KR100523601B1 - Method of purification of dicyclopentadiene from C5 and C9+ fractions - Google Patents

Abstract

The present invention relates to a method for purifying dicyclopentadiene, the method of purifying dicyclopentadiene by thermal decomposition of a final mixture obtained by mixing a dicyclopentadiene-containing mixture obtained by distillation under reduced pressure from a C5 fraction with at least 9 carbon atoms. It is about. According to the present invention, it is possible to prevent the blockage of the pyrolysis device due to coke generated in the pyrolysis process, and to recover 80 to 90% of the DCPD in the final mixture.

Description

Method of purification of dicyclopentadiene from C5 and C9 + fractions}

The present invention relates to a method for purifying dicyclopentadiene (DCPD) from C5 and an oil having at least 9 carbon atoms (C9 +), and more specifically, distilled under reduced pressure to obtain a concentrated mixture of dicyclopentadiene. The present invention relates to a method for effectively separating and purifying DCPD by mixing pyrolysis with an oil having at least 9 carbon atoms.

DCPD is a dimer of cyclopentadiene (CPD) and is a compound that is used in a variety of polymer resins, synthetic rubber, reaction injection molding (RIM) molding materials, fine chemical materials, and missile propellant fuels. As a general method for recovering DCPD from a DCPD-containing mixture, a method of first pyrolyzing a mixture containing DCPD to obtain a monomer CPD and then re-dimerizing the CPD is used.

DCPD is produced during the pyrolysis of naphtha and is contained in an amount of 10 to 20% by weight in a C5 fraction obtained as a by-product from Naphtha cracker and an oil having a carbon number of 9 or more.

The C5 fraction, a naphtha cracker by-product containing 10 to 20% by weight of DCPD, contains components such as heptane, isoprene, and piperylene, which have similar boiling points to CPD, which is a monomer of DCPD. It is difficult to recover only the ingredients. Therefore, in order to recover DCPD from the C5 fraction, the CPD contained in the C5 fraction is dimerized to DCPD, and then low-boiling compounds such as heptane, isoprene, and piperylene are removed by distillation. This is used. In order to commercialize the DCPD thus obtained, the final purification should be at least 95% by weight, more preferably at least 99% by weight.

In addition to 10 to 20% by weight of DCPD, 50 wt% of hydrocarbon compounds having dimers of styrene, ethylbenzene, methylcyclopentadiene (MCPD), co-dimers of CPD and MCPD, and boiling points of 200 to 400 ° C. % Or more is included. There is also a need to recover economically useful DCPD in such mixtures.

The decomposition reaction of DCPD and the dimerization reaction of CPD are reversible reactions as shown in Scheme 1, and the equilibrium concentration is determined by temperature.

 DCPD ↔ 2 CPD

The rate of decomposition of DCPD is reported to be 36% / hr at 170 ° C (Kirk-Othmer, Encyclopedia of Chemical Technology, 3ed., 1979, Vol 7). Commercially, CPD is obtained by gas phase pyrolysis of DCPD mixtures at temperatures above 300 ° C. Get In the pyrolysis process of DCPD, it is decomposed into CPD and reacts with DCPD to produce polymer compounds such as CPD trimers and tetramers. If DCPD is allowed to stand for 14 hours at 150 ~ 160 ° C, about 50% of DCPD polymerizes above CPD trimer. The CPD polymer produced during the pyrolysis process and coke generated on the pyrolysis device wall block the pyrolysis device, making it difficult to operate and lowering the DCPD recovery rate. In order to solve this problem, several improved methods have been proposed.

Representative methods are described in USP 5,877,366, wherein a method of heating a co-fluid having a boiling point of 250 ° C. or more and then supplying a DCPD mixture to pyrolyze it into CPD is pyrolyzed by continuously supplying a co-fluid and DCPD mixture to a pyrolysis device. This is disclosed in US Pat. No. 3,007,978. Also disclosed is USP 5,321,177, EP 509,445 A1, and Japanese Patent Laid-Open No. Hei 5-78263 which supply an inert fluid, such as steam, with a DCPD mixture to a pyrolysis device. In the method of using the auxiliary fluid, the high-boiling compounds contained in the DCPD mixture remain in the auxiliary fluid, so that the performance of the auxiliary fluid is degraded and the auxiliary fluid must be continuously supplied to maintain the performance.

In the case of supplying a DCPD-containing mixture to an auxiliary fluid-filled pyrolysis device, as in USP 5,877,366, DCPD is pyrolyzed and vaporized into CPDs, but 'high polymers of CPD' and 'materials with higher boiling points than auxiliary fluids' continue to accumulate. In this case, the polymer gradually accumulates and coke and deteriorates thermal decomposition performance.

In addition, if it is necessary to continuously supply the auxiliary fluid, the used auxiliary fluid should be recycled as expected, and in this case, the 'high polymer of CPD' and 'high boiling point than the auxiliary fluid' remaining in the used auxiliary fluid are removed and reused. There must be a problem that requires an additional process.

In the case of using an inert fluid such as steam, a post-treatment process for separating the inert fluid and the pyrolyzed CPD is required, and since the heat for vaporizing the inert fluid is required, energy efficiency is lowered.

Therefore, in the present invention, as a result of research efforts to overcome the problems of the prior art, when the pyrolysis of the mixture obtained by mixing the oil content of 9 or more carbon atoms in the DCPD mixture obtained from the C5 fraction, it is possible to prevent the formation of coke to block the pyrolysis device While preventing the CPD and re-dimerization it was confirmed that can effectively purify the DCPD, the present invention was completed.

Therefore, the technical problem of the present invention is to provide a purification method of DCPD to prevent the blockage of the device due to coke generation in the pyrolysis device.

In order to achieve the above technical problem, a method for purifying dicyclopentadiene from an oil of C5 and C9 or more,

(a) distillation under reduced pressure of C5 fraction to obtain a dicyclopentadiene-containing mixture (A),

(b) to the dicyclopentadiene-containing mixture (A) is added an oil fraction (B) having at least 9 carbon atoms obtained by pyrolyzing naphtha, and pyrolyzing the final mixture (C);

(c) dimerizing the cyclopentadiene contained in the result of pyrolyzing the final mixture (C) to obtain dicyclopentadiene of high purity.

In the DCPD purification method, the vacuum distillation of step (a) is preferably performed at 100 to 130 Torr.

In the DCPD purification method, the concentration of dicyclopentadiene in the dicyclopentadiene-containing mixture (A) obtained by step (a) is preferably 75 to 85% by weight.

In the DCPD purification method, in the step (b), the combined concentration of cyclopentadiene and dicyclopentadiene in the mixture (C) is preferably 30 to 60% by weight, more preferably 40 to 50% by weight. Do.

In the DCPD purification method, in the step (b), the oil component (B) of 9 or more carbon atoms containing a boiling point of 200 to 400 ℃ and 50 to 60% by weight of hydrocarbon having 9 to 12 carbon atoms which are not thermally polymerized desirable.

In the DCPD purification method, the pyrolysis temperature is preferably 280 to 300 ℃, the pressure is 1.0 to 2.0 kg _f / cm ² is preferred.

Hereinafter, the present invention will be described in more detail.

The present invention provides a method for pyrolyzing without using an auxiliary fluid or an inert fluid in a method for recovering DCPD from a mixture of a low purity DCPD mixture of about 75 to 85 wt% obtained from a C5 fraction and an oil of 9 or more carbon atoms. .

Dicyclopentadiene is separated and purified from the C5 fraction by first distilling the C5 fraction under reduced pressure at 100 to 130 Torr to obtain a dicyclopentadiene-containing mixture (A), and adding an oil (B) having at least 9 carbon atoms thereto. After pyrolyzing the final mixture (C), the cyclopentadiene contained in the pyrolysis product is dimerized to obtain dicyclopentadiene of high purity.

The C5 fraction contains 10 to 20% by weight of DCPD and contains a small amount of unpolymerized CPD. However, distillation of only DCPD using a general distillation method is not preferable in terms of energy efficiency or separation efficiency. When distilled at a high temperature, the DCPD is decomposed into CPD, and the C5 fraction contains a large amount of hydrocarbon compound having a similar boiling point as that of the CPD. Therefore, a method of firstly separating low-boiling compounds from a DCPD mixture is usually used, and DCPD in a C5 fraction is concentrated to a certain concentration through distillation under reduced pressure.

The concentration of dicyclopentadiene in the dicyclopentadiene-containing mixture obtained by distillation under reduced pressure is preferably 75 to 85% by weight. However, when the DCPD is separated at a concentration exceeding 85% by weight, the operation efficiency of the reduced pressure distillation decreases. When the concentration of DCPD in the mixture is less than 75% by weight, the efficiency of pyrolysis decreases, which is undesirable.

In the pyrolysis step, it is preferable that the mixing weight ratio of the dicyclopentadiene-containing mixture (A) and the oil component (B) having 9 or more carbon atoms is 3: 7 to 5: 5, and the cyclo in the mixture (C) mixed at this ratio The combined concentration of pentadiene and dicyclopentadiene results in a range of 30 to 60% by weight, more preferably 40 to 50% by weight. When the mixing ratio of the dicyclopentadiene-containing mixture (A) to an oil content of 9 or more carbon atoms is less than the above range, the efficiency of DCPD separation purification is lowered, and when the mixing ratio of the dicyclopentadiene-containing mixture (A) exceeds the above range It is not preferable because there is a small amount of oil having a carbon number of 9 or more acting as an auxiliary fluid in the total mixture because coke may occur in the pyrolysis apparatus.

In order to prevent coke formation, it was experimentally confirmed that the oil having a carbon number of 9 or more mixed to thermally decompose about 280 to 300 ° C. does not cause problems such as coke formation. However, some coke formation was observed when pyrolyzed at a temperature exceeding 300 ℃ (340 ~ 360 ℃). Based on the above experimental results, CPD was recovered in 95% by weight or more by thermal decomposition by mixing an oil having at least 9 carbon atoms with the DCPD mixture.

As such, the C9 or more oil may function as an auxiliary fluid or an inert fluid of the prior art, thereby effectively recovering the DCPD in the C5 fraction and the C9 or more oil without supplying an additional inert fluid such as another auxiliary fluid or steam.

In the pyrolysis experiment of an oil having a carbon number of 9 or more, it was confirmed that when the pyrolysis temperature was 280 to 300 ° C., pyrolysis was possible without clogging the apparatus and 80 to 90% of DCPD could be recovered. In addition, the pyrolyzed CPD is purified to high purity and the remaining residues are not solidified and there is no problem in transferring to the pump. However, when the pyrolysis temperature exceeds 300 ℃, clogging of the device due to coke generation occurs, and pyrolysis is not effective at a temperature below 280 ℃ is not preferable.

The pyrolysis pressure is preferably 1.0 to 2.0 kg _f / cm ² It is effective in the pyrolysis efficiency to maintain the pressure of the pyrolysis device to the atmospheric pressure.

In order to achieve the effect aimed at by this invention, it is necessary to confirm experimentally the thermal decomposition property of C9 or more oil component.

The low-purity DCPD mixture obtained by distillation under reduced pressure of C5 fraction is composed of 75 to 85% by weight of DCPD, 3 to 7% by weight of CPD, and other high boiling point polymer compounds with boiling point similar to CPD. When the low-purity DCPD mixture alone is pyrolyzed at a high temperature of about 300 ° C., coke is generated, which is not preferable because of a problem such as blocking the pyrolysis device.

The CPD contained in the fraction having 9 or more carbon atoms is mostly present in the form of a codimer with a dimer, DCPD or MCPD, and some are present in the form of polymers of CPD monomer, trimer or more. In order to recover the CPD, it is necessary to pyrolyze the DCPD or CPD / MCPD co-dimer and at the same time suppress the polymerization of the pyrolyzed CPD above the trimer. The fraction of 9 or more carbon atoms contains about 50% by weight of hydrocarbon compounds (mainly C9 to C12 compounds) having a boiling point of 200 to 400 ° C, and these hydrocarbon compounds act as co- or inert fluids, thereby polymerizing CPD to trimer or higher. It is supposed to suppress that.

As described above, hydrocarbons contained at 9 or more carbon atoms are relatively stable compounds, and it is observed that they do not coke even in a pyrolysis apparatus operating at about 300 ° C.

In the present invention, it is experimentally confirmed that the hydrocarbon compound contained in the C9 or more oil fraction acts as an inert fluid, and thermally decomposes DCPD to CPD by mixing the C9 or more CB oil to a low purity DCPD mixture of about 75 to 85% by weight. DCPD was purified by separating CPD and redimerizing it. The present invention was completed by experimentally confirming such pyrolysis conditions, the degree of occlusion of the pyrolysis device, and fluidity of the residue.

In case of recovering CPD by directly distilling C5 fraction after distillation, 5 to 10 wt% of components having similar boiling point (boiling point of 30 to 50 ℃) are included, so that distillation from the pyrolysis result is carried out. It is difficult to separate CPD into high purity. Therefore, in the case of finally separating and purifying DCPD from C5 fraction, it is necessary to first remove the low boiling point compound similar to the CPD by vacuum distillation before pyrolyzing the C5 fraction.

In the subsequent process, the DCPD mixture obtained by distillation under reduced pressure of the C5 fraction is pyrolyzed to decompose DCPD into CPD, and then the CPD is separated from the top of the distillation apparatus. The CPD obtained from the column top produces an exothermic reaction even at room temperature and dimerizes. The reaction rate and equilibrium concentration (DCPD and CPD concentrations in equilibrium) change with temperature. When the top product of the distillation unit is received in a 20-liter tank for 24 hours, the 95% or more CPD can be re-dimerized to DCPD and, if necessary, the degree of dimerization can be improved by using a coil-type re-dimerizer. In addition, CPD remaining in DCPD may be removed by distillation under reduced pressure.

Experiments were conducted under various conditions to determine the pyrolysis characteristics of these naphtha cracker by-products and to find the optimum conditions for increasing the pyrolysis rate and recovery rate within the range where the pyrolysis device was not blocked.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention, and the protection scope of the present invention is not limited by these examples.

Example 1

First, a pyrolysis experiment of at least 9 carbon atoms serving as an auxiliary fluid or inert fluid was carried out. The composition of the at least 9 carbon atoms used in the experiment was shown in Table 1.

compound weight% CPD  2.6 MCPD  1.6 Styrene 10.0 DCPD 16.1 Indene  4.5 BTX  2.3 Other hydrocarbons 62.9 sum 100.0

Pyrolysis experiments of the carbon number 9 or more of the components shown in Table 1 were carried out. The pyrolysis unit was equipped with a 3/8 inch 25m long stainless tube in the furnace and the total volume of the cracking tube was 1.5 liters. Oil containing more than 9 carbon atoms was supplied to the pyrolysis pipe with a metering pump. The pyrolysis pressure was 1.5 kg / cm ² and the retention time in the pyrolysis pipe was about 2.5 to 3.2 seconds. In order to observe whether the pyrolysis device was blocked according to the pyrolysis temperature, the CPD recovery rate and the device blockage were observed while changing the pyrolysis temperature to 260, 300, 340, and 360 ° C.

The gas discharged from the pyrolysis tube was supplied to the distillation apparatus and analyzed using gas chromatography (GC). Table 2 shows the analysis results of the product, which was obtained by pyrolysis experiment of an oil having 9 or more carbon atoms.

 Sample 1  Sample 2  Sample 3  Sample 4 Feed rate of oil with more than 9 carbon atoms (kg / hr) 10 10 10 10 Pyrolysis Temperature (℃) 260 300 340 360 CPD Dimer and Codimer Degradation Rate (%) 87 91 93 95 % Of total recovery of DCPD and CPD 85 88 89 85 Whether the device is blocked after 100 hours of operation (pressure difference before and after pyrolysis pipe) none none 0.2 kg _f / cm ² 0.5 kg _f / cm ²

The pyrolysis temperature is the temperature of the off-gas and the decomposition rate is calculated from the amount of CPD and DCPD of the residues remaining in the distillation apparatus, and the recovery rate is calculated from the amount of DCPD (including CPD) separated and dimerized.

 As can be seen in Table 2, when the pyrolysis temperature was 260 to 300 ° C., no blockage of the device was observed, but blockage of the device occurred at 340 and 360 ° C., which are temperatures exceeding 300 ° C. Through these experimental results, it was found that pyrolysis was suitably performed at 300 ° C. or lower.

Example 2

The C5 fraction was distilled off under reduced pressure to obtain a low purity DCPD compound of about 75 to 85% by weight from the C5 fraction. In order to remove the low boiling point (substance having a boiling point of 30 to 50 ° C at normal pressure) by using a vacuum distillation column, the operation pressure is 120 to 130 Torr, the top temperature is 30 to 40 ° C, and the bottom temperature is 120 to 130 ° C. It was. The vacuum distillation column was filled with 1/4 inch raschig ring in a 2 inch diameter, 4 meter high tower, and was equipped with a condenser, reboiler, temperature, and pressure control device as peripheral equipment.

Purification by the above vacuum distillation apparatus confirmed that 40 to 50% of the low boiling point compound was removed. The composition of the low purity DCPD compound obtained by distillation under reduced pressure of C5 fraction was as shown in Table 3 below.

As shown in Table 3 below, when a low-purity DCPD mixture from which a large amount of low-boiling compounds were removed was subjected to a pyrolysis experiment (pyrolysis temperature of 300 ° C.) using the same pyrolysis apparatus as in Example 1, the decomposition rate was 80 at 50 hours of operation. Pyrolysis could not be continued because it fell below the weight% and the pyrolysis tube was blocked. In addition, after pyrolysis, the CPD was removed and the remaining components solidified, making it difficult to transfer to the pump. Therefore, it was confirmed that DCPD was not effectively separated due to the blockage of the pyrolysis device without adding a mixture to prevent coking of the residue during the pyrolysis process such as an auxiliary fluid or an inert fluid.

ingredient Composition (% by weight) Boiling point (℃)  1,3-butadiene  1.06  -4.4  2-butyne  0.15  27.1  Isopentane  0.62  27.9  1-pentene  0.15  30.0  2-methyl-1-butene  0.20  31.2  Isopropenylacetylene  0.61  32.3  Isoprene  3.10  34.1  Pentane  1.36  36.1  Trans-2-pentene  0.09  36.5  Cis-2-pentene  0.06  36.9  Cyclopentadiene (CPD) 5.21  40.0  Trans-1,3-pentadiene  1.08  42.0  Cis-1,3-pentadiene  0.68  44.1  Cyclopentene  1.17  44.2  Dicyclopentadiene (DCPD)  82.29  170.0  Trimer or higher high boiling point  2.20  -   Sum  100.00

Example 3

Using the pyrolysis device used in Example 1, it was confirmed that DCPD can be recovered in a high yield by mixing pyrolysis of an oil having a carbon number of 9 or more to the DCPD mixture obtained by distillation under reduced pressure using a pyrolysis device. The mixture weight ratio of the DCPD-containing mixture obtained by distillation under reduced pressure of the C5 fraction and the carbon number 9 or more was 3: 7, and the total content of DCPD (including CPD) in the final mixture of the two mixtures was 39 wt%. The DCPD mixture was pyrolyzed at 300 ° C. to obtain a high concentration of CPD mixture, which was then separated by condensation of the CPD at the top of the distillation apparatus.

The high concentration of CPD solution obtained from the top of the distillation apparatus was transferred to a 20 liter tank and left at room temperature to re-dimerize it to DCPD.

Finally, DCPD was obtained with purity of about 98% by weight (including about 2% by weight of CPD), and it was possible to operate the pyrolysis device stably without generating coke, and because the residue was not hardened, it was flowable so that it could be transferred to the pump. It was confirmed that possible.

Example 4

The mixed weight ratio of the DCPD-containing mixture obtained by distillation under reduced pressure in the C5 fraction and the C9 or more fraction was 5: 5, and the total content of CPD and DCPD in the final mixture of the two mixtures was 52 wt%. In addition, the thermal decomposition temperature was 280 degreeC. Except for such conditions, pyrolysis and the result were analyzed in the same manner as in Example 3. As a result, DCPD purity was 96% by weight, and after 50 hours of operation, no blockage of the device was observed.

Example 5

The mixing weight ratio of the DCPD-containing mixture and the oil having a carbon number of 9 or more was 5: 5, and the total content of CPD and DCPD in the final mixture of the two mixtures was 52% by weight. In addition, the thermal decomposition temperature was 300 degreeC. Except for such conditions, pyrolysis and the result were analyzed in the same manner as in Example 3. The DCPD purity of the resultant was 96% by weight, and after 50 hours of operation, slight pressure increase was observed inside the device, but the residue was not hardened, so it was confirmed that it was possible to transfer to the pump because of fluidity.

Comparative Example 1

The mixing weight ratio of the DCPD-containing mixture and the oil having a carbon number of 9 or more was 5: 5, and the total content of CPD and DCPD in the final mixture of the two mixtures was 52% by weight. In addition, pyrolysis temperature was implemented at 320 degreeC which is higher than a suitable temperature. Except for such conditions, pyrolysis and the result were analyzed in the same manner as in Example 3. The DCPD purity of the resulting product was good as 95% by weight, but after 50 hours of operation, an increase in pressure was observed inside the device and some blockage of the device was also observed. In addition, the residue solidified and could not be transferred to the pump due to lack of fluidity.

Comparative Example 2

The mixing weight ratio of the DCPD-containing mixture and the oil having a carbon number of 9 or more was 7: 3, and the total content of CPD and DCPD in the final mixture of the two mixtures was 65% by weight. Pyrolysis temperature was carried out at 300 ℃. Except for such conditions, pyrolysis and the result were analyzed in the same manner as in Example 3. The CPD purity of the resulting product was 93% by weight, and significant pressure rise was observed inside the apparatus even after 50 hours of operation, and the apparatus was blocked. In addition, the residue solidified and could not be transferred to the pump due to lack of fluidity.

Table 4 below summarizes the results carried out according to Examples 3 to 5 and Comparative Examples 1 to 2.

Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Feed rate of oil with more than 9 carbon atoms (kg / hr)    7    5     5    5    3 ~ 85% by weight DCPD feed rate (kg / hr)    3    5     5    5    7 DCPD content of raw material (wt%)    38   52    52   52   65 Pyrolysis Temperature (℃)   300   280    300   320   300 DCPD Resolution (%)    90    85     86    88    80 DCPD purity (% by weight)    98    96     96    95    93 Blocking the device after 50 hours of operation (pressure change before and after pyrolysis pipe)   none   none 0.05 kg _f / cm ² Pressure rise 0.1 kg _f / cm ² Pressure rise 0.2 kg _f / cm ² Pressure rise Residual fluidity (50 ℃) Not hardened Not hardened Not hardened  rigidity rigidity

As described above, according to the present invention, DCPD can be effectively purified from naphtha cracker by-products while improving pyrolysis conversion and energy efficiency, while suppressing CPD polymerization or coke formation in the pyrolysis apparatus. In addition, it can be recovered by CPD by pyrolyzing together the oil having a carbon number of 9 or more and the DCPD mixture without supplying another auxiliary fluid or additional inert fluid such as steam. In addition, when the DCPD concentration of the mixture supplied to the pyrolysis device was 50% by weight or less, stable operation was possible for a long time without clogging the device, and DCPD could be recovered up to 90%.

Claims (7)

In the method of purifying dicyclopentadiene from C5 and C9 or more fraction, (a) distilling the C5 fraction under reduced pressure to obtain a dicyclopentadiene-containing mixture (A); (b) adding an oil (B) having at least 9 carbon atoms obtained by pyrolysing naphtha to the dicyclopentadiene-containing mixture (A), and pyrolyzing the entire mixture (C); And (c) dimerizing the cyclopentadiene contained in the result of pyrolyzing the entire mixture (C) to obtain a high-purity dicyclopentadiene. The method for purifying dicyclopentadiene according to claim 1, wherein the vacuum distillation of step (a) is performed at 100 to 130 Torr. The method for purifying dicyclopentadiene according to claim 1, wherein the concentration of dicyclopentadiene in the dicyclopentadiene-containing mixture (A) obtained by step (a) is 75 to 85 wt%. The method for purifying dicyclopentadiene according to claim 1, wherein the total concentration of cyclopentadiene and dicyclopentadiene in the total mixture (C) is 30 to 60% by weight. The method for purifying dicyclopentadiene according to claim 1, wherein the total concentration of cyclopentadiene and dicyclopentadiene in the total mixture (C) is 40 to 50% by weight. The method of purifying dicyclopentadiene according to claim 1, wherein in the step (b), the oil component (B) having 9 or more carbon atoms contains 50 to 60% by weight of hydrocarbon having 9 to 12 carbon atoms. The method for purifying dicyclopentadiene according to claim 1, wherein the pyrolysis temperature of step (b) is 250 to 300 ° C and a pressure of 1.0 to 2.0 kg _f / cm ² .