问题 问答题 简答题

何谓恒沸精馏?何谓萃取精馏?通常在什么情况下采用恒沸精馏或萃取精馏?

答案

参考答案:若在两组分恒沸液中加入第三组分(称为夹带剂),该组分能与原料液中的一个或两个组分形成新的恒沸液,从而使原料液能用普通精馏方法予以分离,这种精馏操作称为恒沸精馏。恒沸精馏可分离具有最低恒沸点的溶液、具有最高恒沸点的溶液以及挥发度相近的物系。

萃取精馏和恒沸精馏相似,也是向原料液中加入第三部分(称为萃取剂或溶剂),以改变原有组分间的相对挥发度而达到分离要求的特殊精馏方法。但不同的是要求萃取剂的沸点较原料液中各组分的沸点高得多,且不与组分形成恒沸液,容易回收。

单项选择题
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In most of the time, I am devoted to my research in the lab with my friend Dave, who loves traveling very much. To make our life colorful and relax ourselves, in July, my friend and I are taking a camping trip. We will travel for four weeks and will tour the United States and part of Canada. We have decided to camp because it does not cost as much as vacationing (度假) in hotels.

We have to plan very carefully in advance. First, the car we are going to drive is very small, so we have decided to take only one small suitcase each and as few camping things as possible. We will take some medicine with us to prevent insects (昆虫) from hurting us, and also food for picnics. Second, there is a lot to see in the United States and Canada, so we have to decide on the direction (方向) we want to drive.

The date we are leaving is July 2, from which day we will have two months off.  We want to see and do many things on our camping tour. We want to climb in the mountains, visit famous caves, and swim in cool mountain rivers. We want to visit many cities and talk to many people, which I am sure can enrich our experience greatly. We also want to find a hotel room if it rains at night. We expect to have an exciting trip.

小题1: The two friends are going to take a camping trip ________.

A.if they have four weeks’ time off

B.though it will be a long trip

C.so that they can save money

D.because it will be warm enough in July小题2:Which of the following statements is possibly true?

A.They are now on the trip

B.They are going to make a tour all over the U.S and Canada.

C.They are quite rich.

D.July is drawing near.小题3: We learn from the second paragraph that ________.

A.they must be ill.

B.they will bring a lot in the car.

C.they must have studied the map carefully.

D.they must have been hurt by insects.小题4: It is quite clear that ________.

A.there will be no insects at all.

B.they are sure to take some medicine on the trip.

C.the two friends will take turns to drive.

D.the two friends will share a suitcase.小题5: If they are caught in the rain , they will ________.

A.talk to their families while it rains.

B.ask others for help.

C.have to stop climbing.

D.have to stay in a hotel for the night.