A low-pressure steam heated dry dilute acid pretreatment method for lignocellulosic feedstocks

Abstract

The application discloses a low-pressure steam heated dry dilute acid pretreatment method for lignocellulose raw materials, and the specific steps are as follows: (1) performing pretreatment on the lignocellulose raw materials; (2) performing dry dilute acid pretreatment on the lignocellulose raw materials obtained in the step (1), and the heating steam pressure in the pretreatment is 1.0-2.1 MPa low-pressure saturated steam; and (3) performing subsequent biological processing on the pretreated lignocellulose raw materials obtained in the step (2). The application has the following advantages: the low-pressure steam heated dry dilute acid pretreatment can ensure the pretreatment effect, and due to the low heating steam pressure, the equipment investment of the steam boiler is greatly reduced; in addition, the low-pressure steam has a high steam inlet rate, the mixing and heat transfer in the pretreatment process are strengthened, and the generation of inhibitors in the pretreatment process is effectively reduced. The low-pressure steam heated dry dilute acid pretreatment lays a foundation for a small and dispersed pretreatment-large and centralized biological refining mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lignocellulosic biorefinery, and is a low-pressure steam heating lignocellulosic feedstock dry dilute acid pretreatment method. BACKGROUND

[0002] Pretreatment is a necessary step to destroy the structure of lignocellulosic feedstock and improve the subsequent cellulase hydrolysis efficiency in the process of producing biofuels and bio-based chemicals by biorefinery. At present, there are many pretreatment methods, such as dilute acid pretreatment, steam explosion pretreatment, ammonia fiber explosion pretreatment, alkali pretreatment and ionic liquid pretreatment, etc. In almost all these pretreatment methods, temperature is a key factor affecting the pretreatment effect. Generally speaking, relatively high temperature can obtain better pretreatment effect.

[0003] At present, the heating methods for pretreatment temperature rise mainly include oil bath, sand bath and electric heating wire heating, etc., and steam is often used in industry. In order to obtain higher pretreatment temperature, saturated steam with higher pressure or superheated steam with lower pressure is often used for heating in industry, the former has higher requirement for saturated steam pressure, which has significant influence on equipment investment and operation safety, while the latter needs to supply superheated steam from a thermal power plant, which has very high requirement for equipment, and the lignocellulosic feedstock needs to be pretreated in a centralized manner, which affects the economy of the whole biorefinery process.

[0004] The small and dispersed pretreatment-large and centralized biorefinery mode is to disperse the pretreatment operation in the biorefinery process to the raw material producing area. The lignocellulosic feedstock is processed by dry dilute acid pretreatment process and is in the form of dry solid without any wastewater. After drying and balling to increase the material density, the lignocellulosic feedstock is transported to a large biorefinery plant for centralized treatment. This process significantly reduces the raw material collection cost and the production cost of biorefinery products. However, the dispersed pretreatment plant is small and is not suitable for the construction of thermal power plants and high-pressure steam boilers with high investment cost. Therefore, it is crucial to develop a pretreatment method which only needs low-pressure steam for heating. This method can ensure the pretreatment effect of lignocellulosic feedstock, and at the same time, due to the low pressure of heating steam, the equipment investment of steam boiler is greatly reduced, which is conducive to miniaturization. In addition, the low-pressure steam has a high inlet steam rate, which promotes mixing and heat transfer in the pretreatment process, effectively reducing the generation of inhibitors in the pretreatment process. The low-pressure steam heating dry dilute acid pretreatment lays a foundation for the small and dispersed pretreatment-large and centralized biorefinery mode. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a low-pressure steam heating lignocellulosic feedstock dry dilute acid pretreatment method.

[0006] The purpose of the present application is realized by the following technical solutions.

[0007] A low-pressure steam heated dry dilute acid pretreatment method for lignocellulosic feedstock, the specific steps are as follows:

[0008] (1) pretreating the lignocellulosic feedstock;

[0009] (2) dry dilute acid pretreating the lignocellulosic feedstock obtained in step (1), the heating steam pressure during the pretreatment is 1.0-2.1 MPa low-pressure saturated steam;

[0010] The conditions for the dry dilute acid pretreatment are as follows: sulfuric acid dosage 1-10 g / 100 g lignocellulosic feedstock, heating temperature 130-220℃, heating time 0-60 minutes, mass fraction of solid straw during the pretreatment 30-90%, steam heat source pressure 1.0-2.1 MPa;

[0011] The heating steam pressure during the dry dilute acid pretreatment is 1.0-2.1 MPa saturated steam, preferably 1.5 MPa saturated steam;

[0012] The generation mode of the low-pressure steam includes electric heating boiler, coal-fired boiler, oil-fired boiler and gas-fired boiler, etc.

[0013] (3) carrying out subsequent biological processing on the pretreated lignocellulosic feedstock obtained in step (2).

[0014] The subsequent biological processing includes enzymatic saccharification and other biological conversion and chemical conversion processes based on sugar platform to produce liquid fuels and chemicals.

[0015] Compared with the prior art, the present application has the following positive effects:

[0016] Compared with the pretreatment process in which high-pressure saturated steam or low-pressure superheated steam is often used for heating in industry, the present pretreatment process only needs low-pressure steam for heating, which greatly reduces the equipment investment of the steam boiler while ensuring the pretreatment effect of the lignocellulosic feedstock, and in addition, the low-pressure steam has a high steam inlet rate, which promotes mixing and heat transfer during the pretreatment process and effectively reduces the generation of inhibitors during the pretreatment process. The low-pressure steam heated dry dilute acid pretreatment lays a foundation for the small-scale distributed pretreatment-large-scale centralized biorefinery mode.

DETAILED DESCRIPTION

[0017] The following provides a specific embodiment of a low-pressure steam heated dry dilute acid pretreatment method for lignocellulosic feedstock according to the present application.

[0018] Example 1

[0019] After the 1200g dry corn stalks were crushed and de-dusted, 5% mass fraction of 600g dilute sulfuric acid was added to the pretreatment reactor equipped with screw stirring paddle, stirring for 3 minutes, stirring speed 50rpm. The saturated steam pressure of 1.5Mpa saturated steam was introduced into the pretreatment reactor, dry dilute acid pretreatment, reaction temperature 175℃, reaction time 5 minutes. The material was taken out from the reactor, enzyme hydrolysis experiment, enzyme hydrolysis experiment solid content 2.5%, temperature 50℃, stirring speed 150rpm, cellulase dosage 20FPU / g DM, glucose concentration was measured after 72 hours, calculate the cellulose conversion rate, the cellulose conversion rate under this condition was 91.76%.

[0020] Example 2

[0021] After the 1200g dry corn stalks were crushed and de-dusted, 5% mass fraction of 600g dilute sulfuric acid was added to the pretreatment reactor equipped with screw stirring paddle, stirring for 3 minutes, stirring speed 50rpm. The saturated steam pressure of 1.7Mpa saturated steam was introduced into the pretreatment reactor, dry dilute acid pretreatment, reaction temperature 175℃, reaction time 5 minutes. The material was taken out from the reactor, enzyme hydrolysis experiment, enzyme hydrolysis experiment solid content 2.5%, temperature 50℃, stirring speed 150rpm, cellulase dosage 20FPU / g DM, glucose concentration was measured after 72 hours, calculate the cellulose conversion rate, the cellulose conversion rate under this condition was 97.88%.

[0022] Example 3

[0023] After the 1200g dry corn stalks were crushed and de-dusted, 5% mass fraction of 600g dilute sulfuric acid was added to the pretreatment reactor equipped with screw stirring paddle, stirring for 3 minutes, stirring speed 50rpm. The saturated steam pressure of 1.9Mpa saturated steam was introduced into the pretreatment reactor, dry dilute acid pretreatment, reaction temperature 175℃, reaction time 5 minutes. The material was taken out from the reactor, enzyme hydrolysis experiment, enzyme hydrolysis experiment solid content 2.5%, temperature 50℃, stirring speed 150rpm, cellulase dosage 20FPU / g DM, glucose concentration was measured after 72 hours, calculate the cellulose conversion rate, the cellulose conversion rate under this condition was 98.86%.

[0024] Example 4

[0025] After the 1200g dry corn stalks were crushed and dedusted, 600g of 5% mass fraction dilute sulfuric acid was added into the pretreatment reactor equipped with screw stirring paddle, and stirred for 3 minutes at a stirring speed of 50rpm. Saturated steam with a saturated steam pressure of 2.1Mpa was introduced into the pretreatment reactor to perform dry dilute acid pretreatment, and the reaction temperature was 175℃ and the reaction time was 5 minutes. The material was taken out from the reactor to perform enzyme hydrolysis experiment, and the solid content of the enzyme hydrolysis experiment was 2.5%, the temperature was 50℃, the stirring speed was 150rpm, the dosage of cellulase was 20FPU / g DM, and the glucose concentration was measured after 72 hours to calculate the cellulose conversion rate. The cellulose conversion rate under the above conditions was 98.20%.

[0026] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the concept of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A low-pressure steam heated dry dilute acid pretreatment method of lignocellulosic feedstock, comprising the following steps: (1) adding 1200 g of dry corn stover after dedusting and crushing and 600 g of 5% mass fraction dilute sulfuric acid into a pretreatment reactor equipped with screw stirring blades, and stirring for 3 minutes at a stirring speed of 50 rpm; (2) introducing saturated steam with a saturated steam pressure of 1.9 MPa into the pretreatment reactor to perform dry dilute acid pretreatment, and the reaction temperature is 175℃ and the reaction time is 5 minutes; (3) taking out the material from the reactor for subsequent biological processing, which includes enzymatic saccharification and other biological and chemical conversion processes based on sugar platform to produce chemicals. In the step (2), the saturated steam can be generated by an electrically heated boiler, a coal-fired boiler, an oil-fired boiler or a gas-fired boiler. ​ ​ 2. A low pressure steam heated lignocellulosic feedstock dilute acid pretreatment process according to claim 1, characterized in that, ​