超临界水中钾对甲醛降解过程影响的研究

为掌握生物质中钾对生物质超临界水降解过程的影响,选择生物质气化转化过程中生成的重要小分子中间产物甲醛作为研究对象,研究不同工艺条件下(反应温度400～650℃、压力23～29 MPa、停留时间4～12 s),单一钾成分(KHCO₃/K₂CO₃/KCl)或混合钾成分(KHCO₃、K₂CO₃、KCl)对甲醛超临界水降解气体产物的影响。结果表明,KHCO₃、K₂CO₃、KCl、混合钾均降低了气体产物中CO的体积分数,提高了CO₂的体积分数,但KCl的影响程度弱于其他三种钾成分。此外,由于不同钾成分均不利于气体产物中CO和H₂体积分数的提高,从而使得气体产物的热值降低。KHCO₃、K₂CO₃、KCl、混合钾均降低了H₂、CO、CO₂的产率以及气化率,其对H₂产率以及气化率的抑制程度从大到小依次为:混合钾、KHCO₃、K₂CO₃、KCl,且提高反应温度、延长反应停留时间时抑制气体生成的作用相对越明显。而当反应压力改变时,钾成分对H₂产率及气化率的影响程度变化较小。较高反应温度、较高反应压力、较长停留时间时,混合钾中各成分出现协同作用,明显抑制了气体产物的生成。

Influence of potassium salts on the decomposition of formaldehyde in supercritical water

The influences of potassium salts on the decomposition of formaldehyde in supercritical water were investigated in a continuous reactor under 400～650℃, 23～29 MPa and a residence time of 4～12 s, as formaldehyde is one of the most important intermediate products for the gasification of biomass with supercritical water. The results showed that KHCO₃, K₂CO₃, KCl and mixed potassium salts are able to reduce the fraction CO in the gaseous product and increase the fraction of CO₂, which then depresses the heating value of the gaseous product. All these potassium ingredients exhibit an inhibitive effect on the formation of H₂, CO and CO₂ and the gasification efficiency; the inhibition strength of various potassium ingredients follows the order of mixed potassium salts > KHCO₃ > K₂CO₃ > KCl. The inhibitive effect on the formation of gaseous products is enhanced under high reaction temperature and long residence time, but is almost independent on the reaction pressure. Under high temperature, high pressure and long residence time, gas generation may be inhibited considerably by the mixed potassium salts, possibly due to a synergetic effect of different potassium salts.