Processes for making furfurals
View Patent ↗Processes for making furfural and 5-hydroxymethylfurfural from sugars are provided. The processes can be carried out using a batch process or a continuous mode of operation. An aqueous sugar solution is pressurized with CO 2 , thereby producing carbonic acid in situ that catalyzes the dehydration reaction to produce furfural from C 5 sugars and 5-methylhydroxyfurfural from C 6 sugars.
1. A process comprising:
a) providing, in a reaction vessel, an aqueous sugar solution comprising at least one C 5 sugar, at least one C 6 sugar, or a mixture of at least one C 5 sugar and at least one C 6 sugar, and optionally a water-miscible organic co-solvent; and
b) adding the solution to the reaction vessel and pressurizing with CO 2 under agitation to form a reaction mixture;
c) maintaining the reaction mixture at a temperature within a range of from about 90° C. to about 220° C., and a pressure within a range of from 0.1 MPa to about 30 MPa, for a time sufficient to effect a reaction to produce a reaction product comprising:
i) furfural and/or 5-hydroxymethyl furfural,
ii) water, and
iii) an aqueous condensate comprising insoluble humins;
d) quenching the reaction mixture to a temperature of about room temperature;
e) collecting the aqueous condensate from the reaction mixture upon depressurisation through a single or multistage column; and
f) collecting the reaction vessel contents and separating the furfural and/or 5-hydroxymethyl furfural from the reaction vessel contents, and separating the insoluble humins,
wherein said process is conducted in a Batch mode.
2. A process comprising contacting an aqueous sugar solution with CO 2 in a continuous mode of operation, the process comprising:
a) providing an aqueous sugar solution comprising at least one C 5 sugar, at least one C 6 sugar, or a mixture of at least one C 5 sugar and at least one C 6 sugar;
b) providing a reaction vessel;
c) continuously adding the sugar solution to the reaction vessel and CO 2 under agitation to form a reaction mixture, wherein the temperature of the reaction mixture is within a range of from about 90° C. to about 220° C., and the operating pressure is between 0.1 MPa and about 30 MPa;
d) maintaining the reaction mixture temperature and pressure for a time sufficient to effect a reaction to produce a reaction product comprising:
i) furfural and/or 5-hydroxymethyl furfural,
ii) water, and
iii) an aqueous condensate comprising insoluble humins;
e) continuously feeding and removing sugar solution, CO 2 , or both from the reaction vessel;
f) removing vapors of water and furfural and/or 5-hydroxymethylfurfural from the reaction mixture through a single or multistage column; and
g) removing liquid from the reaction vessel through a separation device.
3. The process of claim 1 , wherein the aqueous sugar solution comprises a water-miscible organic co-solvent selected from the group consisting of sulfolane, acetonitrile, and THF.
4. The process of claim 3 wherein the aqueous sugar solution further comprises an acid catalyst selected from the group consisting of a mineral acid, a superacid, a heteropolyacid, an organic acid, a solid acid catalyst and combinations thereof, and the acid catalyst is present at about 0.01 weight percent to about 10 weight percent as a percentage of the weight of the solvent.
5. The process according to claim 1 or 2 , wherein the combined concentration of C 5 sugar and/or C 6 sugar in the aqueous sugar solution is in the range of 0.5-90 weight percent based on the total weight of the aqueous sugar solution.
6. The process according to claim 1 or 2 , wherein the combined concentration of C 5 sugar and/or C 6 sugar in the aqueous sugar solution is in the range of 0.5-50 weight percent based on the total weight of the aqueous sugar solution.
7. A process comprising:
a) providing in a reaction vessel, an aqueous sugar solution comprising at least one C 5 sugar, at least one C 6 sugar, or a mixture of at least one C 5 sugar and at least one C 6 sugar, and optionally a water-miscible organic co-solvent; and
b) adding the solution to the reaction vessel and pressurizing with CO 2 under agitation to form a reaction mixture;
c) maintaining the reaction mixture at a temperature in a range of 90-220° C.,and a pressure in a range of 0.1-30 MPa, for a time sufficient to produce a mixture comprising one or more of furfural, 5-hydroxymethyl furfural and water;
d) quenching the reaction mixture to room temperature and depressurizing the reaction vessel into a condenser to form a condensate,
wherein the condensate comprises one or more of humins, furfural, 5-hydroxymethyl furfural and water, and
wherein the reaction vessel contents comprise one or more of furfural, 5-hydroxymethyl furfural, water and unreacted sugar; and
e) collecting the reaction vessel contents and separating the furfural and/or 5-hydroxymethyl furfural from the reaction vessel contents, and separating the insoluble humins.