TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (claimed): The solid acid catalyst of (I) is prepared by subjecting a metal hydroxide to a sulfonation or phosphonation step; and subjecting the sulfonated and/or phosphonated catalyst to a calcination step in the presence oxygen at 400-700 degrees C for 1-20 hours. Preferred Preparation: The method comprises melting metal salt precursors at 0.1-up to 1 bar to form a melt; reducing the pressure to remove volatile materials and form a solid product; subjecting the resulting material to a calcination step in the presence of oxygen at 400-700 degrees C for 1-20 hours; subjecting the catalyst to a sulfonation and/or phosphonation step by contacting it with a sulfonation and/or phosphonation agent; and subjecting the sulfonated and/or phosphonated catalyst to a calcination step in the presence of oxygen at 400-700 degrees C for 1-20 hours. The metal salt precursors are metal nitrates, chlorides, or ammonium compounds. Preferred Parameter: The solid acid catalyst of (I) has surface area of 60-120, preferably 70-100 m2/g; average pore diameter of greater than or equal to 50, preferably 70-150 Angstrom ; and a pore volume, which is greater than or equal to 0.20, preferably 0.22-0.4 ml/g.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The carboxylic acid is in a feedstock, which comprises 10-18C fatty acids, optionally in combination with fatty acid triglycerides, where alcohol is 1-15C alcohol. The esterification process is carried out in a reactive distillation column, where a carboxylic acid is reacted in a reaction section of a reactive distillation column with an alcohol under esterification conditions in the presence of solid acid catalyst of (I) to form an ester, where a first supply stream comprising the carboxylic acid and a second supply stream comprising alcohol are supplied to the reactive distillation column, where the first supply stream is supplied to the column at a first entry level located just above or at the top of the reaction section and the second supply stream is supplied to the column at a second entry level located in or just below the reaction section and below the first entry level, where a bottom stream comprising the ester formed and a top stream comprising unreacted first alcohol and water are obtained. The unit is provided with a third supply stream comprising entrainer, where third supply stream is supplied to the column at a third entry level located above the first entry level. Preferred Definitions:    M1=Zr, Ti, Y, Sn, V, Nb, Mo, and/or W;and    M2=Zr, Ti, Y, Sn, V, Nb, Mo, W, and/or lanthanide metals, where M1 and M2 can be the same and are Zr, Sn, Ti, or Nb.    EXAMPLE - Metal nitrate precursors were mixed and placed into a vacuum oven set at 115 degrees C. They were allowed to melt for 5 minutes, after which the pressure was lowered to less than 10 mbar in 15 minutes. After 4 hours, the precursors were placed in a muffle oven and calcined for 4-8 hours at 500-650 degrees C in static air (ramp rate: 300 degrees C/hour). The resulting solid was pulverized, ground, and sieved in fractions of 125-212 mu m and less than 125 mu m. The next step was sulfonation. Then the solid was recovered and dried for 15 hours at 110 degrees C, and calcined for 4-8 hours at 500-650 degrees C in static air (ramp rate: 300 degrees C/hour). The resulting solid acid catalyst exhibited surface area of 85 m2/g, pore volume of 0.300 cm3/g, pore diameter mean/maximum of 9.4/16.5 nm, and sulfur content of 7.2%, as compared with reference catalyst i.e. sulfated zirconia, in which 15 ml solution of 1 N sulfuric acid/g zirconium hydroxide (Zr(OH)4) was used as sulfonation agent, of 94 m2/g surface area, 0.198 cm3/g pore volume, 7.5/7.8 pore diameter mean/maximum, and 3.4% sulfur content.