A reconstituted tobacco leaf extract concentration process and concentration system

Abstract

The present invention provides a reconstituted tobacco leaf extract concentration process, which performs layer-by-layer deep concentration on the reconstituted tobacco leaf extract through a membrane distillation process, a nanofiltration membrane process, an evaporation concentration process, and a reverse osmosis membrane process, respectively, to obtain a concentrated reconstituted tobacco leaf extract. The present invention also provides a reconstituted tobacco leaf extract concentration system, comprising: a membrane distillation device, a nanofiltration membrane assembly, an evaporator, a reverse osmosis membrane assembly, and a concentrated liquid storage tank. The membrane concentration combination process and system provided by the present invention can solve the problems of the concentration multiple and concentration efficiency of low-temperature membrane concentration, prevent the loss of effective components of tobacco, and reduce the degree of membrane pollution and the frequency of cleaning, so as to achieve the purpose of improving quality and increasing efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing reconstituted tobacco by papermaking method, and particularly relates to a reconstituted tobacco extract concentration process and a concentration system. Background Art

[0002] Papermaking reconstituted tobacco is a kind of cigarette raw material obtained by extracting and squeezing tobacco waste such as tobacco stems, cigarette dust or broken tobacco pieces to achieve solid-liquid separation, concentrating the obtained extract to obtain a certain concentration of concentrated liquid, and then making the obtained solid slurry into a substrate by papermaking on a paper machine, and then recombining the concentrated liquid and the substrate in a coating system, and finally drying and cutting. Because it plays a great role in reducing tar and harm in cigarettes, its application in the cigarette industry is becoming more and more extensive.

[0003] At present, the papermaking reconstituted tobacco extract needs to be concentrated by evaporator after filtration until the solid content of the concentrate rises to about 35% before it can be used for subsequent production. The whole concentration process generally adopts multi-effect vacuum distillation. Under the condition of 60-80℃, the tobacco extract is gradually concentrated. Due to the high concentration temperature, the evaporator concentration process consumes a lot of energy and causes a large loss of tobacco flavor substances in the concentrate. Therefore, low-temperature membrane concentration has gradually begun to be tried and applied.

[0004] Patent CN103919272A discloses a low-temperature concentration system and a low-temperature concentration method for a reconstituted tobacco leaf extract. The system uses a disc-tube reverse osmosis membrane for concentration. Since high-temperature concentration is not required, the loss of heat-sensitive substances in the extract is greatly reduced. However, the method has a high operating pressure and high energy consumption. Patent CN103349351A invented a method for reconstituted tobacco leaves by a papermaking method based on membrane separation technology. The method separates and purifies the obtained crude extract of reconstituted tobacco leaves through a ceramic microfiltration membrane to remove macromolecular substances such as proteins, sugars, and pectin, and then uses an organic filter membrane for further purification. The subsequent treatments include organic membrane and double-effect evaporation concentration, coating and drying. The method can remove macromolecular proteins and pectin from tobacco extract and retain effective substances in tobacco, but the concentration process of this method is relatively long. Ordinary alumina ceramic membranes are very easy to clog during actual operation, and the membranes need to be cleaned frequently. Patent CN103919272A can concentrate the concentration of tobacco extract from 2.5-8% to 30-45% by using a two-stage reverse osmosis membrane system process. Although adding a reverse osmosis membrane system can increase the concentration multiple of the extract, the concentration efficiency is significantly reduced, and membrane cleaning and replacement are even more difficult. Therefore, the many problems in the above patents have become technical bottlenecks in the development of low-temperature membrane concentration technology. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a reconstituted tobacco leaf extract concentration process and concentration system, which is used to solve the problems of low concentration multiple and concentration efficiency of low-temperature membrane concentration in the prior art, prevent the loss of tobacco active ingredients, and reduce the degree of membrane contamination and cleaning frequency.

[0006] In order to achieve the above-mentioned object and other related objects, the present invention provides a process for concentrating a reconstituted tobacco leaf extract, which mainly comprises the following steps:

[0007] 1) pre-concentrating the reconstituted tobacco leaf extract to a solid content of 10-20 wt % by membrane distillation to obtain a membrane distillation pre-concentrated liquid and membrane distillation process condensed water;

[0008] 2) using a nanofiltration membrane process to concentrate the membrane distillation pre-concentrated liquid to a solid content of 20-25 wt % to obtain a nanofiltration membrane concentrated liquid and a nanofiltration membrane clear liquid;

[0009] 3) using an evaporation concentration process to concentrate the nanofiltration membrane concentrate to a solid content of 35-40 wt %, to obtain an evaporator concentrate;

[0010] 4) using a reverse osmosis membrane process to concentrate and dehydrate the membrane distillation process condensate and the nanofiltration membrane clear liquid, recovering the tobacco active ingredients, with the concentration multiple being 20 to 25 times, to obtain a reverse osmosis membrane concentrated liquid;

[0011] 5) Mixing the reverse osmosis membrane concentrate with the evaporator concentrate to obtain a concentrate of the reconstituted tobacco leaf extract.

[0012] Preferably, the membrane distillation process in step 1) is to use a membrane distillation device to pre-concentrate the reconstituted tobacco leaf extract to obtain a membrane distillation pre-concentrated liquid; the membrane distillation device contains a hot side flow channel and a cold side flow channel, and the hot side flow channel and the cold side flow channel are separated by a porous hydrophobic membrane; the hot side flow channel is injected into the reconstituted tobacco leaf extract, and the cold side flow channel is injected into the purge gas.

[0013] Preferably, the nanofiltration membrane process in step 2) is to further concentrate the membrane distillation pre-concentrated liquid using a nanofiltration membrane assembly to obtain a nanofiltration membrane concentrated liquid.

[0014] Preferably, the evaporation concentration process in step 3) is to use an evaporator to concentrate the nanofiltration membrane concentrate to obtain an evaporator concentrate.

[0015] Preferably, the reverse osmosis membrane process in step 4) uses a reverse osmosis membrane assembly to concentrate and dehydrate the condensed water from the membrane distillation process and the nanofiltration membrane clear liquid to obtain a reverse osmosis membrane concentrated liquid.

[0016] The present invention also provides a system for concentrating a reconstituted tobacco leaf extract, comprising: a membrane distillation device, a nanofiltration membrane assembly, an evaporator, a reverse osmosis membrane assembly and a concentrated liquid storage tank; the feed inlet of the membrane distillation device is connected to the feed pipeline of the reconstituted tobacco leaf extract, and the membrane distillation device contains a membrane distillation pre-concentrated liquid outlet and a membrane distillation process condensed water outlet; the membrane distillation pre-concentrated liquid outlet is connected to the feed inlet of the nanofiltration membrane assembly, and the nanofiltration membrane assembly contains a nanofiltration membrane concentrated liquid outlet and a nanofiltration membrane clear liquid outlet; the nanofiltration membrane concentrated liquid outlet is connected to the feed inlet of the evaporator, and the outlet of the evaporator is connected to the concentrated liquid storage tank; the membrane distillation process condensed water outlet and the nanofiltration membrane clear liquid outlet are both connected to the feed inlet of the reverse osmosis membrane assembly, and the outlet of the reverse osmosis membrane assembly is connected to the concentrated liquid storage tank.

[0017] As described above, the reconstituted tobacco extract concentration process and concentration system of the present invention have the following beneficial effects:

[0018] (1) In the reconstituted tobacco leaf extract concentration process of the present invention, the membrane distillation process has lower energy consumption than conventional membrane concentration, and the PTFE material on the surface of the porous hydrophobic membrane is extremely resistant to pollution and temperature. When it is operated for a long time, the membrane cleaning frequency is low and the service life is long. Ordinary organic membranes have poor temperature resistance, and the general use temperature cannot exceed 45°C, while the outlet temperature of the reconstituted tobacco leaf extract is generally above 55°C. Therefore, porous hydrophobic membranes with better temperature resistance have better technical advantages. At the same time, the characteristics of higher steam pressure due to higher feed temperature can be used to improve the pre-concentration effect of the reconstituted tobacco leaf extract, and avoid the cooling treatment of the feed before conventional membrane concentration, thereby reducing the energy consumption cost of the reconstituted tobacco leaf extract concentration process as a whole.

[0019] (2) The reconstituted tobacco leaf extract concentration process of the present invention utilizes the characteristics of the reverse osmosis membrane having a small pore size and being able to intercept small-molecule tobacco flavor components, and concentrates and dehydrates the condensed water of the membrane distillation process and the clear liquid of the nanofiltration membrane, thereby fully recovering the effective components of the tobacco, and ensuring that there is almost no loss of tobacco flavor components.

[0020] (3) The reconstituted tobacco leaf extract concentration process of the present invention combines membrane distillation process, nanofiltration membrane process, evaporation concentration process and reverse osmosis membrane process to concentrate the reconstituted tobacco leaf extract layer by layer to obtain a reconstituted tobacco leaf extract concentrate, thereby overcoming the problems of low concentration multiple and concentration efficiency of low-temperature membrane concentration in the prior art and difficulty in membrane cleaning and replacement, preventing the loss of effective ingredients in tobacco, reducing the degree of membrane pollution, and having high industrial utilization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Shown is a flow chart of the process for concentrating the reconstituted tobacco leaf extract of the present invention. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] Please refer to the attached Figure 1 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0024] The present invention provides a process for concentrating a reconstituted tobacco leaf extract, which mainly comprises the following steps:

[0025] 1) pre-concentrating the reconstituted tobacco leaf extract to a solid content of 10-20 wt % by membrane distillation to obtain a membrane distillation pre-concentrated liquid and membrane distillation process condensed water;

[0026] 2) using a nanofiltration membrane process to concentrate the membrane distillation pre-concentrated liquid to a solid content of 20-25 wt % to obtain a nanofiltration membrane concentrated liquid and a nanofiltration membrane clear liquid;

[0027] 3) using an evaporation concentration process to concentrate the nanofiltration membrane concentrate to a solid content of 35-40 wt %, to obtain an evaporator concentrate;

[0028] 4) using a reverse osmosis membrane process to concentrate and dehydrate the membrane distillation process condensate and the nanofiltration membrane clear liquid, recovering the tobacco active ingredients, with the concentration multiple being 20 to 25 times, to obtain a reverse osmosis membrane concentrated liquid;

[0029] 5) Mixing the reverse osmosis membrane concentrate with the evaporator concentrate to obtain the concentrate of the reconstituted tobacco leaf extract.

[0030] The reconstituted tobacco leaf extract concentration process of the present invention is to pre-concentrate the reconstituted tobacco leaf extract by a membrane distillation process to obtain a membrane distillation concentrate and a membrane distillation process condensed water, respectively; wherein the membrane distillation concentrate is further concentrated by a nanofiltration membrane process to obtain a nanofiltration membrane concentrate and a nanofiltration membrane clear liquid, respectively. The obtained membrane distillation process condensed water and the nanofiltration membrane clear liquid are concentrated by a reverse osmosis membrane process to obtain a reverse osmosis membrane concentrate. The nanofiltration membrane concentrate is subjected to an evaporation concentration process to obtain an evaporator concentrate. The reverse osmosis membrane concentrate is mixed with the evaporator concentrate to obtain a concentrate of the reconstituted tobacco leaf extract. The reconstituted tobacco leaf extract concentration process of the present invention is to concentrate the reconstituted tobacco leaf extract layer by layer by a membrane distillation process, a nanofiltration membrane process, an evaporation concentration process and a reverse osmosis membrane process to obtain a concentrate of the reconstituted tobacco leaf extract, thereby avoiding the cooling treatment of the feed liquid before conventional membrane concentration and reducing the energy consumption cost of the reconstituted tobacco leaf extract concentration process as a whole.

[0031] In an optional embodiment, the reconstituted tobacco leaf extract concentration process of the present invention comprises: pre-concentrating the reconstituted tobacco leaf extract using a membrane distillation device to obtain a membrane distillation pre-concentrated liquid. The membrane distillation device comprises a hot side flow channel and a cold side flow channel, the hot side flow channel and the cold side flow channel are separated by a porous hydrophobic membrane; the reconstituted tobacco leaf extract is injected into the hot side flow channel, and the cold side flow channel is injected with a purge gas, and the purge gas is preferably air.

[0032] Among them, membrane distillation is an organic combination of membrane technology and distillation process, with a porous hydrophobic membrane as the separation medium. The porous hydrophobic membrane has air permeability but water-impermeability. Therefore, under the action of the vapor pressure difference on both sides of the membrane (hot side and cold side), the liquid water in the reconstructed tobacco leaf extract gradually evaporates in the hot side flow channel to form water vapor that penetrates into the membrane pores, and then is condensed into water droplets in the cold side flow channel, and the reconstructed tobacco leaf extract is pre-concentrated in this process. That is, by pumping the reconstructed tobacco leaf extract into the hot side flow channel of the membrane distillation device, and then injecting air as a purge gas into the cold side flow channel of the device, water vapor continuously evaporates from the hot side feed liquid, penetrates the porous hydrophobic membrane and enters the cold side flow channel, and is finally brought into the condenser by the purge gas for condensation to obtain membrane distillation process condensed water, and the reconstructed tobacco leaf extract in the hot side flow channel is dehydrated at low temperature to form a membrane distillation pre-concentrated liquid.

[0033] The porous hydrophobic membrane is a flat composite membrane, the surface layer is made of polytetrafluoroethylene (PTFE), and the support layer is made of polypropylene (PP). The pore size of the porous hydrophobic membrane can be 0.1-0.5 μm, for example, 0.1-0.2 μm, 0.2-0.4 μm or 0.4-0.5 μm, and the porosity can be 80-90%, for example, 80-82%, 82-84%, 84-86%, 86-88% or 88-90%. The air permeability of the porous hydrophobic membrane can be 500-1000 m 3 ·m -2 ·h -1, for example, 500 to 600 m 3 ·m -2 ·h -1 , 600~700m 3 ·m -2 ·h -1 , 700~800m 3 ·m -2 ·h -1 , 800~900m 3 ·m -2 ·h -1 or 900~1000m 3 ·m -2 ·h -1 The contact angle of the porous hydrophobic membrane may be 120° to 140°, for example, 120° to 125°, 125° to 130°, 130° to 135°, or 135° to 140°. The flow rate of the purge gas in the cold side flow channel may be 1 to 10 m / s, for example, 1 to 2 m / s, 2 to 4 m / s, 4 to 6 m / s, 6 to 8 m / s, or 8 to 10 m / s. The vacuum degree of the cold side flow channel can be 0.01-0.05Mpa, for example, 0.01-0.02Mpa, 0.02-0.03Mpa, 0.03-0.04Mpa or 0.04-0.05Mpa; the condensation temperature of the condenser can be 0-10°C, for example, 0-2°C, 2-4°C, 4-6°C, 6-8°C or 8-10°C, and the solid content of the membrane distillation pre-concentrate can be 10-20wt%, for example, 10-12wt%, 12-14wt%, 14-16wt%, 16-18wt% or 18-20wt%.

[0034] In an optional embodiment, the reconstituted tobacco leaf extract concentration process of the present invention comprises: using a nanofiltration membrane assembly to further concentrate the membrane distillation pre-concentrate to obtain a nanofiltration membrane concentrate. The nanofiltration membrane cut-off molecular weight can be 300-400, for example, 300-320, 320-340, 340-360, 360-380 or 380-400. The operating pressure of the nanofiltration membrane assembly can be 1-2 MPa, for example, 1-1.2 MPa, 1.2-1.4 MPa, 1.4-1.6 MPa, 1.6-1.8 MPa or 1.8-2 MPa. The solid content of the nanofiltration membrane concentrate can be 20-25 wt%, for example, 20-21 wt%, 21-22 wt%, 22-23 wt%, 23-24 wt% or 24-25 wt%. The solid content of the nanofiltration membrane concentrate in the reconstituted tobacco leaf extract concentration process of the present invention is 20-25wt% in order to prevent serious membrane pollution and ensure the normal operation of the nanofiltration membrane assembly under appropriate concentration multiples. If the operating pressure is further increased, the concentration multiple of the extract can continue to increase, but the service life of the nanofiltration membrane will be seriously affected.

[0035] In an optional embodiment, the reconstituted tobacco leaf extract concentration process of the present invention comprises: using an evaporator to concentrate the nanofiltration membrane concentrate to obtain an evaporator concentrate; the evaporator is a mechanical vapor recompression (MVR) evaporator. The evaporation temperature of the evaporator can be 60-80°C, for example, 60-65°C, 65-70°C, 70-75°C or 75-80°C. The pressure ratio of the mechanical vapor recompression evaporator can be 1.2-1.4, for example, 1.2, 1.3 or 1.4. The solid content of the evaporator concentrate can be 35-40wt%, for example, 35-36wt%, 36-37wt%, 37-38wt%, 38-39wt% or 39-40wt%. The reconstituted tobacco leaf extract concentration process of the present invention uses a mechanical vapor recompression (MVR) evaporator instead of a traditional high-pressure membrane concentration device or a multi-effect evaporator to continue to concentrate the extract to the production requirements of the reconstituted tobacco leaf product, thereby achieving the purpose of improving quality and increasing efficiency.

[0036] In an optional embodiment, the reconstituted tobacco leaf extract concentration process of the present invention comprises: using a reverse osmosis membrane assembly to concentrate and dehydrate the membrane distillation process condensate and the nanofiltration membrane clear liquid to obtain a reverse osmosis membrane concentrate. The reverse osmosis membrane cutoff molecular weight can be 50-100, 50-60, 60-70, 70-80, 80-90 or 90-100. The operating pressure of the reverse osmosis membrane assembly can be 1.5-3Mpa, for example, 1.5-1.8Mpa, 1.8-2.1Mpa, 2.1-2.4Mpa, 2.4-2.7Mpa or 2.7-3Mpa. The reverse osmosis membrane concentration multiple can be 20-25 times, for example, 20-22 times, 22-24 times or 24-25 times. The reverse osmosis membrane assembly used in the reconstituted tobacco leaf extract concentration process of the present invention has a relatively small pore size, which can not only intercept small-molecule tobacco flavor components, but also further concentrate and dehydrate the condensed water of the membrane distillation device and the nanofiltration membrane clear liquid, thereby fully recovering the tobacco effective components.

[0037] The present invention also provides a system for concentrating a reconstituted tobacco leaf extract, comprising: a membrane distillation device, a nanofiltration membrane assembly, an evaporator, a reverse osmosis membrane assembly and a concentrated liquid storage tank; the feed inlet of the membrane distillation device is connected to the feed pipeline of the reconstituted tobacco leaf extract, and the membrane distillation device is provided with a membrane distillation pre-concentrated liquid outlet and a membrane distillation process condensed water outlet; the membrane distillation pre-concentrated liquid outlet is connected to the feed inlet of the nanofiltration membrane assembly, and the nanofiltration membrane assembly is provided with a nanofiltration membrane concentrated liquid outlet and a nanofiltration membrane clear liquid outlet; the nanofiltration membrane concentrated liquid outlet is connected to the feed inlet of the evaporator, and the outlet of the evaporator is connected to the concentrated liquid storage tank; the membrane distillation process condensed water outlet and the nanofiltration membrane clear liquid outlet are both connected to the feed inlet of the reverse osmosis membrane assembly, and the outlet of the reverse osmosis membrane assembly is connected to the concentrated liquid storage tank.

[0038] The reconstituted tobacco leaf extract concentration system of the present invention is to send the extracted reconstituted tobacco leaf extract into a membrane distillation device, and obtain a membrane distillation concentrate and a membrane distillation process condensed water through a membrane distillation process. The membrane distillation concentrate enters a nanofiltration membrane assembly and is concentrated through a nanofiltration membrane process to obtain a nanofiltration membrane concentrate and a nanofiltration membrane clear liquid. The nanofiltration membrane concentrate enters an evaporator and is concentrated through an evaporation process to obtain an evaporator concentrate, and the evaporator concentrate is passed into a concentrated liquid storage tank for collection. The membrane distillation process condensed water and the nanofiltration membrane clear liquid first enter a reverse osmosis membrane assembly for further concentration, and are concentrated through a reverse osmosis membrane process to obtain a reverse osmosis membrane concentrate, and the reverse osmosis membrane concentrate is passed into a concentrated liquid storage tank for collection to obtain a concentrated solution of the reconstituted tobacco leaf extract.

[0039] The reconstituted tobacco leaf extract concentration process and concentration system provided by the present invention overcome the problems of low concentration multiple and low concentration efficiency of low-temperature membrane concentration in the prior art, and effectively prevent the loss of tobacco active ingredients, reduce the degree of membrane contamination and the frequency of cleaning.

[0040] The present invention is further illustrated by the following examples, but the scope of the present invention is not limited thereto. Examples 1 to 5 use KF porous hydrophobic membranes from Shanghai Minglie New Materials Co., Ltd., DL2540 nanofiltration membranes and SG2540 reverse osmosis membranes from GE of the United States, including but not limited to other types of raw materials and equipment that can achieve the same effect and the same properties.

[0041] Example 1

[0042] The above-mentioned reconstituted tobacco leaf extract concentration process and concentration system are used to concentrate the reconstituted tobacco leaf extract with an initial solid content of 8.6%, comprising the following steps:

[0043] 1) The reconstituted tobacco leaf extract is pre-concentrated by a low-temperature dehydration membrane distillation process, that is, the reconstituted tobacco leaf extract with an initial solid content of 8.6% is pumped into the hot side flow channel of the membrane distillation device, and then air is injected into the cold side flow channel of the device as a purge gas. The purge gas flow rate in the cold side flow channel is 1 m / s, and the vacuum degree of the cold side flow channel is 0.01 MPa. Water vapor is continuously volatilized from the hot side feed liquid and penetrates the porous hydrophobic membrane into the cold side air. The porous hydrophobic membrane has a membrane pore size of 0.1 μm, a porosity of 80%, and an air permeability of 500 m 3 ·m -2 ·h -1 , the contact angle is 120°, and finally the purge gas is brought into the condenser for condensation to obtain membrane distillation process condensed water. The condensation temperature of the condenser is 0°C, and the reconstituted tobacco leaf extract in the hot side flow channel is low-temperature dehydrated to form a membrane distillation pre-concentrate with a solid content of 10wt%;

[0044] 2) using a nanofiltration membrane assembly to further concentrate the membrane distillation pre-concentrate, the nanofiltration membrane cut-off molecular weight is 300, and the operating pressure of the nanofiltration membrane assembly is controlled to be 1 MPa, and after concentration, a nanofiltration membrane clear liquid and a nanofiltration membrane concentrate with a solid content of 20 wt% are formed;

[0045] 3) using a mechanical vapor recompression (MVR) evaporator to further concentrate the nanofiltration membrane concentrate into an evaporator concentrate having a solid content of 35 wt%, wherein the evaporation temperature is 60° C. and the mechanical vapor compressor pressure ratio is 1.2;

[0046] 4) using a reverse osmosis membrane assembly to concentrate and dehydrate the collected membrane distillation process condensate and nanofiltration membrane clear liquid to recover tobacco active ingredients, the reverse osmosis membrane cutoff molecular weight is 50, the operating pressure of the reverse osmosis membrane assembly is 1.5 MPa, the concentration multiple is 20 times, and then the concentrate is mixed with the evaporator concentrate to obtain a concentrate with a solid content of 33.2% required for the production of reconstituted tobacco leaves.

[0047] 5) The above process saves more than 8.8% of processing time compared with the traditional low-temperature membrane concentration technology.

[0048] Example 2

[0049] The above-mentioned reconstituted tobacco leaf extract concentration process and concentration system are used to concentrate the reconstituted tobacco leaf extract with an initial solid content of 8.6%, comprising the following steps:

[0050] 1) The reconstituted tobacco leaf extract is pre-concentrated by a low-temperature dehydration membrane distillation process, that is, the reconstituted tobacco leaf extract with an initial solid content of 8.6% is pumped into the hot side flow channel of the membrane distillation device, and then air is injected into the cold side flow channel of the device as a purge gas. The purge gas flow rate in the cold side flow channel is 3m / s, and the vacuum degree of the cold side flow channel is 0.02Mpa. Water vapor is continuously volatilized from the hot side feed liquid and penetrates the porous hydrophobic membrane into the cold side air. The porous hydrophobic membrane has a membrane pore size of 0.2μm, a porosity of 82%, and an air permeability of 700m 3 ·m -2 ·h -1 , the contact angle is 125°, and finally the purge gas is brought into the condenser for condensation to obtain membrane distillation process condensed water. The condensation temperature of the condenser is 2°C, and the reconstituted tobacco leaf extract in the hot side flow channel is dehydrated at low temperature to form a membrane distillation pre-concentrate with a solid content of 13wt%;

[0051] 2) further concentrating the membrane distillation pre-concentrate using a nanofiltration membrane assembly, the nanofiltration membrane cut-off molecular weight is 330, the operating pressure of the nanofiltration membrane assembly is 1.2 MPa, and after concentration, a nanofiltration membrane clear liquid and a nanofiltration membrane concentrate with a solid content of 22.5 wt% are formed;

[0052] 3) then using a mechanical vapor recompression (MVR) evaporator to further concentrate the nanofiltration membrane concentrate into an evaporator concentrate having a solid content of 36.9 wt%, wherein the evaporation temperature is 70° C. and the mechanical vapor compressor pressure ratio is 1.2;

[0053] 4) using a reverse osmosis membrane assembly to concentrate and dehydrate the collected membrane distillation process condensate and nanofiltration membrane clear liquid to recover tobacco active ingredients, the reverse osmosis membrane cutoff molecular weight is 50, the operating pressure of the reverse osmosis membrane assembly is 2.3 MPa, the concentration multiple is 23 times, and then the concentrate is mixed with the evaporator concentrate to obtain a concentrate with a solid content of 34.2% required for the production of reconstituted tobacco leaves.

[0054] 5) The above process saves more than 11.4% of processing time compared with the traditional low-temperature membrane concentration technology.

[0055] Example 3

[0056] The above-mentioned reconstituted tobacco leaf extract concentration process and concentration system are used to concentrate the reconstituted tobacco leaf extract with an initial solid content of 9.3%, comprising the following steps:

[0057] 1) The reconstituted tobacco leaf extract is pre-concentrated by a low-temperature dehydration membrane distillation process, that is, the reconstituted tobacco leaf extract with an initial solid content of 8.6% is pumped into the hot side flow channel of the membrane distillation device, and then air is injected into the cold side flow channel of the device as a purge gas. The purge gas flow rate in the cold side flow channel is 7m / s, and the vacuum degree of the cold side flow channel is 0.04Mpa. Water vapor is continuously volatilized from the hot side feed liquid and penetrates the porous hydrophobic membrane into the cold side air. The porous hydrophobic membrane has a membrane pore size of 0.3μm, a porosity of 90%, and an air permeability of 800m 3 ·m -2 ·h -1 , the contact angle is 130°, and finally the purge gas is brought into the condenser for condensation to obtain membrane distillation process condensed water. The condensation temperature of the condenser is 6°C, and the reconstituted tobacco leaf extract in the hot side flow channel is low-temperature dehydrated to form a membrane distillation pre-concentrate with a solid content of 15wt%;

[0058] 2) further concentrating the membrane distillation pre-concentrate using a nanofiltration membrane assembly, the nanofiltration membrane cut-off molecular weight is 380, the operating pressure of the nanofiltration membrane assembly is 1.5 MPa, and after concentration, a nanofiltration membrane clear liquid and a nanofiltration membrane concentrate with a solid content of 23.5 wt% are formed;

[0059] 3) then using a mechanical vapor recompression (MVR) evaporator to further concentrate the nanofiltration membrane concentrate into an evaporator concentrate having a solid content of 38.8 wt%, wherein the evaporation temperature is 70° C. and the mechanical vapor compressor pressure ratio is 1.3;

[0060] 4) using a reverse osmosis membrane assembly to concentrate and dehydrate the collected membrane distillation process condensate and nanofiltration membrane clear liquid to recover tobacco active ingredients, the reverse osmosis membrane cutoff molecular weight is 80, the operating pressure of the reverse osmosis membrane assembly is 2.5 MPa, the concentration multiple is 24 times, and then the concentrate is mixed with the evaporator concentrate to obtain a concentrate with a solid content of 34.7% required for the production of reconstituted tobacco leaves.

[0061] 5) The above process saves more than 13.7% of processing time compared with the traditional low-temperature membrane concentration technology.

[0062] Example 4

[0063] The above-mentioned reconstituted tobacco leaf extract concentration process and concentration system are used to concentrate the reconstituted tobacco leaf extract with an initial solid content of 9.3%, comprising the following steps:

[0064] 1) The reconstituted tobacco leaf extract is pre-concentrated by using a low-temperature dehydration membrane distillation process, that is, the reconstituted tobacco leaf extract with an initial solid content of 8.6% is pumped into the hot side flow channel of the membrane distillation device, and then air is injected into the cold side flow channel of the device as a purge gas. The purge gas flow rate of the cold side flow channel is 9 m / s, and the vacuum degree of the cold side flow channel is 0.04 MPa. Water vapor is continuously volatilized from the hot side feed liquid and penetrates the porous hydrophobic membrane into the cold side air. The porous hydrophobic membrane has a membrane pore size of 0.4 μm, a porosity of 86%, and an air permeability of 900 m 3 ·m -2 ·h -1 , the contact angle is 140°, and finally the purge gas is brought into the condenser for condensation to obtain membrane distillation process condensed water. The condensation temperature of the condenser is 7°C, and the reconstituted tobacco leaf extract in the hot side flow channel is low-temperature dehydrated to form a membrane distillation pre-concentrate with a solid content of 17wt%;

[0065] 2) further concentrating the membrane distillation pre-concentrate using a nanofiltration membrane assembly, the nanofiltration membrane cut-off molecular weight is 350, the operating pressure of the nanofiltration membrane assembly is 2 MPa, and after concentration, a nanofiltration membrane clear liquid and a nanofiltration membrane concentrate with a solid content of 24.2 wt% are formed;

[0066] 3) then using a mechanical vapor recompression (MVR) evaporator to further concentrate the nanofiltration membrane concentrate into an evaporator concentrate having a solid content of 39.2 wt%, wherein the evaporation temperature is 80° C. and the mechanical vapor compressor pressure ratio is 1.3;

[0067] 4) using a reverse osmosis membrane assembly to concentrate and dehydrate the collected membrane distillation process condensate and nanofiltration membrane clear liquid to recover tobacco active ingredients, the reverse osmosis membrane cutoff molecular weight is 100, the operating pressure of the reverse osmosis membrane assembly is 2.8 MPa, the concentration multiple is 24.5 times, and then the concentrate is mixed with the evaporator concentrate to obtain a concentrate with a solid content of 35.2% required for the production of reconstituted tobacco leaves.

[0068] 5) The above process saves more than 14.5% of processing time compared with the traditional low-temperature membrane concentration technology.

[0069] Example 5

[0070] The above-mentioned reconstituted tobacco leaf extract concentration process and concentration system are used to concentrate the reconstituted tobacco leaf extract with an initial solid content of 9.3%, comprising the following steps:

[0071] 1) The reconstituted tobacco leaf extract is pre-concentrated by a low-temperature dehydration membrane distillation process, that is, the reconstituted tobacco leaf extract with an initial solid content of 8.6% is pumped into the hot side flow channel of the membrane distillation device, and then air is injected into the cold side flow channel of the device as a purge gas. The purge gas flow rate in the cold side flow channel is 10m / s, and the vacuum degree of the cold side flow channel is 0.05Mpa. Water vapor is continuously volatilized from the hot side feed liquid and penetrates the porous hydrophobic membrane into the cold side air. The porous hydrophobic membrane has a membrane pore size of 0.5μm, a porosity of 90%, and an air permeability of 1000m 3 ·m -2 ·h -1 , the contact angle is 140°, and finally the purge gas is brought into the condenser for condensation to obtain membrane distillation process condensed water. The condensation temperature of the condenser is 10°C, and the reconstituted tobacco leaf extract in the hot side flow channel is low-temperature dehydrated to form a membrane distillation pre-concentrate with a solid content of 20wt%;

[0072] 2) further concentrating the membrane distillation pre-concentrated liquid using a nanofiltration membrane assembly, the nanofiltration membrane cut-off molecular weight is 400, the operating pressure of the nanofiltration membrane assembly is 2 MPa, and after concentration, a nanofiltration membrane clear liquid and a nanofiltration membrane concentrated liquid with a solid content of 25 wt% are formed;

[0073] 3) then using a mechanical vapor recompression (MVR) evaporator to further concentrate the nanofiltration membrane concentrate into an evaporator concentrate having a solid content of 40 wt%, wherein the evaporation temperature is 80° C. and the mechanical vapor compressor pressure ratio is 1.4;

[0074] 4) using a reverse osmosis membrane assembly to concentrate and dehydrate the collected membrane distillation process condensate and nanofiltration membrane clear liquid to recover tobacco active ingredients, the reverse osmosis membrane cutoff molecular weight is 100, the operating pressure of the reverse osmosis membrane assembly is 3 MPa, the concentration multiple is 25 times, and then the concentrate is mixed with the evaporator concentrate to obtain a concentrate with a solid content of 36.6% required for the production of reconstituted tobacco leaves.

[0075] 5) The above process saves more than 16.9% of processing time compared with the traditional low-temperature membrane concentration technology.

[0076] In summary, the reconstituted tobacco leaf extract concentration process and concentration system of the present invention effectively overcome the problems of low concentration multiples and concentration efficiency of low-temperature membrane concentration in the prior art and difficulty in membrane cleaning and replacement, prevent the loss of effective ingredients in tobacco, reduce the degree of membrane pollution, and have high industrial utilization value.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A process for concentrating a reconstituted tobacco leaf extract, characterized in that: The main steps include: 1) Pre-concentrating the reconstituted tobacco extract to a solid content of 10-20wt% by membrane distillation process, obtaining membrane distillation pre-concentrated liquid and membrane distillation process condensed water; the membrane distillation process is to pre-concentrate the reconstituted tobacco extract by a membrane distillation device to obtain the membrane distillation pre-concentrated liquid; the membrane distillation device comprises a hot side flow channel and a cold side flow channel, the hot side flow channel and the cold side flow channel are separated by a porous hydrophobic membrane; the hot side flow channel is injected with the reconstituted tobacco extract, and the cold side flow channel is injected with a purge gas; the porous hydrophobic membrane is a flat composite membrane, the surface layer is made of polytetrafluoroethylene material, and the support layer is made of polypropylene material; 2) using a nanofiltration membrane process to concentrate the membrane distillation pre-concentrated liquid to a solid content of 20-25 wt % to obtain a nanofiltration membrane concentrated liquid and a nanofiltration membrane clear liquid; 3) using an evaporation concentration process to concentrate the nanofiltration membrane concentrate to a solid content of 35-40 wt %, thereby obtaining an evaporator concentrate; 4) using a reverse osmosis membrane process to concentrate and dehydrate the condensed water from the membrane distillation process and the nanofiltration membrane clear liquid, recovering the tobacco active ingredients, with a concentration multiple of 20 to 25 times, to obtain a reverse osmosis membrane concentrate; the reverse osmosis membrane process is to use a reverse osmosis membrane assembly to concentrate and dehydrate the condensed water from the membrane distillation process and the nanofiltration membrane clear liquid to obtain a reverse osmosis membrane concentrate; the reverse osmosis membrane has a molecular weight cutoff of 50 to 100; 5) The reverse osmosis membrane concentrate is mixed with the evaporator concentrate to obtain a concentrate of the reconstituted tobacco leaf extract.

2. The process for concentrating the reconstituted tobacco leaf extract according to claim 1, characterized in that: The porous hydrophobic membrane has a pore size of 0.1-0.5 μm and a porosity of 80-90%; And / or, the air permeability of the porous hydrophobic membrane is 500-1000 m 3 ·m -2 ·h -1 ; And / or, the contact angle of the porous hydrophobic membrane is 120° to 140°; and / or, the flow rate of the cold side flow channel purge gas is 1-10 m / s; And / or, the vacuum degree of the cold side flow channel is 0.01~0.05 Mpa.

3. The process for concentrating the reconstituted tobacco leaf extract according to claim 1, characterized in that: The nanofiltration membrane process uses a nanofiltration membrane assembly to further concentrate the membrane distillation pre-concentrated liquid to obtain a nanofiltration membrane concentrated liquid.

4. The process for concentrating the reconstituted tobacco leaf extract according to claim 3, characterized in that: The nanofiltration membrane has a molecular weight cut-off of 300-400; And / or, the operating pressure of the nanofiltration membrane assembly is 1~2 Mpa.

5. The process for concentrating the reconstituted tobacco leaf extract according to claim 1, characterized in that: The evaporation concentration process is to use an evaporator to concentrate the nanofiltration membrane concentrate to obtain the evaporator concentrate.

6. The process for concentrating the reconstituted tobacco leaf extract according to claim 5, characterized in that: The evaporator is a mechanical vapor recompression evaporator; And / or, the evaporation temperature of the evaporator is 60-80°C; And / or, the pressure ratio of the evaporator is 1.2~1.

4.

7. The process for concentrating the reconstituted tobacco leaf extract according to claim 1, characterized in that: The operating pressure of the reverse osmosis membrane assembly is 1.5~3 Mpa.

8. A concentration system for concentrating a reconstituted tobacco leaf extract, characterized in that: include: A membrane distillation device, a nanofiltration membrane assembly, an evaporator, a reverse osmosis membrane assembly and a concentrated liquid storage tank; the feed inlet of the membrane distillation device is connected to the feed pipeline of the reconstituted tobacco leaf extract, and the membrane distillation device is provided with a membrane distillation pre-concentrated liquid outlet and a membrane distillation process condensed water outlet; the membrane distillation pre-concentrated liquid outlet is connected to the feed inlet of the nanofiltration membrane assembly, and the nanofiltration membrane assembly is provided with a nanofiltration membrane concentrated liquid outlet and a nanofiltration membrane clear liquid outlet; the nanofiltration membrane concentrated liquid outlet is connected to the feed inlet of the evaporator, and the outlet of the evaporator is connected to the concentrated liquid storage tank; the membrane distillation process condensed water outlet and the nanofiltration membrane clear liquid outlet are both connected to the feed inlet of the reverse osmosis membrane assembly, and the outlet of the reverse osmosis membrane assembly is connected to the concentrated liquid storage tank.

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