阅读说明：本技术 一种油莎豆热化学转化联产“生物柴油”和“绿色柴油”的方法 (Method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus ) 是由 王枫 李光 张丽娜 马书启 许玉平 于 2020-06-01 设计创作，主要内容包括：本发明公开了一种油莎豆热化学转化联产“生物柴油”和“绿色柴油”的方法,属于新能源技术领域,包括：以粉碎的油莎豆颗粒为原料,首先采用水-甲醇双溶剂耦合体系对油莎豆颗粒进行超临界酯交换和近/超临界水热转化处理,得到油莎豆液化油；然后,用正己烷对油莎豆液化油进行分离分别得到“生物柴油”和重质油；最后,将重质油进行催化加氢改质处理,得到“绿色柴油”。本发明是一种能源综合转化利用技术,能够将超临界酯交换和近/超临界水热转化在同一体系中进行,既可以将油莎豆中的脂肪全部转化为“生物柴油”,又能够实现剩余有机组分的转化并最终得到“绿色柴油”,从而实现油莎豆等富脂类生物质的高效转化和高值利用。(The invention discloses a method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus, which belongs to the technical field of new energy and comprises the following steps: taking crushed cyperus esculentus particles as raw materials, firstly, adopting a water-methanol double-solvent coupling system to carry out supercritical ester exchange and near/supercritical hydrothermal conversion treatment on the cyperus esculentus particles to obtain cyperus esculentus liquefied oil; then, separating the cyperus esculentus liquefied oil by using normal hexane to respectively obtain biodiesel and heavy oil; finally, carrying out catalytic hydro-upgrading treatment on the heavy oil to obtain the green diesel oil. The invention relates to an energy comprehensive conversion and utilization technology, which can carry out supercritical ester exchange and near/supercritical hydrothermal conversion in the same system, can convert all fat in cyperus esculentus into biodiesel, can realize the conversion of residual organic components and finally obtain green diesel, thereby realizing the high-efficiency conversion and high-value utilization of lipid-rich biomass such as cyperus esculentus.)

1. A method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus is characterized by comprising the following steps: taking crushed cyperus esculentus particles as raw materials, firstly, adopting a water-methanol double-solvent coupling system to carry out supercritical ester exchange and near/supercritical hydrothermal conversion treatment on the cyperus esculentus particles to obtain cyperus esculentus liquefied oil; then, separating the cyperus esculentus liquefied oil by using normal hexane to respectively obtain biodiesel and heavy oil; finally, carrying out catalytic hydro-upgrading treatment on the heavy oil to obtain the green diesel oil.

2. The process for the thermochemical conversion co-production of "biodiesel" and "green diesel" of cyperus esculentus according to claim 1, characterized in that it comprises the following steps:

1) adding the cyperus esculentus particles, water and methanol into a high-pressure reaction kettle in proportion, introducing hydrogen or nitrogen at a certain pressure after sealing and emptying, heating in high-temperature molten salt to the reaction temperature to start reaction, cooling after the reaction is finished, adding an organic solvent to extract a mixture in the high-pressure reaction kettle, filtering and separating, and removing the organic solvent by rotary evaporation to obtain cyperus esculentus liquefied oil;

2) adding an organic solvent into the cyperus esculentus liquefied oil, separating to obtain light oil soluble in the organic solvent and heavy oil insoluble in the organic solvent, and removing the organic solvent from the light oil by rotary evaporation to obtain biodiesel;

3) adding heavy oil, a hydrogen donor and a catalyst into a high-pressure reaction kettle in proportion, introducing hydrogen with certain pressure after sealing and emptying, reacting in high-temperature molten salt, cooling after the reaction is finished, adding an organic solvent to extract a mixture in the high-pressure reaction kettle, filtering and separating, and performing rotary evaporation to remove the organic solvent to obtain modified oil, namely the green diesel oil.

3. The method for the thermochemical conversion of cyperus esculentus to co-produce biodiesel and green diesel according to claim 1 or 2, wherein the size of the cyperus esculentus particles is 100-200 meshes.

4. The method for the thermochemical conversion of cyperus esculentus to co-produce biodiesel and green diesel according to claim 2, characterized in that in step 1), the ratio of the cyperus esculentus particles to the total mass of water and methanol is 1: 9; the mass ratio of the methanol to the water is (0-9): (9-0).

5. The method for coproducing biodiesel and green diesel through thermochemical conversion of cyperus esculentus according to claim 2, wherein in the step 1), when the introduced gas is hydrogen, the pressure is 1-10 MPa, and when the introduced gas is nitrogen, the pressure is 4 MPa; the reaction temperature is 200-400 ℃, and the reaction time is 0-60 min; the organic solvent used for extraction is dichloromethane, chloroform, benzene, dichloroethane or diethyl ether.

6. The method for coproducing biodiesel and green diesel through thermochemical conversion of cyperus esculentus according to claim 2, wherein in step 2), the organic solvent is n-hexane.

7. The method for the thermochemical conversion of cyperus esculentus to co-produce biodiesel and green diesel according to claim 2, wherein in step 3), the hydrogen donor is n-hexane, cyclohexane, tetrahydronaphthalene or decahydronaphthalene; the catalyst is Pt/C, and the mass fraction of Pt is 5%; the organic solvent used for extraction is dichloromethane; the mass ratio of the heavy oil, the hydrogen donor and the catalyst is 5:5: 1.

8. The method for coproducing biodiesel and green diesel through thermochemical conversion of cyperus esculentus according to claim 2, wherein in the step 3), the reaction temperature is 300-450 ℃, the reaction time is 2-8 h, and the pressure of introduced hydrogen is 0.1-6 MPa.

9. The method for the thermochemical conversion of cyperus esculentus to co-produce biodiesel and green diesel according to claim 2, wherein the element composition of the prepared biodiesel comprises, in mass percent: carbon: 71.2% -84.7%, hydrogen: 10.9% -12.6%, oxygen: 1.3 to 17.2 percent of nitrogen and 0.0 to 2.3 percent of nitrogen; the heat value is 36.6-45.0 MJ/kg.

10. The method for the thermochemical conversion of cyperus esculentus to co-produce biodiesel and green diesel according to claim 2, wherein the elemental composition of the green diesel produced is such that it comprises, in mass%: carbon: 76.6% -90.5%, hydrogen: 9.6% -12.9%, oxygen: 0.7 to 13.5 percent of nitrogen and 0.0 to 0.3 percent of nitrogen; the heat value is 40.7-47.2 MJ/kg.

Technical Field

The invention belongs to the technical field of new energy, and relates to a method for coproducing biodiesel and green diesel by thermochemical conversion of cyperus esculentus.

Background

Excessive dependence on fossil fuels is gradually causing serious energy crisis and environmental problems. Therefore, it is urgent to find renewable and pollution-free alternative new energy sources. Biomass, as a renewable energy source raw material, has attracted attention because of its advantages of wide distribution, high yield, low pollution, zero emission of carbon dioxide, and the like. The biomass can produce various biofuels through a series of thermochemical conversions, and is the most potential energy for dealing with the exhaustion of fossil energy in the future.

Cyperus esculentus, also called Cyperus esculentus, belongs to Cyperus family herbaceous plants, is originally produced in Africa and coastal countries of the Mediterranean sea, is introduced by China later, is planted in more than 20 provinces and municipalities such as Guangxi and Shandong, has long-round underground tubers and is rich in grease, starch and sugar, and is a typical lipid-rich biomass. And the nitrogen and sulfur contents of the cyperus esculentus are far lower than those of straw and algae biomass. The planting of the cyperus esculentus has low requirements on soil conditions, can be planted in beach lands, wasteland (barren mountains, barren beaches, barren slopes, barren lands), saline-alkali lands and the like, and does not compete with herbaceous oil crops such as soybeans, peanuts, rapes and the like and staple grain crops such as rice, corns and the like; and the growth cycle is short (100-120 days), the yield is high (tuber yield is 800 kg/mu), the adaptability is wide, the plant diseases and insect pests are few, and the biomass energy source material is ideal.

At present, the mode of obtaining the biofuel by the cyperus esculentus is mainly to prepare the biodiesel by an acid-base catalyzed ester exchange method. The preparation process comprises the steps of extracting fatty glyceride contained in the cyperus esculentus tuber by a physical or chemical method to form cyperus esculentus crude oil, and preparing high-grade fatty acid methyl ester or ethyl ester, namely the biodiesel, from the cyperus esculentus crude oil serving as a raw material through links such as oil dehydration, esterification, ester exchange, dealcoholization, rectification and the like. The process converts lipid substances in biomass raw materials only by a transesterification method, and the yield of the process is mainly determined by the fat content of biomass. Despite the relatively high fat content of cyperus esculentus, other components such as starch, sugars and cellulose cannot be converted by this process to produce diesel fuel, the major component of which is a hydrocarbon, i.e. "green diesel fuel".

The hydrothermal liquefaction technology is to prepare biological crude oil by hydrolysis under the near-critical and supercritical states by using water as a reaction medium. In view of the unique properties of near/supercritical water, it is not necessary to dry biomass, and thus has wide application in the field of liquefaction of high-moisture biomass. The direct treatment of biomass by hydrothermal liquefaction can not only convert the fat in the biomass into bio-oil, but also convert other organic components such as starch, sugar and cellulose. Therefore, the method for preparing the biofuel by treating the cyperus esculentus by adopting the near/supercritical water is expected to become a potential feasible way. However, hydrothermal liquefaction of cyperus esculentus also has its disadvantages. Although it can achieve full-component conversion of organic components in cyperus esculentus, fats, which are important sources of main components of the biodiesel, are only partially hydrolyzed in a hydrothermal system, and the generated fatty acids and glycerin not only do not contribute to improving the calorific value of the biological oil, but also increase the acid value and instability of the biological oil. Therefore, the hydrothermal liquefaction technology is suitable for biomass raw materials with low fat content. The advantage of high fat content of the cyperus esculentus is certainly killed by adopting hydrothermal liquefaction to the cyperus esculentus.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

the invention discloses a method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus, which comprises the following steps: taking crushed cyperus esculentus particles as raw materials, firstly, adopting a water-methanol double-solvent coupling system to carry out supercritical ester exchange and near/supercritical hydrothermal conversion treatment on the cyperus esculentus particles to obtain cyperus esculentus liquefied oil; then, separating the cyperus esculentus liquefied oil by using normal hexane to respectively obtain biodiesel and heavy oil; finally, carrying out catalytic hydro-upgrading treatment on the heavy oil to obtain the green diesel oil.

Preferably, the method for the thermochemical conversion coproduction of the biodiesel and the green diesel by the cyperus esculentus comprises the following steps:

1) adding the cyperus esculentus particles, water and methanol into a high-pressure reaction kettle in proportion, introducing hydrogen or nitrogen at a certain pressure after sealing and emptying, heating in high-temperature molten salt to the reaction temperature to start reaction, cooling after the reaction is finished, adding an organic solvent to extract a mixture in the high-pressure reaction kettle, filtering and separating, and removing the organic solvent by rotary evaporation to obtain cyperus esculentus liquefied oil;

2) adding an organic solvent into the cyperus esculentus liquefied oil, separating to obtain light oil soluble in the organic solvent and heavy oil insoluble in the organic solvent, and removing the organic solvent from the light oil by rotary evaporation to obtain biodiesel;

3) adding heavy oil, a hydrogen donor and a catalyst into a high-pressure reaction kettle in proportion, introducing hydrogen with certain pressure after sealing and emptying, reacting in high-temperature molten salt, cooling after the reaction is finished, adding an organic solvent to extract a mixture in the high-pressure reaction kettle, filtering and separating, and performing rotary evaporation to remove the organic solvent to obtain modified oil, namely the green diesel oil.

Preferably, the size of the cyperus esculentus particles is 100-200 meshes.

Further preferably, in step 1), the ratio of the cyperus esculentus particles to the total mass of water and methanol is 1: 9; the mass ratio of the methanol to the water is (0-9): (9-0).

Further preferably, in the step 1), when the introduced gas is hydrogen, the pressure is 1-10 MPa, and when the introduced gas is nitrogen, the pressure is 4 MPa; the reaction temperature is 200-400 ℃, and the reaction time is 0-60 min; the organic solvent used for extraction is dichloromethane, chloroform, benzene, dichloroethane or diethyl ether.

Further preferably, in the step 2), the organic solvent is n-hexane.

Further preferably, in the step 3), the hydrogen donor is n-hexane, cyclohexane, tetrahydronaphthalene or decahydronaphthalene; the catalyst is Pt/C, and the mass fraction of Pt is 5%; the organic solvent used for extraction is dichloromethane; the mass ratio of the heavy oil, the hydrogen donor and the catalyst is 5:5: 1.

Further preferably, in the step 3), the reaction temperature is 300-450 ℃, the reaction time is 2-8 h, and the pressure of the introduced hydrogen is 0.1-6 MPa.

Further preferably, the element composition of the prepared biodiesel comprises the following components in percentage by mass: carbon: 71.2% -84.7%, hydrogen: 10.9% -12.6%, oxygen: 1.3 to 17.2 percent of nitrogen and 0.0 to 2.3 percent of nitrogen; the heat value is 36.6-45.0 MJ/kg.

Further preferably, the element composition of the prepared green diesel oil comprises the following components in percentage by mass: carbon: 76.6% -90.5%, hydrogen: 9.6% -12.9%, oxygen: 0.7 to 13.5 percent of nitrogen and 0.0 to 0.3 percent of nitrogen; the heat value is 40.7-47.2 MJ/kg.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a method for coproducing 'biodiesel' and 'green diesel' by thermochemical conversion of cyperus esculentus, which is an energy efficient comprehensive utilization technology, compared with the traditional acid-base catalysis ester exchange method, the invention adopts a water-methanol double-solvent coupling system, by adjusting the alcohol/water ratio, supercritical ester exchange and near/supercritical hydrothermal reaction can be simultaneously realized in a single system, the lipid content in the cyperus esculentus can be completely converted into esters, the residual organic components can be converted together, ester-rich light oil is obtained by extraction and separation of an organic solvent and is used for preparing biodiesel, the heavy oil enriched in the low-ester component is modified and upgraded to obtain hydrocarbon liquid fuel, namely 'green diesel oil', and the thermochemical conversion of the cyperus esculentus is finally realized to produce 'biodiesel' and 'green diesel oil', so that the efficient comprehensive conversion of the cyperus esculentus raw material is realized.

Further, the thermochemical conversion of the cyperus esculentus in a water-methanol coupling system can obtain higher yields of biodiesel and liquefied oil under the conditions of 280 ℃, 20min and 6MPa of hydrogen. The content of saturated methyl ester in the biodiesel almost reaches 100 percent, and the viscosity and the oxidation stability of the biodiesel can be obviously reduced. The main component of the green diesel oil obtained by catalytic hydrogenation modification of the heavy oil is saturated hydrocarbon, and the biodiesel and the green diesel oil obtained by experiments can hopefully replace the diminishing fossil fuel.

The yield of the biodiesel prepared by the process is 18.3-47.6 wt.%, and the yield of the heavy oil is 9.8-35.9 wt.%; the yield of the obtained green diesel oil (based on the mass sum of the heavy oil and the hydrogen donor) is 82.5-96.0 wt.%.

Drawings

FIG. 1 is a block diagram of a process flow of the present invention;

FIG. 2 is a total ion chromatogram of "biodiesel" obtained in example 28 (under optimal conditions) according to the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

the invention adopts the methanol in the supercritical state as a reaction substrate to directly participate in the reaction, and the dielectric constant and the polarity of the methanol are obviously changed in the supercritical ester exchange process, so that the methanol can dissolve lipids to form a single phase, and then the ester exchange reaction is carried out, even no catalyst is needed. The water and impurities contained in the lipid raw material do not influence the reaction, and the ester exchange reaction of the fatty glyceride and the esterification reaction of the free fatty acid are carried out simultaneously, so that the process is simplified and the pretreatment cost is saved. More importantly, the critical parameter (T) of methanol_c＝239℃，p_c8.09MPa) is significantly below the critical parameter (T) of water_c＝374℃，p_c22.1 MPa). Based on the method, water-methanol double-solvent coupling is adopted, and supercritical transesterification and near/supercritical hydrothermal reaction are carried out in the same system by adjusting the alcohol/water ratio, so that not only can lipid parts be converted into esters, but also the residual organic components can be converted together, ester-rich light oil is obtained by extraction and separation of the organic solvent and is used for preparing 'biodiesel', the heavy oil enriched with the ester-poor components is modified and upgraded to obtain hydrocarbon liquid fuel- 'green diesel', and finally the thermochemical conversion of cyperus esculentus to coproduce 'biodiesel' and 'green diesel', so that the comprehensive utilization efficiency of cyperus esculentus raw materials is improved.

The method comprises the following steps:

1) sequentially adding 100-mesh 200-mesh cyperus esculentus particles, water and methanol into a 50mL high-pressure reaction kettle according to a certain proportion, sealing, filling hydrogen or nitrogen with a certain pressure into the kettle after emptying, and screwing a valve; then putting the reaction kettle into high-temperature molten salt preheated to a certain temperature and reacting for a period of time; after the reaction is finished, cooling the reaction kettle to room temperature in a water bath, and opening the reaction kettle after pressure reduction; extracting the mixture obtained by the reaction with dichloromethane, filtering, separating liquid to obtain an organic phase, and removing the dichloromethane in the organic phase by rotary evaporation to obtain the cyperus esculentus liquefied oil;

2) adding normal hexane into the cyperus esculentus liquefied oil, separating to obtain ester-rich light oil soluble in normal hexane and ester-poor heavy oil insoluble in normal hexane respectively, and removing normal hexane from the ester-rich light oil by rotary evaporation to obtain the biodiesel.

3) Adding the heavy oil obtained in the step 1), the Pt/C catalyst and the hydrogen donor into a 50mL high-pressure reaction kettle according to a certain proportion, sealing, emptying by using hydrogen, filling hydrogen with a certain pressure into the kettle, and screwing a valve; then putting the reaction kettle into high-temperature molten salt preheated to a certain temperature and reacting for a period of time; after the reaction is finished, cooling the reaction kettle to room temperature in a water bath, and opening the reaction kettle after pressure reduction; and (3) extracting the mixture obtained by the reaction by using dichloromethane, filtering, separating liquid to obtain an organic phase, and performing rotary evaporation to remove the dichloromethane to obtain modified oil, namely the green diesel oil.

In a preferred embodiment of the invention, the mass ratio of cyperus esculentus particles, water and methanol in step 1) is 1:3: 6; the pressure of the added hydrogen is 6 MPa; the reaction temperature is 280 ℃; the reaction time was 20 min.

In a preferred embodiment of the present invention, the mass ratio of the Pt/C catalyst, the tetralin, and the heavy oil in step 3) is 1:5: 5; the pressure of the added hydrogen is 2 MPa; the reaction temperature is 400 ℃; the reaction time is 8 h.

In a preferred embodiment of the present invention, the yield of the liquefied oil obtained in step 1) is 72.6 wt.%, the "biodiesel" yield is 42.3 wt.%, and the heavy oil yield is 30.3 wt.%.

In a preferred embodiment of the present invention, the yield of "green diesel" of step 3) based on the sum of the mass of heavy oil and hydrogen donor is 93.4 wt.%.