Method of fabricating medium-high temperature CO2 sorbents made of alkali metal promoted calcium aluminate carbonates
A dry material is synthesized by alkali metal (Li, Na and K) promoted calcium aluminate carbonates to obtain a CO 2 sorbent used at a temperature higher than 600 Celsius degrees (° C.). The key composition of the sorbents is 52˜69% of CaO, which is beneficial to capture CO 2 at 400˜800° C. A breakthrough result is achieved by using this sintering-resistant sorbent, which includes the features of 50% initial carbonation capacity and 20 folds CO 2 capturing performance maintained after 40˜60 hours. Besides, alkali bearing material provides good velocity in CO 2 capturing/releasing cycles; for example, by using Li and K series sorbents, 40 hours is required for 40 cycles only.
1. A method of fabricating medium-high temperature CO 2 sorbents made of alkali metal promoted calcium aluminate carbonates, comprising steps of:
(a) mixing a source of Ca ions and Al(NO 3 ) 3 .9H 2 O to obtain an acid solution,
wherein said source of calcium ions is selected from a group consisting of CaCl 2 , Ca(NO 3 ) 2 and Ca(CH 3 COO) 2 .xH 2 O and x is a value between 0 and 1; and
wherein a mole ratio of said source of calcium ions to said Al(NO 3 ) 3 .9H 2 O is between 1:1 and 30:1 in said acid solution;
(b) mixing NaOH and a carbonate to obtain an alkali solution,
wherein said alkali solution has 1.6 mole of NaOH; and
wherein said carbonate is selected from a group consisting of Li 2 CO 3 , Na 2 CO 3 and K 2 CO 3 ;
(c) mixing said acid solution and said alkali solution to obtain a mixed solution and staying still said mixed solution; and
(d) after staying still said mixed solution, filtering said mixed solution to remove impurities and drying said mixed solution to be sintered in an oven to obtain a CO 2 sorbent,
wherein, according to said carbonate used in step (b), said CO 2 sorbent thus obtained is selected from a group consisting of Li—Ca—Al—CO 3 , Na—Ca—Al—CO 3 and K—Ca—Al—CO 3 .
2. The method according to claim 1 ,
wherein said CO 2 sorbent captures CO 2 at a temperature between 400° C. and 800° C.;
wherein said CO 2 sorbent has an initial CO 2 capture ratio bigger than 50 wt %; and
wherein said CO 2 sorbent captures CO 2 for a time period between 40 hours (hrs) and 60 hrs.
3. The method according to claim 1 ,
wherein Li—Ca—Al—CO 3 spends 40 hrs to process 40 cycles of CO 2 capture with a capture ratio higher than 51 wt %;
wherein Na—Ca—Al—CO 3 spends 60 hrs to process 40 cycles of CO 2 capture with a capture ratio higher than 49 wt %; and
wherein K—Ca—Al—CO 3 spends 40 hrs to process 40 cycles of CO 2 capture with a capture ratio higher than 49 wt %.
4. The method according to claim 1 ,
wherein said CO 2 sorbent has an average amount ratio of CaO between 52% and 69%.