用偏铝酸钠直接制取高纯拟薄水铝石

Preparation of Ultra-pure Pseudo-boehmite from Sodium Meta-aluminate

利用自制的超深度脱硅剂将山西铝厂生产的偏铝酸钠母液进行精制 ,使母液中的硅铝比 (m(SiO2 ) /m(Al2 O3 ) )和铁铝比(m(Fe2 O3 ) /m(Al2 O3 ) )稳定达到万分之一以下 ,以制取高纯拟薄水铝石 .用氨气作为循环介质 ,采用缓冲溶液沉淀法 ,研究了反应物浓度、加料方式、pH值、反应温度、反应时间及老化洗涤等条件对拟薄水铝石比表面积和孔体积的影响 .结果表明 ,制得的粉末状拟薄水铝石的比表面积达到 30 0m2 / g以上 ,孔体积达到 0 7ml/ g左右 .经自制的高效脱钠剂处理 ,可使拟薄水铝石中杂质钠的质量分数降到 5× 10 -5以下 ,其性能达到了德国用有机醇铝法生产的同类产品的技术指标 .

Ultra-pure activated alumina is one of commonly-used catalyst supports. Its precursor is chiefly ultra-pure pseudo-boehmite. A direct method for preparation of ultra-pure pseudo-boehmite with large specific surface area and large pore volume from sodium meta-aluminate solution obtained from Shanxi Aluminium Plant was provided. With the aid of laboratory-made de-silicon agent, the SiO 2/Al 2O 3 and Fe 2O 3/Al 2O 3 mass ratios in the solution could be reduced to below 1×10 -4. The pseudo-boehmite was obtained by deposition from buffer solution with ammonia gas as circulation medium, through the neutralization of sodium meta-aluminate and ammonium bicarbonate. The effects of colloid-forming conditions, such as reactant concentration and adding way, pH value, temperature, time and aging variables, on the specific surface area and pore volume of the pseudo-boehmite were studied. For the prepared pseudo-boehmite, its specific surface area can reach up to 300 m 2/g and its pore volume can reach about 0.7 ml/g. The prepared pseudo-boehmite was treated by laboratory-made de-sodium agent, and the sodium content was reduced to below 5×10 -5. This method can overcome the disadvantage through neutralization of NaAlO 2-CO 2, where there are two parallel reactions during precipitation. The experimental conditions can be easily controlled. After calcination at 560 ℃ for 3 h, the prepared pseudo-boehmite can commendably turn into γ-Al 2O 3, and keep biggish specific surface area.