Process of making bioderived propylene glycol
An improved process for making bioderived propylene glycol from a feed composition including at least one of lactic acid, glycerol, a five carbon sugar, a five carbon sugar alcohol, a six carbon sugar and a six carbon sugar alcohol, wherein production of four carbon and higher diols is reduced by adding base after the initiation of the reaction. In preferred embodiments, the process pH and other process conditions are initially established at targeted values for obtaining the highest conversion for a given catalyst consistent with the production of substantially no pentanediol byproducts in the product mixture, and base is added thereafter to control the process pH proximate to the initially targeted value.
1. In a process of making bioderived propylene glycol by reacting a feed composition including at least one of lactic acid, glycerol, a five carbon sugar, a five carbon sugar alcohol, a six carbon sugar and a six carbon sugar alcohol with hydrogen in the presence of a suitable catalyst for catalyzing the reaction and under conditions effective for carrying out the reaction, the improvement comprising:
establishing a targeted pH value beyond which pentanediols begin to be formed;
initiating the reaction of the feed composition and hydrogen in the presence of the catalyst at a pH value not exceeding the targeted pH value; and
adding base as the reaction proceeds to adjust the pH in the reaction system toward the targeted pH value, but not exceeding the same.
2. An improved process according to claim 1 , wherein the process is a continuous process and wherein base is added to a reactor in which the reaction is carried out, in at least one location downstream of the reactor inlet.
3. An improved process according to claim 2 , wherein the amount of base added in each such downstream location is substantially the same as was added to the reactor at its inlet.
4. An improved process according to claim 1 , wherein the process is conducted in a batchwise manner and wherein base is added to a reactor in which the reaction is carried out, at one or more times after the initiation of a batch.
5. An improved process according to claim 4 , wherein the amount of base added at each such time is substantially the same as added at the initiation of a batch.
6. An improved process according to claim 2 , wherein:
the feed composition comprises glycerol;
the catalyst comprises rhenium and nickel;
the amount of base added at the reactor inlet is from 0.05 to 0.3 percent by weight of the feed composition of sodium hydroxide or the equivalent amount of another base; and
the same amount of sodium hydroxide or the same equivalent amount of the same other base is added to the reactor after the initiation of the reaction.
7. An improved process according to claim 1 , wherein the process is carried out at from 200 to 220 degrees Celsius, a liquid hourly space velocity of from 0.7 to 1.4 hr −1 and a hydrogen pressure of from 10.3 MPa to 13.8 MPa, gauge.
8. An improved process according to claim 7 , wherein the process is carried out at a hydrogen pressure of from 11.7 to 12.4 MPa, gauge.
9. A continuous process for making bioderived propylene glycol, comprising:
causing an aqueous feed composition comprising glycerol to react with hydrogen in the presence of a catalyst comprising rhenium and nickel and further with the addition at initiation of the reaction of from 0.05 to 0.2 weight percent of the aqueous feed composition of sodium hydroxide or an equivalent amount of another base; and
adding the same amount of sodium hydroxide or an equivalent amount of the same other base to the reactor in which the process is carried out, after the initiation of the reaction.