Pre-esterification Of Tallow And Methanol Using S₂O₈^2--TiO₂/HZSM-5 Solid Acid

Arborescence oil plant is one of the competitive raw materials of biodiesl production. Because of its long growth cycle and harvests in many years after grown,it can decrease the cost of biodiesl.Planted in China widely,Chinese tallow's seeds have a high content of oil.The tallow has a appropriate carbon length,and can be used to produce biobisel.Due to its high content of free fatty acid(FFA),it needs pre-esterification to reduce its acid number.Homogeneous acid is the traditional catalyst for esterification.In esterification catalyzed by homogeneous acid,the separation of the products is complex.Further more, the catalyst is difficult to be recycled.Solid acid catalyst which has high activity,which is easy to be separated from products,which is environmental-friendly,and can be recycled easily,is getting more and more attention.This article chose tallow to be the raw material to produce biodisel.Due to the difference of tallow from planting area,its chemical property,water content,and its fatty acid composition was analyzed.The catalyst zeolite HZSM-5 loaded SO₄^2-/M_xO_y solid acid catalyst which had a structure of mesoporous material,large surface,appropriate acid strength,high catalysis activity,was used to catalyze the pre-esterification.The solid super acid molecular sieves composite catalyst was prepared and used to catalyze the pre-esterification of tallow and methanol.The factors which effected the pre-esterification,including content of TiO₂,the impregnation concentration and time,the calcining temperature and time were studied.The catalyst was characterized by particle diameter analysis,SEM,BET,XRD and FT-IR.The results showed that the catalyst had a structure of the mesoporous material and strong acid activity.In the process of loading TiO₂,the academic load of TiO₂ is 40% is the best.As the academic load of TiO₂ inreased,much of the TiO₂ seperated out and reunited except for the loading.In the process of promoting by(NH₄)₂S₂O₈,the optimal concentration was 1.0mol/L,and the best impregnation time for it was 4 hours.Excessive concentration and too long time made the catalyst have a small BET;On the contrary,the too low concentration and too short made less acid center.The calcining temperature affected the activity of the catalyst seriously.For S₂O₈^2--TiO₂/HZSM-5,the best calcining temperature was range from 400℃to 450℃.When the tenperature was higher than 500℃, the TiO₂ was over crystal,which made low content of S₂O₈^2- and little acid center.The time for calcining had little effect on the structure and activity of the catalyst.At 450℃,as long as the time for calcining was longer than 1 hour,the catalyst would get good activity. The catalyst was used for the pre-esterification of tallow and methanol.The reaction conrition was as follow.At reaction temperature 70℃;the mol ratio of methanol and tallow was 10:1,and the mass of catalyst was 5%of tallow.After 4 hours stirring at 300r/min,the conversion rate of pre-esterifitation was about 80%.After regenaration by simply calcining,the activity of the catalyst got back 78%of the activity of fresh catalyst. This showed that the carbon deposition on surface caused by tallow was just part of the reason for catalyst deactivation.