SYNTHESIS OF FURFURAL, LEVULINIC ACID AND
5-HYDROXYMETHYLFURFURAL BY ACID HYDROLYSIS OF LACTUCA SATIVA WASTE FEEDSTOCK FROM THE RESTAURANT WOK®.
Degree project by:
NICOLÁS RODRÍGUEZ GONZÁLEZ
Submitted to the office of Graduate Studies of Universidad de los Andes
In partial fulfillment to the requirements for the degree of:
CHEMICAL ENGINEER
Advisor:
M. Sc, Ph. D ROCÍO SIERRA
UNIVERSIDAD DE LOS ANDES ENGINEERING FACULTY
CHEMICAL ENGINEERING DEPARTMENT BOGOTÁ D.C. 2014
SYNTHESIS OF FURFURAL, LEVULINIC ACID AND
5-HYDROXYMETHYLFURFURAL BY ACID HYDROLYSIS OF LACTUCA SATIVA WASTE FEEDSTOCK FROM THE RESTAURANT WOK®.
Degree project by:
NICOLÁS RODRÍGUEZ GONZÁLEZ
M. Sc, Ph. D ROCÍO SIERRA Advisor
Ph. D PABLO ORTIZ Committee member
UNIVERSIDAD DE LOS ANDES ENGINEERING FACULTY
CHEMICAL ENGINEERING DEPARTMENT BOGOTÁ D.C. 2014
Abstract
Furfural (F), Levulinic acid (LA) and 5-hydroxymethylfurfural (HMF), can be synthesized by breaking down cellulose to simpler sugars followed by a dehydration process. These products have a wide variety of applications that make them economically suitable for production. In this study, pre-treated (dry and grinded) lettuce wastes are used as raw material for synthesis of F, LA, and HMF. For determination of structural carbohydrates in lettuce waste feedstock, the material was dried (at 105ºC), grinded (knife mill), and then submitted to a two-stage acid hydrolysis process using concentrated (72% w/w) H2SO4 at 30ºC and diluted (4% w/w) H2SO4 at 121ºC. Sugar recovery standards (SRS) were run alongside to correct for losses due to degradation of monomeric carbohydrates. It was determined that cellulose is present in 23.2% (w/w) and hemicellulose in 13.7% (w/w) which are over expected ranges although there is a significant difference in hemicellulose content within different lettuce feedstock. Temperature and acid concentration were manipulated to maximize the amount of products of interest by changing the temperature between 150ºC and 190ºC with 10ºC intervals while acid concentration was varied between 0.01 M, 0.05 M, 0.1 M, 0.5 M and 1 M of H2SO4. The best yields of desired products were 1.6% for F at 160ºC and 0.1 M H2SO4, 12% for LA at 190ºC and 1 M H2SO4 and 4% for HMF at 160ºC and 0.05 M H2SO4.
Resumen
Furfural (F), el ácido levulínico (AL) y el 5-hidroximetilfurfural (HMF), pueden ser sintetizados al romper la celulosa en azúcares simples seguido de un proceso de deshidratación. Estos productos tienen una gran diversidad de usos que los hace económicamente favorables para producir. Para este estudio, residuos de lechuga pretratada (Secada y molida) se emplearon como materia prima para la síntesis de F, AL y HMF. Para la determinación de carbohidratos estructurales en los residuos de lechuga, los residuos fueron secados (a 105ºC), molidos (knife mill) y procesados por hidrólisis ácida de dos pasos usando H2SO4 concentrado (72% p/p) a 30ºC y H2SO4 diluido (4% p/p) a 121ºC. Estándares de recuperación de azúcares fueron producidos para la corrección de azúcares perdidos debido a la degradación de carbohidratos monoméricos.Se encontró que la celulosa está presente en 23.6% (p/p) y la hemicelulosa en 13.69% (p/p) los cuales están por encima de los rangos esperados aunque se encontró una diferencia significativa en el contenido de hemicelulosa en distintos residuos de lechuga. La temperatura y la concentración de ácido se manipularon para maximizar la cantidad de productos de interés cambiando la temperatura entre 150ºC y 190ºC con intervalos de 10ºC mientras que la concentración de ácido se evaluó a 0.01M, 0.05 M, 0.1 M, 0.5 M y 1 M de H2SO4. Los mejores rendimientos de los productos de interés obtenidos fueron 1.6% para F a 160ºC y 0.1 M H2SO4, 12% para LA a 190ºC y 1 M H2SO4 y 4% para HMF a 160ºC y 0.05 M H2SO4.
DEDICATIONS
This work is dedicated to my family and all those who made this project possible. I am convinced that teamwork is the best way to achieve great things in life. This graduation project is one more opportunity that life has given me to learn and understand the importance of education and therefore, this graduation project is dedicated as well to each and everyone who wants to learn and progress in life.
Last but not least, this work is dedicated to my beautiful Colombia that certainly needs more investigation and further technological investment in order to achieve, someday, a developed and well-educated society.
ACKNOWLEDGEMENTS
I would like to thank Ph. D. Rocío Sierra for her support, knowledge and enthusiasm applied to this work. She is one more example of commitment and beloved dedication to achieve her goals.
Moreover, I would like to thank all the different lettuce suppliers for their constant and unconditional contribution of organic residues to this project, as without their help, this project would not have been the same.
Special thanks to Alfredo Santamaría, Viviana Ferreira, Deicy Tique and Mauricio Gómez for their support in all the experimental work.
Thanks as well to Andrés Simbaqueva, Nicolás Auza, Rafael Amaya and Juan Chiriví for their knowledge contribution to this work.
TABLE OF CONTENTS
Abstract ... 4
Resumen ... 5
Objectives ... 9
General Objective: ... 9
Specific Objectives: ... 9
1. Introduction ... 10
2. Literature Review ... 11
2.1. Lignocellulosic Feedstock ... 11
2.2. Products ... 12
2.2.1. 5-‐Hydroxymethylfurfural ... 12
2.2.2. Furfural ... 13
2.2.3. Levulinic Acid ... 13
2.3. Acid Hydrolysis ... 14
3. Methodology ... 15
3.1. Drying Residues ... 15
3.2. Characterization of lettuce residues ... 15
3.3. Sugar Recovery standards (SRS) ... 16
3.4. LA, HMF, and F production ... 17
3.4.1. Experimental Design ... 18
4. Results ... 19
4.1. Dry matter results for lettuce feedstock ... 19
4.2. Lettuce characterisation for structural carbohydrates ... 19
4.2.1. HPLC Results and Sugar Recovery correction. ... 19
4.2.2. Statistical analysis of the different lettuce feedstock samples ... 22
4.3. Effect of Temperature and Acid concentration in % Yields of desired products. 27 5. Conclusions ... 29
Appendix A: Molecules of Lignocellulosic feedstock and its structural carbohydrates ... 31
Appendix b: Structural Formula of Products of Interest and Further Products and Uses. ... 32
Appendix C: Synthesis Routes For The Desired Products ... 34
Appendix D: Experimental Illustrations ... 36
Objectives
General Objective:
Determine yields for furfural, Levulinic acid and 5-hydroxymethylfurfural per gram of feedstock produced through acid hydrolysis of lettuce (Lactuca Sativa) wastes at varying reaction conditions (temperature and acid concentration)
Specific Objectives:
• Determine the amounts of structural cellulose and hemicellulose per gram of lettuce
residue through standard analytical procedures.
• Determine the yields for structural carbohydrates degradation into Furfural,
Levulinic acid, and 5-hydroxymethylfurfural performed in acid reactions run in batch mode on lettuce waste at varying temperatures and acid concentrations.
1. Introduction
Organic wastes have become a major concern for the local government in Bogotá due to the lack of alternatives for waste treatments in the city. Around 6000 tonnes correspond to daily wastes produced in Bogotá, from which 35% are organic wastes and just 6% is being used for fertilizers production (El Espectador, 2013). The food industry is one of the main waste producers as they generate 46.48% of the total daily organic wastes and therefore they have a great impact on environment since these are not properly depleted generating several odours and substances leading to contamination (Unidad Administrativa Especial de Servicios Públicos, 2011).
Biomass can be effectively treated throughout different processes that result in a wide range of useful substances that can even help as fossil fuel alternatives. These products have a high commercial value, which allow the development of sustainable projects that contribute to solve waste treatment issues. Processes such as pyrolysis, gasification, liquefaction or hydrolysis have been proven to work for biomass conversion (Cai et al., 2012). However, biomass characterization can help to improve efficiency of the processes as it permits a specialized process for each type of biomass waste.
2. Literature Review
2.1. Lignocellulosic Feedstock
The main sources of biomass wastes come from vegetables and legumes that must be cleaned and selected before reaching the target audience. This is known as cellulosic material due to its main components: cellulose, hemicellulose and lignin. These renewable polymers can be converted into ethanol, citric acid, aromatic hydrocarbons and other liquid fuels (Lucia, 2008). Lettuce (Lactuca sativa) is one of the most popular vegetables found in salad therefore it releases significant quantities of useful feedstock. Restaurants already separate these lettuce residues from others enabling a better study of this type of biomass and a better application of treatment technologies.
The main advantage on working with Lignocellulosic feedstock is that its processing will become less expensive as fossil fuel prices rise and a lower environmental impact will be produced compared to petrochemicals nowadays (Lucia, 2008). The following figure shows the basic composition of Lignocellulosic material.
Figure 1. Chemical groups of lignocellulosic material (Kamm et al., 2013)
In appendix A is possible to find the molecular structure of Lignocellulosic feedstock and how it breaks down to simple sugars. Since glucose is the main C-6 sugar produced from cellulose, other hexoses will not be taken into account during the hydrolysis process.
2.2. Products
2.2.1. 5-Hydroxymethylfurfural
The most relevant advantage of 5-hydroxymethylfurfural (HMF) is the amount of intermediates it can produce at last. Nowadays, there is no industrial production of HMF due to the lack of efficient processes (lopes et al., 2012). It can be synthesized from glucose, fructose or even inulin and lead to 2,5-furandicarboxylic acid (FDCA) production, which is commonly used in pharmacology or 2,5-furancarbaldehyde (FDC) which can undergo different aldehyde reactions and its one of the best intermediates for synthesizing macrocyclic compounds, polyesters and polyamides (Lekowsky, 2001). Additionally, it is
an intermediate component for the production of Levulinic acid, which will be analysed as well.
2.2.2. Furfural
Due to its unsaturated bonds and aldehyde group, furfural is widely applied in agrochemical, pharmaceutical and plastic industries for example. It is rated within the top 30 high-value bio-based components (Werpy et al., 2004) and can be used as solvent and as intermediate for nylon and lubricant production. Its annual production reached up to 250.000 tonnes probably being the only unsaturated, large volume organic chemical produced from carbohydrate sources (Mamman et al., 2008). Throughout Lignocellulosic materials, furfural is produced from pentoses which are obtained as xylan, mannan or glucan is broken down (Wyman et al., 2005). On the other hand, furfural can further degrade into formic acid if temperature is kept high and in an acidic environment (Rose et al., 2000).
2.2.3. Levulinic Acid
Also known as 4-oxopentanoic acid. Even though it has never reached commercial use in significant volumes, Levulinic acid is also considered one of the 12 bio-based chemicals with a high potential platform (Werpy et al., 2004). Its ketone and carboxylic group allow the synthesis of several levulinic esters that could be used as gasoline additives. Additionally, it can be used for production of polymers, herbicides and anti-freeze agents. Glucose is the raw material for its production by a two-step acid hydrolysis. Two of the
most important final products that can be achieved through Levulinic acid are: γ -valerolactone and methyltetrahydrofuran (MTHF), which are high-value chemicals synthesized by catalytic reactions (Wang et al., 2013). Other substances that can be produced using Levulinic acid are shown in appendix B with their respective structural formula.
2.3. Acid Hydrolysis
The cellulose and hemicellulose found in lettuce feedstock can be broken down to simpler sugars by acid hydrolysis. This process requires H3O+ ions to break down the hydrogen bonds in cellulose and hemicellulose reducing its particle size to monosaccharides (glucose, xylose mainly). The amount of glucose is an estimate of the total cellulose in the feedstock while xylose will represent an estimate of hemicellulose in the original amount of sample analysed. H2SO4, HCl, HNO3, H3PO4 or organic acids can be used for acid hydrolysis but results may vary significantly (Cortinez, 2010). Since harsh conditions are to be applied, glucose and xylose may degrade to further products (Wyman et al., 2005), including the chemicals of interest.
Furthermore, to pass from monosaccharide molecules to the products of interest, a catalyst must be employed where metal (IV) phosphates (Weingarten, et al., 2013), ionic resins (Heguaburu et al., 2012) and acidic solutions (Marcotullio et al., 2010) have been used. A dehydration process takes place over pentoses leading to furfural while dehydration of hexoses would lead to 5-HMF and a further hydration would result in Levulinic acid and formic acid (see APPENDIX C for details).
3. Methodology
Lettuce organic residues were obtained from three specific sources: Go Green restaurant, Simone restaurant and WOK restaurant.
3.1. Drying Residues
Temperature was set up at 45ºC in a drying oven and lettuce feedstock (see APPENDIX D) was placed for over 48 hours. Water content was reduced below 10% in order to apply NREL Laboratory Analytical Procedure for determination of structural carbohydrates and Lignin in Biomass (Sluiter et al., 2008). Particle size was reduced for better surface area contact and storage advantages using a knife mill. The procedure was repeated with different samples of lettuce feedstock to analyse separately.
3.2. Characterization of lettuce residues
Standard analytical procedures were used to obtain reliable and replicable quantification of structural carbohydrates in lettuce residue following the NREL Laboratory Analysis Procedure (Sluiter et al., 2008). Using this protocol, 0.300 g of dried lettuce were mixed with 3 mL of 72% w/w H2SO4 and placed in a water bath at 30ºC during 1 hour (see APPENDIX D). Moreover, the solution was diluted with 84 mL of deionized water and placed in the autoclave at 121ºC for 1 hour. After cooling off, the solution was vacuum filtered through ceramic crucibles to retain insoluble lignin. Crucibles were dried at 105ºC during 6 hours and their masses were recorded afterwards. Then, crucibles were placed in the muffle at 450ºC during 24 hours. Weight difference corresponds to insoluble lignin.
An aliquot of 5 mL was taken from each filtered solution and neutralized with CaCO3 in order to avoid any further degradation of simple sugars. Samples were taken into vials for HPLC analysis and remaining solution was frozen in case future analysis is needed. This procedure was repeated for 4 different samples of dry lettuce feedstock and 5 samples of each lettuce feedstock were treated for analysis. To determine the acid insoluble lignin as a percentage of the lettuce feedstock, the following formula was implemented:
%𝐴𝐼𝐿= !!"#$%"&'#%!#&()!!!"#$%" !"#$%&$"'(
!"# (14)
3.3. Sugar Recovery standards (SRS)
Since sugar monomers obtained can degrade into other components, it would severely affect the glucose and xylose content found in the samples. Therefore, known contents of glucose and xylose were hydrolysed to find an estimate of the total glucose and xylose that could not been analysed due to degradation. 0.025g and 0.012g of glucose and xylose were mixed with 3 mL of 72% w/w sulphuric acid and 84 mL of deionized water. Solutions were filtered, neutralized and placed in vials for HPLC analysis. This procedure was repeated each time lettuce samples were introduced in the autoclave. Once obtained the SRS concentrations, the following formulas were applied for correction (Sluiter et al., 2012):
% 𝑅!"#$% = !!"#$
!!"!#. ×100 (15)
𝐶! = !!"#$
For polymeric sugar determination, an anhydrous correction is applied to monomeric sugar concentration. For C-5 sugars and C-6 sugars, Canhydro is 0.9 and 0.88 respectively (Sluiter et al., 2012). With the anhydrous correction done and applying eq. (4), it is possible to determine the cellulose and hemicellulose percentage present in the dry matter lettuce sample.
%𝑆𝑢𝑔𝑎𝑟!"# !"##$% = !!"!!"#$×!!"#$%&$'× !!
!"""!"
!"# (17) Where:
Wafter filtration: Weight of crucibles after filtration and dried during 6 h.
Wbefore filtration: Weight of crucibles after being dried during 24 h and before filtration.
%AIL: Percentage of acid insoluble lignin present in samples.
%Sugardrymatter: Polymeric Sugar percentage found in dry matter sample CHPLC: Concentration obtained by HPLC analysis (mg/mL).
Cinit: Known concentration of recovery sample before hydrolysis (mg/mL).
%Rsugar: Sugar recovery percentage.
%Rave.sugar: Average sugar recovery percentage.
Cx: Sugar concentration after hydrolysis and correction (mg/mL).
Canhydro: Sugar concentration after anhydrous correction (mg/mL).
Vfiltrate: Volume of water and H2SO4 added for solution (87 mL).
ODW: Weight of dry matter sample (g).
3.4. LA, HMF, and F production
The production phase was separated in two steps. First, as there is not enough information about LA, HMF and F production with lettuce feedstock, it is important to find out the
optimal conditions for acid concentration and temperature operation for further analysis. Once the optimal conditions are stated, a kinetic analysis can be done to find kinetic constants that fit properly in experimental data.
3.4.1. Experimental Design
Taking into account that there are many variables that may affect the production of F, LA and HMF, it is stated to analyse the effect of temperature and acid concentration on the production of F, HMF, and LA. A PARR multiple reactor was implemented for the experimental reaction. It is necessary to maintain a constant stirring of 200 rpm and a reaction time of 1h. A solid : liquid ratio of 1:50 was kept constant as well. The temperatures to be analysed start from 150ºC until 190ºC with 10ºC intervals. With respect to concentration, molarities 0.01 M, 0.05 M, 0.1 M, 0.5 M and 1 M are to be analysed.
Table 1. Design of Experiments for Degradation of Structural Carbohydrates
Temperature (ºC)
Concentration (M)
0.01 0.05 0.1 0.5 1
150 160 170 180 190
The results will be analysed through HPLC in order to determine the best conditions to obtain a higher yield of desired products.
4. Results
4.1. Dry matter results for lettuce feedstock
The drying process allows the removal of water that may affect characterisation results if water content was above 10%. Additionally, it allows an estimation of the remaining dry matter if an industrial process is taken place in future.
Table 2. Mass of lettuce feedstock after drying process
Sample lettuce Feedstock
Weight before drying process (g)
Weight after drying
process (g) %Difference
1 398,07 23,48 5,90
2 407,24 21,36 5,25
3 482,45 25,81 5,35
4 513,92 27,39 5,33
4.2. Lettuce characterisation for structural carbohydrates
4.2.1. HPLC Results and Sugar Recovery correction.
Determination of structural carbohydrates in based on a dry matter basis. The results obtained from HPLC correspond to structural carbohydrates.
Table 3. Structural carbohydrates concentration of the different analysed samples.
Lettuce Feedstock Sample
Experimental (mg/mL) After Correction (mg/mL) Glucose Xylose Glucose Xylose 1
A 0,6368 0,3660 0,8021 0,6083
B 0,7185 0,3916 0,9050 0,6509
C 0,7743 0,3937 0,9753 0,6544
2 A 0,7078 0,3496 0,8915 0,5811
B 0,7446 0,3639 0,9379 0,6048
3
A 0,7017 0,2664 0,8838 0,4427
B 0,7100 0,2681 0,8943 0,4456
C 0,6393 0,2225 0,8053 0,3697
4
A 0,7378 0,3081 0,9293 0,5120
B 0,7218 0,3528 0,9091 0,5864
C 0,7003 0,2920 0,8821 0,4853
D 0,7073 0,2990 0,8908 0,4970
TOTAL AVERAGE 0,8922 0,5365
Sugar recovery standards (SRS) are presented in Table 4. Since the concentration of every standard is known, it is expected to find a lower concentration from the original sample and the difference will correspond to sugar degradation.
Table 4. Sugar Recovery standards results
SRS
Experimental
Concentration(mg/mL) %Rsugar
glucose xylose glucose xylose
1 0,1577 0,0558 54,9 40,5
2 0,1806 0,0626 62,9 45,4
3* 0,3860 0,2460 134,4 178,4
4 0,1568 0,0547 54,6 39,7
5 0,2342 0,0893 81,5 64,7
6 0,2178 0,0861 75,8 62,4
7 0,2402 0,0870 83,6 63,1
8 0,2674 0,0941 93,1 68,3
9 0,2699 0,1020 94,0 74,0
10 0,2159 0,0900 75,2 65,3
11 0,2692 0,0798 93,7 57,8
*Sample 3 was removed from the average sugar recovery since the results are out of bounds.
Lignin and protein are considered in the same range since it is expected that the crucibles filter both and there is no experimental information required to analyse them separately.
Table 5. Insoluble Lignin and protein found in lettuce samples
Sample Lettuce Feedstock Weight of crucible before filtration(g) Weight of crucible after filtration(g) to lignin and protein(g) Weight corresponding
1
A 50,9631 50,9698 0,0067
B 51,0578 51,0648 0,0070
C 50,8822 50,9192 0,0370
2
A 50,9438 50,9598 0,0160
B 51,0434 51,062 0,0186
C 50,8672 50,8859 0,0187
3
A 51,0416 51,0652 0,0236
B 50,9929 51,0138 0,0209
C 50,9439 50,9679 0,0240
D 50,8232 50,86 0,0368
4
A 50,834 50,8425 0,0085
B 50,681 50,6931 0,0121
C 50,863 50,8838 0,0208
D 50,972 50,9984 0,0264
TOTAL AVERAGE 0,0198
With the average concentrations and weights of structural carbohydrates and insoluble lignin found in the samples, it is possible to calculate the percentage with respect to dry matter of lettuce feedstock.
Table 6. Percentage of the different components found in lettuce samples on a dry
matter basis
Compound Analysed
Average composition (% w/w)
Glucose 23,28
Xylose 13,69
Lignin + Protein 6,59
4.2.2. Statistical analysis of the different lettuce feedstock samples
In order to validate the results obtained in the lettuce characterisation, statistical analysis was made for the concentrations and weights obtained experimentally. ANOVA One-Way was implemented with Minitab® software following different assumptions (Hayden, 1980):
• Data evaluated is normally distributed. • Data has homogeneity in the variance.
• Populations must be independent from each other.
4.2.2.1. Data Validation
With figures (2), (3) and (4) it is possible to evaluate that these assumptions are properly followed.
Figure 4. Residual Plot for Insoluble Lignin
Figures (2), (3) and (4) show the data follow a normal distribution as seen in the normal probability plots since all data are close enough to the blue line and they are not randomly distributed. Analysing the residuals vs. fitted values plot, it is found a random distribution of residuals and no trend on their distribution meaning that the homoscedasticity (equity in variances) is fulfilled. This can be reassured with the histogram plot as it shows symmetry with no evidence of outliers. Therefore, conclusions based on the analysis of variance are experimentally valid.
4.2.2.2. Difference between lettuce feedstock samples.
Since analysed lettuce feedstock was received from different suppliers and these have different suppliers as well, with an ANOVA analysis is intended to evaluate significant differences within lettuce feedstock samples and results obtained on characterisation. The main hypothesis (H0) is that there is no difference between lettuce samples while the
alternative hypothesis (Ha) is that there is in fact a difference in their structural carbohydrates and lignin content. Therefore if p-value>0.005 then H0 is accepted while if p-value <0.005, H0 is rejected and Ha is accepted (University of reading, 2011).
Figure 5. p-value analysis and confidence intervals for glucose concentration of lettuce feedstock.
Figure 6. p-value analysis and confidence intervals for Xylose concentration of lettuce feedstock
Figure 7. p-value analysis and confidence intervals for insoluble lignin of lettuce feedstock
Evaluating the p-values in figures (5) and (7) it is stated that there is no significant difference in glucose and insoluble lignin between any of the lettuce samples. However, as shown in figure (8), there is a significant difference in xylose content with lettuce samples. This is confirmed by evaluating the confidence intervals showing that sample 3 is not within tolerance values of any other result. Moreover, samples 1 and 4 are different from each other as well.
4.3. Effect of Temperature and Acid concentration in % Yields of desired
products.
Figure 8. Percentage Yield of Formic Acid at different temperatures and acid concentrations
Figure 9. Percentage Yield of Furfural at different temperatures and acid concentrations
Figure 10. Percentage Yield of Levulinic Acid at different temperatures and acid concentrations.
Figure 11. Percentage Yield of 5-hydroxymethylfurfural at different temperatures and acid concentrations.
Figures (8), (9), (10) and (11) are the graphical representation of results obtained in the design of experiments. Levulinic acid and formic acid are similarly affected by temperature and acid concentration which can be explained by the reaction mechanism shown in APPENDIX C. For each molecule of LA produced, a molecule of formic acid is produced as well. HMF decomposes at high temperatures (Chang, 2006) and high concentrations of acid are no suitable for HMF stability since it can decompose into humins and LA (Girisuta
et al., 2013). In fact, the most favoured yield of LA is at conditions where yield of HMF is very low. F has its highest yield at around 160ºC and 0.1 M of H2SO4 but has the lowest yield of all 4 analysed components. This can be explained by furfural decomposition into formic acid (Rose et al., 2000). It is also stated that when furfural is present with xylose, the decomposition process into humins is accelerated affecting the final yield (Huber, 2010).
These results allow the reproduction of the degradation process to study each component separately if required since higher yields can be achieved and therefore permits a further analysis on the topic.
5. Conclusions
The sugar composition established in this study is over the boundaries found in literature. Baslam et al. found that inner leaves contain no more than 100 mg/g of dry matter, while outer leaves contain between 80 and 170 mg/g of dry matter that corresponds to 8-17% (Baslam et al., 2013). However, Baslam et al. used potassium phosphate buffer and they selected the three types of lettuce instead of lettuce as a whole. Even though residues are classified in Colombian restaurants, lettuce residues are not classified in types of lettuce used and therefore literature results are analysed in a more accurate way. Other studies show much lower values of glucose in lettuce. Pinho et al. (2007) presents a glucose content of 3 mg g-1, which is further apart from Baslam et al. (2013).
The xylose content in lettuce feedstock evaluated is significantly different from the analysed samples as ANOVA analysis showed a p-value >0.005. Further and detailed
analysis is recommended to verify this result since glucose content and insoluble lignin have no significant variation between samples.
The highest yield of furfural at the design of experiments was about 1.5 % with respect to dry matter of lettuce feedstock. This value is relatively low compared to the other components studied. Yields for FA and LA around 190ºC should be an inconsistency in data. Girisuta et al. (2006) evaluated as well the effects of acid concentration and temperature on LA yield and such a value is not presented, although the effect of acid concentration is similar to the one presented in this study.
Appendix A: Molecules of Lignocellulosic feedstock
and its structural carbohydrates
Figure 12. Illustration of a cell wall containing cellulose, hemicellulose and lignin as main components.
Appendix b: Structural Formula of Products of Interest
and Further Products and Uses.
a) b) c)
Figure 14. Structural formula of desired products. a) levulinic acid b) furfural c) 5-hydroxymethylfurfural
Figure 16. The different applications of furfural (Wondu Research and Technology Services, 2006)
Appendix C: Synthesis Routes For The Desired
Products
Figure 17. Production route of desired compounds using lignocellulosic feedstock. (Girisuta et al., 2006)
Figure 18. Reaction Mechanism for levulinic acid and formic acid production from hexoses. (Girisuta et al., 2006)
Appendix D: Experimental Illustrations
Figure 20. Lettuce Feedstock as received and after cleaned
Figure 22. Lettuce feedstock for characterisation
Figure 24. Filtration process to remove insoluble lignin
Appendix E: HPLC Results
The following HPLC results were done at the same conditions. The following table show the conditions applied for analysis.
Table 7. HPLC conditions for analysis
Flow rate (mL/min) 0.5
Aqueous phase 0.005 M H2SO4 Temperature (ºC) 65
Figure 26. HPLC Result for Furfural (min 56). Droplets of ethanol (min 26) were used to increase solubility.
Figure 27. HLPC Results for Formic Acid (min 16.7)
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