松子壳连续热解制备木醋液试验

Experiment of wood vinegar produced from pine nut shell continuous pyrolysis

木醋液的应用十分广泛,但其成分较复杂。该文研究了松子壳热解过程中不同反应温度和时间对制备木醋液产物的影响,并对木醋液成分和性质进行了分析。结果表明随着反应温度的升高,木醋液产率先升高,在500℃左右时达到最大,然后迅速降低;含水率由94%左右降至85%左右;黏度降低,流动性变强;pH值由3.2左右降至2.6左右。随着处理时间的增加,木醋液产率、含水率、黏度、流动性和pH值变化的趋势均不明显。优化工艺(500℃、8 min)下热解制备的木醋液,其成分主要包括酚类、酮类、醚类、酯类、醛类、酸类、醇类和胺类,其中酚类和酮类物质的含量较高,质量分数分别为53.88%和20.93%,所以其抗氧化性较强,并且尽管其pH值较低,但腐蚀性较同pH值甲酸弱。

With China’s growing energy problems, biomass conversion technologies have attracted considerable attention for converting biomass into energy products. These technologies can be divided into four main categories： direct-combustion processes, thermochemical conversion, biochemistry and liquefaction technology, respectively. Of the variety of technologies, thermochemical conversion and, particularly, pyrolysis have aroused great attention all over the world in recent years. Biomass as a renewable energy source has significant potential to transform into high-value and high-grade charcoal, bio-oil and combustible gas by the pyrolysis process. The wood vinegar refined from pyrolysis bio-oil can be used as insect repellents, plant growth-promoting liquid fertilizer, and as a soil improver after appropriate treatment, which has a very broad market prospects. The use of wood vinegar presents some problems due to its complex ingredients and big quality differences obtained by different materials and process conditions. However, there are very limited studies on the produced conditions and properties of biomass pyrolysis wood vinegar. 〈br〉 In this paper, red pine nut shell, which is a specialty in the northeast of China, was pyrolysed as raw material. The characteristics of wood vinegar have been investigated, including proximate analysis, elemental analysis, composition analysis, heating value analysis and thermo-gravimetric analysis （TGA）. The experiments were conducted on the biomass continuous pyrolysis reaction device with a variable pitch spiral conveyor to obtain wood vinegar at different reaction temperatures （300℃,400℃, 500℃600℃and 700℃） and different reaction times （4min、6min、8min、10min and 12min）. The characteristics of wood vinegar consisting of water content, viscosity, pH value, chemical compositions, the antioxidant activity and corrosion properties were determined by the Karl Fischer method, viscometer, acidity meter, gas chromatography and mass spectrometry （GC-MS）, ultraviolet spectrophotometer, and scanning electron microscope （SEM）, respectively, which provided a scientific basis for the study of the pine nut shell pyrolysis process. 〈br〉 The results were as follows：with pyrolysis temperature increasing, the yield of wood vinegar increased gradually until the temperature reached 500 ℃, which provided the maximum yield, then reduced quickly. The moisture content of wood vinegar gradually decreased from about 94% to 85%; the viscosity decreased gradually; the liquidity became stronger; and the pH showed a slow decreasing trend, from 3.2 down to about 2.6. With increased pyrolysis time, the yield of wood vinegar had no significant change, water content basically appeared as an inconspicuous trend, the viscosity showed almost no obvious trend, the liquidity also almost had no significant change, and the pH ranging of wood vinegar made little change by contrast. In addition, the main ingredients of wood vinegar were phenols, ketones, ethers, esters, aldehydes, acids, alcohols and amines at a pyrolysis temperature of 500℃and a pyrolysis time of 8min, in which the contents of phenols and ketones were 53.88%and 20.93%, respectively. Under the same pyrolysis conditions, the hydroxyl radical scavenging rate of wood vinegar was 66.63%, equivalent to 3μmol/L of ascorbic acid. SEM images showed that wood vinegar had a significant role in scavenging hydroxyl free radicals, which had a strong antioxidant activity. Wood vinegar gained under the condition of 500℃and 8min had weak corrosion, despite the low pH value of 3.1. All of the above results provided a theoretical basis for experimental study of wood vinegar prepared from pine nut shell continuous pyrolysis.