Effects of ion-exchanged calcium, barium and magnesium on cross-linking reactions during direct liquefaction of oxidized lignite

In this work the influences of alkaline earth metals on cross-linking reactions (CLRs) during direct liquefaction of lignite were investigated. The oxidized lignite, which has been proved to be appropriate for quantitatively examine the extent of CLR during direct liquefaction, was used as a model coal to study the effects of ion-exchanged calcium, barium and magnesium on CLR during direct liquefaction of the oxidized lignite. The amounts of tetrahydrofuran (THF) insoluble solid products after liquefaction were used to quantitatively evaluate the CLR during liquefaction of the ion-exchanged coal. The results show that the oxidized coal is appropriate to quantitatively examine the extent of CLR and the targeted ions are exchanged to the oxidized coal in the form of highly-dispersed ion. The ion-exchanged Mg 2 + suppresses the CLR during direct liquefaction of coal at both low and high temperature. However, the exchanged Ca 2 + always promotes the CLR at the selected temperatures. While the exchanged Ba 2 + promotes the CLR at low temperature, but suppresses it at high temperature. ► The oxidized coal is appropriate to study the cross-linking reactions (CLRs). ► The targeted-ions are exchanged to the coal in the form of highly-dispersed ion. ► The ion-exchanged Mg 2+ suppresses the CLR during direct liquefaction of coal. ► Ca 2+ always promotes the CLR at the selected temperatures. ► Ba 2+ promotes the CLR at low temperature, but suppresses it at high temperature.