PROCESS FOR MAKING D-FRUCTOSE

METHODE DE PRODUCTION DE FRUCTOSE-D

English Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a method for
producing D-fructose and D-glucose. The method
comprises the steps of epimerizing D-glucose to a
mixture of D-glucose and D-mannose, separating the
D-glucose from the mixture, hydrogenating the D-
mannose in a fixed catalyst bed to provide D-mannitol,
oxidizing the D-mannitol to provide a D-fructose
solution and crystallizing the solution to provide
D fructose crystals.

Claims

I CLAIM:

1. A method for producing D-fructose from
D-glucose, which comprises the steps of:
a) epimerizing D-glucose to a mixture of
D-glucose and D-mannose;
b) separating said D-glucose from the mixture
of D-mannose;
c) hydrogenating said D-mannose to provide
D-mannitol;
d) oxidizing said D-mannitol to provide a
solution of D-fructose; and
e) crystallizing said D-fructose solution to
provide crystals of D-fructose.

2. The method according to claim 1, wherein said
D-glucose is in a 10 to 70% aqueous solution.

3. The method according to claim 1, wherein the
epimerization of said D-glucose takes place in a fixed
catalyst bed of silicotungstic acid on silica gel.

4. The method according to claim 1, wherein said
D-mannose is hydrogenated in a fixed catalyst bed at a
temperature ranging from about 100 to about 150°C.

5. The method according to claim 1, wherein said
D-glucose is replaced by a solution of crude starch
hydrolyzate.

6. The method according to claim 1, wherein the
oxidation of D-mannitol and D-fructose is carried out
with an oxygen containing gas in the presence of
Gluconobacter suboxydans.

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Description

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BACKGROUND OF THE INVENTION
This invention relates to a method for commercially
producing a sweetener for foodstuffs and more particularly
to a method for producing D-fructose.




It has been known that sugars, i.e., D-sugars such
as D-glucose, D-fructose and D-saccharose and others
have been useful as sweeteners. According to U.S.
Patents 2,753l279 and 2,845,369, the intermediate
product, D-mannitol was oxidized to provide D-fructose.
~wever, this process was discontinued since its cost
was excessive and impractical for producing the
sweetener, D-fructose, commercially.

The production of synthetic sweeteners such as
D-sugars has been done commercially. However, since
there is a need for producing sugars such as D-fructose
on a commercial basis that would be both economical
and practical, the present method for producing such
sugars is provided.

5UMMARY OF THE INVENTION
-
The present invention provides a method for
producing D-~ruatose and D-glucose. The method
comprises the ~teps of epimerizing D-glucose to a
mixtuxe o D-ylucose and D-mannose, separating the
D-glucose fr~m the m;xtuxe, hydrogenating the D-mannose
in a ~ixed catalyst bed to provide D-mannitol, oxidiz-
in~ the D~mannitol to provide a D-fructose solution and
3n cr~8tall~zing the solut~on `to provide D-ructose
crystals.

BRIEF DESCRIPTION OF THE DR~ING
The present invention will be understood more
clearly by considerlng the following description in
con~unction with the drawing, wherein:

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FIG. 1 is a flow diagram illustrating the process
for producing D-fructose and D-glucose according to the
present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. l, there is shown a flow diagram
illustratin~ the present process for producing D-fructose
and D-glucose. D-fructose is a sweetener for most
foodstuffs.
FIG. 1 shows the step-wise process for producing
D-fructose and D-glucose. According to the present
process, an aqueous solution of D-glucose is first
epimerized to a mixture of D-glucose and D~mannose,
preferably in a fixed catalyst bed. This mixture is
then passed to a fractional crystallizer where the
D-glucose is separated from the mixture, i.e., D-mannose,
and recycled to the epimerization zone to be further
epimerized. After the separation of the D-glucose,
the D-mannose is hydrogenated to provide a solution of
D-mannitol.

The ~-mannitol, in solution, is then treated with
oxygen or a~r in the presence of oxidizing microbes,
i.e., Gluconohacter suboxydans which are also referred
to as cetobacter suboxydans. The mannitol after being
oxygenated, pro~ides a solution of D-fructose which is
treated, i.e., crystallized into crystals.

~here may be unoxidized D-mannitol passed with
; 30 the D-~ructose solution to the crystallizer. This
unoxidized, i.e., residual, D-mannitol is then
recycled to the oxidation zone to be oxidized with
that being passed from the hydrogenation zone.
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The catalyst of the fixed bed in which th~
D-glucose is epimerized, is preferably silicotungstic
acid on silica gel. There are other catalysts which
may be used in this epimerization process which include
molybdic acid on silica gel, phosphomolybdic acid
on silica gel, and similar derivatives of molybdenum
and tungsten, on a silica gel that is preferably acid
washed. This same fixed catalyst bed is used in the
hydrogenation of D-mannose to D-mannitol.
The epimerization process, where D-mannose is
produced, uses a 10 to 70~ aqueous D-glucose solution
and most preferably, a 50 to 70% aqueous D-glucose
solution at 100-125C., and a pH of 3 to 5 and a reaction
time of 30 to 120 minutes. Also, in place of the pure
D-glucose, solutions of crude start hydrolyzate can be
used for producing the D-mannitol and eventually
D-fructose.

In the hydrogenation of D-mannose with the fixed
catalyst bed, the hydrogen flow rate is related to the
liquid feed rate and by the quantity of catalyst used,
as the hydrogen gas flo~ provides for carrying the feed
liquid dropleks through the fixed-catalyst type beds to
achieve intimate contact with the catalyst particles.
The liquid ~eed rate in the present hydrogenation
ranges ~rom about 0.3 to about 10.0 g./hr./g. of
catalyst, and preferably from about 0.4 to about 8.0
~.~hr.~g. of catalysk. ~ccordingly, t:he ratio o~
hydrogen yas to liquid ~eed rate at s~.andard conditions
ranges from about 500 tto about 5000 for achieving
~atis~actory conversion of D~mannose to D-mannitol.




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The aerobic fermenting bacteria include:
Gluconobacter suboxydans (subsp. suboxydans). The
amount of suboxydans used is generally related to the
amount of D-mannitol being oxidized. This amount
ranges from about 20 g to about 80 g./liter reactor
~olume~hr.

The conditions under which the D-mannose is
hydrogenated to D-mannitol in the fixed catalyst bed
is at a temperature ranging from about 100 to about
150C. and a pressure ranging from about 500 to about
2000 psig hydrogen partial pressure.
D-fructose may be utilized as a sweetening material
for foodstuffs of all kinds. The D-fructose is a
sweetening agent which is calorific and is twice as
sweet as saccharose. Thus, only half as much
D-fructose is needed to sweeten foodstuffs.