共查询到20条相似文献，搜索用时 906 毫秒
1.
研究了在中性至微碱性水溶液中ＮａＣｌＯ与紫胶树脂环状组分代表物——壳脑酸的反应。结果表明该反应为一复杂反应，除氯对双键的加成反应外，还有其它副反应，而且反应的复杂程度与反应温度有关；对主反应而言，降低ｐＨ或提高反应温度均可加速反应；反应体系中其它无效离子的存在对主反应没有阻滞作用。文章还用计算机软件模拟了主反应的动力学方程；计算出反应在ｐＨ８．５、３０～４０℃进行时的表观活化能为１９０ｋＪ／ｍｏｌ。 相似文献
2.
以固体酸ZnO为催化剂,在加压条件下使松香与不同碳链长度的一元醇酯化反应,制备松香甲酯、正丁酯和正辛酯,探讨反应温度、反应压力、催化剂用量、原料配比及反应时间等对酯化反应的影响。结果表明:适宜的酯化反应工艺条件:①松香甲酯化反应:反应温度220℃,反应压力5.5 MPa,催化剂用量1%,醇酸比25∶1,反应时间5 h;②松香丁酯化反应:反应温度220℃,反应压力3.5 MPa,催化剂用量1%,醇酸比8∶1,反应时间5 h;③松香辛酯化反应:反应温度210℃,反应压力2.0 MPa,催化剂用量1%,醇酸比4∶1,反应时间5 h。加压条件下可以显著促进松香与一元醇的酯化反应,反应时间比常压下大大缩短,酯化率明显提高,压力对酯化反应影响效果与一元醇的碳数成正比,即辛醇>丁醇>甲醇。工业上常用的固体酸ZnO催化剂可用于松香与系列一元醇的加压酯化反应。 相似文献
3.
4.
棉秆与麦草蒸煮反应的动力学比较 总被引：1，自引：0，他引：1
比较了棉秆和麦草蒸煮反应的脱木质素速率常数,提出一种研究蒸煮反应动力学的实验和计算新方法。通过对不同恒温条件下的反应速率常数计算,采用与实际蒸煮反应相同的液比,用较短时间周期的有效碱浓度变化值和木质素含量变化值计算得出了两种原料烧碱-蒽醌法蒸煮反应的活化能。棉秆烧碱-蒽醌法蒸煮反应的活化能和麦草烧碱-蒽醌法蒸煮反应的活化能在整个脱木质素阶段基本是不变的。麦草烧碱-蒽醌蒸煮反应的活化能为51.0 kJ/mol。棉秆烧碱-蒽醌法蒸煮反应的活化能是138.1 kJ/mol,高于麦草蒸煮反应活化能,说明麦草蒸煮脱木质素反应比棉秆更容易。 相似文献
5.
二氢月桂烯亚临界水合过程的初步研究 总被引：1，自引：0，他引：1
采用强酸型阳离子交换树脂NKC-9作催化剂,研究了亚临界水(SCW)中二氢月桂烯水合制备二氢月桂烯醇的反应。探讨了可能的反应机理,并考察了反应温度、催化剂用量、反应压力及水和二氢月桂烯物质的量之比(水烯比)对水合反应的影响。结果表明,二氢月桂烯醇是主要的水合产物,反应温度升高反应速率增大,催化剂用量增加反应速率加快,反应压力对水合反应的影响不大。在催化剂用量19%、水烯比35∶1、压力8.0 MPa的条件下反应6 h后,二氢月桂烯的转化率可达到13.27%,产物的收率为4.56%。 相似文献
6.
对湿固化异氰酸酯胶黏剂粘接高含水率桦木的胶接机理进行系统研究。利用计算化学方法这一崭新的手段,采用Material Studio软件中DMol3模块,采用基于密度泛函理论的量子化学程序,通过模拟胶接体系中异氰酸酯基团(NCO)与自由水(H2O)及桦木中不同化学环境羟基(—OH)的反应历程,搜索反应的过渡态,计算反应活化能以及反应总能量,判定反应进行的难易以及先后次序。研究结果表明胶接体系中—NCO基团与自由水反应的活化能与—NCO基团与纤维素中—OH的反应活化能相接近,反应存在竞争关系。胶接体系中—NCO与纤维素上—OH相对来说较容易反应,且反应进行的顺序是C6C3C1C2,均为放热反应;与木质素上—OH不容易反应,反应进行的顺序是紫丁香基丙烷(Lig-S)愈创木基丙烷(Lig-G)对羟苯基丙烷(Lig-H),其中羟基与Lig-S和Lig-G的反应是放热反应,与Lig-H的反应是吸热反应。 相似文献
7.
《林产化学与工业》2017,(1)
为揭示磷酸催化纤维素热解时可以显著促进脱水反应发生的催化机理,以β-D-吡喃葡萄糖为纤维素模型化合物,利用密度泛函理论方法研究了磷酸对其热解脱水反应的作用机理。结果表明:催化热解过程中β-D-吡喃葡萄糖和磷酸通过氢键作用形成多个可能的反应复合物,氢键能够稳定反应复合物结构,不同反应复合物引发β-D-吡喃葡萄糖不同位点的1,2-脱水反应和1,3-脱水反应。与非催化相比,磷酸催化作用下β-D-吡喃葡萄糖的脱水反应活化能显著降低,其中8个位点的1,2-脱水反应活化能降低了79~129 k J/mol,2个位点的1,3-脱水反应活化能降低了28~60 k J/mol。β-D-吡喃葡萄糖发生1,2-脱水反应的活化能更低,比1,3-脱水反应更容易发生,且以4-OH+3-H、1-OH+2-H、3-OH+2-H和3-OH+4-H这4个位点的1,2-脱水反应为主。 相似文献
8.
歧化松香(丙烯酸-2-羟基乙基酯)酯的合成 总被引：12，自引：0，他引：12
通过对歧化松香(DPR)分别进行酰氯化和酯化反应成功制备了DPR(丙烯酸-2-羟基乙基酯)酯.考察了反应过程中反应温度、反应时间以及原料物质的量之比对DPR酰氯化反应的影响,确定了DPR酰氯化反应的最佳条件(DPR与三氯化磷(PCl3)的物质的量比为1∶0.33,反应温度50 ℃,反应时间3 h),并对DPR酰氯的酯化反应进行了研究.实验结果表明:温度对于DPR酰氯化反应的影响较小;而原料物质的量之比对反应程度的影响较大,PCl3用量的增加有利于反应程度的增加.实验结果还显示IR、13C NMR和GC-MS联用分析技术可有效地对反应过程进行跟踪. 相似文献
9.
为了解NaClO与紫胶树脂反应的规律,用壳脑酸与NaClO及壳脑酸二甲酯与溴反应,模拟了紫胶树脂与游离氯间的反应。结果表明NaClO与壳脑酸的反应为一表观复杂反应,反应前15min进行得很快,降低pH和提高温度均可加速反应。溴与壳脑酸二甲酯反应的活化能为66.2kJ/mol。由此可知,用NaClO漂白紫胶时,游离氯必然会进入树脂,成为树脂的结合氯,从而危害漂白紫胶产品的贮存性。 相似文献
10.
HMC-60催化α-蒎烯异构化反应动力学研究 总被引：2，自引：2，他引：0
用HMC 6 0催化剂催化α 蒎烯异构化反应 ,考察了反应温度、反应时间和催化剂用量对反应结果的影响 ,研究了反应动力学。确定在 140～ 156℃范围α 蒎烯异构化反应均为一级反应。分别求出在 140、150和 156℃时的反应速率常数为 4 .4 1× 10 - 4、4 6 9× 10 - 4和 5.11× 10 - 4;表观活化能为 1.75kJ/mol,频率因子A =5.314×10 - 4。建立了反应速率方程式和反应速率常数与温度的关系式。 相似文献
11.
12.
Five-year-old 'Spring' navel (Citrus sinensis (L.) Osbeck) orange trees were completely defruited, 50% defruited or left fully laden to study effects of fruit load on concentrations of nitrogen (N) and carbohydrate, net assimilation of CO2 (Ac) and stomatal conductance (gs) of mature leaves on clear winter days just before fruit harvest. Leaves on defruited trees were larger, had higher starch concentrations and greater leaf dry mass per area (LDMa) than leaves on fruited trees. Both Ac and gs were more than 40% lower in sunlit leaves on defruited trees than in sunlit leaves on trees with fruit. Leaves immediately adjacent to fruit were smaller, had lower leaf nitrogen and carbohydrate concentrations, lower LDMa and lower Ac than leaves on non-fruiting branches of the same trees. Removing half the crop increased individual fruit mass, but reduced fruit color development. Half the trees were shaded with 50% shade cloth for 4 months before harvest to determine the effects of lower leaf temperature (Tl) and leaf-to-air vapor pressure difference on leaf responses. On relatively warm days when sunlit Tl > 25 degrees C, shade increased Ac and gs, but had no effect on the ratio of internal to ambient CO2 (Ci/Ca) concentration in leaves, implying that high mesophyll temperatures in sunlit leaves were more important than gs in limiting Ac. Sunlit leaves were more photoinhibited than shaded leaves on cooler days when Tl < 25 degrees C. Shade decreased total soluble sugar concentrations in leaves, but had no effect on leaf starch concentrations. Shading had no effects on canopy volume, yield or fruit size, but shaded fruit developed better external color than sun-exposed fruit. Overall, the presence of a normal fruit crop resulted in lower foliar carbohydrate concentrations and higher Ac compared with defruited trees, except on warm days when Ac was reduced by high leaf temperatures. 相似文献
13.
Linnea J. Hansson John Koestel Eva Ring Annemieke I. Gärdenäs 《Scandinavian Journal of Forest Research》2018,33(2):166-177
Due to the great year-round demand for forest products, off-road forestry traffic occurs even when the ground is susceptible to soil compaction and rutting. We investigated the impacts of repeated passes with a laden forwarder (34?Mg) on the soil physical properties of two clear-cuts on stony till soils in northern Sweden. Core samples (n?=?71) were collected from the top 5?cm of mineral soil in and beside wheel tracks, after six passes with the forwarder. Soil physical properties were quantified using classical soil physical analyses and X-ray tomography. The hydraulic conductivity was 70% lower in the wheel tracks than in the soil beside. The X-ray image analysis indicated that this was due to the smaller total volume and lower connectivity of structural pores (φ?>?60?µm). Total porosity was 24% and 12% lower in the tracks at the two sites respectively, and mean bulk density was 1.39?g?cm?3 in the tracks, compared to 1.13?g?cm?3 beside them. To conclude, traffic changed the soil physical properties in a way that may lead to longer periods of high water content in the wheel tracks, increased risk of surface runoff and insufficient aeration for optimal seedling growth. 相似文献
14.
Potassium,calcium, and magnesium dynamics during litter decomposition in a cool temperate forest 总被引：3，自引：0，他引：3
The dynamics of K, Ca, and Mg were investigated during the decomposition of 14 litter types over a 3-year period on the upper and lower parts of a forest slope in a cool temperate forest in Japan. Potassium dynamics were divided into initial leaching phase and late phase. Initial K concentrations for the initial phase were correlated with the rate of decrease in K concentration during the initial phase. The late phase was characterized by seasonal fluctuations in concentration: K concentration increased from April to November and decreased during the winter period. The pattern of change in Ca concentration was divided into initial increase phase and late decrease phase in some litter types, or consisted of the late phase only in other litters. Calcium concentration of the initial litter was not predictable for the pattern of change in Ca concentration nor the rate of change in Ca concentration during the initial phase. Initial Ca concentration for the late phase was correlated with the rate of change in Ca concentration during the late phase. The pattern of change in Mg concentration was divided into initial leaching phase and late immobilization phase. Initial Mg concentration for the initial phase was correlated with the rate of change in Mg concentration during the initial phase. At the lower site, initial Mg concentration for the late phase was correlated with the rate of change in Mg concentration during the late phase, while such a relationship was not observed at the upper site. Concentrations of K, Ca, and Mg showed a convergent trend at the end of the study period. The final concentration differed between the upper and lower sites. 相似文献
15.
Progression from the juvenile to mature phase in woody plants is accompanied by changes in characteristics as diverse as adventitious rooting capacity, leaf morphology, canopy architecture, wood anatomy and reproductive development. Many concepts of phase change, the intensity and duration of changes that occur during the phase transition, and the practical consequences of plant maturation for growth and development, are poorly understood. Little is known about the physiological and environmental control of maturation in woody plants compared with herbaceous plants, and reliable markers of phase state have only been developed for a few species, mainly conifers. Understanding the mechanisms and forms of phase change is a prerequisite for achieving maturation or rejuvenation for applications such as seed production or clonal propagation. This review describes concepts, terminology and consequences of phase change, combining theoretical and practical aspects of tree maturation that relate to clonal forestry. 相似文献
16.
多功能林业发展的三个阶段 总被引：2，自引：1，他引：1
发展多功能林业是中国林业发展的内在要求和必然选择。从理论上, 多功能林业发展需要经历3个阶段。文中概述了这3个阶段的发展特点, 并提出了措施建议。第1阶段是多功能林业的科研与试点准备阶段, 实现多功能林业从理论到实践的跨越。第2阶段是多功能林业的县域或市域范围试点阶段, 在试点地区实现多功能林业从小到大、由单功能向多功能的转变。第3阶段是多功能林业的大范围推行阶段, 实现多功能林业从点到面、从试点向更大范围乃至全国推广应用的转变。每经过一个阶段, 多功能林业的理论内涵、实践经验和发展模式都将得到丰富和提升。 相似文献
17.
18.
《Forest Ecology and Management》2005,204(1):131-137
The effects of soil compaction and cultivation on soil mineral N dynamics were investigated through an 18-month, in situ N mineralisation experiment during the inter-rotation and early establishment period of a second rotation (2R) hoop pine (Araucaria cunninghamii Aiton ex A. Cunn) plantation in southeast Queensland, Australia. Treatments were 0, 1 and 16 passes of a fully laden forwarder (gross weight, 40.2 Mg) and cultivation by disc plough (zero cultivation and cultivation). Nitrate N was the dominant form of mineral N throughout the 18-month sampling period in both non-cultivated and cultivated soils, varying between 10 and 40 kg ha−1 whilst ammonium N remained <10 kg ha−1. Compaction had no significant effect on N mineralisation or nitrification. However, the remediation of the effects of compaction on soil through the use of the disc plough had significant impacts on N mineralisation, nitrification and N leaching. On a seasonal basis, the mean net N mineralisation increased from around 30 to 53 kg ha−1, nitrification from 28 to 43 kg ha−1 and nitrate N leaching from around 10 to 73 kg ha−1 following cultivation. 相似文献
19.
经调查,荔枝不同时期抽生的末次梢次年开花座果率不同;不同年份同一时期抽生的末次梢其次年开花盛果率也不同;荔枝早秋梢经冬梢处理后,成花率比晚秋梢高,但晚梢晚穗座果率较高,应视末次梢抽生情况及气候条件来决定培养早秋梢还是晚秋梢。花期气候反常时更要加强促花、控梢控穗,适时喷施增加光合作用的药剂,以保证荔枝丰产、稳产。 相似文献