生物質燃氣熱處理木材品質與微觀力學性能研究
發(fā)布時間：2018-08-11 18:45
【摘要】：目前木材高溫熱處理技術主要是利用氮氣、真空、蒸汽或植物油等作為保護介質,而對于生物質燃氣熱處理木材的研究相對比較缺乏。與其他傳統(tǒng)的工業(yè)化木材熱處理技術相比,生物質燃氣高溫改性處理在生產效率、產品質量和污染排放等方面有其獨特的優(yōu)勢。根據我國木材產品市場日益突出的供需矛盾,針對生物質燃氣高溫熱處理技術的研究,對于拓展生物質燃料的應用領域,豐富熱處理工藝和改善人工林速生材的利用率、產品附加值具有極其重要的現(xiàn)實意義。本文以落葉松(Larix gmelinii (Rupr) Kuzen)為試材,熱處理溫度分別為150℃C、160℃C、170℃C、180℃C、190℃C、200℃C和210℃C,保溫時間分別為2h、4h、6h和8h的條件下,對高溫熱處理技術進行了系統(tǒng)性的研究。研究了各種熱處理工藝條件對木材物理性能、化學組分、燃燒性能、人工老化性能和細胞壁微觀力學性能的影響,并系統(tǒng)性的比較了生物質燃氣和氮氣熱處理材性能的差異性。其中主要的研究結果包括：1、隨著處理溫度的提高和處理時間的延長,熱處理落葉松心邊材的各向及體積干縮率及濕脹性、吸水性、心邊材明度值L*均顯著降低,同時其尺寸穩(wěn)定性也隨著逐漸增加。處理溫度和時間對熱處理材性能有決定性影響,其中處理溫度的影響更大。相同熱處理工藝,氮氣和生物質燃氣處理落葉松吸濕膨脹性基本相同。當熱處理溫度達到190℃C,處理時間為6h時,落葉松心材和邊材顏色(特別是明度值L*)基本一致,克服了心邊材顏色不均勻的問題,熱處理材可部分代替珍貴木材使用。2、紫外照射和濕氣噴淋人工加速老化條件下,木材表面趨于灰白色,細胞壁出現(xiàn)裂痕。在短期老化條件下,210℃C熱處理木材顏色較為穩(wěn)定；而長期老化條件下,熱處理材與未處理材顏色穩(wěn)定性差異不大。3、錐形量熱儀CONE用于測試木材燃燒性能參數(shù)。由于熱處理造成木材組分含量的變化和微觀結構的轉變,2100C熱處理材燃燒過程的MLR失重峰值和平均熱釋放速率峰值分別降低46%和42%,對于減少火災危害有積極的作用。4、通過木材化學組分分析,熱處理過程使落葉松邊材半纖維素和a-纖維素含量分別由33.3%和38.8%降低到11.24～23.3%和33.7-38.3%,而木質素相對含量則由26.4%增加到36.7-49.3%；熱處理后落葉松心材半纖維素和α-纖維素含量分別由32.7%和37.9%降低到11.2-22.6%和33.6-37.2%,而木質素相對含量則由26.9%增加到37.5-48.7%。生物質燃氣熱處理后木材各組分含量變化與實驗室氮氣熱處理基本一致。5、高溫熱處理過程中,半纖維素乙酰基斷裂形成乙酸,進一步促進半纖維素和無定形區(qū)纖維素酸性條件下的水解反應,分子鏈斷裂聚合度降低,從而形成低聚糖、二糖甚至單糖。熱重-紅外聯(lián)用儀TG-FTI R檢測到木材熱解過程中的大量溢出氣體,如水、CO、CO2、甲醛等羰基類物質、酚類物質和甲烷等。熱處理后,木材熱解逸出氣體的演變曲線發(fā)生明顯變化。熱解溫度在250℃C以下時,非共軛C=O鍵發(fā)生裂解從而形成C02；當熱解溫度達到250-340℃C時大量p-0-4鍵發(fā)生斷裂并迅速釋放CO／。當熱解溫度超過260℃C,醚鍵和二芳基醚鍵的斷裂從而形成CO。高溫熱解過程木質素發(fā)生二苯基甲烷的縮聚反應和脫甲氧基的反應,脫去大量甲氧基,芳環(huán)活性點數(shù)量增加,木質素反應活性提高。由于木質素所具有的復雜化學結構,通常酚類物質包括愈創(chuàng)木酚、二甲氧基苯酚以及其衍生物。熱重-氣質聯(lián)用儀TG-GC-MS檢測到大量熱裂解產物,包括酸類、酯類、醇類和呋喃類物質。熱處理后木材熱解溢出氣體明顯減少,同時其逸出氣體的成分更為復雜多樣。6、裝備熱平臺的納米壓痕儀對熱處理木材細胞壁微觀機械性能的溫度響應機制進行了實時監(jiān)測。室溫下熱處理材S2層細胞壁彈性模量由20.8GPa降低到18.8～19.2GPa,而其硬度則由0.61 N/mm2增加到0.69～0.74N/mm2。高溫環(huán)境下,熱處理材細胞壁彈性模量和硬度較穩(wěn)定。利用Burge r模型J(t):J0+J1 t+J2 [1-exp(-t/τ0B)]可以良好的擬合木材細胞壁的蠕變行為。熱處理木材細胞壁表現(xiàn)出更低的蠕變率,這主要是與木質纖維素結構的再冷凝和交聯(lián)反應以及纖維素結晶性提高等因素有關。7、本試驗中,比較了多種保護介質(氮氣、空氣、生物質燃氣和植物油)下熱處理木材的材性。結果表明,隨處理溫度的提高木材降解反應逐漸增強,質量損失率隨之增加。氮氣和生物質燃氣熱處理材細胞壁出現(xiàn)少量細小裂痕,而空氣下熱處理細胞壁產生更多更嚴重的裂痕。油熱處理木材細胞壁彈性模量和硬度的標準差較大,與植物油浸漬入木材細胞壁內部有關�？傮w上看,不同熱處理介質下木材細胞壁的蠕變行為均有所減弱。應根據熱處理木制品的最終使用用途來選擇合適的熱處理介質、處理溫度和時間。
[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.
【學位授予單位】：東北林業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：S781
，
本文編號：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.
【學位授予單位】：東北林業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：S781
，
本文編號：2177889
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