Integration of Solvent Extraction and Noncatalytic Esterification for the Treatment of Acidic Feedstocks

Abstract

The possibility of directly feeding the extract of a liquid−liquid extraction unit to a chemical reactor is analyzed. An example of extraction and noncatalytic esterification of naphthenic acids from acid petroleum crudes is used. Methanol is used both as a solvent and as a reactant. Separate tests of extraction and reaction are performed, and the performance of an integrated process is deduced by computer simulation. Thermodynamic and kinetic parameters for the extraction of naphthenic acids from an acid crude were determined. A partition coefficient of m = 0.66 at 60 °C between the alcoholic and petroleum phases was found. Three successive batch extractions with a 1:1 v/v ratio reduced the acidity from 4.3 to about 1.1 mg KOH g −1 . Naphthenic acid concentrates were reacted with supercritical methanol in a batch reactor at high temperatures (280 °C), yielding naphthenic esters. Reaction of 1−2 h with methanol-to-oil molar ratios of 3−6 yielded 92−96% conversion because of a relatively low value of the equilibrium constant. Total conversion could, however, be achieved with the highly diluted extracts. Simulations were run using three countercurrent mixer−settlers and a noncatalytic reactor. The results indicated that extraction/supercritical esterification is a convenient pretreatment step of acidic feedstocks because of its simplicity, the good quality of the deacidified feedstock (acidity <0.5 mg KOH g −1 ), the total removal of the acids, and the good properties of the ester product as a fuel additive. Characterization of the methyl naphthenate product showed that it had a lower viscosity than the crude or the naphthenic acids; a high flash point; and total miscibility in gasoline, kerosene, and diesel. These and other properties showed that it could be sent to the diesel or fuel oil pools. 46 extraction does not act as a reagent but it is a suitable solvent 47 for carrying out a reaction on the solute with good activity and 48 selectivity to the desired product. These two requirements add 49 to other requirements for choosing a suitable solvent for 50 extraction. These have been extensively reviewed in the 51 literature 4−6 and can be summarized as follows: (a) a high 52 solubility for the solute and low solubility for the feed; (b) a 53 density difference with the feed, higher than 0.15 g cm −3 ; (c) a 54 medium value of surface tension (5−30 dyne cm −1 ); (d) a high 55 resistance to thermal degradation if solvent regeneration by 56 evaporation is used; and (e) a low viscosity for ease of 57 handling. 58 Noncatalytic esterification is a brute-force method making 59 use of the nucleophilic reactive properties of supercritical 60 alcohols. From a process point of view, it has the advantage 61 that it is scalable to any scale of production and is easily 62 implemented. Major drawbacks in comparison to catalytic 63 esterification are the high temperature and pressure levels 64 involved and the need for efficient heat-recovery schemes. 7−10 65 In this report, the esters obtained in the supercritical reactor

Supercritical transesterification route for biodiesel production: Effect of parameters on yield and future perspectives

“…For conducting transesterification at very high temperature and pressure, the previous researchers reported the reactor and accessories made of stainless steel grade of 304 and 316, which is itself a costly material in the engineering field. The authors also reported no reactivity of reactant media with SS‐316 and SS‐304 36,37 . Although, a search for better and feasible material can also be the future scope from the reactor design point of view.…”

“…Lamba et al 85 concluded the superiority of this method for Neem and Mahua as feedstock and reported the yield of 83% in 15 min and 99% in 10 min, respectively. Naphthenic acid was also tried as feedstock for supercritical esterification and found the end product a good fuel additive 36 . Some of the past investigations are showing exciting results for algae and stabilizing it as the future's most productive feedstock for biodiesel production 35,45,90 …”