CN114712895B - Double-part discarding method with additional chromatographic column for improving yield of simulated moving bed - Google Patents
Double-part discarding method with additional chromatographic column for improving yield of simulated moving bed Download PDFInfo
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Abstract
The invention discloses a double-part discarding method with an additional chromatographic column for improving the yield of a simulated moving bed, which comprises the following steps: establishing a model of a simulated moving bed system; calculating performance parameters of a group of new process points based on a model of the simulated moving bed system, and selecting one of the process points as a target process point; temporarily discarding the raffinate product which is lower than the first integral purity threshold value and is operated under the new process point by the simulated moving bed, and collecting the raffinate product with the first integral purity threshold value as a first product; and introducing the temporarily discarded raffinate product into an additional chromatographic column for separation to obtain additional products A and B, determining the collection cut-off time of the additional products A and B according to the integral purity threshold value of the additional products A and B, respectively collecting the additional products A and B before the additional product collection cut-off time, and respectively mixing the additional products A and B with the extracted product and the raffinate product to form a final product. Can improve the recovery rate of raw materials under the condition of ensuring the purity of the product.
Description
Technical Field
The invention relates to the technical field of optimization of industrial production processes, in particular to a double-part discarding method with an additional chromatographic column, which improves the yield of a simulated moving bed.
Background
The simulated moving bed (Simulated Moving Bed, abbreviated as SMB) chromatography technology is an important separation and purification technology in chemical engineering, and the technology mainly utilizes the affinity difference between each component in the feed and the stationary phase adsorbent to realize the separation between the components. The simulated moving bed technology has been expanded from petrochemical industry, sugar industry to biopharmaceutical industry, fine chemical industry and other industries because of its unique advantages such as large mass transfer driving force, strong separation capability, less eluent consumption, continuous production and the like.
The mechanism of the simulated moving bed separation process is complex, and there is a strong competition relationship between performance parameters (such as purity, yield, recovery rate, etc.) of the separation process, so how to improve the separation performance has been one of the important points of research on the simulated moving bed separation process. The solution strategies for improving the separation performance can be mainly classified into two types, one is to search a Pareto optimal solution of the process parameters through a multi-objective optimization algorithm according to different requirements on the performance parameters. Such as: a two-stage optimization algorithm, a multi-objective teaching optimization algorithm, a parallel particle swarm optimization algorithm, a dynamic sequential quadratic programming optimization algorithm, NSGA-II and the like. Another is to develop new operating strategies based on traditional simulated moving bed technology, such as: variable strategies for the number of columns per zone, powerFeed strategies for adjusting feed flow, modicon strategies for adjusting feed concentration, batch simulated moving bed, three zone simulated moving bed and Partial Discard (PD) strategies, etc. can be varied. The working principle of the PD strategy is to discard a part of the extracted product containing impurities (weakly adsorbed components) at the initial stage or discard a part of the raffinate product containing impurities (strongly adsorbed components) at the final stage of each switching cycle, so as to improve the purity of the product. While PD strategies can increase the purity of the product, the high concentration of product discarded can result in a large loss of product recovery. To improve this strategy, i.e., to reduce the loss of product recovery as much as possible while ensuring high purity of the product, researchers have proposed fractionation and feedback strategies, recovery partial discard strategies, power partial discard strategies, full recovery partial discard strategies, and strategies with product columns, among others.
The two solutions described above, while improving the separation performance from different points of view, are mostly based on the ideal design tool of the chromatographic equilibrium theory, i.e. to find the desired process point (including the flow at the inlet and outlet) in the complete separation zone, which limits the choice of feed flow and thus the yield of the separation process. In addition, the strategy with product columns suggests that the reject product stream of a simulated moving bed is passed into one product column, and that effective separation of the two products of the reject fraction can be achieved by rational design of column length, flow rate, adsorbent properties, etc., but this strategy requires the development of new adsorbents with high adsorption capacity and partition coefficients, a time-consuming and costly process.
Disclosure of Invention
The invention aims to solve the technical problem of providing a double-part discarding method with an additional chromatographic column, which utilizes raw materials with higher recovery rate and improves the yield of a simulated moving bed under the condition of ensuring the purity of products.
In order to solve the above problems, the present invention provides a dual-part discarding method with additional column for increasing yield of simulated moving bed, comprising the steps of:
s1, performing mathematical modeling of a simulated moving bed separation process, and establishing a model of a simulated moving bed system;
s2, selecting a group of new process points with increased feed flow rate in the pure extraction product and non-pure extraction residual product areas based on a chromatographic balance theory, calculating performance parameters of the group of new process points based on a model of a simulated moving bed system, and selecting one of the process points as a target process point;
s3, the simulated moving bed operates under a target process point, the collection cut-off time of the raffinate product is determined according to the set integral purity threshold value of the raffinate product, the raffinate product before the collection cut-off time of the extract product is collected, and the raffinate product after the collection cut-off time of the raffinate product is temporarily discarded;
s4, adding an additional chromatographic column independent of the simulated moving bed, introducing the temporarily discarded raffinate product into the additional chromatographic column as feed for separation to obtain additional products A and B, determining the collection cut-off time of the additional products A and B according to the set integral purity threshold value of the additional products A and B, respectively collecting the additional products A and B before the additional product collection cut-off time, and respectively mixing the additional products A and B with the extracted product and the raffinate product to form a final product.
As a further improvement of the invention, the model of the simulated moving bed system comprises an equilibrium diffusion model of a chromatographic column, an equilibrium model of a simulated moving bed at a material inlet and outlet node and an equilibrium model of a joint of the simulated moving bed and an additional chromatographic column.
As a further improvement of the present invention, the equilibrium diffusion model of the chromatographic column comprises:
mass conservation equation for mobile phase:
wherein, c i And q i Respectively representing the concentration of component i (i=a, B) in the mobile phase and the stationary phase; v represents the flow velocity of the mobile phase in the column; epsilon represents the void fraction of the bed; d (D) a Representing the apparent axial diffusion coefficient; z and t represent space and time coordinates, respectively;
linear adsorption equilibrium equation:
q i ＝H i c i (2)
wherein H is i A henry coefficient representing component i;
initial and boundary conditions of the chromatographic column:
in the method, in the process of the invention,
represents the concentration of component i at the inlet of the column, and L represents the column length of the column.
As a further improvement of the present invention, the equilibrium model of the simulated moving bed at the material inlet and outlet nodes comprises:
eluent inlet node:
extract outlet node:
at the feed inlet node:
raffinate outlet node:
in which Q j (j=i, II, III, IV) represents the volumetric flow rate of region j, Q k (k=d, E, F, R) represents the volume flow of eluent, extract, feed and raffinate,
represents the outlet or inlet concentration of component i in zone j, c i,k (k=d, E, F, R) represents the concentration of component i in the eluent, extract, feed and raffinate.
As a further improvement of the invention, the equilibrium model at the junction of the additional chromatographic column is:
t F,EC ·Q F,EC ＝t R,discard ·Q R (10)
wherein t is F,EC 、Q F,EC And c i,F,EC The recycle feed length, recycle feed flow and the concentration of component i in the recycle feed for the additional column are shown, respectively; t is t R,discard And
the duration of the simulated moving bed raffinate discarding stage and the average concentration of component i are shown, respectively.
As a further improvement of the present invention, step S2 includes:
calculating a flow ratio relation at a new process point based on a chromatographic balance theory;
when the feeding flow of the simulated moving bed is increased, a group of uniformly distributed new process points are selected at the part of the straight line, which is positioned in the pure extraction product and the non-pure extraction residual product area, according to the flow ratio relation at the new process points, the selected new process points are substituted into the model of the simulated moving bed system to obtain the performance parameters under the new process points, and one of the new process points is selected as a target process point according to the performance parameters.
As a further improvement of the invention, the flow ratio relationship at the new process point is:
wherein m is 2 And m 3 Flow ratios of zones 2 and 3, respectively; t is t s Indicating the switching time, V C Representing the volume of the chromatographic column; epsilon represents the void fraction of the bed; q (Q) F Indicating the volumetric flow of the feed.
As a further improvement of the present invention, in step S3, the raffinate product after the raffinate product collection cutoff time is temporarily discarded in the buffer tank.
As a further improvement of the invention, in step S4, the additional products a and B after the additional product collection deadline are permanently discarded.
As a further improvement of the present invention, the additional chromatography column has the same specifications as the chromatography column of the simulated moving bed.
The invention has the beneficial effects that:
1. the invention significantly improves the yield of the simulated moving bed separation process, and ensures the purity of the product and higher recovery rate by introducing an additional chromatographic column independent of the traditional simulated moving bed and two partial discarding operations.
2. The method is simple to operate, can remarkably improve the separation performance, and does not need to take time and labor to additionally develop some novel adsorbents.
3. The present invention may determine the performance parameters of the final product based on the integrated purity threshold of the additional product.
The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention, as well as the preferred embodiments thereof, together with the following detailed description of the invention, given by way of illustration only, together with the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of a two-part discard process with additional chromatography columns to increase simulated moving bed yield in an embodiment of the invention;
FIG. 2 is a system according to the invention depicted by a linear adsorption isotherm, at m 2 -m 3 Schematic representation of different separation areas on a plane;
FIG. 3 is a flow ratio (m) at a new process point of an simulated moving bed in an embodiment of the invention 2 ,m 3 ) At m 2 -m 3 Schematic distribution on a plane;
FIG. 4 is a schematic representation of the concentration of raffinate product obtained when the simulated moving bed is operated at a new process point in an embodiment of the invention;
FIG. 5 is a schematic representation of the variation of purity of the raffinate product in the examples of the present invention;
FIG. 6 is a schematic representation of the change in integrated purity of the raffinate product when the simulated moving bed is operated at a new process point in an embodiment of the invention;
FIG. 7 is a schematic of the outlet concentration of an additional chromatographic column in an embodiment of the invention;
FIG. 8 is a schematic of the outlet concentration of additional product in an embodiment of the invention;
FIG. 9 is a graphical representation of the variation of integrated purity of additional products in an embodiment of the present invention;
FIG. 10 is a graph showing the effect of integrated purity threshold of additional product on overall performance parameters in an embodiment of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
As shown in FIG. 1, the preferred embodiment of the present invention discloses a dual-part discarding method with additional column for increasing yield of simulated moving bed, which comprises the following steps:
s1, performing mathematical modeling of a simulated moving bed separation process, and establishing a model of a simulated moving bed system;
in some embodiments, the model of the simulated moving bed system includes an equilibrium diffusion model of the chromatography column, an equilibrium model of the simulated moving bed at the material inlet and outlet nodes, and an equilibrium model of the simulated moving bed at the junction with the additional chromatography column. The equilibrium diffusion model of the chromatographic column is a single chromatographic column model, and mainly has the following assumed conditions:
1) The temperature in the adsorption separation process is kept unchanged;
2) The balance of the components between the stationary phase and the mobile phase is instantaneously achieved;
3) The influence of axial diffusion and mass transfer resistance is concentrated to be apparent axial diffusion coefficient;
4) Each chromatographic column is filled uniformly and has uniform void ratio;
5) The mobile phase is plug flow and the flow velocity in each zone is constant;
6) The radial concentration gradient in the column was ignored.
The equilibrium diffusion model of the chromatographic column comprises:
mass conservation equation for mobile phase:
wherein, c i And q i Respectively representing the concentration of component i (i=a, B) in the mobile phase and the stationary phase; v represents the flow velocity of the mobile phase in the column; epsilon represents the void fraction of the bed; d (D) a Representing the apparent axial diffusion coefficient; z,t represents space and time coordinates, respectively;
linear adsorption equilibrium equation:
q i ＝H i c i (2)
wherein H is i Representing the henry coefficient of component i.
Initial and boundary conditions of the chromatographic column:
in the method, in the process of the invention,
represents the concentration of component i at the inlet of the column, and L represents the column length of the column.
The balance model of the simulated moving bed at the material inlet and outlet nodes comprises the following steps:
eluent inlet node:
extract outlet node:
at the feed inlet node:
raffinate outlet node:
in which Q j (j=i, II, III, IV) represents the volumetric flow rate of region j, Q k (k=d, E, F, R) represents the volume flow of eluent, extract, feed and raffinate,
represents the outlet or inlet concentration of component i in zone j, c i,k (k=d, E, F, R) represents the concentration of component i in the eluent, extract, feed and raffinate. .
The model of the additional chromatographic column can likewise be constituted by the formulae (1) - (5).
The equilibrium model at the junction of the additional chromatographic column is:
t F,EC ·Q F,EC ＝t R,discard ·Q R (10)
wherein t is F,EC 、Q F,EC And c i,F,EC The recycle feed length, recycle feed flow and the concentration of component i in the recycle feed for the additional column are shown, respectively; t is t R,discard And
the duration of the simulated moving bed raffinate discarding stage and the average concentration of component i are shown, respectively.
In some embodiments, further comprising: performance parameters of the separation process, including purity, recovery, yield, etc., were evaluated. During a switching period in the steady state of the simulated moving bed cycle, these performance parameters are defined as follows:
1. for the convenience of subsequent representation, first the following qualities (units: g) are defined
Mass of component i obtained in the product stage of the SMB extraction port:
the mass of component i obtained in the product stage of the SMB raffinate:
mass of component i obtained in the initial stage of EC:
mass of component i obtained in the final stage of EC:
mass of component i in the feed to SMB:
M i,F , SMB ＝Q F ·t s ·c i , F (16)
wherein t is E,product And t R,product Respectively representing the duration time of the product stage of the extraction port and the raffinate port of the simulated moving bed, t initial,EC And t last,EC The duration of the initial and final stages of the additional column, respectively; q (Q) initial,EC And Q last,EC The volume flows of the initial and final stages of the additional chromatographic column are shown respectively;
and->
Represents the average concentration of component i, < >/in the product stage of the simulated moving bed extraction port and the raffinate port, respectively>
And->
The average concentration of component i at the initial and final stages of the additional column is shown, respectively.
2. Purity (Pu, unit:%)
Purity reflects the quality of the product, which is defined as the ratio of the amount of the target product collected in the product stream to the total amount of both products collected during one switching cycle, then:
the purity of the product A is as follows:
the purity of the product B is as follows:
3. recovery (Re, unit:%)
For value added products, a large investment is already made in producing the mixture to be separated, so recovery of the target product is important. The recovery reflects the utilization of the feed, defined as the ratio of the amount of the target product collected in the product stream to the total amount of the product in the feed over a switching period, then:
the recovery rate of the product A is as follows:
the recovery rate of the product B is as follows:
4. yield (Pr, unit: g/(ml p))
The efficiency of the productive reaction separation process, which is a very heavy economic indicator defined as the total mass of two products obtained per unit volume of adsorbent in one switching cycle, is:
wherein p represents the unit of switching period, N C Representing the number of simulated moving bed chromatography columns, V C Representing the volume of the simulated moving bed chromatography column, V EC Representing the volume of the additional column.
5. Relation between yield and recovery
It is not difficult to find that the denominator of formulae (19) - (21) is kept constant, so that the yield of the separation process will be maximized when the recovery of product a and product B, respectively, is maximized.
Since the main objective of the present invention is to optimize the performance parameters of the separation process, a typical 8-column 4-zone structure of a conventional simulated moving bed system is chosen as an example, and specific model parameters are derived from the reference literature, referring to table 1.
TABLE 1 model parameters and initial process parameters for simulated moving bed
S2, selecting a group of new process points with increased feed flow rate in the pure extraction product and non-pure extraction residual product areas based on a chromatographic balance theory, calculating performance parameters of the group of new process points based on a model of a simulated moving bed system, and selecting one of the process points as a target process point; specifically, calculating a flow ratio relationship at a new process point based on a chromatographic balance theory; when the feeding flow of the simulated moving bed is increased, a group of evenly distributed process points are selected at the part of the straight line, which is positioned in the pure extraction product and the non-pure extraction residual product area, according to the flow ratio relation at the new process points, the selected new process points are substituted into the model of the simulated moving bed system to obtain the performance parameters under the new process points, and one of the new process points is selected as the target process point according to the performance parameters.
More specifically, in the case of a linear adsorption isotherm, the conditions for complete separation of the binary mixture are:
(23)
H A ＜m 1
H B ＜m 2 ＜m 3 ＜H A
wherein m is j (j=1, 2,3, 4) represents the flow ratio of zone j, which is defined as the ratio of the net flow of liquid phase to the net flow of solid phase in zone j, and is simplified as follows:
t is in s Indicating the switching time, V C Representing the volume of the column.
According to formula (23), m may be 2 -m 3 The plane is divided into the different separation zones shown in fig. 2, wherein the zone defined by the three points w, a and b is the fully separated zone of the two components. When the process point is selected in this area, the purity of the two products obtained is close to 100%. Directly above the fully separated zone is a zone of pure extracted product and non-pure raffinate product, when the process point is selected in this zone, the purity of the extracted product obtained is close to 100%, whereas the purity of the raffinate product is generally poor. The process point of the separation process can then be determined approximately from the different separation zones. To increase the yield of the simulated moving bed separation process, the most straightforward approach is to increase the feed flow, but ifThe increase in the amount exceeds the adsorption capacity of the column, so that more strongly adsorbed components are discharged with the raffinate product, and the recovery rate of the extract product and the purity of the raffinate product are reduced. If the feed rate is further increased, the regenerated eluent containing weakly adsorbed components will pass through the transition zone, reducing the purity of the extracted product. In consideration of the subsequent simple design, the invention increases the feed flow rate to move the process point from the initial fully separated region to the pure extracted product and the non-pure extracted product region while ensuring that the purity of the extracted product is acceptable. However, this operation loses purity of the raffinate product, which in turn requires further separation of the raffinate product containing impurities, i.e. strongly adsorbed components.
To increase the yield of the simulated moving bed, while taking into account the total pressure drop requirement in the chromatographic column, the feed flow to the simulated moving bed is now increased from 0.02ml/s at the initial process point to 0.03ml/s at the new process point, the flow of zone I and eluent remaining unchanged. Equation (25) can be deduced from the equilibrium equations (6) - (9) and flow ratio equation (24) of the simulated moving bed at the nodes, and the flow ratio (m) at the new process point can be easily found 2 ,m 3 ) The relation is m 2 -m 3 A straight line on the plane, as shown by the black dotted line L in FIG. 3 new As shown.
Because the operation strategy provided by the invention selects the process point in the areas of the pure extracted product and the non-pure extracted residual product, the broken line L in the areas new And selecting a group of evenly distributed process points. Based on the actual control accuracy of the flow pump, 26 process points are finally selected, as shown by a set of consecutive dots in fig. 3, where p represents the initial process point and a set of consecutive dots represents a set of process points that increase the yield. Table 2 summarizes the performance parameters obtained for the simulated moving bed operating sequentially at these 26 process points (only purity and recovery are considered here), it can be seen that as m 2 Or m 3 The purity of the extracted product a increases and the recovery rate decreases; phase (C)Conversely, the purity of the raffinate product B decreases and the recovery increases. Depending on the actual use of both products, it is now assumed that the required purity is 98%. In consideration of the robustness of the purity of the extracted product in the separation process and the requirement of the recovery rate, the invention selects the 3 rd (m 2 ＝0.2950,m 3 = 0.5589) as a new process point.
TABLE 2 simulated moving bed operating at New Process Point, performance parameters obtained
S3, the simulated moving bed operates under a target process point, the collection cut-off time of the raffinate product is determined according to the set integral purity threshold value of the raffinate product, the raffinate product before the collection cut-off time of the extract product is collected, and the raffinate product after the collection cut-off time of the raffinate product is temporarily discarded; optionally, the raffinate product after the raffinate product collection deadline is temporarily discarded in the surge tank. The purified product of the simulated moving bed is A, and the extracted product B contains impurity A.
Specifically, when operating at the new process point selected in step S2, the simulated moving bed is switched 51 times to reach a circulating steady state, at which point the outlet concentration of the raffinate product is shown in fig. 4. As can be seen from fig. 4, the raffinate product contains a higher concentration of impurities (strongly adsorbed component a) at the final stage of each switching cycle in the steady state of the cycle, which affects the purity of the raffinate product and the recovery rate of the extract product. Thus, it is next desirable to treat this portion of the raffinate product containing high concentrations of impurities using a partial discard strategy.
The raffinate product, prior to isolation, requires a specific purity depending on its end use. As shown in fig. 5, since the purity of the raffinate product (referred to as differential purity) is different at each time in the switching cycle, a concept of integrated purity is defined herein. For example, the integrated purity of the raffinate product is defined as the time from the beginning of the switching cycle (τ=0) to the end of the collection (τ=τ) end ) Cumulative purity of the raffinate productWhere τ is the dimensionless time in one switching cycle, as defined by equation (26). Now assuming that the purity of the desired raffinate product is 98%, it can be seen from fig. 5, where the solid line represents the integrated purity and the black dot represents the differential purity, the integrated purity of the raffinate product over the entire switching cycle is 97.32%, which is lower than the desired purity. If the collection of the raffinate product is stopped at τ of 0.93, the integral purity of the raffinate product is exactly 98% and the smaller τ, the greater the integral purity, but this would result in a significant loss of high concentration raffinate product, affecting the recovery of raffinate product. Thus, it is possible to decide when to stop collecting the raffinate product and discard the remainder based on the integrated purity. The operation strategy proposed by the invention suggests tau end The prior raffinate product is collected, tau is collected end The remaining product is then temporarily discarded.
τ＝t/t s ,0≤τ≤1 (26)
Specifically, the change in integrated purity of the raffinate product during one switching period in the steady state of the simulated moving bed cycle is shown in FIG. 6. It is not difficult to find that at the collection cutoff time τ of the raffinate product end The integral purity of the product is continuously reduced from nearly 100% to 92.93% in the process of increasing from 0 to 1, and the purity of the corresponding obtained raffinate product is changed from pass to fail. Notably, τ at 98% integrated purity of the raffinate product end At 0.74, the requirements for the assumed purity of the raffinate product are just met. τ can then be determined based on the partial discard strategy end The later raffinate product was discarded, at which point the recovery of raffinate product was only 69.91%. The discarded raffinate product, although not meeting purity requirements, contains a significant amount of product in high concentration, so this fraction is simply discarded temporarily and collected in a buffer tank and then passed as feed to an additional chromatographic column for further separation.
Since it is difficult to separate two components having a small difference in henry coefficients effectively by a single column, this results in a serious overlap of the outlet concentration of the trailing edge of the weakly adsorbed component B and the outlet concentration of the leading edge of the strongly adsorbed component a, as shown in fig. 7, in which the dotted line represents the boundary between the feeding stage and the eluting stage in each injection cycle. However, if the concentrations of the two components in the feed to the additional column differ significantly, the outlet concentrations of the product will also differ significantly. It is still possible to collect a portion of product B of a specified purity at the initial stage or a portion of product a of a specified purity at the final stage of each injection cycle, guided by the integrated purity, where the collected products a and B are referred to as additional product a and additional product B, respectively.
The invention improves the purity of the obtained raffinate product by improving the threshold value of the integral purity of the raffinate product. And then compensating an additional product B with substandard purity by utilizing the high-purity raffinate product, wherein the final purity of the product B is the total purity of the two parts of products after being mixed. A set of evenly distributed data between 98% and 99.60% was selected as the threshold for integrated purity of the raffinate product, and the performance parameters of the raffinate product after partial discarding at this set of purity thresholds are shown in table 3.
TABLE 3 Performance parameters of the raffinate product after partial discarding at different purity thresholds
As can be seen from table 3, as the integrated purity threshold of the set raffinate product increases, the purity of the raffinate product increases correspondingly, but the recovery rate decreases significantly. Comprehensively considering two performance parameters of purity and recovery rate of the raffinate product, and finally setting the integral purity threshold of the raffinate product to 98.50 percent, wherein tau is calculated at the moment end 0.71 as shown in fig. 6. After the collection of the raffinate product meeting the purity requirement, the remaining raffinate product was collected in a buffer tank as recycle feed to the lower additional chromatographic column, at which point the recycle feed had a concentration of 0.0939g/ml for component A and 0.4691g/ml for component B.
S4, adding an additional chromatographic column independent of the simulated moving bed, introducing the temporarily discarded raffinate product into the additional chromatographic column as feed for separation to obtain additional products A and B, determining the collection cut-off time of the additional products A and B according to the set integral purity threshold value of the additional products A and B, respectively collecting the additional products A and B before the additional product collection cut-off time, and respectively mixing the additional products A and B with the extracted product and the raffinate product to form a final product. Optionally, the additional products a and B after the additional product collection deadline are permanently discarded. Wherein, the additional product B flows out of the additional chromatographic column after separation, and the additional product A flows out of the chromatographic column after separation.
Specifically, when the raffinate product to be discarded in a switching cycle is collected in the buffer tank, it is stirred well and injected as feed into an additional column, and this portion of feed is called recycle feed, which is then flushed with eluent. The total length of the additional chromatographic column in the feed stage and the eluent stage is defined as an injection period equal in size to the switching period of the simulated moving bed to ensure continuous operation of the whole separation process. In view of the simple design, the additional column and the simulated moving bed column have the same specifications, such as the same column length, diameter, solid phase adsorbent, etc.
Specifically, the flow rate of the recycle feed is first set to remain the same as the flow rate of the simulated moving bed in the adsorption zone, and when the recycle feed injection is completed, the additional column is then flushed with eluent during the other times of the injection cycle. The additional chromatographic column can realize continuous production by circulating and reciprocating in this way.
FIG. 8 is a schematic of the outlet concentrations of additional products, it being readily apparent that the concentrations of the two additional products overlap but differ significantly. In addition, during the first half of each injection cycle, a large amount of relatively pure eluent can be discharged, and this portion of the eluent can be collected for recycling to reduce eluent consumption. The integrated purity of the two additional products was calculated according to the previously defined concept of integrated purity, as shown in fig. 9. It can be seen that the moment of product flow from the additional column (τ pro ) Initially, the integrated purity of additional product B gradually decreased from 100% to 83.37%; from τ=1 to τ pro The integral purity of the additional product a varies widely from 100% to 16.63%. Thus, by setting the integral purity threshold of the two additional products, the collection deadline and the collection deadline of the additional products B are calculatedThe collection start time of the additional product a and the product in the remaining time is permanently discarded as an impurity. Finally, the additional product A and the additional product B are mixed with the extracted product and the residual product obtained before, respectively, and the total performance parameter is calculated according to formulas (17) - (21).
Figure 10 analyzes the effect of integrated purity threshold of additional product on product purity and recovery. Where figure a is the additional product a and figure B is the additional product B, it can be seen from figure 10a that during the gradual increase of the integrated purity threshold of the additional product a from 90% to 98%, the purity of product a is continually increasing and always higher than 98%, since the large amount of extracted product obtained before with a purity higher than 98% compensates for the additional product a where the purity is less than 98%. On the other hand, the recovery of product A was continuously decreasing from 91.98%, but was also higher than 90.50%. Thus, the integrated purity threshold for additional product a can be set to 90% to enable product a to achieve maximum recovery while meeting a given purity requirement. As can be seen from fig. 10B, when the integrated purity threshold of the additional product B is less than 96.4%, the purity of the product B is always less than 98%, and the product B obtained is not acceptable. Only when the threshold value of the integrated purity of the additional product B is set to 96.4% and above, the product B can reach the required purity (the portion above the dotted line), and the corresponding recovery rate drops below 94.32% (the portion below the dotted line). Thus, the integrated purity threshold for additional product B can be set to 96.4% to allow maximum recovery of product B. At this time, as can be seen from the formula (22), the yield of the separation process also reaches the maximum.
Specifically, table 4 summarizes the performance parameters obtained for the proposed EC-BiPD strategy, traditional SMB and PD strategy of the present invention. It can be seen that both product a and product B obtained from the EC-BiPD strategy met the 98% purity requirement and both recovered the feed at higher recovery rates, which, although slightly less than the traditional SMB, was superior to the PD strategy. Most importantly, the EC-BiPD strategy increased the yield from 0.0215 g/(ml p) to 0.0280 g/(ml p), i.e. 30.23% compared to traditional SMB. The EC-BiPD strategy proposed by the invention is proved to be superior to the traditional SMB and PD strategies.
TABLE 4 comparison of Performance parameters between different strategies
The invention significantly improves the yield of the simulated moving bed separation process, and ensures the purity of the product and higher recovery rate by introducing an additional chromatographic column independent of the traditional simulated moving bed and two partial discarding operations. The method is simple to operate, can remarkably improve the separation performance, and does not need to take time and labor to additionally develop some novel adsorbents. The present invention may determine the performance parameters of the final product based on the integrated purity threshold of the additional product.
The above embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.
Claims (8)
1. A two-part discard process with additional chromatography column to increase simulated moving bed yield comprising the steps of:
s1, performing mathematical modeling of a simulated moving bed separation process, and establishing a model of a simulated moving bed system;
s2, selecting a group of new process points with increased feed flow rate in the pure extraction product and non-pure extraction residual product areas based on a chromatographic balance theory, calculating performance parameters of the group of new process points based on a model of a simulated moving bed system, and selecting one of the process points as a target process point;
s3, the simulated moving bed operates under a target process point, the collection cut-off time of the raffinate product is determined according to the set integral purity threshold value of the raffinate product, the raffinate product before the collection cut-off time of the extract product is collected, and the raffinate product after the collection cut-off time of the raffinate product is temporarily discarded;
s4, adding an additional chromatographic column independent of the simulated moving bed, introducing the temporarily discarded raffinate product into the additional chromatographic column as feed for separation to obtain additional products A and B, determining the collection cut-off time of the additional products A and B according to the set integral purity threshold value of the additional products A and B, respectively collecting the additional products A and B before the additional product collection cut-off time, and respectively mixing the additional products A and B with the extracted product and the raffinate product to form a final product;
the model of the simulated moving bed system comprises a balanced diffusion model of a chromatographic column, a balanced model of the simulated moving bed at a material inlet and outlet node and a balanced model of the joint of the simulated moving bed and the additional chromatographic column;
the equilibrium model at the junction of the additional chromatographic column is:
t F,EC ·Q F,EC ＝t R,discard ·Q R (10)
wherein t is F,EC 、Q F,EC And c i,F,EC The recycle feed length, recycle feed flow and the concentration of component i in the recycle feed for the additional column are shown, respectively; t is t R,discard And
the duration of the simulated moving bed raffinate discarding stage and the average concentration of component i are shown, respectively.
2. A dual portion reject process with additional chromatography column to increase simulated moving bed yield according to claim 1, wherein said equilibrium diffusion model of chromatography column comprises:
mass conservation equation for mobile phase:
wherein, c i And q i Respectively representing the concentration of component i (i=a, B) in the mobile phase and the stationary phase; v represents the flow velocity of the mobile phase in the column; epsilon represents the void fraction of the bed; d (D) a Representing the apparent axial diffusion coefficient; z and t represent space and time coordinates, respectively;
linear adsorption equilibrium equation:
q i ＝H i c i (2)
wherein H is i A henry coefficient representing component i;
initial and boundary conditions of the chromatographic column:
in the method, in the process of the invention,
represents the concentration of component i at the inlet of the column, and L represents the column length of the column.
3. The dual portion reject process with additional chromatography column for increasing the yield of a simulated moving bed according to claim 1, wherein the equilibrium model of the simulated moving bed at the material inlet and outlet nodes comprises:
eluent inlet node:
extract outlet node:
at the feed inlet node:
raffinate outlet node:
in which Q j (j=i, II, III, IV) represents the volumetric flow rate of region j, Q k (k=d, E, F, R) represents the volume flow of eluent, extract, feed and raffinate,
represents the outlet or inlet concentration of component i in zone j, c i,k (k=d, E, F, R) represents the concentration of component i in the eluent, extract, feed and raffinate.
4. The method for discarding the two parts with additional columns according to claim 1, characterized in that step S2 comprises:
calculating a flow ratio relation at a new process point based on a chromatographic balance theory;
when the feeding flow of the simulated moving bed is increased, a group of uniformly distributed new process points are selected at the part of the straight line, which is positioned in the pure extraction product and the non-pure extraction residual product area, according to the flow ratio relation at the new process points, the selected new process points are substituted into the model of the simulated moving bed system to obtain the performance parameters under the new process points, and one of the new process points is selected as the target process point according to the performance parameters.
5. A dual-portion discard process with additional chromatography column for increasing the yield of a simulated moving bed as claimed in claim 4, wherein the flow ratio relationship at said new process point is:
wherein m is 2 And m 3 Flow ratios of zones 2 and 3, respectively; t is t s Indicating the switching time, V C Representing the volume of the chromatographic column; epsilon represents the void fraction of the bed; q (Q) F Indicating the volumetric flow of the feed.
6. A two-part discarding method with additional column for improving yield of simulated moving bed according to claim 1, wherein in step S3, the raffinate product after the raffinate product collection cutoff is temporarily discarded in buffer tank.
7. A method for the two-part discarding with additional chromatographic column to increase yield of simulated moving bed according to claim 1, wherein in step S4, the additional products A and B after the additional product collection cutoff time are permanently discarded.
8. The method for two-part discarding with additional chromatography column to increase yield of simulated moving bed according to claim 1, wherein said additional chromatography column has the same specification as the chromatography column of simulated moving bed.
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