Process for nitrate ester formation of an α,ω-alkanediol monoacylate
The invention relates to a safe and efficient process for the nitrate ester formation of an α,ω-C 3-10 alkanediol monoacylate. The process is safer to operators and allows to obtain advantageous yields on industrial scale.
1 . A continuous process for nitrate ester formation of an α,ω-C 3-10 alkanediol monoacylate, wherein the process comprises a step of:
reacting a nitrating agent with a solution comprising an α,ω-C 3-10 alkanediol monoacylate and an inert solvent in a group of pieces of equipment comprising at least two reactors in series, wherein
the reacting step comprises:
(i) simultaneously feeding the solution into a first reactor and a second reactor of the at least two reactors in series, and
(ii) allowing the nitrating agent to react with the solution in the first and second reactors for a mean residence time of about 5 seconds to about 30 seconds.
2 . The process for the continuous nitrate ester formation according to claim 1 , wherein step (i) comprises feeding 40 to 60% of the total mass flow of the solution into the first reactor, while simultaneously feeding a remaining portion of the total mass flow of the solution into the second reactor.
3 . The process for the continuous nitrate ester formation according to claim 1 , wherein the α,ω-C 3-10 alkanediol monoacylate in the inert solvent in a concentration of from 10 to 60 wt.-%.
4 . The process for the continuous nitrate ester formation according to claim 1 , wherein the nitrating agent is a mixture of H 2 SO 4 and HNO 3 , wherein
a) the mol ratio of HNO 3 to the α,ω-C 3-10 alkanediol monoacylate is selected in the range from 1 to 1.5, and
b) the mole ratio of the H 2 SO 4 to the HNO 3 is selected in the range from 1.5 to 2.5.
5 . The process for the continuous nitrate ester formation according to claim 1 , wherein the reaction volume ratio of the first reactor to the second reactor is selected in the range from 4:1 to 1:4.
6 . The process for the continuous nitrate ester formation according to claim 1 , wherein the mean residence time of the solution in the first and second reactors is about 10 to about 20 seconds.
7 . The process for the continuous nitrate ester formation according to claim 1 , wherein
a) the first reactor has an outlet reaction temperature which is equal to or below 40° C., and
b) the second reactor has an outlet reaction temperature which is equal to or below 25° C.
8 . The process for the continuous nitrate ester formation according to claim 1 , wherein the process forms an α,ω-C 3-10 alkanediol mononitrate, and wherein the process further comprises a step (A) preceding the reacting step which consists of:
(A) an acylation reaction step by conducting an acylation reaction of an α,ω-C 3-10 alkanediol with an acylation agent, wherein α,ω-C 3-10 alkanediol monoacylate and α,ω-C 3-10 alkanediol diacylate back into the acylation reaction such that the acylation reaction comprises adding water in an amount of 0.5 to 1.5 mole per mole of recycled acylate groups, and a molar ratio of a molar sum of the acylating agent, α,ω-C 3-10 alkanediol monoacylate and 2 times of α,ω-C 3-10 alkanediol diacylate to the sum of the α,ω-C 3-10 alkanediol, α,ω-C3-10alkanediol monoacylate and α,ω-C 3-10 alkanediol diacylate is in a range from 0.5 to 1.1 mol per mol of α,ω-C3-10alkanediol, and wherein
the process comprises a step (C) and optionally a step (D) subsequent to the reacting step which consist of:
(C) conducting a two-phase hydrolysis of the α,ω-C3-10alkanediol mononitrate monoacylate by continuously feeding a base and a solution comprising the α,ω-C3-10alkanediol mononitrate monoacylate and an inert solvent into a cascade reactor to obtain a solution comprising the inert solvent and α,ω-C3-10alkanediol mononitrate, and optionally
(D) removing and recovering the inert solvent from the solution by distillation, the process comprising partial condensation and continuous back-feeding of liquid fractions comprising mixtures of the inert solvent and α,ω-C3-10alkanediol mononitrate into the distillation.
9 . The process according to claim 8 , wherein the acylation reaction step
(A) is a continuous process carried out in a vessel cascade set-up.
10 . The process according to claim 8 , wherein the acylation reaction step
(A) comprises a separation step comprising separating the α,ω-C 3-10 alkanediol monoacylate such that:
a) an amount of α,ω-C 3-10 alkanediol in the α,ω-C 3-10 alkanediol monoacylate is less than 0.5 wt.-%, and/or
b) an amount of the α,ω-C 3-10 alkanediol diacylate in the α,ω-C 3-10 alkanediol monoacylate is less than 5 wt. %.
11 . The process according to claim 8 , wherein the acylation agent in the acylation reaction step (A) is a carboxylic acid.
12 . The process according to claim 8 , wherein the two-phase hydrolysis step (C) comprises continuously feeding the base and the solution comprising an α,ω-C 3-10 alkanediol mononitrate monoacylate and an inert solvent a stirred cascade reactor.
13 . The process according to claim 8 , wherein the base in the two-phase hydrolysis step (C) is selected from the group consisting of NaOH, KOH, Ca(OH) 2 , ammonia, and aqueous solutions thereof.
14 . The process according to claim 8 , wherein the two-phase hydrolysis step (C) comprises continuously feeding an aqueous solution of the base in a concentration of from 1 to 50 wt.-%.
15 . The process according to claim 8 , wherein the two-phase hydrolysis step (C) is conducted at a reaction temperature of 20 to 70° C.