SANDMEYER PRIZE 2003 799 CHIMIA 2003, 57, No.12

Chimia 57 (2003) 799–801 © Schweizerische Chemische Gesellschaft ISSN 0009–4293

Process for the Continuous Production of Fatty Acid Esters via Reactive Distillation

Claudia von Scala*, Peter Moritz, and Peter Fässler Sandmeyer Prize Laureates 2003

Abstract: Sulzer Chemtech develops chemical processes in close collaboration with its customers that lead to lower operating and investment costs as well as reduced environmental impact, while at the same time increasing the yield. In this context, innovative technologies and collaboration in global teams play an important role. This is exemplified by the continuous production of fatty acid esters using reactive distillation. Keywords: Esterification · Fatty acid esters · Katapak · Reactive distillation · Sandmeyer Prize

Fatty Acid Esters Reactive Distillation Processes of applications can be found in the article of Götze et al. [2]. Furthermore, Sulzer Food, textiles, and cosmetic applications Reactive distillation, i.e. the combina- Chemtech has developed many processes comprise the largest use of fatty acid esters. tion of chemical reaction and distillative using reactive distillation. The scope of Other uses for fatty acid esters are in the product separation in one equipment, offers supply for the reactive distillation technol- processing of rubbers and plastics, metal several advantages over conventional ogy provided by Sulzer Chemtech can in- treatment, synthetic lubricants, and various processes in which the reaction and the clude the process design, pilot tests and test household products. Methyl esters are used product separation are done in series, espe- runs, basic engineering, and the supply of mainly as intermediate raw material for fur- cially for reactions limited by equilibrium Katapak and other distillation column inter- ther chemical conversion into other esters, constraints. As the products in reactive dis- nals. The design of these plants incorpo- amides, ester sulfonates, and fatty alcohols. tillation are continuously separated from rates modern methods for process synthe- Fatty acids, mainly from vegetable the reaction zone, no limiting chemical sis. In addition, Sulzer Chemtech has a sources such as palm trees, soybean, equilibrium can be established and thus the broad know-how and experience in the dis- coconuts, rapeseed or sunflowers, are reaction velocity is maintained at a high tillation of fatty acids, gained during the last mainly produced in the tropical belt, espe- rate, resulting in greater yields. Other ben- 30 years of business in this field. cially in South East Asia, India, China, and efits of reactive distillation can include the Brazil. Processing into fatty acid esters – minimization of side reactions and the uti- esterification – is done mainly in Europe, lization of the heat of reaction for the mass Japan, or the USA. transfer within the same column. Therefore In the esterification reaction, a fatty acid the capital investment and operating costs (e.g. palmitic, myristic, stearic acid) reacts are significantly lower with reactive distil- with an alcohol (e.g. 2-propanol, ethanol, lation than for conventional processes. Ex- butanol, 2-ethyl-1-hexanol) to form the cor- amples for successful applications of reac- respondent fatty acid ester and water. This tive distillation have, among others, been reaction is equilibrium limited, i.e. if at reported for esterifications, etherifications, least one of the products is not removed, the alkylations and isomerizations [1]. conversion will not be complete. Sulzer Chemtech has developed a spe- cial structured catalytic packing, named Katapak, to be used in reactive distillation Fig. 1. Katapak, structured catalytic packing columns (Fig. 1). In this packing, the cata- lyst particles are immobilized between two *Correspondence: Dr. C. von Scala Sulzer Chemtech Ltd. sheets of metal wire gauze. Therefore, con- Conventional Semi-Batch Process P.O. Box 65 ventional catalyst particles can be used, e.g. CH–8404 Winterthur the ones normally recommended by the Esterification of fatty acids with differ- Tel.: +41 52 262 61 41 Fax: +41 52 262 00 68 process or lisense owner. Technical infor- ent alcohols is nowadays mainly performed E-Mail: [email protected] mation of this packing type and further field in a semi-batch mode in large stirred tank SANDMEYER PRIZE 2003 800 CHIMIA 2003, 57, No.12 reactors. A large vessel is filled with the fat- about 100–120 °C. The reactivity of fatty sis. About 15% of the sites were lost be- ty acid mixture to be esterified and heated acids is, however, lower compared with tween the first and the second samples, but up to temperatures above 100 °C. Catalyst shorter acid molecules, and in order to the decrease in reactivity was less intense in is added to the mixture and the whole batch achieve sufficient conversion it was neces- the next samples and stabilized with time. is held at reaction temperature. Alcohol is sary to find solid acid catalysts which are continuously fed to the reaction mixture active in the temperature range of 120–140 and the resulting water is continuously re- °C. By-product formation was also an issue Final Design moved from the column together with the to be considered. A catalyst screening with excess alcohol by a column situated above various potential solid acids was performed In October 2001, after the evaluation of the vessel. Through continuous removal of at the University of Oldenburg, Germany, the pilot tests and based on the process sim- the water produced during the process it is in February 2001. The catalyst chosen was ulation results, the equipment of the plant possible to drive the reaction to completion. a Rohm and Haas cation exchange resin es- was designed. Already by the end of 2001 it At the end the reaction mixture is further pecially developed for the above tempera- was possible to present to the customer an heated and vacuum is applied to remove the ture range. The reaction kinetics were also offer for the production plant. In March excess alcohol and water still present in the determined and used to plan the pilot test 2002, after clarification of the final details, batch. program. the customer ordered the plant, which is While batch processes have the advan- now in the start-up phase. Sulzer Chemtech tage of flexibility in multi-product opera- has also applied for a patent for this pro- tion for small production capacities, their Pilot Tests cess. lower productivity is limiting for larger pro- The total development time of the duction volume. Further disadvantages of After a suitable catalyst was found, the process of less than two years is extremely batch processes are the product quality pilot reactive distillation experiments were short. The development time of similar degradation due to relatively long exposure started in June 2001. In these experiments a processes, from the synthesis in laboratory to heat and the necessity of emptying, part of the future production plant was re- scale to commercial realization, is normal- cleaning and refilling between each batch. produced in small scale to find the optimal ly significantly longer. Through the combi- The catalysts used are normally liquid process conditions and to determine the in- nation of experiences in the field of reac- acids, e.g. sulphuric acid. These acids have fluence of the most important design pa- tion, distillation and membrane technology to be neutralized and separated, generating rameters, like reflux ratio and internal col- a process was realized which has the poten- large amounts of waste products and waste- umn loads on the behaviour of the system. tial to replace in many cases the conven- water. The first pilot tests were performed in a re- tional batch production of fatty acid esters. active distillation column with 50 mm di- ameter at atmospheric pressure. These tests Development of the New Process showed that a higher temperature, i.e. a Process Description higher pressure, in the reactive distillation One of the most important producers column was required. The general tenden- The following description shows the ba- and processors of palm oil and palm oil cies of the system, like the effect of reactant sic principles and suggests a possible pro- products in Malaysia planned to increase its ratio and other distillation parameters, were cess set-up. Depending on (among others) portfolio with fatty acid esters and ap- determined. the raw material composition, the alcohol proached Sulzer Chemtech Singapore in Following the pilot tests at ambient used, the site conditions, and the product the middle of 2000. Sulzer’s idea to devel- pressure, an additional test series was car- specifications, various alternatives can be op a new continuous process with reactive ried out in August 2001 at a higher pressure proposed, fitted to the customer’s individ- distillation utilizing solid catalysts instead (between 3 and 5 bars), with the aim to de- ual requirements. of building a conventional system readily termine the optimal reaction temperature in In this example, the esterification of iso- attracted the attention of the customer. Un- the reactive distillation column. The pro- propyl palmitate with isopropyl alcohol is til now, this technology had not been im- duced ester was distilled and the resulting described (Fig. 2): Palmitic acid (PA) is plemented for the production of fatty acid product was sent to the customer for quali- first reacted with isopropyl alcohol (IPA) in esters. The Malaysian customer was, how- ty analysis. The vapour pressure of the es- a pre-reactor. The pre-reacted stream is then ever, convinced of the potential advantages ter was also determined. All the data pro- introduced into the reactive distillation col- of the technology, so that at the beginning duced in these tests enabled Sulzer Chem- umn, which operates at slight elevated pres- of 2001 he placed an order for the process tech to carry out the scale-up from pilot to sure. Excess IPA is added below the reac- development. Under the leadership of Sulz- production scale. tive section of the reactive distillation col- er Chemtech, an international team of spe- umn to increase conversion and enhance cialists from Asia and Europe started work the stripping of the formed reaction water. on the new technique. Long-Term Activity Tests At the top of the column a mixture of re- action water and IPA is obtained, together A long-term activity test with the cho- with small amounts of diisopropylether Kinetic Tests sen catalyst was also undertaken to deter- (DIPE). At the bottom of the column a mix- mine its stability at operating conditions. ture of isopropyl palmitate (IPP) and unre- The first task was to find a suitable sol- For this, the chosen catalyst was placed in a acted PA with a small amount of IPA is ob- id catalyst for the esterification reaction. pressure vessel. The reactants were added tained. For this task a special tailored Kata- Other reactive distillation processes devel- and the closed vessel placed in an oven to pak packing was used, in which a catalyst oped, e.g. for the production of ethyl and reach operating temperature and pressure. amount of more than 50 vol.-% in the reac- butyl acetate, use ion exchange resins From time to time a sample was taken and tion zone is reached. This allows a signifi- which are only stable up to temperatures of sent to the catalyst manufacturer for analy- cant reduction of the size of the reactive dis- SANDMEYER PRIZE 2003 801 CHIMIA 2003, 57, No.12

Fig. 2. New process. The new process con- sists of pre-reactor, reactive distillation col- umn, membrane module, flash unit, and vac- uum distillation column.

tillation column and leads to a compact tion, with reduced processing time. This performed work was acknowledged with construction of the plant. leads to constant high product quality and at the Sandmeyer Prize of the Swiss Chemical The bottom product of the reactive dis- the same time simpler maintenance and Society (SCS), which was awarded to the tillation column is fed to a flash unit where process control, which is especially worth- team of Sulzer Chemtech in March 2003. the remaining IPA is separated from the while for larger production capacities. Well mixture. This recovered IPAcan be fully re- defined and narrow residence time under Received: October 15, 2003 cycled to the process. The water/IPA mix- gentle conditions throughout the whole ture with traces of DIPE leaving the top of plant minimizes degradation of the fatty [1] M.F. Doherty, G. Buzad, Trans IchemE the reactive distillation column is treated in acids and fatty acid esters. No neutraliza- 1992, 70, 448. a membrane system. Water is pervaporated tion, separation or recycling of catalyst is [2] L. Götze, O. Bailer, P. Moritz, C. von Scala, Catalysis Today 2001, 69, 201. through the membrane and the dry IPA can necessary. There is no necessity to empty be recycled to the pre-reactor or to the re- and clean the equipment, reducing the active distillation column. A purge is pro- waste streams to the absolute minimum. vided to eliminate the DIPE and other low The energy consumption of the new process boiling components which may be present is only half of the conventional batch one. in the feed. Also the size of the plant could be drasti- IPP and PA leaving the flash unit are cally reduced. For the treatment of the dis- separated in a distillation column operated tillate stream from the top of the reactive under vacuum. Special design features en- distillation column – a mixture of isopropyl sure superior IPP product quality. Unreact- alcohol and water – a membrane module is ed PA, collected at the bottom of the distil- used. The so-called pervaporation through lation column, is collected and recycled to a semi-permeable membrane can replace the process, whereas a heavies purge pre- two distillation columns, reducing the total vents the accumulation of impurities in the investment costs of the plant. It also allows process. a direct recycle of surplus alcohol. The same esterification method can be used for any other type of purified fatty acid. A similar approach can be used with Summary methanol or ethanol. In this case no mem- brane unit is needed, but an additional dis- Sulzer Chemtech showed with this de- tillation column to separate the alcohol velopment that, besides the broad know- from the water. Other alcohols like butanol how in the field of process engineering, al- or 2-ethyl-hexanol can be separated by so innovative engineering achievements phase separation from the produced water. and the coordination and management of complex projects in international teams are key competencies of the company. Only Advantages of the New Process through the close cooperation with the client, partners and suppliers in a very ear- The combination of reaction and sepa- ly stage, was it possible to develop a new ration by distillation in one reactive distil- process in extremely short time and to build lation column allows a continuous produc- it in commercial scale. The quality of the