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Polyethoxylation and polypropoxylation

Summary of the work made

We have studied in detail many aspects of ethoxylation and propoxylation reactions for obtaining polyethoxylated surfactants or polymers. At this purpose, we helped Pressindustria Co. in developing their technology based on the use of Spray Tower Loop Reactors. We studied for example the ethoxylation of fatty alcohol in any kind of reactor from semibatch laboratory reactors to pilot and industrial Spray Tower Loop Reactors. Adequate kinetic models have been developed for simulating the behavior of all the mentioned reactors. The aspects related to the safety in managing the EO plants have also been studied.



Polyethoxylation and polypropoxylation reactions are performed, in industry, for preparing non ionic surfactants and polymers. These reactions are highly exothermic (~20 Kcal/mole) and require an efficient heat exchange to avoid the hazard of runaway that is particularly dangerous for the possible intervention, at high temperature, of explosive side reactions. The reaction is, normally, promoted by alkaline catalysts, such as, NaOH or KOH. It has been generally accepted that ethoxylation and propoxylation promoted by alkaline catalysts occur through a nucleophilic substitution SN2. Therefore, the nucleophilicity of the anion, that is a peculiarity of the type of used starter, is very important in promoting the oxirane ring opening. As a consequence, the differences observed in the activities of respectively alkoxide, phenoxide and carboxylic anions are dramatic [1-3]. The acidity of the starter, is important, too, strongly influencing the proton transfer equilibria and, hence, affecting the oligomers distribution. The alkaline catalysts act as an ionic couple [1] and larger is the ionic radius of the cation more active is the catalyst. On the basis of the above mentioned experimental observations we can write:

In the case R’= H the two carbon atoms are identical, while, in the case R’= CH3 the attack to the methylenic carbon atom is more favorite [4]. The difference between EO and PO addition is that in the former case we always obtain primary alcohols otherwise, in the latter case we obtain secondary alcohols that are less reactive. Considering the mentioned intervention of the ionic couple we can write for an alkoxylation reaction the following mechanism:





Proton transfer

As the alkoxylation reactions occur with a SN2 mechanism, we can write the following kinetic laws:




       i=1,…, n

The concentration of charged species, appearing in the kinetic laws, can be calculated by combining equations of proton transfer equilibria with mass and charge balance equations:



By assuming with a reasonable approximation




we obtain


where B° is the overall catalyst concentration.

It is, therefore, possible to calculate the concentration of each ionic pair (active species) by introducing the corresponding equilibrium constant Kei and the concentrations of the oligomers.

As it can be seen the alkoxylation rate can be affected by the following four factors: (i) the type of used starter influencing the concentration of the ionic pair; (ii) the type and the concentration of the alkaline catalyst, respectively influencing the values of k0 and ki and the concentration of the ionic pairs; (iii) the concentration of the alkylene oxide that is related to its solubility in the starter and to its partial pressure in the reactor; (iv) the temperature strongly influencing all the kinetic constants and the alkylene oxide solubility.

Despite the industrial importance of the mentioned reactions different papers have been published on the kinetic aspects and reactor technology of ethoxylation and propoxylation almost exclusively by our group [1-25]. As seen, key factors in alkoxylation technology are respectively: 1) The type of starter employed (hydrophobic like nonylphenol [1], fatty alcohol [2], fatty acid [3] or hydrophilic as ethylene or propylene glycols [4,5,25]; 2) The solubility of ethylene or propylene oxide in the starter [7,8]; 3) The types of reactors employed and their performances [9- 14]; 4) The role of kinetics and mass transfer in the process [1-5, 9-12]; 5) The safety problems [15-18]. All these aspects have been studied in detail by us and much information can be found in our literature [1-18, 24,25]. The study of the performances of Narrow Range Catalysts is also worth to be mentioned [19-23]. The reaction is, normally, performed into gas-liquid mixed reactors, Venturi loop reactors or spray tower loop reactors. The schemes of the three mentioned reactors are respectively reported in Figures 1, 2 and 3. As it can be seen, in the first two reactors, the gas phase is dispersed into the liquid one and mass transfer and reaction occur in the same zone of the reactor. On the contrary, in the last reactor, the liquid phase is dispersed in the form of small drops in the gaseous one and mass transfer and reaction occur in two different zones of the reactor. Two different models are necessary, therefore, to reproduce the performances of the mentioned reactors, one considering the behaviour of a semibatch stirred tank reactor and another one considering the behaviour of a spray tower loop reactor with a plugflow-like behaviour. These two different models and the key factors respectively influencing the kinetics, the heat and the mass transfer and the safety are largely discussed in the cited literature. We have intensively collaborated in the past with Pressindustria, Scientific Design and Desmet Ballestra improving the performances of their reactors and increasing in the meantime the safety of the operation.

Figure 1 – Schemes of Semibatch Stirred Tank Reactors mainly employed industrially for alkoxylation processes, differing only in the heat exchange system adopted.


Figure 2 – Scheme of the Venturi Loop Reactor.

Figure 2 – Scheme of the Venturi Loop Reactor.


Fig. 4 - Spray nozzle characterization

Fig. 5 - Laboratory plant of a spray tower loop reactor

Literature on polyethoxylation and polypropoxylation

Kinetics, mass transfer and reactos modelling

  1. E. Santacesaria, M. Di Serio, L. Lisi, D. Gelosa; "Kinetics of nonylphenol polyethoxylation catalyzed by potassium hydroxide". Ind.Eng.Chem. Research 29, 5, 719 (1990).

  2. E. Santacesaria, M. Di Serio, R. Garaffa, G. Addino; "Kinetics and mechanisms of fatty alcohol Polyethoxylation. 1.The Reaction Catalyzed by Potassium Hydroxide" Ind. Eng. Chem. Research 31,11,2413 (1992)

  3. M. Di Serio, S. Di Martino, E. Santacesaria; “Kinetics of Fatty Acids Polyethoxylation" Ind. Eng. Chem. Res.33,3,509(1994)

  4. M. Di Serio, G. Vairo, P. Iengo, F. Felippone, E. Santacesaria; “ Kinetics of ethoxylation and Propoxylation of 1 and 2-octanol catalyzed by KOH” Ind. and Eng. Chem. Research, 35, 3848 (1996)

  5. M. Di Serio, R. Tesser, A. Dimiccoli, E. Santacesaria; “Kinetics of Ethoxylation and Propoxylation of Ethylene Glycol Catalyzed by KOH” Ind. Eng. Chem. Res. 41 (2002) 5196-5206

  6. E. Santacesaria, M. Di Serio, P. Radici, L. Cavalli, R. Garaffa; "Kinetics and Mass Transfer in Polyethoxylation Reactions". La Rivista Italiana delle Sostanze Grasse 68,5,261 (1991) require abstract to

  7. E. Santacesaria, M. Di Serio, R. Tesser; “Role of ethylene oxide solubility in the ethoxylation processes”; Catalysis Today 24,23-28 (1995)

  8. M. Di Serio, R. Tesser, F. Felippone, E. Santacesaria; “Ethylene oxide solubility and ethoxylation kinetics in the synthesis of nonionic surfactants”; Ind. Eng. Chem. Research 34, 4092-4098 (1995)

  9. E. Santacesaria, M. Di Serio, P. Iengo; “Kinetic and reactor simulation for polyethoxylation and polypropoxylation reactions”. (G.F. Froment and K.C. Waugh Eds) Reaction Kinetics and the Development of Catalytic Process, 267-274, Elsevier Science B.V. (1999)

  10. E. Santacesaria, M. Di Serio, P. Iengo; “Mass transfer and kinetics in ethoxylation spray tower loop reactors”. Chem. Eng. Sci. 54, 1499-1504 (1999).

  11. Dimiccoli, M. Di Serio, E. Santacesaria; “Mass Transfer and Kinetics in Spray-Tower-Loop Absorbers and Reactors”. Ind. Eng. Chem. Res. 39, 4082-4093 (2000)

  12. A. Dimiccoli, M. Di Serio, E. Santacesaria; “Key factors in ethoxylation and propoxylation technology”. 5RD CESIO, Proceedings, World Surfactant Congress, Firenze, vol. 1, 99-110 (2000)

  13. Di Serio, Martino; Tesser, Riccardo; Santacesaria, Elio. “Comparison of Different Reactor Types Used in the Manufacture of Ethoxylated, Propoxylated Products.” Industrial & Engineering Chemistry Research (2005), 44(25), 9482-9489.

  14. Santacesaria, Elio; Di Serio, Martino; Tesser, Riccardo. “Gas-Liquid and Gas-Liquid-Solid Reactions Performed in Spray Tower Loop Reactors.” Industrial & Engineering Chemistry Research (2005), 44(25), 9461-9472

Safety problems in polyethoxylation

  1. Salzano, Ernesto; Di Serio, Martino; Tortora, Ciro; Santacesaria, Elio. Consequence-based safety analysis of alkoxylation processes. Institution of Chemical Engineers Symposium Series (2007), 153 paper109/1-paper109/6.

  2. Salzano, Ernesto; Di Serio, Martino; Santacesaria, Elio. The role of recirculation loop on the risk of ethoxylation processes. Journal of Loss Prevention in the Process Industries (2007), 20(3), 238-250.

  3. Salzano, Ernesto; Di Serio, Martino; Santacesaria, Elio. The evaluation of risks of ethoxylation reactors. Process Safety Progress (2007), 26(4), 304-311.

  4. Salzano, Ernesto; Tortora, Ciro; Di Serio, Martino; Santacesaria, Elio. The evaluation of risks of ethoxylation processes. AIChE Spring National Meeting, Conference Proceedings, Houston, TX, United States, Apr. 22-27, 2007 (2007)

Narrow Range Ethoxylation

  1. E. Santacesaria, M. Di Serio, R. Garaffa, G. Addino; "Kinetics and mechanisms of fatty alcohol polyethoxylation 2.Narrow-Range ethoxylation obtained with Barium Catalyst. Ind. Eng. Chem. Research 31,11,2419 (1992)

  2. E. Santacesaria, M. Di Serio, G. Addino, R. Garaffa; Mechanisms of the Narrow Range Ethoxylation. 3RD CESIO, Procedings, World Surfactant Congress, vol. 2, 281-290 (1992)

  3. M. Di Serio, P. Iengo, R. Gobetto, S. Bruni, E. Santacesaria; “ Ethoxylation of fatty alcohols promoted by an aluminum alkoxide sulphate catalyst”; Journal Molecular Catalysis A: Chemical 112, 235 (1996).

  4. E. Santacesaria, M. Di Serio, P. Iengo; Narrow Range Ethoxylation obtained with alkoxides sulphate catalysts; 4th World Surfactant Congress Barcelona, 3-7 (1996) 497-506

  5. M. Di Serio, P. Iengo, G. Vairo, E. Santacesaria; “Narrow range ethoxylation of fatty alcohols promoted by zirconium alkoxide sulphate catalyst”. Journal of Surfactant and Detergent 1 (1998) 1, 83-91.

Chapters in books

  1. E. Santacesaria, P. Iengo, M. Di Serio;“Catalytic and kinetic effects in ethoxylation processes”. (D.R. Karsa Ed.) Design and Selection of Performance Surfactants, Sheffield Accademic Press (1999)

  2. Santacesaria, Elio; Di Serio, Martino; Tesser, Riccardo “Production of ethylene oxide/propylene oxide block copolymers”. Surfactant Science Series (2009), 142 (Handbook of Detergents, Part F)