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Estimation of the components in titanation mixture used in the synthesis ofpolyolefin catalysts

Krishna R. Sarma,* Sudhakar Padmanabhan* and Viral Patel

Received 19th January 2010, Accepted 20th April 2010

First published as an Advance Article on the web 20th May 2010

DOI: 10.1039/c0ay00040j

Traditional Ziegler Natta catalysts used for making polyethylene and polypropylene involve titanation

of Mg based supports like magnesium ethoxide using a mixture of TiCl4 and chlorobenzene.

Chloroalkoxy titanium species like TiCl3(OEt) are generated in the process which gets mixed with the

titanation mixture. This necessitates the need for a quick, reliable and easy method of analysis for

arriving at the correct composition of the residual titanation mixture so that the same can be reused

after adjusting the TiCl4 and chlorobenzene contents. Estimation of TiCl3(OEt) and TiCl4 separately

and also in synthetic mixtures of both has been carried out through a simple acid–base titration. The

method is based on the concept that TiCl3(OEt) and TiCl4 liberate stoichiometric amounts of HCl on

aqueous or alkaline hydrolysis which can be estimated by an acid–base titration. The analysis has been

carried out using different synthetic mixtures of TiCl3(OEt) and TiCl4 in chlorobenzene. TiCl3(OEt)

and TiCl4 were subsequently estimated by a combination of acid–base titration/UV-vis spectroscopy

and gas chromatography (GC). By accounting for the titanium content due to TiCl3(OEt) and

subtracting the same from the overall titanium content, the titanium content from TiCl4 was worked

out. The concept and the method developed have been validated through a parity plot. A

complementary method for estimating the ethoxy content in TiCl3(OEt) was also used wherein the

ethoxy group was quantitatively converted into ethylbenzoate (EB) through esterification employing

benzoyl chloride. The TiCl4.ethyl benzoate adduct was further hydrolysed to liberate an equivalent

amount of ethylbenzoate which was estimated by quantitative GC.

Introduction

The Ziegler Natta type polyolefin catalyst involves the titanation

of magnesium based supports like magnesium ethoxide using

a mixture of TiCl4 and chlorobenzene. The catalyst synthesized is

mainly used for polyethylene production and the same can be

used for polypropylene by introducing suitable adjuvants like

esters, ethers etc. at appropriate steps in the catalyst synthesis.1

During the titanation process huge quantities of chloroalkoxy

titanium containing species are generated which get mixed with

the titanation mixture. Reuse of the titanation mixture necessi-

tates a correct understanding of the proper composition of the

components. Due to the corrosive nature of TiCl4 routine esti-

mation methods involving chromatography and spectroscopy

are limited.2–5 Even recent findings in this subject use highly

sophisticated techniques which are far away from practical use in

industries.6,7

The estimation of TiCl3(OEt) and TiCl4 in the titanation

mixtures used during the catalyst preparation using reused and

recovered mixed solvent assumes significance since the compo-

sition of the mixture is of utmost importance.8–14 TiCl3(OEt)

which gets generated as an intermediate gets mixed with TiCl4and chlorobenzene generating mixed solvent. This mixed solvent

goes to the solvent recovery unit and the distillate analysis

Reliance Technology Group, Vadodara Manufacturing Division, RelianceIndustries Limited, Vadodara, India 391 346. E-mail: Krishna.sarma@ril.com; Sudhakar.padmanabhan@ril.com; Fax: +91 265 669 3934; Tel:+91 265 669 6494

912 | Anal. Methods, 2010, 2, 912–915

towards the TiCl3(OEt), TiCl4 and chlorobenzene contents

decide how much of TiCl4 or chlorobenzene has to be added to

get the desired composition of the titanation mixture. An idea of

the composition of such mixed solvent in terms of TiCl4 and

TiCl3(OEt) content can be obtained through a combination of

UV-vis spectroscopy15,16 and GC from titanium and ethoxy

content estimation.17 The present work also describes the esti-

mation of TiCl4 and TiCl3(OEt) using simple acid–base titration

along with GC. Results have been compiled on synthetic mixtures

made in the laboratory and the same has been compared against

results of mixed solvent generated in the lab. The merits and

demerits of the technique have also been discussed.

Experimental

General experimental manipulations

All glasswares used were oven dried and cooled under N2 flow

before the experiment. Experiments were performed in a well

ventilated fume hood, wherever possible and applicable. Safety-

wares were used while handling corrosive and toxic materials like

TiCl4. All manipulations like handling and transfer of reagents

were carried out in a nitrogen glove bag as far as possible.

Preparation of synthetic mixtures of TiCl3(OEt) and TiCl4 in

chlorobenzene

A known amount of freshly synthesized TiCl3(OEt) was weighed

into a dry 50 mL reagent bottle to which a known quantity of

This journal is ª The Royal Society of Chemistry 2010

Table 1 The composition of the four synthetic mixtures made andanalyzed

Samplenumber

% of TiCl3(OEt)(By weight)

% of TiCl4(By weight)

% of Chlorobenzene(By weight)

1 4.92 27.30 67.802 8.05 37.09 54.913 14.75 40.02 45.314 19.46 41.39 39.22

Table 2 The composition of the four reaction mixtures studied

Sample number TiCl3(OEt) (g)Benzoylchloride (mL) Solvent (mL)

1 0.20 0.2 252 0.50 0.4 253 1.03 0.8 254 1.82 1.5 25

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freshly distilled chlorobenzene was added to dissolve the

TiCl3(OEt). Subsequently a known quantity of TiCl4 was added

and the mixture homogenized to get a synthetic mixture of

known composition (Table 1).

Aqueous hydrolysis

In a typical experiment 0.1786 g of TiCl3(OEt) was transferred

quickly into an Erlenmeyer flask containing 30 mL of chilled

distilled water. The flask was stoppered immediately to prevent

the escape of the generated HCl vapor. After swirling the flask to

homogenize the contents it was titrated against 0.268 N NaOH

using phenolphthalein as the indicator. The end point (appear-

ance of pink color) was not steady since the rate of hydrolysis was

sluggish especially near the end point due to incomplete hydro-

lysis. Further addition of a couple of drops of alkali completed

the hydrolysis and gave the correct end point.

Alkaline hydrolysis

This experiment was carried out in an analogous manner as

described above, except the material was hydrolysed using excess

of standard NaOH solution and the excess alkali was determined

through back titration. For 0.2 g of sample, 25 to 30 mL of 0.25

N NaOH was enough for the experiment. Here there was no

ambiguity on the end point since complete hydrolysis and

neutralization had taken place.

Estimation of total titanium by UV-vis method

The titanium content was determined by digesting a known

quantity (�0.5 g) of the synthetic mixture with 4 N sulfuric acid,

making up to a known volume (250 mL) and then treating an

aliquot with hydrogen peroxide in a 100 mL volumetric flask—

the dilutions were done with distilled water, wherever needed.

The absorbance of the yellow solution was then taken at 410 nm

on a UV-vis spectrophotometer as per standard operating

procedure.15 The absorbance was then converted to concentra-

tion of Ti using the calibration curve already generated. The

overall Ti percentage in the synthetic mixture was computed.

This procedure was adopted for the four synthetic mixtures.

Reaction of TiCl3(OEt) with benzoyl chloride (formation of

TiCl4.ethyl benzoate adduct)17

A weighed quantity of TiCl3(OEt) was dissolved in a conical flask

using dry chlorobenzene. Benzoyl chloride was then added

dropwise under stirring for about 15 min at ambient temperature

resulting in a bright yellow precipitate. The entire contents of the

flask were then subjected to hydrolysis using 0.5 N sulfuric acid

This journal is ª The Royal Society of Chemistry 2010

to liberate the ethyl benzoate. The reaction mixture was then

subject to extraction (thrice) with n-heptane. The heptane

extracts containing ethyl benzoate were made up to a known

volume for quantitative GC analysis. The aqueous portion was

also made up to a known volume for quantitative GC analysis

for ethoxy content, if any (Table 2).

Estimation of ethoxy content by GC

The ethoxy content was determined by hydrolysing a known

quantity (�10 to 20 g) of the synthetic mixture with 0.5 N sulfuric

acid, separating the chlorobenzene layer and making up the

aqueous portion to a known volume. The aqueous portion

containing the liberated ethanol was quantitatively analyzed by

GC to get the ethoxy content in the synthetic mixture. Sub-

tracting this value from the overall Ti, the Ti content due to TiCl4was calculated.

Results and Discussion

The typical Ziegler–Natta catalyst synthesis for ethylene or

propylene polymerization involving titanation of Mg support by

TiCl4 is a well studied area.1 During this process TiCl3(OEt)

which gets generated as an intermediate gets mixed with TiCl4and the solvent used. Thus, if a suitable method could be

improvised to accurately weigh these materials which are

hygroscopic and further prevent the escape of the liberated HCl

during hydrolysis, the concept of a simple acid–base titration in

estimating them should work as shown in the chemical eqn (1)

and (2) using phenolphthalein as indicator. Depending upon the

care taken during weighing, transfer and storage of the sample,

results in the range of 99 � 1% were obtained. Accommodating

the slight error margin (on the higher side), the method probably

is the easiest classical way of analyzing TiCl3(OEt) and TiCl4.

TiCl4 + 4H2O / TiO2.2H2O + 4HCl (1)

TiCl3(OEt) + 4H2O / TiO2.2H2O + 3HCl + EtOH (2)

Replacing water in eqn (1) and (2) with excess of NaOH

considerably favors the forward reaction resulting in quick

neutralization of the acid generating sodium chloride as shown in

eqn (3).

HCl + NaOH / NaCl + H2O (3)

When both TiCl4 and TiCl3(OEt) are present as in the case of

a synthetic mixture or in mixed solvent, the estimation of the

ethoxy content through quantitative GC gave the amount of

TiCl3(OEt) present in the system. This helped in distributing the

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liberated HCl in the correct proportion based on the TiCl4 and

TiCl3(OEt) content so that the composition could be calculated

properly using the above equations and information.

Fig. 2 TiCl3(OEt) estimation parity plot.

Estimation of TiCl3(OEt) by aqueous hydrolysis

Based on the theoretically expected quantity of HCl that will be

generated from the amount of TiCl3(OEt) taken and converting

the volume of standard NaOH to the equivalent amount of HCl

(practically obtained), the assay or purity of TiCl3(OEt) was

calculated. Results obtained indicated a value of 2 to 3% on the

higher side in most of the cases. The probable reason for this was

the extreme hygroscopicity of this material which always resulted

in some free HCl present along with the material even during the

weighing/transferring process. If utmost care could be taken

during weighing/transfer/storage of the sample, the results were

in the range of 99 � 1%. The assay obtained through ethoxy

group estimation by quantitative GC was about 99 � 2%, also

complementing the titration method.

Estimation of TiCl3(OEt) by alkaline hydrolysis

This experiment was carried out through hydrolysis using excess

of standard NaOH solution and the excess alkali was determined

by back titration. The results were on the higher side to an extent

of 2 to 3% for the reasons discussed under aqueous hydrolysis.

Estimation of TiCl4 by aqueous hydrolysis and alkaline

hydrolysis

This involved weighing of an extremely hygroscopic and reactive

liquid and hence proper care had to be taken during weighing

and transfer of TiCl4 to prevent loss of HCl vapour.6,7 If the

reagent bottle was not stoppered under nitrogen properly,

progressive hydrolysis took place resulting in the material getting

contaminated with free HCl thus giving rise to higher values

(�3–5%).

Typical results obtained on a random basis are depicted

graphically as shown in Fig. 1. It can be clearly seen that there are

values below 100% also indicating that sample handling during

weighing/transfer/storage was of utmost importance.

Estimation of TiCl3(OEt) and TiCl4 in synthetic mixtures by

alkaline hydrolysis

The synthetic mixtures prepared as per Table 1 were analyzed for

validating the concept. 0.54 g of synthetic mixture 1 was

Fig. 1 TiCl4 estimation by acid–base titration.

914 | Anal. Methods, 2010, 2, 912–915

neutralized with 40 mL of 0.268 N NaOH and 19.2 mL of

0.2036 N HCl was required for back titration of the excess

NaOH. This worked out to 0.249 g of HCl which was liberated

during the hydrolysis of TiCl3(OEt) and TiCl4 present in the

synthetic mixture. The theoretically expected amount of HCl was

0.2382 g (0.0053 g from TiCl3(OEt) and 0.2329 g from TiCl4).

This revealed that the estimated result was slightly on the higher

side. A similar trend was also observed while analyzing the other

synthetic mixtures. Overall titanium content in the synthetic

mixtures was independently determined by standard UV-vis

spectroscopic method and the results were in agreement with the

titration results.

A parity plot correlating the theoretically expected and prac-

tically obtained amounts of TiCl3(OEt) and TiCl4 in the synthetic

mixtures through acid–base titration are given in Fig. 2 and

Fig. 3.

The slope and R2 values from the parity plots justify the

agreement between theoretically expected and practically

obtained results for the components in the synthetic mixtures.

Conversion of TiCl3(OEt) in the synthetic mixtures into

TiCl4(ethyl benzoate) adduct and subsequent estimation of ethyl

benzoate

All the synthetic mixtures prepared vide Table 2 where the

conversion of TiCl3(OEt) into TiCl4 (ethyl benzoate) adduct

through benzoyl chloride reaction was accomplished were sepa-

rately hydrolysed. The heptane extracts and the aqueous

portions were analysed for ethyl benzoate and ethanol respec-

tively by quantitative GC (Table 3).

Fig. 3 Parity plot-estimation of TiCl4..

This journal is ª The Royal Society of Chemistry 2010

Fig. 4 Ethoxy in TiCl3(OEt) to EB through benzoyl chloride—parity

plot.

Table 3 Estimation of ethoxy content

Samplenumber TiCl3(OEt) (g)

Ethylbenzoate(Theoretical, g)

Ethylbenzoate(Obtained by GC, g)

Ethanol(Theoretical, g)

Ethanol(Obtained by GC, g)

1 0.20 0.15 0.14 Nil Not detected2 0.50 0.40 0.38 Nil Not detected3 1.03 0.80 0.78 Nil Not detected4 1.82 1.50 1.37 Nil Not detected

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A parity plot correlating the theoretically expected and prac-

tically obtained amount of ethyl benzoate is shown in Fig. 4.

The slope and R2 values reflect the close agreement between

theoretically calculated and practically obtained results for ethyl

benzoate in the synthetic mixtures. The absence of ethanol in the

aqueous portion indicated that the ethoxy group had quantita-

tively reacted with benzoyl chloride to generate the TiCl4 (ethyl

benzoate) adduct. This technique served as an alternate method

for estimating TiCl3 (OEt) in isolation or in a mixture.

The developed concept was extended to real time mixed

solvent samples generated in the catalyst preparation stage in the

laboratory. The ethoxy content was quantitatively determined by

GC. This enabled the total HCl liberated to be proportioned

between TiCl3(OEt) and TiCl4 present in the mixture. This

composition of the used titanation mixture could be adjusted

accordingly for further reuse in subsequent catalyst synthesis.

Conclusions

TiCl4 and TiCl3(OEt) could be estimated through simple and

elegant ways either separately or in a mixture. The determination

is based on the simple concept of acid–base titration which could

be carried out easily in a laboratory. The parity plots reflect the

excellent agreement between the theoretical and experimental

This journal is ª The Royal Society of Chemistry 2010

values, thus validating the concept. The efficiency of the method

should improve if the technique of weighing TiCl4 and mixed

solvent could be perfected.

Acknowledgements

The authors sincerely thank Dr. R. V. Jasra and Dr. A. B.

Mathur for their continuous encouragement to carry out this

work. The authors also thank Dr. Pradip Munshi and Dr. Sumit

Bhaduri for their valuable suggestions during the course of this

work.

References

1 For synthesis of catalyst recipes from Mg(OEt)2 + TiCl4 see:J. Berthold, B. Diedrich, R. Franke, J. Hartlapp, W. Schafer andW. Strobel, US 4447587, 1984; US 4448944, 1984.

2 R. F. Rolsten and H. H. Sisler, J. Am. Chem. Soc., 1957, 79(8),1819–1821.

3 R. E. Sievers, WheelerJr, G. Ross and W.O., Anal. Chem., 1966, 38(2),306–309.

4 R. S. JuvetWachi and F. M, Anal. Chem., 1960, 32(2), 290–291.5 E. Rytter and S. Kvisle, Inorg. Chem., 1985, 24(5), 639–640.6 Y. K. Agrawal and S. Sudhakar, Talanta, 2002, 57(1), 97–104.7 T. Kapias and R. F. Griffiths, J. Hazard. Mater., 2005, 119(1–3),

41–52.8 J. H. Haslam, Chemistry and Uses of Titanium Organic Compounds,

Metal–Organic Compounds, Chapter 25, 1959, 272–281.9 J. E. McMurry, Acc. Chem. Res., 1974, 7, 281–286.

10 I. Shiihara, W. T. SchwartzJr. and H. W. Post, Chem. Rev., 1961, 61,1–30.

11 O. Babaiah, C. K. Rao, T. S. Reddy and V. K. Reddy, Talanta, 1996,43(4), 551–558.

12 P. J. Elving and E. C. Olson, Anal. Chem., 1955, 27(11), 1817–1820.13 M. K. Akhtar, S. Vemury and S. E. Pratsinis, AIChE J., 1994, 40,

1183.14 M. Rigo, P. Canu, L. Angelin and G. Della Valle, Ind. Eng. Chem.

Res., 1998, 37, 1189–1195.15 A text book of quantitative inorganic analysis including elementary

instrumental analysis by A. I. Vogel, third edition (1975), ELBSLongman publications.

16 W. C. Wolfe, Anal. Chem., 1962, 34(10), 1328–1330.17 D. Lee, Y. Jeong and K. Soga, Ind. Eng. Chem. Res., 1992, 31,

2642–2647.

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