Synthesis Of 1-(2-hydroxyethyl)-4-(2-hydroxypropyl) Piperazine By Aqueous Phase Method

Hydroxylpiperazine organic amines have been widely used in flue gas desulfurization due to their excellent absorption/desorption properties of SO₂.In this paper,1-（2-hydroxyethyl）-4-（2-hydroxypropyl）piperazine（HEHPP）with asymmetric structure was synthesized from piperazine（PZ）,ethylene oxide（EO）and propylene oxide（PO）with water as solvent by a step-by-step aqueous phase method and a water-phase single-ended group protection method,respectively.Two steps of PZ-EO-PO synthesis reaction and PZ-PO-EO synthesis reaction were designed and studied.In the synthesis route of PZ first reacting with EO and then with PO,the parameters of the synthesis reaction were optimized,and the optimal conditions were obtained that the initial concentration of PZ was 0.1g/m L H₂O,the molar ratio of PZ:EO:PO was 1:0.8:1.2,and the reaction temperature of PZ with EO and PO was 35℃and 25℃respectively.The relative content of HEHPP was 51.33%,and the main by-products were N-（2-hydroxyethyl）piperazine（HEP）,N-（2-hydroxyethyl）piperazine（HPPZ）,N,N’-bis（2-hydroxyethyl）piperazine（BHEP）,N,N’-bis（2-hydroxyethyl）piperazine（HPP）,with a total content of 45.18%.In the synthesis route of PZ first reacting with PO and then with EO,the parameters of the synthesis reaction were optimized,and the optimal conditions were obtained that the initial concentration of PZ was 0.1g/m L H₂O,the molar ratio of PZ:PO:EO was 1:0.8:1.2,the reaction temperature of PZ with PO and EO was 15℃and 25℃respectively.The relative content of HEHPP in the prepared product was 46.05%,and the total content of four main by-products was53.13%.Aiming at the poor selectivity of piperazine symmetric structure substitution reaction,an aqueous phase single-ended group protection method was designed to synthesize HEHPP with asymmetric structure.PZ first undergoes a single-end protonation protection reaction with H₂SO₄,and then reacts with PO through hydroxyl alkyl substitution reaction.After the reaction is completed,HPPZ solution is prepared through Ba（OH）₂desorption protection,precipitation filtration separation,etc.,And HEHPP is synthesized by the HPPZ solution continues to react with EO through hydroxyl alkyl substitution reaction.The processes such as single-ended matrix protectant reaction,hydroxylalkyl substitution reaction,Ba（OH）₂neutralization reaction,precipitation filtration and asymmetric hydroxylalkyl substitution reaction were studied,and the parameters of different processes were optimized.Under the optimal conditions,the initial concentration of PZ was 0.2g/m L H₂O,the molar ratio of PZ:H₂SO₄was 1:0.6,the reaction temperature of PZ and PO was 20℃,the reaction temperature of HPPZ and EO was 50℃,the reaction temperature of HPPZ and EO was 180min,and the reaction temperature of PZ:PO:EO was 1:1.2:0.7,the content of HEHPP in the synthesized product was 78.19%.The main by-product was HPP,with the content of 18.14%.The synthesized product has a saturated absorption capacity of 0.6673 mol·mol^-1for SO₂and a desorption rate of 96.72%.HEHPP was synthesized by water phase method and water phase single-ended group protection method in the paper.The composition of the product synthesized by water phase method is relatively complex and the content of the target product is low.With the protection of piperazine symmetric structure,the selectivity of hydroxyl alkyl substitution reaction was improved,and the content of HEHPP was increased from51.33%to 78.19%,and the composition of the synthesized product was relatively simple.