CN102268303B - Method for preparing biological diesel oil by using sludge from municipal wastewater treatment plant - Google Patents

Abstract

The invention relates to development of clean energy, in particular to a method for preparing biological diesel oil by using sludge from a municipal wastewater treatment plant. The method comprises the following steps of: with primary sludge or remaining sludge produced by the wastewater treatment plant as a raw material, precipitating and concentrating, then adding 20-40ml of pure yeast with OD600 of 0.5-0.6, and performing enhanced hydrolysis at the temperature of 35 DEG C for 2-4 days; adding methanol and a concentrated sulfuric acid solution, stirring and performing esterification reaction at the temperature of 70-80 DEG C for 24 hours; and finally, naturally cooling the chemically esterified mixed solution to room temperature in air, adding normal hexane, mixing for 3-5 minutes, centrifuging at the rotation speed of 3,000-3,500rpm for 3-5 minutes and extracting. On the premise of saving energy, esterifiable components in the remaining sludge are retained as much as possible, so that the concentration of high molecular organic acid is increased, and further, the conversion rate of the biological diesel oil is increased to the greatest extent and the cost for preparing the biological diesel oil from the sludge is reduced.

Description

Method for producing biodiesel from urban sewage plant sludge

technical field

The invention belongs to the field of clean energy development, and relates to the preparation of biodiesel, in particular to a method for preparing biodiesel from sludge of urban sewage plants.

Background technique

The massive construction of urban sewage treatment plants has produced a large amount of excess sludge and has become an important source of pollution affecting the atmosphere and water environment. However, excess sludge contains about 20% of esterifiable components. On the other hand, as a clean renewable energy source, biodiesel is a high-quality substitute for petroleum diesel. Biodiesel is made from oil-bearing crops such as soybeans and rapeseeds, oil-bearing forest fruits such as oil palm and pistachio, engineering microalgae and other oil-bearing aquatic plants, animal fats, and waste catering oils, etc., and 75% of its preparation cost comes from raw materials .

There are no reports in China on the production of biodiesel from sludge from urban sewage treatment plants. There are currently two foreign patents: (1) Patent application number: US20040956069, patent holder: Zappi Mark E; FrenchWilliam Todd; Hernandez Rafael; Dufreche Stephen Thomas, patent name: Production of biodiesel and other valuable chemicals from wastewater treatment plant sludges; (2) patent application number: US20090429858, patent holder: Miguel ASCON; DoloresASCON, patent name: Methods and systems for production of biofuels y rombioener g sewage sludge.. The above patents all use dry sludge for in-situ esterification, but during the sludge drying process, the phospholipids that make up the cell wall are in the outermost layer of the biomass, making the conditions for converting them into organic esters very harsh, and they are enclosed in the cell wall. organic acids can only be partially esterified. On the other hand, in the sludge drying process, in order to obtain dry sludge with a moisture content of 5%, it needs to go through processes such as centrifugation, drying, and crushing, which will consume a lot of energy, and in the sludge drying process, some VFA and alcohols will also inevitably volatilize, reducing the conversion rate of excess sludge to biodiesel. In short, the in-situ esterification and drying of excess sludge cannot avoid the problems of high esterification conditions, high energy consumption, and low conversion rate of biodiesel.

Contents of the invention

In order to overcome the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for producing biodiesel from sludge from urban sewage plants. On the premise of energy saving, the esterifiable components in the remaining sludge should be kept as much as possible to increase the biodiesel production efficiency. The concentration of molecular organic acids can increase the conversion rate of biodiesel as much as possible and reduce the cost of producing biodiesel from sludge.

In order to achieve the above object, the technical scheme adopted in the present invention is:

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, biologically enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration within the range of 20-25g/L, and then add 20-40ml of pure yeast with OD ₆₀₀ of 0.5-0.6, strengthen hydrolysis at 35°C for 2-4 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1-1.2L of methanol, and then dropwise add 0.07-0.1L of concentrated sulfuric acid solution with a mass fraction of 98%, at 70-80°C Stirring reaction at high temperature for 24 hours;

The third step, extraction: naturally cool down the chemically esterified mixture to room temperature in the air, add 1 L of n-hexane, mix for 3-5 minutes, and centrifuge at 3000-3500 rpm for 3-5 minutes.

In order to increase the yield, the extraction process can be repeated three times.

Compared with prior art, the beneficial effect of the present invention is:

Using sludge from urban sewage treatment plants as raw material to strengthen hydrolysis and esterify its supernatant to produce biodiesel, no sludge centrifugal drying and oil extraction process, the conversion rate of sludge to biodiesel has increased by 25% 20-30% of the cost of producing biodiesel from sludge can be reduced under certain conditions.

Detailed ways

The present invention will be described in further detail below in conjunction with the examples.

Embodiment one

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, bio-enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 20g/L, and then add OD ₆₀₀ to each liter of concentrated sludge as 0.5 pure yeast 40ml, strengthen hydrolysis at 35°C for 4 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1L of methanol, then dropwise add 0.1L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir and react at 80°C for 24 hours;

The third step, extraction: naturally cool down the chemically esterified mixture to room temperature in the air, add 1 L of n-hexane, mix for 5 minutes, and centrifuge at 3000 rpm for 5 minutes to obtain biodiesel.

Embodiment two

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, biologically enhanced hydrolysis: using the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 25g/L, and then add OD ₆₀₀ to each liter of concentrated sludge as 0.5 pure yeast 20ml, strengthen hydrolysis at 35°C for 2 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1.2L of methanol, then dropwise add 0.07L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir and react at 70°C for 24 hours ;

The third step, extraction: naturally cool the mixture after chemical esterification to room temperature in the air, add 1 L of n-hexane, mix for 3 minutes, and centrifuge at 3000 rpm for 5 minutes to obtain biodiesel.

Embodiment Three

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, bio-enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 21.5g/L, and then add OD ₆₀₀ to each liter of concentrated sludge 35ml of 0.56 pure yeast, enhanced hydrolysis at 35°C for 3 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1.2L of methanol, then dropwise add 0.084L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir and react at 80°C for 24 hours ;

The third step, extraction: naturally cool down the chemically esterified mixture to room temperature in the air, add 1 L of n-hexane, mix for 5 minutes, and centrifuge at 3500 rpm for 3 minutes to obtain biodiesel.

Embodiment Four

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, biologically enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 24g/L, and then add OD ₆₀₀ to each liter of concentrated sludge as 25ml of 0.6 pure yeast, enhanced hydrolysis at 35°C for 4 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1L of methanol, then dropwise add 0.1L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir and react at 75°C for 24 hours;

The third step, extraction: naturally cool down the chemically esterified mixture to room temperature in the air, add 1 L of n-hexane, mix for 5 minutes, and centrifuge at 3300 rpm for 4 minutes to obtain biodiesel.

Embodiment five

The method for producing biodiesel from sludge of urban sewage plant comprises the following steps:

The first step, bio-enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 23g/L, and then add OD ₆₀₀ to each liter of concentrated sludge as 0.5 pure yeast 40ml, strengthen hydrolysis at 35°C for 4 days;

The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1.04L of methanol, then dropwise add 0.07L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir and react at 80°C for 24 hours ;

The third step, extraction: naturally cool the mixture after chemical esterification to room temperature in the air, add 1 L of n-hexane, mix for 3 minutes, and centrifuge at 3000 rpm for 3 minutes to obtain biodiesel.

Under the conditions of Example 5, the yield of biodiesel was 9.24% (in terms of dry sludge). The reagents such as pure yeast, concentrated sulfuric acid, methyl alcohol and normal hexane used in the present invention are cheap and have a wide range of sources, effectively reducing the production cost. cost.

In addition, in order to further increase the yield of biodiesel, the extraction during the preparation process can be repeated three times, and the supernatant of the last extraction result is taken each time for further extraction, and the amount of n-hexane added can be slightly reduced.

Claims (1)

1. the method utilizing city sewage plant sludge to produce biodiesel is characterized in that, comprises the following steps: The first step, bio-enhanced hydrolysis: use the primary sludge or excess sludge produced by the sewage treatment plant as raw material, first precipitate and concentrate to make the concentration 23g/L, and then add OD ₆₀₀ to each liter of concentrated sludge as 0.5 pure yeast 40ml, strengthen hydrolysis at 35°C for 4 days; The second step, chemical esterification: take 1L of the hydrolyzed biologically enhanced hydrolyzed sludge mixture, add 1.04L of methanol, then dropwise add 0.07L of concentrated sulfuric acid solution with a mass fraction of 98%, and stir the reaction at a temperature of 70-80°C 24 hours; The third step, extraction: naturally cool the mixture after chemical esterification to room temperature in the air, add 1L of n-hexane, mix for 3-5 minutes, and centrifuge at 3000-3500rpm for 3-5 minutes to obtain biodiesel. The extraction process was repeated three times.