化工系外文翻譯

1、焦?fàn)t煤氣在活性碳作用下干燥重整合成甲摘要焦?fàn)t煤氣在以活性炭為催化劑進(jìn)行干燥重整已經(jīng)被研究用來(lái)生產(chǎn)合適的甲醇合 成氣，這項(xiàng)工作的主要目的是研究焦?fàn)t煤氣中氫數(shù)量對(duì)焦?fàn)t煤氣干燥重整的影響, 以及其它條件的影響，利如溫度和體積空速的影響。結(jié)果發(fā)現(xiàn)，反向水煤氣變換 （RWGS）反應(yīng)的發(fā)生是由于焦?fàn)t煤氣中氫的存在，而且它對(duì)反應(yīng)的影響隨著溫度 的降低過(guò)程而增加。這種情可能引起的焦?fàn)t煤氣中的氫組成的變化，并由此預(yù)計(jì)。 這種反應(yīng)可以在約1000度的高溫下生產(chǎn)適合用于合成甲醇的合成氣。結(jié)果還發(fā) 現(xiàn)，空速的增加對(duì)水煤氣變換反應(yīng)有利。此外，活性炭被證明是最適合焦?fàn)t煤氣 生產(chǎn)合成甲醇的合成氣的催化劑。關(guān)鍵詞：焦?fàn)t煤氣;

2、干重整，合成氣，甲醇1 簡(jiǎn)介合成氣是大多數(shù)氫產(chǎn)品和各種有機(jī)物的生產(chǎn)原料，它主要由氫氣和一氧化碳組成, 它基本上產(chǎn)自天然氣和石油，但有限的化石燃料的供應(yīng)和應(yīng)對(duì)氣候變化以及溫室 氣體（GHG）的排放，加強(qiáng)了對(duì)生產(chǎn)的替代工藝，如生物質(zhì)氣化1或沼氣重整研 究3。焦?fàn)t氣體（焦?fàn)t煤氣），它可以被認(rèn)為是焦化廠的副產(chǎn)品，主要由氫氣（55-60%）,甲烷（23-27%），氧化碳（5-8%）和 N2 （3-5%），以及其他碳 氫化合物，其中硫化氫和氨的比例小。這種氣體大部分是用作煉焦?fàn)t和鋼鐵廠的 燃料，但往往對(duì)過(guò)剩焦?fàn)t煤氣的使用不能使用這種方式，所以通常放散燃燒，這 也引起了環(huán)境污染的問(wèn)題和如何解決環(huán)境的問(wèn)題 4

3、-9。對(duì)于多余的焦?fàn)t煤氣如 何處理，我們可以通過(guò)氫分離手段加以利用或通過(guò)部分氧化 8,10,11蒸汽重整 7,12,14,15或干燥重整4,5,16來(lái)生產(chǎn)合成氣 12,13，生。這樣生產(chǎn)的合成氣可 以反過(guò)來(lái)用于不同其他有機(jī)合成產(chǎn)品，主要是甲醇。雖然大多數(shù)研究者都集中在 焦?fàn)t煤氣水蒸汽轉(zhuǎn)化法的研究，在過(guò)去的幾年焦?fàn)t煤氣干燥重整也已經(jīng)被深入的 研究4,5,16。由于它提供了比水蒸汽重整更理想的反應(yīng)條件和環(huán)境，如二氧化 碳消耗的能源或節(jié)能，有著許多優(yōu)勢(shì)。另一個(gè)重要的優(yōu)勢(shì)在于焦?fàn)t煤氣干燥重整 的好處是獲得了氫氣和一氧化碳的比率約2的合成氣，這是一個(gè)理想中合成甲醇 的合成氣的比率17,18圖中所示只有一

4、個(gè)步是提供甲烷和二氧化碳反應(yīng)時(shí)的化 學(xué)計(jì)量條件。從圖1中可以看出，這個(gè)過(guò)程可以被視為一種方法，即二氧化碳的 部分再循環(huán)、部分參加反應(yīng)“，在理論上甲醇燃燒時(shí)會(huì)產(chǎn)生一半的二氧化碳。 這項(xiàng)技術(shù)的研究的前景是深遠(yuǎn)的，由于汽車燃料對(duì)甲醇的需求，和氫燃料電池或 生物柴油的原料量的迅速增加19。這項(xiàng)工作主要目的是對(duì)焦?fàn)t煤氣的干燥重整的研究，以生產(chǎn)合適的原料氣 H2/C0作為合成甲醇的合成氣。焦?fàn)t煤氣干燥重整中的活性炭，已被證明是一個(gè) 對(duì)甲烷干燥重整有效的催化劑。氫氣數(shù)量是影響焦?fàn)t煤氣干燥重整和其它反應(yīng)條 件，如溫度或空速度，是目前研究重心。2實(shí)驗(yàn)焦?fàn)t煤氣的干燥重整是在常壓下固定床石英反應(yīng)器及其在電毛皮納采激

5、烈。 在催化劑床中的反應(yīng)溫度進(jìn)行監(jiān)測(cè)，并通過(guò)一個(gè)K型熱電偶手段控制。商業(yè)活性 炭具有高比表面積（Filtracarb FY5）,表1中列出了其主要特點(diǎn)，它可以被用 來(lái)作焦?fàn)t煤氣干燥重整的催化劑。在前一次實(shí)驗(yàn)中，甲烷和二氧化碳在原料中的比例為1：1，在余下的實(shí)驗(yàn) 當(dāng)中，增加了氫氣的量以便研究對(duì)甲烷在干燥重整過(guò)程中存在的影響。氫氣除了 引起三元混合氣體的組成變化，其中氫氣占53%、甲烷和二氧化碳各占23%, 為了使H2/CH4的比率在焦?fàn)t氣特性的范圍內(nèi)，所以干燥重整中甲烷和二氧化碳 的反應(yīng)的條件應(yīng)控制在反應(yīng)的化學(xué)計(jì)量值的范圍之內(nèi)，對(duì)于焦?fàn)t煤氣中的CO的 影響已超出目前的范圍這項(xiàng)工作，將在適當(dāng)時(shí)候研

6、究。為了評(píng)估對(duì)焦?fàn)t煤氣干 重整溫度的影響，試驗(yàn)完成了大氣壓力下的三個(gè)不同 溫度（800, 900，和1000C 型）下的反應(yīng)，此外，在以上3個(gè)不同的反應(yīng)下，每小時(shí)的總體積空速，體積空 速每小時(shí)（0.75，1,和 1.5Lg-1 h-1，它代表了 0.16，0.22， 0.32 Lg-1 h-1 r 的甲烷含量，VHSVCH ）進(jìn)行研究后，發(fā)現(xiàn)如空速增加則會(huì)減少了催化劑床層的CH 4質(zhì)量。干燥重整反應(yīng)中碳催化劑在石英反應(yīng)器內(nèi)進(jìn)行，該系統(tǒng)是用氮?dú)鉀_洗（流 量為15分鐘60mLmin率），然后加熱到預(yù)先設(shè)定的反應(yīng)溫度。該產(chǎn)品在Tedlar 氣體樣品采集實(shí)驗(yàn)期間定期袋。由于在實(shí)驗(yàn)中形成一些蒸汽，冷凝器

7、置于反應(yīng)器 后以防止水流入袋。樣品的分析在長(zhǎng)瓦里安-3800用熱導(dǎo)檢測(cè)器和裝備色譜分 析儀（80/100 Hayesep Q和 80/100 Molesieve 13X 型）串聯(lián)。第二格是由一名 為二氧化碳和碳?xì)浠衔锓治隽ㄩy通過(guò)。甲烷和二氧化碳的轉(zhuǎn)化率和H2的選擇性分別計(jì)算后確定所生產(chǎn)的水量和出 水口流量，通過(guò)關(guān)于非線性方程組的牛頓迭代法的一個(gè)程序和使用微軟Excel 的規(guī)劃求解工具進(jìn)行計(jì)算，并在5%誤差收盤質(zhì)量平衡。使氫的選擇性，（如 輕烴，C2,或水），甲烷轉(zhuǎn)化為氫氣或其它物種數(shù)量最大。參數(shù)按質(zhì)量標(biāo)準(zhǔn)按照 式1-3進(jìn)行計(jì)算：出甲烷，二氧化碳和氫氣在反應(yīng)器入口處和出口處的摩爾分子 質(zhì)量。

8、3結(jié)果與討論在我們之前的試驗(yàn)中20，對(duì)干燥重整的甲烷與二氧化碳（反應(yīng)1）通過(guò)對(duì) 活性炭FY5進(jìn)行了研究（見圖2）。對(duì)該干燥重整反應(yīng)中二氧化碳作用進(jìn)行討論。 實(shí)驗(yàn)進(jìn)行了 6小時(shí)以上的時(shí)間，在反應(yīng)在溫度為800r和常壓下進(jìn)行甲烷和二氧化碳在空速為0.16Lg-ih-1小時(shí)（共0.32Lg -1 h -1VSHV）轉(zhuǎn)化率超過(guò)40%。如果反應(yīng)過(guò)程進(jìn)行采用三元混合氣體，（GTM）在三元?dú)怏w中的氫的存在， 有兩種不同的現(xiàn)象可能發(fā)生：（i）均衡轉(zhuǎn)移到反應(yīng)物（見反應(yīng)1），產(chǎn)生較低甲 烷和二氧化碳，（ii）以及反向水煤氣變換反應(yīng)（RWGS）發(fā)生（反應(yīng)2）造成在 CO2轉(zhuǎn)化的增加和水的形成16,21,22。這兩種

9、作用的結(jié)果會(huì)降低氫化物的產(chǎn)量。這兩種現(xiàn)象都是發(fā)生在溫度為800度時(shí)氣體混合物的干燥重整，并導(dǎo)致了 甲烷和從甲烷干重整造成二氧化碳轉(zhuǎn)換的變化。正如圖3所示，甲烷轉(zhuǎn)化降至 40%以下開始的反應(yīng)，反應(yīng)6小時(shí)后達(dá)到20%左右。仔細(xì)的觀察，在減少可能 由于初始不穩(wěn)定的第一分鐘。此外，二氧化碳轉(zhuǎn)化率比在干燥的甲烷重整（圖2）, 這表明RWGS比對(duì)的平衡轉(zhuǎn)移效應(yīng)的影響更大。在冷凝器收集的大量水，約占8vol% 反應(yīng)的產(chǎn)品，這個(gè)也是由其他研究者報(bào)告的建議16。除了降低氫氣的產(chǎn)量和改 變H2/C0比，水也會(huì)阻礙甲醇合成，因?yàn)樗鼤?huì)使銅催化劑的失能的影響23。溫度的影響圖4顯示了在900C時(shí)的三元混合氣體干燥重組反

10、應(yīng)?？梢钥闯?，此時(shí)甲烷 轉(zhuǎn)化率大于50%,在整個(gè)反應(yīng)實(shí)驗(yàn)中可以看出，這個(gè)轉(zhuǎn)化率是800C時(shí)測(cè)試所達(dá) 不到的，CO2的轉(zhuǎn)化率也高于它在800C的。由于RWGS反應(yīng)（反應(yīng)2）小于甲 烷干重整（反應(yīng)1）吸熱，反應(yīng)溫度的增加提高了干燥改革吸熱，便出現(xiàn)了較高 的甲烷轉(zhuǎn)化率，因此，會(huì)產(chǎn)生更多的氫，而水則會(huì)減少。實(shí)際上，隨著CO2轉(zhuǎn) 化率的增加，會(huì)使干燥重整反應(yīng)增強(qiáng)，而不是RWGS反應(yīng)，因?yàn)榉磻?yīng)所需的水量， 在近3次的實(shí)驗(yàn)明中顯低于800C時(shí)的。其他可能的解釋是甲烷水蒸在高溫度下 進(jìn)行重整（反應(yīng)3）。但是，這個(gè)機(jī)制似乎不太可能，因?yàn)樗鼤?huì)導(dǎo)致甲烷和二氧化碳的轉(zhuǎn)換而沒 有發(fā)生類似的增量，在圖4中可以看到。然而，

11、RWGS反應(yīng)（反應(yīng)2）和蒸汽重 整反應(yīng)（反應(yīng)3）引起的干重整反應(yīng)（反應(yīng)1），這使得難以區(qū)分此種反應(yīng)遵循什 么樣的規(guī)律。圖5顯示了在1000C時(shí)所進(jìn)行的測(cè)試的轉(zhuǎn)換結(jié)果。反應(yīng)溫度的增加同時(shí)也增加 了轉(zhuǎn)換結(jié)果，多達(dá)80%的甲烷和95%的二氧化碳的實(shí)驗(yàn)后6小時(shí)。此外，在1000C 時(shí)沒有水的生產(chǎn)。所以，在此溫度下工作，它有可能避免水煤氣變換的發(fā)生，最大限度 地利用氫。3.2空速的影響的體積空速在900C和1000C研究空速對(duì)反應(yīng)過(guò)程的影響。在800C溫度，因?yàn)樵诳账?增加而導(dǎo)致轉(zhuǎn)換物的進(jìn)一步減少20和水的形成，這將使它很難研究的空速變化 和對(duì)反應(yīng)進(jìn)程的影響。三元混合氣體在900C時(shí)采用三種不同的空速（

12、分別是0.75，1，1.5Lg-1 h-1小時(shí)下進(jìn)行干燥重整反應(yīng)，圖6所示反應(yīng)的結(jié)果?？梢钥闯?，甲烷和二氧化 碳的轉(zhuǎn)換是受空速變化的影響。因此，轉(zhuǎn)換率的影響在于空速變化，轉(zhuǎn)換率隨著 空速增加而降低。隨著水煤氣變換反應(yīng)空速增加。反應(yīng)器中二氧化碳濃度的也增 加。由于存在較高氫氣的含量，二氧化碳可能是限制水煤氣變換反應(yīng)的物種。因 此，二氧化碳的轉(zhuǎn)換應(yīng)避免高的轉(zhuǎn)換，以防止水煤氣變換的副反應(yīng)。圖7顯示了通過(guò)在1000C和0.75Lg-ih-1和1.50Lg-1 h-1時(shí)兩次測(cè)試，出現(xiàn)了兩種不同的結(jié)果。正如上文所述，在反應(yīng)條件為0.75Lg-1 h-1 1000C時(shí)不產(chǎn)生 水。當(dāng)空速增加到1.50Lg -

13、1 h -1小時(shí)，則會(huì)產(chǎn)生一些水，由于干重整反應(yīng)轉(zhuǎn)化減 少而造成的二氧化碳濃度增加。然而，水收集不到產(chǎn)品總額的1vol%，因?yàn)樵?1000 C二氧化碳轉(zhuǎn)化率不夠高，盡管空速的增加。3.3 合成氣分析為了確定在甲烷轉(zhuǎn)化為氫氣時(shí)有多少氫氣的生成以及其他物種，有必要對(duì)其 選擇性進(jìn)行評(píng)估（式（3）。表2所示為每一個(gè)實(shí)驗(yàn)H2的選擇性。在800C時(shí) 氫氣的選擇性最低，主要是氫氣與二氧化碳發(fā)生反應(yīng)，并生成大量的水。在這個(gè) 溫度下觀察到低的選擇性，不僅僅是因?yàn)闅涞漠a(chǎn)量低，而且原料中含氫量少也占 一部分原因。水產(chǎn)量較低在900C或1000C時(shí)，此時(shí)氫氣選擇性達(dá)到較高值，超過(guò)90%，沒有水的產(chǎn)生（1000C和0.

14、75Lg-1 h-1），因?yàn)樘細(xì)浠衔镌诜磻?yīng)過(guò)和中的產(chǎn)量（少于 1）比例微不足道，可以消耗這部分氫。很顯然，在空速的增 加必會(huì)對(duì)選擇性產(chǎn)生影響，由于在水產(chǎn)生的增加。因此，在溫度一定時(shí)，空速增 加則選擇性下降，這種下降在900C時(shí)比1000C更為明顯比.要確定合成氣是否適用于生產(chǎn)甲醇，在干燥重整反應(yīng)過(guò)程后要記錄 H2/CO 比以便 進(jìn)行比較得到合適的氣氣比。甲醇合成適宜的H2/C0比為2（反應(yīng)4）2 17,18。這兩種蒸汽和甲烷干重整引起的比率大大高于或遠(yuǎn)低于此值（即， 3例在蒸汽重 整和干燥重整中的實(shí)驗(yàn)1）。因此，必須要包含反應(yīng)進(jìn)程的其他反應(yīng)條件，以調(diào) 節(jié)適合用于生產(chǎn)甲醇的合成氣 17。然而，

15、在焦?fàn)t煤氣氫的存在使干燥重整只 須一步就可能達(dá)到接近適用于合成甲醇的 H2/CO 比率。 H2/CO 比雖然是最常用 的因素來(lái)評(píng)價(jià)一個(gè)合成氣的成分，但是有些人建議，在原料氣中二氧化碳的影響 也應(yīng)考慮對(duì)甲醇合成階段的影響6,17,24， 25甲醇合成反應(yīng)（反應(yīng) 4）。二氧 化碳可以與氫氣發(fā)生反應(yīng)生成甲醇和水（反應(yīng)5），它有助于保持了催化劑的活 性。氫氣，二氧化碳和一氧化碳在合成甲醇的原料氣中的比例關(guān)系及R參數(shù)，其 定義如下是指：17,24,25其中氫氣，二氧化碳，和一氧化碳的摩爾數(shù)是在甲醇 中每一個(gè)合成階段。為了優(yōu)化其反應(yīng)過(guò)程中，參數(shù)R必須等于或略低于2 17,24,25高。如果R 值需小于2，

16、它會(huì)導(dǎo)致在甲醇合成期間副產(chǎn)品量的增加，而當(dāng)值大于2時(shí)，有必 要增加甲醇合成階段甲醇的回收率，由于反應(yīng)過(guò)和中氫過(guò)剩，這使得反應(yīng)過(guò)程效 率變低和合成成本高。表2顯示了干H2/CO比率和R參數(shù)在不同的溫度和空速的情況下的GTM干燥 重整實(shí)驗(yàn)?？梢钥闯?，在800C，盡管二氧化碳的轉(zhuǎn)化率大大超過(guò)了甲烷轉(zhuǎn)化率，H2/CO 比率大于3。這是由于強(qiáng)烈的影響，原料氣中的氫轉(zhuǎn)換時(shí)，此參數(shù)是最低的。這 種影響會(huì)隨著轉(zhuǎn)換的增加而降低（900 C and 1000C型）。此外，即使甲烷和二 氧化碳的轉(zhuǎn)換有很大的不同（900C），但H2/CO摩爾比接近2,這是最合適的 甲醇合成的比率。至于R參數(shù)，在800C進(jìn)行的實(shí)驗(yàn)產(chǎn)生

17、合成氣值不適合用于甲醇合成。這可 能是由于低轉(zhuǎn)換率造成的，從而導(dǎo)致在生成大量的二氧化碳。在900C和1000C 時(shí)其值略高于2,它可被視為用于甲醇生產(chǎn)的合成氣可以接受的R值。在空速變化既影響H2/CO比和R參數(shù)?？账俚脑黾幼鳛镠2/CO比的增加，由 于減少了轉(zhuǎn)換。這種情況可能會(huì)導(dǎo)致H2/CO比的降低，由于轉(zhuǎn)換時(shí)甲烷比二氧化 碳損失高，即在生產(chǎn)氫比減少有限公司生產(chǎn)的大。然而，由于在這兩個(gè)轉(zhuǎn)換的降 低,氫氣在原料氣中的影響增加，這就會(huì)引起H2/CO摩爾比的變化.相反的趨勢(shì)，可觀察到的H2/C0比率，因?yàn)楫?dāng)空速增加時(shí)則參數(shù)R減小，由于生產(chǎn)的合成氣中 有大量的二氧化碳存在。4結(jié)論這項(xiàng)工作的主要目標(biāo)是研

18、究了活性炭焦?fàn)t氣的干重整，以生產(chǎn)適用于合成甲醇的 合成氣，對(duì)焦?fàn)t煤氣中氫含量在干燥重整反應(yīng)中對(duì)反應(yīng)進(jìn)程的影響進(jìn)行了研究， 研究發(fā)現(xiàn)氫的最明顯的影響是對(duì)反相水煤氣變換反應(yīng)的影響最大。在800C時(shí)， 在這種情況下，轉(zhuǎn)換率比較低，導(dǎo)致了焦?fàn)t煤氣中的氫部分消耗和水的產(chǎn)生。因 此所產(chǎn)生的合成氣H2/CO比值較高和R參數(shù)較低，這對(duì)合成甲醇條件來(lái)說(shuō)不合 適。隨著溫度的增加，則轉(zhuǎn)換率也隨之變大，甲烷和二氧化碳的轉(zhuǎn)化率會(huì)別達(dá)到 80%和95%。因此水的產(chǎn)量下降，在1000C時(shí)則完全沒有水的產(chǎn)生，當(dāng)反應(yīng)進(jìn) 程采用較低空速時(shí)。這種情況下便會(huì)引起H2/CO值降低，R參數(shù)增加，從而能 夠生產(chǎn)出適合用于生產(chǎn)甲醇的合成氣，

19、即H2/CO比為2.2,和R的參數(shù)為2.13， 此時(shí)H2的選擇性高（高達(dá)90%）?？账賹?duì)反應(yīng)過(guò)程的影響是相反的，因?yàn)榭账?增加時(shí)則會(huì)導(dǎo)致轉(zhuǎn)換率的降低和產(chǎn)水量的增加。在這種情況下，H2/CO比值的 增加，R參數(shù)減小，因而值過(guò)高和過(guò)低的分別的生產(chǎn)甲醇。因此，可以得出結(jié)論認(rèn)為，在（1000C ）和VHSVs不高于1.5Lg-1 h-1時(shí)，活性炭為焦?fàn)t煤氣干燥 重整生產(chǎn)甲醇的最佳催化劑。Dry reforming of coke oven gases over activated carbon to produce syngas formethanol synthesisabstractThedry

20、reforming of cokeoven gases(COG) over an activated carbon used as catalyst has been studied inorder toproduce asyngas suitable formethanol synthesis. The primary aim of this workwas tostudy theinfluence of the high amount of hydrogen present in the COG on the process of dry reforming, as well asthe

21、influence of other operation conditions, such us temperature and volumetric hourly space velocity(VHSV). It was found that the reverse water gas shift (RWGS) reaction takes place due to the hydrogenpresent in the COG, and that its influence on the process increases as the temperature decreases. This

22、 situation may give rise to the consumption of the hydrogen present in the COG, and the consequent formation of a syngas which is inappropriate for the synthesis of methanol. This reaction can be avoided byworking at high temperatures (about 1000 C) in order to produce a syngas that is suitable for

23、methanolsynthesis. It was also found that the RWGS reaction is favoured by an increase in the VHSV . In addition,the active carbon FY5 was proven to be an adequate catalyst for the production of syngasfrom COG.Keywords:Coke oven gasDry reformingSyngasMethanol1. IntroductionSynthesis gas, or simply s

24、yngas, is a raw material for the largescale production of hydrogen and a wide variety of organic products, consisting mainly of hydrogen and carbon monoxide 1,2.It is basically produced from natural gas and oil, but the limitedsupply of fossil fuels and the fight against climate change andgreenhouse

25、 gas (GHG) emissions have intensified the search foralternative processes of production, such as biomass gasification1 or biogas reforming 3.Coke oven gases (COG), which can be considered a byproduct ofcoking plants, consist mainly of H2 (55 60%), CH4 (23 27%), CO(5 8%) and N2 (3 5%), along with oth

26、er hydrocarbons, H2S andNH3 in small proportions. Most of this gas is used as fuel in thecoke ovens and other processes of the steel plant, but very oftenthe excess of COG cannot be used in this way and so it is burntin torches. But this gives rise to environmental problems that urgently need to be

27、solved 4 9. An alternative option for the excessCOG is for it to be valorized by means of hydrogen separation8,10,11 or syngas production through partial oxidation 12,13,steam reforming 7,12,14,15 or dry reforming 4,5,16. The syngasthus produced can in turn be used for the synthesis of differentothe

28、r organic products, mainly methanol. Although most authorshave concentrated their attention on the steam reforming of COG7,12,14,15,inthe lastfewyearsthedryreformingofCOGhasalsobeen investigated 4,5,16, due to the numerous advantages that itoffers compared to steam reforming, such as the saving of e

29、nergyor CO2 consumption. Another important advantage of the dryreforming of COG is the possibility of obtaining a syngas with aH2/CO ratio of about 2, which is the ideal proportion for methanolsynthesis 17,18, in only one step provided the process is carriedoutunderstoichiometricconditionsofCH4 andC

30、O2.Ascanbeseenin Fig. 1, the process can be considered as a way of partial recycling”ofCO2 since it consumes, at least theoretically, half of theCO2 producedwhen methanolis burnt.The prospects for thistechnology are far-reaching, since the demand for methanol for vehiclefuel,asasourceofhydrogenforfu

31、elcellsorbiodieselproductionisrapidly increasing 19.Themainobjectiveofthisworkistoinvestigatethedryreforming of COG in order to produce a syngas with a ratio of H2/CO suitable for methanol production. The dry reforming of COG is carriedoutoveranactivatedcarbon,whichhasbeenproventobeaneffectivecataly

32、stforthedr yreformingofmethane20.Theinfluenceofthelargehydrogenamountwhichispresentinth eCOGontheprocess of dry reforming and other operating conditions, such as temperature or space velocity, are studied.2. ExperimentalThe dry reforming of COG was carried out in a fixed-bed quartzreactor under atmo

33、spheric pressure and heated in an electric furnace. The reaction temperature in the middle of the catalyst bedwas monitored and controlled by means of a type KA commercial activated carbon with a high surface area (FiltracarbFY5),whosemaincharacteristicsare shownin Table1,was usedascatalyst.In the f

34、irst test, CH4 and CO2 were fed in at a ratio of 1:1. In therest of the experiments, H2 was added in order to study the effectof the presence of H2 in the feed stream on the process of dryreforming of methane. The addition of H2 gave rise to a gaseousternary mixture (GTM) composed of 54% H2, 23% CH4

35、 and 23%CO2 (vol.%), in order that the H2/CH4 ratio was within the rangecharacteristic of COG (22.7). The CH4 and C02 were kept understoichiometric conditions for the dry reforming of the methane.The influence of the CO present in the COG is beyond the scopeof this work and will be studied in due co

36、urse.In order to assesstheinfluenceoftemperatureonthedryreformingoftheCOG,testswere performed at atmospheric pressure and at three differenttemperatures (800, 900, and 1000C). In addition, tests at threedifferent total volumetric hourly space velocities, VHSV (0.75,l,and 1.5Lg -1 h -1, which represe

37、nt 0.16, 0.22, and 0.32 Lg -1 h-1 for the methane respectively, VHSVCH ) were carried out with theaim of studying the effect of this variable upon the process andthe composition of the products. The VHSV was increased byreducing the mass of the catalyst bed.Dry reforming reactions were performed in

38、a quartz reactorcharged with the carbon catalyst, which had previously been driedover night at 110 C. Before starting the reaction, the system wasflushed with N2 (flow rate of 60mLmin for 15min) and then,heated up to a pre-set operating temperature. The gas productwas collected in Tedlar sample bags

39、 periodically during theexperiment. Due to the formation of steam insomeoftheexperiments,acondenserwasplacedafterthereactorinordertopreventwaterfromreachingt hebags.ThesampleswereanalyzedinaVarian CP-3800 gas-chromatograph equipped with a thermal conductivity detector TCD and two columns (an 80/100

40、Hayesep Q and an80/100 Molesieve 13X) connected in series. The second columnwasbypassedbyasix-portvalvefortheanalysisofCO2 andhydrocarbons (PC2).The CH4 and CO2 conversions and the selectivity to H2 were calculated after determining the amount of water produced and thecomposition of the outlet strea

41、m by means of an iterative procedure based on the Newton method for non-lineal equations andusing the Solver Microsoft Excel tool, and closing mass balanceswithin a5% error margin. Selectivity to hydrogen gives anapproximate idea of the amount of methanetransformed into H2or into other species (such

42、 as light hydrocarbons, C2, or water).The parameters were calculated according to Eqs. (1) -3): where CH4in,CO2in and H2in, are moles of each gas at the inlet ofthe reactor and CH4 out,CO2 out and H2 out are moles of each gas atthe outlet.CHg con version (%) CHg con version (%) = 100 yC03 ccnversion

43、 (% = 100 xH2 selectivity, S (%) - 100 xCH4 in CH4 cutCHin COj cutQ)g inH2 C1jt Hj inQ)2 - 匚出s匸比諒一3 ResuIts and discussionIn a previous work by our group 20, the reformingof CH4 withCO2 (Reaction 1) carried out over the activated carbon FY5 wasstudied (see Fig. 2). A possible mechanism for the dry r

44、eformingreactionand the role of CO2 introduced were discussed. The experiments were conducted over a period of 6h, at 800C and atmosphericpressure, under stoichiometric conditions of the methaneand carbon dioxide and at a VHSVCH of 0.16Lg -1 h -1 (total VSHVof0.32Lg -1 h -1 )andconversionsofmorethan

45、40%wereachieved.匚H“ 十匚一 2內(nèi)十丄匚0, = 247.3 kJ/mol(Reaaknl)If the process is carried out introducing the GTM, i.e., in thepresence ofhydrogeninthe feed, two different phenomena maytake place: (i) the equilibrium is shifted to thereactants (see Reac-tion 1), which results in lower CH4 and CO2 conversions

46、, and (ii)the reverse water gas shift reaction (RWGS) occurs (Reaction 2),giving rise to an increase in CO2 conversion and the formation ofwater 16,21,22. Both effects result in a decrease in hydrogenproduction.H2 + C02 H2D + C0, AH = 41 衛(wèi) kJ /mol(Reaction)Tjt)k! 1Milii chemical diaraCTtrtsnc? and r

47、extural properdei M Ttie acttvj rH cartwn F5,PLDjeirkUce ALUlyii wl%)UlEiouif dLdly山M OiLiLAstrV口皿阻i贓皿產(chǎn)cNSObH/C6.72.B3U917Q505CU(13D.OGLw 呼 rwcoinpiKihinn ct the-eMprcsscd 2s vjt.% irf mhal化3iEh3NjJ3弧伽Ni539.7925-40些D5咅ah.41012.77Z?11 1Rnd5jd5TcKrurai prDiwrtlffi勾口 l訐閭叫如(cm3/F0250.34032叫B佃0.Z5Dry 斶Is

48、.CMLuldLud的di血陽(yáng)盤.N0左MLgTiwni gpcdhc perp s/cHunwSpcclhc vol u me of m icrjpDn?5 pores ofin rtrnal width 2 nmjiSwciric boiumeEsmall mlrnjaoR-ttoorw witu an inrcrnai width0.7nml.LJW. iSerriiu-dex er uf./f ne f20 tO) jcgs?wFig.乙 cHji arxl CQj CHMivcrslons for itic dry refer Fig.乙 cHji arxl CQj CHMivcrs

49、lons for itic dry refer m ln cr 網(wǎng) at BOO T. HTime mini)FI& 4. CH4nd CO2 ccrwereiorts for rtie dry nefoLiYiine ot tlw GTM WJ C. Cl-U co2-1.*HSVc出-0.I6LE- h.VH5V-D.75Lf1 Ir1 and 1 atm.Both phenomena occurred in the case of the dry reforming of the GTM at 800 C, and led to changes in the CH4 and CO2 co

50、nversions resulting from the dry reforming of CH4. As can be seen in Fig. 3, methane conversion fell to below 40% from the very beginning of the reaction, reaching values of about 20% after 6h of reaction. The sharp decreasing observed during the first minutes maybe due to initial instabilities. In

51、addition, carbon dioxide conversion was higher than in the case of the dry reforming of methan(Fig. 2), which suggests that RWGS had more influence on the process than the effect of the shift of the equilibrium. The large amount of water collected in the condenser, representing about8vol.% of the pr

52、oducts of the reaction, reinforces this suggestionwhich has also been reported by otherauthors 16. Besides reducing H2 production and changing the H2/CO ratio, water could also obstruct the synthesis of methanol, since it has a deactivating effect on the Cu catalyst 23.Effect of the temperatureFig.

53、4 shows the dry reforming of the GTM at 900C. As can be seen, CH4 conversion is higher than 50% throughout the experiment, a level of conversion never reached in tests carried out at 800C. CO2 conversion is also higher than it is at 800C. Since the RWGS reaction (Reaction 2) is less endothermic than

54、 the dry reforming of methane (Reaction 1), an increase in the operating temperature enhances dry reforming, giving rise to a higher methane conversion and, therefore, greaterhydrogen production, whereas the production of water is reduced. In actual fact, the increase in CO2 conversion may have been

55、 due to anenhancement of The dry reforming reaction,and not to the RWGS reaction,since the amount of water collected was nearly three times lower than that in the experiment at 800C.Other possible explanation to these results is that at higher temperatures the steam reforming of methane (Reaction 3)

56、 can occur, i.e. the water produced in the RWGS could react with the methane.However, this mechanism seems less probable since it would lead to similar increments in both CH4 and CO2 conversions which did not take place,as can be seen in Fig. 4.Nevertheless,the sum of RWGS reaction (Reaction 2) and

57、steam reforming reaction (Reaction 3) gives rise to the dry reforming reaction (Reaction 1), which makes difficult to distinguish the path followed by the reaction.Fig.5 shows the conversion results corresponding to the test carried out at 1000C. This increment in temperature results in an increase

58、in the conversions, up to 80% for CH4 and 95% for CO2 after 6h of experimentation.Moreover,no production of water was detected at 1000C. Therefore, by working at this temperature, it is possible to avoid the occurrence of RWGS, and so maximize the production of hydrogen.Effect of the volumetric hour

59、ly space velocity (VHSV)The effect of the VHSV on the process was studied at 900C and 1000C.The temperature of 800C was discarded since an increase in VHSV would lead to a further decrease in conversions 20 and to the formation of more water, which would make it difficult to study the effect of the

60、variation of VHSV and its influence on the process.10020160邕 UQmEA 匚口04010020160邕 UQmEA 匚口0402同3 o30亠 CH出-O-CO2060120160240300360Time (mln)Fig. 3. Fig. 3. (IL jnd.CO. cMivrhiflns for Itie y refornungnf tlw CT何 Jl HCunC,匸 匚6 = I, VHSV - 0.16 L E1 tiVHSV = 05 Lfi- hf Jnd 1 JtfTLPig. 1 CIL Jhnd tOjCMwr