Catalytic Fast Pyrolysis Of Lignin Research Articles

Catalytic upgrading of lignin-derived bio-oils over ion-exchanged H-ZSM-5 and H-beta zeolites

H-ZSM-5 and H-Beta zeolites ion-exchanged with alkali (Na+ and K+) and alkaline-earth (Mg2+) metals have been explored for the catalytic fast pyrolysis of lignin. Incorporating these metals led to a significant change in the acidic properties of the parent zeolites turning into mostly Lewis-type acidity. Catalytic fast pyrolysis experiments of lignin were performed in a fixed bed reactor with ex-situ configuration operating at 550 °C (thermal zone) and 450 °C (catalytic zone), atmospheric pressure and under a nitrogen flow. Moreover, two catalysts to lignin mass ratios (C/L = 0.2 and 0.4) were studied. Compared with non-catalytic tests, the use of parent zeolites caused a decrease in the bio-oil* (water-free basis) yield due to enhanced production of gases, water, and the coke deposition on the catalyst. In addition, the quality of bio-oil* was improved since it presents a lower oxygen content regarding the thermal test. H-Beta zeolite showed a higher deoxygenation degree than H-ZSM-5, but the latter exhibited a higher share of light components in the bio-oil* that can be detected by GC-MS analyses. Both catalysts promoted the production of light oxygenates, aromatics, and oxygenated aromatics. Regarding the effect of the incorporation of metals, oxygenated aromatic compounds were the predominant family in the bio-oil* obtained with all ion-exchanged zeolites. Likewise, significant differences were observed among the catalysts regarding the main components of this family (alkylphenols, guaiacols, syringols, catechols, and methoxybenzenes), achieving guaiacols concentrations in bio-oil* near to 24 wt.% for NaH-ZSM-5 and KH-ZSM-5 catalysts, and alkylphenols concentrations close to 16 wt.% for MgH-Beta and KH-Beta zeolites.

Catalytic conversion of lignin into monoaromatic hydrocarbons over a Ni/Al hydrotalcite-derived catalyst

Lignin is the most abundant aromatic biopolymer. Thus, preparation of BTX (benzene, toluene and xylenes) by catalytic fast pyrolysis (CFP) of lignin is attractive. Ni-Al mixed metal oxide (MMO) catalysts, derived from pyrolyzing Ni-Al layered double hydroxides (LDH), were prepared for the catalytic fast pyrolysis of lignin. The effects of catalyst Ni/Al ratio, catalyst dosage and pyrolysis temperature on the liquid products were investigated by Py-GC/MS. The Ni3Al3-MMO produced the best liquid product distribution from lignin at 700 ℃. The selectivity of Ni3Al3-MMO for aliphatic hydrocarbons and monocyclic aromatic hydrocarbons (MAHs) was 18.0% and 78.2%, respectively. The selectivity to polyaromatic hydrocarbons (PAHs) was 3.8%. No phenols and phenolic derivatives were produced. This is related to the mesoporous catalytic structure (pore size of 14.37 nm), large external surface area (134.74 m2/g) and strong acidity (4.92 mmolNH3/g) of Ni3Al3-MMO. In addition, a mechanistic study was performed with the lignin model compound (guaiacol) showing that Ni3Al3-MMO exhibits strong deoxygenation activity for aromatic C–O bond cleavage of lignin.

Pretreatment of HZSM-5 with organic alkali and cobalt: Application in catalytic pyrolysis of lignin to produce monocyclic aromatic hydrocarbons

In this work, we adopted organic alkali and cobalt pretreated HZSM-5 zeolites as catalysts for monocyclic aromatic hydrocarbons production via catalytic fast pyrolysis of lignin in a two-stage fixed bed reactor. For the treatment, four kinds of organic hydroxides (tetraalkylammonium hydroxides, denoted as TMAOH, TEAOH, TPAOH, and TBAOH) were chosen as the desilication agent, and cetyltrimethylammonium bromide (CTAB) was introduced as assistant to control the pretreating process. In addition, cobalt modification was further conducted over the optimized alkali-treated sample for acidity adjustment. The treated zeolites were systematically characterized by XRD, SEM, NH3-TPD, and N2-adsorption/desorption techniques. The characterization results were analyzed together with the catalytic testing data to reveal the structure-function relationship of the catalysts in catalytic pyrolysis of lignin. As it turned out, the HZSM-5 zeolite pretreated by 0.5 mol/L of TPAOH in the presence of CTAB exhibits a coordinated micropore/mesopore proportion, proper average mesopore size, and a successful preservation of acidic properties. The addition of CTAB in the alkali treatment process was not only beneficial to preventing the over-treatment of HZSM-5, but could also regulate the mesoporous structure of zeolite. Eventually, the highest production of monocyclic aromatic hydrocarbons (31.8%, relative content) was achieved by the TPAOH pretreated HZSM-5 (2C-0.5TPHZ) at 500 °C, far exceeding that of the parent HZSM-5 (17.3%, relative content). Further modification of the 2C-0.5TPHZ sample with 1 wt% of cobalt could enhance the acidity of the alkali-treated zeolite, leading to a further improvement of the monocyclic aromatic hydrocarbons production to 38.3%. The reusability of the pretreated sample was further evaluated by cyclic reaction for 5 times, which demonstrated its reactivity stability for monocyclic aromatic hydrocarbons production.

Catalytic pyrolysis of lignin over ZSM-5, alkali, and metal modified ZSM-5 at different temperatures to produce hydrocarbons

Temperature and catalyst type greatly influence the chemical processes as well as the quality of the pyrolysis products. Catalytic fast pyrolysis (CFP) of lignin isolated from rice straw using three different catalysts was performed at different pyrolysis temperatures (450, 500, 550, and 600 °C) using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to explore the suitable catalytic performance for hydrocarbon production. The shape selectivity and acidity of the three catalysts (ZSM-5, NaOH-modified ZSM-5 (0.4 M), and nickel modified ZSM-5 (8 wt.%)), showed a substantial effect on the product distribution during CFP of lignin. Ni-ZSM-5 (8 wt.%) demonstrated effective performance for the transformation of oxygenated compounds through demethoxylation and dehydroxylation into aromatics. The most suitable pyrolysis temperature for catalytic pyrolysis of lignin was 550 °C in which a maximum selectivity of 72% for hydrocarbon was obtained over Ni-ZSM-5 (8 wt.%) followed by ZSM-5 (0.4 M) and ZSM-5. This research provides a suitable pyrolysis temperature and catalyst for high hydrocarbon production from catalytic pyrolysis of lignin.

Enhancing aromatic yield from catalytic pyrolysis of Ca2+-loaded lignin coupled with metal-modified HZSM-5

Catalytic fast pyrolysis of lignin is easy to cause agglomeration and coking, resulting in low-yield aromatic hydrocarbons. Catalytic pyrolysis of modified lignin combined with metal-modified HZSM-5 was proposed to enhance the aromatic yield. The experiment results showed that chemical modification with Ca(OH)2 not only inhibited the agglomeration behavior of lignin but also increased the yield of light phenolic compounds. Moreover, Ca2+-loaded lignin combined with metal-modified HZSM-5 was conducive to the formation of aromatics. The total yield of aromatics from the catalytic fast pyrolysis of Ca2+-loaded lignin over Zn/HZSM-5 was improved from 31.1 to 46.1 mg/g. The mechanism insight showed that Ca2+ modification realized the chemical combination between Ca2+ and the functional groups which are responsible for the agglomeration of lignin, and then the introduction of the Zn species suppressed the hydrogen transfer reaction and enhanced the dehydrogenation pathway, resulting in the increase of aromatic yield.

In situ catalytic fast pyrolysis of lignin over biochar and activated carbon derived from the identical process

In this study, a sustainable in situ catalytic fast pyrolysis (CFP) of lignin was developed by using biochar and activated carbon (AC) as catalysts, which is derived from the same CFP of lignin process. The results showed that using biochar as the catalyst mainly promoted the production of non-condensable gas, water, and guaiacol-rich oil regardless of the biochar-to-lignin ratio. The catalytic effect of the biochar was mainly attributed to the surface sodium and alkali metals. Using AC44.7% and AC48.6% as the catalyst resulted in a high yield of guaiacol-rich oil, whereas using AC64.3% induced a great decrease of the tarry oil yield and a significant increase of the phenol concentration in bio-oil. The diffusion efficiency of the reactive intermediates inside the catalysts determined by the pore size was believed to be the greatest determinant of the catalytic performance of the ACs. The mesopores were large enough to allow most of the reactive intermediates to diffuse quickly and react. Moreover, by using the same catalyst, char agglomeration was almost completely suppressed after in situ CFP. Two major problems, tar production and char agglomeration, which limit the large-scale application of fast lignin pyrolysis are believed to be solved.

Bio-BTX production from the shape selective catalytic fast pyrolysis of lignin using different zeolite catalysts: Relevance between the chemical structure and the yield of bio-BTX

As the most abundant aromatic bio-polymer in nature, lignin can be converted into bio-BTX via the shape selective catalytic fast pyrolysis process (SS-CFP). In this work, three types of MWL were isolated from softwood (Chinese fir), hardwood (poplar), and herbaceous biomass (corn stover), namely CF-MML, P-MWL, and CS-MWL. The chemical structural of lignin was analyzed by gel permeation chromatography (GPC), 2D-HSQC-NMR, and 31P NMR. Five types of the parent zeolites (HZSM-5 (25), HZSM-5 (85), Al-MCM-41, HY, and USY) and the Zn modified HZSM-5 (25) with different loading amounts (1% to 4%) were screened. Results showed that CF-MWL had the highest carbon content (59.90%). P-MWL had highest content of β-O-4 linkage (53.90%) and Mw (2778 g/mol). Among the five parent zeolites, HZSM-5 (25) was the most effective catalyst to produce bio-BTX with the highest selective yield of 56.56% at the optimal operation parameters. As a bi-functional catalyst, the incorporation of Zn on zeolite promoted the formation of BTX, where metal promoted the reaction rates of de‑oxygenation reaction and aromatization reaction, while the HZSM-5 remains the ability of shape selectivity. The maximum selective yields of BTX were 65.02% (CF-MWL) > 63.77% (CS-MWL) > 63.41% (P-MWL) when the Zn loading amount was 2%.

Controlling Deoxygenation Pathways in Catalytic Fast Pyrolysis of Biomass and Its Components by Using Metal-Oxide Nanocomposites.

SummarySelectively breaking the C-O bonds within biomass during catalytic fast pyrolysis (CFP) is desired, but extremely challenging. Herein, we develop a series of metal-oxide nanocomposites composed of W, Mo, Zr, Ti, or Al. It is demonstrated that the nanocomposites of WO3-TiO2-Al2O3 exhibit the highest deoxygenation ability during CFP of lignin, which can compete with the commercial HZSM-5 catalyst. The nanocomposites can selectively cleave the C-O bonds within lignin-derived phenols to form aromatics by direct demethoxylation and subsequent dehydration. Moreover, the nanocomposites can also achieve the selective breaking of the C-O bonds within xylan and cellulose to form furans by dehydration. The Brønsted and Lewis acid sites on the nanocomposites can be responsible for the deoxygenation of lignin and polysaccharides, respectively. This study provides new insights for the rational design of multifunctional catalysts that are capable of simultaneously breaking the C-O bonds within lignin and polysaccharides.

Catalytic Fast Pyrolysis of Lignin Isolated by Hybrid Organosolv—Steam Explosion Pretreatment of Hardwood and Softwood Biomass for the Production of Phenolics and Aromatics

Lignin, one of the three main structural biopolymers of lignocellulosic biomass, is the most abundant natural source of aromatics with a great valorization potential towards the production of fuels, chemicals, and polymers. Although kraft lignin and lignosulphonates, as byproducts of the pulp/paper industry, are available in vast amounts, other types of lignins, such as the organosolv or the hydrolysis lignin, are becoming increasingly important, as they are side-streams of new biorefinery processes aiming at the (bio)catalytic valorization of biomass sugars. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis of softwood (spruce) and hardwood (birch) lignins, isolated by a hybrid organosolv–steam explosion biomass pretreatment method in order to investigate the effect of lignin origin/composition on product yields and lignin bio-oil composition. The catalysts studied were conventional microporous ZSM-5 (Zeolite Socony Mobil–5) zeolites and hierarchical ZSM-5 zeolites with intracrystal mesopores (i.e., 9 and 45 nm) or nano-sized ZSM-5 with a high external surface. All ZSM-5 zeolites were active in converting the initially produced via thermal pyrolysis alkoxy-phenols (i.e., of guaiacyl and syringyl/guaiacyl type for spruce and birch lignin, respectively) towards BTX (benzene, toluene, xylene) aromatics, alkyl-phenols and polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes), with the mesoporous ZSM-5 exhibiting higher dealkoxylation reactivity and being significantly more selective towards mono-aromatics compared to the conventional ZSM-5, for both spruce and birch lignin.

Catalytic pyrolysis of lignin using low-cost materials with different acidities and textural properties as catalysts

Catalytic fast pyrolysis of lignin was performed using low-cost materials with different acidities and textural properties as catalysts in the present work. The main focus is to understand the role of low-cost catalysts in the fast pyrolysis of lignin. The four most commonly used low-cost catalysts, ilmenite (FeTiO3), bentonite (Al-Si-OH), activated carbon (AC) and red mud (RM), were selected. The results show that bentonite, red mud and activated carbon effectively enhance the dehydration reaction, which is regarded as the dominant way to eliminate oxygen during the pyrolysis process, due to the existence of strong acidic sites. However, only activated carbon is found to be effective in promoting the production of monocyclic aromatic hydrocarbons (MAHs). Two metallic catalysts, i.e., bentonite and red mud, have strong acidities but quite low surface areas and less porous structures. Therefore, the dehydrated intermediates produced are especially easy to repolymerize to form char or coke without the restriction of obtaining a porous structure during the pyrolysis process. Activated carbon has not only a certain acidity but also a rich porous structure. Lignin fast pyrolysis-derived oxygenates can diffuse and react on the well-dispersed active sites within the pores of activated carbons. The catalytic performance of the activated carbon are supposed to be determined by the pore size. Only pores of similar size to lignin fast pyrolysis-derived oxygenates (0.6–1 nm) seems to be effective for the production of MAHs. Pores larger or smaller than lignin fast pyrolysis-derived oxygenates both tend to cause coke deposition rather than MAHs formation.

Catalytic fast pyrolysis of lignin to produce aromatic hydrocarbons: optimal conditions and reaction mechanism.

Catalytic fast pyrolysis of lignin with zeolite catalysts is a promising method to produce aromatic hydrocarbons. In this paper, alkali lignin was used as a model compound to pyrolyze with HZSM-5 (silica to alumina ratio, SAR = 23), HZSM-5(50), HZSM-5(80), HY and Hβ. Non-condensable vapours and condensable fractions were determined and quantified by GC/FID and GC/MS respectively. 7.63 wt% of aromatic hydrocarbons and 3.34 wt% of C1–C4 alkanes and alkenes were acquired. The effects of catalysts and pyrolysis parameters were studied in this work. Different reaction pathways were compared and discussed by combining density functional theory (DFT) calculations. Cyclization reactions to form aromatic hydrocarbons were thought to be the main reaction pathway, while direct demethylation, demethoxylation and dehydration reactions were the secondary reaction pathway to convert phenolic lignin monomers to non-oxygenated aromatic hydrocarbons.

Catalytic pyrolysis of lignin over hierarchical HZSM-5 zeolites prepared by post-treatment with alkaline solutions

The application of hierarchical HZSM-5 zeolite catalysts in the catalytic fast pyrolysis (CFP) of lignin was investigated using a pyrolyzer coupled with gas chromatography-mass spectrometry (Py-GC–MS). A series of modified HZSM-5 zeolites were prepared by the post-treatment desilication of commercial HZSM-5 zeolite with varying concentrations of sodium hydroxide (NaOH) solutions (0.1 – 0.5 mol/L) and the following solutions: 0.3 mol/L of sodium aluminate (NaAlO2), 0.3 mol/L of sodium carbonate (Na2CO3), and 0.3 mol/L of tetrapropylammonium hydroxide (TPAOH). The catalyst samples were characterized by XRD, XRF, TEM, N2 adsorption–desorption, and NH3-TPD techniques. The crystallinity, the SiO2/Al2O3, the morphology, the pore properties, and the density of acid sites of the HZSM-5 zeolites were changed after alkali treatment. The alkali treatment improved the catalytic performance of HZSM-5 zeolite for cracking bulky oxygenates released from lignin (such as guaiacol, syringol, and their derivatives from the pyrolysis of lignin) to produce aromatic hydrocarbons. The HZSM-5 zeolite treated with 0.3 mol/L NaOH was the optimal choice for the catalytic fast pyrolysis of lignin for producing aromatic hydrocarbons.

Visualization of Structural Changes During Deactivation and Regeneration of FAU Zeolite for Catalytic Fast Pyrolysis of Lignin Using NMR and Electron Microscopy Techniques

AbstractCatalytic fast pyrolysis of pretreated lignin (with hydrogen chloride solution) over FAU (15) zeolite uniquely yielded a high fraction of phenols, phenol alkoxys, and aromatic hydrocarbons. However, the zeolite underwent rapid deactivation. This paper reports the visualization of the structural changes during deactivation and regeneration of the zeolite is reported. The deactivated and regenerated zeolites were characterized by means of N2 physisorption, electron microscopy, X‐ray diffraction, magic angle spinning (MAS), and multiple quantum (MQ) nuclear magnetic resonance (NMR) techniques. The results indicated that, during catalyst deactivation, there was excessive coke deposition in the zeolite pore structure resulted in both pore blockage and active site poisoning. The coke was removed by calcination of the spent catalyst in air at high temperature >550 °C which resulted in restoring the porosity and the activity to a large extent. However, the recovery of catalytic activity was incomplete attributing to irreversible structural changes in the catalyst during the deactivation and regeneration process. By fine‐tuning the reaction conditions and the regeneration of the catalyst, the catalyst performance after reactivation was optimized. Catalyst regeneration after mild coke deposition (that is, after a few catalytic cycles) and mild oxidation conditions (low temperature and slow‐heating ramp) are beneficial.

Catalytic Fast Pyrolysis of Kraft Lignin With Conventional, Mesoporous and Nanosized ZSM-5 Zeolite for the Production of Alkyl-Phenols and Aromatics.

The valorization of lignin that derives as by product in various biomass conversion processes has become a major research and technological objective. The potential of the production of valuable mono-aromatics (BTX and others) and (alkyl)phenols by catalytic fast pyrolysis of lignin is investigated in this work by the use of ZSM-5 zeolites with different acidic and porosity characteristics. More specifically, conventional microporous ZSM-5 (Si/Al = 11.5, 25, 40), nano-sized (≤20 nm, by direct synthesis) and mesoporous (9 nm, by mild alkaline treatment) ZSM-5 zeolites were tested in the fast pyrolysis of a softwood kraft lignin at 400–600°C on a Py/GC-MS system and a fixed-bed reactor unit. The composition of lignin (FT-IR, 2D HSQC NMR) was correlated with the composition of the thermal (non-catalytic) pyrolysis oil, while the effect of pyrolysis temperature and catalyst-to-lignin (C/L) ratio, as well as of the Si/Al ratio, acidity, micro/mesoporosity and nano-size of ZSM-5, on bio-oil composition was thoroughly investigated. It was shown that the conventional microporous ZSM-5 zeolites are more selective toward mono-aromatics while the nano-sized and mesoporous ZSM-5 exhibited also high selectivity for (alkyl)phenols. However, the nano-sized ZSM-5 zeolite exhibited the lowest yield of organic bio-oil and highest production of water, coke and non-condensable gases compared to the conventional microporous and mesoporous ZSM-5 zeolites.

Optimization of the Reaction Conditions for Catalytic Fast Pyrolysis of Pretreated Lignin over Zeolite for the Production of Phenol

AbstractThe catalytic fast pyrolysis of lignin for the production of phenols over commercial zeolites was studied in‐depth. The results show that the production of phenols depended on several parameters, such as lignin pretreatment methods, pyrolysis temperature, zeolite structure and acidity, pyrolysis time, and feed‐to‐catalyst weight ratio. Lignin pretreatments had a significant influence on the liquid‐product distribution. Hydrogen chloride pretreatment of lignin increased the depolymerization of the lignin matrix, resulting in an increase of the liquid yield, as well as the phenol fraction. High temperature (e.g., 650 °C) and a fast heating rate (20 °C ms−1) were required to depolymerize lignin and increase the yield of liquid products, and large‐pore‐size zeolites (e.g., FAU) with Si/Al of approximately 15 favored the formation of phenols. A long pyrolysis time (20 s) was also beneficial for phenol to desorb from the catalyst. The medium feed‐to‐catalyst weight ratio of approximately 1:1 prevented further conversion of phenols to deoxygenated products such as aromatic hydrocarbons (benzene, toluene, and xylene).

Highly selective BTX from catalytic fast pyrolysis of lignin over supported mesoporous silica

The post synthesis of Al3+ or Zr4+ substituted MCM-48 framework with controlled acidity is challenging because the functional groups exhibiting acidity often jeopardize the framework integrity. Herein, we report the post-synthesis of two hierarchically porous MCM-48 composed of either aluminum (Al3+) or zirconium (Zr4+) clusters with high throughput. All prepared catalysts have been characterized by HR-TEM, XRD, IR, N2-adsorption, NH3-TPD, TGA and MAS NMR. They exhibit BET surface areas of 597 and 1112m2g⿿1 for 8.4% Al/MCM-48 and 2.9% Zr/MCM-48, respectively. XRD analysis reveals that the hierarchical porosity of parental MCM-48 is reserved even after incorporation of Al3+or Zr4+. Zr/MCM-48 catalysts are demonstrate a superior performance versus that of Al/MCM-48 and MCM-48 because of the mild (ZrO2) or nil (SiO2) Lewis acidity contributed from Zr-μ2-O group as well as smaller pore sizes suitable for the restriction of unwanted side reactions. The reaction conditions which were affecting the catalytic pyrolysis and final products were gas flow rate, pyrolysis temperature, and catalyst to lignin ratio. A total of 49% of BTX product were obtained over 2.9% Zr/MCM-48 at 600°C. The Lewis acid character was the governing factor which helps in pyrolysis and directly affects the BTX formation.

Catalytic Fast Pyrolysis of Lignin over High‐Surface‐Area Mesoporous Aluminosilicates: Effect of Porosity and Acidity

Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst.

Selective deoxygenation of lignin during catalytic fast pyrolysis

Catalytic fast pyrolysis of lignin was investigated in a pyroprobe microreactor with different catalysts, including (non-)acidic alumina silicates, transition metal oxides, and zeolite-supported transition metals. The results indicate that the selectivity to the desired product can be controlled to some extent. Non-catalytic fast pyrolysis yields a complex mixture of valuable chemicals, such as vanillin, guaiacol, phenols and aromatic hydrocarbons. Therefore, a separation–purification process is necessary before the product steam can be used, thus increasing the overall cost of the process. Deoxygenation can be done efficiently to give a small amount of different products, mainly aromatic hydrocarbons. These aromatics can be used as platform chemicals using current technology, such as further hydrogenation for fuels. Strong variation in selectivity was observed depending on the catalyst. A high yield of vanillin was obtained over copper oxide. The development of highly active and selective catalysts would significantly improve the feasibility, economics and performance of catalytic fast pyrolysis of lignin.

The role of shape selectivity in catalytic fast pyrolysis of lignin with zeolite catalysts

Catalytic fast pyrolysis (CFP) of lignin with four different zeolite catalysts was investigated to determine the role of shape selectivity of zeolites in CFP. These zeolites included ZSM-5, mordenite, beta, and Y zeolites, which have various crystallographically determined static pore sizes between 5.6 and 7.6Å. The molecular dimensions of pyrolysis products, including lignin-derived oxygenates and aromatics, were calculated using quantum chemical computations. The effective pore sizes of the four zeolites at 650°C were then determined by analyzing the molecular size and conversion behavior of the pyrolysis products in CFP. Results suggest that thermal distortion of the zeolite pore structure under high-temperature conditions of CFP effectively enlarge the crystallographically determined pore sizes of the zeolites by 2.5–3.4Å. Therefore, many lignin-derived oxygenates with a molecular size considerably larger than the static pore size were able to enter the pores of the zeolites and become effectively converted in our CFP tests. Bulkier monolignols derived from syringyl lignin, however, could not be effectively converted by ZSM-5 and mordenite zeolites due to size exclusion or pore blockage. Among the four zeolites, ZSM-5 produced the highest aromatic yield, followed in order by beta, mordenite, and Y zeolites. Beta and Y zeolites were the most effective catalysts for deoxygenating lignin-derived oxygenates. This analysis indicates that for CFP of softwood, ZSM-5 is the optimal catalyst because it can achieve satisfactory deoxygenation and aromatic production simultaneously, whereas for hardwood feedstock, beta zeolite may be used to convert bulky oxygenates derived from syringyl lignin.