Separation of different paraffin wax grades using two comparative deoiling techniques

Separation of different paraffin wax grades using two

comparative deoiling techniques

Magdy T. Zaky

⁎

, Nermen H. Mohamed, Amal S. Farag

Petroleum Refining Division, Egyptian Petroleum Research Institute (EPRI), Nasr City, P. O. Box 11727, Cairo, Egypt

Received 26 November 2006; received in revised form 26 April 2007; accepted 30 April 2007

Abstract

One stage fractional crystallization and solvent percolation techniques have been used to separate different grades of paraffin waxes; with

different characteristics; from El-Ameria light, middle and heavy slack waxes. The two deoiling techniques were performed using ethyl acetate

and butyl acetate solvents at ambient temperature of 20 °C, at different dilution solvent ratios (S/F by weight) ranging from 2:1 to 8:1 and constant

washing solvent ratio of 2:1 for the first technique and at different percolation solvent ratios ranging from 4:1 to 14:1 for the second one. The

resulting data revealed that fractional crystallization technique is more suitable for deoiling the heavy slack wax using butyl acetate solvent than

the percolation technique. While, percolation technology is a preferable technique using ethyl acetate or butyl acetate solvent for separation of

paraffin waxes from light and middle slack waxes.

© 2007 Elsevier B.V. All rights reserved.

Keywords:Paraffin waxes; Fractional crystallization; Solvent percolation; Deoiling techniques; Slack waxes

1. Introduction

Generally, paraffin waxes are derived from low-boiling wax

distillate fractions (light and middle ones). They consist mainly of

n-paraffins ranging from C

to C

and possibly higher. Varying

proportions of slightly branched-chain paraffins (C

–

C

) and

naphthenes are present.

Fully, semi- and scale refined paraffin waxes are produced

from slack waxes. Slack waxes separated from lubricating oil

feedstocks by dewaxing operation, usually contain from 2 to

45 wt.% oil. Low oil content paraffin waxes with a specific

melting point and needle penetration are produced by selective

removal of the oil and low melting waxes from the slack waxes.

This process is called deoiling or wax fractionation.

The commercial wax fractionation processes are the wax

sweating, the re-crystallization, the warm-up and the spray

de-oiling ones

[1,2]

.

The most predominant process is the wax re-crystallization

which was developed as a replacement for the wax sweating

process. It is sometimes called wax fractional crystallization

process and can be used to fractionate or deoil all types of

waxes. The wax cake from the primary or the secondary

dewaxing filters is heated until the wax is totally dissolved in

the solvent. Additional warm solvent is blended with the wax

cake solution. The mixture is cooled in double pipe scraped

surface equipment to a predetermined temperature to crystallize

the desired wax fractions. The mixture is filtered through a

rotary vacuum filter and the wax cake receives a final wash. The

filtration temperature of the wax in the third stage is conducted

at a higher temperature than that used in the first or second

dewaxing filtrations and the temperature used is selected to

adjust wax melting point and penetration. This process can be

operated in series with the solvent dewaxing unit of similar

design, which uses double or incremental dilution and single or

two-stage filtration

[2]

.

The characteristics of an ideal dewaxing or deoiling solvent

include the following: low solvent power of wax, high solvent

power for oil, low freeze point, low viscosity, low in cost,

non-toxic and have chemical and thermal stability

[2]

.

In our previous study, n-hexane, dioxane, ethyl acetate and

butyl acetate solvents were compared with methyl isobutyl

⁎Corresponding author. Tel.: +202 2745902; fax: +202 2747433.

E-mail address:[email protected](M.T. Zaky).

0378-3820/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2007.04.011

ketone (MIBK) solvent and methyl ethyl ketone (MEK),

benzene (B) and toluene (T) (60:20:20 by weight respectively)

solvent mixture; the conventional solvents generally used in

refineries as dewaxing and deoiling solvents. The study

indicated that, the most suitable solvents for separating paraffin

waxes; with the standard specifications; from light, middle and

heavy slack waxes are MIBK, ethyl and butyl acetates and the

mixture of MEK, B & T. Moreover, butyl acetate and MIBK

solvents and MEK, B & T solvent mixture can give paraffin

waxes having nearly the same congealing points, needle

penetrations and mean molecular weights range. However

from the economical point of view, ethyl acetate and butyl

acetate solvents are the most popular fractionating solvents due

to their lower prices than MIBK solvent and their advantages of

saving energy in the solvent distillation step over the solvent

mixture of MEK, B &T

[3]

.

Other authors carried out a study deals with the application of

solvent percolation technique to separate oil from commercial

microcrystalline wax flakes produced from tank bottom sludges.

Wax deoiling has been accomplished by percolating industrial

hexane through a packed bed of the wax flakes at ambient

temperature and removing the solvent from the wax and oil phases

to get hard wax and foot oil respectively. In this technology,

mechanical mixing and filtration operation have been substituted

with percolation of solvent through wax flakes, thereby

eliminating mixed phase in the process and the need of expensive

scraped surface crystallizers, rotary

–

drum filters and refrigeration

equipment as required in conventional solvent deoiling

[4]

.

Thus, the present study deals with the differentiation between

the fractional crystallization and solvent percolation techniques

using ethyl acetate and butyl acetate solvents by variation the

solvent feed ratios, for separation of various grades of paraffin

waxes of different specifications from light, middle and heavy

slack waxes.

2. Experimental

2.1. Materials

Three appropriate crude waxes; light, middle and heavy slack waxes; from El-Ameria Refining Company with different characteristics are used in this study for isolation of different grades of paraffin waxes.

Ethyl and butyl acetate solvents are used for separation of paraffin waxes by both fractional crystallization and solvent percolation techniques.

2.2. Isolation of paraffin waxes

The three slack waxes were subjected practically to one stage fractional crystallization and solvent percolation techniques using ethyl and butyl acetate solvents at ambient temperature of 20 °C and at different solvent feed ratios (S/F, by weight) ranging from 2:1 to 8:1 at fixed washing solvent ratio of 2:1 for the former technique and from 4:1 to 14:1 for the latter technique to produce different grades of paraffin waxes.

2.2.1. Fractional crystallization technique

A known weight of slack wax was dissolved in the corresponding amount of solvent or solvent mixture in a beaker and heated till the mixture becomes homogenous. Then the mixture was cooled gradually at room temperature. The beaker and the buchner funnel were transferred to a controlled temperature unit and gradually cooled to the desired temperature. The beaker contents were transferred to the funnel and filtered through a Whatman filter paper No. 43 by using gentle suction. The wax cake was washed with additional solvent at the same temperature and added at small increments. Solvents were removed from the wax cake by distillation.

2.2.2. Solvent percolation technique

A known weight of slack wax flakes was random packed in a jacketed glass column (diameter 3 cm, length 130 cm). A certain quantity of solvent was percolated under gravity over the packed bed of wax flakes from the top, Table 2

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of light slack wax using butyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Light

slack wax

Waxes isolated at different dilution solvent to feed ratios (S/F) by using Butyl acetate 2:1 (L4) 4:1(L5) 6:1 (L6) Congealing point, °C 48 54 55.5 56.5 Kinematic viscosity at 98.9 °C, mm2_s−1 _{3.04 3.12 3.18 3.30} Refractive index at 98.9 °C 1.4224 1.4179 1.4193 1.4199 Mean molecular weight 384 406 414 421 Oil content, wt.% 5.32 0.33 0.20 0.06 Needle penetration at 25 °C 43 22 19 17

Color (ASTM-D 1500) 1.0 0.0 0.0 0.0

Refractive index by TAPPI-ASTM equation

– 1.4245 1.4250 1.4254 Ultraviolet absorbance at 290 nm – 0.057 0.056 0.052

Type of wax Macro-crystalline

Table 1

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of light slack wax using ethyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Light

slack wax

Waxes isolated at different dilution solvent to feed ratios (S/F) by using Ethyl acetate 4:1 (L1) 6:1 (L2) 8:1 (L3) Congealing point, °C 48 54 54.5 55 Kinematic viscosity at 98.9 °C, mm2s−1 3.04 3.06 3.16 3.18 Refractive index at 98.9 °C 1.4224 1.4189 1.4191 1.4193 Mean molecular weight 384 400 406 408 Oil content, wt.% 5.32 0.49 0.29 0.08 Needle penetration at 25 °C 43 24 19 14

Color (ASTM-D 1500) 1.0 0.5 0.0 0.0

Refractive index by TAPPI-ASTM equation

– 1.4245 1.4247 1.4249 Ultraviolet absorbance at 290 nm – 0.420 0.058 0.053

Molecular type composition

Total saturates, wt.% 97.63 100 – 100 n-paraffins content, wt.% 74.71 88.32 – 89.90 Iso- and cyclo-paraffins content, wt.% 22.92 11.68 – 10.10 Iso- and cyclo-paraffins/n-paraffins ratio 0.31 0.13 – 0.11 Total aromatics, wt.% 2.37 0.00 – 0.00 Mono-aromatics, wt.% 2.37 0.00 – 0.00 Degree of branching (% CH3content) 12.52 8.96 – 8.30

maintaining the temperature of the column at 20 °C. After the percolation run, wax and oil solution phases were made free from the solvent by distillation to get hard wax and soft wax, respectively.

2.3. Methods of analysis

The three slack waxes and the isolated paraffin waxes were physically characterized according to American Society for Testing and Materials (ASTM) standard methods[5].

The type of the isolated paraffin waxes was specified according to Technical Association of the Pulp and Paper Industry (TAPPI)—ASTM equation[6,7]. The aromatic contents of the slack waxes and the isolated paraffin waxes were determined using liquid - solid column chromatography technique[8].

n-paraffin contents were determined for the slack waxes and the isolated paraffin waxes using GC technique. The GC apparatus used was model 6890 plus Aglient, equipped with a hydrogen flame ionization detector and fused silica capillary column (30 m × 0.25 mm i.d.), packed with poly (dimethyl siloxane) HP-1 (non-polar packing) of 0.5μm film thickness. The peak area of each resolved component (consisting of either n- and iso-paraffin) is determined individually. However, the unresolved complex mixtures (humps); composed of non n-paraffins presumably mainly cyclo-paraffins and aromatics with long side chains; were determined only as a total.

The degree of branching (%CH3content) of the slack waxes and the isolated paraffin waxes was determined using proton nuclear magnetic resonance (Varian Mercury H-NMR spectrometer-Danemark) at 300 MHz in deutrated chloroform

[9].

Ultraviolet absorbance for the fully refined paraffin waxes was determined at 290 nm by using UV-Visible Spectrophotometer.

3. Results and discussion

3.1. Fractional crystallization and solvent percolation of crude

waxes

3.1.1. Effect of dilution and percolation solvent ratios

The dilution and the amount of solvent used in fractional

crystallization and percolation respectively, have an obvious

effect upon the yield and quality of the waxes isolated from

light, middle and heavy slack waxes by using ethyl and butyl

acetate solvents at ambient temperature of 20 °C

.

Data are

represented in

Tables 1–11

.

The wax yield decreases with increasing of dilution or

percolation solvent ratios (

Fig. 1

), with the improvement of wax

quality in terms of increasing the congealing point and mean

molecular weight and lowering the needle penetration as a result

of the decrease of oil content for the separated waxes. It can be

noticed also that, the improvement in the wax quality is more

pronounced with lower wax yield by using butyl acetate solvent

than those obtained by ethyl acetate solvent for both techniques.

This may be due to the higher solvent power of butyl acetate

towards the oil inherent to such waxes (

Tables 1–11

).

It is interest to note that the decrease in the oil content is

accompanied with an increase in the viscosities and refractive

indices of the waxes separated from light and middle slack

waxes by increasing the dilution or percolation solvent ratios

(

Tables 1–8

) while for the heavy slack wax, the decrease in the

oil content is accompanied with the decrease in the viscosities

and refractive indices of the separated waxes (

Tables 9

–

11

).

This may be attributed to the type of the entrained oil which is

mainly iso-paraffins having lower refractive indices and

viscosities in the former case and aromatic constituents for the

Table 3

Effect of percolation solvent ratio on the physical characteristics and type of isolated waxes by solvent percolation of light slack wax using ethyl acetate solvent at percolating temperature of 20 °C

Characteristics Light slack wax

Waxes isolated at different percolation solvent to feed ratios (S/F) by using Ethyl acetate 6:1 (PL1) 8:1 (PL2) 10:1 (PL3) 12:1 (PL4) 14:1 (PL5) Congealing point, °C 48 52.5 53 53.5 54 54 Kinematic viscosity at 98.9 °C, mm2_s−1 3.04 3.05 3.07 3.09 3.12 3.12 Refractive index at 98.9 °C 1.4224 1.4181 1.4183 1.4187 1.4196 1.4196 Mean molecular weight 384 393 397 400 406 406 Oil content, wt.% 5.32 1.58 1.31 0.81 0.31 0.30 Needle penetration at 25 °C 43 35 32 27 21 21 Color (ASTM-D 1500) 1.0 0.5 0.5 0.5 0.0 0.0 Refractive index by TAPPI-ASTM equation – 1.4240 1.4242 1.4243 1.4245 1.4245 Ultraviolet absorbance at 290 nm – – – – 0.04 0.04

Type of wax Macro-crystalline

Table 4

Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by solvent percolation of light slack wax using butyl acetate solvent at percolating temperature of 20 °C Characteristics Light

slack wax

Waxes isolated at different percolation solvent to feed ratios (S/F) by using Butyl acetate 4:1 (PL6) 6:1 (PL7) 8:1 (PL8) 10:1 (PL9) 12:1 (PL10) Congealing point, °C 48 52.5 53.5 54 57.5 58 Kinematic viscosity at 98.9 °C, mm2s−1 3.04 3.07 3.10 3.15 3.25 3.38 Refractive index at 98.9 °C 1.4224 1.4189 1.4199 1.4204 1.4213 1.4218 Mean molecular weight 384 397 400 412 432 438 Oil content, wt.% 5.32 0.71 0.45 0.31 0.02 0.02 Needle penetration at 25 °C 43 26 22 20 16 15 Color (ASTM-D 1500) 1.0 0.5 0.0 0.0 0.0 0.0 Refractive index by TAPPI-ASTM equation – 1.4240 14243 1.4245 1.4257 1.4259 Ultraviolet absorbance at 290 nm – – 0.039 0.025 0.022 0.019

Molecular type composition

Total saturates, wt.% 97.63 – 100 – 100 – n-paraffins

content, wt.%

74.71 – 80.01 – 89.83 – Iso- and

cyclo-paraffins content, wt.%

22.92 – 19.99 – 10.17 – Iso- and cyclo-paraffins/

n-paraffins ratio 0.31 – 0.25 – 0.11 – Total aromatics, wt.% 2.37 – 0.00 – 0.00 – Mono-aromatics, wt.% 2.37 – 0.00 – 0.00 – Degree of branching (% CH3content) 12.52 – 9.52 – 8.80 – Type of wax Macro-crystalline

latter case as they have higher refractive indices and viscosities

than the other constituents of the wax.

Data of molecular type composition confirm the above

findings as the iso- and cyclo-paraffins contents of the waxes

separated from the three slack waxes are decreased by

increasing the dilution or percolation solvent ratios (

Tables 1,

4 and 5–10

) and the decrease is more pronounced by using

butyl acetate solvent than ethyl acetate solvent (Compare

Tables

5 and 6

or

7 and 8

). Meanwhile there is a valuable decrease in

the mono-aromatic constituents accompanied with the absence

of di-aromatic ones for the waxes separated from the heavy

slack wax (

Tables 9 and 10

).

Moreover, the degree of branching decreases with increasing

dilution or percolation solvent ratios, is mainly due to the

decrease of iso-paraffins content for the waxes separated from

the three slack waxes (

Tables 1, 4 and 5

–

10

) beside the decrease

of aromatics content which is mainly mono-aromatic

constitu-ents attached with long side chain for the waxes separated from

the middle and heavy slack waxes (

Tables 5, 7, 9 and 10

).

Comparing the effect of increasing the quantity of solvent

used in fractional crystallization technique; solvent feed ratios

of dilution and washing; with those in solvent percolation

technique, it can be noticed that, the two techniques behave the

same trend upon increasing the solvent feed ratio as the

iso-and cyclo-paraffins iso-and mono-aromatic constituents of lower

melting points and mean molecular weights decrease in the

paraffin waxes isolated from the three slack waxes. But, the

solvent percolation technique needs higher quantity of solvent

necessary for deoiling to obtain paraffin wax with nearly the

same specifications as those obtained by fractional

crystalliza-tion. Thus, to obtain paraffin wax with penetration value of

nearly 19 by percolation and fractional crystallization

techni-ques, the quantities of butyl acetate required per unit slack wax

are 8:1 & 6:1 respectively (compare PL

in

Table 4

with L

in

Table 2

). Also, the quantities of butyl acetate required per unit

slack wax are 10:1 & 8:1 to obtain paraffin wax with

pen-etration value of 13 by percolation and fractional crystallization

techniques respectively (compare PM

in

Table 8

with M

in

Table 6

).

It is interest to note that fractional crystallization technique is

more suitable for deoiling the heavy slack wax by butyl acetate

solvent than the percolation technique (

Tables 10 and 11

respectively). Whereas by increasing the quantity of the solvent

in fractional crystallization technique, the heavy slack wax (wax

and entrained oil within and oil outside the wax crystals) is

totally dissolved in the solvent by heating till the mixture

becomes homogenous. Then the wax is recrystallized by

gra-dual cooling to the desired fractionating temperature (20 °C),

while in percolation technique the solvent dissolves only the oil

outside the wax crystals at the desired percolating temperature

Table 5

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of middle slack wax using ethyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Middle Slack Wax

Waxes isolated at different dilution solvent to feed ratios (S/F) by using Ethyl acetate 2:1 (M1) 4:1 (M2) 6:1 (M3) Congealing point, °C 59 61.5 62.5 63.5 Kinematic viscosity at 98.9 °C, mm2s−1 4.30 4.10 4.15 4.23 Refractive index at 98.9 °C 1.4270 1.4229 1.4234 1.4243 Mean molecular weight 446 449 455 463

Oil content, wt.% 6.23 1.39 1.14 0.09 Needle penetration at 25 °C 40 23 19 16 Color (ASTM-D 1500) 1.5 1.0 1.0 0.5 Refractive index by TAPPI-ASTM equation – 1.4271 1.4275 1.4278 Ultraviolet absorbance at 290 nm – – – 0.283

Molecular type composition

Total saturates, wt.% 96.97 98.82 99.01 100 n-paraffins content, wt.% 62.89 64.02 65.93 69.50 Iso- and cyclo-paraffins

content, wt.%

34.08 34.80 33.08 30.50 Iso- and cyclo-paraffins/

n-paraffins ratio 0.54 0.54 0.50 0.44 Total aromatics, wt.% 3.03 1.18 0.99 0.00 Mono-aromatics, wt.% 3.03 1.18 0.99 0.00 Degree of branching (% CH3content) 10.78 9.65 9.54 8.56

Type of wax Macro-crystalline

Table 6

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of middle slack wax using butyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Middle

Slack Wax

Waxes isolated at different

dilution solvent to feed ratios (S/F) by using Butyl acetate 2:1 (M4) 4:1 (M5) 6:1 (M6) Congealing point, °C 59 64 65.5 67.5 Kinematic viscosity at 98.9 °C, mm2_s−1 _{4.30 4.19 4.22 4.38} Refractive index at 98.9 °C 1.4270 1.4224 1.4236 1.4242 Mean molecular weight 446 451 461 469

Oil content, wt.% 6.23 1.07 0.65 0.03 Needle penetration at 25 °C 40 18 16 13 Color (ASTM-D 1500) 1.5 1.0 0.5 0.0 Refractive index by TAPPI-ASTM equation – 1.4280 1.4285 1.4292 Ultraviolet absorbance at 290 nm – – – 0.312

Molecular type composition

Total saturates, wt.% 96.97 100 100 100 n-paraffins content, wt.% 62.89 79.23 82.32 84.10 Iso- and cyclo-paraffins content, wt.% 34.08 20.77 17.68 15.90 Iso- and cyclo-paraffins/

n-paraffins ratio

0.54 0.26 0.21 0.19 Total aromatics, wt.% 3.03 0.00 0.00 0.00 Mono-aromatics, wt.% 3.03 0.00 0.00 0.00 Degree of branching (% CH3content) 10.78 8.70 8.65 7.40

(20 °C) but it can't penetrate them to dissolve the entrained oil.

Oil content data confirm the previous findings. Comparing H

in

Table 10

with PH

in

Table 11

, it was found that both paraffin

waxes are obtained with the same quantity of butyl acetate

per unit slack wax (10:1) by fractional crystallization and

percolation techniques having oil contents of 0.05 & 2.5 wt.%

respectively.

Generally, paraffin waxes with different specifications can be

produced from different slack waxes by fractional

crystalliza-tion or percolacrystalliza-tion technique using ethyl or butyl acetate solvent

at different solvent feed ratios and at ambient temperature of

20 °C. Thus, paraffin waxes of the same needle penetration of

22, 19 and 15 and having different mean molecular weights and

congealing points can be obtained. Compare H

in

Table 9

with

both L

in

Table 2

and PL

in

Table 4

, compare L

in

Table 1

with both M

in

Table 5

and PM

in

Table 8

and compare also

PL

in

Table 4

with PM

in

Table 8

respectively.

3.2. Isolated wax type

Examining the isolated wax type in

Tables 1–11

on the basis

of

TAPPI-ASTM

equation, it can be noticed that all the studied

waxes isolated from the three slack waxes lie in the category of

macro-crystalline waxes; as they characterized by refractive

indices lower than those obtained by the equation and by

viscosities at 98.9 °C lower than 7.4 mm

s

; except the waxes

(PH

and PH

) isolated from heavy slack wax by using butyl

acetate at percolation solvent ratios of 6:1 and 8:1 by weight

(

Table 11

) lie in the category of semi-microcrystalline waxes as

they characterized by refractive indices higher than those

obtained by the equation and by viscosities at 98.9 °C lower

than 10 mm

s

.

According to

petroleum wax specifications

, all the tested

crystalline waxes lie also in the category of

macro-crystalline waxes, except the needle penetration for the

separated waxes L

in

Table 1

, PL

-PL

in

Table 3

, PL

in

Table 4

, M

in

Table 5

and H

in

Table 9

are higher than the

macro-crystalline wax group limit (22).

Different grades of paraffin waxes can be produced from the

three slack waxes by using fractional crystallization and solvent

percolation techniques at ambient temperature of 20 °C and at

various solvent to feed ratios.

•

Eleven of fully refined food grade paraffin waxes were

separated from the light slack wax as they are white in color

Table 7

Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by solvent percolation of middle slack wax using ethyl acetate solvent at percolating temperature of 20 °C Characteristics Middle

slack wax

Waxes isolated at different percolation solvent to feed ratios (S/F) by using Ethyl acetate 4:1 (PM1) 6:1 (PM2) 8:1 (PM3) 10:1 (PM4) 12:1 (PM5) Congealing point, °C 59 62 62.5 63.5 64 64.5 Kinematic viscosity at 98.9 °C, mm2_s−1 4.3 4.11 4.16 4.19 4.24 4.26 Refractive index at 98.9 °C 1.4270 1.4224 1.4229 1.4236 1.4239 1.4241 Mean molecular weight 446 450 455 461 465 465 Oil content, wt.% 6.23 1.39 1.12 0.68 0.05 0.04 Needle penetration at 25 °C 40 22 19 16 15 15 Color (ASTM-D 1500) 1.5 1.0 1.0 0.5 0.0 0.0 Refractive index by TAPPI-ASTM equation – 1.4273 1.4275 1.4278 1.4280 1.4282 Ultraviolet absorbance at 290 nm – 0.351 – – 0.231 0.220

Molecular type composition

Total saturates, wt.% 96.67 99.26 – – 100 – n-paraffins

content, wt.%

62.89 74.45 – – 76.28 – Iso- and cyclo-paraffins

content, wt.%

34.08 24.81 – – 23.72 – Iso- and cyclo-paraffins /

n-paraffins ratio 0.54 0.33 – – 0.31 – Total aromatics, wt.% 3.03 0.74 – – 0.00 – Mono-aromatics, wt.% 3.03 0.74 – – 0.00 – Degree of branching (% CH3content) 10.78 9.86 – – 8.80 – Type of wax Macro-crystalline

Table 8

Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by solvent percolation of middle slack wax using butyl acetate solvent at percolating temperature of 20 °C Characteristics Middle

slack wax

Waxes isolated at different percolation solvent to feed ratios (S/F) by using Butyl acetate 4:1 (PM6) 6:1 (PM7) 8:1 (PM8) 10:1 (PM9) 12:1 (PM10) Congealing point, °C 59 64 64.5 65 66 66 Kinematic viscosity at 98.9 °C, mm2s−1 4.3 4.20 4.22 4.24 4.30 4.30 Refractive index at 98.9 °C 1.4270 1.4234 1.4238 1.4244 1.4255 1.4255 Mean molecular weight 446 459 461 463 469 469 Oil content, wt.% 6.23 1.10 0.85 0.60 0.05 0.02 Needle penetration at 25 °C 40 19 17 15 13 13 Color (ASTM-D 1500) 1.5 1.0 1.0 0.5 0.0 0.0 Refractive index by TAPPI-ASTM equation – 1.4280 1.4282 1.4284 1.4287 1.4287 Ultraviolet absorbance at 290 nm – 0.364 – – 0.210 0.210

Molecular type composition

Total saturates, wt.% 96.97 100 – – 100 – n-paraffins

content, wt.%

62.89 76.52 – – 83.26 – Iso- and cyclo-paraffins

content, wt.%

34.08 23.48 – – 16.74 – Iso- and cyclo-paraffins/

n-paraffins ratio 0.54 0.31 – – 0.20 – Total aromatics, wt.% 3.03 0.00 – – 0.00 – Mono-aromatics, wt.% 3.03 0.00 – – 0.00 – Degree of branching (% CH3content) 10.78 9.25 – – 8.22 – Type of wax Macro-crystalline

[7]

, their oil contents less than 0.5 wt.% and their ultraviolet

absorbance at 290 nm less than 0.12

[2]

. They are as follows:

- Five paraffin waxes (L

–

L

) were produced by fractional

crystallization technique at ethyl acetate dilution solvent

ratios of 6:1 & 8:1 for L

& L

respectively (

Table 1

) and at

butyl acetate dilution solvent ratios of 2:1, 4:1 & 6:1 for L

,

L

& L

respectively (

Table 2

).

- Six paraffin waxes (PL

, PL

& PL

–

PL

) were produced

by solvent percolation technique at ethyl acetate percolation

solvent ratios of 12:1 & 14:1 for PL

& PL

respectively

(

Table 3

) and at butyl acetate percolation solvent ratios of 6:1

to 12:1 for PL

to PL

respectively (

Table 4

).

•

Six of fully refined grade and nine of semi-refined grade

paraffin waxes were isolated from the middle slack wax.

They are as follows:

- Six paraffin waxes (M

, M

, PM

, PM

, PM

& PM

) are

classified as fully refined grade paraffin waxes as their oil

contents are less than 0.5 wt.%. M

& M

were produced by

fractional crystallization technique using ethyl and butyl

acetate solvents respectively at dilution solvent ratio of 6:1

(

Tables 5 and 6

). Meanwhile PM

–

PM

& PM

–

PM

were

obtained by solvent percolation technique using ethyl and

butyl acetate solvents respectively at percolation solvent feed

ratios of 10:1 & 12:1 (

Tables 7 and 8

).

- Nine paraffin waxes (M

, M

, M

, PM

–

PM

& PM

–

PM

)

are classified as semi-refined grade paraffin waxes as their

oil contents are higher than 0.5 and less than 1.5 wt.%

[1]

.

M

, M

& M

were obtained by fractional crystallization

technique at ethyl acetate dilution solvent ratio of 4:1 for M

(

Table 5

) and at butyl acetate dilution solvent ratios of 2:1 &

Table 9

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of heavy slack wax using ethyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Heavy

slack wax

Waxes isolated at different

dilution solvent to feed ratios (S/F) by using Ethyl acetate 4:1 (H1) 6:1 (H2) 8:1 (H3) Congealing point, °C 62.5 67 68 69 Kinematic viscosity at 98.9 °C, mm2s−1 6.00 5.50 5.44 5.38 Refractive index at 98.9 °C 1.4402 1.4287 1.4282 1.4274 Mean molecular weight 477 524 529 536 Oil content, wt.% 23.05 6.03 2.22 1.69 Needle penetration at 25 °C 59 24 22 21 Color (ASTM-D 1500) 3.0 2.0 1.5 1.0 Refractive index by TAPPI-ASTM equation – 1.4290 1.4294 1.4297 Ultraviolet absorbance at 290 nm – – – –

Molecular type composition

Total saturates, wt.% 86.18 96.09 97.98 – n-paraffins content, wt.% 36.62 59.20 62.46 – Iso- and cyclo-paraffins content, wt.% 49.56 36.89 35.52 – Iso- and cyclo-paraffins/n-paraffins ratio 1.35 0.62 0.57 – Total aromatics, wt.% 13.82 3.91 2.02 – Mono-aromatics, wt.% 11.52 3.91 2.02 – Di-aromatics, wt.% 2.30 0.00 0.00 – Degree of branching (% CH3content) 16.64 10.06 8.70 –

Type of wax Macro-crystalline

Table 10

Effect of dilution solvent ratio on the physical characteristics, type and molecular type composition of isolated waxes by one stage fractional crystallization of heavy slack wax using butyl acetate solvent at fractionating temperature of 20 °C and S/F for washing of 2:1

Characteristics Heavy

slack wax

Waxes isolated at different

dilution solvent to feed ratios (S/F) by using Butyl acetate 4:1 (H4) 6:1 (H5) 8:1 (H6) Congealing point, °C 62.5 69.5 70.5 71.5 Kinematic viscosity at 98.9 °C, mm2s−1 6.00 5.30 5.27 5.20 Refractive index at 98.9 °C 1.4402 1.4279 1.4260 1.4221 Mean molecular weight 477 533 535 540 Oil content, wt.% 23.05 2.04 0.15 0.05 Needle penetration at 25 °C 59 15 12 11 Color (ASTM-D 1500) 3.0 1.0 1.0 0.5 Refractive index by TAPPI-ASTM equation – 1.4299 1.4303 1.4306 Ultraviolet absorbance at 290 nm – – 0.468 0.283

Molecular type composition

Total saturates, wt.% 86.18 97.14 98.84 – n-paraffins content, wt.% 36.62 72.19 74.60 – Iso- and cyclo-paraffins content, wt.% 49.56 24.95 24.24 – Iso- and cyclo-paraffins/n-paraffins ratio 1.35 0.35 0.32 – Total aromatics, wt.% 13.82 2.86 1.16 – Mono-aromatics, wt.% 11.52 2.86 1.16 – Di-aromatics, wt.% 2.30 0.00 0.00 – Degree of branching (% CH3content) 16.64 9.47 8.09 –

Type of wax Macro-crystalline

Table 11

Effect of percolation solvent ratio on the physical characteristics and type of isolated waxes by solvent percolation of heavy slack wax using butyl acetate solvent at percolating temperature of 20 °C

Characteristics Heavy slack wax

Waxes isolated at different percolation solvent to feed ratios (S/F) Butyl acetate 6:1 (PH1) 8:1 (PH2) 10:1 (PH3) 12:1 (PH4) Congealing point, °C 62.5 66.5 67.5 68.5 68.5 Kinematic viscosity at 98.9 °C, mm2s−1 6.00 5.80 5.60 5.48 5.48 Refractive index at 98.9 °C 1.4402 1.4329 1.4306 1.4289 1.4289 Mean molecular weight 477 514 520 529 529 Oil content, wt.% 23.05 7.02 5.32 2.5 2.49 Needle penetration at 25 °C 59 32 30 22 22 Color (ASTM-D 1500) 3.0 2.5 2.0 1.0 1.0 Refractive index by TAPPI-ASTM equation – 1.4289 1.4292 1.4296 1.4296

Type of wax

Semi-microcrystalline

Macro-crystalline

4:1 for M

& M

respectively (

Table 6

). Meanwhile PM

–

PM

& PM

–

PM

were separated by solvent percolation

technique using ethyl acetate solvent for PM

–

PM

(

Table 7

)

and butyl acetate solvent for PM

–

PM

(

Table 8

) at

percolation solvent feed ratios of 4:1 to 8:1 for both solvents.

•

Two of fully refined grade and five scale grade paraffin waxes

were isolated from the heavy slack wax. They are as follows:

- Two paraffin waxes (H

& H

) are classified as fully refined

grade paraffin waxes (ceresins) as their oil contents are 0.15

& 0.05 wt.% and having congealing points of 70.5 & 71.5 °C

respectively

[10]

. They were separated by fractional

crys-tallization technique with butyl acetate solvent at dilution

solvent feed ratios of 6:1 & 8:1 respectively (

Table 10

).

- Five paraffin waxes (H

–

H

, PH

& PH

) are classified as

scale grade paraffin waxes as their oil contents are more than

1.5 and less than 3 wt.%. H

–

H

were obtained by fractional

crystallization technique at ethyl acetate dilution solvent

ratios of 6:1 & 8:1 for H

& H

respectively (

Table 9

) and at

butyl acetate dilution solvent ratio of 4:1 for H

(

Table 10

).

Meanwhile PH

& PH

; with nearly the same physical

Fig. 1. Effect of solvent feed ratio on the yield of waxes isolated from light (A), middle (B) and heavy (C) slack waxes. FC: Fractional crystallization technique, P : Percolation technique, EA: Ethyl acetate solvent, BA: Butyl acetate solvent.

characteristics; were separated by solvent percolation

technique with butyl acetate solvent at percolation solvent

feed ratios of 10:1 & 12:1 respectively (

Table 11

).

4. Conclusions

The study shows that fractional crystallization and solvent

percolation techniques using ethyl acetate and butyl acetate

solvents could be employed for separation of paraffin waxes

from light and middle slack waxes. While, solvent percolation

technology is preferable due to it eliminates the need of

crystallization and filtration steps and saving of time required in

solvent fractional crystallization.

Also, it was found that fractional crystallization technique is

more suitable for deoiling the heavy slack wax by butyl acetate

solvent than the percolation technique as by increasing the

quantity of the solvent, the solvent dissolves the entrained oil

within and oil outside the wax crystals during the

re-crystalliza-tion step while in percolare-crystalliza-tion technique, the solvent dissolves only

the oil outside the wax crystals.

References

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[9] K.M. Agrawal, G.C. Joshi, Microcrystalline Waxes. 1. Investigation on the Structure of Waxes by Proton Nuclear Magnetic Resonance Spectroscopy, J. Chem. Tech. Biotechnol., vol. 31, 1981, pp. 693–696.

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