Morphological silica-supported acid catalyst for esterification of aliphatic fatty acid

Figures & data

Figure 1.  SEM micrographs of catalysts (a) SiO₂-1; (b) SiO₂-1-SO₄; (c) SiO₂-1-SO₄-400; (d) SiO₂-2, (e) SiO₂-2-SO₄; and (f) SiO₂-2-SO₄-400.

Figure 2.  Particle size distribution of silica supports (a) SiO₂-1 and (b) SiO₂-2.

short-legendScheme 1. Synthesis of silica-supported sulfuric acid catalyst.

Figure 3.  FT-IR spectrum of catalysts.

Table 1. Physico-chemical characteristics of catalysts.

Catalyst	Acid amount (wt%)	Specific surface area (m^2/g)	Pore volume (cm^3/g)
SiO2-1-SO4	60.4	405	2.8
SiO2-1-SO4-400	3.2	323	2.0
SiO2-2-SO4	40.2	371	0.6
SiO2-2-SO4-400	0.6	282	0.7

Table 2. Surface elemental distributions of catalysts by EDX in wt%.

Catalyst	Si	O	S
SiO2-1	28.7	71.3	–
SiO2-1-SO4	11.6	67.2	21.2
SiO2-1-SO4-400	35.6	63.4	1.1
SiO2-2	34.8	65.2	–
SiO2-2-SO4	25.2	64.0	10.8
SiO2-2-SO4-400	26.8	72.6	0.6

Figure 4.  Reaction profile of myristic acid with isopropyl alcohol.

Note: Reaction conditions: myristic acid 2 g, catalyst (SiO₂-1-SO₄) amount 0.2 g, isopropyl alcohol 20 ml, reaction temperature 100±2°C, reaction time 6 hours.

Table 3. Catalytic activities of silica-supported catalysts.

Catalyst	Time (hours)	Conversion (%)	Selectivity (%)
SiO2-1-SO4	6	95	98
SiO2-1-SO4-400	6	32	100
SiO2-1-SO4-400	24	76	98
SiO2-2-SO4	6	64	99
SiO2-2-SO4	24	95	99
SiO2-2-SO4-400	6	19	99
SiO2-2-SO4-400	24	42	99
Note: Reaction conditions: myristic acid 2 g, catalyst amount 0.2 g, isopropyl alcohol 20 ml, reaction temperature 100±2°C.

Table 4. Catalytic activities of other heterogeneous catalysts.

Catalyst	Time (hours)	Conversion (%)	Selectivity (%)
Raw Bentonite clay	6	8	100
Clay–acid activation by 1N H2SO4	6	11	96
Clay–acid activation by 2N H2SO4	6	13	97
Clay–acid activation by 4N H2SO4	6	14	99
Clay–acid activation by 4N H2SO4	24	30	99
Clay–acid activation by 8N H2SO4	6	6	99
Acidic Al2O3	6	3	100
Acidic Al2O3	24	13	99
Note: Reaction conditions: myristic acid 2 g, catalyst amount 0.2 g, isopropyl alcohol 20 ml, reaction temperature 100±2°C.

Table 5. Effect of process parameters on conversion using SiO₄-1-SO₄ catalyst.

Catalyst amount (g)	Isopropyl alcohol (ml)	Temperature (°C, ±2°C)	Time (hours)	Conversion (%)
0.05	20	100	3	69
0.05	20	100	6	84
0.1	20	100	3	79
0.1	20	100	6	95
0.2	20	100	3	95
0.2	20	100	6	97
0.2	10	100	3	88
0.2	10	100	6	97
0.2	40	100	3	95
0.2	40	100	6	97
0.2	20	80	3	87
0.2	20	80	6	95
0.2	20	60	3	45
0.2	20	60	6	54
Note: Reaction conditions: myristic acid 2 g.

Table 6. Catalytic activities of recycled catalysts.

Catalyst	Time (hours)	Conversion (%)	Selectivity (%)
SiO2-1-SO4, first recycle	6	23	100
SiO2-1-SO4, first recycle	24	68	99
SiO2-1-SO4-400, first recycle	6	29	100
SiO2-1-SO4-400, first recycle	24	71	98
Note: Reaction conditions: myristic acid 2 g, catalyst amount 0.2 g, isopropyl alcohol 20 ml, reaction temperature 100±2°C.

Figure 5.  Comparison of supported catalyst with homogeneous catalyst.

Note: Reaction conditions: myristic acid 2 g, catalyst amount 0.2 g, isopropyl alcohol 20 ml, reaction temperature 100±2°C, reaction time 6 hours.