Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
1999-10-11
2001-04-10
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S046200, C127S058000
Reexamination Certificate
active
06214124
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to an industrial process for the production of lactulose by isomerization of lactulose using sodium aluminate.
STATE OF THE ART
Lactulose is a synthetic disaccharide normally used in the form of a syrup for the treatment of intestinal disorders and in the form of crystalline product as sweetener substituent of saccarose. It is also used as food supplement in pediatric and geriatric diets.
Many processes for the preparation of lactulose by isomerization of lactose, which is a natural disaccharide widely available, are known.
Some of this processes are essentially based on the isomerization of lactose by strong bases as for example Ca(OH)
2
, NaOH, KOH and strong organic bases.
These processes present the drawbacks that the sugars can be randomly degraded; such degradations cause a fall in the lactulose yield, complicate the extraction steps necessary to eliminate the degraded products, impoverish the syrups quality and make more difficult the preparation of crystalline lactulose. Another group of processes uses, as isomerizing agents, sodium tetraborate and sodium aluminate.
These processes, although allow to obtain higher yields of lactulose and a purer product, are not industrially acceptable for the difficulty presented by the necessary filtration of aluminum hydroxide and by the total elimination of boric acid.
Other processes, using strongly basic ion-exchange resins for the isomerization, are too much expensive and do not allow the production of lactulose at acceptable prices.
Processes for the isomerization of lactulose using magnesium compounds are also known.
These processes present the drawbacks to require very high reaction volumes for obtaining small quantities of lactulose.
An improved process is described in U.S. Pat. No. 4,957,564 wherein the isomerization of lactulose is obtained by catalysis with sodium aluminate followed by neutralization with sulphuric acid. However, in performing this process high quantities of sodium sulphate are produced and the elimination of this product implies ecological problems difficult and expensive to solve.
SUMMARY OF THE INVENTION
We have now found a process for the preparation of lactulose which allows to overcome the prior art problems.
In particular we have found a process for the isomerization of lactose to lactulose using sodium aluminate which allows an easy filtration of the aluminum hydroxide and its easy reconversion into the sodium aluminate to be used in the following cycle and moreover allows to avoid ecological problems.
The process according to the present invention comprises the following steps:
a) reaction of an aqueous solution or suspension of lactose with sodium aluminate in order to produce the isomerization of lactose to lactulose with a low conversion of lactose or with an high conversion of lactose;
b) quenching with ice of the mixture obtained in step (a);
c) neutralization of the mixture obtained in step (b) with precipitation of the aluminum hydroxide;
d) separation of the aluminum hydroxide by filtration;
e) deionisation of the solution obtained in step (d);
f1) concentration of the solution obtained in step (e) up to obtaining a technical syrup in the case of high conversion of lactose;
f2) concentration of the solution obtained in step (e) to be treated according to following step (i) in the case of low conversion of lactose;
g) treatment of the aluminum hydroxide obtained in step (d) with NaHCO
3
, Na
2
CO
3
or with NaOH, in the quantity necessary to convert the aluminum hydroxide into sodium aluminate;
h) calcination of the product from step (g) to obtain the sodium aluminate which is recycled in step (a);
i) crystallization from the solution of step (f2) of the non-isomerized lactose, which is recycled in step (a),
this process being characterised by the fact that said low conversion of lactose is limited to 55-65%, said high conversion of lactose is comprised between 90 and 95% and said neutralization of step (c) is performed by treatment with gaseous CO
2
under pressure.
Besides the above mentioned advantages, by performing the process according to the present invention it is also possible to obtain a product having higher purity and with higher yield.
DETAILED DESCRIPTION OF THE INVENTION
The advantages and characteristics of the process for the preparation of lactulose by isomerization of lactose according to the present invention will be better illustrated in the following description.
According to the process for lactulose preparation of the present invention, first of all a solution or suspension of lactose in water is prepared, wit a lactose content of 20-50% by weight; said solution or suspension is warmed at temperature comprised between 25°-50° C.
To such lactose solution or suspension a solution of sodium aluminate (30%-40% by weight) is added, in few minutes an homogeneous solution is obtained which is reacted at a temperature comprised between 25-50° C. for 6-16 h.
The sodium aluminate is used with a molar ratio of 0.5:1-2:1 calculated on lactose.
The obtained mixture is poured on ice (30-40% by weight calculated on the mixture) in order to produce a quick cooling, to stop the transformation of lactose into lactulose and to inhibit all secondary reactions.
By stirring for 10-20 minutes an homogeneous solution having temperature 15-18° C. is obtained.
By following the above reported procedure and choosing the appropriated molar ratios between sodium aluminate and lactose and the reaction time and temperature, as described also in the following examples, it is possible to obtain a low lactose conversion, for example 55-65% with a lactulose yield of 83-85% or it is possible to obtain a high conversion of lactose, for example 90-95% with a lactulose yield of 68-75%. The homogeneous solution obtained as above described is continuously neutralized by treatment with gaseous CO
2
at 0.25-0.5 MPa at a temperature from 20° to 32°-35° C. for at least 1 h.
With this procedure a mixture consisting of a solution of lactulose and lactose containing dissoived NaHCO
3
and suspended aluminum hydroxide, is obtained. The obtained mixture after neutralization is filtered preferably by filter press.
The solid obtained by filtration, consisting essentially of aluminum hydroxide and sodium bicarbonate, is suspended in water and filtered again. The obtained liquid, consisting essentially of a solution of lactulose, lactulose and soluble salts, is deionized using ion-exchange resins according to known techniques and thereafter is concentrated up to a saccharimetric content of 60°-80° Brix.
The concentration is performed under reduced pressure (0.0026-0.0046 MPa) at a temperature of the concentrated solution of 45-50° C. or lower.
In the case of high lactose conversion, a technical, commercializable syrup is obtained.
In the case of low lactose conversion the concentrated mixture is cooled down under stirring at 20° C. and thereafter at 5-15° C. for 120-130 h, giving the crystallization of the lactose non-converted during the isomerization step.
The lactose is separated by centrifugation and the remaining liquid is a lactulose syrup having high purity, a lactulose concentration of 50-55% by weight and little quantities of other sugars like lactose and galactose.
The crystallized lactose, after washing with cold water at the end of the centrifugation, is recycled to the initial step as starting material for a new cycle. In step g) the solid from the filtration performed after neutralization, is mixed up with NaHCO
3
, Na
2
CO
3
or NaOH, added as solids or in aqueous solution, preferably as solids, in the appropriated quantity to obtain a sodium quantity useful for the production of sodium aluminate (NaAlO
2
or Na
2
O—Al
2
O
3
) according to known techniques, for the production of aluminate (according to such techniques besides the stoichiometric quantity of sodium in respect of Al, it is necessary to add a further quantity in the form of a base containing sodium).
Normally the solid from the filtration performed after the neutralization, consisting esse
Bimbi Giuseppe
Carobbi Renato
Cipolletti Giovanni
Brunsman David
Hedman & Costigan ,P.C.
Inalco S.p.A.
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