超临界水中Ni/ZrO_2催化气化聚乙烯醇水溶液的产氢特性

POLYVINYL ALCOHOL GASIFICATION IN SUPERCRITICAL WATER FOR HYDROGEN PRODUCTION WITH Ni/ZrO_2 CATALYST

以追求产氢及降解有机污染物作为协同目标,利用一套连续式超临界水气化装置,在设定压力24MPa,反应温度400—500℃,反应停留时间20—120s条件下,以Ni/ZrO2为催化剂考察了聚乙烯醇(PVA)水溶液的超临界水气化产氢特性.实验结果显示,催化剂Ni/ZrO2能有效促进PVA水溶液的分解产生富氢气体,气体产物中氢气的含量最高可达81.40%.过程探索发现:反应温度的升高能提高PVA气化效率,但气体产物中H2的含量随反应温度的升高有所下降;随着反应温度的升高,PVA分解趋于彻底,在压力24MPa、温度500℃、停留时间120s的条件下,TOC去除率、有机碳气化率和氢气化率分别达到71.46%,67.97%和157.24%;停留时间的变化对气体产物含量没有明显的影响,但延长停留时间能提高PVA的气化效率;PVA气化反应中间产物主要为链状烷烃、环烷烃、芳香烃及小分子酸,根据中间产物出现的顺序推测PVA的降解为由C—C键断裂形成小分子物质,这些小分子物质一部分转化为H2,CO,CH4和CO2,一部分形成难降解的芳香族化合物.

Supercritical water gasification （SCWG） of polyvinyl alcohol （PVA） solution was studied in a continuous flow reactor with Ni/ZrO2 catalyst at 24 MPa, 400--500℃, and residence times of 20-120 s to decompose organic contaminants and produce clean hydrogen energy. The results showed that the PVA solution was decomposed effectively and a hydrogen-rich gas could be obtained by SCWG with Ni/ZrO2. The molar fraction of H2 was up to 81.4%. The gasification efficiency increased and the molar fraction of H2 decreased with an increase in the reaction temperature. The decomposition of PVA was more complete at higher temperatures. At 24 MPa, 500℃ and 120 s, the TOC remove rate, the carbon gasification rate and the hydrogen gasification rate were up to 71.46%, 67.97% and 157.24% respectively. A change in the residence time had no significant effect on the molar fraction of gas production but an increase in the residence time could enhance the gasification efficiency of PVA. It was found that the intermediates were mainly alkane, cycloparaffin, aromatic hydrocarbons, and low-molecular weight acids. It was supposed that PVA was degraded into small molecules through breaking of C--C bonds. Parts of the molecules were converted into H2, CO, CH4 and CO2 while some was converted into aromatic hydrocarbons.