Improvements in or relating to Refining Sugar.
Year: 1892

page_text: Date of Application, 22nd Nov., 1892-Accepted; 21st Jan., 1893
COMPLETE SPECIFICATION.
Improvements in or relating to Refining Sugar.
A communication by Dr. FRANZ SOXHLET, of 46, Louisenstrasse, Munich; in
the Empire of Germany, Professor:
I, WILLIAM PHILLIPS THOMPSon, F.C.S., M.I.M.E., of the Agency for
Foreign Patent. Solicitors,. 6, Lord. Street, Liverpool, and 6, Bank Street, Man-
chester both. in the County of Lancaster & 323 High Holborn in the County of
Middlesex, Civil Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
In the processes hitherto employed for refining sugar, the raw sugar after being.
cleaned is melted at the temperature of boiling. point, the saccharine solutions.
usually rendered alkaline by the addition of. lime thereto; is then. treated with.
clarifying. substances, and, after a preliminary mechanical filtration; is strained
whilst warm through bone black, and, finally; boiled in a vacuum pan to a masse™
cuite. The sugar solution from the commencement of the melting, process to its..
conveyance into the vacuum pan, is maintained for at least twelve hours, and on the
average sixteen, and frequently for twenty or more hours, at a temperature which
almost always commences with 102-103 degrees Celsius, and gradually drops to:
80 degrees or preferably to 70 degrees. During this maintained boiling of the..
saccharine'solution at a high temperature, more particularly during the predominance.
of the strong alkaline element (during the melting after the lime has been added, and
in the first stages of the filtration over bone black) brown coloured and adhesive
products of the sugar are formed which not only cause a direct loss of sugar, but also
damage the yield, owing to the fact, that they form syrup and their strong adherence
to.ther sugar crystals necessitates a greater consumption of clarifying.liquid. After
this long treatment at a high temperature simultaneously with a considerable quantity
of alkali and an abundant supply of air, the material is subjected to a short,
2 to 2 hour, heating to 72 to 85 degrees Celsius, with a minimum quantity of
alkáli; and a scanty supply of air during the boiling to a masse cuite in the vacuum
pan. The unavoidable heating during the boiling down has the smallest share, and
the heating before the boiling down has the largest share in producing deleterious
products of decomposition. The large consumption of bone black. is mainly
necessitated by the discolouration produced during the long heating before the
boiling down; and the latter again is mainly caused by the bone black filtration.
This process has for its object to reduce to a minimum the formation of brown
products of decomposition, by limiting the treatment of the sugar. solution by heat
to the unavoidable short heating during the boiling down, and it has further for its
object to limit the use of bone black to those sugar solutions in which the reddish-
brown products1 of.decomposition, formed during the repeated boilings; down; or
derived from the originali raw sugar, have accumulated to such an extent as: to
deleteriously affect the formation of colourless crystals.
It is as follows-
1. The sugar which it is intended to refine is first dissolved in cold water, a
stirring apparatus being employed. This cold' prepared, almost saturated solution
(of 60-68 Brix) which in the: treatment of washed ordinary beet root sugar is
even perceptibly alkaline, is freed from: discolouring: particles in a cold state by a
mechanical filtering process with the addition of lime or other solvents or so called
chemical clarifying: substances: In the treatment of acid sugar;, the minimum
amount of alkali necessary for the boiling down is produced before the filtration.
by the addition of lime..

page_text: 2. The filtered cleare is kept cold until its admission to the vacuum pan, and
cold drawn.
As regards the filtration of the cold sugar solution by means of filter presses,
filter cloths, etcetera, this is carried out in the following manner-
A cold solution of sugar naturally filters much more slowly than a hot one; for
the former, in order to obtain an equal result from a qualitative and quantitative
point of view, at least five times as much filtering surface will be required as for the
latter. However successful one may be, by the use of known filtering devices by
means of thick cloths and slow filtration, in obtaining filtrates which, with the
exception of a slight opalescence are free from discolourations, it is still desirable
for the production of finest products-clear loaf,' namely loaves with quite
'clear' points to obtain absolutely clear sparkling' (feurige) filtrates, and such
kind of filtrates are also advantageous since such are free from microbes, therefore
these solutions if concentrated over 60% and kept at a temperature under
30 degrees will remain at least a week absolutely free from invert sugar. Such
sparkling (feurige) and microbeless filtrates are obtained when the sugar solution
is filtered through fine plates of silicious sinter which is placed on a loose woven
filter cloth of a filter press, and is obtained by filtering through the filter press, before
commencing the actual filtration, a sludge of finely powdered silicious sinter in
water, or in a sugar solution which has already passed the filter or by using pressed
cakes as filtering layer, which have been formed in the chambers of a filter press
from silicious sinter sludge and wood sawdust.
$
In the first case 50 to 100 grammes of finely powdered raw or calcined silicious
sinter (infusorial or diotomaceous earth) is suspended per square metre in so much
water or sugar solution as is requisite for the lining of the filter press, is filtered
through, and the filtrate again returned until it runs clear, and, finally, the sugar
solution is filtered through (water being used after the latter has been pressed
through) at a pressure of 4 to 5 atmospheres avoiding as far as possible any running
in of the liquid in such a way as to shake it up. As a rule, the filtering layer must
be renewed after 2, 5 or 8 hours filtration. In order to treat 1000 metric centners
of raw sugar in 24 hours, a filtering surface of 75 square metres must constantly
run clear; and therefore with a view of affording interchanges and in view of many
sugar solutions being difficult to filter, it is preferable to have twice 75 square
metres.
At a single employment of the silicious sinter a quantity is used equal to '04 to 1%
of the sugar treated. The used silicious sinter may be cleansed by washing and then
used again. In the second method of working, 0.5 % of wood sawdust (dry fine
ground wood) calculated on the sugar is employed, which sawdust has been
previously repeatedly washed with hot water, together with 0.25% silicious
sinter, afterwards both these are suspended in about a 25 fold quantity of
sugar solution, and the press is filled until cakes are formed, and it is filtered
through at a pressure of 4 to 5 atmospheres. As regards the filtering surface, the
one herein before described is sufficient. The filtering substance, when used, may
be cleaned by boiling and allowing it to settle more rapidly, and with less loss
than is the case with silicious sinter alone and therefore the consumption of filtering
material is in this case rather less and its re-utilisation is simplified.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is-
1. The improvement in sugar refining which consists in dissolving in cold water
the sugar which is to be refined, in filtering the cold sugar solution, and in keeping
the same cold until it is run into the vacuum pan.
2. The filtration of sugar solutions through a layer of silicious sinter impervious
to microbes, with which an ordinary filter cloth is coated by means of a previous
filtration of a sludge of silicious sinter; or the filtration through a filter press cake,

page_text: acting in a similar manner, which is formed by the filtration of a sludge composed
of wood sawdust and silicious sinter, substantially as and for the purpose set forth.
Dated this 21st day of November 1892.
WM. P. THOMPSON & Co.,
Agents for the Applicant.