[0001] This invention relates to the solubilisation and hydrolysis of glycosidically linked
carbohydrates having reducing groups and in particular to the solubilisation and hydrolysis
of starch and cellulose to glucose.
[0002] Cellulose is a polysaccharide which forms the main component of the cell walls of
most plants. It is a polymer of B-D-glucose units which are linked together with elimination
of water to form chains of 2000-4000 units. In plants it occurs together with other
polysaccharides and hemicelluloses derived from other sugars such as xylose, arabinose
and mannose. In the woody parts of plants cellulose is intimately mixed and sometimes
covalently linked with lignin. Wood, for example, normally contains on a dry weight
basis 40-50% cellulose, 20-30)6 lignin and 10-30% hemicelluloses together with mineral
salts, waxes, resins and proteins.
[0003] The solubilisation and hydrolysis of cellulose may be brought about by various treatments,
including treatment with acids and with enzymes present in certain bacteria, fungi
and protozoa. Such treatments result mainly in cleavage of the glycosidic links in
the cellulose chain with a consequent reduction in molecular weight. Partial hydrolysis
with acids produces a variety of products, often termed "hydrocelluloses", whose properties
are determined by the hydrolysis conditions employed. Complete acid hydrolysis of
cellulose yields glucose. Treatment with acid by solution and reprecipitation often
increases the accessibility and susceptibility of cellulose to attack by enzymes,
microbes and chemical reagents. Solubilisation and hydrolysis of cellulose by enzymes
leads to various intermediate products depending upon the enzyme employed. The final
product of enzymic treatment of cellulose is usually glucose but rigorous treatment
may produce a further breakdown to ethanol, carbon dioxide and water.
[0004] In our published European Patent Specification No. 44622 we describe and claim a
process for the modification, solubilisation and/or hydrolysis of a glycosidically
linked carbohydrate by treatment with a mixture comprising an aqueous inorganic acid
and a halide of lithium, magnesium and/or calcium or a precursor of said halide. The
process of European Patent Application Specification No. 44622 is very successful.
However easy separation of the metallic species from the organic products of the reaction
cannot always be achieved by this process.
[0005] According to the present invention we provide a process for the modification, solubilisation
and/or hydrolysis of a glyc- sidically linked carbohydrate to produce one or more
of the following effects:-
(A) modification of the carbohydrate to induce increased accessibility and susceptibility
to enzymes, microbes and chemicals,
(B) solubilisation of the carbohydrate, and
(C) solubilisation and hydrolysis of one or more glycosidic linkages in the carbohydrate
to produce soluble oligosaccharides and/or glucose, wherein the carbohydrate is contacted
with a mixture comprising an aqueous inorganic acid and a hydrated halide of aluminium
or a precursor of said halide, at a temperature within the range 200 to 100°C, a reaction product is separated and aluminium ions are recovered from the
separated product.
[0006] Whilst the process of the invention is generally applicable to glycosidically linked
carbohydrates, it is particularly applicable to starch and cellulose.
[0007] The products of solubilisation and/or hydrolysis include oligosaccharides, as well
as tri-, di- and mono- saccharides. Specifically the products from cellulose include
cellodextrins, cellotriose, cellobiose and glucose. When the process is used to produce
carbohydrate of enhanced susceptibility to enzymic hydrolysis, the susceptible carbohydrate
may be treated with an enzyme in which case the exact nature of the final products
will depend upon the enzyme employed and upon the reaction conditions. In the case
of cellulose treatment with cellulases the product under appropriate conditions will
be glucose.
[0008] The glycosidically linked carbohydrate can be present in any suitable state. It can
be present as free or combined carbohydrate, in its natural state or in a processed
or converted form. The process is particularly useful when applied to the conversion
of the following types of carbobydrate-containing feedstocks:-
(a) silvicultural products such as wood, wood residues, mechanical and chemical wood
pulps, various grades of recycled paper and other wood based products, and
(b) agricultural products and residues such as straw, bagasse, corn stover and other
pulp and grain by-products. The process is also applicable to carbohydrates which
exist in highly oriented forms such as crystalline cellulose, cotton and other ordered
structures which are normally inaccessible to enzymes and other catalysts. Such inaccessibility
may be compounded by the occurrence of a polysaccharide with other polymers such as
the cellulose with ligain. The process of the invention is applicable to the modification
or solubiliaation of cellulose without prior delignification.
[0009] The process is applicable to glycosidically linked carbohydrates whether the glycosidic
linkage is a β-linkage as in cellulose, yeast glucan or laminarin, or an α-linkage
as in starch, glycogen, dextran or nigeran. In particular it is applicable to starch
which is converted to lower sugars including maltose and, as the main product, glucose.
The process is also applicable to glycosidically linked carbohydrates with other constituent
pentoses, hexoses, heptoses, amino sugars and uronic acids, as well as to the previously
mentioned naturally occurring polymers of D-glucose. Such polymers with other constituents
having industrial significance include wood hemicelluloses, yeast mannan, bacterial
and seaweed alginates, industrial gums and mucilages and chitin. Carbohydrates containing
0- sulphate, N- sulphate, N- acetyl, 0- acetyl and pyruvate groups can also be treated
by the process of the invention as can carbohydrates derived by carboxymethylation,
acylation, hydrox
yetbylation and other substitution processes provided that such carbohydrates contain
glycosidic linkages. Acid labile substituents on carbohydrates may be lost during
the process of the invention.
[0010] Preferred inorganic acids are hydrochloric, hydrobromic and hydriodic acids, hydrochloric
acid being most economical and especially prefferred.
[0011] The preferred hydrated aluminium halide is the hexahydrate A1 Cl
3.6H
2O. The hydrated aluminium halide can be present as the sole metal halide or in combination
with other metal halides or precursors thereof. When more than one metal halide is
to be present, the halide present together with the hydrated aluminium halide is preferably
a halide (especially a chloride) of lithium, calcium and/or magnesium or a precursor
of such a halide. It should be understood that in the reaction mixture the halide
ions can be present as complex halide ions, these complex ions being generated within
the mixture. In operation of the process of the invention, an aqueous solution of
the hydrated aluminium halide is prepared and is thereafter acidified. Preferably
the acid is added to the aqueous solution of the halide. However acidification can
be achieved in the reverse manner, i.e. by adding the aqueous solution of the metallic
salt to the acid. Preferably the acid employed has a concentration in the range 0.5
to 5 molar and is added to the aqueous solution of the metallic salt. The acidified
aqueous solution of the metallic salt is used to treat the carbohydrate - preferably
being added thereto. It should be noted that the extent to which aluminium chloride
is soluble in aqueous hydrochloric acid varies inversely with the concentration of
the acid.
[0012] In the process of the invention the treatment of the carbohydrate is preferably carried
out at a temperature in the range 50° to 90°, especially in the range 65° to 75° where
the aim is to achieve solubilisation and hydrolysis. In general the conditions employed
in the process of the present invention are similar to those employed in that of published
European Patent Specification No. 44622.
[0013] The process of the invention may be used as stated above to produce carbohydrate
of enhanced susceptibility to enzymic hydrolysis. In this case the susceptible carbohydrates
can then be treated with an enzyme in a second step, which is preferably carried out
at a pH in the range 4 to 9, to produce the final product which can be for example
glucose.
[0014] When the hydrated aluminium halide is used together with another metal halide, such
as a lithium, magnesium and/or calcium halide, the relative proportions in which the
two halides are present is preferably in the range 10:1 and 1:10 w/w.
[0015] The process of the present invention has the following advantages:-1. Ability to
dissolve and hydrolyse to soluble oligosaccharides as well as. to tri-, di and mono-
saccharides such as glucose without prior delignification.
[0016]
2. Ability to handle high concentrations of difficultly soluble polysaccharides such
as cellulose.
3. Ability to handle a wide range of potential sources of monosaccharides, especially
glucose.
4. Easier separation and recovery of the metal ions.
[0017] Any suitable technique may be used to separate aluminium ions from the mixture produced
by solubilisation and hydrolysis. Two suitable techniques are illustrated in Examples
2 and 3.
[0018] The invention is illustrated by the Examples given below in which Examples the analytical
methods used are as described in European Patent Specification No. 44622:-EXAMPLE
1
Starch hydrolysis using aqueous solutions of AlCl3.6H2O and aqueous H C1
[0019] A series of starch hydrolysis reactions was performed using either technique 1 or
technique 2, the technique used in any particular reaction depending upon convenience
and upon the concentration of AlCl
3.6H
2O employed. Technique 1: To an aqueous solution of aluminium chloride AlCl
3.6H
2O (saturated at 20°C) was added concentrated (10 M) hydrochloric acid to give a final
hydrochloric acid concentration of 2 M. Dottles were prepared containing hydrochloric
acid saturated with aluminium chloride and starch and were allowed to stand at room
temperature for 15 minutes. At the end of this time the bottles were placed in a water
bath at 70°C. After one hour at 70°C the contents of the bottles were analysed for
D-glucose by the glucose oxidase method.
[0020] Technique 2: Solid aluminium chloride AlCl
3.6H
2O was added to concentrated hydrochloric acid and thereafter water was added to raise
the volume and to give the required final concentrations. Bottles containing solutions
of hydrochloric acid, aluminium chloride and starch were prepared and were allowed
to stand for 15 minutes at room temperature. After this time the bottles were placed
in a water bath at 70°C for 1 hour and thereafter the contents were analysed for D-glucose
by the glucose oxidase method.
[0021] The results are set out in Table 1. In the table the experiment marked with an asterisk
is a comparative experiment with an alternative catalyst system using magnesium chloride
Mg Cl
2.6H
20.
[0022] Using technique 2 further experiments were carried out in which starch hydrolysis
was continued for periods exceeding one hour, percentage yields of glucose being measured
at intervals. The results are shown in Figures 1 and 2 of the drawings.
[0023] Figares 1 and 2 of the drawings are graphs of percentage yield of glucose against
time in hours for starch solutions hydrolysed in the presence of hydrochloric acid
and aluminium chloride Al Cl
3.6H
2O.
[0024] In Figure 1 the hydrochloric acid concentration used was 3 molar and the aluminium
chloride concentration was 0.5 molar. Curve A in Figure 1 is for a 30% w/v starch
solution showing a yield of 87% after 3 hours. Curve B in Figure 1 is for a 40% starch
solution showing a yield of 70% after 3 hours.
[0025] In Figure 2 the hydrochloric acid concentration used was 2 molar and the aluminium
chloride concentration was 0.5 molar. Curves C, D and E in Figure 2 are for starch
solutions having concentrations of 26% w/v, 33% w/v and 40%
w/v respectively. In curves C and D there are peaks at 93% yield after 4 hours and
81% yield after 3 hours respectively in the two curves. In curve E the yield after
3 hours is 57% and after 6 hours 65%.
EXAMPLE 2
Recovery of aluminium from reaction product
[0026] A solution of a mixture of 1 molar hydrochloric acid, 2 molar aluminium chloride
(Al Cl
3.6H
2O) containing 20%
w/v glucose was reduced in volume from 200 ml to 100 ml by heating to 60°C under reduced
pressure. At this volume the crystals which formed were removed from the glucose solution
by filtration. These crystals (37 g wet) contained 9.1%
w/w aluminium (81% w/w Al Cl
3. 6H20) and 8.4% w/w glucose. This represents 35% of the original aluminium content
of the hydrochloric acid/aluminium chloride/ glucose mixture. The remaining syrup
contained 28.9%
w/w glucose and 4.6%
w/w aluminium (i.e. the remainder or 65% of the original aluminium). This recovery
procedure is set out in Table 2.
[0027]
N.B. 87% of the original aluminium and 88% of the original glucose were accounted
for by analysis.
EXAMPLE 3
Recovery of aluminium from reaction product
[0028] A solution of a mixture of 2 molar hydrochloric acid, 2 molar aluminium chloride
Al Cl
3.6H
2O containing 20% w/v glucose was reduced in volume from approximately 400 ml to approximately
250 mls by heating to 60°C under reduced pressure. 92 g of crystals formed and were
removed by filtration. These crystals contained 9.7%
w/w aluminium (86.8% Al Cl
3.6H
2O) and 7.1%
w/w glucose.
[0029] Hydrochloric acid (10 M strength) was then added to samples of the remaining glucose
syrup solution in various proportions to give 7.4%
w/w, 13%
w/w and 22%
w/w final concentrations of hydrochloric acid. This caused more crystals to form in
proportion to the concentration of hydrochloric acid. Thus:-
(a) 13% of the aluminium was recovered as crystals from the 7.4% w/w HCl sample;
(b) 23% of the aluminium was recovered as crystals from the 13% w/w HCl sample; and
(c) 39% of the aluminium was recovered as crystals from the 22% w/w HCl sample.
[0030] These crystals were composed of 5.6 to 5.9 %
w/w aluminium but still contained 5 to 10% w/w glucose.
[0031] The first stage of this separation process gave a yield of aluminium of 41% while
the second stage gave a maximum yield of a further 20% of aluminium leaving 1.6%
w/w aluminium in the glucose syrup.
[0032] This recovery procedure is set out in Table 3.
1. A process for the modification, solubilisation and/or hydrolysis of a glycosidically
linked carbohydrate to produce one or more of the following effects:-
(A) modification of the carbohydrate to induce increased accessibility and susceptibility
to enzymes, microbes and chemicals,
(B) solubilisation of the carbohydrate, and
(C) solubilisation and hydrolysis of one or more glycosidic linkages in the carbohydrate
to produce soluble oligosaccharides and/or glucose, wherein the carbohydrate is contacted
with a mixture comprising an aqueous inorganic acid and a hydrated halide of aluminium
or a precursor of said halide, at a temperature within the range 200 to 100°C, a reaction product is separated and aluminium ions are recovered from the
separated product.
2. A process according to claim 1 for the solubilisation and/or hydrolysis of cellulose
to produce a cellodextrin, cellotriose, cellobiose and/or glucose.
3. A process according to claim 1 for the solubilisation and/or hydrolysis of starch
to produce D-glucose or a mixture of sugars containing D-glucose.
4. A process according to any one of the preceding claims wherein the inorganic acid
is hydrochloric acid.
5. A process according to any one of the preceding claims wherein the hydrated halide
of aluminium or precursor of said halide is aluminium chloride hexahydrate Al C13.6H20.
6. A process according to any one of the preceding claims wherein there is present,
in addition to the hydrated halide of aluminium or precursor thereof, a halide of
lithium, calcium and/or magnesium or a precursor of such a halide.
7. A process according to any one of the preceding claims wherein an aqueous solution
of the hydrated aluminium halide or precursor thereof is prepared and an inorganic
acid having a concentration in the range 0.5 to 5 molar is added to this aqueous solution,
the acidified aqueous solution thereafter being added to the carbohydrate.
8. A process according to any one of the preceding claims wherein the carbohydrate
is contacted with the mixture at a temperature in the range 50° to 90°C.
9. A process according to claim 8 wherein the temperature is in the range 65° to 75°C.
10. A process according to claim 6 wherein the mixture contains two metal halides,
a hydrated halide of aluminium and a halide of lithium, calcium or magnesium, the
relative proportions of the two halides being in the range 10:1 to 1:10 w/w.
11. A process for the modification, solubilisation and/or hydrolysis of a glycosidically
linked carbohydrate substantially as described and as shown in the Examples.
12. A saccharide-containing product whenever produced by a process according to any
one of the preceding claims.