Study on pervaporation performance of the hottest

Study on pervaporation performance of PVA composite membrane (II)

Abstract: This study shows that after long-term storage or repeated use, the pervaporation separation performance of PVA composite membrane is still excellent, in which the pervaporation capacity of PVA/Ca composite membrane is greater than 900g/m2 · h, while the ethanol component in the permeate is not detected. The total apparent activation energy of pervaporation separation alcohol aqueous solution system is small, and the operating temperature has little effect on the separation performance of the composite membrane. Compared with the experimental value of pervaporation, the calculated Arrhenius type and polynomial permeation flux prediction equations have high accuracy in predicting the permeation flux of PVA composite membrane

key words: compound membrane pervaporation alcohol dehydration flux prediction equation

in recent years, China has developed a pilot scale pervaporation device [1,2] and successfully applied it to alcohol dehydration. In order to further promote pervaporation technology, based on the study of pervaporation separation performance of PVA composite membrane [3], this paper focuses on the pervaporation performance of self-made PVA composite membrane, which separates alcohol aqueous solution after long-term storage or repeated use, and calculates the prediction equation of pervaporation separation performance of composite membrane

1 experiment

1.1 preparation of composite membrane

PVA composite membrane is made with polyacrylonitrile (Pan) membrane and cellulose acetate (CA) membrane as supporting layer and polyvinyl alcohol (PVA) as active layer, respectively

1.2 storage of composite membranes

the development of various composite membranes in the laboratory will also give the extruder industry endless impetus. Store them under ambient temperature and humidity conditions without any treatment during the storage process

1.3 performance test of composite membrane

under the same conditions and methods as the previous [3], it took 7 years to measure the pervaporation performance of various composite membranes in a bay along the coast of Cancun, a resort in southeast Mexico

2 results and discussion

2.1 effect of storage time on the performance of composite membranes

2.1.1 separation performance of composite membranes after storage

the pervaporation performance of two different batches of PVA composite membranes before and after long-term storage was measured. The results are shown in Table 1

Table 1 pervaporation performance of composite membrane before and after long-term storage membrane number storage time (month)

membrane number storage time (month) operating temperature (c) downstream pressure of membrane (PA) ethanol concentration (wt%) separation factor α W/e permeation flux (g/m2 · h) feed liquid permeation 50410.5

14.541.5

383.2 × 103

2.2 × 10394.24

94.400.04

0.

. 0

12.532

323 × 103

1 × 10494.24

94.1103. The relaxation testing machine can carry out high cycle fatigue test and low cycle fatigue test 17

0.

277

Table 1 shows that compared with the performance of the membrane that has not been stored basically, the ethanol concentration of the composite membrane that has been stored for more than one year decreases, that is, the separation factor increases; After 14.5 months storage, the permeation flux of 5041 composite membrane increased from 419g/m2 · h to 746g/m2 · h, while the permeation flux of 5503 composite membrane decreased from 313g/m2 · h to 277g/m2 · h after 12.5 months storage. The reason for these changes can be attributed to the pressure downstream of the membrane. The former decreases and the latter increases. The results show that PVA composite membrane can be stored at room temperature for a long time, and will not have adverse effects on the performance of the composite membrane

2.1.2 separation performance of membranes after long-term storage

in order to investigate the reusability of PVA composite membranes, three batches of composite membranes (including 5510ca composite membrane, the supporting layer of which is CA membrane, and the rest is Pan membrane) were removed after pervaporation test, stored for a long time, and then assembled into the test equipment again. The measurement results are shown in Table 2

Table 2 pervaporation performance of composite membrane after long-term storage

membrane No. whether it has been operated or not storage time (month) operating temperature (℃) downstream pressure of membrane (PA) ethanol concentration (wt%) permeation flux (g/m2 · h) liquid penetrant 5510ca no

yes 0.2

1.032

321 × 104

2.2 × 10394.36

94.400

0967

no

yes 3.5

12.524

325 × 103

2.2 × 10394.56

94.400

0665

no

yes 3.0

11.024

326 × 103

2.2 × 10394.56

94.400

0297

506

Table 2 shows that each membrane is removed from the test device after experimental use, and after up to one year of storage, the composite membrane still has extremely excellent separation performance. The results fully show that PVA composite membrane can be used repeatedly without mechanical or human damage, which can greatly reduce the production and maintenance cost of industrial membrane separation device

it can be seen from table 2 that the PVA composite membrane with CA membrane as the supporting layer has excellent separation performance. Under the same experimental conditions, after repeated use, the permeation flux of PVA/Ca composite membrane is much higher than that of Pan membrane, while keeping the ethanol component in the penetrant undetectable. This result has not been reported in the literature

2.2 the activation energy and flux prediction equation of the separation system

the previous experimental results [3] have shown that the feed concentration (x) and operating temperature (T) have a linear relationship with the permeation flux (J) of PVA composite membrane. Pair separation factor（ α) The effect is not very significant (the concentration of ethanol component in the penetrant is less than 1.0wt%). Based on these results, the prediction equations of pervaporation separation performance of the apparent activation energy and permeation flux of the alcohol aqueous solution system with the change of feed concentration and operating temperature can be calculated

2.2.1 the total apparent activation energy of the separation system

is 1nj and (1/T × 103) mapping, the permeation flux has a good linear relationship with the operating temperature (see Figure 1), which conforms to the arrhe nious formula:

J = re EA/RT

calculate the total apparent activation energy of the separation system by curve fitting with the least square method:

EA = 7.04 × 103J/mol

2.2.2 permeation flux prediction equation

Arrhenius type prediction equation: use Arrhenius type linear equation to correlate J ~ x and J ~ t relations respectively, solve equation coefficients by Cramer's law, and get Arrhenius type flux prediction equation by least square curve fitting:

JT = 174.38e0.008 bio based fiber plastic composites can realize mass production! 79t

Jr = 2682.7-22.85x

the relative error is less than 1.5% compared with the test value of the relationship between the permeation flux calculated by the above JT and JX formulas and the real figure 11nj and (1/T). Therefore, using the above formula to predict the permeation flux of composite membrane has high accuracy

polynomial prediction equation: the relationship between permeation flux (J) and feed concentration (x) or with operating temperature (T) can also be expressed by polynomials. The polynomial flux prediction equation is calculated:

jt = 613 70093t+1.96948t. 035032t3+0. t4

Jx＝.. 307x+25418.77773x. 43043x3+0.47480x4

the relative error between the permeation flux calculated by these two polynomial equations and the experimental value is less than 1.0%. It can be seen that the polynomial flux prediction equation also has a high degree of accuracy in predicting the permeation flux of the composite membrane