Method of synthesizing biodiesel oil using fixed bed gaseous phase esterification reaction

Abstract

The present invention belongs to a method for synthesizing biological diesel oil by adopting fixed bed gas-phase esterification reaction, in the concrete, said invention provides a method for synthesizing biological diesel oil by using animal and plant oil and fat and low-carbon alcohol (for example methyl alcohol) as raw material and making the above-mentioned raw material be reacted with fixed granular esterification catalyst in the fixed bed under the gas condition. Said invention also provides the equipment for implementing said method and catalyst required for fixed bed esterification reaction.

Description

technical field [0001] The invention belongs to the technical field of biodiesel production using animal and vegetable oils as raw materials; specifically, it relates to a method for synthesizing biodiesel by reacting various raw materials with an esterification catalyst in a fixed bed in a gaseous state; technical background [0002] Biodiesel is an esterification product (such as fatty acid methyl ester or ethyl ester) produced by transesterification of low-carbon alcohols (such as methanol or ethanol) with animal and vegetable oils (carboxyglycerides containing C16 to C18); The combustion physical properties of diesel oil and petroleum diesel are basically the same and are widely used in the energy market. It is a new energy source called green and renewable; there are many reports on the technology of producing biodiesel with animal and vegetable oils and fats. In CN200510011997.1, it is reported that methanol enters the reaction kettle in the liquid phase, discharges fr...

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Problems solved by technology

[0002] Biodiesel is an esterification product (such as fatty acid methyl ester or ethyl ester) produced by transesterification of low-carbon alcohols (such as methanol or ethanol) with animal and vegetable oils (carboxyglycerides containing C16 to C18); The combustion physical properties of diesel oil and petroleum diesel are basically the same and are widely used in the energy market. It is a new energy source called green and renewable; there are many reports on the technology of producing biodiesel with animal and vegetable oils and fats. In CN200510011997.1, it is reported that methanol enters the reaction kettle in the liquid phase, discharges from the top of the reaction kettle in the gas phase, condenses the gas phase methanol into a liquid, and cyclically enters the liquid methanol into the reaction kettle to participate in the esterification method; it is characterized in that it uses The vapor phase volatilization of methanol takes away the methyl ester and a certain amount of glycerin produced in the reactor to achieve continuous production; the defect of this method is that the raw material oil and the product methyl ester are mainly composed of C16 or C18 organic matter. Compounds, their boiling points are close to each other. Practice has proved that the gas phase of methanol can not only take away the methyl ester and glycerin in the reactor, but also take away a large amount of fatty acid glycerides that can form hydrogen bonds with methanol to the separator discharged from the rectification tower In, the product methyl fat and raw material oil are miscible together, can not separate them by density difference in the separator, because the circulation of gaseous phase methanol in the reaction can not separate raw material (fatty acid glyceride) and product methyl ester, cause the characteristic of this invention and Industrial practicability cannot be implemented; the cyclic condensation and thermal vaporization of methanol consume a large amount of energy and increase the production cost; in the esterification reaction of this technology, there is no co-solvent and no method for the solid catalyst to diffuse into the liquid raw material, and the catalyst cannot be mixed with the raw material. Full contact and reaction, so that the catalytic reaction rate of transesterification is slow, and the yield of esterification is low;

[0003] Publication No. CN1718679A reported the subcritical methanol phase and Publication No. CN1594504A reported the method of producing biodiesel through esterification reaction between gas phase methanol and liquid phase oil under supercritical conditions. The above two methods all adopt the intermittent production of high-pressure reactors. The higher the pressure of the reaction, the thicker the wall of the reactor needs to be, and the investment in equipment is very large; the reaction mechanism of the esterification reaction under critical or subcritical conditions is that the molar ratio of low-carbon alcohol (such as methanol) to oil is higher. The larger the ratio, the more conducive to the mutual solubility of the two substances and to accelerate the process of the esterification reaction. Generally, the molar ratio must be several times or dozens of times to meet the mutual solubility temperature suitable for the current industrial production and the mutual solubility pressure that the equipment can withstand; However, a large amount of residual methanol in the recovery reaction system will increase production costs and equipment investment; in particular, the production of high-pressure vessels under high-pressure conditions is very unsafe, and once the welds are corroded for a long time or desoldered, bursting accidents will occur in high-pressure vessels; The separation of the added solid catalyst in the reactor is also very troublesome, resulting in poor practicability;

[0004] In CN02133591.5, methanol and oil are subjected to liquid----liquid phase transesterification under normal pressure, which is characterized in that the azeotrope of methanol and water is discharged into the rectification tower after passing through the top of the reactor for separation Methanol and continuously remove water; to reduce the amount of product (water) in the reversible reaction system, accelerate the forward reaction, improve the conversion reaction speed and product percentage of methyl ester; its defects are: polarity The immiscibility between low-carbon alcohols (such as methanol) and acidic catalysts (such as sulfuric acid or alkylbenzene yellow acid) and non-polar polymer oils, and the ineffectiveness between polar molecules and non-polar molecules Contact, mixing and reaction will result in slow and incomplete esterification reaction;

[0017] According to the principle of chemical equilibrium reaction, in the above-mentioned reversible esterification reaction, increasing the concentration of the reactant (methanol) or / and reducing the concentration of the product (methanol or glycerol or water), the equilibrium reaction is conducive to the positive reaction direction (or the formation of biological Diesel) method; On the contrary, dilute or reduce the concentration of methanol or increase the moisture in the equilibrium system (H 2 O) weight percent content (Wt%), equilibrium reaction then carries out towards the reverse reaction method, that is, carries out towards the method that does not generate biodiesel (or methyl ester); property) mutual exclusion or immiscibility in the liquid state, so that the oily ester molecules and methanol molecules in the esterification reaction system in the liquid phase environment are not easy to contact or difficult to carry out transesterification; especially, the water produced by the esterification The increase of the proportion will dilute the concentration of methanol in the reaction system, resulting in an increase in the degree of reverse reaction or incomplete esterification; moisture will also greatly dilute the concentration of acidic or basic catalyst in the reactor, affecting the normal effect of the catalyst; Although the addition of co-solvent in the reaction system can strengthen the contact between oil molecules and methanol molecules, the recycling of co-solvent needs to consume a lot of energy, increase equipment investment and increase production costs. Therefore, the liquid of methanol and oil--- --- There are many defects in the liquid phase esterification reaction;

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