Nitric acid oxidation processes
A process utilizing nitric acid and oxygen as co-oxidants to oxidize aldehydes, alcohols, polyols, preferably carbohydrates, specifically reducing sugars to produce the corresponding carboxylic acids.
1. A method of synthesizing a mixture of organic acids, the method comprising the steps of:
(a) combining, over time, in one or more closed reaction vessels, under a positive pressure of oxygen and with continuous stirring mixing an organic compound suitable for nitric acid oxidation and an aqueous solution of nitric acid to form a reaction mixture, wherein the organic compound and the aqueous solution of nitric acid are concurrently introduced into the one or more closed reaction vessels;
(b) flowing said reaction mixture through the one or more closed reaction vessels while (i) maintaining a controlled temperature of from about 5° C. to about 105° C. in a liquid phase portion of the reaction vessel, (ii) maintaining a reaction vessel headspace temperature of from about 80° C. to about −42° C. ; and (iii) maintaining a controlled positive pressure of oxygen of from about 0 barg to about 1000 barg for a time period suitable to oxidize the organic compound to a subsequent reaction mixture comprising a mixture of organic acid products and nitrogen oxides; and
(c) recirculating the subsequent reaction mixture to the reaction vessel vapor space headspace until the nitric acid oxidation is quenched; and
(d) removing most of nitric acid from the subsequent reaction mixture to give a final reaction mixture of organic acids suitable for further processing, wherein the organic compound suitable for nitric acid oxidation is selected from the group consisting of monohydric alcohols, diols, polyols, aldehydes, ketones, carbohydrates, hydroxyacids, cellulose, starch and combinations thereof.
2. The method of claim 1 , wherein the one or more closed reaction vessels comprises one or more reactors.
3. The method of claim 2 , wherein the one or more closed reaction vessels are in series or in parallel with one another.
4. The method of claim 2 , wherein the reactor is a continuously stirred tank reactor (CSTRs) or a tubular type plug flow reactor.
5. The method of claim 1 , wherein the method is a continuous process.
6. The method of claim 1 , wherein the method is a batch process.
7. The method of claim 1 , wherein the organic compound comprises a single organic material or a mixture of organic materials suitable for nitric acid oxidation.
8. The method of claim 1 , further comprising the step of removing a significant portion of the nitric acid from the subsequent reaction mixture.
9. The method of claim 8 , wherein the removal of the nitric acid is accomplished by an evaporation, distillation, nanofiltration, diffusion dialysis or alcohol or ether precipitation.
10. The method of claim 8 , further comprising the step of making basic the subsequent reaction mixture from which a portion of nitric acid has been removed to convert residual nitric acid to inorganic nitrate and the mixture of organic acids to a mixture of organic acid salts.
11. The method of claim 1 , wherein the carbohydrates are selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, aldonic acids, aldonic acid esters, aldonic acid salts, aluronic acids, alduronic acid esters, alduronic acid salts, alditols, cyclitols, corn syrups with different dextrose equivalent values, and monosaccharides, disaccharides, oligosaccharides and polysaccharides derived from plants, microorganisms or biomass sources.