关于甲醇反应部分控制点？ 二氧化碳含量对甲醇合成反应的影响： 二氧化碳也能参加合成甲醇的反应，对于铜系催化剂，二氧化碳的作用比较复杂，既有动力学方面的作用，还可能具有化学助剂的作用，归纳起来，其有利的方面为： ①含有一定量的co2可促进甲醇产率的提高； ②提高催化剂的选择性，可降低醚类等副反应的发生； ③ 可更有利于调节温度，防止超温，延长催化剂的寿命； ④防止催化剂积炭。 其不利方面为： ① 与co合成甲醇相比，每生成1kg甲醇多消耗0.7m3的h2； ② 使粗醇中水含量增加，甲醇浓度降低。 总之，在选择操作条件时，应权衡co2的利弊。通常，在使用初期，催化剂活性较好时，应适当提高原料气中co2的浓度，使合成甲醇的反应不致过分剧烈，以利于床层温度的控制；在使用后期，可应适当降低原料气中co2的浓度，促进合成甲醇反应的进行，控制与稳定床层温度。 在采用铜基催化剂是，原料气中co2的含量通常在6%（体积）左右，最大允许co2含量为12%-15%。查看更多
五个原因让本届世界杯进球如此之少？ after every world cup team had played once, scoring remained at historical lows in the tournament. the 32 teams combined for just 25 goals in the first 16 games of the cup, a rate of 1.56 goals per game. that's well down from 2.44 goals in the first 16 games at the 2006 world cup, and 2.88 goals in 2002. overall in the cup's first 16 games, teams took 410 shots, but just 106 of them were on target, according to espn's stats. that's a rate of 26%. in the first 16 games in 2006, there were 435 shots--barely more than this year. but 44% of them were on target. that percentage held for the entirety of the 2006 tournament. errant shooting appears to be the decisive factor in the low-scoring start to the cup. of the shots on goal in teams' first games this year, 23% found the back of the net--slightly higher than the rate of 20% in the first 16 games last year, and the 18% mark for the tournament overall. this year's rate also is in line with the 23% of shots on goal that were scores in 2002. what might explain all the misfires? here are some possible explanations: the ball some players have complained about it, and it does seem like an inordinate number of shots are sailing over the woodwork (perhaps because of the altitude, not the ball). but players must adjust to the ball at each world cup, and an unpredictable flight can affect goalies as well as shooters. lack of scoring talent perhaps players are shooting poorly because they are poor shooters. if that were the case, though, we might also expect scoring to be down in other top competitions. yet during the 29 games in the knockout stage of this year's champions league - the premier european club tournament, featuring most of the world's best players--teams scored 82 goals, compared to 59 in the equivalent 29 games in 2006. stat-keeping quirks whether a shot is on target is a judgment call, one different scorers make differently. for instance, while espn recorded 25 shots for spain, five of them on goal, in its game against switzerland on wednesday, those numbers were 24 and eight, respectively, according to fifa, the tournament organizers. similarly, while espn had nine shots for the swiss, two of them on target, fifa had eight and three, respectively. that adds up to big differences: fifa has an overall shooting percentage - the term i'll use for percentage of shots that are on goal, whether or not they go in - for the first 16 games of 33%, compared to 26% of shots on target by espn's count. (it's possible this is because fifa doesn't count blocked shots as shots.) similarly fifa had an overall shooting percentage of 48% in 2006, compared to 44% for espn. however, they corresponded closely in 2002. and both data sources agree that there was a big drop between last year and this year, and that the shooting percentage in the first 16 games in 2006 was 44%. a statistical fluke as the montreal canadians demonstrated during their run deep into the nhl playoffs, and the capitals did with their early exit, some teams shoot at surprisingly high percentages, and such performances tend not to be sustainable. perhaps players have been unlucky and will gain their shooting touch in the last three quarters of the tournament. parity and tactics every team has played effective defense at times. the tournament's weakest teams seem to have taken to heart the lesson of greece, the stunning 2004 champions of europe, who jammed the box with defenders and stymied high-powered offenses. just two teams have yielded more than two goals in the first 17 games of the tournament, and both reached that ignominious mark only after losing a player to a red card. one sign that players indeed have been frustrated and pushed to take shots far from the goal: fifa has recorded 241 shots from outside the penalty area through the first 17 games, compared to 186 shots inside the penalty area. of the closer shots, 40% were on goal, compared to 27% on the farther shots (the rest were blocked or wide). equivalent stats for prior tournaments aren't readily available, though, so it's impossible to say if this represents a trend toward shooting from farther away. 在每只球队都出场亮相过一次后，本届南非世界杯的进球数仍处在历史低点。在前16场比赛中，32只球队总共踢进25个球，平均每场进球1.56个。这一数据远低于2006年德国世界杯同期的2.44个和2002年韩日世界杯的2.88个。 espn 的数据显示，在本届杯赛前16场比赛中，32只队伍共有410次射门机会，其中只有106次射正，射正率为26％。相比而言，2006年世界杯前16场比赛共有435次的射门机会（与本届比赛相差无几），但是其中有44％射正，这一比例也几乎贯穿整届杯赛。 射门失误看似是今年世界杯开场至今进球数少的决定性因素。在前16场比赛中，射正的球中只有23％最终入门，比上届杯赛的20％和历届世界杯平均18％的数字略高，而与2002年持平。 射门哑火，原因何在？下面提供几个可能的解释： 比赛用球 一些球员曾表达过对比赛用球“普天同庆”的不满。看起来的确好像飞过门框的球数多了点（也许是因为门框高度的原因，而不是球本身）。但是，每届世界杯上，球员都要适应比赛用球，诡异的飞行路线影响的不仅仅是守门员，还有射手。 缺乏得分能力 也许球员射门不正是因为他们本来就不是好射手。但如果真是如此，其他顶级赛事的进球数也应该低。可是，在今年欧洲冠军联赛淘汰赛阶段的29场比赛中，共有82个进球，而2006年那届比赛同样有29场比赛，总进球数则为59个。欧洲冠军联赛是欧洲顶级俱乐部赛事，集中了大部分全世界最好的球员。 数据统计 不管所谓的射正率这一说法是否带有主观性，不同数据统计者提供的数据会有所不同。比如，西班牙和瑞士的那场比赛，espn的数据是25次射门，五次射正；而赛事组织方国际足联公布的数据则是24次射门，八次射正。与此同时，espn数据显示瑞士队有九次射门，两次射正；国际足联的则是八次射门，三次射正。这样一算，区别就大了。国际足联得出的整体射门率（我将用这个词来表示射正的球的比例，不管最终是进还是没进）是33％，espn的则是 26％。（很有可能国际足联没有将被扑救的球算在其中）。类似的，2006年世界杯，国际足联统计出来的射门率是48％，而espn则是44％。不过在 2002年，双方的数据倒是几乎一致。两大数据来源都表示，与上届相比，本届世界杯的射门率大幅下跌。2006年，这一数字是44％。 低概率的意外 就像蒙特利尔加拿大人爆冷闯进冰球大联盟季后赛（nhl），而华盛顿首都队（capitals）却早早被淘汰出局一样，有些球队的射门率出人意料地高，不过这样的表现并不能稳定地保持下去。或许，球员们只是现在还不太走运，在接下来的四分之三程比赛中他们将享受进球得分的乐趣。 球队兵力对峙和战术打法 每只球队时不时地都能做到有效防守。世界杯上实力最弱的球队似乎将希腊队2004年赢得欧洲杯时的排兵布阵牢记在心。当时，希腊队坚持防守反击的打法，后防线上重兵把守，将对手的强势进攻一一击退。本届世界杯前17场比赛中，只有两只球队（德国和乌拉圭）进球数超过两个，而且两队都是在对手有一名球员被红牌罚下场的情况下取得这一战绩的。有迹象表明，在对手固若金汤的防线面前，球员们被迫不得已在远离门框范围的区域里试图射门。根据国际足联的统计，前17场比赛中，有241个射门是从禁区之外的地方完成的，而在禁区里的数字是186。在近距离的射门中有40％射正，而较远距离射门的射正率则为27％（剩下的要不是被扑救，要不就是踢出边线）。不过因为其他足球赛事在这方面的数据目前尚不得知，所以还不能就此得出结论说这代表了一种较远距离射门的趋势。 转摘自海词，供朋友们分享查看更多
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