selecting pour depressants for diesel fuels

309

____________________________________________________________________________________________________

Shanghai Institute of Technology; Research China Shenhua Coal to Liquid and Chemical Shanghai Research

Institute. Dalian Polytechnic University, Shanghai Hiri Lubricants R&D Centre, PR of China. Translated from

Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 18 – 24, September – October , 2010.

0009-3092/10/4605–0309 © 2010 Springer Science+Business Media, Inc.

Chemistry and Technology of Fuels and Oils, Vol. 46, No.5, 2010

SELECTING POUR DEPRESSANTS FOR DIESEL FUELS

Sheng Han, Kui Zeng, Hualin Lin, and Peng Wang

The correlation between effectiveness and composition was investigated to choose the most effective

pour depressant from the multitude on the market. Samples of pour depressants from the main

manufacturers were collected and their ability to improve the low-temperature properties of diesel fuels

was evaluated. The composition and structure of the additives with the best results and their solvents

after separation by crystallization were investigated by Fourier-transform infrared spectroscopy, proton

nuclear magnetic resonance spectroscopy, and chromatography-mass spectrometry. It was shown that

copolymers of ethylene and vinyl acetate are the most effective pour depressant additives. Their solvents

contain aromatic compounds.

The pour depressants added to diesel fuel to improve its low-temperature properties modify crystallization

of waxes [1-5]. They basically contain polymers [6-14] such as copolymers of ethylene and vinyl acetate, polyalkyl

methacrylate, maleic anhydride, alkylnaphthalenes, nitrogen-containing, and other polymers. These compounds

are usually soluble in crude oil and have very complex compositions [15, 16].

Diesel fuel, with additive Decrease, deg

LFT ts

A-1 10 25

Haote 11 25

KT8804 13 27

T803 3 18

V-385 3 20

10-320 1 13

10-330 2 22

ACLUBE148 2 14

ACLUBE134 3 20

CS 8 21

Table 1

310

The manufacturers of pour depressants market them under different trade marks without revealing the

composition. For this reason, the assortment of products of similar composition on the market is very wide.

However, there are few effective additives among them [17], which makes it difficult for the consumer to select

them since selection should be based on a significant number of screening experiments, and this will result in

losses of time, feedstock, and consequently increased costs.

The composition of the basic pour depressants must be characterized for selecting the best products.

Pour depressants f rom the fo l lowing manufac turers were se lec ted for the s tudy: Haote (Bei j ing

Haote), A-1 (Tianyu Petroleum Additives), KT8804 (Shanghai Boda Chemical), CS (Jinan Three Metallurgical

Fig. 1. IR spectra of pour depressants: a) A-1; b) Haote; c) KT8804.

Wavenumber, cm-1

Tran

smis

sion

, % b

a

c

311

Table 2Pe

ak n

umbe

r in

sp

ectr

um

(s

ee F

ig. 3

c)

Ret

entio

n tim

e,

min

Component Structural formula

Accuracy, %

Are

a of

pea

k, %

1 2 3 4 5 6

1 9.96 1-Methyl-2-ethylbenzene

95 1.24

2 10.46 1,4-Dimethyl-2-ethylbenzene

94 1.35

3 10.90 1,2,4,5-Tetramethylbenzene

91 2.20

4 11.03 1,3-Dimethyl-2-ethylbenzene 87 3.40

5 11.28 4,7-Methanoindene

98 9.87

6 11.36 Undecane 87 2.42

7 11.65 1,2,3,4-Tetramethylbenzene 97 4.41

8 11.71 1,2,3,5-tetramethylbenzene

97 4.78

9 12.13 Indene

94 2.14

10 12.24 1-Methyl-4-isopropylbenzene

91 3.18

11 1..51 1-Methyl-4-propylbenzene

95 9.66

12 12.60 Ethylcyclohexane

89 4.01

13 12.93 Naphthalene

93 7.77

14 13.16 Dodecane

97 4.20

312

Table 2 (continued)

Fig. 2. 1H NMR spectra of pour depressants: a) A-1; b) Haote; c) KT8804.

δ, ppm

1 2 3 4 5 6

15 13.36 6-Methyldodecane

94 2.75

16 14.30 2,6-Dimethyloctadecane 90 2.77

17 14.76 1-Methylnaphthalene 91 2.88

18 14.99 2-Methylnaphthalene 90 1.01

19 15.60 1,2,3,4-Tetrahydronaphthalene

95 0.71

20 16.02 1,4-Dimethylnaphthalene

98 0.65

313

Fig. 3. Results of chromatography-mass spectrometry of solvents in additives; a) A-1;

b) Haote; c) KT8804.

Time, min-1

a

b

c

314

Table 3P

eak

num

ber

in

spec

trum

(see

Fig

. 3c)

Ret

entio

n ti

me,

m

in


Accuracy, %

Are

a of

pea

k, %

1 2 3 4 5 6

1 6.58 Nonane 95 1.04

2 7.58 3-Methylnonane 90 1.97

3 8.83 1-Methyl-2-propylcyclohexane 92 2.89

4 9.06 1,2,4-Trimethylbenzene 91 4.98

5 9.25 Decane 91 3.79

6 9.66 1,2,3-Trimethylbenzene 98 4.66

7 9.95 Propylbenzene 90 2.82

8 10.26 1,4-Diethylbenzene 90 2.00

9 10.49 1-Ethyl-3,5-dimethylbenzene 94 4.06

11 10.77 3-Methyldecane 93 2.15

11 10.85 1,2-Dimethyl-4-ethylbenzene

95 3.49

12 10.90 1-Ethyl-2,4-dimethylbenzene

94 4.27


97 7.38

14 11.38 Undecane

90 8.05

315

Chemical), V-385 (Xian Qichuang Chemical), 10-320 and 10-330 (Rohmax), ACLUBE148 and ACLUBE134 (Sanyo

Chemical Industries, Japan). The efficacy of these additives was assessed by the improvement in the

low-temperature properties of diesel fuel No. 0 supplied by Lanzhou Petroleum Refining Co.

Most pour depressants are viscous polymers, so that a solvent is added to them to increase solubility in

petroleum products. The solvent must be separated to analyze the additive. Separation is conducted by

crystallization, which is based on the different solubility of the components at different temperatures and

precipitation of the additive at low temperatures. The necessary amount of additive in the solvent was cooled in

a SYP1022-2 ins t rument . When the t empera ture became lower than the l imi t ing f i l t e rab i l i ty

temperature (3°C), the additive begin to precipitate into sediment. The supernatant liquid was collected as the

solvent.

The compos i t ion and s t ruc ture o f the add i t ives were de te rmined by Four ie r- t rans form

infrared (IR) spectroscopy and proton nuclear magnetic resonance spectroscopy (1H NMR). A small amount of

the polymer granulated with KBr was analyzed in an American Nicolet IR 100/200 IR spectrometer, and

a smal l amount o f po lymer d i sso lved in deu te ra ted ch loroform (CDCl3) was ana lyzed in

a Varian VNS-400 NMR spectrometer.

The composition of the solvents separated from the additives was determined by chromatography–mass

spectrometry. An Agilent 5975 GC-MS with a HP-5 capillary column (30 m × 0.32 mm × 0.5 μm) was used for

the analysis. The analysis was conducted in the following conditions: the temperature in the column was increased

from 40 to 280°C at the rate of 10°/min, the interface temperature was 280°C, the injector temperature

was 300°C, and the sample volume was 0.1 μl.

The viscosity at low temperatures, solid point, and limiting filterability temperature (LFT) of diesel fuel

with additives in the concentration of 1000 ppm were determined on a Shanghai Boli SYP1022-2 multifunctional

instrument [17, 18]. The results of determination of the solid point ts and LFT are reported in Table 1.

T803, ACLUBE148, ACLUBE134, V-385, 10-320, and 10-330 pour depressants decreased the solid point

by 13-22°, but the decrease in the LTF was a total of 1-3°. With A-1, Haote, KT8804, and CS additives, both the

Table 3 (continued)

1 2 3 4 5 6

15 11.66 1,2,4,5-tetramethylbenzene

97 6.96

16 11.73 1-Methyl-4-isopropylbenzene

87 6.62

17 12.08 2,3-Dihydro-5-methylindene

89 2.11

18 12.23 1-Methylindene

95 1.87

19 12.29 1,2,3,5-Tetramethylbenzene

91 2.74


94 3.60

316

Pea

k nu

mbe

r in

sp

ectr

um (

see

Fig

. 3c

)

Ret

enti

on ti

me,

m

in


Accuracy, %

Are

a of

pea

k, %

1 2 3 4 5 6

1 9.66 Toluene

89 0.56

2 9.98 1-Methyl-2-ethylbenzene

90 4.32

3 10.26 1,3-Dimethylbenzene

91 1.19

4 10.34 1-Methyl-2-propylbenzene

92 0.97

5 10.45 1,2,3-Trimethylbenzene

86 2.99


95 0.87

7 11.08 4-Ethylstyrene

90 4.07

8 11.35 4,7-Methanoindene

96 19.56

9 11.69 Dodecane

90 2.28

10 12.05 2,3-Dihydro-4-methylindene

95 3.45

11 12.12 2,4-Dimethylstyrene

93 8.14


94 6.13

13 12.59 1,2,3,4-Tetrahydronaphthalene

89 17.73


97 7.02

Table 4

317

solid point and the LFT of the diesel fuel decreased. Most of the additives thus decreased the solid point with a

comparatively small decrease in the LFT.

The three most effective pour depressants were selected for further investigation based on the results of

the tests: A-1, Haote, and KT8804. Their IR spectra are shown in Fig. 1a-c. The IR spectra of the additives are

very similar. The absorption bands in the 2948 and 2830 cm-1 regions correspond to stretching vibrations of

methylene and methyl groups, and the absorption bands in the 1738 and 1457 cm-1 regions correspond to stretching

vibrations of C=O and C–O groups. The absorption bands in the 1241 cm-1 region correspond to deformation

vibrations of the methylene group, while the bands in the 1036 cm-1 region correspond to stretching vibrations of

the O–C=O group. The absolution band in the 733 cm-1 region indicate rocking vibrations of (CH2)

n groups

for n > 4. The analysis of these spectra showed their similarity to the spectra of the copolymer of ethylene and

vinyl acetate. As a consequence, these pour depressants can be assigned to additives of this type.

The 1H NMR spectra of additives A-1, Haote, and KT8804PPD are shown in Fig. 2a-c. The peak in

the 0.89 ppm region indicates the presence of a CH3 group in a long hydrocarbon chain [14]. The peak

at 1.25 ppm relates to protons in the long –(CH2)

n– chain and the peak at 1.50 ppm belongs to a methylene group

bound with CH2O–. The peak at 2.04 ppm characterizes the CH

2O– group, and the one at 4.87 ppm characterizes

a –CH2OCO– group. The results obtained also confirm that these additives are the copolymer of ethylene and

vinyl acetate. However, the structure and composition of the copolymer in the investigated samples differ.

As noted previously, the additives consist of polymers and solvents. The latter affect the efficacy of the

our depressants differently, so that it was necessary to analyze the composition of the solvents. The solvents

separated from A-1, Haote, and KT8804 additives were analyzed by gas chromatography–mass spectrometry.

The spectra obtained are shown in Fig. 3a-c, and the results of their analysis are reported in Tables 2-4.

As Tables 2 and 3 show, derivatives of benzene, cyclohexane, naphthalene, indene, and paraffins with

long hydrocarbon chains are the basic components of the solvents in A-1 and KT8804.

Table 4 (continued)

1 2 3 4 5 6

15 13.33 Cyclohexane

86 1.64

16 13.85 Tetradecane

93 1.22

17 14.05 Phenol

87 1.04

18 14.26 Propylcyclohexane

83 0.56

19 15.95 3,4-Dihydronaphthalene

97 0.64

20 15.95 1-Methylnaphthalene

97 0.64

x

318

The basic components of the solvent in the Haote additive (see Table 4) include derivatives of benzene,

naphthalene, indene, and long-chain paraffins. The basic components of the solvents in the A-1 and Haote additives

are aromatic hydrocarbons (approximately 58%) and long-chain paraffins (approximately 17%).

In view of the earlier studies in [20] which showed the similarity of this composition to the composition

of the naphtha cut, we can conclude that the naphtha cut is the solvent in pour depressants A-1 and Haote.

The solvent in additive KT8804 primarily consists of aromatic hydrocarbons (of the order of 80%), and

the content of paraffins is only 3.5%. Based on the previous studies [21], we can thus conclude that aromatic

petroleum oil is the solvent in this additive. Since the aromatic hydrocarbon content in all three solvents is

significant, we can conclude that aromatic solvents cause both the good solubility and dispersion of the additive

and consequently increase its efficacy in improving the low-temperature properties.

The research was conducted with the support of Shanghai Leading Academic Discipline Project (Project

No. J51503), National Natural Science Foundation of China (Project No. 20976105), Science and Technology

Commission of Shanghai Municipality (Project No. 09QT1400600), and Innovation Program of Shanghai

Municipal Education Commission (Project No. 09YZ387).

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selecting pour depressants for diesel fuels

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