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Article

Furthering the Application of a Low-Moisture Anhydrous Ammonia Pretreatment of Corn Stover

by
Ming-Hsun Cheng
1,2 and
Kurt A. Rosentrater
3,*
1
Department of Natural Resources and Society, University of Idaho-Idaho Falls, Idaho Falls, ID 83401, USA
2
Center for Advanced Energy Studies, Idaho Falls, ID 83401, USA
3
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA
*
Author to whom correspondence should be addressed.
Processes 2025, 13(8), 2643; https://doi.org/10.3390/pr13082643
Submission received: 30 May 2025 / Revised: 4 August 2025 / Accepted: 18 August 2025 / Published: 20 August 2025
(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design (2nd Edition))
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Abstract

The use of an ammonia fiber expansion pretreatment using low-moisture anhydrous ammonia (LMAA) is a promising strategy for biomass deconstruction, with significant effects on depolymerizing lignin and hemicellulose. An LMAA pretreatment provides several advantages, including compatibility with the high-biomass loading of solids, efficient ammonia recovery, and scalability for industrial operations. In this study, the reactor was revisited and optimized to improve glucan digestibility from corn stover through enzymatic hydrolysis, building on our previous findings that identified limitations in ammonia distribution. The effects of the biomass particle size, the reaction time, and their interaction on glucose yields were investigated to determine their influence on the subsequent enzymatic hydrolysis kinetics. The best glucose yield of 83% was achieved using an LMAA pretreatment of biomass with a 0.5 mm particle size, representing an improvement of approximately 5% compared to biomass with a 1 mm particle size. Additionally, reactor optimization led to a 22% improvement in the glucose yield compared to the previous reactor configuration. According to the results of the reaction kinetics fitting, the enzymatic hydrolysis data indicated that the reaction followed a pseudo-first-order model.

1. Introduction

A resilient biomass-to-bioproduct pipeline is regarded as a promising strategy to sustain the resource–energy–environment nexus. Lignocellulosic materials, the major residues from the agricultural, food, and forest industries and operations, offer significant opportunities for biorefining in producing value-added bioproducts. Cellulosic sugars derived from structural carbohydrates of lignocellulose (i.e., cellulose and hemicellulose) are the critical chemical building blocks for downstream upgrading and applications to benefit the circular bioeconomy [1].
Corn stover, which includes stalks, leaves, and cobs, is the most abundant agricultural crop residue in the Midwest States. It contains over 50% cellulose and hemicellulose [2,3]. However, its valorization is hindered by the recalcitrant cellulose–lignin matrix within the plant cell wall, which limits the accessibility of structural carbohydrates. To effectively maximize the upcycling of structural carbohydrates, a feasible pretreatment is essential to disrupt the recalcitrance of its cell wall structure, thereby enhancing the extraction of cellulosic sugars, mainly glucose, xylose, and arabinose. Despite its importance, pretreatment remains one of the most technically and economically challenging steps in biomass-to-bioproduct conversion, representing a major bottleneck in the development of viable biorefinery processes [4].
Several biomass pretreatment approaches have been introduced to disrupt the lignocellulose matrix, including physical, chemical, and physical–chemical technologies [5]. For physical pretreatments, milling and steam explosion are the conventional methods used to reduce the particle size in order to increase the reaction surface [6,7]. Chemical pretreatments, including acid and alkaline methods, are used to solubilize hemicellulose and alter the lignin structure to increase the accessibility of the biomass to subsequent enzymatic hydrolysis and further bioproduct conversions [1]. An acid pretreatment using sulfuric acid is a well-developed technology that is regarded as a promising method to loosen the biomass structure and increase glucose extraction; however, its potential to degrade free xylose and glucose into furans and organic acid can cause inhibitory effects on bioconversion with microorganisms [8]. As for alkaline pretreatments, their major effect is to remove lignin and part of the hemicellulose by attacking the linkage between lignin and hemicellulose in lignin–carbohydrate complexes and de-esterifying the intermolecular bonds [8]. Though there are some inhibitory byproducts generated from the process such as phenolic compounds, this method can still retain more fermentable sugars, such as hexose and pentose, for further fermentation [9].
Sodium hydroxide and sodium carbonate are the most commonly used bases in alkaline pretreatments. They are derived from the Kraft pulping process [10]. An ammonia-based pretreatment is also considered a promising alkaline treatment technology due to its relatively lower corrosive potential and economic advantages compared to acid pretreatments [11]. An aqueous ammonia pretreatment was investigated for treating lignocellulosic biomass with a percolation reactor, and it was found to be effective at removing lignin by more than 80% [12,13]. However, this method is energy-intensive, as it requires elevated temperatures (130–170 °C) and subsequent ammonia recovery steps [14]. Additionally, the high liquid throughput associated with aqueous ammonia systems poses significant operational and economic disadvantages [15,16].
To address these limitations, an alkaline pretreatment under mild reaction conditions has been developed. The process of soaking in aqueous ammonia (SAA) was investigated to improve the aqueous ammonia pretreatment. A mild temperature and a longer treatment time were applied; a range of 40–70% lignin removal was reached and a significant increase in the cellulosic sugar yields was observed [17,18]. Yet, the high liquid throughput was still a main flaw. For reducing the chemical and water inputs, a low-liquid ammonia (LLA) pretreatment was developed under mild reaction conditions and an extended treatment period. This method led to over 70% theoretical ethanol yields [19].
Among the various approaches used in alkaline pretreatments, the ammonia fiber expansion (AFEX) process has been introduced and further developed to enhance biomass deconstruction for woody materials and agricultural residues [20,21]. A key advantage of the AFEX pretreatment over conventional alkaline pretreatments is its ability to operate as a dry-to-dry process, which significantly increases the loading of biomass solids and minimizes water usage [21]. Aligned with this principle, the low-moisture anhydrous ammonia (LMAA) process was introduced to further reduce the water and ammonia input for cellulosic ethanol production. A small-batch reactor (690 mL) was first applied, and the theoretical ethanol yield was increased to 89% [22]. Yang and Rosentrater (2017) performed the LMAA process for a corn stover pretreatment on a larger scale using a three-liter reactor and obtained the best glucan digestibility of 71.6% [23]. The LMAA pretreatment has also shown a broad adaptability across different biomass types, yielding up to 90% [20]. These high-solids, low-moisture features of the LMAA pretreatment offer potential to reduce the operating costs and ease downstream product recovery, thereby enhancing the feasibility of biomass-to-bioproduct conversion at industrial scales [24].
According to the previous studies, key factors, including ammonia loading, the biomass particle size, the moisture content, and the ammoniation duration, significantly influence the total cellulosic sugar yields [20,23]. Notably, the reactor configuration has emerged as a critical determinant of the pretreatment efficiency, directly impacting the extent of biomass deconstruction and subsequent enzymatic hydrolysis. To improve the cellulosic glucose yield of LMAA-pretreated biomass at larger scales, this study focused on modifying the reactor apparatus and optimizing the reaction conditions based on the experimental setup used by Yang and Rosentrater in 2017 [23]. Additionally, this work included kinetic modeling to better understand the glucan digestibility of the LMAA-pretreated biomass through enzymatic hydrolysis under scaled-up conditions.

2. Materials and Methods

2.1. Biomass

Air-dried corn stover was provided by Lincolnway Energy, Ames, Iowa. The quality of the corn stover was routinely verified by Lincolnway Energy and was found to contain over 65% structural carbohydrates (i.e., glucan and xylan). The air-dried corn stover was first ground and sieved into two sizes (<0.5 mm, 0.5~1 mm) prior to the pretreatment. The sieved corn stover was kept at room temperature (~21 °C) until used [20,23].

2.2. Biomass Composition Analysis

The chemical composition of the raw and LMAA-pretreated corn stover, including the extractives, glucan, xylan, lignin, and ash content, was characterized following the protocols developed by the National Renewable Energy Laboratory (NREL), Golden, CO, USA, to evaluate the effect of ammoniation on altering the biomass composition [25,26,27]. A high-performance liquid chromatography (HPLC) system equipped with a Bio-Rad Aminex HPX-87P column (Aminex HPX-87P, Bio-Rad Laboratories, Hercules, CA, USA) and a refractive index detector (Varian 356-LC, Varian, Inc., Palo Alto, CA, USA) was used to quantify glucose and xylose in the hydrolysate obtained from the structural carbohydrate assays [25]. The acid-soluble lignin (ASL) content was determined with a UV–visible spectrophotometer (UV-2100 Spectrophotometer, Unico, United Products & Instruments, Inc., Dayton, NY, USA).

2.3. Ammoniation Reactor for LMAA Pretreatment

The 3 L reactor used in Yang and Rosentrater’s study was revisited in this study (Figure 1). Their original setup achieved 72% glucan digestibility [23]. Based on a detailed assessment of the reactor configuration, we identified that modifying the ammonia input system could substantially improve the LMAA pretreatment efficiency and sugar yields. Specifically, enhancing the contact between the corn stover and ammonia during the reaction is expected to facilitate more effective biomass deconstruction.
Due to the low density (0.77 kg/m3 at 0 °C, 1 atm) of anhydrous ammonia gas, the gas tends to accumulate near the top of the reactor, limiting its contact with the biomass. To address this issue, the ammonia gas inlet was extended to the bottom of the reactor to enhance contact between the corn stover and ammonia during the reaction (Figure 1). In Yang and Rosentrater’s (2017) [23] study, limited interaction between ammonia and biomass, caused by ammonia remaining at the top, may have contributed to the lower glucan digestibility observed. This modification is expected to improve the ammoniation efficiency by ensuring a more uniform exposure of the biomass to ammonia.

2.4. LMAA Pretreatment

Prior to the LMAA pretreatment, the moisture content of ground, air-dried corn stover with particle sizes of 1 mm and 0.5 mm was adjusted to a 50% (w.b.) moisture content and equilibrated for 24 h. A total of 1 Kg of moisturized corn stover was placed in the sealed reactor (Figure 1), and anhydrous ammonia was introduced. A pipe was connected from the top of the reactor to the fume hood to safety vent excess ammonia. A pressure gauge was installed on the reactor to monitor the pressure change during the ammoniation process.
Anhydrous ammonia was added until the targeted pressure, corresponding to 0.18 g NH3/g of dry matter biomass, was achieved. The ammoniation reaction was performed for 60 min in order to achieve the best reaction condition, as described by Yang and Rosentrater (2017) [23]. After ammoniation, the reactor was allowed to cool for 5 min. The lid was removed inside the fume hood, and the treated corn stover was transferred into several glass screw-cap bottles (250 mL). The bottles containing treated corn stover were then incubated at 75 °C. Two incubation durations, 72 h and 144 h, were tested to evaluate the effect of the residence time on glucan digestibility via enzymatic hydrolysis. After the completion of the pretreatment, the bottle lids were removed inside a fume hood, and residual ammonia was removed over 12 h through aeration.

2.5. Enzymatic Hydrolysis

GC 220 cellulase was purchased from Genencor International, Inc. (Rochester, NY, USA). The cellulase activity was expressed in filter paper units (FPUs). In this study, the average activity of GC 220 was determined to be 45 FPU/mL. The β-glucosidase enzyme (Novozymes 188) was obtained from Sigma-Aldrich, Inc. (St. Louis, MO, USA). The activity of Novozymes 188 was 750 cellobiase units (CBUs)/mL.
Enzymatic hydrolysis was conducted following the NREL protocol [28]. The experiments were performed in duplicate using 250 mL Erlenmeyer flasks containing 0.1 M sodium citrate buffer (pH of 4.8) supplemented with 40 mg/L of tetracycline and 30 mg/L of cycloheximide to prevent microbial contamination. The initial glucan concentration was set at 1% (w/v). Cellulase (GC 220) was added at a loading of 15 FPU/g of glucan, and β-glucosidase (Novozym 188) was added at 60 CBU/g of glucan. The flasks were incubated at 50 ± 1 °C and shaken at 150 rpm using an Excella E24 incubator shaker (New Brunswick Scientific, Edison, NJ, USA). Hydrolysis was carried out over a time course ranging from 0 to 144 h for subsequent glucose quantification.
The total glucose concentration of the hydrolysate detected from HPLC was used to calculate the glucan digestibility following Equation (1) below. The conversion factor for glucose to equivalent glucan was 0.9.
G l u c a n   D i g e s t i b i l i t y ( % ) = g r a m s   c e l l u l o s e   d i g e s t i e d g r a m s   c e l l u l o s e   a d d e d × 100 × 0.9

2.6. Kinetics of Glucan Digestibility Through Enzymatic Hydrolysis

According to the cellulose hydrolysis reaction (Equation (2)), the reaction was assumed to follow pseudo-first-order kinetics. It can be expressed as shown in Equation (3). In this model, Ccellulose, CH2O, and Cglu represent the molar concentration of cellulose, H2O, and glucose, respectively. R denotes the reaction rate and k is the reaction rate constant.
C e l l u l o s e + H 2 O → k G l u c o s e
− d C c e l l u l o s e d t = − R = k C c e l l u l o s e C H 2 O
During the reaction, the concentration of water (CH2O) is significantly greater than that of cellulose (Ccellulose). Therefore, CH2O can be approximated as its initial concentration (CH2O(i)). With this assumption, the reaction rate expression is simplified, as shown in Equation (4). Equation (5) can be obtained by solving the differential form of Equation (4). According to Equation (5), the reaction rate constant can be determined from the linear relationship between the reaction time (t) and the natural logarithm of the cellulose concentration (Ccellulose). The slope of this linear plot is equal to the product of k and CH2O(i). Here, Ccellulose(i) indicates the initial cellulose concentration. In this study, the reaction kinetics were applied to both untreated and pretreated corn stover during the first 24 h of hydrolysis, which corresponds to the period before the reaction rate enters the plateau phase [29,30].
− d C c e l l u l o s e d t = − R = k C H 2 O i C c e l l u l o s e
ln C c e l l u l o s e = − k C H 2 O i t + ln C c e l l u l o s e i

3. Results and Discussion

3.1. Effect of LMAA Treatment with Higher Ammonia Loading on Biomass Composition

The changes in the corn stover’s chemical composition are summarized in Table 1. Compared to the untreated (raw) corn stover, the LMAA pretreatment removed lignin and xylan by 11–26% and 6–14%, respectively. A longer ammoniation duration and a smaller biomass particle size led to greater lignin and xylan removal, which in turn increased the glucan content, an effect that is expected to enhance the glucose yield during enzymatic hydrolysis.
Table 1 and Table 2 present the main effects of the pretreatment conditions on the biomass composition. Specifically, increasing the ammoniation duration from 72 to 144 h resulted in statistically significant improvements in the glucan content and reductions in the xylan and lignin levels (p < 0.05). While decreasing the particle size from 1 mm to 0.5 mm showed moderate effects on the cellulose and AIL contents, it did not significantly affect the hemicellulose or lignin content. Notably, the glucan content was slightly lower in the smaller particle size group, which may be attributed to increased cellulose loss during the pretreatment. This could be due to the higher surface area and reactivity of smaller particles, which enhance their interaction with ammonia and alter the cellulose structure [31].
For conventional alkaline pretreatments using sodium hydroxide or aqueous ammonia solutions, the lignin removal efficiencies generally exceed 60%, which is higher than what was observed for the LMAA (~26%) in this work [10,32,33]. However, these conventional methods are generally limited to low solids loadings (~20%) and require extensive washing steps to remove residual alkaline reagents after the pretreatment, which can substantially increase the overall operating costs. In contrast, the LMAA process offers the advantage of a one-pot operation, which simplifies the processing steps and potentially enhances its overall feasibility for industrial-scale applications.

3.2. Effect of LMAA Treatment on Glucan Digestibility via Enzymatic Hydrolysis

The glucan digestibility of different LMAA pretreatment conditions is illustrated in Figure 2. Also, the effects of the ammoniation duration, the corn stover particle size, and their interaction on glucan digestibility are summarized in Table 3.
Based on the results, the glucan digestibility under all LMAA conditions exceeded 70%, with the highest digestibility reaching 85%, a substantial improvement of approximately 25% compared to the 46% glucan digestibility reported under the same LMAA conditions in the study by Yang and Rosentrater (2017) [23]. This result indicates that the modification of the ammoniation reactor significantly enhanced the efficiency of the LMAA pretreatment by increasing the accessibility of the biomass to enzymatic hydrolysis.
As shown in Table 3, the ammoniation incubation time and the biomass particle size were evaluated as optimization factors. The results indicate that the ammoniation time plays a critical role in determining the final enzymatic digestibility; longer treatment durations led to a significantly higher glucan conversion. The particle size also had a notable effect (p < 0.001), as biomass with a smaller particle size (<0.5 mm) exhibited a higher digestibility than that with larger particles. Both factors were statistically significant. Although the interaction between time and particle size was weak, the combination of a smaller particle size and a longer treatment (144 h) yielded the highest average glucan digestibility of 83.69%. These results suggest that extended ammoniation and a reduced particle size synergistically improve substrate accessibility, which could enhance sugar release and increase the downstream fermentation yields.
Additionally, the highest glucan digestibility achieved in this study is comparable to the reported 80% glucan digestibility of LMAA-treated corn fiber under similar pretreatment conditions [20]. The one-pot configuration of the LMAA process also produced glucose yields similar to those reported for conventional aqueous alkaline pretreatments, which typically operate at lower solids loadings [10,34]. Furthermore, compared to a recently developed one-pot alkaline solvent process [35], the LMAA process exhibited an approximately 20% higher glucan digestibility. These findings collectively highlight the scalability potential of high-solids, one-pot LMAA pretreatment systems, particularly for application at larger scales.

3.3. Kinetics of Enzymatic Hydrolysis

From the results of glucan digestibility via enzymatic hydrolysis, the kinetics were used to determine the reaction rate constant for the hydrolysis process. The results of 72 h ammoniation and 144 h ammoniation are shown in Figure 3 and Figure 4.
For the 72 h ammoniation, the reaction constants (k) for corn stover with a 1 mm or a 0.5 mm particle size were determined as 1.16 × 10−3 h−1 and 1.33 × 10−3 h−1, respectively. These results indicate an improved hydrolysis performance for smaller particle sizes. The coefficient of determination (R2 > 0.8) further suggests that enzymatic hydrolysis follows pseudo-first-order kinetics during the initial 24 h of the reaction. Additionally, the y-intercepts of the linearized kinetic plots represent the initial cellulose concentrations, estimated to be 0.0514 M for 1 mm particles and 0.0494 M for 0.5 mm particles. The combination of a higher reaction rate constant and a slightly lower initial substrate concentration for the smaller particle size suggests an enhanced hydrolysis efficiency under these conditions.
For the 144 h ammoniation, a similar trend was observed. The reaction rate constants for the 1 mm and 0.5 mm particle sizes were determined to be 1.35 × 10−3 h−1 and 1.67 × 10−3 h−1, respectively, representing an increase of approximately 16–26% compared to the 72 h ammoniation results. The initial cellulose concentrations estimated from kinetic fitting were 0.053 M for 1 mm particles and 0.0512 M for 0.5 mm particles. Compared to the 72 h ammoniation condition, these higher initial cellulose concentrations suggest an enhanced cellulose accessibility resulting from prolonged ammoniation.
These findings align with the reported literature on the effects of a pretreatment on enzymatic hydrolysis kinetics. Untreated or insufficiently pretreated biomass often exhibits complex or non-pseudo-first-order kinetics due to limited enzyme access, which results from a high cellulose crystallinity, the lignin content, and the dense structure of plant cell walls. As a result, hydrolysis may display multi-phase or heterogeneous kinetics, reflecting the substrate heterogeneity and diffusion limitations. In contrast, effective pretreatments, especially those involving lignin removal and cellulose amorphization, improve enzyme accessibility and allow the reaction to approximate pseudo-first-order behavior during the early stages of hydrolysis [36].

4. Conclusions

An LMAA pretreatment with an ammonia loading of 0.18 g NH3/g of dry biomass, conducted in the modified ammoniation reactor, effectively solubilized lignin and hemicellulose and increased the cellulose content in the biomass. The enhanced ammonia diffusion during pretreatment contributed to an improved glucan digestibility. The results indicate that the ammoniation duration and biomass particle size are critical factors influencing both biomass accessibility and glucose yield. The highest glucose yield, exceeding 83%, was achieved using the LMAA pretreatment with a 0.5 mm particle size. Kinetic modeling of the enzymatic hydrolysis data suggests that the reaction follows a pseudo-first-order model during the initial 24 h. However, this model may not adequately describe the complete hydrolysis process beyond this time frame. Further detailed kinetic analyses will be necessary to fully characterize the LMAA process. Overall, biomass with a smaller particle size subjected to longer ammoniation incubation produced the highest enzymatic digestibility.

Author Contributions

Conceptualization, K.A.R.; formal analysis, M.-H.C.; investigation, M.-H.C.; writing—original draft, M.-H.C.; writing—review and editing, K.A.R.; supervision, K.A.R. All authors have read and agreed to the published version of the manuscript.

Funding

This study received no external funding.

Data Availability Statement

The data presented in this study are available from the corresponding author upon request. The data are not publicly available due to privacy and ethical restrictions.

Conflicts of Interest

The authors declare no conflicts of interest.

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Processes 13 02643 g001
Figure 1. Configuration change of ammoniation reactor.
Figure 1. Configuration change of ammoniation reactor.
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Figure 2. Glucan digestibility during corn stover hydrolysis; (a) 72 h ammoniation incubation and (b) 144 h ammoniation incubation.
Figure 2. Glucan digestibility during corn stover hydrolysis; (a) 72 h ammoniation incubation and (b) 144 h ammoniation incubation.
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Figure 3. The kinetics fitting of 72 h ammoniation.
Figure 3. The kinetics fitting of 72 h ammoniation.
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Figure 4. The kinetics fitting of 144 h ammoniation.
Figure 4. The kinetics fitting of 144 h ammoniation.
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Table 1. Main effects on biomass composition before and after LMAA pretreatment.
Table 1. Main effects on biomass composition before and after LMAA pretreatment.
FactorLevelsGlucan (%)Xylan (%)AIL (%)ASL (%)
Time (h)7236.55 (1.70) b27.03 (1.04) b13.31 (1.57) c2.87 (0.15) b
14439.74 (1.46) a24.82 (0.80) c15.03 (0.87) b2.71 (0.16) b
Particle Size (mm)0.537.05 (2.33) b25.95 (1.85) b15.93 (0.95) b2.93 (0.22) a
139.25 (1.67) a25.89 (1.09) b14.88 (1.61) c2.91 (0.12) a
Raw Materials34.73 (1.20) c38.8 (1.08) a17.87 (1.09) a3.19 (0.14) a
Values in parentheses are the standard deviations, and each level of the main factor indicates insignificant differences at α = 0.05. Different letters indicate significant differences amongst levels within each independent factor.
Table 2. The p-values of each effect on the LMAA pretreatment.
Table 2. The p-values of each effect on the LMAA pretreatment.
FactorCelluloseHemicelluloseAILASL
Time<0.0001<0.0001<0.00010.001
Particle Size0.020.930.030.75
Time × Particle Size0.140.620.040.40
Each level of the main factor indicates insignificant differences at α = 0.05.
Table 3. Effects of LMAA pretreatment on glucan digestibility via enzymatic hydrolysis.
Table 3. Effects of LMAA pretreatment on glucan digestibility via enzymatic hydrolysis.
FactorLevelsDigestibility (%)p-Value
Time (h)7272.29 (2.05) b<0.0001
14480.50 (3.71) a
Particle Size (mm)0.578.76 (5.61) a0.0003
174.03 (3.67) b
Time × Particle Size144 × 0.583.69 (1.72) a0.0662
144 × 177.31 (0.94) b
72 × 0.573.83 (1.72) b,c
72 × 170.74 (0.65) c
Values in parentheses are the standard deviations, and each level of the main factor indicates insignificant differences at α = 0.05. Different letters indicate significant differences amongst levels within each independent factor.
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Cheng, M.-H.; Rosentrater, K.A. Furthering the Application of a Low-Moisture Anhydrous Ammonia Pretreatment of Corn Stover. Processes 2025, 13, 2643. https://doi.org/10.3390/pr13082643

AMA Style

Cheng M-H, Rosentrater KA. Furthering the Application of a Low-Moisture Anhydrous Ammonia Pretreatment of Corn Stover. Processes. 2025; 13(8):2643. https://doi.org/10.3390/pr13082643

Chicago/Turabian Style

Cheng, Ming-Hsun, and Kurt A. Rosentrater. 2025. "Furthering the Application of a Low-Moisture Anhydrous Ammonia Pretreatment of Corn Stover" Processes 13, no. 8: 2643. https://doi.org/10.3390/pr13082643

APA Style

Cheng, M.-H., & Rosentrater, K. A. (2025). Furthering the Application of a Low-Moisture Anhydrous Ammonia Pretreatment of Corn Stover. Processes, 13(8), 2643. https://doi.org/10.3390/pr13082643

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