Use Of Lime In The Chemical Industry
Lime is a basic industrial chemical that is used as a component in many
other chemical processes. We manufacturers and suppliers of hydrated lime
and other lime chemicals.
Alkalis
Alkali plants with access to natural soda ash use the “lime-soda
process to manufacture caustic soda (sodium hydroxide). Sodium carbonate
(soda ash) reacts with a lime slurry to form caustic soda and precipitated
calcium carbonate as co-products.
Calcium Carbide and Cyanimide
Calcium carbide, the oldest source of acetylene, is formed by mixing
quicklime and coke and heating to a temperature of 2000 degrees C. Molten
carbide is removed from the furnace continuously, and upon solidifying, is
crushed and ground to the desired size. Calcium cyanamide, a nitrogen
fertilizer, is made by heating calcium carbide in the presence of nitrogen.
Acetylene gas is generated from carbide by adding water, yielding a waste
hydrated lime.
Citric Acid
Lime is used in the purification of citric acid. Hydrated lime is added to
a solution of citric acid that has previously been filtered to remove
suspended solids. Calcium citrate is precipitated and removed. Citric acid
can later be regenerated from the calcium citrate by reacting it with
sulfuric acid to precipitate calcium sulfate.
Magnesia
Lime is used in the two major processes to manufacture magnesia (magnesium
oxides): the seawater process and production from brines. In the seawater
process, milk of lime precipitates magnesium hydroxide from seawater. Where
dolomitic lime is used, up to half of the Mg(OH)2 derives from the lime. So
too, in the production of Mg(OH)2 from brine, lime acts as a precipitant.
Use Of Lime In Sugar Refining
Hydrated lime is essential to the production of sugar from both sugar cane
and sugar beets. It is also used to purify sugar from other sources, such as
maple or sorghum, although these are produced in much smaller quantities.
Sugar cane and sugar beets are harvested and processed with water to form
raw juice, which has low pH and contains dissolved impurities. Hydrated lime
is added to the juice to raise the pH and to react with the impurities to
form insoluble calcium organic compounds that can be removed. Excess lime is
removed by carbonation or by the addition of phosphoric acid. This process
may be repeated several times depending on the purity of final product
required.
Use Of Lime In Refractory Products
High-purity refractory “dolomite” (frequently called Doloma) and
lower purity fettling grade “dead-burned dolomite” (usually
referred to as DBD) are both manufactured by calcining dolomitic limestone.
The method is similar to the manufacture of ordinary lime, except that the
burning time is longer and temperatures considerably higher (in the range of
1600 – 1850º C). High purity doloma is fired in rotary or shaft
kilns to the upper end of the temperature range without the addition of
impurities. The lower-purity DBD is fired in rotary kilns to the lower end
of the temperature range, and iron oxides are added during calcinations to
stabilize the resulting hard-burned quicklime against decomposition from
moisture. High purity doloma is used to manufacture refractory bricks
employed in cement and lime rotary kiln linings, and in steel ladles and
refining vessels. DBD is used for the manufacture of monolithic patching and
repair materials for steel furnaces.
Large quantities of light-burned dolomitic lime are also employed in the
production of synthetic refractory grade Magnesia (MgO). The quicklime is
slaked in a magnesium chloride brine, precipitating magnesium hydroxide. The
mag-hydroxide is calcined and fired into dense, high-purity magnesium oxide.
Refractory magnesia is used in the production of linings for cement and lime
kilns, in addition to steel ladles and furnaces.
Stabilized zirconium oxide (ZrO2) is produced by the addition of about 3%
lime during the fusion or sintering process, and is widely used for analysis
crucibles and thermocouple tubes, in addition to crucibles and furnaces used
for the production of high-temperature aero-space alloys.
One form of silica brick, a specialized refractory used for lining coke
ovens and glass furnaces, is made by thoroughly mixing ground silica
(usually quartzite) with the addition of ½ to 3 percent milk-of-lime as
a sintering (firing) aid. This mixture is formed into various shapes and
then fired in kilns.
Use Of Lime In The Food Industry
Lime serves a myriad of uses in the food industry. Some examples:
Dairy Industry
When cream is separated from whole milk, lime water is often added to the
cream to reduce acidity prior to pasteurization when butter is produced. The
skimmed milk is next acidified to separate casein. The casein is mixed with
lime and a small amount of sodium fluoride to produce calcium caseinate, a
form of glue. Fermentation of the remaining skimmed milk (whey) and the
addition of lime forms calcium lactate, which is marketed as a medicinal or
acidified to produce lactic acid.
Glue and Gelatin
Waste materials from rendering plants are treated with lime in slurry form.
This process swells the collagen, thereby facilitating subsequent
hydrolysis. After liming, the treated stock is washed to remove lime,
albumin, and mucin. The washed stock is dried, and the final product is sold
as glue or gelatin.
Baking Industry
In the preparation of a common type of baking powder, monocalcium phosphate
is required as an ingredient. This is made by reacting pure phosphoric acid
with a high calcium lime.
