An Improved Process for the Production of Hydrate of Magnesia.
Year: 1890

page_text: Date of Application, 26th Mar., 1890
Complete Specification Left, 19th Dec., 1890-Accepted, 14th Feb., 1891
PROVISIONAL SPECIFICATION.
An Improved Process for the Production of Hydrate of Magnesia.
I, HEINRICH PRECHT, of Lüderberg, near Stassfurt, in the Empire of
Germany, Doctor of Philosophy, do hereby declare the nature of this invention
to be as follows:-
My invention relates to the production of hydrate of magnesia from calcined
magnesia.
Magnesia, obtained in any suitable manner, such as by calcining magnesite, takes
up water but slowly and only becomes completely transformed into hydrate of
magnesia after being in contact with the water for several months. Highly heated
magnesia under ordinary circumstances does not absorb hydrate water at all.
According to my invention in order to accelerate the absorption of water by
slightly heated magnesia and to induce highly heated magnesia to absorb hydrate
water, the magnesia is submitted in a closed apparatus to steam under pressure or
to the action of water or steam at a temperature above 105° C. The period during
which the hydrating should continue depends partly on the quality of the magnesia
but more especially on the temperature of the water or steam.
In a tem-
The higher the temperature the more rapid is the hydrating process.
perature of from 140 to 150° C. corresponding to a steam pressure of 3.5 to
5 atmospheres above the normal atmospheric pressure the hydrating of magnesia at
a clear red heat takes from 2 to 3 hours, while at a temperature of from 140° down
to 105° it takes from 5 to 30 hours to convert all the magnesia into hydrate of
magnesia. For ordinary purposes it is preferable to work at about 150° C. as with a
higher temperature, although it may be more favourable to hydration, the steam
pressure would be so high that the apparatus would have to be of extraordinary
strength or of very small size.
The process can be carried out in two different ways, namely, by the employment
of steam or of water, each process consisting as before stated mainly in exposing
the magnesia in hermetically covered vessels to the action of water or steam at a
temperature of at least 105° C.
When steam is used the magnesia in the vessel should be placed in thin layers on
iron sheeting or boards and any steam of the above temperatures is caused to act
upon it until the absorption is completed. These temperatures can be obtained by
the introduction into the vessels of steam at any of the before mentioned pressures
or of superheated steam.
When the hydration is to be effected by the employment of water under pressure
it will be necessary to continuously stir the inagnesia by means of suitable stirring
mechanism, otherwise it will form into a solid stone-like mass. The pressure can
be obtained by simply heating the air-tight vessel or by introducing superheated
high pressure steam until the necessary temperature above 105° C. is produced.
The result of this treatment is that the magnesia appears in a mud-like form and
can be separated by means of filter presses or other similar contrivances.
The magnesia to be hydrated may be either pure or impure, that is to say,
combined with lime, sesquioxide of iron or soluble salts, such as chloride of
magnesium or sulphate of magnesium.

page_text: COMPLETE SPECIFICATION.
An Improved Process for the Production of Hydrate of Magnesia.
I, HEINRICH PRECHT, of Löderburg, near Stassfurt, in the Empire of
Germany, Doctor of Philosophy, 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:
My invention relates to the production of hydrate of magnesia from calcined
magnesite.
Magnesia obtained in any suitable manner, such by calcining magnesite, takes
up water but slowly and only becomes completely transformed into hydrate of
magnesia after being in contact with water for several months. Highly heated
magnesia, under ordinary circumstances, does not absorb hydrate water at all.
According to my invention in order to accelerate the absorption of hydrate water
by slightly heated magnesia and to induce highly heated magnesia to absorb
hydrate water, the magnesia is submitted in a closed apparatus to the action of
water in a state of vapour, that is, to the action of steam or to the action of water
in the liquid state under pressure or at a temperature above 105° C. The period
during which the hydrating should continue depends partly on the composition of
the magnesia but more especially on the temperature of the water or steam.
higher the temperature the more rapid is the hydrating process. In a temperature
of from 140 to 150° C. corresponding to a steam pressure of 3-5 to 5 atmospheres
above the normal atmospheric pressure the hydrating of the magnesia at a clear
red heat takes from two to three hours while at a temperature of from 140° down
to 105° it takes from five to thirty hours to convert all the magnesia into hydrate
of magnesia. For ordinary purposes it is preferable to work at about 150° C. as
with a higher temperature although it may be more favorable to hydration, the
steam pressure would be so high that the apparatus would have to be of extra-
ordinary strength or of very small size.
The
The process can be carried out in two different ways, namely, by the employment
of steam or of water each process consisting as before stated mainly in exposing the
magnesia in hermetically covered vessels to the action of water or steam at a
temperature of at least 105° C.
When steam is used the magnesia in the vessel should be placed in thin layers on
iron sheeting or boards and any steam of the above temperatures is caused to act
upon it until the absorption is completed. These temperatures can be obtained by
the introduction into the vessels of steam at any of the before mentioned pressures
or of superheated steam.
When the hydration is to be effected by the employment of water under pressure
it will be necessary to continuously stir the magnesia by means of suitable stirring
mechanism otherwise it will form into a solid stone-like mass. The pressure can be
obtained by simply heating the air-tight vessel or by introducing superheated high
pressure steam until the necessary temperature above 105° C. is produced. The
result of this treatment is that the magnesia appears in a mud-like form and can be
separated by means of filter presses or other similar contrivances.
The magnesia to be hydrated may be either pure or impure, that is to say,
combined with lime, sesquioxide of iron or soluble salts, such as chloride of
magnesium or sulphate of inagnesium.
In carrying out the above process a strong covered vessel is employed provided
with suitable means for opening and closing the inlet and outlet orifices. As the
vessel is subjected to great internal
cylindrical form and in the latter case there it is preferably of a spherical or
vessel may be placed either horizontally
or vertically. When the hydration is effected by steam, the inside of the vessel
is provided with several shelves or partitions on which the magnesia is spread; but
if the hydration is effected by water under pressure the vessel must be provided
with a stirrer.

page_text: In the accompanying drawing
Figure 1 is a longitudinal section of a suitable hydrating vessel for carrying out
my invention, and
Figure 2 is a plan of the same.
A is the hydrating vessel provided with openings B B for filling or emptying the
vessel. The inner part of the vessel is provided with a stirrer C driven from out-
side the apparatus by gearing D and pulleys E.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
A process for the production of hydrate of magnesia from magnesia, con-
sisting in treating magnesia with water (liquid or in a state of vapour) in closed
vessels at a temperature of above 105 C. substantially as hereinbefore described.
Dated the 19th day of December 1890.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.