Upgrading of a raw blend into a diesel fuel substitute: poly(dimethoxymethane)
A method for forming poly(dimethoxymethane) includes a step of separating a formaldehyde-containing blend into a first bottom stream and a first top stream. The first formaldehyde-containing blend includes methanol, formaldehyde, and water while the first bottom stream includes water. The first top stream includes dimethoxymethane that is produced from the reaction between methanol and formaldehyde. The first top stream is separated into a second bottom stream and a second top stream. The second bottom stream includes poly(dimethoxymethane) while the second top stream includes dimethoxymethane, methanol, and ethanol. The second top stream is separated into a third bottom stream and a third top stream. Third bottom stream includes methanol and ethanol while the third top stream includes dimethoxymethane. The third top steam can be recycled to form additional poly(dimethoxymethane). A system that implements the method is also provided.
1. A method comprising:
a) heating a formaldehyde-containing blend to breakdown poly(oxymethylene) glycols and poly(oxymethylene) hemiformals into formaldehyde, methanol, water and shorter oligomers;
b) separating the formaldehyde-containing blend into a first bottom stream and a first top stream by reactive distillation, the formaldehyde-containing blend including methanol, formaldehyde, and water, the first top stream including dimethoxymethane that is produced from a reaction between methanol and formaldehyde contained in the formaldehyde-containing blend, the first bottom stream including water in an amount of 30 to 100 mole percent;
c) synthesizing poly(dimethoxymethane) n by heating the first top stream to form a heated top stream where n is 2 to 8 and separating the heated top stream into a second bottom stream and a second top stream, the second bottom stream including poly(dimethoxymethane) and the second top stream including dimethoxymethane, methanol and ethanol; and
d) separating the second top stream into a third bottom stream and a third top stream, the third bottom stream including methanol and ethanol while the third top stream includes dimethoxymethane.
2. The method of claim 1 wherein step a) is performed by reactive distillation.
3. The method of claim 1 wherein a feedstock is composed of at least 40-70 mole % alcohols, 5-20 mole % aldehydes and 15-40 mole % water.
4. The method of claim 1 wherein the third top stream is recycled to form additional poly(dimethoxymethane) n , where n is 2 to 8.
5. The method of claim 1 wherein the formaldehyde-containing blend includes up to 30 mole % water.
6. The method of claim 1 wherein the first top stream includes methylol, methanol, ethanol and unreacted formaldehyde.
7. The method of claim 1 wherein step a) is performed at a first separation station that includes a first separation column.
8. The method of claim 7 wherein the first separation column includes an acid catalyst that promotes acetylation.
9. The method of claim 1 wherein step b) is performed at a second separation station that includes a second separation column.
10. The method of claim 9 wherein the second separation column includes an acid catalyst that promotes and/or accelerates equilibrium between dimethoxymethane, formaldehyde, and methanol.
11. The method of claim 10 wherein the acid catalyst also promotes reaction between dimethoxymethane, poly(dimethoxymethane), and formaldehyde to produce poly(dimethoxymethane) n , with n=3-5.
12. The method of claim 9 wherein the second separation station includes a catalytic reaction vessel followed by a distillation column.
13. The method of claim 1 wherein step c) is performed at a third separation station that includes a distillation column in which dimethoxymethane is separated from methanol and ethanol.
14. The method of claim 1 wherein the formaldehyde-containing blend is heated to a temperature from 250 to 275 F.