93
5
cakes from drying out during prolonged
storage. Glycerol has about 60% of the sweetening power of sucrose and about the same
number of calories per gram. Compared to
sucrose, glycerol does not increase the blood
sugar level and does not enable bacterial
growth.
5 Other direct applications of glycerol include
adhesives, plasticizers in regenerated cellulose
and special paper grades.
5 Finally, there are a number of technical
applications in which glycerol is chemically
converted. These include, for instance, the use
as polyol in polyurethane foams or alkyd resins. We will learn more about this follow-up
chemistry of glycerol in the coming sections
of this chapter.
. Figure 5.3 attempts to summarize these applications once again. The percentages are estimates. What is striking is the large market share
of pharmaceuticals and personal care products,
both of which require very high glycerol purity.
At the end of this section, we have a look at
some market data. The worldwide fat production, currently approx. 200 million tons per year,
has already been discussed in 7 Sect. 2.3. About
10% of this amount (about 20 million tons per
year) is glycerol! However, we have also heard
that the majority of fats and oils are used in the
food sector (approx. 75%) and thus do not serve
glycerol production. Approx. 22% of fats and oils
(approx. 44 million tons per year) are processed
industrially either to chemicals or fuels, whereby
larger quantities of glycerol are produced.
In recent decades, the European glycerol market has had a volume of 250,000–400,000 tons
per year. This has changed significantly in the last
decades: With the introduction of biodiesel, i.e.
fatty acid methyl esters especially based on rapeseed, as a fuel, additional quantities of glycerol
were brought onto the market. In 2006, global
biodiesel production amounted to approx. 6 million tons per year and by 2014 had risen to just
under 30 million tons per year. This means that
several hundred thousand tons of glycerol have
been added to the European market that were not
needed by traditional customers.
Accordingly, glycerol prices changed: While
in the years 2000–2003 prices of 1000–1300 Euro
per ton could still be achieved, between 2004 and
5 Via Route I, propene is the first chlorinated
to allyl chloride. This is converted with
hypochlorous acid to the two dichlorohydrins, which react with calcium hydroxide to
epichlorohydrin. Subsequently, the latter is
converted into glycerol with caustic soda.
5 Route II also goes via allyl chloride, which
reacts with caustic soda to form allyl alcohol.
However, there are also some chlorine-free
alternatives to obtain allyl alcohol from propene. Allyl alcohol subsequently is catalytically
converted with hydrogen peroxide into glycidol, which is finally hydrolyzed to glycerol.
Both routes have four stages and are therefore very
complex. If chlorine is used, it finally ends up as
worthless salts. Nevertheless, for a long time, synthetic glycerol was a strong competitor to natural
glycerol, as the raw material propene obtained
from crude oil was available at relatively low cost.
Due to the increased supply of natural glycerol due
to biodiesel production, synthetic glycerol processes have lost much of their importance.
Glycerol has found a wealth of direct applications for many decades. The most important are
listed below:
5 Glycerol is often used in medical and pharmaceutical formulations because of its
non-toxicity, e.g. in cough syrups or expectorants. Very often, its hygroscopic property also
plays an important role: Glycerol helps to keep
a drug moist and to control water activity.
5 The use of glycerol in body care products is
very similar: Glycerol is used as a solvent,
plasticizer, lubricant and humectant in skin
creams, toothpastes, mouthwashes, shaving
foam, hair care products and glycerol soaps.
With the help of glycerol, it is possible to
re-soften dry skin.
5 Glycerol is also used in the tobacco industry
because of its moisturizing properties: The
crumbling of pipe tobacco or cigarettes is
prevented by soaking them with glycerol.
5 There are also many applications in the food
industry: Glycerol is used as a solvent and
sweetener with the European designation
(E)422 in food and beverages. It is classified
by the US Food and Drug Administration
(FDA) as “generally recognized as safe
(GRAS)”. In sweets and cakes, it acts as a
softener and humectant. Glycerol can prevent
5.1 · Properties and Use of Glycerol
5
cakes from drying out during prolonged
storage. Glycerol has about 60% of the sweetening power of sucrose and about the same
number of calories per gram. Compared to
sucrose, glycerol does not increase the blood
sugar level and does not enable bacterial
growth.
5 Other direct applications of glycerol include
adhesives, plasticizers in regenerated cellulose
and special paper grades.
5 Finally, there are a number of technical
applications in which glycerol is chemically
converted. These include, for instance, the use
as polyol in polyurethane foams or alkyd resins. We will learn more about this follow-up
chemistry of glycerol in the coming sections
of this chapter.
. Figure 5.3 attempts to summarize these applications once again. The percentages are estimates. What is striking is the large market share
of pharmaceuticals and personal care products,
both of which require very high glycerol purity.
At the end of this section, we have a look at
some market data. The worldwide fat production, currently approx. 200 million tons per year,
has already been discussed in 7 Sect. 2.3. About
10% of this amount (about 20 million tons per
year) is glycerol! However, we have also heard
that the majority of fats and oils are used in the
food sector (approx. 75%) and thus do not serve
glycerol production. Approx. 22% of fats and oils
(approx. 44 million tons per year) are processed
industrially either to chemicals or fuels, whereby
larger quantities of glycerol are produced.
In recent decades, the European glycerol market has had a volume of 250,000–400,000 tons
per year. This has changed significantly in the last
decades: With the introduction of biodiesel, i.e.
fatty acid methyl esters especially based on rapeseed, as a fuel, additional quantities of glycerol
were brought onto the market. In 2006, global
biodiesel production amounted to approx. 6 million tons per year and by 2014 had risen to just
under 30 million tons per year. This means that
several hundred thousand tons of glycerol have
been added to the European market that were not
needed by traditional customers.
Accordingly, glycerol prices changed: While
in the years 2000–2003 prices of 1000–1300 Euro
per ton could still be achieved, between 2004 and
5 Via Route I, propene is the first chlorinated
to allyl chloride. This is converted with
hypochlorous acid to the two dichlorohydrins, which react with calcium hydroxide to
epichlorohydrin. Subsequently, the latter is
converted into glycerol with caustic soda.
5 Route II also goes via allyl chloride, which
reacts with caustic soda to form allyl alcohol.
However, there are also some chlorine-free
alternatives to obtain allyl alcohol from propene. Allyl alcohol subsequently is catalytically
converted with hydrogen peroxide into glycidol, which is finally hydrolyzed to glycerol.
Both routes have four stages and are therefore very
complex. If chlorine is used, it finally ends up as
worthless salts. Nevertheless, for a long time, synthetic glycerol was a strong competitor to natural
glycerol, as the raw material propene obtained
from crude oil was available at relatively low cost.
Due to the increased supply of natural glycerol due
to biodiesel production, synthetic glycerol processes have lost much of their importance.
Glycerol has found a wealth of direct applications for many decades. The most important are
listed below:
5 Glycerol is often used in medical and pharmaceutical formulations because of its
non-toxicity, e.g. in cough syrups or expectorants. Very often, its hygroscopic property also
plays an important role: Glycerol helps to keep
a drug moist and to control water activity.
5 The use of glycerol in body care products is
very similar: Glycerol is used as a solvent,
plasticizer, lubricant and humectant in skin
creams, toothpastes, mouthwashes, shaving
foam, hair care products and glycerol soaps.
With the help of glycerol, it is possible to
re-soften dry skin.
5 Glycerol is also used in the tobacco industry
because of its moisturizing properties: The
crumbling of pipe tobacco or cigarettes is
prevented by soaking them with glycerol.
5 There are also many applications in the food
industry: Glycerol is used as a solvent and
sweetener with the European designation
(E)422 in food and beverages. It is classified
by the US Food and Drug Administration
(FDA) as “generally recognized as safe
(GRAS)”. In sweets and cakes, it acts as a
softener and humectant. Glycerol can prevent
5.1 · Properties and Use of Glycerol