Development of Light Naphtha Aromatization (LNA) Process

石油学会誌 Sekiyu Gakkaishi, 40, (6), 529-533 (1997) 529

[Technical Note]

Development of Light Naphtha Aromatization (LNA) Process-Demonstration Plant Work-

Koichi KATO†1)*, Satoshi FUKASE†2), Yasushi ISHIBASHI†3),

and Manabu YAMAMOTO†3)

†1) Petroleum Refining Dept., Japan Energy Corp., 10-1 Toranomon 2-chome, Minato-ku, Tokyo 105

†2) Petroleum Refining Research and Technology Center, Japan Energy Corp.,

17-35 Niizo-minami 3-chome, Toda, Saitama 335†3) Mizushima oil Refinery, Japan Energy Corp., 2-1 Ushiodori, Kurashiki, Okayama 712

(Received October 7, 1996)

A fixed-bed process to convert light paraffins to aromatics was completed, test operated in a

demonstration plant. Normally, this reaction is conducted in a continuous or swing type regenerationsystem to prevent carbon build-up on the catalyst. The new light naphtha aromatization (LNA) processis catalyzed by zinco-aluminosilicate, that has higher activity and extended stability. In a 2250 barrels perday demonstration plant, the process was operated continuously for more than 1000h, attaining over95wt% conversion and over 50wt% aromatics yield.

The demonstration unit consists of two sections, reaction and separation. The former includes threefixed bed reactors arranged with preheaters in series, replacing the conventional heavy naphtha reformingunit. Catalyst regeneration is semi regenerative.

The catalyst was discharged from the reactor after regeneration and analyzed for properties and activity.The results indicated that the catalyst is stable, after cyclic operation of reaction and regeneration.

1. Introduction

There are several light naphtha aromatization

processes, which are being developed for com-mercial operation1)-3), but, so far without notablesuccess, especially those using C5-C6 paraffins asfeedstock. We undertook the development ofLight Naphtha Aromatization (LNA) Processwhich employs zinco-aluminosilicate catalyst

using afore mentioned feedstock4)-7). Generally,zeolitic catalysts with MFI structure are chosen forthe aromatization of light paraffin because of theirlower coking tendency. The operating condi-tions required for the processes, however, result ina catalyst carbon laydown which is unfavorable fora conventional fixed bed catalytic operation.Thus, the development of pioneer processes weredirected towards continuous or swing-type regener-ation because of rapid decline in catalyst activity.

In contrast with the afore mentioned, our effortwas focused on utilizing a conventional fixed bed

unit in the development of a new process to convertlight paraffins of high concentration, C5-C6

paraffins, to aromatics. In the basic researchstage, a new catalyst with extended stability, wasinstrumental to develop a fixed bed process forthis reaction4)-7). The catalyst used is a zinco-aluminosilicate, which was stabilized by pro-

prietary technique of steaming, developed by theauthors.

A 2250 BPD (357.7m3/d) demonstration unitwas designed and erected to testify the performanceof the process. The objective of this paper is tosummarize performance of the LNA demonstra-tion unit, using a newly developed catalyst.

2. Demonstration Plant

A basic concept of a new light naphtha aromati-zation (LNA) process, with some design analyses,was proposed in the authors previous paper4).

The flow scheme of the LNA demonstration

plant, having a designed capacity of 2250 BPD, isshown in Fig. 1. It is essentially the same as thatof a conventional fixed bed reformer. In fact, amain section of a conventional heavy naphthareforming unit, having 5000 BPD capacity, was

* To whom correspondence should be addressed. (Present

address) Nikko Consulting & Engineering Co., Ltd.,

Yamakatsu Bldg., 1-40 Toranomon 4-chome, Minato-ku,

Tokyo 105

石油学会誌 Sekiyu Gakkaishi, Vol. 40, No. 6, 1997

530

utilized for this unit. It consists of two major sec-tions: reaction and product recovery, respectively.

The reaction section contains three fixed bedadiabatic reactors, each having preheaters,connected all in series. Economics leads us to useadiabatic reactors. Because of the high level ofendothermic heat of reaction, there could besubstantial drop in temperature along the reactorbed. The catalysts are, therefore, distributed overthree fixed bed adiabatic reactors, having feed

preheaters installed in between the reactors. TheLNA kinetic model was used with a processsimulator to carry out reactor design, and toinvestigate the optimal catalyst loading pattern forthe unit5).

The reaction section is designed to continuously

produce aromatics and hydrogen within a timetable dictated by catalyst life. Semi-regenerationis a remarkable feature of this LNA process6). Themethod of regeneration is similar to that ofconventional catalytic reforming. By introduc-ing diluted air into the catalyst bed, the coke onthe catalyst is burned off. A temperature swingadsorption type dryer was installed to eliminatethe water produced by burning the coke duringregeneration, in order to prevent catalyst degrada-tion.

The recovery section separates the reaction

product into four product streams such as off gas,hydrogen rich gas, C3/C4 LPG and aromaticsfraction. A rather high concentration of non-condensing gas components in the reactor effluentcauses considerable high consumption of electri-

city in the section. Aromatics recovery rate of 98%

can be achieved in this section.

A picture of the demonstration unit is exhibited

in Fig. 2.

3. Performance and Discussion

The purpose of the demonstration unit was to

provide and establish a LNA process, which iscommercially feasible, providing continuous,

steady and long term operation, resulting in highlyimproved performance.

After resolving few mechanical problems, the

plant achieved continuous operation. Duringthis period, the authors carried out a number

of runs to investigate yield of aromatics and

deactivation of coke, in various conditions, and

Fig. 1 A Schematic Flow Diagram of LNA Demonstration Plant

Fig. 2 A Picture of the Demonstration Unit


531

also to study the regeneration of catalyst after

reaction cycles.

The feedstock used during test runs was straight

run light naphtha derived from the Middle East

crudes. The typical properties of the feedstock

are shown in Table 1. Attributed to refinery

operation pattern, the butanes content in the

feedstock is considerably higher than that in thebasic research work4).

Considering the nature of demonstration plant,reaction condition was varied widely to investigatethe effect of reaction conditions on product yield.The varied operating conditions and correspond-ing product yield of demonstration plant areshown in Table 2. More than 50wt% of aromatics

(BTX+A9+) was obtained. In order to clarify therelationship between the results of large scaledemonstration unit (2250 BPD) and those of smallscale experimental unit (0.04 BPD), both results arecompared. The details of the small scale experi-mental unit were shown in the authors' previous

paper4). In Fig. 3 is shown the comparison of dataof demonstration unit with those of experimentalunit, using the same feedstock in reaction pressureof 0.4MPa, WHSV 0.7h-1. The temperature ofthe demonstration unit shown in Fig. 3 is weightaverage bed temperature, while that of the ex-perimental unit, which was operated isothermal,is actual bed temperature. The result of thedemonstration unit, however, is fairly comparableto that of the experimental unit.

The reactor temperature profile during opera-

tion is illustrated in Fig, 4. The temperatures are

higher than 520℃ at each reactor inlet, but drop

lengthwise of the reactor, attributed to the

endothermic nature of the whole reaction. The

changes in temperature drops caused by reaction

through each reactor with time on stream are

shown in Fig. 5 as an example. ΔT1, ΔT2, and

ΔT3, shown in Fig. 5, correspond to the tem-

perature drops lengthwise along the reactors 1, 2and 3, respectively, in Fig. 4. A summation oftemperature drops through the three reactorscorresponds to conversion, being due to theadiabatic endothermic reaction, and temperature

goes down when catalyst activity deteriorates inkeeping same average bed temperatures. During

period (1) in Fig. 5, hydrogen gas was not recycledthrough the reactors, while during period (2) equalmole of hydrogen gas to the feed naphtha was

Table 1 Typical Properties of Feedstock

Table 2 Typical Operating Conditions and Reaction

Yield of Demonstration Plant

a) Weight average bed temperature.

Fig. 3 Comparison of Demonstration Unit Data with

Experimental Work

Demonstration unit:

3 Adiabatic reactors in series, Capacity 2250 BPD,

Pressure 0.4MPa, WHSV 0.7h-1.

Experimental unit:

1 Isothermal reactor, Capacity 0.04 BPD, Pressure 0.4

MPa, WHSV 0.7h-1.

Fig. 4 Illustration of Temperature Profile through

Reactor Train


532

recycled through the reactors. Enthalpy of hydro-

gen gas in the feed stream caused temperature dropwhen giving almost the same conversion. As

shown in Fig. 5, total temperature drop lengthwise

three reactors decreased from 190 to 170℃ during

800h on stream (1), while very little decrease wasobserved during 200h on stream (2). In this testrun, a 1000h continuous operation was achieved,maintaining conversion above 96wt%. Further-more, negligible temperature drop during period

(2) suggested extended of catalyst life in casehydrogen was recycled from the beginning. Onthe contrary, hydrogen recycle cuts aromatic yieldslightly and is power consuming. It should,therefore, be decided carefully, in actual com-mercial plant design, whether, or not hydrogenshould be recycled.

The plant operation showed both very lowtendency to form coke and good catalyst stability,after regeneration, as reported in the previous

paper6).The catalyst was discharged from the reactor

after the send regeneration was completed in thedemonstration plant and its acidity was measured.

Shown in Fig. 6 are NH3-TPD profiles of both freshand spent catalysts. Temperature-programmeddesorption (TPD) of ammonia was performed witha conventional TPD apparatus equipped with athermal conductivity detector. Catalyst sampleswere evacuated in a quartz cell at 500℃ for one

hour and cooled to 100℃. Then the ammonia

was desorped at that temperature. The catalyst

sample was degassed at 100℃6) for 20min and the

temperature was raised to 650℃ at a rate of 7℃/

min. The spectra was obtained in a helium flow

of W/F 4.2×10-4g・min/ml. No loss in acidity

was observed even after repetitive operation ofreaction and regeneration. No major change incatalyst composition was also observed.

The activity of the discharged catalyst was

Fig. 5 Changes in Temperature Drops Caused by Reaction in Train Reactor

Fig. 6 NH3-TPD Profiles of Fresh and Spent Catalysts

Fig. 7 Aromatics Yields of Fresh and Spent Catalysts


533

examined in a micro reactor to compare with that

of the fresh catalyst. The feedstock used was the

same as the one described in a previous paper4).

At first, catalyst activity was examined in fol-

lowing condition: reaction temperature 520℃,

pressure 0.4MPa, WHSV 0.7h-1, then was raisedthe feed rate to 5.0h-1 to carry out accelerated agingtest, and finally the activity of coked catalyst in theinitial condition was examined. Aromatics yieldsof fresh and spent catalysts are shown in Fig. 7.No loss in activity was observed with the spentcatalyst.

Above results indicate that the catalyst used indemonstration plant operation is stable after cyclicoperation of reaction and regeneration.

4. Conclusion

A 2250 BPD demonstration plant was operatedin the course of the LNA (Light Naphtha Aromati-zation) process development. The performanceof the LNA catalyst and technology for thearomatization of light naphtha fraction was

demonstrated. The demonstration work is pro-ceeding to achieve extended continuous operation,

exceeding more than 1000h at the higher yield of

aromatics product.The LNA process was shown to convert light

naphtha, yielding more than 50wt% aromaticsselectively. A new catalyst with long life, wasintroduced and verified.

AcknowledgmentThe demonstration work was sponsored by

Petroleum Energy Center, Japan.

References

1) Mowry, J. R., Anderson, R. F., Johnson, J. A., Oil & Gas J.,83, (48), 128 (1985).

2) Scruton, M., Petroleum Review, 45, (533), 270 (1991).3) Kondoh, T., Inoue, S., Hirabayashi, K., Shibata, S., Zeolite

News Lett., 9, (1), 20 (1992).4) Kato, K., Fukase, S., Sekiyu Gakkaishi, 37, (1), 77 (1994).5) Kato, K., Fukase, S., Amaya, T., Sato, Y., Sekiyu Gakkaishi,

38, (1), 9 (1995).6) Kato, K., Fukase, S., Yamamoto, M., Sekiyu Gakkaishi, 39,

(4), 290 (1996).7) "News front," Chemical Engineering, December, 42 (1994).8) Fukase, S., Igarashi, N., Aimoto, K., Kato, K., "Deactiva-

tion and Testing of Hydrocarbon-Processing Catalysts,"ACS Symposium Series 634, (1996), p. 219.

要旨

ライトナフサの芳香族化 (LNA) プロセスの開発

-デモンストレーションプラントによる実証化-

加藤恒一†1), 深瀬聡 †2), 石橋泰 †3), 山本学 †3)

†1) (株)ジャパンエナジー精製部, 105東京都港区虎ノ門二丁目10 -1

†2) (株)ジャパンエナジー精製技術センター, 335埼玉県戸田市新曽南3-17-35

†3) (株)ジャパンエナジー水島製油所, 712岡山県倉敷市水島潮通2-1

固定床による新しいライトナフサ芳香族化 (LNA) プロセ

スを開発するため, 2250BPD規模のデモンストレーションプ

ラントによる実証化研究を行った。

ペンタンを主成分とするライトナフサの芳香族化反応は, 従

前は触媒の劣化が激しいため連続再生型か, またはスウィング

再生型の反応器を用いるものであった。

新規に開発されたゼオライト触媒を充てんした固定床反応器

を中心とする実証化プラントにより転化率95wt%以上, 芳香

族収率50wt%以上を与える1000h以上の長期連続運転が達

成された。実証化プラントは, 通常タイプの重質ナフサ改質用

の固定床プロセスの反応セクションを転用して建設され三個の

断熱反応器および生成物の分離セクションを備えている。触媒

再生は反応を中断して行う半再生式である。

再生後の触媒を抜き出して, 物性, 活性を測定し, 本触媒の

安定性を確認した。

Keywords

Light naphtha, Aromatization, Zinco-aluminosilicate, Fixed bed, Demonstration plant, Process development


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Development of Light Naphtha Aromatization (LNA) Process