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Formaldehyde-free urea granules
THOMAS KRAWCZYK Uhde Fertilizer Technology B.V.
Roermond, The Netherlands
Urea formaldehyde is the currently state of the art urea
granulation additive. Its use is absolutely crucial in order to
achieve the required product quality such as crushing strength,
bulk density or low caking tendency. Furthermore it is also an
inherent granulation aid which ensures a proper performance of the
granulation process itself by limiting the generation of dust and
providing a high build up rate of the granules. Unfortunately there
are also some negative aspects to the use of the pre-condensates of
formaldehyde and urea (UF 80, UF85). A major disadvantage is that
it still contains a considerable amount of free formaldehyde which
is harmful to health. It is categorized as a carcinogenic substance
by the IARC (International Agency for Research on Cancer). In
addition to that UF solutions contain a certain amount of methanol.
Hence, it contributes to a significant part to the VOC emissions
from an ammonia/urea complex, which might be requested to be very
low by the local authorities. Furthermore urea product treated with
formaldehyde cannot be sold as technical grade for most
applications. It is not within the specification for the
preparation of DEF (Diesel Exhaust Fuel) also known as AdBlue®.
It was UFTs goal in the past years to develop an alternative
additive which is capable to guarantee the same product quality as
well as at least the same process performance parameters while not
contributing to any environmental impact. The result of the
development is an alternative additive, which shows a product
quality and a granulation performance which is at least as good as
the bench mark UF. Different from UF solutions it is not harmful to
health or the environment, since it consists of components which
are biodegradable and are allowed to come into contact with food.
Additionally the application of the alternative additive bears the
possibility of utilizing the same urea granules for fertilizer,
technical and DEF applications. This extends the range of
application of urea ganules and reduces the efforts with regard to
logistics for all producers of multiple urea grades
drastically.
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T. Krawczyk
418 Nitrogen + Syngas 2017 International Conference &
Exhibition (London 27 February-2 March 2017)
1. MOTIVATION For more than three decades formaldehyde has been
known as a substance potentially causing cancer. Recent research
confirmes what has been suspected by most of its users. Over 80% of
today’s urea production which, exceeds 180 million tons per annum,
is used as fertilizer. This fertilizer grade urea, granular as well
as most prilled urea, is treated with formaldehyde mostly applied
as urea-formaldehyde pre-condensate (UF80, UF85). In order to
ensure certain process parameters such as
- a controlled granule growth rate and limited dust formation
during the production process, - a good product quality (crushing
strength, dust and caking),
remain stable over a long period of time, an additive is needed.
Although the formaldehyde is applied in the form of a
pre-condensate in which most of the formaldehyde has already
reacted with urea to form methylolurea, it still contains with
usually more than 23% by weight a substantial amount of free
formaldehyde. Therefore extensive safety precautions are required
in order to make the handling safe. The discussions about the
toxicity of formaldehyde, its carcinogenic and mutagenic effect on
humans and animals started in the early 1980s.. However the recent
Report on Carcinogens released by the National Toxicology Program
(NTP) of the US department of Health and Human Services leaves no
doubt with respect to the causal relationship between the exposure
to formaldehyde and cancer in humans. A vast number of
epidemiological studies have evaluated this relationship, including
cohort and case-control studies of different professional groups.
In particular, the National Cancer Institute (NCI) cohort of over
25,000 workers within industries producing or using formaldehyde
indicates the coincidence between the occupational exposure to
formaldehyde and nasopharyngea, sinonasal and lymphohematopeotic
cancer risk. While in the past formaldehyde was classified as
“suspected of causing cancer”, the International Agency for
Research on Cancer (IARC) as part of the World Health Organisation
(WHO) classified formaldehyde in 2011 as “known to may cause
cancer”.
Fig. 1: left: Pictogram for substances hazardous to the human
health as implemented by the GHS
right: classification of the carcinogenity of formaldehyde
The European Union has placed formaldehyde on the list of
Substances of Very High Concern. These compounds have been listed
in the Substitute It Now List (www.sinlist.org). The European Union
wants such compounds to be replaced as soon as possible. As a
consequence of numereous studies and the evidence of coincidence of
cancer and the exposure to formaldehyde the legal authorities and
dedicated organizations have adapted their classification regarding
the carcinogenity of formaldehyde. As a consequence of the
introduction of the GHS, the Globally Harmonized System of
Classification and Labelling of Chemicals and its subsequent
implementation within the American OSHA and the European CLP, the
hazards of formaldehyde are more than ever in focal point of
interest.
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Formaldehyde-free urea granules
Nitrogen + Syngas 2017 International Conference & Exhibition
(London 27 February-2 March 2017) 419
Although the carcinogenity of formaldehyde is evident, the
different examinations also show that there is a dependency of its
carcinogen effect and the related level of exposure in terms of
concentration and duration. The German Institute for Risk Assesment
(Bundesinstitut für Risikobewertung BfR) has conducted a study
which came to the conclusion that at concentration of below 124
microgram per norm cubic meter (0.1 ppm) the cancer risk is
neglieable. Vice versa, it can be concluded, that a repeated,
considerably higher or prolonged exposure to formaldehyde may
potentially cause cancer. Formaldehyde can be detected by its smell
at concentration of 0.07 to 0.12 ppm if the sensivity for the
detection is not reduced as a result of a prolonged exposure. This
means that if formaldehyde is detected by smell then the
concentration is already critical. Despite the difficulty of
finding an appropriate threshold value for the exposure of a worker
handling formaldehyde, the responsible authorities have adjusted
the permissible exposure limits to accommodate the aforementioned
findings as shown in table 1.
Table 1 Permissble Exposure Limits defined by different
authorities.
Specification mg/m3 (ppm) USA (Occupational Safety and Health
Administration - OSHA) PEL 0.92 (0.75) EU / Germany (TRGS 900) PEL
0.37 (0.3)
USA (National Institute for Occupational Safety and Health -
NIOSH) REL IDLH CREL
0.02 (0.016) (10h-TWA) 24.56 (20) 0.12 (0.1)
USA (American Conference of Governmental Industrial Hygenists –
ACGIH) TLV-C 0.37 (0.3) TWA – eight-hours time weighted average PEL
– permissible exposure limit Max – maximum value on short-time
basis REL – recommended exposure limit
IDLH – Immediately dangereous to life and health CREL – Ceiling
recommended exposure limit TLV-C – Threshold limit value
ceiling
In addition to the harmful nature of formaldehyde itself there
is an additional, often over looked, limitiation to the application
of urea-formaldehyde pre-condensate for urea production. The
formaldehyde is produced via the catalytic oxidation of methanol
therefore a certain amount of methanol remains in the UFC solution
(e.g. 0.1 – 0.3 %wt Methanol). This methanol as a volatile organic
compound is most likely released during the granulation process and
emitted to the atmosphere. Consequently, it adds a quite
significant amount of VOC emission to an ammonia/urea complex,
which might be limited by local authorities. The absence of an
adequate substitute and a partially ambiguous classification of
formaldehyde have limited the efforts for a substitution of
formaldehyde in by the fertilizer industry in the past, but this
has changed now.
2. EFFECTIVNESS OF A GRANULATION ADDITIVE Before elaborating the
route to such an alternative additive, it might be worthwile to
have a closer look on how formaldehyde acts as an additive within
the fluidized bed urea granulation process. Formaldehyde is both a
granulation aid, which plays a key role during the granulation
process itself, and an additive resulting in the desired product
quality parameters for transport and handling. The mixing of urea
with formaldehyde leads to a eutectical mixture. Although the urea
solution is completely mixable in liquid state, there is an
immiscibility of the corresponding solid phases. At the eutectic
point the corresponding melting point is the lowest possible within
all possible mixtures of urea and the additive and its reaction
products. The presence of such an eutectical point leads to a
liquid film on the surface of the granule which ensures a proper
pick up of the sprayed material.
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T. Krawczyk
420 Nitrogen + Syngas 2017 International Conference &
Exhibition (London 27 February-2 March 2017)
Fig. 2: Reaction scheme between urea and formaldehyde to form
urea formaldehyde resin
Furthermore formaldeyde reacts with urea to form methylolurea
via polycondensation. The nucleophile addition of the formaldehyde
occurs at different locations which leads to a cross linking
effect, that makes up the backbone of the latter granule. This
gives the product the desired crushing strength and reduces the
amount of abrasion dust.
3. DEVELOPMENT OF AN ALTERNATIVE ADDITIVE Starting point for
UFTs efforts to develop such an alternative additive was the
collaboration with an well known and experienced specialist in the
field of fertilizer additives: Holland Novochem. At first different
agents were tested on lab scale with respect to their ability to
act as a granulation additive for urea fluidized bed granulation.
Only components which are not harmful to health or the environment
were chosen. After identifying the potential specific effects of
the different agents with regard to the desired product properties
(e.g. particle growth, dust, hardness), different components and
mixtures were tested in UFT’s batch operated pilot plant located in
Leuna. With the data of the pilot plant trials it was possible to
basically generate a database to carry out a product design for the
alternative additives in terms of the desired urea product quality.
Much lower dose of additive with much higher effect In a second
campaign the potential additive compositions were applied in
different combinations and dosages and benchmarked against urea
formaldehyde. As a result, an alternative additive has been found
which is at least as effective as urea formaldehyde. UFT’s newly
developed alternative is composed of different functional polymers
in combination with a carboxylic acid. All of these agents are much
less toxic (non hazardous) and all of them have several FDA (Food
and Drug Administration) approvals for direct and/or indirect food
contact. The functional polymers are generally exempted from the
European REACH programme due to their polymeric nature.The
carboxylic acid is classified as a not hazardous substance. The
dosage of the alternative additive which is necessary in order to
achieve at least the same product quality as well as the same
process parameters is less than half of the amount of formaldehyde.
As shown in table 2 the new alternative additive formulations are
able to produce a granular urea product which shows at least the
same product quality as is possible with urea fromaldehyde.
Furthermore this product opens up additional fields of application
of the product not limited to the fertilizer industry.
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Formaldehyde-free urea granules
Nitrogen + Syngas 2017 International Conference & Exhibition
(London 27 February-2 March 2017) 421
Table 2 Comparison of product quality parameters for urea
granules treated with urea
formaldehyde and UFT’s alternative additive.
Treated with UFC (UF80)
Treated with Alternative Additive
Total Nitrogen % wt > 46.2 > 46.2 Biuret Content * % wt
0.7 – 0.8 0.7 – 0.8 Formaldehyde % wt 0.4 0 Alternative Additive %
wt 0 ~0.2 Moisture % wt 0.2 – 0.3 0.2 – 0.3 Crushing Strength kg
4.1 on ∅ 3.15 mm >4.1 on ∅ 3.15 mm Caking tendency - same or
less Dust % same or less
Application Fertilizer Fertilizer,DEF,Technical,
Cattle Feed
4. TECHNICAL AND DEF GRADE UREA GRANULES The fertilizer grade
urea demand is steadily growing due to the fact that there is a
steady growth of the world’s population and its standard of living
(change in diet towards more meat). However there is an even higher
increase for the demand of non-fertilizer grade urea. The IFA
forecasts the non-fertilizer demand will account for almost half of
the net increase of the global urea demand. The root cause of the
growth of the non-fertilizer urea demand is due to the increased
usage for UF resins and deNOx applications. Due to stricter
regulations concerning the emission figures for nitrogen oxides in
all kinds of diesel engines the demand for DEF (Diesel Exhaust
Fluid) has exploded in the last years. The annual production of DEF
used as a consumable for the selective catalytic reduction of
nitrogen oxides accounts for approximately 2.3 million metric tons
of urea. Its contribution to the global urea production in 2020 is
estimated to be more than 4 million metric tons. Currently the
price for DEF solution on the US market is at about 2.80 $ per
gallon, which can be converted into a urea price of more than 2,000
$ per metric ton assuming that the costs for deionized water can be
neglected. In other words, the revenue for almost the same product
is ten times the revenue of a regular fertilizer product.
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T. Krawczyk
422 Nitrogen + Syngas 2017 International Conference &
Exhibition (London 27 February-2 March 2017)
Fig. 3: Estimated development of future urea demand
The key for a today’s producer of fertilizer grade urea to enter
the DEF market is the product quality. In order to comply with the
requirements for the urea as raw material for DEF the composition
of the solid material dissolved in deionized water must fulfill the
requirements of the norms ISO 22241 or DIN 70070. Ultimately all
impurities or contaminations contained in the solid material will
be present in the final DEF solution. Primarily the tolerated
amount of only 5 ppm of aldehydes forms the main obstacle which
producers have to overcome. With UFT’s approach to a new
alternative additive it is possible to produce granular urea which
complies with the aforementioned norms specifying the requirements
for DEF with limited additional costs. Why is it interesting to
deliver DEF in solid form? Another major advantage of the
production of DEF in its most reduced form namely as a DEF
compliant solid which includes all benefits of a granular product
with respect to the mechanical properties, is that the supply chain
can be reduced to a minimum. The application of the alternative
additive is carried out by simple substitution of the content of
the urea formaldehyde tank. As it is illustrated by figure 4
neither additional equipment nor any other mechanical modification
to an exisiting plant is necessary. Furthermore, all provisions
within the urea synthesis to enable the production of DEF solution
such as tanks, piping or instrumentation etc. are obsolete. In
comparison to application ready DEF solution only a third of the
tonnage needs to be stored and transported. .
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Formaldehyde-free urea granules
Nitrogen + Syngas 2017 International Conference & Exhibition
(London 27 February-2 March 2017) 423
Fig. 4: Benefits of “DEF granules”
The final dissolving of the urea in deionized water poses the
only minor additional step within the supply chain. During the
Integer Emission Summit & DEF Forum in 2013 the feasibility of
the route via a solid distribution has been evaluated and found to
be the most cost effective. The costs for blending DEF from dry
urea were mentioned to be very low and amounting to the range of 5
to 7 $ cents per gallon. In line with these thoughts figure 5 shows
a comparison of the relative production costs for DEF starting from
the urea synthesis normed to the cost for the preparation via DEF
complaint granules. Obviously the difference in costs is directly
related to the transport distance between production and final
consumption.
Fig. 5: Comparison of Production costs for DEF via granular urea
and application ready DEF solution
5. SUMMARY AND OUTLOOK The perception of formaldehyde has
changed and the need for its substitution is stronger than ever.
Producers of urea already face difficulties to ensure the supply of
formaldehyde due to limitations by stricter regulations.
Furthermore studies, national and global regulations unambiguously
confirm that banning of formaldehyde will turn a urea plant into a
much healthier working place for the operators.
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T. Krawczyk
424 Nitrogen + Syngas 2017 International Conference &
Exhibition (London 27 February-2 March 2017)
Now a big step has been taken to be able to substitute
formaldehyde as a chemical with a very high concern within a urea
granulation plant. In addition UFT’s newly developed alternative
additive also offers the opportunity to gain an added value for
granular urea products far beyond fertilizer applications. It is
now as easy as it gets to enter the still growing and higly
profitable business of the DEF market for instance. Furthermore
also other technical applications of the granular formaldehyde-free
product are possible, which are more lucrative than the same
product on the rather stagnant fertilizer market. The envisaged
next step is the industrial application of the alternative
additive, which is carried out by means of a simple refill of an
existing urea formaldehyde tank with an alternative additive,
neither being harmful to humans nor to the environment.
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