Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-04-27
2003-05-27
Peselev, Elli (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C518S715000
Reexamination Certificate
active
06570043
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of converting sugars to sugar alcohols using aqueous phase catalytic hydrogenation.
BACKGROUND OF THE INVENTION
Conventional heterogeneous catalysis has usually involved petroleum processing; however, in recent years there has been an increased emphasis on aqueous systems. As opposed to petroleum- or hydrocarbon-based systems, water-based systems have less toxicity and fewer environmental problems. Additionally, aqueous systems are well-suited for biologically-produced feedstocks. For example, sugars from biological sources can be extracted with or produced in water. Then, to prepare sugar alcohols from these sugar solutions, it is economically necessary to conduct catalytic hydrogenation in the aqueous phase.
For the commercially important glucose to sorbitol hydrogenation, Gallezot et al. remarked that the challenge was to obtain a high conversion of glucose with a high selectivity to sorbitol and “a high stability of the catalyst during a long period of time.” See Gallezot et al., “Glucose Hydrogenation on Ruthenium Catalysts in a Trickle-Bed Reactor.” However, despite the work of Gallezot et al. and others, there remains a need for improved methods of aqueous phase hydrogenation of sugars to sugar alcohols.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides a method of converting sugar to sugar alcohol by catalytic hydrogenation in the aqueous phase. In this method, an aqueous sugar solution is passed into a reaction chamber. Temperature of solution in the reaction chamber is maintained at less than 120° C., and pressure in the reaction chamber is maintained at 100 to 3000 pounds per square inch gauge hydrogen gas overpressure. The reaction chamber contains a hydrothermally stable catalyst and, in the reaction chamber, the sugar reacts with hydrogen to produce a sugar alcohol. The reaction conditions are such that, when measured after 300 hours at the same reaction conditions, at least 97% of the sugar is converted to a sugar alcohol. Of course, each sugar is converted to its corresponding sugar alcohol, e.g. glucose to sorbitol, lactose to lactitol, etc. That the conversion of sugar to sugar alcohol is measured at 300 hours means that to test satisfactory reaction conditions (including selection of catalyst), a measurement is made after continuing to run 300 hours of operation at the same conditions without intervening steps of reactivating or replacing the catalyst; it does not mean that the invention is limited to reactions run for 300 hours or more.
In a second aspect, the invention provides a method of converting sugars to sugar alcohols by passing an aqueous sugar solution over a catalyst comprising ruthenium on a titania support, where the titania in the support is 75% or more in the rutile phase as measured by x-ray diffraction.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The aqueous sugar solutions used in the inventive methods contain at least one sugar dissolved in water. The sugar to be converted is preferably a mono—or disaccharide. Examples of preferred sugars that are hydrogenated in the present invention include: glucose, lactose, lactulose, fructose, erythrose, arabinose, mannose, xylose, galactose, and talose.
The aqueous sugar solutions are usually derived from biological sources, typically plants such as corn. The invention is defined in terms of converting a single type of sugar; however, the aqueous solutions may contain a mixture of sugars. Preferably, the sugar feedstocks are obtained pure or are purified prior to use in the reactor—impure feedstocks (often containing sulfur-containing species) may poison the catalyst, and thus require more frequent catalyst regeneration steps. Preferably, the sugar solutions are more than 99% by weight, more preferably 99.9%, water and sugar. Preferably the sugar is a single type of sugar such as glucose, arabinose, etc.
The sugar solutions are preferably 1 to 70 weight % sugar, more preferably 7 to 45 weight % sugar. The aqueous sugar solutions are preferably fed into the reaction chamber at fast rates, preferably fed into the reaction chamber at a rate of at least 0.5 kg sugar per liter of catalyst bed per hour, more preferably 0.9 kg sugar per liter of catalyst bed per hour, and still more preferably a rate of 1.2 kg/L/hr to 1.9 kg/L/hr.
Temperature in the reaction chamber is preferably maintained below 120° C. Higher temperatures require too much energy and can result in poorer selectivities and can cause faster catalyst degradation. More preferably, the temperature is maintained in a range of 90 to 120° C. Temperature is measured by placing a thermocouple in (or on) a catalyst bed in the reaction chamber. Pressure in the reaction chamber is preferably maintained in the range of 100 to 3000, more preferably 250 to 1900 pounds per square inch gauge. Pressure is generated by the hydrothermal conditions and is maintained in a desired range by hydrogen gas overpressure.
The hydrogenation catalyst must be an active hydrogenation catalyst and must also be stable in hydrothermal conditions. It has been discovered that a Ru on rutile catalyst exhibits exceptional properties for the aqueous phase hydrogenation of sugars to their corresponding sugar alcohols. It is believed that additional catalysts might be developed by routine testing utilizing the conditions and results described herein. Use of impure feed can poison the catalyst leading to loss of activity; the catalyst can be regenerated either by discontinuing reaction and hydrogen treatment or by switching to a purer feed solution.
Preferably, the catalyst that has an active metal on a titania support. The active metal preferably includes ruthenium and the titania is at least 75% rutile as measured by x-ray diffraction. Additionally, the catalyst is preferably essentially nickel-free and/or rhenium-free. It is desirable that catalyst metal be distributed over the surface of a support in a manner that maximizes surface area of the ruthenium. The metal preferably constitutes 0.1 to 10 weight % of the catalyst. Amounts of ruthenium above this range may not increase the catalyst's activity, while amounts below this range can have undesirably low processing rates. More preferably, ruthenium constitutes 1 to 5 weight % of the catalyst, and still more preferably 2 to 3 weight %. In a preferred embodiment, the active metal consists essentially of pure ruthenium. The ruthenium preferably constitutes at least 95 weight percent of the active metal, more preferably more than 98%, and still more preferably more than 99.8%.
The catalyst is preferably essentially without nickel, that is, nickel does not make a significant contribution to the catalytic activity of the catalyst. Nickel is prone to dissolution in the aqueous phase processing conditions and may contaminate the product. This is especially a problem where a food-grade product is desired, for example in hydrogenating carbohydrates. Moreover, nickel in the product stream can also present a problem with waste disposal. Additive metals such as nickel can also present complications when disposing or recovering catalyst. Preferably, the catalyst contains less than 0.1 weight % nickel, more preferably, less than 0.01 weight %.
Rhenium is another metal that can present the problems discussed above for nickel. The catalyst is preferably essentially without rhenium. This means that the rhenium to ruthenium ratio in the catalyst is less than 1:20 by weight. Preferably, rhenium, if present at all, is present in less than 0.005 weight % of the catalyst. Similarly, the catalyst is preferably essentially without cobalt.
The metal, preferably ruthenium, is preferably disposed on a titania support. For optimum activity, the metal should exist in small particles on the surface of the support. The surface of the support typically includes not only the exterior surfaces but also interior surfaces of a porous support. The support may be in a variety of forms such as powder, pellets, honeycomb, etc. The titania is preferably composed of at least 75% rutile
Elliott Douglas C.
Frye, Jr. John G.
Wang Yong
Werpy Todd A.
Battelle (Memorial Institute)
Peselev Elli
Wells St. John P.S.
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