Technical Field

The present invention relates to a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation.

Technical Background

Cassava is one of the three major root and tuber crops in the world, and is the first choice for bio-ethanol production. By 2005, the planting area of cassava in China has already reached 6,570,000 Chinese acres, and there are more than 200 factories producing starch and ethanol from cassava in China, with annual starch production of 500,000 ton, and cassava-derived ethanol 250,000 ton. As waste liquor resulted from ethanol production through cassava fermentation contains high concentration of organic compounds, and the waste liquor is directly discharged from most ethanol factories without any effective treatment, local and downstream water environment is severely affected.

Presently, treatment methods of waste liquor resulted from ethanol production through cassava fermentation include: 1. incineration method, i.e. incinerating the waste liquor after concentration, which is likely to cause secondary pollution after incineration; 2. marsh gas production through fermentation of the waster liquor, which has the disadvantage of high investment and high requirement for control techniques.

Thus, presently the available treatment method of waste liquor resulted from ethanol production through cassava fermentation is to use solid residue recovered from the waste liquor as feed, which comprises removing water from the waste liquor by filtering to give solid production, and then drying the solid production. This treatment method has the advantage of low investment, simple operation, and environmental friendliness. Thereby, treatment capacity for solid-liquid separation is the key factor for determining the treatment capacity of waste liquor.

The problem existing in the traditional method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, is that the time for solid-liquid separation is too long, thus causing the low treatment capacity of waste liquor, and causing the low load of the equipments used in producing ethanol. Therefore, the production capacity of the equipments for producing ethanol can not meet the requirement.

Summary of the Invention

The object of the present invention is to overcome the long time disadvantage in available methods for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, and provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation which takes short time for solid-liquid separation.

The present invention provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, which comprises the steps of: introducing water-soluble ester of alginic acid and/or water-soluble salt of alginic acid into the waste liquor; and subjecting the waste liquor to solid-liquid separation.

The inventive method can significantly reduce the time for solid-liquid separation, and enormously increase the treatment capacity of waste liquor in unit time without adding extra equipments, by introducing water-soluble ester of alginic acid and/or water-soluble salt of alginic acid into the waste liquor before the step of solid-liquid separation. Thereby, the inventive method solves the technical difficulty resulting in low load of the equipments used in producing ethanol through cassava fermentation, and enormously increases the production capacity of the equipments for producing ethanol.

Embodiments

The present invention provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, which comprises the steps of: introducing water-soluble ester of alginic acid and/or water-soluble salt of alginic acid into the waste liquor; and then subjecting the waste liquor to solid-liquid separation.

According to the present invention, there is no special limitation on adding amount of the water-soluble ester of alginic acid and/or water-soluble salt of alginic acid, as long as it can reduce the time for solid-liquid separation. Preferably, the adding amount of said water-soluble ester of alginic acid and/or water-soluble salt of alginic acid is 0.05-1 kg, relative to 1000 kg of waste liquor; and more preferably, the adding amount of said water-soluble ester of alginic acid and/or water-soluble salt of alginic acid is 0.1-0.5 kg, relative to 1000 kg of waste liquor.

There is no special limitation on the type of said water-soluble salt of alginic acid, as long as it can intensify the impacting among the molecules, and make the small molecules combine into larger flocculate. Preferably, the relative molecular weight of water-soluble salt of alginic acid is 30000-200000. The term "the relative molecular weight" refers to a ratio of average mass of substance molecule or special unit to 1/12 atomic mass of nuclide ¹² C. For example, said water-soluble salt of alginic acid can be one or more selected from the group consisting of sodium alginate, potassium alginate, and ammonium alginate. The water-soluble salt of alginic acid which meets the requirement above can be purchased commercially, such as sodium alginate manufactured by Qingdao Nanyang Seaweed Industrial Co., Ltd., potassium alginate manufactured by Qingdao Bright Moon Seaweed Group Co., Ltd., and ammonium alginate manufactured by Handan Marine Medical Seaweed Co., Ltd..

There is no special limitation on the type of said water-soluble ester of alginic acid, as long as it can intensify the impacting among the molecules, and make the small molecules combine into larger flocculate. Preferably, the relative molecular weight of water-soluble ester of alginic acid is 30000-200000. The term "the relative molecular weight" refers to a ratio of average mass of substance molecule or special unit to 1/12 atomic mass of nuclide ¹² C. For example, said water-soluble ester of alginic acid can be one or more selected from the group consisting of propylene glycol alginate, ethylene glycol alginate, and butanediol alginate; preferably, said water-soluble ester of alginic acid is propylene glycol alginate. The water-soluble ester of alginic acid which meets the requirement above can be synthesized through common method known by person skilled in the art, and also can be purchased commercially, such as propylene glycol alginate manufactured by Qingdao Bright Moon Seaweed Group Co., Ltd.. Preferably, both of the water-soluble ester of alginic acid and water-soluble salt of alginic acid can be introduced into the waste liquor before the step of liquid-solid separation. While both of the water-soluble ester of alginic acid and water-soluble salt of alginic acid are introduced into the waste liquor, the time for solid-liquid separation can be further decreased, and the treatment capacity of waste liquor in unit time can be further increased. There is no special limitation on adding amounts of the water-soluble ester of alginic acid and water-soluble salt of alginic acid; preferably, the adding amount of the water-soluble salt of alginic acid is 10-1000 parts by weight, relative to 100 parts by weight of the water-soluble ester of alginic acid . More preferably, the adding amount of the water-soluble salt of alginic acid is 40-300 parts by weight, relative to 100 parts by weight of the water-soluble ester of alginic acid.

According to the present invention, various common methods known by the person skilled in the art can be used to perform the solid-liquid separation, such as filtration. The filtration can be performed by filter press, such as chamber filter press manufactured by Jingjin Filter Press Group. There is no special limitation on filtering conditions; preferably, the filtering conditions comprise filtering pressure of 0.4-1 MPa, and filtering time of 1-3 hr.

However, the present inventors have found that while the filtration is performed by chamber filter press, the waste liquor enters the space between the common filter plates of the filter press, solid particles are trapped in space between the filter plates by the filter medium of the filter plate, and while liquid passes through the filter medium and is discharged via outlet; with ongoing of the filtering process, thickness of the solid production increases gradually, and resistance to the dehydrating multiples, which leads to dramatic decrease of treatment capacity; moreover, due to limitation of inherent properties of the common filter plate, filter pressure can not be further increased (usually below IMPa), thus, water content of the obtained solid production can not be further decreased, and the energy consumption of subsequent drying is too high.

Therefore, the solid- liquid separation is preferably performed by filtration and squeeze.

According to the present invention, various equipments can be used to filter and squeeze the waste liquor, and membrane filter press is preferably adopted.

The membrane filter press has not only filtering function same as that of common filter press, but also squeezing function for further dehydrating solid production. In the membrane filter press, common filter plate and membrane filter plate are alternately arranged, and the middle core plate and two side membranes of the membrane filter plate are tightly pressed to form two sealed sandwich layers. The membrane filter plate has the same filtering function as common filter plate, but additionally has squeezing function, i.e. after filtering is finished, squeezing medium is injected into the sealed sandwich layer via the inlet hole of the core plate, and the filtered solid production can be swollen and squeezed for further dehydrating by the elastic action of the membrane.

The numbers of common filter plates and the membrane filter plates in the membrane filter can be adjusted according to the concentration of the waste liquor, and preferably, the number of the common filter plate is 50-60. The common filter plate can be purchased commercially, such as chamber filter plate manufactured by Jingjin Filter Press Group. The number of the membrane filter plates is preferably 50-60. The membrane filter plate can be purchased commercially, such as 1250-type membrane filter plate manufactured by Jingjin Filter Press Group. The common filter plates and the membrane filter plates are alternately arranged at number ratio of 1:1. The membrane filter press satisfying the aforementioned requirements can be commercially purchased, such as X _M ^A ZG600/1500 X 2000U\-type membrane filter press manufactured by Jingjin Filter Press Group.

The inventor of the present invention has found that the membrane filter press can not only significantly reduce water content of the obtained solid production, but also dramatically decrease impurity content in water removed therefrom, so as to alleviate impurity-induced wearing to equipment and lower maintenance cost; and the COD of the removed water is low, such that impact on environment is lowered.

In the present invention, the waste liquor resulted from ethanol production through cassava fermentation refers to residual solid-liquid mixture resulted from ethanol distillation during ethanol production through cassava fermentation.

In the present invention, there is no special limitation on filtering conditions and squeezing conditions, preferably, the filter conditions and squeezing conditions make the solid production have water content less than 60wt%; more preferably, the filtering conditions comprise filtering pressure of 0.4-1 MPa, and filtering time of 1-2 hr; and the squeezing conditions comprise squeezing pressure of 10-25 MPa, and squeezing time of 0.2-1 hr.

In the present invention, the squeezing pressure can be realized by filling squeezing medium into the membrane filter press, and the said squeezing medium can be various common squeezing medium for membrane filter press, such as compressed air and/or water.

According to the present invention, the inventive method further comprises drying the solid production obtained by the solid-liquid separation to obtain solid residue. The drying equipment can be various routine drying equipments, such as HZG- series dryer manufactured by Shenyang Yuanda Co. Ltd, and combined WJI-900B fluid-bed dryer and XLS-100 type flash dryer manufactured by Beijing Yimin Gongmao Co. Ltd. The drying conditions are well known to those skilled in the art, for example, the drying conditions include drying temperature of 100-200 ⁰ C, and drying time of 0.2-2 hr, preferably, drying temperature of 120-150°C, and drying time of 0.5-1 hr.

The present invention will be explained in further detail through the following examples.

Example 1

10 kg of propylene glycol alginate (Qingdao Bright Moon Seaweed Group Co., Ltd., relative molecular weight of 40000) is introduced into the waste liquor(100 tons) with water content of 95wt% resulted from ethanol production through cassava fermentation, and then, the waste liquor is charged into chamber filter press (Jingjin Filter Press Group) for filtering, wherein the chamber filter press has 100 common chamber filter plates (Jingjin Filter Press Group). Solid production Al having water content of 75wt% is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time 2 hr. The time of solid- liquid separation and the treatment capacity (single set of equipment) of waste liquor in unit time are shown in table 1.

Comparison example 1

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the example 1, except that the propylene glycol alginate is not introduced into the waste liquor. The comparison solid production CAl having water content of 75wt% is obtained, and the time of solid-liquid separation and the treatment capacity(single set of equipment) of waste liquor in unit time are shown in table 1. Example 2

30 kg of sodium alginate (Qingdao Nanyang Seaweed Industrial Co., Ltd., relative molecular weight of 80000) is introduced into the waste liquor (100 tons) with water content of 95wt% resulted from ethanol production through cassava fermentation, and then, the waste liquor is charged into chamber filter press (Jingjin Filter Press Group) for filtering, wherein the chamber filter press has 100 common chamber filter plates (Jingjin Filter Press Group). Solid production A2 having water content of 75wt% is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time 1.8 hr. The time of solid- liquid separation and the treatment capacity (single set of equipment) of waste liquor in unit time are shown in table 1.

Example 3

15 kg of potassium alginate (Qingdao Bright Moon Seaweed Group Co., Ltd., relative molecular weight of 150000) and 15 kg of propylene glycol alginate (Qingdao Bright Moon Seaweed Group Co., Ltd., relative molecular weight of 100000) are introduced into the waste liquor(100 tons) with water content of 95wt% resulted from ethanol production through cassava fermentation, and then, the waste liquor is charged into chamber filter press (Jingjin Filter Press Group) for filtering, wherein the chamber filter press has 100 common chamber filter plates (Jingjin Filter Press Group). Solid production A3 having water content of 75wt% is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time 1.4 hr. The time of solid-liquid separation and the treatment capacity (single set of equipment) of waste liquor in unit time are shown in table 1.

Table 1

It can be observed from the table 1 that the inventive method reduced the time for removing water from the waste liquor significantly, and increased the treatment capacity of waste liquor in unit time enormously without adding extra equipments, thus solving the technical difficulty resulting in low load of the equipments used in producing ethanol through cassava fermentation, and increasing the production capacity of the equipments for producing ethanol.

Example 4

10 kg of ammonium alginate (Handan Marine Medicical Seaweed Co., Ltd., relative molecular weight of 100000) and 10 kg of propylene glycol alginate (Qingdao Bright Moon Seaweed Group Co., Ltd., relative molecular weight of 50000) are introduced into the waste liquor(100 tons) with water content of 95wt% resulted from ethanol production through cassava fermentation, and then, the waste liquor is charged into chamber filter press (Jingjin Filter Press Group) for filtering, wherein the chamber filter press has 100 common chamber filter plates (Jingjin Filter Press Group). Solid production A4 is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time 1.8 hr.

The water content of solid production A4 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in table 2.

The obtained solid production A4 is placed into airflow rotary drum dryer (JB/T 10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 180°C to obtain solid residue, the water content in the solid residue is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the drying energy consumption of the solid residue is shown in table 2.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 5

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the example 1, except that the solid- liquid separation is performed by using membrane filter press (Jingjin Filter Press Group, X _M ^A ZG600/1500 X 2000U ^B _K ), wherein the membrane filter press has 50 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 50 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Solid production is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time lhr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the solid production at squeezing pressure lOMPa for 0.8hr to obtain solid production A5.

The water content of the solid production A5 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in table 2.

The obtained solid production A5 is placed into airflow rotary drum dryer (JB/T 10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 120°C to obtain solid residue, the water content in the solid residue is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the drying energy consumption of the solid residue is shown in table 2.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 6

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the example 5, except that the solid production is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time lhr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the solid production at squeezing pressure lOMPa for 0.5hr to obtain solid production A6.

The water content of the solid production A6 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in table 2. The obtained solid production A6 is placed into airflow rotary drum dryer (JB/T 10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 120°C to obtain solid residue, the water content in the solid residue is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the drying energy consumption of the solid residue is shown in table 2.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 7

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the example 5, except that the membrane filter press has 55 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 55 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Solid production is obtained at the filtering conditions of filtering pressure 0.7MPa and filtering time 0.6 hr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the solid production at squeezing pressure 15MPa for 0.5 hr to obtain solid production A7.

The water content of the solid production A7 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in table 2.

The obtained solid production A7 is placed into airflow rotary drum dryer (JB/T 10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 140°C to obtain solid residue, the water content in the solid residue is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the drying energy consumption of the solid residue is shown in table 2.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 8

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the example 5, except that the membrane filter press has 60 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 60 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Solid production is obtained at the filtering conditions of filtering pressure 0.5MPa and filtering time 0.9 hr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the solid production at squeezing pressure 22 MPa for 0.3 hr to obtain solid production A8.

The water content of the solid production A8 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in table 2.

The obtained solid production A8 is placed into airflow rotary drum dryer (JB/T 10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 180°C to obtain solid residue, the water content in the solid residue is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the drying energy consumption of the solid residue is shown in table 2.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Table

It can be observed from the Table 1 that the water contents of the solid productions A5-A8 obtained in the examples 5-8 are respectively 55wt%, 58wt%, 54wt%, and 52wt%, while the water content of the solid production A4 obtained in the example 4 is as high as 74wt%; therefore the solid production obtained by filtering and squeezing the waste liquor using membrane filter press has significantly reduced water content. In addition, compared with the example 4, the examples 5-8 have dramatically reduced energy consumption for drying, indicating that the energy consumption required by recovery of the solid residue is reduced significantly by using membrane filter press.

Examples 9-13

Impurity contents and COD values in water removed by squeezing in the examples 4-8 are respectively determined by the following methods:

Determination of impurity content

The determination method comprises stirring water removed by squeezing in the examples 4-8 well to form suspension, taking l,000g of the suspension, allowing it to stand for 24hr, removing the supernatant, and weighing the precipitate to obtain impurity content in the water removed by squeezing. And the result is shown in Table 3.

Determination of COD value

COD values of the water removed by squeezing in the examples 4-8 are respectively determined by Chinese National Standard GB11914-89 Water quality-Determination of the chemical oxygen demand-Dichromate method. And the result is shown in Table 3.

Table 3

It can be obtained from the Table 3 that compared with the removed water obtained in the example 4, the water removed by squeezing in the examples 5-8 has significantly lower impurity contents and COD values, indicating that the inventive method by using membrane filter press can not only significantly reduce energy consumption required for recovery of the solid residue, but also dramatically lower impurity content and COD value of water removed by squeezing, so as to reduce impurity-induced wearing of equipment, lower maintenance cost, and reduce adverse impact on environment.