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// //«■ el aL I Fuel 86 (2007) 442-447

materiał. For inslancc. swill oil and frying oil. which acid valuc and wutcr contcnt arc vcry high and composition is complcx. can be easily transformed into biodicscl in super-critical mcthanol.

Because of the advantageous merits of supercritical method. many rcsearchers have eonsidered it important. and a scrics of research work [1,3-6] havc bccn conductcd. However, conipared to the catalytic method. research on the supercritical preparation method are slill limited. Espccially in the field of supercritical production tcchnol-ogy, it is rarely reported. Generally, biodicsel is produced by the batch-type proccss. The disadvantages of the batch-typc proccss arc obvious: the quitc long proccss, unrcliablc production qualily and high labor cost. Now. researchcrs havc put forward scvcral continuous production proccsscs using catalytic methods. which can inerease the production cfticiency and quality of biodiesel fuel according to the reports [7 11]. In this report, a ncw continuous production processes of biodicscl from vegetablc oil with supercritical method is proposed. which takes a short timc, and docs not need any catalyst. The fundamenta! research on the continuous production processes is reported and a novel tcchnology was dcviscd for dccrcas-ing the loss of unsaturated FAMĘ at high reaclion temperaturę in this report.

2. Materials, method and analysis

2.1.    Materials

Soybean oil was bought from Shanxi province. China. Anhydrous mcthanol and /;-hcxane was supplied by the Beijing reagent manufactory. Methyl esters of palmitic, heptadecanoic. stearic, oleić, lenoleic and linolenic acids wcrc supplied by Sigma.

2.2.    Method

As depicted in Fig. 1. the reaction of transestcrification was carricd out in a 75 ml tubę rcactor (tf> 6x1, 6 m), cquippcd w ith a preheater. blendcr, condcnser and separa-

Fig. I, Supercritical continuous reaction device. 1, 2. high-pressure pump; 3. 4. 10. 12. IS. 16. valve; 5. preheater. 6. blender, 7. tubę rcactor; 8. thermometer; 9. manometer. II. condenser; 13. pressure regulator. 14. separatory funnel.

tory funnel. An cłectric thermostat was used to control the temperaturę of the rcactor.

First, the preheater (50 400°C) and rcactor (200 400 °C) wcrc preheated at a designated temperaturę rcspcc-tively. Then calculated amounts of soybean oil and mcthanol (the molar ratio of mcthanol to oil was taken at 6:1 80:1) wcrc synchronously pumped into the tubę preheater by high pressure pump and hcated to the predetermined temperaturę. At the blendcr. the soybean oil and methanol wcrc mixcd at a constant slirring ratę. And then the rcac-tion niixturc was pumped into the lube rcactor. The resi-dence time (12.5 50 min) of reactants in the rcactor could be regułated by adjusting the flux of the high-pressure pump (0.10 9.99 ml/min). The reaction temperaturę (240 340 °C) and pressure (10 40 MPa) insidc the tubę rcactor could be adjusted by an electric thermostat and pressure regulator. respectively. Through the condenscr. the product was coolcd to the normal temperaturę, and then the crudc methyl esters could be obtained in the separatory funnel.

2.3. Analysis

The methyl ester conccnlration was quantificd using a Hewlett Packard 6890 gas chromatograph cquippcd with a HP-INNOWAX capillary column (30 mx 0.15 mm) and a flamc ioni/ation dctcctor. 4 pi of crudc ester laycr was dissolvcd in 300 pi /i-hexane and lOOpl intcrnal stan-dards (heptadecanoic acid methyl ester) for GC analysis.

Samples (1 pi) wcrc injcctcd by a samplcr at an ovcn temperaturę of 220 °C. After an isothermal period of 4 min. the GC oven was heated at 10°C/min to 230 °C, and hcld for 7.5 min. Nitrogcn was used as carricr gas at a flow ratę of 2 ml/min measured at 20 °C. The dctcctor make up gas was used at a flow ratę of 30 ml/min. The inlet pressure was 96.4 kPa. The Split ratio was 10:1. And the injcctor and detector temperatures wcrc 300 °C and 320 °C. rcspcctivcly.

The methyl ester yield of oil in cach cxperimcnt was cal-culatcd by the following expression:

yield = ^m"“" x 100% » ^Cw" ^X " ^{X |/}°'^m x 100%

W|hcv.lrtl..l    nt„ I

^C'"^{m xnxy}°"_x 100% g ^{Ccucn Xn} X 100%

^moi    Poił

where both m^u«i [g] and /Hthcorctkui [g] arc tłie mass of methyl ester; w₀u [g] is the mass of vegetable oil which is used in the reaction; Ccuet [g/ml] is the mass conccnlration of methyl ester which is acquircd by GC; n is the diluted multiple of methyl ester: V_CMn [ml] and Von [ml] arc the volumcs of the crude ester layer and vegetablc oil respec-tively; and p_oll [g/ml] is the density of vegetable oil. In the cxpcrimcnt, we analy/cd the fivc kinds of fatty acid methyl esters: palmitic (06:0), stearic (08:0), oleić (08:1). lenoleic (08:2) and linolenic (08:3) acids methyl ester (Cm:n: m is the number of carbon atoms; n is the number of double bonds).