction Acid value and OH number The values obtained for the OH number and acid value are shown in the table below (Table 1). 0,9 0,8 0,7 0,6 0,5 0, Wavenumber (cm -1 ) Potato Liquefied Polyols Sugar Figure 9 - ATR-FTIR spectra of potato peel, liquefied extract polyols and sugar. 1 7

8 Sweet Potato 2-ethylhexanol solvent and the catalyst DEG 1 0,9 0,8 catalyzed by p-toluenesulphonic acid Potato 0,7 0,6 0,5 0, Wavenumber (cm-1) Figure 12 - Images of fresh biomass (potato) obtained by scanning electron microscope. Sweet potato Liquefied polyols sugar Figure 10 - ATR-FTIR spectra of sweet potato peel, liquefied extract polyols and sugar Carob 1,0 0,9 0,8 0,7 0,6 0,5 0, Carob Liquefied polyols sugar Figure 13 - Images of the residue after the liquefaction reaction (time = 60 minutes) obtained by a scanning electron microscope Sweet Potato Figure 11 - ATR-FTIR spectra of carob, liquefied extract polyols and sugar SEM The residues which are formed during the liquefaction process were analyzed by scanning electron microscopy (SEM) which Figure 14 - Images of fresh biomass (sweet potato) obtained by scanning electron microscope. allows to obtain high-resolution images of a sample surface morphology. It was intended to compare the surface of each fresh biomass with the residues obtained from the liquefaction reaction at 160 C with 8

9 4. Conclusions The aim of this work was the study of the liquefaction process of three biomasses: potato and sweet potato peel and carob Figure 15 - Images of the solid residues after the liquefaction reaction (time = 50 minutes) obtained by a scanning electron microscope Carob Figure 16 - Images of fresh biomass (carob) obtained by scanning electron microscope. pod. The assays were carried out in a 100 ml reactor for all biomasses. The biomass were liquefied in DEG and 2-ethylhexanol in the ratio 1: 3 catalyzed by p-toluenesulfonic acid, at a temperature of 160ºC. For each biomass various reaction times was tested in order to achieve the highest yield, i.e. the least amount of solid residue at the end of the reaction. The highest yields were obtained: for the potato skins was 70% at 120 minutes. Concerning the sweet potato peel was 74% at 50 minutes and for carob 88 % of the was liquefied after 90 minutes. The sweet potato peel was the biomass that needs less time to achieved the higher yield. The sweet potato was also carried out a study at different temperatures, 120 C, 140 C and 160 C for the reaction time which was obtained in a higher yield. At 120 C the reaction leaded to a 19% yield. While for a temperature of 140 C the liquefaction affords 66% of bio-oil. Figure 17 - Images of the residue after the liquefaction reaction (time = 90 minutes) obtained by a scanning electron microscope. The same experiments were conducted to characterize the raw materials, being all in acordande with the expected. In the ATR-FTIR spectra the most affected band by liquefaction were : cm -1 corresponding to stretching vibration of the hydroxyl groups; region of cm -1 9

10 corresponding to stretching of the CH bonds, decreasing throughout the reaction time, and the peaks 1057 cm -1 and 1033 cm - 1 corresponding to the CO vibrations. review. Renew. Sustain. Energy Rev. 15, (2011). References 1. Balat, M., Balat, M., Kırtay, E. & Balat, H. Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 1: Pyrolysis systems. Energy Convers. Manag. 50, (2009). 2. Rutz, D. Biofuel Technology Handbook. Contract 152 (2008). doi: / Balat, M. Mechanisms of Thermochemical Biomass Conversion Processes. Part 3: Reactions of Liquefaction. Energy Sources, Part A Recover. Util. Environ. Eff. 30, (2008). 4. McKendry, P. Energy production from biomass (part 3): gasification technologies. Bioresour. Technol. 83, (2002). 5. Balat, M., Balat, M., Kırtay, E. & Balat, H. Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 2: Gasification systems. Energy Convers. Manag. 50, (2009). 6. Seljak, T., Rodman Oprešnik, S., Kunaver, M. & Katrašnik, T. Wood, liquefied in polyhydroxy alcohols as a fuel for gas turbines. Appl. Energy 99, (2012). 7. Pan, H. Synthesis of polymers from organic solvent liquefied biomass: A 10