development of variants to increase … of variants to increase productivity and effectiveness of...

UDC 66.021.2.3.048

DEVELOPMENT OF VARIANTS TO INCREASE PRODUCTIVITYAND EFFECTIVENESS OF O-XYLENE PRODUCTION

AT JSC “SALAVATNEFTEORGSINTEZ”

J.N. Fayruzova1, D.M. Perevezentsev "Salavatnefteorgsintez" JSC, Salavat, Russia

e-mail: 1 [email protected]

M.V. KlikovUfa State Petroleum Technological University,

Salavat Branch, Salavat, Russia

Abstract. The article describes the current process flow installation for o-xylene at JSC "Salavatnefteorgsintez". Considered various options for increasing production efficiency of o-xylene: the replacement of the nozzle in the column, by installing an additional column, the use of xylene isomerization. To investigate and compare the options used models based on the simu-lation system PRO/II. Technical and economic analysis.

Keywords: o-xylene, structured packing, distillation column, isomerization, dis-proportionation

At present time on JSC"Salavatnefteorgsintez" there is a lack of o-xylene, as a

feedstock for phthalic anhydride production. Acting unit of o-xylene production, situ-

ated in shop 34, is not put into full capacity (15 thousands tones per year). This is con-

nected with low efficiency of packing Mellapack 452 in column K-2.

In this work it is offered following variants to solve this problem:

– replace packing to more effective in existing scheme;

– to use additional distillation column (three-column scheme);

– to apply xylene isomerization process;

To study and compare possible variants of increase efficiency in o-xylene pro-

duction simulations in PRO/II were carried out.

First variant: to change existing packing to more effective. It is supposed that

additional quantity of o-xylene containing solvent should be bought (28 th.t/year).

Existing simplified process flowsheet is presented on Fig. 1.

_____________________________________________________________________________ Electronic scientific journal “Oil and Gas Business”, 2011, №1 http://www.ogbus.ru/eng/

142

Figure 1. Existing simplified process flowsheet of o-xylene production at the JSC “ Salavatnefteorgsintez ”

According to bibliographic analysis of regular packing’s which are presented by

producers with worldwide reputation, the most effective packings are a grid type ВХ

and ВХPlus. They differs by hydraulic resistance and price. Characteristics of different

regular packings is presented on figure below (Fig. 2).


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Figure 2. Characteristics of regular packingsAccording to received results of simulations, we can conclude, that this variant

allows us to satisfy a need of phthalic anhydride production. Recovery ratio will be inc-

reased from 66 % to 90 % mass. Material balance presented in the Table 1.

Table 1. Material balance of o-xylene production in case of packing replacement

Inlet kg/t Outlet kg/tSolvent 7800 o-xylene 1274,1

С+9 579,8

Light cut from К-2 5946,1Total 7800 Total 7800

Technical and economic calculations shown (Fig. 3), that the least operating

costs per one ton of feedstock can be reached with column efficiency at level 80 t.t.

Figure 3. Unit cost – number of theoretical trays diagram

As another variant it is considered application of three-column scheme for separ-

ation (Fig. 4). To decrease capital expenditures, linked with additional column construc-

tion, it is offered to use removed from service column K-19, which is located in shop

33 unit L-35-6 JSC Salavatneftergsintez (SNOS).


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Figure 4. Simplified flowsheet of o-xylene production (three-column separation)

This simulation of scheme was made in PRO/II. According to simulation results

this variant allow to increase unit production up to demanding value. The material bal-

ance of the process is presented here below (Table 2).

Table 2. Material balance for three-column scheme

Inlet kg/t Outlet kg/tSolvent 7800 o-xylene 1206,65

С+9 568,84

Light cut from К-19 3580,13Light cut from К-2 2444,38

Total 7800 Total 7800

For the purpose of researching and obtaining optimum operating parameters of

distillation columns K-2, K-6 and K-19 we defined and graphed the dependence of

column operating parameters from pressure.

For column K-19 the maximum allowed pressure is 0,9 bar, for column К-2 –

1,2 bar, for the column К-6 – 1,55 bar, as with increase of pressure relative volatility


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decrease and reflux ratio increase, that leads to overtolerance liquid loading below (20

m3/m2·h-1) maximum recommended for SULZER packing.

Thus, we determined performance characteristics of columns К-2, К-6 and К-19

such that will provide maximum o-xylene yield with minimum cost (Table 3).

Table 3Performance characteristics of columns for o-xylene production

Item Pro/II simulation resultsК-19 К-2 К-6

Feedstock temperature, °С 124 120 155,8Feedstock capacity, kg/h 7800 4219 1775,75Reflux ratio 8,05 7,34 6,5O-xylene in distillate, % wt. 0,9 4,2 97,6Temperature of the top, °С 122,7 135,5 131,1Temperature of the bottom, °С 135,9 148,7 150,3Pressure of the top, barg 0,8 0,9 0,7Pressure of the bottom, barg 0,8102 0,98 0,7Theoretical trays 40 70 50Feed tray* 28 32 20Market o-xylene yield, kg/h - - 1292,3*Trays count start from top

The advantage of three-column scheme of o-xylene production is the lowest

cost, because we offer to use already existing equipment, with the assumption of pur-

chasing lacking quantity of feedstock (solvent) on the third hand.

As in previous case the main shortcoming of this variant is the lack of feedstock.

Partially this problem can be solved by new toluene disproportionation unit con-

struction.

In disproportionation process benzene reduction occurs from toluene with

hydrodealkylation and oxidation to o-xylene, as methyl group is linking to other toluene

molecule. As catalyst platinum, palladium, rear earth metals and neodymium on alumin-

um oxide are used. Also chromium on aluminum silicate can be used.

Schematic process flowsheet represented on figure below (Fig. 5).


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Figure 5. Schematic toluene disproportionation process flowsheet

At present time at SNOS research center the research works of toluene dispro-

portionation process are carried out. The main aim of this works is additional quantity

of benzene and xylenes evaluation.

In the course of carried out research the following composition of catalysate was

obtained: in ratio toluene/hydrogen = 1/2 with 450 °C on Y type zeolite catalyst,

LHSV=1h-1 (Table 4).

Table 4. Composition of catalysate

Component amount, % wt.Benzene 24,7Toluene 57,0Total C8 15,8 ( including m+p-xylenes 77,8 %: о-xylene 22,2)

ethylbenzene 0,7ethyltoluene 0,4

С+9

1,8 (including 1,3,5- trimethylbenzene – 27,8 %;1,2,4- trimethylbenzene – 61,1 %; others – 11,1 %)


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The material balance of toluene disproportionation process at JSC SNOS is

presented in Table 5.

Table 5. Material balance of toluene disproportionation process on JSC SNOS

Feedstock, kg/h Reactor feedstock including recycle, kg/h Products, kg/h

toluene 3968,3 toluene 9228,5 benzene 2279,4hydrogen 7936,5 hydrogen 18456,9 xylenes 1458,1

Including o-xylene 323,6C+

9 166,1including 1,3,5-

trimethylbenzene 2565,5

1,2,4- trimethylbenzene 5638,6others 1024,3

∑ 3968,3 ∑ 3903,6

This process will allow to decrease o-xylene purchasing from JSC “Ufanefte-

him” on 65 % and increase benzene production on 50 %.

The problem with lack of o-xylene can be solved by xylenes isomerization pro-

cess.

In simulation of this process we used ceolite catalyst IK-78 which operates with

increased LHSV=3 h-1. Catalyst life cycle time exceed 4 years. Isomerization process

flowsheet represented on Fig. 6.

We developed simulation of xylenes isomerization unit for o-xylene production.

As thermodynamic model the Grayson-Streed was chosen.

It is supposed that columns К-2, К-6, К-19 – existing equipment, К-3 – new one.

With the view of optimization columns К-2, К-6, К-19 and К-3 performance and

increase of productive efficiency we researched the effect of pressure in system on dif-

ferent process parameters.

On figure below (Fig. 7) o-xylene yield-pressure in columns diagram is repres-

ented.


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Figure 6. Xylenes isomerization process flowsheet

Figure 7. O-xylene yield-pressure in columns diagram

The variation of pressure in column K-3 have the most effect on o-xylene yield,


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as with increase of pressure less light cut and o-xylene returns to isomerization loop.

Thus, we can conclude that o-xylene yield rise with decrease of pressure in

columns К-3, К-2, and with increase of pressure in К-6, К-19.

To determine necessary number of theoretical trays in К-3 we graphed the

curves: Unit cost to theoretical trays diagram and reboiler duty to theoretical trays

diagrams (Fig. 8).

According to this graph 60…65 is the optimal number of theoretical trays.

Figure 8. Unit cost and reboiler duty – number of theoretical plates in column diagram

On the base of developed simulation we determined range of columns stable

operation with given distillate and residue composition. The limiting factor are pressure

drop in trays and liquid load. For the columns with SULZER packing – pressure drop

should be less or equal to 3 mbar/m, and liquid load should not exceed 20 m3/m2·h-1

(Fig. 9, 10).

The curves (Fig. 9, 10) shows that column К-2 can be operated in range of pres-

sure 1…1,23 barg, К-6 in range 1…1,7 barg, and К-3 in range 0,3…4,5 barg.


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Figure 9. Pressure drop in theoretical trays –pressure in system diagram

Figure 10. Liquid load-pressure in column diagram


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Thus, according to carried out analysis we chose optimal process-dependent

parameters of columns, which allow providing maximum o-xylene yield with minimum

expenditures (Table 6).

Table 6. Process-dependent parameters of o-xylene production columns

Item К-2 К-6 К-3 К-19Temperature of the top, °С 145,1 158,1 105,3 111Temperature of the bottom, °С 159,4 177,1 113,7 157,7Pressure of the top, barg 1,23 1,4 0,4 1,6Pressure of the bottom, barg 1,29 1,41 0,42 1,6Reflux ratio 5,1946 5,1646 4,6575 5,0345Pressure drop, mbar/m 2,2851 0,8533 1,7306Liquid load, m3/(m2.h) 19,9987 17,824 13,0791 10,741Loading factor, Pa0,5 1,95 1,53 2,29 1,21Condenser duty, Mcal/h 4,5087 1,9768 6,3161 0,33Reboiler duty, Mcal/h 4,3446 1,8533 5,9518 0,5116

Material balance of xylenes isomerization unit presented in Table 7.

Table 7Material balance of xylenes isomerization unit

Input kg/h Output kg/hsolvent 4200 o-xylene 2462,5

C+9 1737,5

∑ 4200 ∑ 4200

The shortcoming of this loop (isomerization) is high capital expenditures linked

with necessity of furnace, reactor and column K-3 development.

To define economic expediency of revamping we calculated the main economic

indicators for all presented variants: 1) replacement of packing to more effective in

existing scheme; 2) use of additional distillation column (three-column scheme); 3)

application of xylene isomerization process. The main efficiency indexes of revamping

are presented in Table 8.

The information of equipment cost was given by Department of material support

JSС SNOS and Sulzer Chemtech company.


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Table 8. Main efficiency indexes of revamping (rub.)

Index Unit

Without feedstock purchasing

With feedstock purchasing

Variant 1 - packing

replacement

Variant 2- three-

column scheme

packing replacement

three-column scheme

investment Mln.rub. 35 21,4 35 21,4

cost price rub. 18893,27 18999,2 22856,5 22977,3

gross margin Mln.rub. 602,22 587,07 328,8 328,46

internal rate of return

(IRR)% 218 % 334 % 126 % 193 %

pay-back time year 0,50 0,33 0,87 0,57

All presented variants in work allow to increase unit capacity to required value.

1st variant – packing replacement. This variant is the simplest one with a view of

building and construction works, as it’s implementation don’t require additional equip-

ment installation. We offer only to replace packing M452 to more effective -Zultser BX.

Their price exceed price of actual packing on 87 %.

2nd variant – three-column scheme. This variant requires minimal investments. In

this case main costs are bounded up with building and construction works.

The main drawback of 1st and 2nd variants is necessity of raw material (solvent)

purchasing. Partially the problem with lack of o-xylene we can solve by toluene dispro-

portionation unit development, that allow to decrease o-xylene purchasing on 65 %.

3rd variant – xylenes isomerization. this is long-term investment project, which

require significant investments. But it allow to completely cover phthalic anhydride pro-

duction requirement in o-xylene at the expense of own feedstock.


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References

1. JSC «Salavatnefteorgsintez». Tekhnologicheskii reglament proizvodstva o-

ksilola v tsekhe №34 (Technological rules of production properties of o-xylene in the

shop N34). Salavat, 2005.

2. Koch-Glitsch. http://www.koch-glitsch.com

3. Martin C.L., Bravo J.L and Fair J.R. Performance of Structured Packings in

Distillation Service – Experimental and Modeling Results, presented at the AlChE Nati-

onal Meeting, New Orleans, March 6-10, 1988.

4. ACS Industries, LP, Separations & Mass-Transfer Products. http://www.ac-

sseparations.com

5. Jaeger products. http://www.jaeger.com

6. Kempro. http://www.kempro.eu

7. Zhorov Yu.M. Izomerizatsiya uglevodorodov. Khimiya i tekhnologiya (Iso-

merization of hydrocarbons. Chemistry and Technology). Moscow, Khimiya, 1983.

304p.

8. Patent 2197462. RF, MPK C07C15/08. Sposob polucheniya o-ksilola (Pro-

cess for obtaining o-xylene), app. №2001130644, date of receipt: 12.11.2001. Priority

from 12.11.2001. Author (s) of the invention: E.V. Panteleyev.


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