Patent Application
20230365764
The uninterrupted fossil fuel extraction for consumption, as an energy source or raw material for chemicals, is leading to an energy crisis [85,87]. The need for alternate renewable sources has been globally recognized and supported through changes in laws and regulations [19,87,119,130]. Several lignocellulosic waste products from the agricultural and pulp and paper industries have shown potential in acquiring key bio-based chemical building blocks for applications, including chemical and energy production [74]. Concurrent technological advancement in material thermochemical conversion methodologies such as pyrolysis and liquefaction of lignocellulosic biomass has paved the way toward synthesizing high-yield biooil [87].
Pyrolysis, a relatively low-cost thermochemical method than compared to liquefaction [59], has been studied for biooil synthesis. The feedstock materials used in those studies include wood [17,67], cellulose [17,47], sawdust [16], corn stover [16,70,117,135], and Kraft lignin [10,13,22,24]. In pyrolysis, the microwave reactor temperature (TR) and heating rate are the major variables that determine the yield of pyrolytic products. Research has shown that fast (TR˜500-650° C.) and slow pyrolysis (TR˜400° C.) produce two different outcomes, biooil and biochar, respectively [59]. Fast microwave pyrolysis produces a biooil with low oxygen but high carbon content along with superior heating value [57]. This former feature is of interest in the context of converting biooil into a low-viscous thermoplastic polymeric content. Crude and modified Kraft lignin (KL) biooils contain highly aromatic compounds that can replace petroleum-based chemicals in various applications [7,50,66]. The current global lignin production amounts to ˜50 million tonnes per year. Although Kraft lignin is applied in water purification, soil treatment, and chemical production, it remains an underused by-product of the pulp and paper industry [7]. There have been attempts of using natural fibres and bio-based fillers in polymer manufacturing; however, most polymer matrices are made of petroleum-based by-products and diluents, e.g., vinyl-ester and styrene [4,96,118]. Studies have shown that crude or modified Kraft lignin biooil can be successfully used to synthesize resins that have comparable properties to petroleum-based resins [125,132].
To facilitate further description of the embodiments, the following drawings are provided in which:
In one aspect, the present disclosure relates to investigating the impact of using spruce and hemp biochar, at varied ratios and operating temperatures, on the yield and composition of the biooil from pyrolyzed KL. In another aspect, the final goal of this present disclosure is to synthesize a biooil that can be taken as a precursor material for conversion into a novel bio-based thermoplastic polymer. Hence, testing and characterization of the biooil produced from the study described in the present disclosure are key to establish new ‘optimal’ feedstock and operating conditions and determining whether the biooil has to be upgraded.
In one aspect, the present disclosure relates to a method of pyrolysis of Kraft lignin, including providing a microwave generator system, providing a Kraft lignin feedstock in the system, providing a biochar in the system as a microwave receptor, providing nitrogen atmosphere in the system, and heating the feedstock and receptor using microwave energy to make a biooil. In another embodiment of the method, the microwave receptor may be selected from the group consisting of a spruce biochar, a hemp biochar, and both a spruce biochar and a hemp biochar. In another embodiment of the method, the microwave energy may be generated at a power level in the range of 300 W to 600 W. In another embodiment of the method, the microwave energy is generated at a power level selected from the group consisting of 300 W, 450 W and 600 W. In another embodiment of the method, the feedstock and the receptor are heated for a residence time of 30 minutes. In another embodiment of the method, the microwave energy is applied using a power level selected such that the temperature of the feedstock does not exceed 600° C. In another embodiment of the method, the microwave energy is applied for a residence time such that the temperature of the feedstock does not exceed 600° C. In another embodiment of the method, the microwave energy is applied using a combination of a power level and a residence time selected such that the temperature of the feedstock does not exceed 600° C. In another embodiment of the method, the receptor is 50 wt. % of the feedstock and the receptor. In another embodiment of the method, the wt. % of the receptor is 60 wt. % or 70 wt. % of the feedstock and the receptor. In another embodiment of the method, the wt. % of the receptor is in the range of 50 wt. % to 70 wt. % of the feedstock and the receptor. In another embodiment of the method, the method further includes the step of collecting the biooil as a non-condensable gas. In another embodiment of the method, the non-condensable gas is cooled. In another aspect, the present disclosure relates to a biooil made according to any of the above methods, where in one aspect, the biooil includes a phenolic content in the range of 86.6% to 97.9%, greater than 86.6%, in the range of 86.6% to 90%, in the range of 90% to 95% or in the range of 95% to 97.9%. In a further aspect, the present disclosure relates to a biooil including a phenolic content in the range of 86.6% to 97.9%, greater than 86.6%, in the range of 86.6% to 90%, in the range of 90% to 95% or in the range of 95% to 97.9%.
In another aspect, at this stage, the observation and primary quantitative results are available to be discussed. The KL biooil synthesized is divided in two phases i.e., the light and heavy phases which are translucent off-white and opaque dark-brown, respectively. It was found an ice bath and cooling water of 16° C. biooil yield is insufficient to reach ‘expected’ pyrolysis oil range, i.e. 20 wt. %. Spruce biochar, as a microwave receptor, demonstrated a higher average KL biooil yield at all power levels compared to hemp biochar. With increasing power level from 300 W to 600 W, the biooil yield increased while the biochar yield reduced. 50:50 ratio of KL and wood biochar feedstock exhibited the highest biooil yield. On pyrolyzing, KL turned into a shiny char that bonds with the spruce/hemp char to form agglomerates. In another aspect, further testing is conducted to analyze the biochar and biooil composition.
Microwave pyrolysis was chosen to treat KL as it allows for uniform heating and provides benefits such as cost avoidance by using a sample in original size and low ash production.
The feedstock and operating conditions investigated in this research were chosen after conducting literature review and understanding the current information gaps. To our knowledge, the impact of spruce and hemp biochar on KL biooil and biochar yields and compositions have not been investigated. The power levels, i.e. 300 W, 450 Wand 600 W, were undertaken to attain the targeted feedstock temperature range, i.e. 450-650° C. and attempt to obtain a highly aromatic biooil with low moisture content. Based on previous knowledge, nitrogen was chosen as a pyrolysis atmosphere since it outputs a higher yield of phenols in lignin biooil over 450-750° C. compared to carbon-dioxide.
In another aspect, according to data obtained, we can conclude that the combination of spruce, 600 W and 50:50 KL-wood char feedstock ratio appear to be the most ‘optimal’ operating conditions to obtain the highest KL biooil yield in a microwave-assisted pyrolysis treatment in the presence of nitrogen. In order to form a KL bio-based polymer, the monomers present in the biooil have to be determined and studied in comparison to petrochemical monomers. Consequently, additional tests including, H NMR and GC-MS, are carried out to present the detailed composition of the biooil. The moisture, ash, C, H, N, O and S contents in the Kraft lignin and biochar were determined using proximate and ultimate analysis. SEM and FT-IR was also carried out to understand the morphological and chemical properties of the biochar.
In one aspect, the present disclosure relates to a method of pyrolysis of Kraft lignin, including providing a microwave generator system, providing a Kraft lignin feedstock in the system, providing a biochar in the system as a microwave receptor, providing nitrogen atmosphere in the system, and energizing the system at a power level and heating the feedstock using microwave energy for a residence time to create a biochar from the feedstock. In another aspect, the biochar added as a microwave receptor is selected from the group consisting of a spruce biochar, a hemp biochar, and both a spruce biochar and a hemp biochar. In another aspect, the power level is in the range of 300 W to 600 W. In another aspect, the power level is selected from the group consisting of 300 W, 450 W and 600 W. In another aspect, the residence time is 30 minutes. In another aspect, the microwave power level and residence time is selected such that the temperature of the feedstock does not exceed 600° C. In another aspect, the receptor is 50 wt. % in the feedstock. In another aspect, the wt. % of the receptor in the feedstock is selected from the group consisting of 50 wt. %, 60 wt. % and 70 wt. %. In another aspect, the present disclosure relates to a biooil with a phenolic content in the range of 86.6% to 97.9% produced according to methods described in this disclosure. In another aspect, the present disclosure relates to a biooil with a phenolic content in the range of 86.6% to 97.9%.
The present invention in one embodiment relates to a method of microwave pyrolysis of Kraft lignin (“KL”) to boost the content of phenolic compounds in a biooil. In another embodiment, the method relates to microwave pyrolysis process conditions based on Kraft lignin biomass with an interest in bio-replaced phenolic chemical blocks, a precursory material for thermoplastic polymeric chain derivation. In another embodiment, the method relates to the synthesis and characterization of biooil leading to phenolic chemical blocks identification and yield. In another embodiment, the method relates to a highly phenolic KL biooil applied in a controlled polymerisation process (e.g., ATRP or RAFT) to synthesize a Kraft lignin biooil-based thermoplastic.
For certain embodiments, the present inventors have found that the microwave receptor percentage and power level, as well as the interaction between microwave receptor percentage and microwave receptor type, have a significant contribution toward achieving both a high-yield biooil and a phenolic-rich composition. In one embodiment, a 50 wt. % microwave receptor in the feedstock yielded the highest biooil yield across most power levels studied, noting that pyrolysis of KL at 450 W and 600 W yielded relatively similar biooil yields. The obtained phenolic content ranged between 47-97% in the KL biooil samples, with high yield compounds accounting for creosol, guaiacol, and 4-ethylguaiacol. At increasing power levels, the phenolic content in KL biooil was primarily observed to decrease. In another embodiment, the method included an operating power level of 450 W applied to a 50 wt. % spruce biochar added to KL as microwave receptor.
Materials and Methods
Microwave Pyrolysis
Nitrogen atmosphere was used to create an inert environment in the reactor. Compared to CO2 and H2, pyrolysis in N2 atmosphere can produce higher and similar biooil yields, respectively. The Bioenergy and Bioproducts Research Laboratory (BBRL) is equipped with a VWR generator that uses a pressure swing adsorption to remove the oxygen, carbon dioxide and water vapor from air to provide high purity nitrogen. In order to promote uniform heating in the feedstock and to determine whether the compositional difference of microwave receptors generated from wood and grass biomass impacts the biooil yield and composition, spruce and hemp were selected for the pyrolysis process. Additionally, these biomass were locally sourced waste products, thus their valorization in the microwave pyrolysis process promotes a circular bioeconomy. Spruce and hemp biochar were produced in the BBRL. The biochar was synthesized by pyrolysis of 1 kg hemp and spruce at 2700 W for one hour in a nitrogen atmosphere; 100 g of biochar were added as microwave receptors. The power level and residence time were chosen based on previous research indicating that the lowest moisture content in biochar was achievable at 2700 W [133]. A schematic of the microwave pyrolysis system has been illustrated in
The VWR generator extracts and converts air into nitrogen. Nitrogen was supplied at 95 psi and 1 SLPM. Before starting a trial, the system was purged with nitrogen for a minimum of 5 minutes, to ensure an oxygen-free environment, and the cooling water was stabilised at 20° C. MUEGGE (manufacturer of the microwave system) software was used to select the desired power level (the power level dictates the reactor temperature). Stub tuners, mica sheet and Teflon sheet were used to ensure that the microwave reflection is always lower than 5%. PicoLogo software, connected to a thermocouple, records the reactor temperature with an error of ±10° C.
Water was supplied at 19-21° C. and maintained between 20-25° C. to cool the magnetron, power generator and condenser columns during pyrolysis. The feedstock was pyrolyzed by microwave heating to produce biochar, biooil and gas. The biochar was collected in the reactor, non-condensable gas flowed to the fume hood and condensable gas was partially cooled down and collected as biooil. The condensation system was made up of two water-cooled Allihn (bulb) condenser columns and a round bottomed flask placed in an ice bath. The biooil was collected and stored in a freezer.
The goal of the microwave pyrolysis trials was to determine the impact of (1) percentage of microwave receptor in the feedstock, (2) microwave receptor type and (3) microwave power level on the KL biooil yield and composition.
Material and Microwave Design-of-Experiments
A factorial design was used to carry out KL microwave pyrolysis and address the hypothesis connecting the biooil yield and composition. The parameters to be varied were percentage of microwave receptor applied in feedstock (3 levels), microwave receptor type (2 levels) and power level (3 levels), and as described in the Table 1.
Each combination, e.g., adding 50 wt. % of microwave receptor to KL in the feedstock pyrolyzed at 20% (600 W), was repeated three times, amounting to a total of 54 runs for microwave pyrolysis of KL as described in Table 2. In order to reduce the experimenter's bias, the runs defined in Table 2 were carried out in a randomized trial order as generated in MiniTab. The randomized trial order can be found in Table 3.
Based on the factorial design exercise, the statistical model for the study described in the present disclosure was created, as shown by Equation 1.
Y
ijk=μ∝i+τj+∝τij+βk+∝βik+τβjk+ατβijk+εijk Equation 1
The significance for hypothesis testing in the study described in the present disclosure was set at 0.1 as it would be expensive, e.g., recommendation to use a less effective feedstock and wrong cost estimations, to miss the impact of the above process parameters on the biooil yield based on the 54 samples. The microwave pyrolysis parameters for KL biooil yield optimization were evaluated by statistical and graphical analysis of 54 trials. In order to optimize for both KL biooil yield and phenolic content in the biooil, the factor combinations conducive for higher yields were used as the foundation for selection of KL biooil samples analyzed to investigate the impact on the chemical distribution. Sections “Optimized Conditions for KL Biooil Yield” and “Overview of Chemical Composition for KL Biooil” in this specification provide further information on the selection of the 12 KL biooil samples for GC-MS analysis. Characterization of the 12 samples did not only provide biooil compositional details for relevant factor combinations, but it was also cost-effective and favorable for the project timeline.
Biooil Characterization
The chemical composition of KL biooil was analyzed in order to discuss its suitability in a resinification process. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was carried out to determine the concentration and yield of aromatic and aliphatic compounds in the biooil (<200 g/mol) [21]. During the GC-MS analysis, GC uses distinctive chemical properties to separate molecules into pure compounds. GC is followed by MS, whereby the pure compounds are accurately identified and quantified based on their mass-to-charge ratio [3]. GC-MS analysis was conducted with a PerkinElmer Clarus 680 GC coupled to a Clarus SQ 8 MS, as illustrated in
For GC-MS characterization of the KL biooil samples in the study described in the present disclosure, the GC injection port was operated at 280° C. in split ratio of 10:1, and 1 mL/min helium was used as carrier gas. 1 μL of the biooil was analysed in an Rxi-5 ms column(30 m length, 0.25 mm diameter, 0.25 μm stationary phase) with a low-polarity phase. For a total run of 25 mins, the initial oven temperature was held at 70° C. for 2 min, then firstly increased to 250° C. at a heating rate of 10° C./min and finally increased to 280° C. at a heating rate of 6° C./min. An electron impact (EI) source with electron energy of 70 eV, operating in the range 45-400 m/z, was used. The source and transfer line temperatures were 150° C. and 200° C., respectively. A 6.6 min solvent delay was applied to protect the MS. The 30 largest peaks, based on the integrated peak areas in total ion chromatogram (TIC), were identified by using NIST library.
Kraft Lignin Biooil Production
Variation in Feedstock Temperature
The pyrolysis power level or operating temperature has a significant impact on the yield and quality of KL pyrolytic products. In order to analyze the impact of operating temperature, the Kraft lignin and biochar mixture were pyrolyzed at 300, 450 and 600 W for 30 minutes. This section analyses the heating rate and temperature ranges achieved in the feedstock at applied power levels. Table 4 summarizes the pyrolytic products favored at varied temperatures during decomposition of KL [9,41,65].
The choice of power level can be made such that the feedstock will decompose selective to the desired product. According to Table 4, in order to promote the production of biooil, the operating temperature should not exceed 600° C.
Table 5 summarizes the average (of three repeated trials for each factor combination) timely key changes observed in the feedstock temperature and during pyrolysis of Kraft lignin and biochar (50 wt. %:50 wt. %). Temperature analysis for microwave pyrolysis of KL has been previously completed [41], however in the study not include the application of spruce and hemp biochar in the feedstock.
During the first 10 minutes of KL microwave pyrolysis, the heating rate rose rapidly at average heating rates of 26-50° C./min and 21-33° C./min in presence of spruce and hemp biochar, respectively. According to Table 5, the largest rise in temperature was observed from 0-15 minutes, where the temperature increase is above 200-400° C. The last 15 minutes of the KL microwave pyrolysis trials displayed the lowest thermal gradient, resulting in an average temperature change of approximately 20° C.
KL-spruce trials at 600 W reached the highest heating rate (50° C./min) during the first 10 minutes of pyrolysis. After reaching the peak operating temperature, during breakdown of KL-spruce biochar, the temperature stabilizes to reach steady state. When KL and hemp biochar were pyrolyzed at 600 W, the heating rate recorded during the first 10 minutes was 26° C./min; it was half the heating rate recorded compared to when spruce biochar was applied. At increased power levels, in presence of hemp biochar, at 450 W for a 50 wt. %:50 wt. % KL to microwave receptor distribution in the feedstock, it was observed that hemp biochar as microwave receptor, promoted a faster heating rate of the feedstock compared to spruce biochar.
On addition of hemp biochar, as the power level was raised from 300 W to 600 W, a gradual increase in the final operating temperature was recorded at the end of the 30-minute interval. However, on application of spruce biochar, the operating temperature recorded at 450 W was lower than 300 W. This unexpected temperature observation can be allocated to random errors related to the variation in the biochar and Kraft lignin distribution for the three trials completed and the approximation when trying to position the thermocouple probe in the same position as other trials. Moreover, the systematic error associated with thermocouple can also influence the temperature measurements.
By combining the findings in Tables 4 and 5, it was observed that microwave pyrolysis of KL-spruce biochar at 300 W and 600 W or KL-hemp biochar at 450 W for 30 minutes can be selective for higher biooil yields as the final temperature achieved, i.e., 530-540° C., is selective towards the production of biochar and biooil. It can also be suggested that if 50 wt. % hemp biochar is applied to KL at 600 W, the residence time for microwave pyrolysis should be lower than 30 minutes in order to prevent the temperature to reach above 600° C., thus preventing chemical reactions that further breakdown the biooil and shifts selectivity towards biogas.
Biooil Yield
Based on the factorial design described in section “Materials and Methods” of this specification, 54 trials were completed for microwave pyrolysis of Kraft lignin. Table 6 shows the 18 distinct factor combinations applied during KL pyrolysis, highlighting the trials that produced the highest biooil yield from the three repeated trials carried out for each factor combination. The results for all 54 trials can be viewed in Table 3.
In order to ensure reliable hypothesis testing by application of statistical tools and tests, the data distribution was analyzed for normality. Reliability of the data and hypotheses testing were completed in R-Console software in the study described in the present disclosure. Summarized statistical output is discussed later in this specification.
A normality test was completed to determine the validity of the following hypothesis:
While it has been previously observed that the addition of biochar as a microwave receptor impacts the heating rate during pyrolysis, this study investigated whether biochar synthesized from different biomass has a varied impact on the yield of KL pyrolytic products and composition of KL biooil. Additionally, from the present inventors' knowledge, spruce and hemp biochar have yet to be used as a microwave receptor during microwave pyrolysis of KL. This contributes to using “use of renewable feedstocks” based on the 12 Green Principles of Chemistry [1] and “renewable rather than depleting” based on the 12 Green Principles of Engineering [2].
The model Equation 1 was modified into Equation 2, in order to present biooil yield as the output influenced by the main effects and the interactions.
BiooilYieldijk=μ+∝i+τj+∝τij+βk+∝βik+τβjk+ατβijk+εijk Equation 2
The hypotheses evaluated in this section include whether:
The null hypothesis, as described by Equation 3, are valid if there is evidence that the main effects and interactions do not have significant impact on the biooil yield. From Table 6, all the model terms with a p-value <0.1 shows evidence of significant impact on the biooil yield; it suggests that the alternate hypotheses, described by Equation 4 are valid.
Null hypotheses: all ∝i=0; τj=0; βk=0; ∝τij=0; ∝βik=0; τβjk=0; ατβijk=0 Equation 3
Alternate hypotheses: some ∝i≠0; τj≠0; βk≠0; ∝τij≠0; ∝βik≠0; τβjk≠0; ατβijk≠0 Equation 4
Three ANOVA tests were carried out, including Test 1, Test 2 (excluding 3-way interactions) and Test 3 (excluding all interactions). Table 7 summarises partial results from the ANOVA tests.
Based on the results from Test 1, there is evidence that the microwave receptor percentage, power level and the interaction between the microwave receptor percentage and microwave receptor type have significant impacts on the KL biooil yield produced from microwave pyrolysis. Consequently, the following alternate hypotheses ∝i≠0, βk ≠0 and ∝τij≠0 are valid. Tests 2 and 3 were carried out by eliminating the 2-way and 3-way interactions from the ANOVA tests; Tests 2 and 3 support the evidence found in Test 1. According to the analysis, in process design for microwave pyrolysis of KL for biooil yield optimization, the following have to be strongly considered:
Impact of Microwave Percentage and Receptor Type in Feedstock
In regard to the influence on the biooil yield, the percent microwave receptor and its interaction with the microwave receptor type were found to have a significant impact. The percentages of microwave receptor used in the feedstock were 50 wt. %, 60 wt. % and 70 wt. %. The impact of microwave receptor type and percentage on KL biooil yield can be observed in
Application of spruce biochar as the microwave receptor resulted in higher KL biooil yields in comparison to hemp biochar. The lowest and highest KL biooil yields were obtained when using 70 wt. % and 50 wt. % spruce biochar, respectively. Yerrayya et al. [147] observed that utilizing a high percentage of microwave receptor requires a longer residence time for completion of pyrolysis and leads to controlled heating of the feedstock. The biooil yield could be higher when the wt. % microwave receptor was increased, i.e., 60 and 70 wt. %, if the residence time was extended beyond 30 minutes to allow for additional biooil collection. In presence of hemp biochar, as illustrated in
Overall, it was observed that using 50-60 wt. % of microwave receptor in the feedstock outputs a biooil yield approximately 10 wt. % of total pyrolysis product yield. In contrast to observations made by Yerraya et al. [147], that the highest biooil yield was obtained from 10 g lignin: 90 g microwave receptor (activated carbon), in the study described in the present disclosure the biooil yield decreased when the percentage of microwave receptor was increased. This can be attributed to differences in the microwave receptor particle size, distribution in the feedstock and the condensation conditions. Moisture present in receptor capillaries (nano-sized) contributes to steam cracking of Kraft lignin particles, leading to high biooil yield. Thus, molecular steam cracking would be considerably higher in the presence of activated carbon since its moisture content is 15 wt. % while the moisture content of spruce and hemp biochar is approximately 3.9 and 2.7 wt. %, respectively.
The only interaction, i.e., the two-way interaction between wt. % microwave receptor and type, that showed evidence for influence on the biooil yield has been depicted in
This significance of the interaction reinforces that the wt. % microwave receptor in feedstock has a significant impact on the biooil yield. From
Impact of Power Level
From the ANOVA test, the power level was one of the main effects that showed to have a significant impact on the biooil yield.
This was further supported by the analysis of the KL-hemp biochar trials. When the power level was increased from 450 to 600 W, no change or reduction in the biooil yield (in case of the 50-50 wt. % KL to biochar) was observed. Additionally, when increasing the power level from 300 to 450 W, it was observed that for 50 wt. % of hemp biochar in the feedstock, the biooil yield increased by 31%; for 60 wt. % and 70 wt. % of hemp biochar in the feedstock, the change in biooil yield was below 3%.
Optimized Conditions for KL Biooil Yield
The optimized microwave pyrolysis conditions, 4 out of 18 factor combinations, for efficiently achieving a high KL biooil yield have been described in Table 9. According to analysis of experimental data, 50 wt. % microwave receptor in the feedstock outputs the highest biooil yield; the only exception was the trial completed at 300 W with hemp biochar. Consequently the probability of obtaining the highest biooil at 50 wt. %, indifferent of microwave receptor type and power level, is 0.94. By proposing 50 wt. % as the optimal percentage for the microwave receptor, 6 out of 18 factor combinations remained as potential considerations for yield optimization.
Spruce biochar was previously determined as the more effective microwave receptor when the wt. % applied is within 50-62 wt. %. However it should be noted that spruce and hemp have dissimilar lignocellulosic composition, thus both biochar were considered for evaluation of the overall optimized conditions. The power levels recommended for biooil yield optimization are 450 and 600 W. This is because the highest yield in presence of spruce and hemp biochar were obtained at 600 and 450 W, respectively. Additionally, it was observed that while at 600 W the highest biooil yield was obtained, operating around 450 W might be the most cost effective. This is because the rise in biooil yield from 300 to 450 W is significant (17-65%) while beyond 450 W, the percentage increase was 0-22%. The operating temperature influences KL depolymerization reactions, thus the impact of all power levels on the biooil composition were investigated for phenolic content optimization. Section “Biooil Composition” in this specification analyses the operating conditions based on the KL biooil composition, with the goal to optimize the phenolic content.
Biooil Composition
Microwave pyrolysis of KL was completed to synthesize a source of greener chemical building blocks in the form of KL biooil as for resin manufacturing and optimizing the microwave pyrolysis conditions to improve the phenolic content in KL biooil. Gas Chromatography-Mass Spectrometry characterization was carried out to define the chemical composition of KL biooil obtained at different microwave conditions and analyze the suitability of KL biooil as a source of bio-based monomers to replace petroleum-based alternatives. The sample from each test contained two phases, i.e. the biooil heavy phase (BOH) and the biooil light phase (BOL), as shown in
Based on information acquired from yield optimization analysis, the biooil samples as described in Table 10 were analyzed through GC-MS testing.
The heavy and light phases were analyzed separately, thus a total of 12 samples were tested.
The microwave receptors were synthesized from two different lignocellulosic biomass, thus there was an interest to see if further decomposition of distinct biochar will impact the KL biooil. A comparison of KL biooil formed in presence of different biochar has not been completed. Additionally, the power level directly impacts the extent of depolymerization during pyrolysis, hence its effect on chemical composition were analyzed. Table 12 displays the sample composition analysis obtained for one phase of the biooil through GC-MS analysis.
Overview of Chemical Composition for KL Biooil
The synthesized KL biooil consisted of two phases, i.e., the heavy phase (BOH) and the light phase (BOL). In the study described in the present disclosure, the yield of BOL (˜60 wt. %) was larger in comparison to BOH (˜40 wt. %). Each phase was analyzed separately to identify the type and the relative yield of different chemical groups produced in the biooil. The major chemical compounds present in the biooil samples have been described in
Phenol represents the largest chemical compound formed in the KL biooil. Thus, it will be discussed in detail in section “Phenolic Content” of this specification. As seen in
The chemical composition of the heavy biooil was affected by the microwave receptor type applied. Spruce is a tree-based biomass while hemp is a fiber crop, thus the organic composition of these raw materials differs.
In this section, the sources and reactions that produce major non-phenolic chemical groups in the KL biooil will be discussed. The optimized conditions to synthesize a phenolic KL biooil will thus take into account factors that are conducive for production of non-phenolic groups and the potential impacts or challenges for the targeted application, i.e. as a raw material for resin manufacturing.
Monosaccharides
Monosaccharides are simple sugars (smallest carbohydrates) that cannot be reduced to smaller molecules by hydrolysis [8]. In previous studies, application of KL biochar, naphthalene and retene in pyrolysis of KL lead to production of monosaccharides [7,41]. As illustrated in
Light biooil (BOL) produced from KL-spruce biochar trials contained a larger yield of monosaccharides. At 600 W, the monosaccharides formed during KL-spruce trials included d-allose, levoglucosan (1,6 anhydro-a-d-glucopyranose), 2,3-anhydro-d-mannosan, 1 methyl- and 2-methyl naphthalene. For the same power level, the quantity and variety of monosaccharides obtained during KL-hemps trials were considerably lower, including 1,6 anhydro-a-d-glucopyranose and retene.
As seen in
Amides
Amides are carboxylic acid derivatives that contain the —CONH2 functional group [110]. Amides have not been commonly found in KL pyrolytic biooil [7,41]. Similarly in most KL-spruce trials, the synthesized KL biooil did not contain amides, except for microwave pyrolysis completed at 450 W; 1% of N-Acetylprocainamide was obtained in the biooil. KL-hemp trials produced a higher amide content in the biooil. Pyrolysis of KL and hemp biochar at 600 and 450 W produced 10 and 9% of AICAR (N1-(β-D-Ribofuranosyl)-5-aminoimidazole-4-carboxamide), respectively. Conventional pyrolysis of hemp does not produce amides [116]. Consequently, the amides could be a result of internal to external heating that allows production of functional groups which would be otherwise trapped or by chemical interaction between compounds formed from decomposition of KL and secondary decomposition of the hemp biochar. Amides can increase the instability and corrosiveness of the biooil; on a larger scale additional investment in storage facilities could be needed [73].
Ketones
Ketones are chemical compounds that contain a carbonyl group (C═O) attached to two carbon atoms. Ketones have previously been observed in pyrolytic KL biooil, however the compounds formed in the study described in the present disclosure differ from previous studies [7,41].
As illustrated in
Esters
Esters are carboxylic acid derivatives formed when acids react with alcohols [11]. In previous studies, esters have been previously obtained in pyrolytic KL biooil as a low yield non-phenolic compound [41].
During the KL-spruce trials, the yield of esters was larger in the BOL compared to the BOH. Additionally, as the power level was increased from 300 to 600 W, the ester in in BOL decreased from 6 to 0%. For both spruce and hemp trials, the ester yield in BOH did not fluctuate significantly; the yield comprised of ˜1-2% of the non-phenolic compounds in the biooil. Methyl dehydroabietate was the most common ester formed in the study described in the present disclosure. It was produced at all microwave pyrolysis conditions applied, except for the BOL from the KL-spruce trial completed at 600 W. According to a previous study, pyrolysis of without catalysts did not yield ester in the biooil [18]. Addition of hemp and spruce biochar as microwave receptors increased the selectivity of KL biooil towards esters.
Acids
Acids are usually present in relatively low quantities in KL biooil. According to
Several studies have been conducted by using an ‘ideal’ version of Kraft Lignin biooil, whereby a blend of desired and pure phenolic compounds were polymerised to form resins. In the section “Overview of Chemical Composition for KL Biooil” in this specification, varied chemical compounds in the biooil were investigated to understand the potential impact on the polymerisation of crude KL biooil. The next section entitled “Phenolic Content” investigates the impact of experimental conditions on the phenolic yield and compositional distribution in the KL biooil.
Phenolic Content
Phenolic hydroxyl groups in Kraft lignin decompose to form monophenols, including phenols, guaiacols, benzenes and catechols in the oil phase [4,40]. Only 10% of the aliphatic hydroxyl groups that was originally present in the KL is usually transferred into the oil phase. In this section, the major phenolic compounds obtained in biooil will be discussed. The impact of microwave receptor type and power level on the selectivity of phenolic compounds have been presented in
The three primary phenolic compounds that had a yield of at least 10% in the KL biooil, in both phases, included creosol, guaiacol and 4-ethylguaiacol. ‘Low yield phenols’ represents the sum of approximately 30 distinct phenolic compounds, e.g., catechol, eugenol and vanillin, present on a relatively small scale in the KL biooil; percentages varied from 1-6%. In order to define the optimized conditions for the targeted biooil composition, the impact of microwave receptor type and power level on the phenolic content in KL biooil has been discussed in this section.
Impact of Microwave Receptor Type
As illustrated in
From Table 11, it can be observed that application of a lignocellulosic-based microwave receptor yields similar phenolic compounds, e.g., creosol and guaiacol, in larger quantities. If the phenolic selectivity was the only factor to be considered, hemp biochar would be the ideal choice as a microwave receptor in comparison to spruce biochar. The wt. % of BOL is larger in the synthesized biooil samples. KL-hemp trials produced a higher yield of phenolic content in the BOL phase and a slightly lower phenolic content in the BOH phase. However, the remaining non-phenolic compounds and yield optimization should also be considered.
Impact of Power Level
The impact of the power level on the phenolic content yield can be observed by analysis of the BOH phase during KL-spruce trials; when the power level doubled from 300 W to 600 W, the total phenolic content in KL biooil reduced by 10%. This can be related to secondary decomposition of KL as well as breaking down of KL biooil, whereby more compounds were transferred in the gas phase. In contrast to KL-spruce trials, doubling the power level (300 to 600 W) during KL-hemps trials improved the phenolic content in the BOH phase; the total phenolic content improved by 5%. For both KL-spruce and KL-hemp trials, when doubling the power level (300 W to 600 W), the phenolic content in the BOL phase reduced. At 600 W, the BOL phase synthesized during the KL-hemp trial yielded more phenolic compounds compared to the KL-spruce trial. With increasing power levels, it can be observed that the selectivity towards guaiacol and 4-ethylguaiacol decreases.
Pyrolysis of KL and microwave receptors at 450 W yielded a phenolic content and composition which was relatively similar to results obtained at 300 W. When increasing the power level from 300 to 450 W, only a slight change in the heating rate and the final operating temperature is achieved, thus the impact on the phenolic yield and selectivity is not significant. At 450 W, when using spruce as the microwave receptor, the KL biooil is more selective towards creosol and guaiacol by an approximately additional 4% in the BOL phase relative to 300 W, thus leading to a slightly larger phenolic yield at 450 W. In the BOH phase for the KL-spruce trials, while the selectivity towards 4-ethyl guaiacol is reduced at 450 W, a larger number of low yield phenols (<10%) are formed in comparison to 300 W. Consequently, this results in similar phenolic yields in the BOH phase; 97.7% and 96.8% for 300 and 450 W, respectively. Pyrolysis of KL and hemp biochar at 300 W produced the largest yield for creosol, guaiacol and 4-Ethylguaiacol in BOH and BOL phases compared to other power levels. The phenolic composition of biooil from KL-hemp trials at 450 W was similar to 300 W; at 450 W, the creosol content was slightly lower in both phases.
Major Phenolic Compounds
As described in the section, Overview of Chemical Composition for KL Biooil in this specification, over 90% of the synthesized KL biooil is phenolic. From the GC-MS results, found in Tables 12 to Table 18, distinct phenolic compounds formed in the biooil were determined. In this section, the sources and reactions that produce the high yield phenolic compounds in the KL biooil will be discussed.
Table 12 displays an example of the raw data obtained from GC-MS characterization. The GC-MS data was rearranged, in Tables 13 to 18 for ease of analysis.
Creosol
Creosol, also known as 4-methyl-guaiacol, was present in the highest concentration in the heavy phase of the biooil, indifferent of the biochar type and power level. Pyrolytic KL biooil usually consists of phenols, guaiacols and syringols as the primary chemical content. In the study described in the present disclosure, the significant presence of creosol can be related to further decomposition of the pre-processed lignocellulosic material used as microwave receptors (pyrolysis of biochar produces tar that can be further broken down) [82]. Creosol was also obtained as the most abundant chemical in KL biooil synthesized by Farag et al. [41], where the microwave receptor applied was KL biochar.
During pyrolysis, sinapyl alcohol, one of the three major phenylpropane monomers in KL, breaks down to form syringols which can further decompose into creosol [67]. It was observed that during pyrolysis of Kraft lignin and the microwave receptor, the KL biochar formed acts as a ‘binder’ for the feedstock. The reaction R2, proposed in
Guaiacol
Guaiacol or 2-methoxy-phenol was present in the highest concentration in the BOL phase and displayed the second highest yield in the BOH phase. Guaiacols are produced during primary decomposition of the KL, when the operating temperature reaches approximately 350-400° C. [65]. Microwave pyrolysis of KL was selective towards the BOL phase during the primary stage, thus explaining the large yield of guaiacol in BOL.
According to R1, coniferyl alcohol, the base monolignol of the guaiacyl hydroxyphenyl unit in KL breaks down during primary decomposition to form guaiacol. Additionally, some syringol can undergo demethylation to form guaiacols. It is also proposed that the remaining lignin chains in the microwave receptor breakdown during pyrolysis and contribute to the guaiacol content in the oil. The guaiacol concentration in the biooil is larger during KL-hemp trials, compared to KL-spruce trials. This was attributed to decomposition at a higher extent of spruce compared to hemp, during synthesis of the microwave receptor (i.e., in-house pyrolysis of spruce and hemp to produce biochar). Microwave pyrolysis of spruce and hemp at 2700 W reaches an operating temperature of ˜600-700° C. and 500-600° C., respectively. Kaal et al. studied the molecular changes in wood and grass biochar to establish three classes of chars, i.e. unaffected biomass, “transition char” and amorphous char, followed by graphite-like structures [61]. Consequently, it is suggested, the spruce biochar partially transitioned into graphite-like structures while hemp was still in the amorphous char phase where small aromatic elements are still present, thus can further decompose and interact with other compounds. Guaiacol-based monomers, benzoaxine, were used to synthesize alternative sustainable copolymers to bisphenol resins [138]. Additionally, guaiacol has been used in phenolic blends, to produce reactive diluents and resins to be applied in composite applications [126].
4-Ethylguaiacol
The yield of 4-Ethylguaiacol was lower in comparison to creosol and guaiacol, however it was still higher than 10% in KL biooil. As shown in
Similar to guaiacol, 4-ethylguaiacol is mainly formed by the breakdown of the guaiacyl hydroxyphenyl group (derived from coniferyl alcohol). The largest yield of 4-ethylguaiacol was obtained in presence of hemp as the microwave receptor and applied power level of 300 W. 4-ethylguaiacol is widely applied as chemical intermediates in synthesis of resins and polymers [146], thus presence of 4-ethylguaiacol in KL biooil is expected to be favorable for polymerization into a thermoplastic resin.
The most abundant phenolic compounds make up to 50-60% of the in the heavy phase and 40-50% in the light phase. The remaining compounds that are part of the phenolic content, include mono and polyphenols and the detailed compositional breakdown of the KL biooil samples can be viewed in Tables 13 to 18. Polymerisation of crude KL biooil synthesized by microwave pyrolysis, has yet to be applied in the synthesis of a thermoplastic resin. By understanding the reaction mechanisms that produce the high yield phenolic compounds in KL biooil, microwave pyrolysis conditions can be tuned to target the production or elimination of specific phenolic monomers.
Optimized Conditions for Phenolic Content
The optimized microwave pyrolysis conditions to achieve a highly phenolic KL biooil have been described in Table 19. These conditions were proposed by taking into consideration the analysis completed in sections “Biooil Yield”, “Overview of Chemical Composition for KL Biooil” and “Phenolic Content” of this specification. By assuming that the volume percentages across the biooil samples are divided such as BOL is 60 wt. % and BOH is 40 wt. %, the overall phenolic content was calculated by equation 5.
P
total
=P
BOL×60 wt. %+PBCH×40 wt. % Equation 5
where,
The application of hemp biochar as a microwave receptor produced the highest relative total phenolic content in KL biooil. KL-spruce trials output the highest phenolic in BOH, however BOH made up the smaller portion (˜40 wt. %) of the total biooil sample. Spruce is still proposed as a suitable microwave receptor type since when applied during microwave pyrolysis of KL at 450 W, the amide content in the synthesized-biooil is lower compared to KL-hemp based biooil; at 300 W KL-spruce based biooil does not contain acid or amide. The highest yield of non-phenolic content was observed when KL was pyrolyzed at 600 W, thus 300 W and 450 W were recommended as a suitable operating power levels. Additionally, the relative total phenolic contents recorded at 300 W and 450 W only differed by 1-4%.
Overall Optimized Microwave Pyrolysis Conditions for KL Biooil
The overall optimized microwave pyrolysis conditions for synthesis of a highly phenolic KL biooil have been developed in response to the objective of proposing the operating conditions that effectively merge the benefits of obtaining a high KL biooil yield and improving the selectivity towards phenolic compounds.
The direct impact of the main effects, i.e. wt. % of microwave receptor, microwave receptor type and power level, and their interactions on the KL biooil yield were investigated in section “Biooil Yield” in this specification. In section “Biooil Composition” of this specification, the results from the GC-MS analysis was applied in compositional analysis of the synthesized KL biooil and the impacts of the main effects on the phenolic selectivity of KL biooil were also investigated. In addition to the main effects, other factors taken into consideration when evaluating the pyrolysis conditions included cost considerations, e.g. “Is the % rise in yield justifiable for increasing the power level applied?”, non-phenolic content in the biooil, the need for upgrading treatments post pyrolysis and potential storage issues.
The overall optimized conditions were proposed in Table 20 findings from the section entitled “Optimizing Conditions for KL Biooil Yields” by combining the KL biooil yield and a suitable composition for application as biobased phenolic monomers in polymerization.
The percentage of microwave receptor used in the feedstock was found to have a significant impact on the biooil yield. Application of 50 wt. % microwave receptor in feedstock, the biooil yield recorded was higher compared to trials using 60 and 70 wt. % microwave receptors for both biochar types and at all power levels, except for pyrolysis of hemp at 300 W. Microwave pyrolysis at 450 W was selected as a favorable operating condition for both biooil yield and phenolic content, thus it was proposed as the overall optimized power level. The biooil yield obtained during the KL-spruce trial at 450 W was ˜20% larger than the yield from the KL-hemp trial. Additionally, when increasing the power level from 450 W to 600 W, the yield increased by only 4%. KL biooil produced in presence of spruce contained a lower acid (300 W) and amide content (300 W and 450 W). By choosing spruce biochar, the presence and negative impacts, e.g. additional post pyrolysis treatment steps and cost of storage, of other chemical groups in the biooil can be reduced. Moreover, the high yield non-phenolic content formed in the light phase of KL-spruce biooil, i.e., monosaccharides and ketones, have been previously applied in manufacturing of polymers.
The present invention in another embodiment relates to a method of microwave pyrolysis of KL to boost the content of phenolic compounds in a biooil. In another embodiment, the method is carried out under operating conditions that optimize both yield and the phenolic content. In another embodiment, KL was pyrolyzed in a small-scale Quartz batch reactor connected to a condensation system. The biooil content was analyzed through a qualitative GC-MS (gas chromatography-mass spectroscopy) analyzer to identify their chemical composition.
The present invention in another embodiment relates to a method of microwave pyrolysis of Kraft lignin in the presence of wood biochar to obtain a biooil with lower moisture and higher aromatic organic content. In other embodiments, spruce and hemp biochar are used, at varied ratios and operating temperatures in a microwave pyrolysis process. In another embodiment, a biooil is synthesized that can be taken as a precursor material for conversion into a novel bio-based thermoplastic polymer. In one embodiment, spruce biochar as a microwave receptor produces a higher average KL biooil yield at all power levels compared to hemp biochar. In other embodiments, with increasing the microwave power level from 300 W to 600 W, the biooil yield increases with reduced biochar yield. In one embodiment, the combination of 50:50 ratio of KL and spruce biochar feedstock exhibited the highest biooil yield.
Materials
Softwood Kraft lignin was supplied from the Resolute Forest Products Thunder Bay Mill through FPInnovations (Ontario, Canada). Spruce and hemp biochar were produced in-house by microwave pyrolysis.
Microwave Pyrolysis Setup and Procedures
Microwave pyrolysis of Kraft lignin was carried out in a nitrogen atmosphere in a setup as depicted in
The microwave pyrolysis design parameters pertaining to the current disclosure were varied as per Table 21.
A trial setup entailed placing half of the desired biochar amount in a quartz glass reactor, followed by KL, then finally adding the remaining biochar. The quartz reactor was placed inside the microwave box and connected to the condensation system. The condensation system consisted of two water-cooled Allihn (bulb) condenser columns and a round-bottom flask placed in an ice bath. Metal tape was used to secure joints and reduce loss of vapours.
The system was purged with nitrogen for approximately five minutes while the ice bath was set up. Cooling water for the microwave generator and the condensation system was allowed to reach steady state while the reactor was purging. The microwave software was used to select and maintain the desired power level constant for a residence time of 30 minutes per trial. During the trial, the thermocouple was used to measure the feedstock temperature with an accuracy of ±2° C. At the end of a trial, the microwave generator was turned off, to allow the system to cool down. When the reactor temperature reached approximately 50-60° C., the biochar was collected from the reactor and stored in a Ziploc® bag. It was key to allow for gradual cooling for the quartz glass and to prevent combustion of biochar by premature exposure to oxygen. The non-condensable gas flowed to the fume hood during the trial. The condensable gas was partially cooled, collected as biooil, then refrigerated.
Analytical Instruments
GC-MS analysis was conducted with a Perkin Elmer Clarus 680 GC coupled to a Clarus SQ8 MS at Dalhousie University Agricultural campus (Truro, Nova Scotia, Canada). The GC injection port was operated at 280° C. in split ratio of 10:1, and 1 mL/min helium was used as carrier gas. 1 μL of the biooil was analysed in a Rxi-5 ms column (30 m length, 0.25 mm diameter, 0.25 μm stationary phase) with a low-polarity phase. For a total run of 25 mins, the initial oven temperature was held at 70° C. for 2 min, then firstly increased to 250° C. at a heating rate of 10° C./min and finally increased to 280° C. at a heating rate of 6° C./min. An electron impact (EI) source with electron energy of 70 eV, operating in the range 45-400 m/z was used. The source and transfer line temperatures were 150° C. and 200° C., respectively. A 6.6 min solvent delay was applied to protect the MS. The 30 largest peaks, based on the integrated peak areas in total ion chromatogram (TIC), were identified by using NIST library.
Result and Discussion
Kraft Lignin Pyrolysis Product Yield
Based on a factorial design, 18 unique combinations of experimental conditions applied were completed to analyze the impact of 1) using spruce or hemp biochar as a microwave receptor, 2) biochar—KL ratio in feedstock (or % of KL in feedstock), and 3) the microwave power level applied. Due to the heterogeneous nature of KL, each combination was repeated three times. Selective results, based on the trials that resulted in the highest biooil yields, have been summarized in Table 22.
While it is known that addition of biochar as a microwave receptor impacts the heating rate during pyrolysis [147], this study investigated whether biochar from different biomass have varied impact on the yield of pyrolytic products and compositions. Yerrayya et al. [147]. observed that utilizing a high percentage of microwave receptor (in their case activated carbon) requires a longer residence time for completion of pyrolysis, but also leads to controlled heating of feedstock. Additionally, moisture present in receptor capillaries (nano-sized) contributes to steam cracking of Kraft lignin particles, leading to high biooil yield. Biochar production is favored during the primary decomposition of KL, at ≤400° C. [47]. Breakdown of KL ether linkages, within the polymer, results in sidechain reactions of phenolic compounds and prevents monomeric products from evaporating, thus forming KL biochar [65].
Biooil Yield
Application of spruce biochar as the microwave receptor displayed higher biooil yields in comparison to hemp biochar. In the presence of spruce biochar, at all power levels applied, 30 wt. % of Kraft lignin (or 70 wt. % of the biochar) in the feedstock outputs the lowest biooil yield. Additionally, the biooil yield increased as higher power levels were applied. In the presence of hemp biochar, the biooil yield did not vary considerably when the power level and the amount of microwave receptor in the feedstock were altered.
These results are in agreement with findings by Yerraya et al. [147] i.e., receptors with high external surface area allow effective degradation of lignin, thus reducing the biooil yield. The BET (Brunauer-Emmett-Teller) external surface area of spruce and hemp biochar are 9.96 m2/g and 12.18 m2/g, respectively [33]. Overall, it was observed that using 50-60 g of microwave receptor in feedstock outputs biooil yield approximately equal to or greater than 10 wt. %. In contrast to an observation made by Yerrayya et al. [147], that the highest biooil yield was obtained from 10 g lignin:90 g microwave receptor, in the study described in the present disclosure the biooil yield was found to decrease when the percentage of receptor was increased in the feedstock. This can be attributed to differences in the microwave receptor particle size and distribution in the feedstock. Moreover, molecular steam cracking would be considerably higher in presence of activated carbon since its moisture content is 15 wt. % while the moisture content of spruce and hemp biochar is approximately 3.9 wt. % and 2.7 wt. %, respectively [133].
Biochar Yield
In presence of both spruce and hemp biochar, the biochar yield increased as the power level was reduced from 600 W to 300 W, as depicted in
The feedstock was subjected to different heating rates based on the power level applied. At a lower power level, the feedstock undergoes primary decomposition longer, versus at higher power levels, thus promoting side chain polymerization reactions (formation of C—C) over evaporation of monomers. Consequently, the polymerized chemicals are stored as KL biochar [65].
GC-MS Analysis of Kraft Lignin Biooil
The goal of GC-MS analysis was to investigate the suitability of KL biooil as a source of bio-based monomers to replace petroleum-based alternatives. In order to optimize yield as well as the composition, biooil samples obtained by pyrolysis of 50 g KL:50 g biochar at varied biochar type and power levels were analyzed.
Overview of KL biooil Chemical Composition
The synthesized KL biooil consisted of two phases, i.e., heavy phase (BOH) and light phase (BOL). The light phase, also referred to as the aqueous phase of the biooil, usually has a high moisture content and a small percentage of organic compounds [40]. The water produced is due to breakdown of binding sites in KL as the temperature increases from room temperature to 450° C. The oil yield is higher than water yield above 450° C. Major organic groups in both aqueous and oil phases include phenols, heavy molecular weight compounds (HMWC), single ring non-phenolic groups, and aliphatic compounds. The yield of phenols and HMWC are higher as lignin is mainly made up of aromatic compounds. Moreover, microwave heating at moderate temperatures prevents secondary reactions that produce aliphatic compounds [39]. The major chemical compounds present in synthesized KL biooil samples have been described in
As seen in
Phenolic Compounds
Phenolic hydroxyl groups decompose to form monophenols, including phenols, guaiacols, benzenes and catechols in the oil phase [1][40]. Only 10% of the aliphatic hydroxyl groups that were originally present in the KL was transferred into the oil phase [40]. However, if the operating pressure of the microwave reactor is reduced, non-aromatic content in the biooil can be relatively high [4].
Creosol was the primary chemical group in the heavy phase of the biooil, indifferent of the biochar type and power level. Pyrolytic KL biooil usually consists of phenols, guaiacols and syringols as the primary chemical content [7][147]. In this case, the significant presence of creosol can be possibly related to further decomposition of a pre-processed lignocellulosic material as the microwave receptor.
2-methoxyphenol was the second most common (obtained at all experimental conditions applied) compound formed in both BOH and BOL during pyrolysis, while 4-ethyl-2-methoxyphenol was mainly found in BOH. Findings by Kawamoto [65] indicate that during secondary decomposition of lignin, guaiacol and syringols are broken down into o-cresols (2-methoxy phenol) alongside other phenol. With increasing power levels, it can be observed that the selectivity towards 2-methoxyphenol and 4-ethyl-2-methoxyphenol decreases. This is due to the faster rise in temperature for the same residence time, whereby beyond 550° C. more monomers start to transfer into gas form while being subjected to the same condensation settings [65].
In one embodiment, microwave pyrolysis of Kraft lignin in the presence of biochar at varied power levels is carried out to optimize the biooil yield and aromatic composition.
In another embodiment, the highest biooil yield is obtained in presence of spruce biochar. In other embodiments, biooil yield increases with rise in power levels when spruce biochar is applied, while change in power level does not have a significant impact on the yield when hemp biochar is used.
In another embodiment, KL biochar yield is at the highest at 300 W due to side reactions and restricted evaporation of monomers.
In another embodiment, results from the GC-MS analysis confirm that the KL biooil is highly phenolic. In another embodiment, hemp biochar as a microwave receptor produces a more phenolic light oil.
In another embodiment, creosol is formed at all experimental conditions applied; however, it is the primary compound in the heavy oil.
The present invention, in another embodiment, relates to optimized microwave pyrolysis and feedstock conditions to produce phenolic-rich biooils that are applied in the production of bio-based monomers to replace petrochemicals. Biooil yield is improved by an improved condensation system and other means. In another embodiment, downstream upgrading and polymerization of biooil is carried out. The polymerization process is optimized for synthesis of a bio-based low viscosity thermoplastic resin.
Pyrolyzed Kraft lignin has shown potential in replacing petroleum-based monomers in synthesis of resins. In certain aspects, the goal of this work was to determine the optimized operating conditions for microwave pyrolysis of Kraft lignin to obtain biobased chemical building blocks in form of KL biooil. Kraft lignin was depolymerised by varying the microwave pyrolysis conditions in a nitrogen atmosphere, in an attempt to achieve the highest biooil yield possible and improve selectivity towards phenolic monomers. The optimal conditions for production of a highly phenolic Kraft lignin biooil was determined by completing microwave pyrolysis at three power levels with two distinct lignocellulosic biochars, as microwave receptors. In certain aspects of the present invention, certain key findings of the research have been summarised as follows:
In one embodiment, condensable KL gas was collected through a two column-condensation system that was cooled by water running at 16-19° C. and an ice bath. The biooil yield was limited by the cooling capacity of the system. Additionally, the heavy biooil is highly viscous and partially condenses at the top of the distillation column during pyrolysis.
In another embodiment, a chiller is connected to the condensation system to provide cooling water at lower temperatures or the number of distillation stages is increased.
In another embodiment, the biooil sample is subjected to Karl Fischer titration, viscosity test and Gel Permeation Chromatography analysis. By determining the moisture, rheological properties and molecular weights of KL biooil, potential impacts on polymer properties can be predicted and avoided by upgrading the biooil.
In another embodiment, polymerization can be implemented wherein crude or purified KL biooil can be successfully applied in production of thermoplastic biopolymers.
P1ht1l1 H., & Tosun, N. (2002). Investigation of the wear behaviour of a glass-fibre-reinforced composite and plain polyester resin. Composites Science and Technology, 62(3), 367-370. doi:10.1016/S0266-3538(01)00196-8
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2021/051699 | 11/26/2021 | WO |
