Study on Synthesis of 9-Fluorenylcarboxylic Acid and Co-production of Phenanthrene by Coconversion of Anthracene Residue and Carbon Dioxide

Abstract

Purposes Anthracene residue is a typical coal-based organic solid waste, which is mainly rich in phenanthrene and fluorene. In order to solve the difficulty in achieving effective separation of phenanthrene and fluorene, this research has been conducted. Methods By conventional separation methods and cooperative utilization of carbon dioxide, a reaction-separation coupling technique was adopted to convert fluorene in anthracene residues with carbon dioxide to 9-fluorenylcarboxylic acid with cesium carbonate as a catalysty. At the same time, co-production of phenanthrene can be realized according to the difference in solubility between 9-fluorenylcarboxylic acid and phenanthrene in alkaline solutions. Thus, the extraction of phenanthrene and the co-production of 9-fluorenylcarboxylic acid with high added value were realized. The effects of the amount and particle size of cesium carbonate on the yield of 9-fluorenylcarboxylic acid, and the catalytic cycling performance were explored. The reaction-separation of model mixture and anthracene residue were further studied. Findings The results show that the yield of 9-fluorenylcarboxylic acid grows with the increasing amount of cesium carbonate, and it is improved from 80.63% to 95.76% when the mole ratios of cesium carbonate to fluorene is increased from 2∶1 to 6∶1. The water content rises with the decrease of the particle size of cesium carbonate, and the declines of catalytic activity, either. Cesium carbonate shows excellent regeneration performance after roasted at 250 ℃ in N2 atmosphere, with the yield of 9-fluorenylcarboxylic acid maintained at 80% after 3 cycles. Other components in anthracene residue, such as phenanthrene, anthracene, and carbazole do not participate in the reaction of fluorene and carbon dioxide, and can be separated in the reaction process. The yield of 9-fluorenylcarboxylic acid reaches 90.63% with a purity of 99.06%, and the isolated phenanthrene is 95.00% with a purity of 99.14% after two reaction-separation cycles for the model mixture. However, with anthracene residue as feedstock, the purity and yield of 9-fluorenylcarboxylic acid falls to 93.33% and 83.80%, respectively. The recovery yield of phenanthrene declines slightly to 93.31% with a purity of 91.03%, owing to the existing of other components in anthracene residue.

Keywords

• coal-based organic solid waste
• carbon dioxide
• reaction-separation coupling technique
• cesium carbonate
• 9-fluorene-carboxylic acid