Note: Descriptions are shown in the official language in which they were submitted.
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Description
Process for reducing fouling in the processing of liquid hydrocarbons
The present invention relates to a process for reducing fouling by liquid
hydrocarbons during the processing thereof at relatively high temperatures,
for
example in refinery operations.
In the course of processing, hydrocarbons such as crude oil and intermediates
in
mineral oil processing, for example, but also petrochemicals and petrochemical
intermediates, are generally heated to temperatures between 100 C and 550 C,
frequently between 200 C and 550 C. In heating and heat exchange systems too,
hydrocarbons used as heat carriers are exposed to such temperatures. In
virtually
all these cases, hydrocarbons used form unwanted breakdown products or by-
products at elevated temperatures, which can separate out and accumulate at
the
hot surfaces of the heat transferers. The formation of these deposits is
generally
attributed to the presence of comparatively unstable compounds, for example
oxidized and/or oxidizable hydrocarbons and olefinically unsaturated
compounds,
but this is also blamed on high molecular weight organic compounds and
inorganic
impurities. In specific cases, the extraneous substances which separate out
and
accumulate may even already be present in the raw material or precursor to be
processed. In the specific case of mineral oil distillation, the crude oils
used for
that purpose generally comprise constituents which lead to deposits, for
example
alkali metal and alkaline earth metal salts, compounds or complexes containing
transition metals, for example iron sulfide or porphyrins, sulfur compounds,
for
example mercaptans, nitrogen compounds, for example pyrroles, compounds
containing carbonyl groups or carboxyl groups, and polycyclic aromatics, for
example asphaltenes and/or coke particles. In addition, the hydrocarbons used
for
processing virtually always contain small amounts of dissolved oxygen.
The deposits which form in the course of processing of the hydrocarbons at
elevated temperatures and settle out on the surfaces in contact with the
liquid are
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referred to as fouling. They form particularly on the hot insides of pipes,
machines
or heat exchangers.
These deposits in the processes mentioned gradually reduce the bore of
pipelines
and vessels, which impairs both the process throughput and heat transfer.
Often,
the deposits even block filter screens, valves and traps, and as a result
cause
plant shutdowns for cleaning and maintenance. In all cases, these deposits are
additionally unwanted by-products which reduce the yield of target product and
hence lower the economic viability of the plant. In the case of heat exchange
systems, the deposits form an insulating layer on the surfaces present, which
restricts heat transfer. Consequently, the deposits necessitate frequent
shutdowns
of the plants for cleaning and in some cases even replacement thereof.
Accordingly, these deposits are highly undesirable in industry.
The above-described deposits are usually higher molecular weight materials,
the
consistency of which may range from tar through rubber and "popcorn" to coke.
The composition thereof may differ in nature and in many cases defies any
detailed analysis. They often contain a combination of carbonaceous phases
which are coke-like in nature, polymers and/or condensates which are formed
from
the hydrocarbons or impurities present therein by various mechanisms. Further
deposit constituents are frequently salts composed primarily of magnesium
chloride, calcium chloride and sodium chloride. The formation of polymers
and/or
condensates is attributed to catalysis by metal compounds, for example
compounds of copper or iron, which are present as impurities in the
hydrocarbons
to be processed. Metal compounds of this kind can, for example, accelerate the
hydrocarbon oxidation rate by promoting degenerative chain branching. The free
radicals formed can in turn trigger oxidation and polymerization reactions,
which
leads to the formation of resins and sediments. Often, relatively inert
carbonaceous deposits are enclosed by more adhesive condensates or polymers.
Fouling deposits are equally encountered in the petrochemical field, where
petrochemicals are either produced or purified. The deposits in this
environment
are primarily polymeric in nature and have a severe effect on the economic
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viability of the petrochemical operation. The petrochemical operations
include, for
example, the preparation of ethylene or propylene, or else the purification of
chlorinated hydrocarbons. Fouling is also observed in the processing of
biogenic
raw materials, for example in the processing of fatty acids and derivatives
thereof,
for example fatty acid esters.
To prevent the formation of deposits, oil-soluble, polar nitrogen compounds
are
used in many cases. These are predominantly reaction products of alkyl- or
alkenylsuccinic acids or anhydrides thereof with polyamines, which are
optionally
derivatized further.
For instance, US-3271295 discloses reaction products of alk(en)ylsuccinic
anhydrides with polyamines for prevention of deposits on metal surfaces in
heat
transferers in mineral oil refining.
WO-2011/014215 discloses the use of mono- and bisimides formed from
polyamines and 010- to Csoo-alkyl- or -alkenylsuccinic anhydrides for
prevention of
deposits in plants for mineral oil refining.
US-5342505 discloses the use of reaction products formed from
poly(alkenyl)succinimides with epoxyalkanols as antifoulants in liquid
hydrocarbons during the processing thereof at elevated temperatures
US-5171420 discloses reaction products formed from alkenylsuccinic anhydrides,
polyols, amines bearing hydroxyl groups, polyalkylenesuccinimides and
polyoxyalkyleneamines for prevention of deposits in the course of heating of
liquid
hydrocarbons. In the preferred embodiments, which are demonstrated by
examples, polyfunctional reagents which lead to highly branched structures are
used.
The reaction products of dicarboxylic acids with polyamines typically have a
relatively low molecular weight, since dicarboxylic acids, when condensed with
primary amines, react preferentially to give imides and form only minor
1
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proportions, if any, of diamides. Typically, the condensation is restricted to
the
reaction of the primary amino groups of the polyamine with one dicarboxylic
acid
each, such that the result is typically molecular weights of not more than
3000 g/mol. Higher molecular weight compounds, which are desirable for the
efficient reduction of fouling, are thus not obtainable in this way.
In addition, it is desirable from an economic point of view to use additives
having a
minimum nitrogen content. As a result, any increase in the nitrogen content of
the
products obtained in the thermal treatment of liquid hydrocarbons and any
occurrence of by-products and residues can be avoided. Both in the thermal
treatment of liquid hydrocarbons themselves and in the subsequent further use
of
the products, by-products and residues obtained, an elevated content of
nitrogen
compounds can lead to unwanted by-products and conversion products. For
example, the combustion thereof forms nitrogen oxides.
There have been no descriptions to date of higher molecular weight oligomeric
or
even polymeric compounds and more particularly of higher molecular weight
oligomeric or even polymeric nitrogen-free compounds for reduction of fouling
by
liquid hydrocarbons during the processing thereof at relatively high
temperatures.
Higher molecular weight and additionally nitrogen-free condensates of
.alkenylsuccinic acids are obtainable only by condensation with polyols, but
these
have been used to date only in entirely different applications.
For instance, EP-0809623 discloses oligomeric and polymeric bisesters of alkyl-
or
alkenyldicarboxylic acid derivatives and polyalcohols, and the use thereof as
solubilizers, emulsifiers and/or wash-active substances. Preferred
polyalcohols are
glycerol and oligomeric glycerols.
WO-2008/059234 discloses oligo- and polyesters based on alk(en)ylsuccinic
anhydrides and polyols having at least 3 hydroxyl groups and the use thereof
as
emulsifiers. These polymers are additionally useful in the oilfield as foaming
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agents in foam drilling fluids, as kinetic gas hydrate inhibitors and as
lubricants in
aqueous drilling fluids.
US-4216114 discloses condensation products of C9_18-alkyl- or -alkenylsuccinic
5 anhydrides with water-soluble polyalkylene glycols and polyols having at
least 3
011 groups and the use thereof for splitting water-in-oil emulsions.
US-3447916 discloses condensation polymers of alkenylsuccinic anhydrides,
polyols and fatty acids for lowering the pour point of hydrocarbon oils. In
these
polymers, the hydroxyl groups of the polyol are very substantially esterified.
DE-A-1920849 discloses condensation polymers of alkenylsuccinic anhydrides,
polyols having at least 4 OH groups and fatty acids for lowering the pour
point of
hydrocarbon oils. Preferably, the stoichiometry of the reactants used for the
condensation is selected such that the number of moles of OH groups and
carboxylic groups is the same, meaning that there is substantially complete
esterification.
WO-2011/076338 discloses low-temperature additives for middle distillates
comprising polycondensates of a polyol containing two primary OH groups and at
least one secondary OH group with a dicarboxylic acid or anhydride thereof or
ester thereof bearing a C16- to C40-alkyl radical or a C16- to C40-alkenyl
radical.
The additives used according to the prior art for suppression or at least for
reduction of fouling often show deficits in the efficacy thereof.
Consequently, there is a need for additives for more efficient suppression or
at
least for reduction of the formation of sparingly soluble deposits on the
apparatus
walls in the thermal treatment of hydrocarbons, for example in processing and
purifying plants, and also in heat exchange systems. These should preferably
be
nitrogen-free. Specifically, this need exists in the distillation of crude
oils and in the
further processing of the mineral oil distillation fractions which remain in
distillation
processes.
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It has been found that, surprisingly, specific polycondensates of dicarboxylic
acids
or dicarboxylic anhydrides bearing Cm-Caw-alkyl radicals or C16-C400-alkenyl
radicals and polyols having two primary and at least one secondary OH group
achieve the stated objects. It has been found that higher molecular weight
condensates having an essentially linear polymer backbone are particularly
useful.
The invention accordingly provides for the use of a polyester which bears
hydroxyl
groups and is preparable by polycondensation of a polyol containing two
primary
OH groups and at least one secondary OH group with a dicarboxylic acid or
anhydride thereof or ester thereof which bears a C16- to C400-alkyl radical or
a C16-
to C400-alkenyl radical as an antifoulant in the thermal treatment of liquid
hydrocarbon media within the temperature range from 100 to 550 C.
The present invention further provides a method for reducing fouling in a
liquid
hydrocarbon medium during the thermal treatment of the medium at temperatures
between 100 and 550 C, in which a polyester which bears hydroxyl groups and is
preparable by polycondensation of a polyol containing two primary OH groups
and
at least one secondary OH group with a dicarboxylic acid or anhydride thereof
or
ester thereof which bears a C16- to Cam-alkyl radical or a Cis- to C400-
alkenyl
radical is added to the liquid hydrocarbon before and/or during the thermal
treatment.
The invention further provides a method for increasing the service life of
plants for
thermal treatment of liquid hydrocarbon media within the temperature range
from
100 to 550 C, in which a polyester which bears hydroxyl groups and is
preparable
by polycondensation of a polyol containing two primary OH groups and at least
one secondary OH group with a dicarboxylic acid or anhydride thereof or ester
thereof which bears a C16- to C400-alkyl radical or a C16- to C400-alkenyl
radical is
added to a liquid hydrocarbon medium to be processed in the plant before
and/or
during the thermal treatment.
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The polyester bearing hydroxyl groups is generally obtained by the
polycondensation of a dicarboxylic acid bearing a C16- to C400-alkyl radical
or
-alkenyl radical, also referred to collectively hereinafter as C16-C400-
alk(en)yl
radical, with the primary hydroxyl groups of the polyol. It is preferable that
the
secondary OH groups remain essentially unesterified. The preferred structure
of
the polyester bearing hydroxyl groups can thus be represented, for example, by
formula (A):
0 R1 R3 0 ¨ 0 R1 R3 0
H0R
0R16 R5
R16¨ o,-H (A)
R2 R4R2 R4
- P- _m_ -9
in which
one of the R1 to R4 radicals is a C16-C400-alkyl or -alkenyl radical and
the other R1 to R4 radicals are each independently hydrogen or an alkyl
radical having 1 to 3 carbon atoms,
R5 is a C-C bond or an alkylene radical having 1 to 6
carbon atoms,
R16 is a hydrocarbyl group which bears at least
one
hydroxyl group and has 3 to 10 carbon atoms,
is a number from 1 to 100,
m is a number from 3 to 250,
is 0 or 1, and
is 0 or 1.
Preferred dicarboxylic acids which bear C16-C400-alkyl- and/or -alkenyl
radicals and
are suitable for preparation of the polyesters A) bearing hydroxyl groups
correspond to the formula (1)
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R1 R3
HOOC ¨ C¨ R5¨ C¨ COOH (1)
R2 R4
in which
one of the R1 to R4 radicals is a C18-C400-alkyl or -alkenyl radical and
the other R1 to R4 radicals are each independently hydrogen or an alkyl
radical having 1 to 3 carbon atoms, and
R5 is a C-C bond or an alkylene radical having 1
to 6
carbon atoms.
More preferably, one of the R1 to R4 radicals is a C18-C400-alkyl- or -alkenyl
radical,
one is a methyl group and the rest are hydrogen. In a specific embodiment, one
of
the R1 to R4 radicals is a C18-C400-alkyl- or -alkenyl radical and the others
are
hydrogen. In a particularly preferred embodiment, R5 is a C-C single bond.
More
particularly, one of the R1 to R4 radicals is a C18-C400-alkyl- or -alkenyl
radical, the
other R1 to R4 radicals are hydrogen and R5 is a C-C single bond.
The dicarboxylic acids or anhydrides thereof bearing alkyl- and/or -alkenyl
radicals
can be prepared by known processes. For example, they can be prepared by
heating ethylenically unsaturated dicarboxylic acids with olefins or with
chloroalkanes. Preference is given to the thermal addition of olefins onto
ethylenically unsaturated dicarboxylic acids or anhydrides thereof ("ene
reaction"),
which is typically conducted at temperatures between 100 and 250 C. The
dicarboxylic acids and dicarboxylic anhydrides bearing alkenyl radicals which
are
formed can be hydrogenated to dicarboxylic acids and dicarboxylic anhydrides
bearing alkyl radicals. Dicarboxylic acids and anhydrides thereof preferred
for the
reaction with olefins are maleic acid and more preferably maleic anhydride.
Additionally suitable are itaconic acid, citraconic acid and anhydrides
thereof, and
the esters of the aforementioned acids, especially those with lower C1-C8-
alcohols,
for example methanol, ethanol, propanol and butanol.
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In a first preferred embodiment, one of the R1 to R4 radicals is a linear C16-
C40-
alkyl- or -alkenyl radical. For the preparation of such dicarboxylic acids or
anhydrides thereof bearing alk(en)yl radicals, preference is given to using
olefins
having 16 to 40 carbon atoms and especially having 18 to 36 carbon atoms, for
example having 19 to 32 carbon atoms. In a particularly preferred embodiment,
mixtures of olefins having different chain lengths are used. Preference is
given to
using mixtures of olefins having 18 to 36 carbon atoms, for example mixtures
of
olefins in the C20-C22, C20-C24, C24-C28, C26-C28, C30-C36 range. Olefin
mixtures
may also comprise minor proportions of shorter- and/or longer-chain olefins
compared to the range specified, for example hexene, heptene, octene, nonene,
decene, undecene, dodecene, tetradecene and/or olefins having more than 40
carbon atoms. Preferably, the proportion of the shorter- and longer-chain
olefins in
the olefin mixture is, however, not more than 10% by weight. More
particularly, it is
between 0.1 and 8% by weight, for example between 1 and 5% by weight.
Olefins particularly preferred for the preparation of the dicarboxylic acids
or
anhydrides thereof bearing C16-C40-alk(en)yl radicals have a linear or at
least
substantially linear alkyl chain. "Linear or substantially linear" is
understood to
mean that at least 50% by weight, preferably 70 to 99% by weight, especially
75 to
95% by weight, for example 80 to 90% by weight, of the olefins have a linear
component having 16 to 40 carbon atoms and especially having 18 to 36 carbon
atoms, for example having 19 to 32 carbon atoms. In a specific embodiment, a-
olefins, wherein the C=C double bond is at the chain end, are used.
Particularly
useful olefins have been found to be technical grade alkene mixtures. These
contain preferably at least 50% by weight, more preferably 60 to 99% by weight
and especially 70 to 95% by weight, for example 75 to 90% by weight, of
terminal
double bonds (a-olefins). In addition, they may contain up to 50% by weight,
preferably 1 to 40% by weight and especially 5 to 30% by weight, for example
10
to 25% by weight, of olefins having an internal double bond, for example
having
vinylidene double bonds having the structural element R17¨ CH = C(CH3)2 where
R17 is an alkyl radical having 12 to 36 carbon atoms and especially having 14
to
32 carbon atoms, for example having 15 to 28 carbon atoms. In addition, minor
amounts of secondary components present for technical reasons, for example
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paraffins, may be present, but preferably not more than 5% by weight.
Particular
preference is given to olefin mixtures containing at least 75% by weight of
linear a-
olefins having a carbon chain length in the range from C20 to C24-
5 In a further preferred embodiment, one of the R1 to R4 radicals is a C41-
C400-alkyl-
or -alkenyl radical and especially a C50- to C300-alkyl or -alkenyl radical,
for
example a C55- to C200-alkyl- or -alkenyl radical. Preferably, this alk(en)yl
radical is
branched. Additionally preferably, these C41-C400-alk(en)yl radicals derive
from
polyolefins preparable by polymerization of monoolefins having 3 to 6 and
10 especially having 3, 4 or 5 carbon atoms. Particularly preferred
monoolefins as
base structures for the polyolefins are propylene and isobutene, which give
rise to
poly(propylene) and poly(isobutene) as polyolefins. Preferred polyolefins have
an
alkylvinylidene content of at least 50 mol%, particularly of at least 70 mol%
and
especially at least 80 mol%, for example at least 85 mol%. "Alkylvinylidene
content" is understood to mean the content in the polyolefins of structural
units
which result from compounds of the formula (3):
R6
H2C (3)
R7
in which R6 or R7 is methyl, ethyl or propyl and especially methyl and the
other
group is an oligomer of the C3-C6-olefin. The alkylvinylidene content can be
determined, for example, by means of 1H NMR spectroscopy. The number of
carbon atoms in the polyolefin is between 41 and 400. In a preferred
embodiment
of the invention, the number of carbon atoms is between 50 and 3000 and
especially between 55 and 200. The parent polyolefins of the C41-C400-alkyl-
or
-alkenyl radical are obtainable, for example, by ionic polymerization and are
available as commercial products (e.g. Glissopale, polyisobutenes from BASF
with
different alkylvinylidene content and molecular weight). Also suitable in
accordance with the invention are mixtures of various polyolefins, in which
case
these may differ, for example, in terms of the parent monomers, the molecular
weights and/or the alkylvinylidene content.
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=
Preferred polyesters bearing hydroxyl groups are preparable by reaction of
alkyl-
or alkenylsuccinic acids and/or anhydrides thereof bearing a C16-C.400-alkyl-
or
-alkenyl radical with polyols bearing two primary and at least one secondary
hydroxyl group.
Preferred polyols may be monomeric, oligomeric or polymeric in terms of
structure.
Polymers and oligomers are referred to collectively as polymers. R16 in
formula A)
is preferably a radical of the formula (2)
¨ (CH2)r¨ (CH(OH))t¨ (CI-12)8¨ (2)
in which
is a number from 1 to 6,
r and s are each independently a number from 1 to 9 and
t+r+s is a number from 3 to 10.
In monomeric polyols, n in formula A) is 1. Preferred monomeric polyols have
three to 10 and especially four to six carbon atoms. They additionally have at
least
one and preferably 1 to 6, for example 2 to 4, secondary OH groups, but not
more
than one OH group per carbon atom. Suitable monomeric polyols are, for
example, glycerol, 1,2,4-butanetriol, 1,2,6-trihydroxyhexane, and also reduced
carbohydrates and mixtures thereof. Reduced carbohydrates are understood here
to mean polyols which derive from carbohydrates and bear two primary and two
or
more secondary OH groups. Particularly preferred reduced carbohydrates have 4
to 6 carbon atoms. Examples of reduced carbohydrates are erythritol, threitol,
adonitol, arabitol, xylitol, dulcitol, mannitol and sorbitol. A particularly
preferred
monomeric polyol is glycerol.
In polymeric polyols, n in formula A) is a number from 2 to 100, preferably a
number from 2 to 50, more preferably a number from 3 to 25 and especially a
number from 4 to 20. Preferred polymeric polyols have six to 150, especially
eight
to 100 and particularly nine to 50 carbon atoms. They bear at least one,
preferably
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two to 50 and especially three to 15 secondary OH groups, but not more than
one
OH group per carbon atom. Polymeric polyols suitable in accordance with the
invention are preparable, for example, by polycondensation of polyols having
two
primary and at least one secondary OH group. A preferred polymeric polyol is
poly(glycerol). "Poly(glycerol)" is especially understood to mean structures
derivable by polycondensation from glycerol. The condensation level of
poly(glycerols) preferred in accordance with the invention is between 2 and
50,
more preferably between 3 and 25 and especially between 4 and 20, for example
between 5 and 15.
The preparation of poly(glycerol) is known in the prior art. It can be
prepared, for
example, via addition of 2,3-epoxy-1-propanol (glycide) onto glycerol. In
addition,
poly(glycerol) can be prepared by polycondensation, as known per se, of
glycerol.
The reaction temperature in the polycondensation is generally between 150 and
300 C, preferably between 200 and 250 C. The polycondensation of glycerol is
normally conducted at atmospheric pressure. Catalyzing acids include, for
example, HCI, H2SO4, organic sulfonic acids or H3PO4; catalyzing bases
include,
for example, NaOH or KOH. The catalysts are added to the reaction mixture
preferably in amounts of 0.01 to 10% by weight, more preferably 0.1 to 5% by
weight, based on the weight of the reaction mixture. The polycondensation of
glycerol can be conducted without solvent, or else in the presence of solvent.
If the
polycondensation is effected in the presence of solvent, the proportion
thereof in
the reaction mixture is preferably 0.1 to 70% by weight, for example 10 to 60%
by
weight. Preferred organic solvents here are the solvents also used and
preferred
for the condensation of the dicarboxylic acid, anhydride thereof or ester
thereof
bearing alk(en)yl radicals with the polyol. The polycondensation of glycerol
generally takes 3 to 10 hours. This process is also applicable mutatis
mutandis to
the polycondensation of other polyols.
The dicarboxylic acid, anhydride thereof or ester thereof bearing alk(en)yl
radicals
are converted to the polyester bearing hydroxyl groups preferably in a molar
ratio
of 1:2 to 2:1, more preferably in a molar ratio of 1:1.5 to 1.5:1 and
especially in a
molar ratio of 1:1.2 to 1.2:1, for example in a equimolar ratio. More
preferably, the
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conversion is effected with an excess of polyol. In this context, molar
excesses of
1 to 10 mol% and especially 1.5 to 5 mol% based on the amount of dicarboxylic
acid used have been found to be particularly useful.
The polycondensation of the dicarboxylic acid, anhydride thereof or ester
thereof
bearing alkyl radicals with the polyol is effected preferably by heating Cm-am-
-
alkyl- or ¨alkenyl-substituted dicarboxylic acid or the anhydride or ester
thereof
together with the polyol to temperatures above 100 C and preferably to
temperatures between 120 and 320 C, for example to temperatures between 150
and 290 C. For adjustment of the molecular weight, which is important for the
efficacy of the polyester bearing hydroxyl groups, it is typically necessary
to
remove the water of reaction or the alcohol of reaction, which can be
effected, for
example, by distillative removal. Azeotropic removal by means of suitable
organic
solvents is also suitable for this purpose. Preferred solvents for the
polycondensation of the dicarboxylic acid, anhydride thereof or ester thereof
bearing alk(en)yl radicals with the polyol are relatively high-boiling, low-
viscosity
solvents. Particularly preferred solvents are aliphatic and aromatic
hydrocarbons
and mixtures thereof. Aliphatic hydrocarbons preferred as solvents have 9 to
20
carbon atoms and especially 10 to 16 carbon atoms. They may be linear,
branched and/or cyclic. They are preferably saturated or at least
substantially
saturated. Aromatic hydrocarbons preferred as solvents have 7 to 20 carbon
atoms and especially 8 to 16, for example 9 to 13, carbon atoms. Preferred
aromatic hydrocarbons are mono-, di-, tri- and polycyclic aromatics. In a
preferred
embodiment, these bear one or more, for example two, three, four, five or
more,
substituents. In the case of a plurality of substituents, these may be the
same or
different. Preferred substituents are alkyl radicals having 1 to 20 and
especially
having 1 to 5 carbon atoms, for example methyl, ethyl, n-propyl, isopropyl, n-
butyl, =
isobutyl, tent-butyl, n-pentyl, isopentyl, tert-pentyl and neopentyl radical.
Examples
of suitable aromatics are alkylbenzenes and alkylnaphthalenes. For example,
aliphatic and/or aromatic hydrocarbons or hydrocarbon mixtures, e.g. petroleum
fractions, kerosene, decane, pentadecane, toluene, xylene, ethylbenzene or
commercial solvent mixtures such as Solvent Naphtha, Shellsol AB, Solvesso
150, Solvesso 200, Exxsol products, ISOPAR products and Shellsol D
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products, are particularly suitable. As well as the solvents based on mineral
oils,
solvents based on renewable raw materials and synthetic hydrocarbons
obtainable, for example, from the Fischer-Tropsch process, are suitable as
solvents. Also suitable are mixtures of the solvents mentioned. If the
polycondensation is effected in the presence of solvent, the proportion
thereof in
the reaction mixture is preferably 1 to 75% by weight and especially 10 to 70%
by
weight, for example 20 to 60% by weight. The condensation is preferably
conducted without solvent.
For acceleration of the polycondensation, it has often been found to be useful
to
conduct the polycondensation in the presence of homogeneous catalysts,
heterogeneous catalysts or mixtures thereof. Preferred catalysts here are
acidic
inorganic, organometallic or organic catalysts and mixtures of two or more of
these
catalysts.
Acidic inorganic catalysts in the context of the present invention are, for
example,
sulfuric acid, phosphoric acid, phosphonic acid, hypophosphorous acid,
aluminum
sulfate hydrate, alum, acidic silica gel and acidic aluminum hydroxide.
Additionally
usable as acidic inorganic catalysts are, for example, aluminum compounds of
the
formula Al(0R15)3 and titanates of the formula Ti(0R15)4, where the R15
radicals
may each be the same or different and are each independently selected from
C1-C10-alkyl radicals, for example methyl, ethyl, n-propyl, isopropyl, n-
butyl,
isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl,
1,2-
dimethylpropyl, isoamyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, 2-ethylhexyl,
n-nonyl
or n-decyl, C3-C12-cycloalkyl radicals, for example cyclopropyl, cyclobutyl,
cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl,
cycloundecyl and cyclododecyl; preference is given to cyclopentyl, cyclohexyl
and
cycloheptyl. Preferably, the R15 radicals in Al(0R15)3 and Ti(0R15)4 are each
the
same and are selected from isopropyl, butyl and 2-ethylhexyl.
Preferred acidic organometallic catalysts are, for example, selected from
dialkyltin
oxides (R15)2SnO where R15 is as defined above. A particularly preferred
representative of acidic organometallic catalysts is di-n-butyltin oxide,
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commercially available as "oxo-tin" or as the Fascat brand.
Preferred acidic organic catalysts are acidic organic compounds having, for
example, phosphate groups, sulfo groups, sulfate groups or phosphonic acid
5 groups. Particularly preferred sulfonic acids contain at least one sulfo
group and at
least one saturated or unsaturated, linear, branched and/or cyclic hydrocarbyl
radical having 1 to 40 carbon atoms and preferably having 3 to 24 carbon
atoms.
Especially preferred are aromatic sulfonic acids and specifically
alkylaromatic
monosulfonic acids having one or more C1-C28-alkyl radicals and especially
those
10 having C3-C22-alkyl radicals. Suitable examples are methanesulfonic
acid,
butanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid,
xylenesulfonic
acid, 2-mesitylenesulfonic acid, 4-ethylbenzenesulfonic acid, isopropylbenzene-
sulfonic acid, 4-butylbenzenesulfonic acid, 4-octylbenzenesulfonic acid,
dodecyl-
benzenesulfonic acid, didodecylbenzenesulfonic acid and naphthalenesulfonic
15 acid. It is also possible to use acidic ion exchangers as acidic organic
catalysts, for
example poly(styrene) resins which bear sulfo groups and have been crosslinked
with about 2 mol% of divinylbenzene.
For the performance of the process according to the invention, particular
preference is given to boric acid, phosphoric acid, polyphosphoric acid and
polystyrenesulfonic acids. Especially preferred are titanates of the formula
Ti(0R15)4and specifically titanium tetrabutoxide and titanium
tetraisopropoxide.
If it is desirable to use acidic inorganic, organometallic or organic
catalysts,
according to the invention, 0.01 to 10% by weight, preferably 0.02 to 2% by
weight, of catalyst is used. In a specific embodiment, the condensation is
effected
without addition of catalysts.
In a preferred embodiment, for adjustment of the molecular weight, minor
amounts
of the dicarboxylic acids, anhydrides thereof or esters thereof bearing
alk(en)yl
radicals are replaced in the reaction mixture by Ci- to C18-monocarboxylic
acids,
preferably C2- to C16-monocarboxylic acids and especially C3- to C14-
monocarboxylic acids, for example C4- to C12-monocarboxylic acids. At the same
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time, however, not more than 20 mol% and preferably 0.1 to 10 mol%, for
example
0.5 to 5 mol%, of the dicarboxylic acids, anhydrides thereof or esters thereof
bearing alk(en)yl radicals is replaced by one or more monocarboxylic acids. In
addition, minor amounts, for example up to 10 mol% and especially 0.01 to 5
mol% of the alk(en)ylsuccinic acids or anhydrides thereof may also be replaced
by
further dicarboxylic acids, for example succinic acid, glutaric acid, maleic
acid
and/or fumaric acid. More preferably, the polyesters bearing hydroxyl groups
are
prepared in the absence of monocarboxylic acids.
In a further preferred embodiment, for adjustment of the molecular weight,
minor
amounts of the polyol are replaced in the reaction mixture by C1- to C30-
monoalcohols, preferably C2- to C24-monoalcohols and especially C3- to
C18-monoalcohols, for example C4- to C12-monoalcohols. At the same time,
preferably not more than 20 mol% and more preferably 0.1 to 10 mol%, for
example 0.5 to 5 mol%, of the polyol is replaced by one or more monoalcohols.
More preferably, the polyesters bearing hydroxyl groups are prepared in the
absence of monoalcohols. In addition, the polyol bearing two primary and at
least
one secondary hydroxyl groups may also be replaced by one or more diols in
minor amounts of up to 10 mol%, for example 0.01 to 5 mol%. Preference is
given
here to diols, for example ethylene glycol, propylene glycol and/or neopentyl
glycol. More preferably, the polyesters bearing hydroxyl groups are prepared
in the
absence of diols.
In a further preferred embodiment, to increase the molecular weight, minor
amounts of the polyol bearing two primary and at least one secondary OH group
are replaced in the reaction mixture by polyols having three or more primary
OH
groups, for example having four, five, six or more primary OH groups. At the
same
time, preferably not more than 10 mol% and more preferably 0.1 to 8 mol%, for
example 0.5 to 4 mol%, of the polyol bearing two primary and at least one
secondary OH group is replaced by a polyol having three or more primary OH
groups. Suitable polyols having three or more primary OH groups are, for
example, trimethylolethane, trimethylolpropane and pentaerythritol.
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The mean condensation level of the polyesters bearing hydroxyl groups used in
accordance with the invention is preferably between 4 and 200, more preferably
between 5 and 150, especially between 7 and 100 and particularly between 10
and 70, for example between 15 and 50, repeat dicarboxylic acid and polyol
units.
The condensation level is understood here to mean the sum of m + p + q as per
formula (A). The weight-average molecular weight Mw of the polyesters bearing
hydroxyl groups, determined by means of GPC in THF against poly(ethylene
glycol) standards, is preferably between 2000 g/mol and 600 000 g/mol. In the
case of polyesters which derive from dicarboxylic acids bearing C16-C40-
alk(en)yl
radicals, it is more preferably between 2000 and 100 000 g/mol and especially
between 3000 and 50 000 g/mol, for example between 4000 and 20 000 g/mol. In
the case of polyesters which derive from dicarboxylic acids bearing C41-C400-
alk(en)yl radicals, it is more preferably between 3000 and 500 000 g/mol,
particularly between 5000 and 200 000 g/mol and especially between 8000 and
150 000 g/mol, for example between 10 000 and 100 000 g/mol.
Preferably, the acid number of the polyesters bearing hydroxyl groups is less
than
40 mg KOH/g and more preferably less than 30 mg KOH/g, for example less than
mg KOH/g. The acid number can be determined, for example, by titration of the
20 polymer with alcoholic tetra-n-butylammonium hydroxide solution in
xylene/isopropanol. Additionally preferably, the hydroxyl number of the
polyesters
is between 40 and 500 mg KOH/g, more preferably between 50 and 300
mg KOH/g and especially between 60 and 250 mg KOH/g. The hydroxyl number
can, after reaction of the free OH groups with isocyanate, be ascertained by
means of 1H NMR spectroscopy, by quantitative determination of the urethane
formed.
Preferably, the polyesters bearing hydroxyl groups used in accordance with the
invention are nitrogen-free. "Nitrogen-free" is understood in accordance with
the
invention to mean that the nitrogen content thereof is below 1000 ppm by
weight
and more preferably below 100 ppm by weight and especially below 10% by
weight, for example below 1 ppm by weight. The nitrogen content can be
determined, for example, according to Kjeldahl.
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The term "liquid hydrocarbon medium", according to the invention, represents
various different mineral oil hydrocarbons and petrochemicals. For example,
mineral oil hydrocarbon feedstocks including crude oils and fractions
obtainable
therefrom, for example naphtha, gasifier fuel, kerosene, diesel, jet fuel,
heating oil,
gas oil, vacuum residues inter alia are covered by this definition. Examples
of
petrochemicals are olefinic or naphthenic process streams, aromatic
hydrocarbons
and derivatives thereof, ethylene dichloride and ethylene glycol. Likewise
covered
by the term "liquid hydrocarbon media" are hydrocarbons used as heat carriers,
for
example fused and/or substituted aromatics. Additionally covered by this
definition
are biogenic raw materials and products obtainable from biogenic raw materials
by
processing, for example animal and vegetable oils and fats and derivatives
thereof, for example fatty acid alkyl esters. The liquid hydrocarbon media may
also
comprise constituents not consisting of hydrocarbons, for example salts,
minerals
and organometallic compounds.
The polyesters used in accordance with the invention are added to the liquid
hydrocarbon media preferably in amounts of 0.5 to 5000 ppm by weight, more
preferably of 1.0 to 1000 ppm by weight, for example of 2 to 500 ppm by
weight.
The polyesters may be dispersed or dissolved in the liquid hydrocarbon medium.
They are preferably dissolved.
For easier handling, the polyesters used in accordance with the invention are
preferably dissolved or dispersed in a polar or nonpolar organic solvent and
added
to the liquid hydrocarbon medium as a concentrate. Preferred solvents here are
the solvents and solvent mixtures already mentioned as solvents for the
condensation reaction between dicarboxylic acid and polyol. Particular
preference
is given to aromatic solvents. Preferably, the proportion of the polyester in
the
concentrate is 5 to 95% by weight, more preferably 10 to 80% by weight and
especially 20 to 70% by weight, for example 25 to 60% by weight.
The polyester is preferably added to the liquid hydrocarbon medium prior to
the
thermal treatment thereof. The addition can be undertaken batchwise, for
example
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into the storage vessel of the liquid hydrocarbon medium, or continuously into
the
feed line to the heat treatment plant. The addition is preferably effected at
a site
where the temperature of the liquid hydrocarbon medium is at least 10 C and
especially at least 20 C, for example at least 50 C, below the maximum heat
treatment temperature. Especially in the case of hydrocarbon media of
relatively
high viscosity, it has often been found to be useful to promote the mixing of
the
polyester into the liquid hydrocarbon medium by means of static or dynamic
mixing
apparatus.
Particular advantages are shown by the inventive use of polyesters bearing
hydroxyl groups and by the method that utilizes them in the processing or
treatment of liquid hydrocarbon media above 100 C, especially between 150 and
500 C and particularly between 200 C and 480 C, for example between 250 C
and 450 C.
The polyesters used in accordance with the invention can be used together with
one or more further additives. Preferred further additives are pour point
depressants and demulsifiers, the latter preferably based on alkoxylated
alkylphenol-aldehyde resins.
The inventive use of polyesters bearing hydroxyl groups in the thermal
treatment
of liquid hydrocarbon media leads to a reduction in fouling superior to the
prior art
additives and often also to the substantial and in some cases even complete
suppression thereof. As a result, the energy requirement in the processing of
liquid
hydrocarbon is lowered and the throughput of the plant and the yield of target
product are increased.
The method of the invention is generally suitable for reducing and often even
for
suppressing fouling in the processing of liquid hydrocarbon media at
relatively high
temperatures. This lowers the energy requirement of the process and increases
the throughput of the plant and the yield of target product. The reduction in
fouling
reduces the frequency of maintenance shutdowns for removal of deposits and
hence increases the plant availability.
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For instance, the methods of the invention have been used successfully for
reduction of fouling in crude oil distillation, in the processing of
intermediates in
mineral oil processing and in the processing of petrochemicals, and also of
5 petrochemical intermediates, for example of gases, oils and reforming
feedstocks,
chlorinated hydrocarbons and liquid products from olefin plants, for example
of
bottoms phases from deethanization. The methods have likewise been used
successfully for reduction and often for suppression of fouling by
hydrocarbons
used as heating media on the 'hot side' of heat exchange systems.
The suitability of the additives used in accordance with the invention for
suppression or at least for reduction of fouling by liquid hydrocarbons in the
course
of thermal treatment thereof can be measured, for example, with commercially
available HLPS (Hot Liquid Process Simulation) systems. In these systems, the
oil
to be treated thermally is pumped continuously through a capillary with a
heating
element present therein. As a result of fouling, deposits gradually form on
the
heating element, which impair heat transfer and lead to a pressure drop over
the
capillary. The extent of fouling can be assessed, for example, via the drop in
the
temperature at the outlet of the capillary. A significant drop in the
temperature
during the experiment indicates the occurrence of fouling. Measurements of
this
kind are generally regarded as a measure for assessment of the tendency of an
oil
to fouling in heat exchangers.
Examples
The a-olefins used were commercially available mixtures of 1-alkenes or
poly(isobutenes) having the compositions specified. The acid numbers were
determined by titration of an aliquot of the reaction mixture with alcoholic
tetra-n-butylammonium hydroxide solution in xylene/isopropanol. The hydroxyl
numbers were determined, after reacting the free OH groups of the polymers
with
isocyanate, by means of 1H NMR spectroscopy, by quantitative determination of
the urethane formed. The values reported are based on the solvent-free
polymers.
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The molecular weights were determined by means of lipophilic gel permeation
chromatography in THE against poly(ethylene glycol) standards and detection by
means of an RI detector.
Polyesters used:
P1) Copolymer of equimolar proportions of C20-24-alkenylsuccinic anhydride
(prepared by thermal condensation of maleic anhydride with technical-
grade C20-24-olefin containing, as main constituents, 43% C20-, 35%
C22- and 17% C24-olefin, with 90% a-olefins and 7.5% linear internal olefins)
and glycerol. The reactants, in the form of a 50% solution in Shellsol AB
(aromatic solvent mixture having a boiling range of about 185-215 C), were
heated to 150 C while stirring until the acid number remained constant. The
water which formed was distilled off. The acid number of the polymer thus
prepared was 7.8 mg KOH/g, the hydroxyl number was 98 mg KOH/g and
the weight-average molecular weight was 6100 g/mol.
P2) Copolymer prepared in analogy to example P1) from equimolar proportions
of C20124-alkenyisuccinic anhydride (prepared by thermal condensation of
maleic anhydride with technical-grade C20124-olefin containing, as main
constituents, 43% C20-, 35% C22- and 17% C24-olefin, with 90% a-olefins
and 7.5% linear internal olefins) and poly(glycerol) having a mean
condensation level of 3. The acid number of the polymer was
6.5 mg KOH/g, the hydroxyl number was 195 mg KOH/g and the weight-
average molecular weight was 8700 g/mol.
P3) Copolymer prepared in analogy to example P1) from equimolar proportions
of C26128-alkenylsuccinic anhydride (prepared by thermal condensation of
maleic anhydride with technical-grade C26-28-olefin containing, as main
constituents, 57% C26-, 39% Ca- and 2.5% C30,-olefin, with 85% a-olefins,
4% linear internal olefins and 9% branched olefins) and glycerol. The acid
number of the polymer was 10.4 mg KOH/g, the hydroxyl number was
68 mg KOH/g and the weight-average molecular weight was 9100 g/mol.
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P4) Copolymer of C20124-alkenylsuccinic anhydride as per example P1, 0.7
molar
equivalent of glycerol and 0.3 molar equivalent of behenic acid. The acid
number of the polymer was 15 mg KOH/g, the hydroxyl number was
32 mg KOH/g and the weight-average molecular weight was 1800 g/mol.
P5) Copolymer of equimolar proportions of C20-24-alkenylsuccinic anhydride
and
ethylene glycol in analogy to example P1. The acid number of the polymer
thus prepared was 8.2 mg KOH/g, the hydroxyl number was 2 mg KOH/g
and the weight-average molecular weight was 5700 g/mol (comparative
example).
P6) C224-Alkenylsuccinic anhydride as per example P1, reacted with 2 molar
equivalents of triethylenetetramine. The reactants, in the form of a 50%
solution in ShelIsol AB, were heated to 150 C while stirring until the acid
number remained constant. The water which formed was distilled off. The
acid number of the polymer thus prepared was 10.2 mg KOH/g and the
weight-average molecular weight was 1000 g/mol (comparative example).
P7) Copolymer prepared in analogy to example P1) from equimolar proportions
of poly(isobutenyl)succinic anhydride (prepared by thermal condensation of
maleic anhydride with poly(isobutene) having a mean molecular weight Mn
of 1000 g/mol and an alkylvinylidene content of 87 mo(%) and glycerol. The
acid number of the polymer was 8.6 mg KOH/g, the hydroxyl number was
47 mg KOH/g and the weight-average molecular weight was 14 000 g/mol.
P8) Copolymer prepared in analogy to example P1) from equimolar proportions
of poly(isobutenyl)succinic anhydride (prepared by thermal condensation of
maleic anhydride with poly(isobutene) having a mean molecular weight Mn
of 2300 g/mol and an alkylvinylidene content of 81 mol%) and poly(glycerol)
having a mean condensation level of 5. The acid number of the polymer
was 7.8 mg KOH/g, the hydroxyl number was 110 mg KOH/g and the
weight-average molecular weight was 21 000 g/mol.
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The efficacy of the additives in terms of their ability to prevent or reduce
fouling by
mineral oils on hot surfaces was tested with the aid of a modified Hot Liquid
Process Simulation (HLPS) system from Alcor. In the HLPS system, the oil to be
examined was pumped continuously from a stirred and heated reservoir vessel
through an electrically heated heating element mounted in a stainless steel
capillary (= hot capillary), before being returned to the reservoir vessel.
During the
experiment, the maximum oil temperature attained after switching on the
heating
(the surface temperature of the heating element was about 400 C) was firstly
registered at the output of the stainless steel capillary (Ti). Secondly, the
oil
temperature was registered at the same point after an experimental duration of
5
hours (T2). Since the deposits formed on the heating element as a result of
fouling
have low thermal conductivity, the maximum temperature initially attained
correlates indirectly (low initial temperature T1 implies immediate onset of
fouling),
and the difference in the temperatures T2 and T1 directly, with the extent of
fouling.
For each experiment, about 500 ml of the oil sample to be examined were
introduced into the reservoir vessel and heated to about 150 C for better
pumpability. The oil was then pumped at a volume flow rate of 3 ml/min through
the stainless steel capillary which has been provided with a clean heating
element
with a bare surface. The heating element was then heated to a temperature of
about 400 C for test oil 1, about 375 C for test oil 2 or about 390 C for test
oil 3,
and the maximum oil temperature which was then established at the capillary
outlet was noted (T1). After a run time of 5 hours, the oil temperature that
was
then present at the end of the stainless steel capillary (T2) was noted and
the
experiment was ended. A high maximum temperature Ti and a low AT
(AT = T2 - Ti) indicate low coverage of the surface of the heating element
with
insulating deposits and hence effective suppression of fouling.
The following test oils were used for the assessment of the fouling-reducing
effect
of the additives:
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. .
_
Test oil 1 2 3
Origin Brazil Malaysia
Thailand
API gravity @15 C [ API] 25.7 47.2
11.4
Viscosity [mPas] 61(25 C)
5 (25 C) 160 (50 C)
Density [g/cm3] 0.900 (20 C)
0.792 (20 C) 0.990 (16 C)
Pour point [ C] -27 +18
+ 33
Asphaltene content [% by wt.] 7.9 3.2
10.3
The viscosity was determined to ASTM D-445, and the density to DIN EN ISO
12185. The pour point was determined to ASTM D-97. The asphaltene content
was determined to IP 143.
Experimental results in test oil 1
Measure- Additive Dosage T1 T1 AT
Fouling
ment rate (t = 0) (t = 5 h)
reduction
[ C] [ C] [ C]
Mi
EPPrrll
1 none - 278 256 22
0
2 P1 5 281 266 15
32
3 P2 5 282 268 14
36
4 P3 5 281 266 15
32
5 P4 5 280 262 18
18
6 (comp.) P5 5 279 257 22
0
7 (comp.) P6 5 280 261 19
14
8 P1 10 283 269 14
36
9 P2 10 285 274 11
50
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10 P3 10 283 271 12 45
11 P4 10 281 265 16 27
12 (comp.) P5 10 279 259 20 9
13 (comp.) P6 10 282 264 18 18
14 P1 15 285 274 11 50
15 P2 15 286 278 8 64
16 P3 15 285 275 10 55
17 P4 15 284 270 14 36
18 (comp.) P5 15 280 261 19 14
19 (comp.) P6 15 283 266 17 23
Experimental results in test oil 2
Measure- Additive Dosage T1 T1 AT Fouling
ment rate (t = 0) (t = 5 h)
reduction
( C] [ C] [ C] Fkl
[PPrn]
,
20 none 0 257 230 27 0
21 P1 10 261 238 23 15
22 ' P2 10 262 239 23 15
23 P3 10 261 238 23 15
24 P4 10 260 236 24 11
25 (comp.) P5 10 258 231 27 0
,
26 (comp.) P6 10 260 235 25 7
27 P1 25 263 244 19 30
28 P2 25 263 243 20 26 ,
i
i
i
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_
29 P3 25 262 243 19 30
30 P4 25 261 240 21 22
31 (comp.) P5 25 258 234 24 11
32(comp.) P6 25 262 239 23 15
33 P1 50 264 253 11 59
34 P2 50 265 256 9 67
35 P3 50 263 253 10 63
36 P4 50 261 247 14 48
37 (comp.) P5 50 260 241 19 30
38 (comp.) P6 50 261 245 16 41
Experimental results in test oil 3
Measure- Additive Dosage T1 T1 AT
Fouling
ment rate (t = 0) (t = 5 h)
reduction
[ C] [ C] [ C]
[ya]
IPPrill
39 none 0 266 244 22 0
40 P1 10 270 254 16 27
41 P2 10 271 256 15
32
42 (comp.) P5 10 265 244 21 5
43 (comp.) P6 10 268 250 18 18
44 P7 10 271 257 14 36
45 P8 10 273 261 12 45
46 P1 20 272 259 13 41
47 P2 20 272 260 12 45
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. . .
48 (comp.) P5 20 265 245 20 9
49 (comp.) P6 20 270 253 17 23
50 P7 20 273 262 11 50
51 P8 20 274 264 10 55
52 P1 40 273 262 11 50
53 P2 40 274 264 10 55
54 (comp.) P5 40 266 246 20 9
55 (comp.) P6 40 271 258 13 41
56 P7 40 275 266 9 59
57 P8 40 275 268 7 68
The decreases in temperature after an experimental duration of 5 hours
observed
in the experiments using the method of the invention are much smaller than in
comparative experiments using other methods or additives. Moreover, higher
maximum temperatures are generally observed at first. Both indicate lower
deposits on the heating element and hence more efficient suppression of
fouling in
the case of inventive use of the additives or of the method that utilizes
them.
Accordingly, the method of the invention entails less frequent maintenance of
the
plant for removal of the deposits and hence longer service lives of the plant.
Since
the target oil temperature is often preset in industrial plants, the method of
the
invention additionally leads to saving of energy.
1
