K_2SiO_3_C颗粒催化大豆油酯交换制备生物柴油_英文(3)

1594 催 化 学 报 Chin. J. Catal., 2011, 32: 1592–1596

cal emission spectroscopy (ICP-OES, Spectro Genesis) to determine the K concentration.

2 Results and discussion

The catalytic activities of carbon particles with different K2SiO3 loadings were measured. For comparison, the same reaction conditions shown in Table 1 were employed in all experiments. The reaction conditions were not optimized for the highest reaction conversion. Non- loaded carbon parti-cles exhibited no activity. When K2SiO3 was loaded on the carbon particles, the supported catalysts showed catalytic activity. It can be concluded that the observed activities of the carbon supported catalysts were due to their basicity, i.e., a higher basicity result in a higher conversion.

Figure 1 shows the XRD patterns of ground original car-bon particles and catalyst particles (loading of 30 wt% K2SiO3 solution). The carbon particles and prepared catalyst particles had the same XRD patterns which was identical to that of C (PDF 261077). No characteristic peak due to K2SiO3 or any new species such as KOH and SiO2 was ob-served, indicating the high dispersion of K2SiO3 on the car-bon support [17].

Intensity

K2SiO3/CCarbon particle

203040

502 /( o )

607080

Fig. 1. XRD patterns obtained from ground original carbon particle and catalyst particle.

Figure 2 shows typical SEM and EDS mapping images of the K2SiO3/C catalyst (30% K2SiO3 solution loading) and a used K2SiO3/C catalyst. These showed that the morphology was irregular and diverse, with smooth surfaces, large pores, and convex surfaces. The distribution of K2SiO3 on the support surface was homogeneous even on the convex sur-faces and in the large pores. K2SiO3 was found to be very effectively distributed on the surface of the support. In order

Table 1 Properties of K2SiO3/C particles used as solid base catalyst for the transesterification of soybean oil with refluxing methanol

Catalyst K2SiO3 solution loading (wt%)

Basic strength

Basicity H_> 9.8 (mmol/g)

0 0 0.018 0.043 0.053 0.052

Conversion* (%) No reaction 23.3 42.5 63.3 82.0 81.2

Carbon 0 H_ < 7.2

K2SiO3/C 10 7.2 < H_ < 9.8 9.8 < H_ < 15.0 K2SiO3/C 15

9.8 < H_ < 15.0 K2SiO3/C 20

9.8 < H_ < 15.0 K2SiO3/C 25

9.8 < H_ < 15.0 K2SiO3/C 30 with conventional heating.

*Reaction conditions: 12.5 g soybean oil, methanol/oil molar ratio 24:1, catalyst amount 2 g, reaction time 3 h, at the methanol re ux temperature

1 μm

Si

OK

1 μm

SiOK

1 μm

SiOK

Fig. 2. SEM and EDS mapping of samples. (a) and (b) Fresh K2SiO3/C catalyst; (c) Used K2SiO3/C catalyst.