Continuous transesterification processes

Ravindranath, K. and Mashelkar, R. A., Modeling of poly(ethylene terephthalate) reactors 2. A continuous transesterification process,./. Appl. Polym. Sci., 27, 471-487 (1982). 

Lion Corporation of Japan developed a continuous transesterification process using unrefined feedstock known as the ES process. The free fatty acid in the oil is pre-esterified by passing the feedstock and methanol through a packed column of a special catalyst resin, after which transesterification is conducted through a two-stage reactor. A high conversion rate of more than 99% is claimed (16). 

Commercial industrial processes can be operated in a either batch or a continuous mode. Batch processes are suitable for small plants, while for larger plants (>100 000 ty ) continuous process tend to be more economical. In the ESTERFIP batch process (IFF license), transesterification occurs in a single stirred-tank reactor. Continuous transesterification processes include the Ballestra, Connemann CD and... 

For both continuous and batch transesterification processes, around 4 kg of salts is co-produced in the glycerol phase per ton of oil processed. This salt is left to be treated by glycerol end users. 

Abstract Biodiesel is a fatly acid alkyl ester that can be derived fiom any v etable oil or animal fat via the process of transesterification. It is a renewable, biodegradable, and nontoxic fuel. In this paper, we have evaluated the efficacy of a transesterification process for rapeseed oil with methanol in the presence of an enzyme and tert-butanol, which is added to ameliorate the negative effects associated with excess methanol. The application of Novozym 435 was determined to catalyze the tiansesterification process, and a conversion of 76.1% was achieved under selected conditions (reaction temperature 40 °C, methanol/oil molar ratio 3 1, 5% (w/w) Novozym 435 based on the oil weight, water content 1% (w/w), and reaction time of 24h). It has also been determined that rapeseed oil can be converted to fatty acid methyl ester using this system, and the results of this study contribute to the body of basic data relevant to the development of continuous enzymatic processes. 

The use of methanol offers the best results in the trans-esterification of oils and fats. Compared with other alcohols, methanol requires shorter reaction times and smaller catalyst amounts and alcohol/oil molar ratios [10,12,15,16,51,52]. These advantages lead to reduced consumption of steam, heat, water, and electricity, and use of smaller processing equipment to produce the same amount of biodiesel. Biodiesel applications continue to expand. Thus, in addition to its use as fuel, biodiesel has been employed in the synthesis of resins, polymers, emulsifiers, and lubricants [53-64]. Concerning the range of applications, new biodiesel production processes should be considered as alternatives to the production based on methanol. Currently, methanol is primarily produced from fossil matter. Due to its high toxicity, methanol may cause cancer and blindness in humans, if they are overexposed to it. Methanol traces are not desired in food and other products for human consumption [15]. In contrast, ethanol emerges as an excellent alternative to methanol as it is mainly produced from biomass, is easily metabolized by humans, and generates stable fatty acid esters. Additionally, fatty acid ester production with ethanol requires shorter reaction times and smaller amounts of alcohol and catalyst compared to the other alcohols, except methanol, used in transesterification processes [11,15,16]. 

Muley, P., Boldor, D., 2013. Scale-up of a continuous microwave-assisted transesterification process of soybean oil for biodiesel production. Transactions of the Asabe56 (5), 1847—1854. 

The deciding factor for optimum temperature of the Upase-catalyzed reaction includes immobilization, stabUity of Upase, alcohol to oil molar ratio and the type of solvent. In the continuous process, temperature is the key operational factor (Fjerbaek et al., 2009). In conclusion, the optimum temperature for the enzymatic transesterification process results fiom the interaction between the operational stability of the Upase and the rate of transesterification reaction (Gog et al., 2012). 

A continuous process has been developed for preparing borate esters usiag transesterification (24). Another modification of this method has been reported where use of molecular sieves (qv) to absorb the low boiling alcohol is used rather than distillation (25). 

For transesterification/esterfication, continuous reactors may be more attractive than batch reactors. This is particularly true if a distillation-column reactor can be adopted, as it tends to use a much lower ratio of reactants to drive the reaction to the desired degree of conversion, entailing lower energy lost. Even when metal alcoholates are used these can be recycled, eliminating problems faced in batch plants. Relative process costs may well approach 50% of those in batch plants. Higher purity, less plant down time, better process control, and improved yield are other attractive features of continuous plants (Braithwate, 1995). 

Esterification of linalool requires special reaction conditions since it tends to undergo dehydration and cyclization because it is an unsaturated tertiary alcohol. These reactions can be avoided as follows esterification with ketene in the presence of an acidic esterification catalyst below 30 °C results in formation of linalyl acetate without any byproducts [71]. Esterification can be achieved in good yield, with boiling acetic anhydride, whereby the acetic acid is distilled off as it is formed a large excess of acetic anhydride must be maintained by continuous addition of anhydride to the still vessel [34]. Highly pure linalyl acetate can be obtained by transesterification of tert-butyl acetate with linalool in the presence of sodium methylate and by continuous removal of the tert-butanol formed in the process [72]. 

Recently, Feng [274] reported a continuous process for the transesterification of EC with methanol in a flow reactor over a dibutyl amine catalyst immobilized on a MCM-41 molecular sieve (n-Bu2N-MCM-41). The catalyst performed well and afforded 25.5% and 41.7% EC conversions at 283 and 323 K, respectively, and also exhibited a good stability. Arai and coworkers [275, 276] subsequently performed the preparation of DMC in two steps (Scheme 7.18). 

On 5-10 000 ton pilot-plant level, chemical and now also biological 1,3-PPD have been incorporated into PPT fibers. The fiber product, Sorona , is synthesized in a continuous process via transesterification from dimethyl terephthalate ( T ) and 1,3-propanediol ( 3-G ) with the help of a catalyst to the polymer ( 3-GT ), finished under vacuum, and pelletized. Figure 20.12 summarizes the process. 

Several technologies can be employed. The most widespread today makes use of homogeneous catalysts, in batch or in continuous-flow environments. Both reaction and separation steps can create bottlenecks. The availability of heterogeneous catalysis allows the suppression of neutralization and washing steps, leading to a simpler and more efficient process. However, the research of super active and robust catalysts is still an open problem. Supercritical hydrolysis and transesterification can be conducted without a catalyst, but in extreme conditions of pressure and temperature. 

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