生物质燃气热处理木材品质与微观力学性能研究
发布时间：2018-08-11 18:45
【摘要】：目前木材高温热处理技术主要是利用氮气、真空、蒸汽或植物油等作为保护介质,而对于生物质燃气热处理木材的研究相对比较缺乏。与其他传统的工业化木材热处理技术相比,生物质燃气高温改性处理在生产效率、产品质量和污染排放等方面有其独特的优势。根据我国木材产品市场日益突出的供需矛盾,针对生物质燃气高温热处理技术的研究,对于拓展生物质燃料的应用领域,丰富热处理工艺和改善人工林速生材的利用率、产品附加值具有极其重要的现实意义。本文以落叶松(Larix gmelinii (Rupr) Kuzen)为试材,热处理温度分别为150℃C、160℃C、170℃C、180℃C、190℃C、200℃C和210℃C,保温时间分别为2h、4h、6h和8h的条件下,对高温热处理技术进行了系统性的研究。研究了各种热处理工艺条件对木材物理性能、化学组分、燃烧性能、人工老化性能和细胞壁微观力学性能的影响,并系统性的比较了生物质燃气和氮气热处理材性能的差异性。其中主要的研究结果包括：1、随着处理温度的提高和处理时间的延长,热处理落叶松心边材的各向及体积干缩率及湿胀性、吸水性、心边材明度值L*均显著降低,同时其尺寸稳定性也随着逐渐增加。处理温度和时间对热处理材性能有决定性影响,其中处理温度的影响更大。相同热处理工艺,氮气和生物质燃气处理落叶松吸湿膨胀性基本相同。当热处理温度达到190℃C,处理时间为6h时,落叶松心材和边材颜色(特别是明度值L*)基本一致,克服了心边材颜色不均匀的问题,热处理材可部分代替珍贵木材使用。2、紫外照射和湿气喷淋人工加速老化条件下,木材表面趋于灰白色,细胞壁出现裂痕。在短期老化条件下,210℃C热处理木材颜色较为稳定；而长期老化条件下,热处理材与未处理材颜色稳定性差异不大。3、锥形量热仪CONE用于测试木材燃烧性能参数。由于热处理造成木材组分含量的变化和微观结构的转变,2100C热处理材燃烧过程的MLR失重峰值和平均热释放速率峰值分别降低46%和42%,对于减少火灾危害有积极的作用。4、通过木材化学组分分析,热处理过程使落叶松边材半纤维素和a-纤维素含量分别由33.3%和38.8%降低到11.24～23.3%和33.7-38.3%,而木质素相对含量则由26.4%增加到36.7-49.3%；热处理后落叶松心材半纤维素和α-纤维素含量分别由32.7%和37.9%降低到11.2-22.6%和33.6-37.2%,而木质素相对含量则由26.9%增加到37.5-48.7%。生物质燃气热处理后木材各组分含量变化与实验室氮气热处理基本一致。5、高温热处理过程中,半纤维素乙酰基断裂形成乙酸,进一步促进半纤维素和无定形区纤维素酸性条件下的水解反应,分子链断裂聚合度降低,从而形成低聚糖、二糖甚至单糖。热重-红外联用仪TG-FTI R检测到木材热解过程中的大量溢出气体,如水、CO、CO2、甲醛等羰基类物质、酚类物质和甲烷等。热处理后,木材热解逸出气体的演变曲线发生明显变化。热解温度在250℃C以下时,非共轭C=O键发生裂解从而形成C02；当热解温度达到250-340℃C时大量p-0-4键发生断裂并迅速释放CO／。当热解温度超过260℃C,醚键和二芳基醚键的断裂从而形成CO。高温热解过程木质素发生二苯基甲烷的缩聚反应和脱甲氧基的反应,脱去大量甲氧基,芳环活性点数量增加,木质素反应活性提高。由于木质素所具有的复杂化学结构,通常酚类物质包括愈创木酚、二甲氧基苯酚以及其衍生物。热重-气质联用仪TG-GC-MS检测到大量热裂解产物,包括酸类、酯类、醇类和呋喃类物质。热处理后木材热解溢出气体明显减少,同时其逸出气体的成分更为复杂多样。6、装备热平台的纳米压痕仪对热处理木材细胞壁微观机械性能的温度响应机制进行了实时监测。室温下热处理材S2层细胞壁弹性模量由20.8GPa降低到18.8～19.2GPa,而其硬度则由0.61 N/mm2增加到0.69～0.74N/mm2。高温环境下,热处理材细胞壁弹性模量和硬度较稳定。利用Burge r模型J(t):J0+J1 t+J2 [1-exp(-t/τ0B)]可以良好的拟合木材细胞壁的蠕变行为。热处理木材细胞壁表现出更低的蠕变率,这主要是与木质纤维素结构的再冷凝和交联反应以及纤维素结晶性提高等因素有关。7、本试验中,比较了多种保护介质(氮气、空气、生物质燃气和植物油)下热处理木材的材性。结果表明,随处理温度的提高木材降解反应逐渐增强,质量损失率随之增加。氮气和生物质燃气热处理材细胞壁出现少量细小裂痕,而空气下热处理细胞壁产生更多更严重的裂痕。油热处理木材细胞壁弹性模量和硬度的标准差较大,与植物油浸渍入木材细胞壁内部有关。总体上看,不同热处理介质下木材细胞壁的蠕变行为均有所减弱。应根据热处理木制品的最终使用用途来选择合适的热处理介质、处理温度和时间。
[Abstract]:At present, wood high temperature heat treatment technology mainly uses nitrogen, vacuum, steam or vegetable oil as protective medium, but the research on biomass gas heat treatment wood is relatively scarce. According to the increasingly prominent contradiction between supply and demand in China's wood products market, the research on biomass gas high temperature heat treatment technology is of great practical significance for expanding the application field of biomass fuel, enriching heat treatment technology and improving the utilization rate of plantation fast-growing timber. In this paper, Larix gmelinii (Rupr) Kuzen was used as the test material. The heat treatment temperatures were 150 C, 160 C, 170 C, 180 C, 190 C, 200 C and 210 C. The heat preservation time was 2h, 4h, 6h and 8h, respectively. The effects of chemical composition, combustion properties, artificial aging properties and cell wall micro-mechanical properties were systematically compared. The main results were as follows: 1. With the increase of treatment temperature and treatment time, the volume and orientation of heat-treated Larch sapwood were dry. The shrinkage, swelling, water absorption and luminosity of core sapwood L* decreased significantly, and the dimensional stability increased gradually. The treatment temperature and time had a decisive effect on the properties of heat treated wood, and the treatment temperature had a greater effect. The moisture absorption and expansion of Larch treated with nitrogen and biomass gas were basically the same under the same heat treatment process. The color of Larch heartwood and sapwood (especially brightness value L*) is basically the same when the heat treatment temperature reaches 190 C and the treatment time is 6 h. The problem of uneven color of heartwood and sapwood is overcome. The heat treated wood can partly replace the precious wood. 2. Under the condition of artificial accelerated aging by ultraviolet radiation and moisture spraying, the wood surface tends to grey-white and the cell wall becomes gray. The color stability of heat treated wood and untreated wood is not different under long-term aging condition. 3. Cone calorimeter CONE is used to test the combustion performance parameters of wood. The MLR weight loss peak and average heat release rate peak decreased by 46% and 42% respectively, which played an active role in reducing fire hazards. 4. The hemicellulose and a-cellulose contents of Larch sapwood were reduced from 33.3% and 38.8% to 11.24-23.3% and 33.7-38.3% respectively by the analysis of wood chemical composition. The relative content of lignin increased from 26.4% to 36.7-49.3%; the hemicellulose and alpha-cellulose contents of Larch heartwood decreased from 32.7% and 37.9% to 11.2-22.6% and 33.6-37.2% respectively after heat treatment, while the relative content of lignin increased from 26.9% to 37.5-48.7%. 5. During high temperature heat treatment, the acetyl group of hemicellulose breaks into acetic acid, which further promotes the hydrolysis of hemicellulose and amorphous cellulose under acidic conditions. The degree of molecular chain breaking polymerization decreases, resulting in the formation of oligosaccharides, disaccharides and even monosaccharides. A large number of overflow gases, such as water, CO, CO2, formaldehyde and other carbonyl substances, phenolic substances and methane, etc. After heat treatment, the evolution curve of the wood pyrolysis escape gases has changed significantly. When the pyrolysis temperature is below 250 C, the non-conjugated C=O bond cracks and forms C02; when the pyrolysis temperature reaches 250-340 C, a large number of p-0-4 bond breaks and occurs. When the pyrolysis temperature is over 260 C, the ether bond and the diaryl ether bond break down to form CO. During the pyrolysis process, the lignin undergoes diphenylmethane condensation and demethoxylation, removing a large number of methoxy groups, increasing the number of aromatic ring active points and increasing the lignin reactivity. A large number of pyrolysis products, including acids, esters, alcohols and furans, were detected by TG-GC-MS. After heat treatment, the overflow gas from wood pyrolysis was significantly reduced, and the composition of the escaped gas was more complex and varied. The temperature response mechanism of the micromechanical properties of the heat treated wood cell wall was monitored by the nanoindentation apparatus. The modulus of elasticity of S2 layer cell wall decreased from 20.8 GPa to 18.8-19.2 GPa at room temperature, while the hardness increased from 0.61 N/mm2 to 0.69-0.74 N/mm2 at high temperature. Burge R model J(t): J0+J1 t+J2[1-exp(-t/0B)] can be used to fit the creep behavior of wood cell wall well. The creep rate of heat treated wood cell wall is lower, which is mainly related to the re-condensation and crosslinking reaction of lignocellulose structure and the increase of cellulose crystallinity. The results showed that the degradation reaction of wood increased gradually with the increase of treatment temperature, and the mass loss rate increased. There were a few small cracks in the cell wall of the heat treated wood with nitrogen and biomass gas, while the cell wall of the heat treated wood with air produced small cracks. More and more serious cracks. The standard deviation of elastic modulus and hardness of wood cell wall after oil heat treatment is larger, which is related to the impregnation of vegetable oil into the wood cell wall. Medium, temperature and time.
【学位授予单位】：东北林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S781
，
本文编号：2177889
[Abstract]:At present, wood high temperature heat treatment technology mainly uses nitrogen, vacuum, steam or vegetable oil as protective medium, but the research on biomass gas heat treatment wood is relatively scarce. According to the increasingly prominent contradiction between supply and demand in China's wood products market, the research on biomass gas high temperature heat treatment technology is of great practical significance for expanding the application field of biomass fuel, enriching heat treatment technology and improving the utilization rate of plantation fast-growing timber. In this paper, Larix gmelinii (Rupr) Kuzen was used as the test material. The heat treatment temperatures were 150 C, 160 C, 170 C, 180 C, 190 C, 200 C and 210 C. The heat preservation time was 2h, 4h, 6h and 8h, respectively. The effects of chemical composition, combustion properties, artificial aging properties and cell wall micro-mechanical properties were systematically compared. The main results were as follows: 1. With the increase of treatment temperature and treatment time, the volume and orientation of heat-treated Larch sapwood were dry. The shrinkage, swelling, water absorption and luminosity of core sapwood L* decreased significantly, and the dimensional stability increased gradually. The treatment temperature and time had a decisive effect on the properties of heat treated wood, and the treatment temperature had a greater effect. The moisture absorption and expansion of Larch treated with nitrogen and biomass gas were basically the same under the same heat treatment process. The color of Larch heartwood and sapwood (especially brightness value L*) is basically the same when the heat treatment temperature reaches 190 C and the treatment time is 6 h. The problem of uneven color of heartwood and sapwood is overcome. The heat treated wood can partly replace the precious wood. 2. Under the condition of artificial accelerated aging by ultraviolet radiation and moisture spraying, the wood surface tends to grey-white and the cell wall becomes gray. The color stability of heat treated wood and untreated wood is not different under long-term aging condition. 3. Cone calorimeter CONE is used to test the combustion performance parameters of wood. The MLR weight loss peak and average heat release rate peak decreased by 46% and 42% respectively, which played an active role in reducing fire hazards. 4. The hemicellulose and a-cellulose contents of Larch sapwood were reduced from 33.3% and 38.8% to 11.24-23.3% and 33.7-38.3% respectively by the analysis of wood chemical composition. The relative content of lignin increased from 26.4% to 36.7-49.3%; the hemicellulose and alpha-cellulose contents of Larch heartwood decreased from 32.7% and 37.9% to 11.2-22.6% and 33.6-37.2% respectively after heat treatment, while the relative content of lignin increased from 26.9% to 37.5-48.7%. 5. During high temperature heat treatment, the acetyl group of hemicellulose breaks into acetic acid, which further promotes the hydrolysis of hemicellulose and amorphous cellulose under acidic conditions. The degree of molecular chain breaking polymerization decreases, resulting in the formation of oligosaccharides, disaccharides and even monosaccharides. A large number of overflow gases, such as water, CO, CO2, formaldehyde and other carbonyl substances, phenolic substances and methane, etc. After heat treatment, the evolution curve of the wood pyrolysis escape gases has changed significantly. When the pyrolysis temperature is below 250 C, the non-conjugated C=O bond cracks and forms C02; when the pyrolysis temperature reaches 250-340 C, a large number of p-0-4 bond breaks and occurs. When the pyrolysis temperature is over 260 C, the ether bond and the diaryl ether bond break down to form CO. During the pyrolysis process, the lignin undergoes diphenylmethane condensation and demethoxylation, removing a large number of methoxy groups, increasing the number of aromatic ring active points and increasing the lignin reactivity. A large number of pyrolysis products, including acids, esters, alcohols and furans, were detected by TG-GC-MS. After heat treatment, the overflow gas from wood pyrolysis was significantly reduced, and the composition of the escaped gas was more complex and varied. The temperature response mechanism of the micromechanical properties of the heat treated wood cell wall was monitored by the nanoindentation apparatus. The modulus of elasticity of S2 layer cell wall decreased from 20.8 GPa to 18.8-19.2 GPa at room temperature, while the hardness increased from 0.61 N/mm2 to 0.69-0.74 N/mm2 at high temperature. Burge R model J(t): J0+J1 t+J2[1-exp(-t/0B)] can be used to fit the creep behavior of wood cell wall well. The creep rate of heat treated wood cell wall is lower, which is mainly related to the re-condensation and crosslinking reaction of lignocellulose structure and the increase of cellulose crystallinity. The results showed that the degradation reaction of wood increased gradually with the increase of treatment temperature, and the mass loss rate increased. There were a few small cracks in the cell wall of the heat treated wood with nitrogen and biomass gas, while the cell wall of the heat treated wood with air produced small cracks. More and more serious cracks. The standard deviation of elastic modulus and hardness of wood cell wall after oil heat treatment is larger, which is related to the impregnation of vegetable oil into the wood cell wall. Medium, temperature and time.
【学位授予单位】：东北林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S781
，
本文编号：2177889
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