CN1054114C - Electric field enhanced plasma catalytic synthesis of C2 hydrocarbon with natural gas - Google Patents

Abstract

The present invention relates to a method for producing C2 hydrocarbon by catalyzing alternate current or direct current field enhanced plasma by means of a metal supported catalyst or a metal oxide supported catalyst, wherein a single methane component is used as raw material, is not added with initiation gas under the conditions of normal pressure (101.3 Pa) and relative low temperature and is not added with oxygen in a coupling process. In an alternating current field, the conversion rate of methane is 6.2 to 8.6% and the selectivity of C2 hydrocarbon is 94.5 to 97.8%. In a direct current field, the conversion rate of methane is 11.5 to 22% and the selectivity of C2 hydrocarbon is 94 to 96%.

Description

The Sweet natural gas electric field enhanced plasma catalytic synthesis of C 2 hydrocarbon

The invention belongs to the gas chemical industry.

Sweet natural gas is very richs in natural resources of reserves, and its major ingredient is a methane, and world's proven reserve are 350 tcms, and China is about 51 tcms.Sweet natural gas and oil, coal are listed as the world today's three big energy, and the development gas chemical industry is the policy that has strategic importance towards 21st century.Because methane molecule is very stable generally will be in pyrolytic conversion, otherwise is difficult to directly use as Organic Chemicals.For example it is converted into the liquid fuel high-carbon hydrocarbon or the organic oxygen-containing thing has become present C ₁Chemical research gaze at problem.Particularly Organic Chemicals such as methane oxidation coupling synthesizing ethylene, ethane are to be future the important channel that raw material replaces petroleum path with the Sweet natural gas.The method that Sweet natural gas be converted into C2 hydrocarbon relevant with the present invention has following several:

1. methane oxidation coupling method (OCM method)

Nineteen eighty-two Keller and Bhasim have reported methane first and oxygen obtains ethene and ethane under catalyst action, though gained ethene amount seldom, but cause gazing at of countries in the world investigators, up to the present existing many research reports, the temperature of reaction of this method is generally more than 700 ℃, methane conversion 20～30%, C2 hydrocarbon selectivity 70～80%.Because side reaction easily takes place at high temperature in the OCM method, the investigator has proposed membrane catalytic reaction and has utilized porous ceramic film metal oxide-loaded, feed gas methane and oxygen are separated charging, in two-tube bilateral membrane reactor, 800 ℃ of temperature of reaction, methane conversion 30%, the C2 hydrocarbon selectivity can bring up to 96～97%.

2. solid electrolyte electrochemical reaction (SSER)

Utilize solid electrolyte to carry out electrochemical reaction, oxygen becomes oxonium ion at the negative electrode electron gain, and methane generates ethane and ethene at anode and oxonium ion effect, the while ejected electron, and 800 ℃ of temperature of reaction, transformation efficiency is below 5%.

3. methane microwave thermal cracking

Utilize microwave induction catalytic cracking methane system ethene, catalyzer is placed under the pulsed microwave radiation, the setting pulse time can get ethylene product, and temperature of reaction is 760～870 ℃, pressure 101.3KPa, burst length is 5 seconds, obtain containing methane 21.8%, ethene 51.3%, oxygen 26.7% in the product composition, because the reaction coking is serious, need continuous termination reaction aerating oxygen to remove coke.

4. laser methane oxidization catalyzing linked reaction

Utilize laser radiation to promote methyl hydride catalyzed oxidative coupling reaction, at LiClO ₄/ Pb ₃(PO ₄) ₂Carry out on the catalyzer, 200 ℃ of temperature of reaction, methane conversion is more than 32%, and ethylene selectivity 93% is higher because of this method cost, does not still have more research report at present.

5. methane plasma reaction.

Du pont company utilizes arc process by methane system acetylene, is reflected at 4000 ° of K high temperature, because of high-temperature plasma reaction current consumption is big, tends to the low-temperature plasma reaction at present.

It is C by the microwave plasma direct catalytic conversion that methane has been reported in researchs such as the Steven L.Suib of U.S. Connecticut university ₂The process of hydrocarbon, reaction is (1.33KPa) under low pressure, utilizes spark generator to excite Ar gas to produce plasma body, methane conversion 52%, selectivity of product is an ethene 25%, ethane 50%, acetylene 25%, methane conversion is 38% when catalyst-free.

France A.Oumghar etc. has studied methane and N ₂The microwave plasma reaction, methane joins N ₂The microwave plasma district, reaction pressure 1.0～4.0KPa, charge ratio CH ₄/ (CH ₄+ N ₂)=17～62% (mol ratio), methane conversion 40～80%, product is formed: C ₂H ₂＜4%, C ₂H ₆＜4%, C ₂H ₄＜2%, CO 80～20%, H ₂60～20%, operation is very not convenient down to be reflected at decompression.

The objective of the invention is to propose a kind of is raw material with the single methane component, the method of catalytic coupling dehydrogenation synthesis of C 2 hydrocarbon, it is characterized in that under normal pressure, relative cold condition, do not add initiation gas and coupling process and do not add oxygen, adopt metal or metal oxide supported type catalyzer, use interchange or DC electric field and strengthen plasma catalytic synthesis of C 2 hydrocarbon.

The present invention adopts the direct coupling synthesis of C 2 hydrocarbon of single methane, and reaction formula is as follows:

△H ₂₉₈＝65.28KJ/mol ${\mathrm{\ΔG}}_{298}^0=69.01\mathrm{KJ}/\mathrm{mol}$

△H ₂₉₈＝202.78KJ/mol ${\mathrm{\ΔG}}_{298}^0=170.43\mathrm{KJ}/\mathrm{mol}$

△H ₂₉₈＝377.88KJ/mol ${\mathrm{\ΔG}}_{298}^0=102.06\mathrm{KJ}/\mathrm{mol}$ Can find out that by above-mentioned thermodynamics of reactions value three reactions all are strong endothermic processes, and the free enthalpy △ G of reaction ₂₉₈ ⁰Also be very big on the occasion of.Explanation is reacted under steady state and is difficult to carry out, and the thermostability of methane molecule has determined this characteristic, need in pyroreaction, but methane deoxidation at high temperature becomes easier the carrying out of reaction of carbon:

△H ₂₉₈＝150.28KJ/mol ${\mathrm{\ΔG}}_{298}^0=51.03\mathrm{KJ}/\mathrm{mol}$ Calculation of thermodynamics side reaction △ G as can be known under the steady state ₂₉₈ ⁰Less than the value of three above-mentioned main reactions, therefore at high temperature become the carbon side reaction more obvious, cause selectivity of product to descend.

The present invention utilizes argon-arc plasma field can make methane molecule activate into C2 hydrocarbon, has produced the electric field enhanced plasma catalytic effect after particularly adopting catalyzer, and reaction conversion ratio is improved.

The present invention has adopted interchange or DC electric field to carry out catalytic synthesis of C 2 hydrocarbon, is characterized in:

1. normal pressure is adopted in reaction, cold operation, and condition relaxes, and is easy to repetition and engineering and amplifies.

2. raw material is a single methane gas, does not add any other component, as N ₂Or Ar gas etc. causes plasma gas, low cost, convenient separation.

3. compare with conventional oxidative coupling of methane, process is oxygen not, has avoided the side reaction of the further oxidation of methane to take place.

4. adopt low power electric field generation plasma body (general power is not more than 42W), power consumption is little.

Now implementation process of the present invention is described below:

The present invention adopts interchange (20KHz) or direct current plasma field generator, and raw material methane is excited into plasma state, reacts C2 hydrocarbons such as generating ethene and ethane on gas-phase reaction district and catalyzer, and the reaction synthesizer as shown in Figure 1.The explanation with accompanying drawing 1 now is presented below: wherein

(1) CH ₄Gas cylinder (2) reducing valve (3) variable valve

(4) surge flask (5) water seal (6) moisture eliminator

(7) mass flowmeter (8) reactor (9) electrode

(10) thermocouple temperature measurement instrument (11) gas chromatograph (12) plasma generator

(13) transformer (14) power regulator (15) gas meter

(16) six-way valve

Methane gas stream from steel cylinder (1) is through reducing valve (2), variable valve (3), surge flask (4), water seal (5), moisture eliminator (6) is mass flowmeter (7) by the time, control certain flow and enter quartz tube reactor (8) (internal diameter 10mm, long 450mm), electrode (9) is equipped with at the reactor two ends respectively, (10) be temperature thermocouple, electrode (9) links to each other with plasma generator (12), and by power regulator (14) and transformer (13) regulation and control, methane gas is excited into methane plasma under electric field action, at gas phase and catalyst reaction district synthesis of C 2 hydrocarbon, reaction back gas enters gas chromatograph (11) on-line analysis product through six-way valve (16) sampling and forms, reaction result is handled with Microcomputer Calculation, the emptying after under meter (15) metering of reaction back tail gas.

＜embodiment one〉the above-mentioned reaction synthesizer of application, adopt interchange (20KHz) electric field, normal pressure (101.3KPa) that feed gas methane is activated into plasma state at reaction zone, 0～45 volt of voltage-regulation scope, raw gas flow regulation range 40～60ml/ branch is respectively charged into three kinds of metals or metal oxide supported type catalyzer: Ni/Al in reaction tubes ₂O ₃, MoO ₃/ Al ₂O ₃, MnO ₂/ Al ₂O ₃Regulating voltage from small to large, indicate unexpected step and observe when electric current and produced plasma reaction when reaction zone has blue tinge light to take place, voltage and the flow of noting this moment also write down reaction zone temperature value (this temperature value is that reaction zone self generation does not have extraneous the heating) with accurate thermocouple temperature measurement instrument, form with the chromatogram monitoring reaction product, contrast experiment when not adding catalyzer simultaneously is calculated as follows reaction conversion ratio X and selectivity of product S numerical value:

Methane conversion $X=\frac{n}{n_0}\×100\%$

The C2 hydrocarbon selectivity $S=\frac{n_2}{n}\×100\%$

By-product acetylene selectivity $S^{\′}=\frac{n^{\′}}{n}\×100\%$ In the formula:

n ₀Enter the methane mole number of reactor

The methane mole number that n reacts away

n ₂Be converted into the methane mole number of C2 hydrocarbon

N ' is converted into the methane mole number reaction result of acetylene and lists in table 1

Table 1 alternating-electric field plasma reaction experimental result

Catalyzer	Voltage (V)	Flow (ml/ branch)	Temperature (℃)	Methane conversion (X%)	C2 hydrocarbon selectivity (S%)	The acetylene selectivity (S ' %)
							Catalyst-free	40 40	47.7 49.4	61 60	4.1 4.4	92.3 90.5	0 0
Ni/Al 2O 3	25 30	47.2 47.0	126.3 157.7	6.2 7.0	97.8 96.2	0 0
							MoO 3/Al 2O 3	30 35	47.7 47.4	93 105	6.2 8.3	94.7 95.0	0 0
MnO 2/Al 2O 3	30 35	47.7 47.7	70.8 75	7.7 8.6	95.5 94.5	0 0

Can find out that by result in the table 1 adding catalyzer afterreaction transformation efficiency and selectivity of product all are improved to some extent, show that the methane plasma reaction has produced electric field and strengthened katalysis on catalyzer.Be that voltage is 20～40V than suitable condition wherein, corresponding power 2～15W, methane feed flow are 40～80ml/ branch, and corresponding reaction time is 12.8～3.1 seconds.

＜embodiment two〉still use above-mentioned reaction synthesizer, adopt DC electric field, normal pressure (101.3KPa), 0～150 volt of volts DS regulation range, raw gas flow regulation range 30～80ml/ branch, three types of catalyzer: Ni/ZSM-5, MnO pack in reactor ₂/ Al ₂O ₃, LaYO ₃, regulating voltage plays ignition voltage after-current generation hop when reaching plasma from small to large, and is very fast then steady, notes reaction conditions and on-line analysis result, lists in table 2.

Table 2 DC electric field plasma reaction experimental result

Catalyzer	Voltage (V)	Flow (ml/ branch)	Temperature (℃)	Methane conversion (X%)	C2 hydrocarbon selectivity (S%)	The acetylene selectivity (S ' %)
							Catalyst-free	110 110	76.6 30.7	129 200	6.7 9.8	92.7 91.9	0 0
Ni/ZSM-5	110 110	80.5 80.5	71.2 70	22 21.4	95.4 90.0	0 0
							MnO 2/Al 2O 3	110 90	30.4 30.4	74.7 100	13.2 11.7	94.1 96.2	8.2 19.2
LaYO 3	110 110	30 30	70 72	11.5 14.8	94.3 94.7	0 0

Can be found out by result in the table 2, add catalyzer and can improve the C2 hydrocarbon growing amount, be that voltage is 90～110V than suitable condition wherein, and corresponding power 10～20W, methane feed flow are 40～80ml/ branch, and corresponding reaction time is 12.8～3.1 seconds.Though but the used suitable catalyzer of alternating-electric field produces effect but by-product acetylene amount increases in DC electric field, show that the selected suitable catalyzer of two kinds of electric fields is variant slightly.

＜embodiment three〉still use above-mentioned reaction synthesizer, adopt DC electric field, under the catalyst-free condition, under different voltages, carry out plasma reaction, the reaction result that obtains correspondence in the time of 80～120 volts is listed in table 3.

Table 3 DC electric field is voltage and reaction result relation under the catalyst-free condition

Voltage (V)	Flow (ml/ branch)	Methane conversion (X%)	C2 hydrocarbon-selective (S%)	The acetylene selectivity (S ' %)
					80	76.6	2.7	97.7	0
90	76.6	4.1	97.9	0
					95	76.6	5.6	95.2	0
110	76.6	6.7	92.7	0
					120	76.6	7.6	90.3	0

Can be found out that by result in the table 3 DC electric field voltage increases, reaction conversion ratio increases, but the C2 hydrocarbon selectivity then reduces.

＜embodiment four〉still use above-mentioned reaction synthesizer, the employing voltage of alternating current carries out the reaction experiment under the different catalysts participation, and the contrast and experiment that change voltage of alternating current scope obtains is listed in table 4.

Table 4 voltage of alternating current changes and reaction result

Catalyzer	Voltage (V)	Flow (ml/ branch)	Methane conversion (X%)	C 2Hydrocarbon-selective (S%)	The acetylene selectivity (S ' %)
						Ni/Al 2O 3	20 25 30 35	47.2 47.2 47.0 40	0.6 6.2 7.0 8.0	98 97.8 96.2 92.6	0 0 0 0
MoO 3/Al 2O 3	20 25 30 35	47.0 47.7 47.7 47.7	0.8 4.1 6.2 8 3	98 96 94.7 95.0	0 0 0 0
						MnO 2/Al 2O 3	25 30 35 40	47.2 47.2 47.7 56.0	5 5 7.7 8.6 10.7	97.4 95.5 94 5 91.3	0 0 0 0

By the voltage of alternating current increase reaction conversion ratio increase as can be known of result in the table 4, whether no matter there is catalyzer to exist, its Changing Pattern all is similar to dc fields and alternating-current field, and just voltage increases, reaction conversion ratio increases, but the C2 hydrocarbon selectivity then has to a certain degree decline.

The present invention compares with relevant reported in literature and sees Table 5.

Table 5 the present invention compares with relevant reported in literature result

Can find out that by comparative result in the table 5 the present invention need not cause gas, under normal pressure, low temperature and low power condition, react to have its originality.

Reference [1] U.S.Pat.4,574,038[2] Steven L.Suib, Richard P.Zerger, J.Catal.1993,139,383～391[3] A.Oumghar, J.C.Legrand, A.M.Diamy, N.Turillon and R.I.Ben-Alm, Plasma Chem.Plasma Process, 1994,14 (3), 229～249

Claims (1)

1. a kind gas chemical industry, with the single methane component is the method for raw material, catalytic coupling dehydrogenation synthesis of C 2 hydrocarbon, it is characterized in that with the single methane component be raw material, under normal pressure 101.3Pa, below 200 ℃, reaction time is 12.8～3.1 seconds at relative low temperature, adopts metal or metal oxide supported type catalyzer, use and exchange or DC electric field enhancing plasma catalytic synthesis of C 2 hydrocarbon

Wherein (1) catalyzer of adopting under alternating-electric field is metal or metal oxide supported type catalyzer: Ni/Al ₂O ₃, MoO ₃/ Al ₂O ₃, MnO ₂/ Al ₂O ₃, the voltage of use is 20～40V, and corresponding power 2～15W, methane conversion are 6.2～8.6%, and the C2 hydrocarbon selectivity is 94.5～97.8%,

(2) catalyzer that adopts under DC electric field is metal or metal oxide supported type catalyzer: Ni/ZSM-5, LaYO ₃, MnO ₂//Al ₂O ₃, the voltage of use is 90～110V, and corresponding power 10～20W, methane conversion are 11.5～22%, and the selectivity of C2 hydrocarbon is 94～96%.

Images